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THE AM BULLETIN BOARD => Class E Forum => Topic started by: N4LTA on August 25, 2019, 12:29:37 PM



Title: Class D 80 meter rig progressing
Post by: N4LTA on August 25, 2019, 12:29:37 PM
Made some progress this weekend on my Class D system. I completed the low voltage poeer supply, a second PWM generator and a large capacitor board for the main power supply.

The cap board has 14000uF at 250 volts worth of filtering. I plan on regulating the output at 150 volts.

Here are a few pictures:

The PWM board based on Steve's circuit

The low voltage power supply board and power transformer. Toroidal power with regulated +12, -12 and +5 volt output plus raw +20 and -20 volts

Test board for four SiC  MosFETS



Title: Re: Class D 80 meter rig progressing
Post by: N4LTA on August 25, 2019, 10:35:08 PM
I got the drivers, the bypass caps and the four MOSFET mounted tonight. Anyone see anything wrong that jumps out?

The drivers are tedious to mount but they all seem to be installed without shorts as tested with a ohmeter.

Also tested the PWM generator and it is working well.

Next I need to build the audio Pre PWM filter. I have a board and hope to build it tomorrow.

I ordered a Hammond 7 inch rack panel and enclosure  to house the complete PWM system. It will probably need some steel structure addition to handle the 35 pound
toroidal power transformer. It is overkill for sure at 1400 VA.

Thanks for looking and comments are appreciated.

Pat


Title: Re: Class D 80 meter rig progressing
Post by: N4LTA on August 27, 2019, 03:28:45 PM
Tested the UCC 2501 Modulator board last night and it is working fine. Frequency was 151 KHz

Layed out an audio processor board using Steve's design as a guide with phase select and a negative peak limiter and a 7.5 KHz filter

Also made another bipolar power supply board. Plotted the boards this morning and just finished etching them. Will drill and stuff them tonight.

I plan on using a larger Hnmmond rack enclosure for the big power supply and PWM generator and driver  and then using a smaller 3" rack enclosure for the compressor and audio chain.

Thanks for looking

Boards about half etched in H2O2 and hydrochloric acid (Muriatic acid)


Pat
N4LTA


Title: Re: Class D 80 meter rig progressing
Post by: vk3alk on August 27, 2019, 07:46:45 PM
All looks good and things moving along nicely  :)

For the PWM are you using Steves output design ( Class D ) or a half bridge like Nigels.....
Have you thought about the LPF yet and the material to use....


Wayne


Title: Re: Class D 80 meter rig progressing
Post by: N4LTA on August 27, 2019, 08:19:02 PM
Wayne,

I plan to use a half bridge. I haven't designed the filter yet, but I have quite a few cores from my past 500 Khz work. My voltage will be higher so it will require
a different filter. I will be  closer to Nigel's  output stage because my RF stages will be with SiC and GaN devices run at higher voltage and less  current.

I am shooting for 300 watts carrier  on 80 meters with four SiC Mosfets. Not having done PWM AM modulation before - I am experimenting. Never having built any PWM system I am learning and having a good time. I'll let the smoke out of some Mosfets for sure.

BTW - TI has a nice 500 KHz discrete PWM generator made for class D audio. will be easy to drop it to 150 KHz  or so and it should adapt well for AM modulation.

The offer full design notes and full double sided PC Board Gerber files. I ordered ten boards from Seeed  Studio for $4.17 pus $13 shipping from China. I have used them before and they do a good job. If anyone wants a board, let me know and I'll send you one or two. We will see how they turn out, but  the last ones they made were nice boards.


Pat


Title: Re: Class D 80 meter rig progressing
Post by: KD6VXI on August 27, 2019, 09:29:34 PM
What's the chip number?  I'm interested.

--Shane
KD6VXI


Title: Re: Class D 80 meter rig progressing
Post by: N4LTA on August 27, 2019, 09:55:00 PM
Look Here

http://www.ti.com/tool/TIPD108

Uses a SMT op/amp and a rail to rail comparator and a voltage reference source

Samples are available for the op/amp and possibly the comparator.

Pat
N4LTA





Title: Re: Class D 80 meter rig progressing
Post by: N4LTA on September 06, 2019, 01:15:35 PM
The analog discrete PWM boards came today. I don't see how they do it. Extremely high quality boards. Cost about $4 and chang3 for ten boards.  Shipping was a little over $12

Took a little over a week - As I said - If anyone want to experiment - I'll send you one.


Title: Re: Class D 80 meter rig progressing
Post by: N4LTA on September 11, 2019, 09:46:12 AM
Finished the PWM generator for the PWM power supply. This is the final circuit board. I added a couple of voltage regulators and RCA type connectors to make hookup easier. The board can run off 9-20 volts now.



Title: Re: Class D 80 meter rig progressing
Post by: N4LTA on September 15, 2019, 12:01:27 PM
Got the enclosure assembled and am ready to punch the front panel for the controls and three meters. The filter cap board has ten  1800 uF 250 volt capacitors. The PWM boar, and the low voltage power supply board are ready. I may or may not rework the power driver board for T0220 FETs to use a more modern MOSFET with higher currrent rating.. I also need to pick a heatsink.
With a newer 60 amp set of MOSFETS, it probably won't need to be large. If I redo the board, I can put a RCA jack on the board to make it plugable to allow changing to a different PWM board for experimenting.

The transformer is reduced to a 800 VA one to reduce the weight. Should still be plenty to do more than the legal limit. Output votage from the high voltage supply will be 150 volts regulated.

Hope to do the meter punching this afternoon - ugh!


Title: Re: Class D 80 meter rig progressing
Post by: vk3alk on September 24, 2019, 11:22:54 PM
Hi Pat...

Wonder what stage your up to now....?

Have been playing around with a CMCD 75M Transmitter and seems to be more or less in the ball park....
If you cannot get Nigel's TX to work this might be worth a try....
Made it only using 2 FETs but 4 or more shouldn't be a problem....

The photos show the testing only at low power levels but run it up to 150Watts for appox 30 minutes into a dummy load .... the FETs temperature got to 38 degrees C ( not sure what that is in F )....
The efficiency is just over 90% post filter but probably with a little more jiggling could go a little higher but as its only an experiment will leave it at that...
Might wind the Transformer using coax just to see if I can squeeze a little more though... ::)

The Class E looking waveforms are at the Drains of the FETs......


Wayne


Title: Re: Class D 80 meter rig progressing
Post by: N4LTA on September 26, 2019, 10:17:11 AM
Looks good Wayne. I am interested in the design.

I am putting the PWM boards in a Rack Mount enclosure and have spent the last week waiting on a punch for the meters. I got it yesterday so I will spend some of the weekend metalworking.

Meters are always fun to mount! Getting the hole is one thing and matching up the 4 mounting studs is even more fun. I also have to punch or some other way cut the rectangular power cord entry on the back. File work most likely.  Waiting for a illuminated toggle switch from Mouser also. Should be here today.

I backed down a bit on the power supply and am using a 600VA transformer rather than the HEAVY 1500 VA.  It fits the enclosure better and should have no problem at 350-400 Watt output. It is good for 15-20% more per the specs. I doubt I ever push more than 400 Watts.

I finished one of the TI boards with the 06 type SMT resistor and caps. Went to the eye doctor yesterday to see if I needed new glasses. That is definately as small as I want to go.
I had a special pair of reading glasses made. My eyes are so weird that I can use the drugstore ones.

I have a good friend who bought a 3CX1200 and socket as a initial special for hams by Eimac. He had it for years and I got it. So that may be another project. I am barefoot on HF. I have a nice 3600 volt power supply that I used with a 4-1000 160 meter amp and a 4CX1500 6 meter amp years ago.

I'll post some pictures later this weekend.


Pat


Title: Re: Class D 80 meter rig progressing
Post by: N4LTA on September 26, 2019, 05:48:08 PM
Decided to go ahead and punch the three meter holes this afternoon. First my 3/4" punch got a slug of 1/8" aluminum stuck in it. The meter punches themselves
require a 3/4" hole for the drive stud. Not getting it loose, I used a 7/8" punch to finish.

Them my really stupid mechanical stunt for the day. I had a 2 1/8 in punch that was just a bit two small. I bought a 2 1/4 greenlee and it arrived today.

After the 3/4 and the one 7/8" holes were done I popped in the big punch and quickly had three large meter holes. I grabbed a meter to test fit and  Uh O I used the wrong punch!

Believe it or nor  I was able to enlarge the hole with the new punch reasonable accurately - not as well as I had planned though. Meter placement is all that good.


Title: Re: Class D 80 meter rig progressing
Post by: Opcom on September 26, 2019, 07:37:28 PM
If the hole that looks lower were elongated upward, would the bottom of the meter still cover the bottom of the hole?
If so, can you beat flat the slug that came from that hole, enlargen the center hole in it, and put it in the panel hole?
Then put the punch in, offset to it elongates the hole enough?
Placing the panel on a 1" thick wood surface with a generous cutout for the punch and clamping it well.
Then punch the elongation!
Only will have one chance to do that.  Otherwise a new panel. It's only 1/8".


Title: Re: Class D 80 meter rig progressing
Post by: N4LTA on September 26, 2019, 10:23:36 PM
I ended up using a file and got it OK looking. All that planning ruined by being stupid!

Not The first time!

Pat


Title: Re: Class D 80 meter rig progressing
Post by: N4LTA on October 13, 2019, 03:45:34 PM
Getting some more metal work done.  Have to add the keying relay. It is due this week. Need to test the voltage on the supply and at no load and design a series MOSFET regulator. I have the PC Board done. Also to wire the Cap board and the low voltage supply board. The bridge is mounted on a small heatsink. Probably didn't need it as the full supply current is about 5 amps.


Title: Re: Class D 80 meter rig progressing
Post by: N4LTA on October 14, 2019, 05:39:52 PM
 Got the enclosure pieces all back together and etched the voltage regulator board. Waiting for a 10 amp power switch and a couple of relays that should show up Wednesday.

Will build the voltage regulator board tonight.


Title: Re: Class D 80 meter rig progressing
Post by: vk3alk on October 14, 2019, 10:21:23 PM
Hi Pat...

Everything seems to be coming along well.....

Is your TX going to be in another box ?
Have you decided on what materials you will use in your PWM LPF yet....?.
Have tried 3 different types and can detail those if you like....
Might be best to build the transmitter first and see what load it places on the modulator and then design the Filter for whatever it is like 6 ohms / 12 ohms etc:
With the TX are you going to try Nigels ..... has he sent you any details at all as he seems to be quiet at the moment....
Hope all is OK with him.......

Are currently building another 160M TX .... all the modules are built and tested and are building the case just like you so might upload some photos for interest sake....

Sounds like your regulator is just a regulator  :-\
Can send you the circuit for the one I use which has variable output voltage and over current with SWR rollback which is a good safe guard really....
You could build that afterwards and install at a later date perhaps...


Thats enough...


Wayne



Title: Re: Class D 80 meter rig progressing
Post by: N4LTA on October 15, 2019, 10:52:44 AM
Thanks Wayne.

Right now I am trying for a simple regulator like Nigel describe on one of his projects. I hope to regulate a few volts above the PS voltage at full load, so that the power disappation on the pass Mosfet is reasonable. Thinking something like 3 volts with 4 amps or 12 Watts. When the transmitter is not running, current will drop and voltage will soar but the current will be low.
Regulation is not a good word for the circuit, it is really an anti voltage soaring circuit. That hopefully will get rid of the relays in older circuits. May not work and I may have to build a regulator with an error amp. The transmitter will go into another enclosure. I do have a board etched that I can do bench testing with.

The filters will probably be on larger toroid forms but I will have to see what the transmitter draws. I  have wondered if the really nice looking air core  speaker crossover coils would work well. Some are available with AWG 12 and 14 wire.

I would be very interested in your regulator and your experiences with PWM filter materials. Also in your 160 meter rig.

Pat


Title: Re: Class D 80 meter rig progressing
Post by: N4LTA on October 19, 2019, 03:48:57 PM
Spent some time refining and slightly revising the power supply on the driver board. Made a new board  for T0220 MOSFETs and built and tested it this morning.

Hope to install it later today or tomorrow and maybe let some smoke out.

Got the MOSFETS  mounted on the heatsink and the board attached to the heatsink. the board will mount above the chassis and the first inductor will mount from under the board
as will the main power supply input .47 mylar capacitor.

Got the HV power supply running and burning in. Line voltage here is a little high and I am a few volts higher than expected. This is with the bleeder resistor drawing 32mA.

I used a large 200 watt 50 ohm resistor to test the full load voltage. It dropped to 157 volt. This works out to about 492 watts. This is about 19 volts difference from no load to full load.
Hopefully I can design a simple regulator to lower this difference substantially. I plane to do something similar to what Nigel has described. I appreciate all that Nigel had published that made this project possible.

One question that I am pondering is should the T/R relay switch the AC side of the power supply going to the bridge (easier to switch AC with a zero crossing with a relay) or to switch the DC input to the PWM board. Opinions would be appreciated.


Title: Re: Class D 80 meter rig progressing
Post by: vk3alk on October 20, 2019, 05:32:03 PM
Hi Pat...

Noticed you were online so thought would reply quickly....

I leave the power supply permanently connect to the PWM FETs.
The T/R switching is to enable / disable the IR2110 driver and have no problems doing this at all....
The pulse train is stopped ......

The TX pulse train is stopped by disabling power to the Flip Flop.....5 volts....

Will post details of the PWM LPF that have used soon....


Wayne




Title: Re: Class D 80 meter rig progressing
Post by: N4LTA on October 20, 2019, 05:51:15 PM
Thank Wayne. That is what I will do.

Did more testing this afternoon. Now messing with a voltage regulator and letting some smoke out. A 175 volt  supply with 18000 uF filter caps makes a nice pop when things go south.

The zener string feeding the gate of a power mosfet via a 47 ohm resistor has given me problems. The mosfet seems to saturate and I get the same output voltage at the source as I do at the drain input. Must be doing something wrong. I have attached an image of what I have tried. I have a 150 volt zener string that measures 150 volts as expected but the output is identical to the input at about 175 volts.

In searching the am technical forum archives I find this circuit for a screen regulator that may be helpful. With no load the power dissipated should be and as the supply droops under load, the power dissipated at full load with a few volts dropped on the MOSFET should also be doable with a decent heat sink.


Title: Re: Class D 80 meter rig progressing
Post by: vk3alk on October 20, 2019, 11:01:02 PM
Hi Pat....

OK on your regulator.....
There was a posting on this type of Regulator not so long ago on the Forum I think.....

Well to be honest ...... I would never use this circuit in this application.
Its just my opinion though ... for whatever that's worth as Nigel uses something similar without any problems ......

What I would do .... is finish your TX without this regulator and assess its performance then....
At a later date you could use feed forward like what Steve uses on his WEB site....maybe.....
You might find that it works well at the 300 Watt level but at 400 watts not so much.....for whatever reason.
At the receiving end no one would know the difference between the power levels....
A nice sounding transmitter is the main thing running a higher power level could come later...


Wayne





Title: Re: Class D 80 meter rig progressing
Post by: vk3alk on October 21, 2019, 04:20:50 AM
What a great response to your regulator post......

Might have some suitable zener diodes in my junk box......I hope.....
If so will build and abuse it a bit.... ;D


Title: Re: Class D 80 meter rig progressing
Post by: N4LTA on October 21, 2019, 06:29:31 PM
Wayne

I got some good advice but am still puzzled as to why my first try did not work at all. It was built like the schematic above missing some protective circuitry but still should have functioned.

The only real difference was I used a 10uF capacitor instead of the .01uF cap which is a big difference but i'm not sure it would cause the circuit to not work at all. I have etched a new circuit board with the added protection zener from gate to source and will test it as soon as I get it built but I am not confident. I am doing something wrong, but I can't find it.
I am using the same Modfet that Nigel suggested and it should do the job rated at 60 amps and 250 volts. I am getting the same voltage at the source as at the drain and the diode string is 150 volts as it should be. I built two boards and tested the first one with clip leads and had the above result. A clip lead slipped and I had a short  and the dropping resistor for the zener string blew up is flame and pretty much ruined the board - Using a multimeter - the Mosfet seemed OK, but I built another board using non electrolytic caps and a new FET with the same results.

Unless the .01uF 1 KV cap rather than the much larger cap changes things - then I am puzzled. I have been making the assumption that the FET pins out as a standard T0220 Mosfet - I better check that before I build the next version.

I am not worried about power dissipation since the supply droops substantially under load and the delta V of full current will be 5-6 volts at 3 amps or so.

Any suggestions or assistance is greatly appreciated.

Pat
N4LTA


Title: Re: Class D 80 meter rig progressing
Post by: WD5JKO on October 21, 2019, 09:55:39 PM
Pat,

   I attach a schematic of something I did years ago on a Sherwood S8000 Tube Amp / FM Receiver.

The FM section needed a stable and ripple free +170 volts. The draw was no more than 100ma, so the need was only modest.

Some things worth noting though:

Your regulator idea needs to be designed on some variables. Here are some:

Low Line voltage, maybe 110vac
Maximum load current, maybe 4 amps
Regulator DC input minimum at dip of the 120hz ripple. Example if the Regulator input is 150vdc at say 4 amps, and there is 10v p-P of 120hz ripple, then the Regulator DC input minimum is 145vdc.
Regulator differential voltage; try to keep this at something like 5v minimum with low line, maximum load current.

You may have to settle for a lower regulation setpoint if the unregulated DC voltage falls too low such that you cannot maintain >5v across the FET. Adding more capacitance after the FW bridge might help as well as it will reduce the ripple P-P amplitude.

A Constant Current Source (CCS) Feed to the Zener string. This helps keep the zener voltage constant when the DC input unregulated has 120hz ripple riding on the DC buss. Using a resistor instead of a CCS works fine, but using a good CCS will provide a lot more ripple reduction by the FET regulator, perhaps as much as 20db more reduction. A CCS will also give you better AC line regulation since the zener diode current stays constant as AC input varies. I attach a schematic of a CCS using a IXYS 10M45.

The R2-C2 time constant to provide a turn on delay, and further ripple reduction to the FET Gate.

It is important to have a 1K or more resistor to the gate as a Parasitic suppressor. For R3 I chose 1K.

I added a current limit resistor, R1. The idea was to help protect the FET when power comes up and the load is a short. The hope and prayer is that the FET will be saturated, and a fuse somewhere upstream will blow instead of the FET. In a high current application, something like R1 being 1 ohm or less might do. Eliminate R1 if you wish.

The Zener D5 is to protect the FET gate to source limit to +6.2v, -.6v. In a higher current application, make D5 something like a 12v or 15v zener.

The Sherwood had 4 separate regulators added, so I needed a FAN to blow on a small CPU heatsink. Zener Diode D1 was there to provide 7.5v to the 12v DC fan as a floating fan supply! Get rid of that diode for a 3-4 amp supply! Get fan power elsewhere...

Jim
Wd5JKO


Title: Re: Class D 80 meter rig progressing
Post by: N4LTA on October 22, 2019, 09:25:46 AM
Jim

Thanks for the excellent ideas for improving the circuit. I especially like the constant current source for the zener string. The 1K resistor in the gate circuit as a parasitic suppressor is interesting since other circuits have suggested 50 ohms. I also like the 1 ohm resistor as a current limit.

Initially this circuit was really meant as sort of an anti - voltage soaring device rather than a true voltage regulator but I can see the advantage of the many suggested improvements.

When I get it sort of working - hopefully soon, I may make a more complete circuit board for sharing as it would be an excellent circuit for this use and others such as screen supplies etc.

Thanks again for your help.


Pat
N4LTA


Title: Re: Class D 80 meter rig progressing
Post by: WD5JKO on October 22, 2019, 09:40:03 AM

Pat,

   I had attached the wrong schematic! Going from one computer to another via wireless, and I grabbed the wrong file. :-\

Anyway, the attached schematic here should better match the text in my last post.

That schematic in the last post was the +375v screen supply for the 7868 power pentodes. That works very well!

Sorry for the confusion.

Jim


Title: Re: Class D 80 meter rig progressing
Post by: N4LTA on October 22, 2019, 01:26:41 PM
Jim
 
I am confused at R1-  I read 55 ohms.

At .1amps that would have a voltage drop of 5.5 volts  - what does this resistor accomplish

Thanks

Pat


Title: Re: Class D 80 meter rig progressing
Post by: WD5JKO on October 22, 2019, 05:23:07 PM
Pat,

   That was only a 100ma regulator, so R1 at 51 ohms will drop 5.5v @ 100ma. In my case this was insignificant. I tested the concept once, and shorted out the output to ground with power off. Then I brought up the Receiver with a variac slowly. The FET had full bias caused from the voltage drop of R1, limited by D5 (6.2v zener). As I advanced the variac, the Receiver primary fuse blew. The regulator was fine since the FET was never in a high dissipation condition. I don't know if this would have worked with a sudden short once the voltage was up or not..I was too chicken to try. Others might add a current sense resistor downstream of the FET, and with a PNP transistor remove the FET gate drive when the current exceeds some threshold )I ~=.6/R). I never tried that, and worried that the FET with the gate bias throttled back would dissipate a lot of power. Plenty of ways to get more sophisticated here, such as current transformers, latches, etc.

Jim


Title: Re: Class D 80 meter rig progressing
Post by: vk3alk on October 22, 2019, 10:29:26 PM
This little circuit might be worth a go......

Should work ...... the 22uF capacitor may need increasing to 100uF to stop surging  :P ......as when the voltage across the .5R resistor reduces due to the shutdown it will fire up again and so forth etc:
The time delay should I think hold it steady......
The 500R trimpot will set the trigger point...

I cannot guarantee this will work satisfactorily but is a good play round.....


Wayne

PS:  I suppose there is a bit of a charge in C2 4.7uF :'(

Ohhh maybe the 6.2V zener will blow......
Will leave the post here now that its done.
Others may want to comment  :)


Title: Re: Class D 80 meter rig progressing
Post by: N4LTA on October 23, 2019, 05:29:29 PM
Worked on some PC Boards to day. Made a new one for the regulator to use a T0247 style device. Ordered a few from Newark and they should be here tomorrow. I get one day serveice as their distribution center is 20 miles away. They had a sale on the INFINEON  IRFP4229PBF  for $1.39 each so I got ten. They are rated at 250 volts at 44 amps. Should work well in the regulator circuit.

The old board was made to fit a T0220 device. I also added the protection devices that were suggested (15 volt zener and 6 amp diodes. I will use a wire leaded ceramic slo blo fuse.

While I was doing the PC Boards, I laid out a VFO based on W1VDs  VFO design which is based on Steve's  design.

I like the idea of a clean VFO and have found that the low cost digital stuff has to many spurs and trash. For AM - super stability is not required - although I have built stable solid state VFOs in the past

I hope to get back at the regulator and modulator tomorrow when the MOSFETS arrive.

Pat
N4LTA


Title: Re: Class D 80 meter rig progressing
Post by: N9NEO on October 27, 2019, 06:04:11 AM
Just curious what a Class D rig is so I thought I would ask here at bottom of thread.   

Is there a switching supply (Modulator) that audio-izes  voltage into rf deck or does rf deck provide modulation as well as carrier?  That would be similar the the RCA ampli-phase sustem of many yers ago.

Is there a link to the RF deck schematic you may have?

Thanks
NEO


Title: Re: Class D 80 meter rig progressing
Post by: vk3alk on October 28, 2019, 07:38:42 AM
Hi Neo...

The systems on this forum are definitely not the ampliphase way of things....

You could write pages on this subject but to cut it short for me anyway...... if you understand Tube technology plate and screen moduation than your there.....
A PWM ( what Pat is building ) is analog in and analog out......in between analog is converted into a digital form for efficiency reasons only really....
The audio is superimposed on the supply to the TX.....just like a 6146 tube stage....

The transmitters are a little different and maybe harder to understand......or maybe not....
They are frequency controlled by a crystal or VFO....the output FETs are pulsed on and off at their Gate inputs.....the output at their Drains shows this pulsed waveform but at a larger voltage......
This output waveform is rich in harmonics so a LPF is used to clean it up and so the output is just a sinewave similar to the crystal oscillator but at a higher level....
This pulsing effect gives to a higher efficiency .......

Jay W1VD has some circuits on the WEB....

Also reading Steve QIX WEB site is a good place.....

Thats all from me...


Wayne


Title: Re: Class D 80 meter rig progressing
Post by: N4LTA on October 28, 2019, 07:41:38 PM
That's a good explanation Wayne. They key thing I guess is that the transistors (MOSFETS) are either all on or all off and because the on resistance is measured in Miliohms the transistors have very low losses.

I had a bit of a setback Sunday after testing the power supply regulator at 3 amps at 150 volts. All was good - the longest key down was about 45 second because the 200 watt wirewound resistor just got too hot . The MOSFET was not a problem even at a delta V of 10 volts across the input and output. I decided to run the regulator at 1 amp for several hours and so what happened. I hooked up the resistor load and turned the power supply on and the AC fuse blew. I refused  with lod load and blew another fuse. I disconnected the rectifier bridge and again blew the fuse.

All the wires were disconnected from the transformer and still blew the fuse - I have ordered another transformer and expect it Wednesday. I know toroidal transformers have heavy magnetizing current - but it had worked for 20 or 30 on/off cycles s oI am pretty sure something internal to the transformer is shorted. Quick ohmeter checks found no winding shorted. I'll take a look after I get things back together. I purchased a relay for a step start but didn't use it. I may add that with the new transformer.

Pat
N4LTA


Title: Re: Class D 80 meter rig progressing
Post by: N9NEO on October 31, 2019, 05:21:58 AM
I think I am about 1/2 way there.  I'll go poke around and come back.

One question tho.  I think I got RF deck is mosfets.  Would the mosfets be switched at the rf frequency? 

Thanks,
NEO


Title: Re: Class D 80 meter rig progressing
Post by: N9NEO on October 31, 2019, 05:48:29 AM
Ok, got it. 

The W1VD design is based on I believe some work David Rutledge did on Class F Inverse.  I worked with David Cripe at Harris.  I believe Cripe has a patent on the design.

I had thought that you might be running the output mosfets at 10x the carrier frequency and filtering that.  At 160m with Gan parts that would be doable.

About 20 years ago I worked with Frank Carcia and Art Pightling on a modern re-invention of the ampli-phase design.  It used 4 fets configured in an H bridge. The antenna was across the 2 poles with a filter in series  The bridge ran at 1.88MHz.  By controlling the phase angle between the two poles the output could be controlled.  It was a slick little transmitter in that there was only one stage rather than a discreet modulator and RF deck. The transmitter was similar to the ampli-phase in that the phase angle between a master and slave was controlled.   I may have the paper on that somewhere.

The concept came to me while I was doing a full-bridge modulator.  You may be interested in the modulator if you like big power.  It was presented in QEX back in late 2003 I think.  If you would like I can probably find it.

Thank you
NEO


 


Title: Re: Class D 80 meter rig progressing
Post by: N4LTA on October 31, 2019, 09:14:43 AM
NEO

That would be great. Anything that involves switch mode transmitters or RF generation in interesting to me. As the MOSFETs get better and faster, there can be some very interesting things done with RF.

Pat
N4LTA


Title: Re: Class D 80 meter rig progressing
Post by: N4LTA on November 07, 2019, 11:15:48 AM
Finally got the W1VD VFO working. Pulled out some hair messing with this project. Could not get the 74F74 flip flop to work as shown in the schematic. Checkd the PC Board against the schematic, Tried several 74F74s, read the data sheet ten times, and changing the FET and Mosfet, etc.

After looking at the schematic 10 times, something didn't look right - after a quick Google check - D and /Q should be jumpered.
That fixed the problem

The schematic as published is not correct.

I'll probably make another circuit board this afternoon and stuff it. I had a few minor irritations on the original that need to be cleaned up.

I'll get it in a solid enclosure soon.

Pat
N4LTA


Title: Re: Class D 80 meter rig progressing
Post by: N4LTA on November 19, 2019, 07:06:57 PM
Finally got the VFO working and got back to the PWM. I installed a step start and did some rewiring to clean things up.

The power supply began blowing fuses and did so with nothing but the power transformer 120 volt winding connected. I assumed that the power transformer was bad and ordered a replacement.

I installed the step start and hooked things back up with the original transformer and it worked with no blown fuses. So I am back to getting the regulator installed and the PWM board. Hope I can get the whole thing going in the next few days. So I have a spare transformer now.

Pat
N4LTA


Title: Re: Class D 80 meter rig progressing
Post by: N4LTA on November 22, 2019, 08:00:25 PM
Gave the power supply some stiff testing today.  Ran it at 250 watts output for 3 hours and then kicked it up to 500 watts  for another two hours. The transformer was somewhat warm, the bridge rectifier was cool. I think it could stand CCS operation at 500 watt with a fan on the Toroidal transformer. I need to wire the meters and install the PWM module and to some more testing this weekend.

Pat
N4LTA


Title: Re: Class D 80 meter rig progressing
Post by: YB1AHY on December 05, 2019, 11:06:53 PM
Hi Pat...

Wonder what stage your up to now....?

Have been playing around with a CMCD 75M Transmitter and seems to be more or less in the ball park....
If you cannot get Nigel's TX to work this might be worth a try....
Made it only using 2 FETs but 4 or more shouldn't be a problem....

The photos show the testing only at low power levels but run it up to 150Watts for appox 30 minutes into a dummy load .... the FETs temperature got to 38 degrees C ( not sure what that is in F )....
The efficiency is just over 90% post filter but probably with a little more jiggling could go a little higher but as its only an experiment will leave it at that...
Might wind the Transformer using coax just to see if I can squeeze a little more though... ::)

The Class E looking waveforms are at the Drains of the FETs......


Wayne

Excuse me for riding on the current topic, but I think it's still relevant. hi Wayne I'm making a class D current mode like the one made by W1VD. the thing that is still mysterious is how to find the LC value that exists between D-D because the value is very uncertain depending on the value of Coss in the operating voltage (I compare it with the settings in class E from Mr. Nathan Shokal's writing). The question is how to set up to get high efficiency by looking at the waveform. Does the waveform before the lowpass filter have to be in the form of a sine wave? please give feedback to all who have tried. Thanks.

BR
Agus YB1AHY (ex YB0DJH)


Title: Re: Class D 80 meter rig progressing
Post by: vk3alk on December 06, 2019, 05:03:24 AM
Hi Agus...

There is not much about the theory of CMCD from what I can find on the WEB apart from Jays Website.....
I read his article .... thought about it and read it again and again really....
I have made two 40M Modules and they gave very similar results...with efficiencies in the low 90% for that band...
I was quite happy with the efficiencies and also the waveform at the drains mainly because of less demands for the LPF....
Its now permanently in my 40M TX and operates at 150Watts of carrier without any problems at all .... have attached a photo...
It will output more power but I'm happy with 150watts....

To be honest I build the 80M CMCD to see how it would go on another band as an experiment .... and also for Pat if he couldn't get Nigels TX going .... and applied whatever knowledge I had in working it out....

For what I know the inductor and capacitor form a low Q resonant circuit at your frequency of choice...with the inductor been adjustable by compressing or expanding etc:
The circuit cancels out the Miller Capacitance .... doesn't matter how thats done whether by the Class E way or this way....

When adjusting the inductor for maximum efficiency I didn't look at the Drain waveforms  ... although I did have a probe connected...
I just compressed and expanded the Inductor ..... changed the number of turns and also the value of the capacitor until I got  something good....
Its not very technical I know but I'm not a engineer.....
I started at lower power levels first and increased slowly until reaching 150watts....

The transformer is made using 4 FB1020-43 cores and do not get warm even under full modulation....
There are 2 turns of coax inside .... the center going to the drains and the braid to ground and LPF...

The Transmitter looks a bit junky .... but goes well...the modulator is a Class H and runs hot but OK using 4 power transistors..
I have moved the LPF and installed a SWR bridge since that photo.....

The FETs I used were STW20NM50 .... there a good Fet but are no longer made....good on you ST....

Hope that explains things somewhat Agus...


Wayne





Title: Re: Class D 80 meter rig progressing
Post by: N4LTA on December 06, 2019, 10:39:46 AM
Wayne

I have been busy with the PWM modulator the last week and finally have a working PWM generator. I made a new surface mount board and got the components mounted last night.
I ordered a low cost Chinese PC board pre-heater to go with my hot air station and I think it is going to work well with the tiny SMT parts and the small pitch spacing. Hopefully I will getthe PWM supply completed this weekend.

I have a four chip board designed and may build it this weekend. It uses the 1200 volt SiC parts. I'll try that with Nigel's circuit first and if I have problems, I am very interested in tour current mode design. I have all of the ferrite for that design and the teflon insulated coax.

I have three projects going on keeping me busy - this project, a SRS 551 small linear using tubes that Nico sent me right before he passed away, and a couple of 2A3 mono block single ended amps for a turntable that I am supposed to get for Christmas.


Pat


Title: Re: Class D 80 meter rig progressing
Post by: vk3alk on December 06, 2019, 05:34:50 PM
Hi Pat..

Give Nigels TX a try first ....be good to see how it all goes....
I always use low voltages first to see how it reacts and slowly wind it up etc:

Noticed you were doing other things too..


Title: Re: Class D 80 meter rig progressing
Post by: N4LTA on January 04, 2020, 03:32:33 PM
Finally got back to the class D RF section. Made a couple of test PC boards using the NC8107A driver. will test with a couple od SiC fets at 75 meters.

I  know that I will need some capacitance to ground? Anyone have an idea for a starting value?

It's getting close to smoke time. That's why I have two boards. Ill try with about 30 volts current limited.


Pat
N4LTA


Title: Re: Class D 80 meter rig progressing
Post by: N4LTA on January 11, 2020, 02:50:57 PM
Did a rework on the pwm driver and built one for testing the two MOSFET RF board.

May drive it with the TI designed  PWM board made for converting audio to PWM for a class D audio amplifier.


Pat
N4LTA


Title: Re: Class D 80 meter rig progressing
Post by: N4LTA on January 21, 2020, 08:36:48 PM
Made some RF today with a pile of boards and clip leads. Initially,  things looked better than I expected. I installed a 5 pole low pass filter on the RF board output About 37 volts peak to ground.


Current was somewhere near .5 amps or a little less. Not sure as my good Fluke has the 10 amp fuse blown and an older Fluke was about .4 amps and an old Simpson analog read .5 or so.

At .5 amps, the input power was 16.25 watts.

That made efficiency decent to good. Good for a low voltage test as the design is for 150 volts

There was some "fuzz" at the tips of the sine wave which concerned my but I was using the old TEK 400 MHz scope with a lousy probe, so I didn't get too concerned.

A look at one of the MOSFET drains concerned me more. I am not familiar  with what the wave forms should look like. The ringing did not concern me, but the high frequency "fuzz" at the top worries me. Any comments on the attached photos would be appreciated.


Pat Bunn
N4LTA


Title: Re: Class D 80 meter rig progressing
Post by: N4LTA on January 21, 2020, 08:59:29 PM
Here is the suspect drain waveform.

After doing some researching it looks pretty bad. I am wondering if the drain capacitors are not properly located. I have a 470uF 1KV silver mica capacitor from each drain to ground. Are these in the wrong place? Data on Nigels actual RF circuit is difficult to decode. I have used his drawing of the GaN 20 meter circuit as a guide.. He states that drain caps for 20 meters are not required?
I assumes those drain caps were from the drain bus on each side to ground, and assumed that the GaN drain capacitance was sufficient at 20 meters.

I am using C2 SiC devices here, using a dual winding 1:1 ration - I used 12 turns on a  powdered iron type 3 -  3" core. I have used the type 3 material up to and beyond 5 MHz in the past. I was looking to up the L to improve the bandwidth - should I go back to type 2? or are the caps in the wrong place.  As it is for testing - the power supply has a 1000 pF bypass cap. When I connect the PWM supply, that cap will be paralleled  with the PWM filter last cap. (something on the order of .2uF, depending on the power supply input impedance.

Pat
N4LTA


Title: Re: Class D 80 meter rig progressing
Post by: vk3alk on January 22, 2020, 03:12:59 AM
Hi Pat....

You seem pretty close really....
The waveform looks good apart from the fuzzy bit at the top...nice steep rise and fall ....

Could you upload the gate waveforms .... both overlapped ...
Same with the drains again both overlapped.....

Have never made a TX like this and not sure what turns using the type 3 material should be used....nor the capacitance to gnd...

What band is this for again... I thought it was 75M....


Wayne


Title: Re: Class D 80 meter rig progressing
Post by: N4LTA on January 22, 2020, 10:24:09 AM
It is for 75 meters. MOV said that he had to add more inductance when he used this circuit on 75 meters. that is why I went with type 3. It is rated up to 5 MHz, but maybe I m pushing it. I'll probably wind another one this afternoon with type 2. He said he had to use two separate transformers on 75. I'll do some experimenting. The PWM is ready to test also - so I am close.

This tangle is a test rig I lashed together to test the layout. I have a positive film ready to make a pc board for the same circuit with 6 devices and drivers. I have a 4" type 2 core  for it if the 3l doesn't work.

I'll post some gate and drain photos later. This is with my digital 200 Mhz scope. Not a great photograph. The fuzz seems to be frequency jitter from my Rigol frequency generator This is a one shot image with the scope. Looks reasonable.This is the gate and drain superimposed.

I raised the voltage to 75 volts and got 60 watts output with nothing nasty happening. The mosfets were not even warm. I may make a small transmitter with this board for local use and run at at 150 volts in to a  PWM modulator  That would give me about 60 watts carrier and 240 watts PEP with a couple of $4 Mosfets.

Thanks

Pat
N4LTA


Title: Re: Class D 80 meter rig progressing
Post by: vk3alk on January 22, 2020, 04:12:37 PM
The waveforms looks fine to me....
Duty Cycle about 43% on both  ...... all good...


Wayne


Title: Re: Class D 80 meter rig progressing
Post by: N4LTA on January 23, 2020, 08:02:35 PM
Decided to try to to get the two MOSFET rig ready to use by the weekend and in a more compact package.

Designed a power supply board with ell the voltage regulators needed and a regulated 150 volt main supply with current limit at approximately 2.5 amps. Also added a 74F74 flip flop to generate the two phase drive signal for the RF board. I have a 400VA transformer that is more compact and lighter. Hopefully it will all fit together in a small 300 watt or so PEP transmitter to test with.

I am waiting for a larger piece of positive resist PC board to arrive to make the larger 6 device board. Should be here before the weekend. I have a completed film positive waiting for it.

I have attached a couple of photos . The board is complete except for a couple of fuses and a bridge rectifier that will be here tomorrow. The MOSFET will need a heatsink. If I choose the proper zeners, it will dissipate  approximately 1.8 amps x 7 volts or  12.6 Watts max, probably a bit less. I am also working on a crystal oscillator board for 80 meters with a phase splitter that uses an inverter and buffer to invert the signal without creating significant delay between the two signals. Hopefully that will allow me to use some old 75 meter crystals with the transmitter.

Pat
N4LTA


Title: Re: Class D 80 meter rig progressing
Post by: N4LTA on January 25, 2020, 01:09:26 PM
Blew a MOSFET out this morning. Not sure what caused it.

I wound a new output transformer on a T300A-2 core. I used 8 turns but the ractance was still not 5 x   50 ohms. I noticed that Nigels 350 watt transfromer was a yellow -red core which  is very similar to the type 3 material I used originally.  The transformer put out a little more power, but as the voltage was increased at about 50 volts the power dropped rather than rising. I was running the drivers at 8 volts.  The fet blew up and the GFI breaker tripped. I am a little suspect of my power supply. The 74F74 phase inverter also seems to have blown and  this could have cause the problem initially. I have not tested the drivers or the other fet. . I will test the drivers and repair the 74F74 chip and set it all up again.

M0VRF  you mentioned using two transformers rather than the single one on 80 meters to get sufficient reactance.  I assume that one it to feed Vdd to the two drains as per Nigel's transformer.you mentioned the other as a 1:1 if I remember correctly.  I am not sure how the primary connects on this one - I assume it connects across the two drains??? -

Thanks for any help or ideas.

Pat
N4LTA


Title: Re: Class D 80 meter rig progressing
Post by: YB1AHY on January 31, 2020, 01:56:07 AM
Blew a MOSFET out this morning. Not sure what caused it.

I wound a new output transformer on a T300A-2 core. I used 8 turns but the ractance was still not 5 x   50 ohms. I noticed that Nigels 350 watt transfromer was a yellow -red core which  is very similar to the type 3 material I used originally.  The transformer put out a little more power, but as the voltage was increased at about 50 volts the power dropped rather than rising. I was running the drivers at 8 volts.  The fet blew up and the GFI breaker tripped. I am a little suspect of my power supply. The 74F74 phase inverter also seems to have blown and  this could have cause the problem initially. I have not tested the drivers or the other fet. . I will test the drivers and repair the 74F74 chip and set it all up again.

M0VRF  you mentioned using two transformers rather than the single one on 80 meters to get sufficient reactance.  I assume that one it to feed Vdd to the two drains as per Nigel's transformer.you mentioned the other as a 1:1 if I remember correctly.  I am not sure how the primary connects on this one - I assume it connects across the two drains??? -

Thanks for any help or ideas.

Pat
N4LTA

My study on the Nigel's transformer seems like the transformer is close to the point of resonance with MOSFET capacitance plus SHUNT Capacitors. If the circuit is at about resonant frequency, Current or Voltage Zero Crossing will occur. If you use rule of thumbs 5 x 50 ohm calculation that is the choke approximation and actually this is not, it is resonance circuit. If you intend to function as a choke as in the W1VD current mode class D circuit  you need a tank circuit to form waves at the resonance (or near) frequency.

My guess cause of you problem is that the left leg and the right leg switcher interact each other, energy that has not been used up on the left side is absorbed by the right side or vice versa. That is why RF output power decreases. in this condition the Mosfet is excess power dissipated and damaged. I recommend to check with the 2 CH Oscilloscope on the left side drain and right side drain at the same time and watch the waveform, make sure there is no part of waveform overlap one another. how to set? set the size of the C shunt, set the inductance of transformer, set the duty cycle of driver, check how proper you drive Mosfet in term of peak Voltage, over drive sometimes creating anomalies in Drain waveform.

My 2 cents.

BR

agus..


Title: Re: Class D 80 meter rig progressing
Post by: M0VRF on January 31, 2020, 03:59:15 AM
8V on the drivers is not enough (for SiC, fine for GaN). The FETs will still be 'resistive' and dissipate a lot.
Try 12V.

J.


Title: Re: Class D 80 meter rig progressing
Post by: vk3alk on January 31, 2020, 06:34:24 AM
Hi all....

8 volts does seem a little low not that I have used those FETs before....

And Agus .... I think your 2 cents is too cheap and agree with your comments.....
You might have 180 degrees phase difference at the gates but not at the Drains...
There is a lot of energy swinging to and throw across the output transformer when switching between each push pull module etc:

Also Pat have built up a TX module that maybe of interest to you......
Its just for your information thats all.....and may give you ideas and stuff..

The module is H Bridge design and definitely does not have the querks of Push Pull TXs....
The load is 13R so its more High Voltage low current unit....
So at appox 50 volts applied the input power is 204 watts and the output is 189 watts ...appox 92%...
This is a little short of what you wanted but building 2 modules and using a Combiner is easy to do......
You could leave it going all night and day most probably.....

Its a different way of doing things but this is good for forums etc:


Wayne


Title: Re: Class D 80 meter rig progressing
Post by: N4LTA on January 31, 2020, 02:03:08 PM
Wayne

What MOSFETS are you using this design. I'd love to see more of the design.

Pat
N4LTA


Title: Re: Class D 80 meter rig progressing
Post by: vk3alk on January 31, 2020, 05:07:53 PM
Hi Pat...

There IRFP240s ....... around $2.50 each .......

To be honest not many FETs work well in H Bridge and of those all probably would work in Push Pull circuits....
These were in my box labelled " there worth a try "......
They needed a lot more drive power then the other FETs I use but they ended up working well.....
I think ....... there is too much induction using 4 cores as using only 2 the efficiency is slightly better...but they run at a higher temperature of 52 degrees which isn't too hot .....
I might order some FT114-43 cores and stack them and make my own core if you know what I mean.....


Wayne


Title: Re: Class D 80 meter rig progressing
Post by: N4LTA on February 05, 2020, 09:00:43 PM
Wayne

What are you using in the CMCD transmitter for the tuned circuit between the drains?  W1VD shows a 1000 volt ATC porcelain and a air coil inductor in parallel. I have not had any luck in the past finding a source for the high Q,  high voltage, low ESR capacitors which I am told are required. In some pictures that you posted, it looks like you may be using a Russian silver mica cap. If those work that would be excellent.

My board layout lends itself to connecting a CMCD configuration.

if I can find a workable parallel tuned set of components, i'd like to try it.

Thanks

Pat
N4LTA


Title: Re: Class D 80 meter rig progressing
Post by: vk3alk on February 06, 2020, 07:25:23 AM
Hi Pat....

Yes there those Russian Silver Mica Capacitors....
I used 2 in parallel .... a 750pF and 1500pF....
The coil gets very very hot so 1.8 to 2mm ECW is best when everything is finished...
I used 1.2mm for testing ... easier to adjust etc:
Had to play around there a bit .... changing the capacitance and expanding / squeezing the coil to get the efficiency right....
The FETs are STW20NM50s ..
If you use different FETs or number of FETs the values will change ... probably not by much...

I rewound the transformer with coax .... can post another photo if you like...

I wound the transformer to give a 6 ohm load to the PWM .... the efficiency was in the low 90s .... winding it to a load of 3 ohms gave slightly better efficiency.
Noticed that Jays CMCD has a very low loading as well...
Cannot explain why but its what my FETs liked....

I built up Steves Duty Cycle circuit as well to obtain appox 43% or so....

I much prefer High Voltage low current though....


Wayne


Title: Re: Class D 80 meter rig progressing
Post by: N4LTA on February 06, 2020, 09:14:29 AM
Another photo would be great. I have some Russian SM caps. I have all the stuff to make Jays transformers also. I may have even some already made. I have three transformers wound. I used a lot of Jay's design's back when I was doing the high powered LF stuff with the experimental license.

Thanks again for all of your help.

Pat
N4LTA


Title: Re: Class D 80 meter rig progressing
Post by: N4LTA on February 11, 2020, 09:24:39 AM
I replaced the blown MOSFET and driver and re-wound the output transformer. I also built up a new phase splitter board using Rod's design. I have a prototype board coming this week for Steve's circuit. I did this one 2 sided so I had to send it off for manufacturing. 2 sided is more trouble for me to do than I like. Steve's circuit allows for duty cycle adjustment.

I also built a Butterworth filter board and a test design for using a crystal at the fundamental frequency, doubling the frequency and then cleaning up the doubled square wave to get a clean 2 x squarewave that will work with the splitter circuits, allowing me to uses a few of my older crystals on 75 meters. This is all SMT and I will have to wait a day or so on the chips.
I have be experimenting with SMT a good bit. I have used a low cost plate heater and a hot air station and have had fair results. I bought an oven from Amazon and am modifying it and changing the software. If it works as expected, I may do less through hole work and save the drilling.

I have used RCA type jacks for most signal leads lately on my boards. Amazon sells RCA to BNC adapters cheap. Probably not great for return loss but cheap and easy for low level digital signals.

I'll build the filter today and may try to generate some RF.



Pat
N4LTA



Title: Re: Class D 80 meter rig progressing
Post by: N4LTA on February 13, 2020, 10:11:59 AM
Got the filter done and changed the bad driver. No drive with the new driver. Oh well must be a bad MOSFET - changed it. No drive on that same side. Checked with a magnifier. Everything looked fine.

Got some new PC boards for 4 MOSFETS, so I assembled 4 drivers and all of driver parts and installed a MOSFET on each side. Plugged in a the drive circuit and put 9 volts on the four drivers.
No drive at the output of any of the four MOSFETS.  What???  Shut down and went to read spec sheets. Nothing. The truth table was as I designed it so I am puzzled.

Went to watch TV and then remembered on thing! I couldn't have done that could I? Yes I did.  The drivers come in an A and B series. The A is 5 vollt TTL and CMOS compatable. The B series is based on the voltage feeding the drivers - I had installed B series drivers .

Went back to the old test board with two MOSFETS. It was late, but I removed the B driver with Quick Chip ( I love that stuff) and installed a A driver. Drive on the gate as expected. Installed a new MOSFET and fired up the board at 6 volts - about 5 watts, a nice sine wave. Shut down and put the heatsink back on.  50 watts with 25 volts, 100 watts with 60 volt - nice smooth adjustment. At about 110 watts, the heatsink was barely warm.

THEN  -  it was late - lets do something stupid - I raised the Vcc on the drivers on the fly to about 12 volts - power went up slightly - running about 110 watts - then 0 watts.

Lowered the driver voltage and turned off the main DC to the board and turned it back on.  It started working again??? repeated the above and it tripped again at 12 volts on the drivers and 110 watts.

Tried it again and this time it tripped at about 50 watts and is now dead - Drivers are gone on both sides, not sure about the MOSFETS.

Went to bed on that!  

Good things learned    - the output transformer worked very well - the output filter worked very well - it appears that the input impedance for the two MOSFET rig is about 30 ohms  so the 4 MOSFET rig will be about 15 ohms. That will make filter inductors for the PWM output smaller and more managable.the driver.

I am still very puzzled as to how the drivers shut down several times before failing? Any ideas? I can find nothing in the specs that describes a overload or any type of shutdown designed in

Pat
N4LTA


Title: Re: Class D 80 meter rig progressing
Post by: N4LTA on February 15, 2020, 03:08:55 PM
Nothing stupid today so far !

Got the 4 MOSFET deck built with a larger transformer. Here is what I got at first RF:

25 volts   1.1 amps   21 watts on my Daiwa CN 901 wattmeter

30 vots   1.3 amps    30 watts

35 volts   1.45 amps   34 watts

40 volts  1.53 amps  55 watts

50 volts   1.8 amps   86 watts

60 volts   2.14 amps  122 watts

70 volts    2.7 amps   175 watts     this is where I am shooting for carrier to give me 700 watts PEP  - may have to drop it a bit depending on my power transformer output current. Looks like about 25 ohms at the power supply so that is what I will design the PWM filter for. Not bad though for 4 Mosfets.

Transformer is a 600VA toroidal at 116 volts so it should be good for a minimum of 5 amps . Supposed to be good for 20% overload.

78.4 volts at  3.26 amps    250 watts - as high as I  could go with my variable bench suoply - it went into current limit at 3.3 amps

The drivers and the heatsink were just barely warm at 122 watts.

But am getting there. The Daiwa meter is fairly close to what I was observing on the scope. The scope after the filter was a nice sine wave.  I need a slug for the Bird for 250 or 500 watts at 2-30 MHz.

Pardon the very cluttered bench.

Pat
N4LTA




Title: Re: Class D 80 meter rig progressing
Post by: vk3alk on February 15, 2020, 06:47:06 PM
Hi Pat....

Things are starting to come along well......
The efficiency is good too so things look OK....

The load impedance ...... if it was my TX would like it to be lower.....28R is rather high for power levels limited by your Power Supply...
And on the Power Supply ... 116VAC only gives you appox 160 volts.....
You have resistive losses in the transformer too and also your regulator ....
I would work around 150 volts under load to the PWM......
Remember as well the PWM works on a Mark to Space ratio best set to 60:40 to allow head room for modulation peaks etc:
So I would work around a maximum of 60 volts to the TX....

Maybe you could comment on that Rod.... :)

For my TXs that H Bridge a few posts back gave 13R load....its perfect for my stuff....
Develops quite some power at 50 volts with the power supplies I have....etc:

I would play around with the turns ratio on your output transformer just to bring it down a bit...

What power levels are you after ....

Wayne


Title: Re: Class D 80 meter rig progressing
Post by: KQ6F on February 15, 2020, 07:09:18 PM
Yes I'm with you, Wayne - 28 ohms is much higher than usual.  Depending upon what power he's hoping for, the power supply may be a challenge.

Am also puzzled by Pat's pix - they show only one transformer.  I was under the impression he was going to follow the topology I have which requires two transformers with their secondaries connected in series.

Oh well, nothing wrong with new circuits and more experiments...

Rod


Title: Re: Class D 80 meter rig progressing
Post by: N4LTA on February 15, 2020, 10:39:21 PM
My boards were layed out with two parallelled FETs on each side so I used Nigel's single transformer. Nigel's load for three FETs on each side was 13 ohms and he got 350 watts out at 70 volts. That made for a legal limit transmitter. I am looking for  about half that power with the same power supply voltage so 25 ohms seems close. I am using SiC 1200 volt mosfets as Nigel used.

My power supply is regulated at 150 volts, as was Nigel's and so the impedance is going to be higher. I was not using my PWM supply  - I was using a bench supply for testing. My PWM supply supplying the modulator deck  is 150 volts regulated at about 5 amps maximum. I have tested it at 3.8 amps for several hours, so that I know the supply can handle that much load. The transformer is good for about 5 amps. Voltage drops to 157 volts and 3.5 amps - so I may need to find out what it drops to at 5 amps and regulate it a bit lower by changing the zeners - but that makes the regulator FET dissipate more heat. May have to change the regulator.

Nigel ran his carrier level at 70 volts and about 350 watts with 6 FETs. At 70 volts, I am getting about 175-180 watts with 4 fets which is a bit low.

I am shooting for 700-750 out PEP.

Using Jim Tonnes paper on PWM filters, The L values are not unreasonable at approx 750 uH and 500uH . Lowering the impedance would lower them.

I need to play with the secondary turns. I am running the drivers at 9 volts

Shooting for about 60 volts on the carrier like Wayne suggests is probably a good starting point

As things are, I am feeling pretty good as the efficiency is good. I may try to excite the deck at 40 meters and see what that does to the efficiency.

I put a bank of power resistor totaling about 25 ohms The power supply voltage dropped to about 144 .7 volts at a current that was about 5.6 amps as read on my Fluke DC clamp on an d the power supply analog meter. That works out to over 800 watts, so the supply can handle my projected load. The supply was run at the level for over 10 minutes. Voltage stayed within 1.3 volts. That was the raw loaded supply.  The load was a couple of 100 ohm plate resistors and a 600 watt dry 50 ohm dummy load. 10 minutes did not overheat anything. The transformer was  just warm. The power supply is a 50 ohm heat sinked bridge rectifier and 10,000uF of filter capacitors.

My voltage regulator will have to have the zener string changed. It is set at 150 volts. A good target is 140  volts. The pass MOSFET will need a larger heatsink.   4.7 volts at say 6 amps will be the likely worst case so a bit under 30 watts is a good bit of heat to get rid of. I may clip lead it in and see how hot it gets.

I am assuming that if I set the carrier level at  60 volts or about 120 watts, that the power supply needs to deliver 480 watts minimum  at 100 percent modulation.


I wish my bench supply that goes up to 120 volts could do another amp or so, so I could see exactly what the deck requires at full modulation.

Pat
N4LTA


Title: Re: Class D 80 meter rig progressing
Post by: KD6VXI on February 26, 2020, 12:29:02 PM
Pat,

Instead of the zener string driving the gate of the regulator fet, why not try a LR8?

The LR8 will regulate to 400 plus volts DC, just at a very low current.  Not a problem when driving the gates of fets however.

Have the LR8 output drive the gate.  Take the resistor divider to the adj pin off the source.  That way you are sensing the output.

Think of them as a low power lm317 that will regulate from something like 4 to 400 volts.

I'm using one as a screen supply for a pair of 250B tubes now.  Two 840 fets as a pass regulator and a 50watt resistor string on the output to sink any negative screen current. I dump 25 watts as heat, but it's below the rf deck in a the pressurized compartment, so heat really isn't an issue.  This gives variable bias from 200 to 350 volts and can vary the power output quite nicely.

Of you'd like, I have a spare LR8 and a couple 840s I can send gratis.

--Shane
KD6VXI


Title: Re: Class D 80 meter rig progressing
Post by: N4LTA on February 26, 2020, 03:58:53 PM
Shane

Thanks for an excellent idea. I was not aware of the LR8.

It sure beats a string of 5 watt zeners and the dropping resistor heat. I have found that if you dissipate more than a couple of watts, a 5 watt zener may get hot enough to melt solder, and this is with long leads.

I just ordered ten and should get them early next week. I'll change the regulator circuit as soon as they arrive.

Thanks again! Also thanks for the offer.  They sound like something I need a lot of so I bought ten of them.

Pat
N4LTA


Title: Re: Class D 80 meter rig progressing
Post by: KD6VXI on February 26, 2020, 07:36:32 PM
The LR8is a Tl431 on some serious steroids.

Yeah, I also buy them by the 10 packs.

With the capabilities of the LR8, I may just use it to run my bias board instead of the 431.

--Shane
KD6VXI


Title: Re: Class D 80 meter rig progressing
Post by: N4LTA on March 02, 2020, 06:36:54 PM
Got some work done on the PWM this weekend. The problem was a bad IR2110. I pulled the old one off the board and replaced it and the inverter works fine now. A strange and not expected problem. Things look fine and I had designed a permanent double sided board which arrived today so I am building a new board. Changing parts had the original board in bad shape.

I'll complete it and test it tonight and tomorrow.

I also got the LR8s in today so I have some more work to do.

Pat
N4LTA


Title: Re: Class D 80 meter rig progressing
Post by: N4LTA on March 04, 2020, 10:15:15 PM
The IR2110 is giving me fits. The input circuit works fine now after changing the chip.

The #1 pin (low side) works fine telling me the enable circuit is working. Pin #7 stays high at 12 volts all the time - no pulses when enable is low.

The relay circuitry works fine and the off delay seem to be working. Maybe an for the high side other bad chip but that seemed pretty unlikely - I changed it but have the same results.

The app notes show a F4007 as the FRED. I have used it and two other freds . The 10 uF electrolytic bootstrap cap  does not seem to be the best cap , but I ordered some special low ESR caps. I changed it to a 4.7uF MLCC and then used a low ESR Tantalum in parallel with a 1uF MLCC.

I still suspect the bootstrap circuit but not sure what to do next. The board is so simple around the chip there is not much to check. Polarity on the FRED has been checked 10 times and all the chip to part connections have been checked multiple times with an ohmeter.

Nothing has helped - It can't be that hard?

Pat
N4LTA


Title: Re: Class D 80 meter rig progressing
Post by: M0VRF on March 05, 2020, 01:03:18 AM
I'd check the input.

JB.


Title: Re: Class D 80 meter rig progressing
Post by: N4LTA on March 05, 2020, 09:22:30 AM
I found the problem. Something stupid. Looked at a TI Ap Note about how the bootstrap works and it was obvious. The previous bad IR2110 had blown out a MOSFET so I was trying to test with no MOSFET. Can't do that as the MOSFET is part of the bootstrap circuit. - Duh

Learned a few things also. I was feeding the board with 3 volt high logic, zero volt low from my function generator which works fine with 5 volt TTL logic. had worked fine with my other circuits.
I had fits with the 2N7000 mosfet inverter. It would not switch reliably with a 3 volt signal. Figured it out by bread boarding the circuit. Works fine at 5 volts high.

I ended up with a 100uF bypass on the IR2110 and a 10uF MLCC chip for the bootstrap capacitor.

With 50 volts on the output it does fine and the unsinked MOSFETs were cool feeding 30 watt 22 ohm resistor to smoking hot. They were so cool that I didn't think they were working and burned myself on the resistor. I  was feeding a square wave  at 100 kHz and could vary the duty cycle with the generator and the output followed the input.

Next I'll hook up the PWM generator and see how that goes.


Pat
N4LTA


Title: Re: Class D 80 meter rig progressing
Post by: vk3alk on March 05, 2020, 09:33:03 PM
Hi Pat...

Sound like things are coming along....

Have you decided what materials / cores your going to use for the PWMs LPF ?
Also Cutoff frequency .... load .... etc:
What sampling frequency are you going to use ?



Wayne


Title: Re: Class D 80 meter rig progressing
Post by: N4LTA on March 09, 2020, 10:17:50 PM
Have tested the Modulator and completed the filter designed for 15 ohms. I have the power supplies, voltage regulator, metering and the modulator board mounted in a rack mount enclosure.

It has been tested with a PWM signal from a generator that is Nigel's design and seems to be working as designed. I have swept it from 100 Hz to 15 kHz and run for 48 hours.

Next I will run it with a load and see where I am with the filter and power supply. The modulator board is shown in the second image with the filter installed connected to the voltage regulator board.

Pat
N4LTA


Title: Re: Class D 80 meter rig progressing
Post by: vk3alk on March 10, 2020, 08:29:02 AM
Hi Pat....

Yes its coming along.....looks good...
Was your transmitter load 28 ohms or have you changed it now....or did you use 15 ohms because of the amount of turns on the toroids etc:
Just wondering.....
Also what cutoff frequency have you used for the LPF ?
I think your sampling frequency was 150-160Khz......


Wayne


Title: Re: Class D 80 meter rig progressing
Post by: N4LTA on March 10, 2020, 12:29:54 PM
Hi Wayne,

I used Jim Tonnes paper to design the filter. Presently the cutoff for the filter is about 9 kHz. The cores are from CWS BYtemark as recommended by Steve and M0VRF and made for this type application. My sampling frequency is about 140kHz  but very easy to change.

I am building a new transmitter double sided board with an onboard 74F74 phase inverter and 3 amp regulated power supply for the drivers and a 5 volt regulator for the 74F74 .

I also have to play with the turns on the output transformer to get the PWM input impedance down and hopefully close to 15 ohms. 15 ohms is about as high as I could get with the cores I have.

I may have to use something else as a core material if I can't get it lower - or maybe better raise the cut toff frequency of the filter.

Pat
N4LTA


Title: Re: Class D 80 meter rig progressing
Post by: vk3alk on March 10, 2020, 05:32:16 PM
Hi Pat...

Jim Tonnes filter calculator is good and use it often....

9Khz is FAR too low for the cutoff frequency for your PWM LPF....
Steve uses 15Khz and I use even higher at 25Khz...
In the real world there is a lot of ripple at the 3db point going back towards your audio frequencies so I would use 15Khz at the minimum  :) .....
I think Steve quoted somewhere that 2.5 times your highest audio frequency is the lowest frequency for the cutoff of your filter....
It saves all those turns on your Toroids as well...

OK on the new TX ...


Wayne


Title: Re: Class D 80 meter rig progressing
Post by: N4LTA on March 11, 2020, 10:22:10 AM
I used Jim Tonnes filter design white paper for Class D and E PWM filters. Have you read it?  I just normalized his 1 ohm design to 15 ohms. I just guessed at the cut off from the graph in his paper.


Pat
N4LTA


Title: Re: Class D 80 meter rig progressing
Post by: M0VRF on March 11, 2020, 02:04:01 PM
You can use a much higher frequency and put a top cap across the last inductor to notch out the clock as that's all the filter is for.

I use a cut off of 45KHz with a -60dB notch at 150KHz.

J.


Title: Re: Class D 80 meter rig progressing
Post by: vk3alk on March 11, 2020, 11:04:29 PM
Hi Pat...
This part of the Modulator is really interesting and is worthwhile spending time reading up on....etc:...
If you play around with the Tonnes Calculator you will discover how the number of poles / cutoff frequency / loading etc: can have on your transmitter overall....
But bad things can happen without you knowing or realizing etc:
I don't use Motor Controllers for any of my PWM Generators .... for 2 main reasons...
......Sawtooth waveform
......Free running oscillator
My Generators are all Crystal locked divided down and pickoff 250Khz .....there is a reason for that frequency but will leave that for now....
Just say you decided on using Jons LPF with a 45Khz cutoff....and notching out the PWM sideband....
Running 1500 watts PEP all good.....but just say at some temperature your Motor Controller went frequency wobbly..... :o won't hurt the motor..
Your only defence is your notch filter now ineffective and relying only on the 40db attentuation of your filter....
Although the chance of this happening is low .... the fact that it can happen is why you design your filters.....

Hope I have not rattled on too much and Jon not saying your filters are a poor design  :)

Thats all....


Wayne



Title: Re: Class D 80 meter rig progressing
Post by: N4LTA on April 11, 2020, 01:00:16 PM
My project took a turn for the worse. Had a serious fire in my garage and lost nearly everything. All is insured but it sill be a long recovery. Will be out of the house for 4-6 months. No one was hurt so all is OK.

Pat
N4LTA


Title: Re: Class D 80 meter rig progressing
Post by: K6IC on April 11, 2020, 01:31:47 PM
WOW,  Pat,   very sorry to hear of this.

Please take care.  Hope that you have a "safe" place to live in the interim.

73  GL,  Vic


Title: Re: Class D 80 meter rig progressing
Post by: vk3alk on April 11, 2020, 07:36:46 PM
Ohhh I'm very sorry to hear that too Pat.....

We never know whats going to happen...


Wayne


Title: Re: Class D 80 meter rig progressing
Post by: YB1AHY on April 11, 2020, 09:53:49 PM
I'm sorry to hear this incident, hopefully returning to normal soon

de agus


Title: Re: Class D 80 meter rig progressing
Post by: N4LTA on April 12, 2020, 04:24:14 PM
Thanks for all of your thoughts. I had a workroom with a large table and two metal lathes and all my power tools and a newly purchased R388 and DX 60. These were melted with everything destroyed. About 35 Akro Mills cabinets full of new and vintage stuff, a new 3cx1200 and socket, a new 4-1000 and socket and two new 4cx400C tubes as well as probably 500 or so vacuum tubes - all good ones not junk TV tubes as well as  thousands of active and passive components. My semiconductor bins had hundreds of older Mosfets and FETs that are no longer available. The more that I search the worse it seems. I think the parts and items will all be paid for but there is no way to replace.

Again - no one was injured and all will work out. I will get a new shop built as I want and a new electronic lab. I lost a $12000 telescope and $5000 more in other telescope equipment.
I have a roll off roof observatory where most of my telescope equipment was located and it was not damaged. I sold a $6500 TEC refractor a couple of week before and it would have been lost if not sold.

Pat
N4LTA
AMfone - Dedicated to Amplitude Modulation on the Amateur Radio Bands