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Class D 80 meter rig progressing




 
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WD5JKO
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WD5JKO


« Reply #25 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
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* SS_HV_REGULATOR.jpg (170.12 KB, 2160x1660 - viewed 63 times.)

* pcb5.jpg (9.42 KB, 500x500 - viewed 68 times.)
* IXCP10M45S.pdf (519.59 KB - downloaded 16 times.)
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N4LTA
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« Reply #26 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
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WD5JKO
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WD5JKO


« Reply #27 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. Undecided

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


* REGULATOR2.jpg (160.39 KB, 2160x1660 - viewed 70 times.)
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N4LTA
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« Reply #28 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
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WD5JKO
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WD5JKO


« Reply #29 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
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vk3alk
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« Reply #30 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  Tongue ......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 Cry

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


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N4LTA
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« Reply #31 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
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N9NEO
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« Reply #32 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
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vk3alk
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« Reply #33 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
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N4LTA
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« Reply #34 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
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N9NEO
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« Reply #35 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
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N9NEO
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« Reply #36 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


 
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« Reply #37 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
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« Reply #38 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
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« Reply #39 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
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