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Class D 80 meter rig progressing




 
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N4LTA
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« 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



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N4LTA
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« Reply #1 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


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N4LTA
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« Reply #2 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
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vk3alk
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« Reply #3 on: August 27, 2019, 07:46:45 PM »

All looks good and things moving along nicely  Smiley

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
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N4LTA
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« Reply #4 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
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KD6VXI
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« Reply #5 on: August 27, 2019, 09:29:34 PM »

What's the chip number?  I'm interested.

--Shane
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N4LTA
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« Reply #6 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



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N4LTA
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« Reply #7 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.


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N4LTA
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« Reply #8 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.



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N4LTA
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« Reply #9 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!


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