Why modulator AND power supply?

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Why modulator AND power supply?

Postby N9NEO » Tue Apr 08, 2003 11:57 am

Can you combine the two.

example - rectuify and filter 120vac. Use half or full bridge topology with smps controller . Use feedback input on controller as audio input.

No input supply voltage maybe 100vdc. With good modulation swings ps goes near zero to near 200vdc.

Seems simple to me.

Regards,
Bob
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The ultimate

Postby steve_qix » Tue Apr 08, 2003 2:01 pm

This is absolutely the ultimate way to go!

By using direct rectification of the line, switching the DC, and feeding this through a transformer, you can completely eliminate the heavy power transformer. The unit will be lighter and much less expensive.

It's simply a matter of "lack of time" at this end :-)

If you have any design ideas, let us know what you've got!

Regards,

Steve WA1QIX
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Postby frank carcia » Mon Apr 14, 2003 3:28 pm

Some day when I get some guts I will take my 2 phase modulator and have 1 phase per final. The duty cycle will run 0 to 50 %. Each phase will have it's own filter. Next I will full wave rectify the 240 volt line making about 180 VDC. Since each modulator phase will only do 50% max each final will see one half the full supply voltage or 90 VDC. This is living in a quite dangerous shack with Ready K.W. as the current limit. That was my intent when I built my rig but still like that isolation transformer as a peak current limiter. 15% total efficiency gain isn't worth the risk yet.
yup i'm chicken. fc
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Postby N9NEO » Mon Apr 14, 2003 11:14 pm

Modulator with power supply design

Read paper on Unitrode phase delay ZVS resonant full bridge. I think part is 3879. Can run easy to 200kHz, and design is straightforward. Transformer leakage inductance resonants with fet capacitances and transformer stray capacitance. Can use 200v mosfets. No ref voltage pin though. Could put audio in series with FB loop. Can wind gate drive xfmrs on little EE19 or smaller core. There is another Unitrode part that has Vref input pin. 3886 maybe.
73
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Postby Dan Brown » Thu Apr 17, 2003 12:56 pm

Hi All:

I have dreamed of this idea for a couple of years now.

I would take an old IBM PC power supply and use the line rectified 200v DC, send that to a PWM regulator isolate it and to regulate to maybe 150V.

I would then use another PWM controller as the modulator.

Maybe this can fit in the box of the PC supply.

Spring is here and I'm too lazy to try it!

73
Dan W1DAN
73
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Postby frank carcia » Thu Apr 17, 2003 4:19 pm

200 volts peak on the final at RF may be pushing it. Hey Steve could you try it on your Rig? Dan, the computer power supply would need a output filter change to allow audio high end through. These configurations were set up for a minimum load so might go unstable near negative peak. Then the output voltage will be kind of low. fc
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more direct mains PWM

Postby VK3KRI » Fri Apr 18, 2003 6:05 am

Dan Brown wrote:Hi All:

I have dreamed of this idea for a couple of years now.

I would take an old IBM PC power supply and use the line rectified 200v DC, send that to a PWM regulator isolate it and to regulate to maybe 150V.

I would then use another PWM controller as the modulator.

Maybe this can fit in the box of the PC supply.

Spring is here and I'm too lazy to try it!

73
Dan W1DAN


Why PWM twice? If you can get a feedback loop stable, yet with decent frequency response, you only need one PWM stage, Of course actually getting the loop fast enough and stable may take more effort that actually saying it!.
Also, you'll have to isolate the ground of the RF amp from 'real' ground as your powersupply ground is going lots of volts + and - at a 50/60 hz rate. This shoulldn't be too much of a problem if you use transformers in and out of the RF amp. (I have done this on my Class D , PWM TX as it was easier to have the modulator MOSFET source grounded and effectively modulate the -ve rail of the amp .. If only I had enough time in one hit to actually finish it!)

PC power supplies make cheap cases, complete with fans. You can't beat the $0 price once you strip the internals..
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Postby Dan Brown » Sat Apr 19, 2003 6:27 am

Hi All:

Interesting notes!

The only reason to PWM twice is to give the second regulator (the real audio modulator) a good steady input and to allow the modulator section to be referenced to ground.

Frank:
Yup all the output filtering and even the switching transformer and regulator would have to be re-designed. With this system, we can create any voltage up to about 200v and have mucho current available. 200v should never get to the FET's though, just the DC voltage required to make whatever + modulation at your interested carrier level. You could have a voltage set pot on the first regulator to set the max DC wanted.

Ian..
I have worked more on audio compression and limiting in my days, and find that 2 separate loops with the separate and isolated time constants (first slow for a compressor and then fast for a limiter) work the best.

I have not designed switching feedback filters, but have read about them in many PDM IC docs. It seems to get difficult real fast (more than one pole). So, my simple thought to get the job done is to have a "slow" DC regulator (can be done with a PDM chip with one R/C time constant on the feedback loop) then have an audio modulator after that (100% duty cycle PDM chip, no feedback). Whenever the line rectified DC gets chopped by the first regulator, it'll go through one of those small isolation transformers. So the other side of this (the modulator) can be at house ground potential.

Tell us more about your transmitter though. Sounds interesting!

Thanx for the ideas!
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