The AM Forum

I built a board using Nigel's PWM modulator circuit. I haven't soldered in the power FETs as I have ordered some better FETs per Nigels comments. ( IRFB4227 FETs)

The PWM Modulator will use a 160 volt power supply with the power transformer rated at 1500 KVA

Hope to start testing this week as soon as I get a PWM generator up and running. I have some 1/8" copper bar to mount the FETS on as a spreader for the heat sink. I really don't expect much heat.

N4LTA

Hi Hugh

All looks good...... :)
Thought I would reply as there was none on your last post a few days ago....
My only advise would be to use a low ESR capacitor in the charge pump area .... pins 6 & 5....nothing but squarewaves there...
This might be interesting reading
https://www.avnet.com/wps/portal/abacus/resources/engineers-insight/article/understanding-esr-in-electrolytic-capacitors/
Also for the fast diode use a known one say from mouser / digikey
Avoid ones from China as a while ago now the ones I ordered were fakes and it blow up destroying extra components....etc:

For the heatsink the photo attached could give you some ideas...its not a PWM but a switcher .....

Only some thoughts thats all.....


Wayne

PS:  found it important to ground the heatsink assembly from my experience anyway.....

Wayne,

Thanks for the advice. The FRED is a uN4007 from Newark so I should be OK there.

Not sure how good the cap is in the charge pump area. I have some better quality tantalum capacitors. I may change that one.

Appreciate the help.

Pat
N4LTA

Hi Hugh...

I would stick to a new 100uF low ESR electrolytic capacitor......

That area of the circuit is important as the top FET does most of the work and needs to be hard ON and OFF if you get what I mean...
uF4007 will be Ok but I now use the BYV26C diode...
They have the same specs but are physically bigger.....will post a photo of both .....

Have now attached photo showing the difference between them....


Wayne

I ordered a couple of low ESR Caps today along with a few of the AVX caps mentioned in the article you suggested.

I am also looking for a typical class D output transformer circuit. I have built them with transmission line type transformers for low frequency but would rather
use conventional transformers.

Some photos on this website (Nigels)  have dual windings but the actual connection is difficult to see. The enamelled winding tie together on one end but the other end is difficult to see.

Same for the plastic insulated winding. I have not seen these shown in any schematic. Can someone describe it or sketch a diagram?




Pat
N4LTA

Привет !

The windings are clear enough and wound in opposite directions with a center tap on the DC side.

There's further clarification in another post, on here somewhere.

You can also use 2 seperate 1:1 toroids as also mentioned in said post.

It's the same design that's been around for a while.

Regards, Stay Well.

JB.

заходите в гости
www.6p3s.ru

I've being using this layout for some time.

Similar to Nigels design, very neat about 1" sq.

Has a DC-DC to give 12V from a Max Vcc of 75V to power the board and the drivers on the RF (4xNCP81074's)

A relay driver is included to switch in the Vcc to the RF whan enabled.

I use a PIC to detect various events to enanble or disable this..

J.