MOSFETs (active rectification) in place of diodes in linear PSU

[UnixMan]

In order to trigger a thyristor, a small current should be made to flow from gate to cathode, so you should connect the secondaries of the pulse transformer between these legs.

OK... BTW, I would say that the return path was there already (via the ground connection). 😕

There is no point in inserting the secondary windings of the main transformer in the trigger loop.

how would you sync the PWM driver to the mains frequency, then? 😕

As a control circuit you may consider the good old TL494 synchronized to the 50/60Hz waveform and with its internal clock programmed for 40Hz or so operation. The TL494 will be fine since it

I'll have a look at it...

I forgot to mention that you are going to need some kind of high frequency pulse generator with on/off in order to feed the trigger transformer. A LM393 comparator may do the job

that could be done... but wouldn't a simple CR do the trick?

 

[UnixMan]

I believe nearly all transformers with voltages for tube B+ will have center taps.

except the one I have. 😀

Indeed, in my case (having only ~220Vac on the secondary) I've been a bit dumb not choosing a center-tapped PT, even if I was planning on using sand anyway. 🙄

But if you consider a PSU for tubes which requires several hundred or even over 1 KV dc, using a center-tap PT would be rather troublesome, or at least quite expensive.

I would focus on the control strategy and topology... the fine points of design. Then, decide which SCR layout makes the most sense to you.

agreed.

Just a thought, there may be silicon modules for light dimming that may be useful for AC synch and control of "firing angle"... might save you a lot of parts.

😀

mmmh... intersting idea... it's definitely worth some search...

 

[poobah]

In any topology you will need a second low voltage winding to derive "house keeping power" for the start-up control. This winding can provide synch.

If you have no center tap, you are forced to use 2 diodes and 2 scr's.

 

[Lars Clausen]

We use it commercial products with good results.

Per Anders: I have always been wondering where you work in the daytime 🙂

All the best from

Lars

 

[Eva]

peranders:

Ouch!!

I have seen these BTSxxx ICs priced anywhere from 3 euro/piece the lowest current models to 12 euro/piece the 8 miliohm version, so I think that I will continue with my discrete solutions...