MOSFETs (active rectification) in place of diodes in linear PSU - Page 5 - diyAudio
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Old 17th January 2006, 02:25 PM   #41
UnixMan is offline UnixMan  Europe
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Quote:
Originally posted by Eva
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).


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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?


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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...


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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?
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Old 17th January 2006, 02:42 PM   #42
UnixMan is offline UnixMan  Europe
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Quote:
Originally posted by poobah

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.


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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.


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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...
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Old 17th January 2006, 03:19 PM   #43
poobah is offline poobah  United States
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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.
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Old 17th January 2006, 03:34 PM   #44
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Old 18th January 2006, 06:45 PM   #45
Eva is offline Eva  Spain
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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...
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