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Registered Member #152
Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384
Hi all, my friend would like to have a portable (light-weight) solution to control the voltage to his DRSSTC bridge. It is fed from doubled 230V mains (~660VDC max on the caps).
Would it be possible to regulate the voltage with a SCR or a Triac?
I guess the peak currents might be huge though, may a moderately-sized inductor fix this problem? What about the SCR gate control, would the simple diac circuit suffice, or would I need a dedicated mains-synchronised adjustable phase-lag circuit?
is solid state control just as good as a variac? could you have a comparator watching the bridge voltage to control the power switch (triac on ac or a fet/igbt after the rectifier) or is a pwm controller like a tl494 necessary?
Registered Member #152
Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384
Thanks for the schematics, but I'm afraid they're a little too complicated for him... I can make a simple adjustable phase lag circuit using a 74HC14 chip and some passive components, I hope that would be just good enough.
My other question was about the choke/inductor, as I have no idea what value to use.
Registered Member #30
Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706
Hey guys
A few people have done simpler versions of my circuit over the years, check the forum and archives.
I myself have a simpler one with two 555s:
This page also discusses inductors. A large one (say 5mH) improves the power factor. But if you don't mind poor power factor, you can get away with a much smaller one. You calculate the required inductance from the peak mains voltage and your SCR's critical di/dt value. For beefy SCR bricks, the stray inductance of the mains wiring may well be enough! But bear in mind that any EMI filter upstream of the SCR may contain capacitors that would negate it.
You may be able to get away with a dimmer switch designed for transformer loads. Or then again, you may not The complexity of my circuits is partly because they're hard fired and guaranteed to "dim" any load.
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SCR voltage controller for a DRSSTC bridge supply
The complexity of my circuits is partly because they're hard fired and guaranteed to "dim" any load.