How fast can garden variety triacs switch?

        I guess this is a loaded question, no pun intended.  If
you trigger a triac gate at the same point in the cycle of a sine
wave, it will turn on during the remainder of that half cycle and
produce pulsating DC much like a diode can except that one can
control the turn-on point.  If the AC voltage was some high
frequency such as 10 to 100 KHZ, then one could produce DC of
either polarity or low-frequency AC by selecting which half-cycle
train to trigger on and by advancing or retarding the pulse to
catch various parts of the quadrant as the half-cycle returned to
0 in order to vary the voltage.
        One would then use a filter choke to remove the actual
oscillator ripple from the output and what is left should look
like an AC sine wave at some lower frequency such as 50 or 60 HZ.

        The advantage would be more efficient AC power inverters
and the like.

        I am guessing that triacs have quite a bit of internal
capacitance, however.  Since they are usually used to switch
mains-frequency signals, a few nanoseconds doesn't matter, but it
would matter at higher frequencies.

        Has anyone actually tried it?  I have gotten them to fire
at audio frequencies, but I don't know how efficiently they did
it.

        If the high-frequency signal was a square wave, the
theory should still work except the output would be a series of
varying-width pulses of DC whose polarity would reverse at the
low-frequency rate.  The filter choke would be what varied the
voltage.

        Just another weird idea.

Martin McCormick WB5AGZ  Stillwater, OK
OSU Center for Computing and Information Services Network Operations Group

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