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Re: Singing light bulb on dimmer switch

A capacitor "attempts" to maintain a constant voltage (I=C dv/dt),
causing a current to keep the voltage the same. An inductor "attempts"
to maintain a constant current (V=L di/dt), causing a voltage to keep
the current the same. When the thyristor turns on, there's 0A going
through the inductor, so the full line voltage ends up across the
inductor. The current then ramps up at a rate inversely proportional to
the inductance (lamp resistance makes this an RL circuit, so it ends up
being an exponential ramp with time constant of L/R, but when the
thyristor first fires, the ramp starts out linear). This is exactly
what we want. The instantaneous current rise is slowed down to several
hundred microseconds of rise time. I can't think of how you'd be able
to limit the current slew rate with a capacitor. Sorry!


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