# Light dimmer with capacitor

by jerrytrey   Last Updated October 09, 2019 23:25 PM - source

I have a capacitor in series after a light dimmer. How could I calculate the voltage and current through the capacitor? simulate this circuit – Schematic created using CircuitLab

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Actually, this could be a tricky question, because a light dimmer will typically have a pulse-width-modulated output, so assuming a sine wave, driving the cap and lamp would not be correct.

If you had a pure sine wave and simply wanted the Magnitude of the current, then you can compute the Reactance of the cap, and add that in series with the lamp resistance as a simple series circuit and compute the sine wave current. For example; Reactance = Xc = 1/ (2 x Pi x F x C) F = Hertz C = Farads

If R is the resistance of the lamp, in ohms, and the AC sine wave voltage is V, then the resulting Magnitude of the current, I is; I = V / ( Xc + R)

I use Spice for most complex circuits. It is a very nice program and there are various free versions. I use LT Spice from Linear Technology. Just do a search engine search and download it. It is very capable.