Can a ac dimmer switch be used with bridge rectifier to convert to dc and control out put?

Question

Can a ac dimmer switch be used with bridge rectifier to convert to dc and control out put?

Answer 1

AC dimmers work on the principle of cutting off the AC voltage at different times in the AC cycle.  Each 1/2 cycle of a 60 Hz sine-wave takes 8.33 milliseconds.  Depending on the dimmer setting (bright to dim), the cycle to the lamp starts late in that 8.33 milliseconds -- from no delay (bright), to say 4 ms delay (dim), to full 8.33 ms delay (off).

The problem is, the peak voltage of the AC is still present for delays up to half of the 8.33 ms, therefore a rectifier will still charge a capacitor up to the full peak voltage of the AC line.  If the dimmer is set for delays past 4.17 ms (1/4 of the cycle time), THEN you can start to see some difference in the DC output.  

If the load is sufficient, and the circuit is designed properly, then current could be drawn from the filter capacitor to make it seem like a DC dimmer, for AC dimmer settings less than 1/4 of the cycle time.  In other words, it would work, but not very well compared with other methods.  You would end up with strange effects up to about 1/2 of the AC dimmer settings, then the current to the load would fade-out fast at the low end of the AC dimmer setting.

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Answer 2

That depends on whether your dimmer is for incandescent or flourescent.

Incandescent dimmers are just a variable resistor, which drops the voltage linearly.  If you reduce the voltage in to a bridge, you'll reduce the voltage out.

Flourescent dimmers wait for an adjustable threshold voltage to be reached along the sine curve, before turning on.  This delay will reduce your RMS voltage, but not necessarily your peak voltage into the bridge.

Assuming you've got a capacitor after the bridge, either should work.

The incandescent dimmer is cheaper, but tends to dissipate more heat, as it is a resistor.