Re: A question for the Electrionic Gurus.....

[Nigel Orr <Nigel.Orr@xxxxxxx>]

At 11:36 07/07/00 +0100, you wrote:
>Can someone please explain to me/the group how you could dim a lamp
using a
>solid state relay? I already have my own thoughts....i.e. turning it on
half
>way though the mains cycle would cause it to be on at 50% (approx)...

That's the usual way of doing it, make sure you don't get a zero-crossing
SSR though, a lot of them are, and they will only switch at the crossings,
not at the peak.

The problem is that this method is electrically noisy, worst at 50%,
because there's a sudden 'step' as the power goes to the bulb, but it's
what is used in the majority of dimmers.

The usual circuit basically charges a capacitor through the variable
resistor, when the capacitor voltage gets to 32V a diac breaks down and
allows a triac/SSR to switch.

The electrically quietest way to do it is to resynthesise an AC waveform at
the required voltage, but that's a lot more complex.

There's probably more info at the Electronics info pages
http://www.epanorama.net , very
useful for the things that haven't yet made
it to http://www.howstuffworks.com !

Nigel


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