Tony Nixon wrote:

>Hi all,
>
>Well I got my wings presented to me the other night :-)
>
>
Congradulations!

>As part of my circuit, I used a relay to convert a full wave rectified
>AC input to a half wave to detect when the "time set" switch is pressed.
>This is just a series diode being switched in and out of a leg of the AC
>path to the full wave rectifier.
>
>Is there a way to do this without a relay?
>
>
Yes.  It's called a Silicon Controlled Rectifier (SCR).  When the scr is
triggered it stays on until the current is zero, and dureing its on time
it acts as a diode.  This is very useful in AC applications as the
current falls to zero 120 times a second.

Put two SCRs in anti parallel in series with the AC line.  Turn them
both on to get full AC.  Turn one off to rectify the AC to DC going one
direction, turn the other off to rectify it the other way, turn both off
to turn the AC off completely.

A triac is essentially two SCRs in anti-parallel with their triggers
connected together.  You're building a triac with two triggers.

-Adam

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