Re: Triac question

["Stuart Meier" <stuartm2007@xxxxxxxxx>]

Hmm, yes, think of it as a simple dimmer (gate current developed via a
diac,
capacitor, resistor combination) on full brightness. That should work one
way only, question is, can one omit the cap and the diac without impinging
on reliability.

Stuart
----- Original Message -----
From: "Nick Austin" <nick.w.austin@xxxxxxx>
To: <ukha_d@xxxxxxx>
Sent: Monday, September 24, 2007 1:16 PM
Subject: Re: [ukha_d] Triac question


> On 9/24/07, Stuart Meier <stuartm2007@xxxxxxx> wrote:
>>
>> Thanks Nick, but I think that as shown it will work when BOTH left
and
>> right
>> are on, but not when EITHER (ie OR!) the left lamp, or the right
>> lamp...hence two relays (or other devices)
>
> Oops.  I didn't read the question correctly.
>
> The problem with TRIACs is generating the gate voltage.  It needs to
> be alternating otherwise the TRIAC will only conduct on one half
> cycle.  It must rise rapidly after the zero crossing point otherwise
> the TRIAC won't switch on soon enough and it acts as a dimmer.
> However it must then stop rising because if the gate voltage is too
> high it destroys the TRIAC.  Tricky.
>
> The relay/contactor solution sounds much easier.
>
> Nick.
>