It is a long time since I last used a TRIAC driver, but the circuits I
used (with the MOC3063) had a resistor between the gate and MT1, to
ensure any leakage current could not build enough voltage to trigger a
sensitive-gate TRIAC.

Isaac



On 24/02/2015 02:52, stephen.forrest@agilent.com wrote:
> Hi Everyone -
> Well, after probably 15 years lurking, a couple of posted responses and a=
 few private ones, I have my very first question of the list!
>
> I am having some trouble with a triac phase control circuit (attached) wh=
ere I am getting a half wave conduction fault with the triacs. (This is a f=
ailure mode where the triac conducts for half a cycle even with no gate sig=
nal.) I have found numerous references to this failure mode around the web =
but never any clue as to its cause. The load is either a resistive heater p=
ad or a blower. Neither are of high power - about 100W - and I have found t=
he fault with both types of loads. I have seen no sign of over-heating, nor=
 of any other stress. The triacs trigger properly on the other half cycle.
>
> Any ideas as to the cause of this type of fault? I am at a loss...
>
> Cheers
> Stephen
>
>
>
>

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