On Friday, Dec 26, 2003, at 13:06 US/Pacific, John N. Power wrote:

>> TR2's data sheet says it needs a max 50mA of gate current to turn on,
>> and 240/5600 is 42mA. From the datasheet's graphs, it looks like the
>> minimum Igt is 16mA. I've tried it with a 9.6K resistor in there and a
>> fresh triac, but still no light.
>
>
You're not wanting to turn the triac on when the voltage is 240V, you
want
to turn it on when the voltage is near zero.  The fairchild data sheets
have MUCH smaller resistors in their "sample schematics" (360 ohm for
240V)
I didn't look carefully enough to see to what extent you MUST limit the
isolator output current, and I don't have any relevant experience.  But
I'll bet 5.6k is way too big...  (This implies that triac circuits
normally
waste quite a bit of gate current.  Interesting.)

BillW

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