Hi,

I'm building some simple pic-based thermostats, which will have to
keep some technical rooms above freezing.
Controller part is fine, and one version of power part is fine, too.
It's based on MOC3062 optocoupler and BT138 triac. Connections are
directly as per MOC's datasheet, with resistors of 360 ohms.
I used ordinary 1/4W resistors, without any problem, that device is
working fine in test mode, switching a 500w heater.
(230 VAC 50Hz here)

For another application, halogen lamp is used as a heater, mainly
because they can be obtained really really cheap, and will direct the
heat, so I can mount it out of way. But those burn out very quickly
when switching on-off too often.
So, I decided to use one-way thyristors instead of triac, so i could
turn on half power initially, then power another one in opposite
direction after a delay. Looking thru available info, it seemed like
same circuit should be fine, in this case, two of them. But the gate
resistor is letting out magic smoke, it receives much more power!
Thyristors used are BT151, from datasheet their gate currents are even
smaller than for BT138.

I have forgotten many things about these, so probably I'm missing
something. Probably MOC3062 can not detect zero crossings, and is
feeding gate current differently? Probably thyristor requires
different circuit? Any ideas?

I really really do not want to just use bigger wattage resistors,
since whole device will be mounted in not-so-big plastic case and
unnecessary heat is unwelcome.

--=20
KPL
--=20
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