Check breakdown voltage of SCR gate when going negative.

I hope this fixes it.

SCR's are nice, TRIACs are just two SCRs after all, when working
with DC some people use TRIACs when it would make sense to use SCRs.

Cheers,
Mario


At 00.22 2011.12.31, you wrote:
>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
>http://www.piclist.com PIC/SX FAQ & list archive
>View/change your membership options at
>http://mailman.mit.edu/mailman/listinfo/piclist

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