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Hi John,

Attached is a Triac schematic I have used for controlling an AC source with a
PIC I/O.  The SCR is really a TRIAC device.  Also, you will have to find a
different TRIAC as I think the T2800 is rated up to 200V.

Cheers,

Paul

In a message dated 11/7/00 8:39:31 AM Central Standard Time,
John.Walshe@INPACTMICRO.COM writes:

<< Hi guys,
     I'm having a bit of a problem driving a triac from a pic.
 The electrical main is 220Vac 50Hz.
 I have the Vdd of the pic connected to the live and Vss is 5v less than
 live.
 I have a PNP transistor: emitter to live, collector to triac trigger,base
 via resistor (1k) to the pic i/o pin. The base is also connected to the live
 via 10k resistor (to prevent false trigger at powerup).

 My theory is that with the pic i/o pin high the transistor is off and
 therfore high z to the trigger so no leakage current can trigger it.Thus the
 triac doesn't conduct.
 With the pic i/o pin low the transistor is switched on and the trigger gets
 all the current it needs and the Triac conducts.

 The triac I'm using is a BTA12 from Philips (logic level driven device).

 My target use is for a small motor but I'm using a lightbulb for testing.

 The Problem: The bulb is always on!

 I thought I had all the bases covered but obviously I'm missing something.

 Has anyone got an idea what this 'something' is.

 Thanks in advance
 John >>

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