Triac help

[Flump]

I am using a BTA 41 Triac in a crowbar circuit which is triggered by a zener diode
the weird thing is the crowbar triggers at slightly different voltages 16.5 and 13.something
depending on which way wound i have the + and -  on the Triac

anyone got any ideas why this should be, I thought it was just two diodes inside so shouldn't
matter which way the + and - go as it just goes closed circuit when tripped.


http://www.farnell.com/datasheets/1689729.pdf

[miceuz]

Posting your schematics would really help the people to answer your question.

[David_AVD]

The MT1 and MT2 terminals on the TRIAC are not always interchangeable from a trigger point of view.  Check the data sheet for the TRIAC you're using and read the section about the different quadrants.

[Richard Head]

That simple circuit is known to be dubious at best. The problem is that the zener leakage current and variable triac trigger current all contribute to alter the trigger point.
A much better option is to use a comparator. This eliminates both issues.
Also, thyristors have a higher surge current rating than triacs, so would be a better choice.

Dick