Triac speed controller for handheld drill

[gaminn]

I modified the circuit a little. The circuit ground is now connected to active in. Therefore the gate drive for triac1 had to be modified also. Please see schematic.



The issue now is that the triac triggers only for one half wave (so it acts like a thyristor). Any idea why this happens? I can't figure it out. Also if you see any other drawback of my update, please let me know. Thank you

[gaminn]

This is what my scope shows me. Green is circuit's ground (just for reference), blue is G of triac related (as I don't have a scope isolated from mains, perform blue minus green to obtain waveform referenced to circuit's ground) and yellow is A2 of triac.

According to https://www.electricalclassroom.com/triac-operation-symbol-circuits/ it seems that the triac has problems to trigger in quadrant IV. Any idea why this happens?

I already tried to decrease resistor in series with the gate of the triac (20 ohm) and I also made the trigger pulse a bit longer (300 us, originally it was 100 us).

The triac is BTA41-600B of an unknown manufacturer...

[gaminn]

OK, I tried the triac out of the circuit, using two power supply units. The first one was set for 22V and max 3A and the second one was set for 5 V and max 0.2 A. The first one was connected between A1 and A2 pins of the triac and the second one between A1 and G pins.

With all possible polarity combinations, I'm not able to trigger the triac in quadrant IV (A2 being positive to A1, and positive trigger pulse).

It seems that the combination of voltage and current on the gate pin that triggers the triac in quadrant IV is V > 10 V and I > 0.1 A. Even V = 7 V and I = 1 A does nothing (the triac conducts only 0,1 A momentarily, once the trigger voltage is removed it stops conducting).

As I already wrote the triac is BTA41 600B. I can't see any text related to my issue in its datasheet. Any idea? Is that just low quality triac out of specs?