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I've built this triac test circuit here: https://320volt.com/en/triyak-tristor-test-devresi/ enter image description here

My transformer only delivers 10.5 V, however.

I've tested some triacs which seems to work well. Both LEDs light up when the button is pressed.

However, when releasing the button the LEDs turn off.

I've already reduced the load resistor from 470 Ohm to 100 Ohm to 10 Ohm hoping that this would make the triacs latch. This increases the current from 22 mA to 105 mA to 1 A.

I've double and tripple checked my circuit, everything seems to be fine.

The datasheet for the BTA16-800B states a holding current of 50 mA.

What could be the reason that the triacs don't latch even with a low load resistor?

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    \$\begingroup\$ Doesn't your 12V AC input go through 0 volts twice in every cycle, so the current would also go to zero? \$\endgroup\$ – Elliot Alderson Feb 24 at 20:12
  • \$\begingroup\$ That's right. So I would need a DC source to make the triac latch. But may I ask if it is necessary at all to test the latching of a triac to see if it is working properly? \$\endgroup\$ – Auto-Mark Feb 24 at 20:16
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    \$\begingroup\$ Whether or not it is necessary depends entirely on how you intend to use the triacs. \$\endgroup\$ – Elliot Alderson Feb 24 at 20:22
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I've tested some triacs which seems to work well. Both LEDs light up when the button is pressed.

Good.

However, when releasing the button the LEDs turn off.

They probably turn off at the end of the half-cycle.

schematic

simulate this circuit – Schematic created using CircuitLab

Figure 1. A low-frequency AC supply with manual alternation.

Connect this to your existing circuit. You'll be able to toggle the supply and hit the test switch and observe the latching operation.

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