TRIACs: A triac is a bidirectional, three-terminal dual, back-to-back connected (SCR) switch. This device will conduct current in both directions when a small current is constantly applied to the Gate.
If the gate is given a small, brief, current during any instant of a cycle, it will remain triggered during the completion of the cycle until the current though the Main Terminals drops to zero.
This means it will conduct both the positive and negative half-cycles of an AC waveform. If it is tuned on half-way up the positive waveform, it will remain on until the wave rises and finally reaches zero. If it is then turned on part-way on the negative wave, the result will be pulses of energy and the end result will be about 50% of the full-energy delivered at a rate of 100 times per second for a 50 HZ supply.
TRIACs are particularly suited for AC power control applications such as motor speed control, light dimmers, temperature control and many others.
BUILD YOUR OWN TRIAC TEST CIRCUIT:
1. Connect an TRIAC with its test points.
2. Apply 12V Dc Power Supply.
3. Press Switch 2.
4. The lamp should not illuminate. If it illuminates, the TRIAC is faulty.
5. Keep Switch 2 PRESSED.
6. Press Sw1 very briefly. The lamp or motor will turn ON and remain ON. If the lamp does not turn on, reverse the TRIAC as the current into the gate must produce a slight voltage between Gate and Main Terminal 1.
7. Release Sw 2 and press it again. The Lamp or motor will be OFF and its Good Condition.