Triac Testing Circuit PCB

Posted on Feb 7, 2014

Here is a very simple triac tester circuit which can be used for testing of SCRs as well as triacs. The circuit could even be used for checking of pnp and npn transistors. The circuit works on 3V DC, derived using a zener diode in conjunction with a step-down transformer and rectifier arrangement, as shown in the figure. Alternatively, one may pow

Triac Testing Circuit PCB
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er the circuit using two pencil cells. For testing an SCR, insert it in the socket with terminals inserted in proper slots. Slide switch S3 to on` position (towards a`) and press switch S1 momentarily. The LED would glow and keep glowing until switch S2 is pressed or mains supply to step-down transformer is interrupted for a short duration using switch S4. This would indicate that the SCR under test is serviceable. With switch S3 in off` position (towards b`), you may connect a milliammeter or a multimeter to monitor the current flowing through the SCR. If the SCR is no good, ` the LED would never glow. If the SCR is faulty (leaky), the LED would glow by itself. In other words, if the LED glows only on pressing switch S1 momentarily and goes off on pressing switch S2, the SCR is good. For testing a triac, initially connect its MT1 terminal to point A (positive), MT2 to point K (negative), and its gate to point G. Now, on pressing switch S1 momentarily, the LED would glow. On pressing switch S2 momentarily, the LED would go off. Next, on pressing switch S5, the LED will not glow. Now reverse connections of MT1 and MT2, i. e. connect MT1 to the negative and MT2 to the positive side. For a good working triac, S2 would not initiate conduction in the triac and the LED would remain off. On the other hand, momentary depression of S5 would initiate conduction of the triac and LED1 would glow. The indication of a leaky triac is...

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