A bidirectional thyristor (also known as a bidirectional silicon controlled rectifier) is a semiconductor device that can conduct in both directions, widely used in power control and conversion circuits. To ensure its normal operation and performance, it is necessary to measure it using a multimeter. This article will detail how to use a multimeter to measure bidirectional electrodes.
1. Identify the T2 Electrode
Using the multimeter set to R×1 or R×100, measure the reverse resistance of each pin. If the measured forward and reverse resistance of the two pins is small (about 100 ohms), then these two pins are T1 and G, and the remaining pin is T2.
2. Distinguish between G and T1 Electrodes
Set the multimeter to R×1.
Assuming one of the two identified T2 pins is T1 and the other is G.
Connect the black probe to T1 and the red probe to T2; the resistance should be infinite.
Short circuit T2 with G using the red probe to apply a trigger signal to G; the resistance should drop to around tens of ohms, indicating that the thyristor is conducting.
Disconnect the red probe from G (while still connected to T2); if the resistance remains unchanged, it proves that the thyristor can maintain the conductive state after being triggered.
Repeat the above steps but connect the red probe to T1 and the black probe to T2, then short circuit T2 with G and observe the change in resistance to verify the bidirectional triggering property.
3. Verify the Performance of the Bidirectional Thyristor
Turn the multimeter knob to R×1.
Connect the red probe to T1 and the black probe to both G and T2.
Ensure that the black probe does not disconnect from T2 while disconnecting G; the needle should indicate tens to over a hundred ohms (this varies depending on the thyristor current size and manufacturer).
Swap the probes and repeat the above steps; the needle should indicate slightly more than the previous reading, indicating good thyristor performance.
4. Precautions
Ensure that the power supply is disconnected during measurement to avoid electric shock hazards.
Before using the multimeter, ensure it is set to the correct measurement range and mode.
During measurement, avoid short-circuiting the probes or accidentally touching other parts of the circuit.
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