Testing a Unidirectional Thyristor Using a Digital Multimeter
Testing a Unidirectional Thyristor Using a Digital Multimeter
A unidirectional thyristor, also known as an SCR (silicon-controlled rectifier), is a controllable rectifying device. Its circuit symbol is shown in Figure 1, where A = anode, K = cathode, and G = gate.
Performance Testing of Unidirectional Thyristors
(1) Identifying the Electrodes
Keep the red test lead connected to one pin, and touch the other two pins in turn with the black lead.
If the meter shows 0.2–0.8 V for one pin and overrange (OL) for the other,the pin connected to the red lead is the gate (G),the pin showing overrange is the anode (A),and the remaining pin is the cathode (K).
If the above result is not obtained, move the red lead to another pin and repeat the test until the correct condition is found.
(2) Checking Triggering Characteristics
The diode range of a digital multimeter supplies only about 1 mA, so it can only test the triggering capability of low-power SCRs.Proceed as follows:
Keep the red lead connected to the anode (A), and touch the cathode (K) with the black lead. The meter should show overrange (OL) (SCR is off).
While keeping the red lead on A, briefly touch the gate (G) with the same red lead. The reading should drop to below 0.8 V (SCR turns on).
Remove the red lead from the gate; the SCR should remain conducting.
If this behavior is consistent in repeated tests, the device has sensitive and reliable triggering.This method only applies to SCRs with low holding current.
