How to Test TRIAC with a Multimeter?

In this article, we will discuss how to test TRIAC with a multimeter. The triac is one of the important devices in the power semiconductor devices family. The triac is widely used for controlling the AC voltage.

Introduction about Triac

The symbol of the triac is given below.

triac symbol
  • The TRIAC is a 5-layer, 3-terminal Power semiconductor device.
  • It has a pair of phase-controlled SCRs connected in an inverse parallel manner on the same chip.
  • It is a bidirectional device, which means it can conduct current in both directions.
construction of triac

Step-by-step Procedure to Test the Triac

  1. The below steps explain how to test triac with a multimeter.
  2. Select the multimeter setting on resistance mode.
  3. find out the polarity of the ohmmeter lead using a P-N junction diode. When positive lead is connected to the anode and negative lead is connected to the cathode shows continuity.
  4.  The triac remains off when the positive voltage is applied at MT1 and the negative voltage is applied at MT2 with gate current zero.
  5. Similarly,  the triac remains in its off state when the positive voltage is applied at MT2 and the negative voltage is applied at MT1 with gate current zero.
  6.  In steps No. 3 &4 of triac testing, the ohmmeter should indicate no continuity through the triac. It means triac offers very high resistance.triac testing-forward blocking mode
  7. In steps No. 3 &4 of triac testing, if the ohmmeter shows continuity through the triac. It means the triac is short-circuited and defective.triac testing-defective-forward blocking mode
  8.  Now, if the gate of the triac gets positive voltage the device turns on either MT1 is positive with respect to MT2 or MT2 is positive with respect to MT1. This can be done by connecting the triac gate to positive lead( It may be the MT1 or MT2 terminal, depending on which terminal has positive voltage through the ohmmeter. 
  9. As per step No.8, the triac must turn on and show low resistance or continuity between MT1 and MT2. If the triac shows continuity, the triac under test is OK. triac testing- ok- forward conduction mode  
  10. If triac does not turn on as per step 8, triac offers very high resistance and triac is defective.triac testing-defective-forward blocking mode
  11. Following the above steps, you can test a Triac using a multimeter.
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