Sunday, August 23, 2009


Triode Alternating Current Switch (TRIAC)

There are three terminal on a triac. These are the Gate and two other terminals. These other triac terminals are often referred to as an "Anode" or "Main Terminal".
On the triac, the gate that acts as the trigger to turn the device on. The current then flows betweent he two anodes or main terminals. These are usually designated Anode 1 and Anode 2 or Main Terminal 1 and Main Terminal 2 (MT1 and MT2).
Simbol TRIACSimbol TRIAC

It can be imagined from the circuit symbol that the triac consists of two thyristors back to back. The operation of the triac can be looked on in this fashion, although the actual operation at the semiconductor level is rather complicated. When the voltage on the MT1 is positive with regard to MT2 and a positive gate voltage is applied, one of the SCRs conducts. When the voltage is reversed and a negative voltage is applied to the gate, the other SCR conducts. This is provided that there is sufficient voltage across the device to enable a minimum holding current to flow.


A multimeter can be used to test the health of a triac. First put the multimeter selector switch in a high resistance mode (say 100K), then connect the positive lead of multimeter to the MT1 terminal of triac and negative lead to the MT2 terminal of triac (there is no problem if you reverse the connection).The multimeter will show a high resistance reading (open circuit).Now put the selector switch to a low resistance mode, connect the MT1 and gate to positive lead and MT2 to negative lead. The multimeter will now show a low resistance reading (indicating the switch ON).If the above tests are positive then we can assume that the triac is healthy. Anyway this test is not applicable triacs that require high gate voltage and current for triggering.


Almost all type of triacs can be tested using this circuit. This circuit is nothing but a simple arrangement to demonstrate the elementary action of a triac. Connect triac to the circuit as shown in circuit diagram and switch S2 ON. The lamp must not glow. Now press the push button switch S1.The lamp must glow indicating the switching ON of triac. When you release the push button, you can see the lamp extinguishing. If the above tests are positive you can assume that the triac is healthy.
Rangkaian untuk mengukur triacRangkaian untuk menguji|mengukur triac

Skema Rangkaian Elektronika