Difference between DIAC and TRIAC

DIAC and TRIAC are two power semiconductor devices that are able to operate in high voltage and current. Both of them belong to a thyristor family. Both of these components have a p-n-p-n structure. But they are different in many ways. In this article, we are going to discuss what is the difference between DIAC and TRIAC.

Difference between DIAC and TRIAC in tabular form

In the following table, we have pointed out the differences between DIAC and TRIAC.

DIAC TRIAC
DIAC stands for Diode AC switch. TRIAC stands for Triode AC switch.
DIAC is a bidirectional device that lets current pass through it in both directions when the voltage across the terminals reaches break-over voltage. TRIAC is also a bidirectional device that lets the current pass through it when its gate terminal is triggered.
DIAC can be considered as an inverse parallel combination of two diodes. TRIAC can be considered as an inverse parallel combination of two SCRs where their GATE terminals are combined to form the GATE of the TRIAC.
DIAC has two terminals named MT1 and MT2 TRIAC has three terminals named MT1, MT2, and GATE.
DIAC does not have any GATE terminal. TRIAC has a GATE terminal.
The DIAC has a low power handling capacity. The power handling capacity of TRIAC is higher than DIAC.
The DIAC is triggered by applying a voltage across its two terminals that is greater than or equals to its break-over voltage. To trigger a TRIAC we need to apply a positive or negative voltage at the gate terminal.
DIAC exhibits negative resistance characteristics that is why this is used to trigger devices like TRIAC and SCR. DIACs are also used as AC switch as it is also bidirectional. TRIACs have many applications in AC circuits such as – switching, phase control circuit, chopper circuits, dimmers for a lamp, speed control for motors, etc.

What is DIAC?

DIAC stands for Diode AC switch. DIAC belongs to the Thyristor family. It is a power semiconductor device that lets the current pass through it in both directions i.e., it is a bilateral component. Thus, DIAC can be switched from OFF state to ON state for both polarities of applied voltage. That is why it is used in AC switching.

DIAC can be considered as an inverse parallel combination of two diodes. The device has a p-n-p-n structure. It can be constructed using two p-type and three n-type semiconductors. DIAC has two terminals termed– MT1 and MT2 where MT stands for Main Terminal. The DIAC conducts when the applied voltage across MT1 and MT2 reaches the break-over voltage of DIAC.

DIACs are used as phase-trigger or variable power control devices due to their ability to provide sharp and instant trigger pulses. DIAC possesses negative resistance characteristics and has a symmetrical characteristics curve. This is why DIACs are used as triggering devices for phase control circuits. It is primarily used to trigger TRIAC and SCR.

What is TRIAC?

The term TRIAC has been derived from the Triode AC switch. TRIAC also belongs to the Thyristor family. It is a three-terminal device. The terminals are termed MT1, MT2, and Gate. It is a power semiconductor device in which the flowing current depends on the voltage applied to the gate terminal.

TRIAC is also a bidirectional device. It is nothing but the inverse parallel combination of two unidirectional SCRs where the gate terminal combined together to form the gate of TRIAC. This is why the current flowing through it does not depend on the polarity of the voltage applied to MT1 and MT2 i.e., TRIAC can conduct for both polarities.

TRIAC can operate in high voltage or high-power circuits. This is why it is used in high-power AC circuits as well. It is used in AC switches, phase control circuits, dimmers, speed controllers, etc. We need a trigger device to trigger the TRIAC. We can use devices which has negative resistance property such as UJT, DIAC, neon lamp, etc.

Conclusion

To summarize the whole article, we can say, DIAC and TRIAC their differences as well as their similarities. There are many differences among them such as – the numbers of pins they have are different, their structures are different, their applications are different. But there are also many similarities among them. Some of their similarities are – both of them belong to the Thyristor family, both of them have p-n-p-n structure, both of them are bidirectional devices, both of them can operate in high-power AC circuits, etc.

Author
Subhrajyoti Choudhury
University of Calcutta, Kolkata

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