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Difference between DIAC and TRIAC
In electrical and electronics engineering, regulating and controlling of the electric power delivered to the load is very important to reduce the wastage of electrical energy. This can be achieved by using DIAC and TRIAC which are two different types of power semiconductor devices.
DIAC and TRIAC are used to control the AC power supplied to the load. Both DIAC and TRIAC can operate at high voltages and currents. Both these devices belong to the thyristor family, having p-n-p-n structure. But, DIAC and TRIAC are also different from each other in many ways. Read through this article to find out the major differences between a DIAC and a TRIAC.
What is a DIAC?
DIAC stands for Diode for Alternating Current. As the name implies, a DIAC is a semiconductor diode for conducting alternating current. Basically, it is a power electronic bidirectional semiconductor uncontrolled switch that is capable of conducting the electric current in both directions.
A DIAC has two terminals and is made from a combination of two antiparallel SCRs without the gate terminal. The two terminals of the DIAC are named as main terminal 1 (MT1) and main terminal 2 (MT2). It is designed such that it is symmetrical from both sides and having equal regions. The symbol and construction of a DIA.
The DIAC starts conducting when the applied voltage across MT1 and MT2 exceeds the break over voltage VBO of the device. The DIAC stops conducting when the voltage across the terminals becomes very low than the break over voltage or the current falls below the holding current. The DIAC is mainly used to trigger the TRIAC to perform symmetrical switching.
What is TRIAC?
TRIAC stands for Triode for Alternating Current. A TRIAC is a power semiconductor controlled switch which can conduct the current in both directions. A TRIAC is a four layer and three terminal power semiconductor device. The terminals of the TRIAC are: main terminal 1 (MT1), main terminal 2 (MT2) and gate terminal. The symbol and construction of the TRIAC is shown in Figure-2.
Basically, a TRIAC is made by combining two SCRs in antiparallel. The gate terminal of the TRIAC is connected to both the P and N regions of each SCR. The TRAIC can be triggered by applying a positive or negative pulse at the gate terminal, where the positive pulse is applied to operate the TRIAC in first quadrant and the negative pulse is applied to operate it in third quadrant. The TRIAC is mainly used to regulate the electric power in high power AC circuits.
Difference between DIAC and TRIAC
The following table highlights the major differences between a DIAC and a TRIAC −
| Basic of Difference | DIAC | TRIAC |
|---|---|---|
| Full form | DIAC stands for Diode for Alternating Current. | TRIAC stands for Triode for Alternating Current. |
| Definition | A two terminal power semiconductor device made by combining two SCRs in antiparallel without the gate terminals and acts as a bidirectional semiconductor uncontrolled switch is known as DIAC. | A three terminal power semiconductor device made by combining two SCRs in antiparallel with gate terminal and acts as a bidirectional semiconductor controlled switch is known as TRIAC. |
| Meaning of name | The name of the DIAC is derived from DI + AC, where DI means 2 and AC means alternating current. | The name of the TRIAC is derived from TRI + AC, where, TRI means 3 and AC means alternating current. |
| What is it? | DIAC is a diode for AC which allows the electric current to flow in both directions when a voltage greater than break-over voltage is applied across it. | TRIAC is a bidirectional SCR (silicon controlled rectifier) which is capable of conducting in both directions when it is triggered by applying a gate pulse. |
| Terminals | DIAC is a two terminal device, where name of the terminals are: main terminal 1 (MT1) and main terminal 2 (MT2). | TRIAC is a three terminal device. The terminals are: main terminal 1 (MT1), main terminal 2 (MT2) and gate terminal. |
| Act as | DIAC acts as an uncontrolled bidirectional switch. | TRIAC acts as a controlled bidirectional switch. |
| Gate terminal | DIAC does not have gate terminal. | There is one gate terminal in case of a TRIAC. |
| Firing angle | DIAC does not have firing angle. | For a TRIAC, there is a firing angle varying from 0° to 180° for positive half cycle and from 180° to 360° for negative half cycle of AC. |
| Symmetricity in structure | DIAC has a symmetrical structure, i.e. the structure of the DIAC is same in both current directions. | TRIAC has a non-symmetrical structure because of the presence of gate regions. |
| Power rating | A DIAC has very low power ratings. | TRIAC has very high power ratings of the order of 15 kW. |
| Voltage control | DIAC cannot block the voltages more than 30 volts. | A TRIAC can block very high voltages in the range of 600 volts to 1000 volts. |
| Power handling capacity | A DIAC has low power handling capacity. | A TRIAC has relatively high power handling capacity. |
| Triggering | In order to trigger the DIAC, a voltage above the break-over voltage is applied across the terminals MT1 and MT2. | TRIAC is triggered by applying a positive or negative gate pulse. |
| Applications | DIAC is mainly used to trigger various power semiconductor devices like TRIAC, SCR. It is also used as an AC switch as it can conduct in both directions. | TRIAC has a number of applications in AC circuits like switching, chopper circuit, dimmer for lamps, motor speed control, phase control, etc. |
Conclusion
To conclude, we can state that both DIAC and TRIAC have many differences as well as similarities. The most significant difference is that a DIAC is an uncontrolled semiconductor switch, while a TRIAC is a controlled semiconductor switch. Some of the similarities are that both DIAC and TRIAC are the members of thyristor family, both have p-n-p-n structure, both are bi-directional devices, etc.
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