What is a DIAC?
A DIAC is a diode that conducts electrical current only after its breakover voltage (VBO) has been reached. DIAC stands for “Diode for Alternating Current”. A DIAC is a device which has two electrodes, and it is a member of the thyristor family. DIACs are used in the triggering of thyristors. The figure below shows a symbol of a DIAC, which resembles the connection of two diodes in series.
Application of DIAC:
The main application of a DIAC is its use in a TRIAC triggering circuit. The DIAC is connected to the gate terminal of the TRIAC. When the voltage across the gate decreases below a predetermined value, the gate voltage will be zero and hence the TRIAC will be turned off.


1. It can be used in the lamp dimmer circuit
2. It is used in a heat control circuit
3. It is used in the speed control of a universal motor

What is a scr?
SCRs are constructed from silicon and are most commonly used for converting AC current to DC current (rectification), hence the name Silicon controlled rectifier. They are also used in other applications such as regulation of power, inversion, etc. The SCRs have an ability to handle high value of current and Voltage hence they are used in most of the industrial applications.

SCR Applications:
1. The silicon controlled rectifier (SCR) is used in AC voltage stabilizers.
2. The silicon controlled rectifier (SCR) is used as switch.
3. It is used in choppers.
4. The silicon controlled rectifier (SCR) is used in inverters.
5. The silicon controlled rectifier (SCR) is used for power control.
6. It is used for DC circuit breaker.

7. Silicon control rectifier (SCR) is used in battery charger.
8. It is used to Adjust light dimmer.
9. It is used to control motors speed.
10. The SCR is used in pulse circuit.
11. It is used for AC power control with solid relay.

Difference between DIAC and TRIAC

S NO DIAC TRIAC
1 The DIAC is “Diode for the alternating current”. The TRIAC is “Triode for the alternating current”.
2 DIAC includes two terminals TRIAC includes three terminals
3 It is a bi-directional and uncontrolled device It is a bi-directional and controlled device.
4 This name is derived from the combination of DI + AC, where DI means 2 & AC means alternating current. This name is derived from the combination of TRI + AC, where TRI means 3 & AC means alternating current.
5  It can control both positive and negative half cycles of AC signal input. DIAC can be switched from its off state to ON state for either polarity of the applied voltage.
6 The DIAC construction  can be done either in NPN otherwise PNP form The construction of TRIAC can be done with two separate devices of SCR.
7 It doesn’t have a firing angle The firing angle of this device ranges from  0-180° & 180°-360°.
8 This device plays a key role inactivate the TRIAC This device is used to control the fan, light dimmer, etc.
9 It has three layers It has five layers
10 The advantages of DIAC are, it can be activated by decreasing the level of voltage under its breakdown voltage. Triggering circuit using DIAC is cheap The advantages of TRIAC are, It can work through the +Ve as well as -Ve polarity of pulses. It uses a single fuse for protection. A secure breakdown can be possible in both directions.
11 The disadvantages of DIAC are, it is a low-power device and doesn’t include a control terminal. The disadvantages of TRIAC are, it is not reliable. As compared with SCR, these have low- ratings. When operating this circuit, we need to be cautious as it can activate in any direction.
12 The applications of DIAC mainly include different circuits like lamp dimmer, heater control, universal motor speed control, etc. The applications of TRIAC mainly include control circuits, fans controlling, AC phase control, switching of high-power lamps, and controlling AC power.

About the Author

Subramanian

Hello! My Dear Friends. I am Subramanian. I am writing posts on androiderode about Electronics testing and equipments.

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