Application of Triacs

The TRIAC (Triode for AC) is a semiconductor device that is commonly used in power regulation and switching applications. It is used in switching, phase control, chopper designs, brilliance control in lights, speed control in fans and motors, and so on. The power control system is intended to regulate the amount of AC or DC distribution. Such power control systems can be used to manually switch electricity to appliances or when temperature or light levels exceed a preset level.


The TRIAC is a three-terminal semiconductor switching device used to regulate the flow of current in a circuit. It is one of the most significant members of the thyristor family; it is a bidirectional device that can carry current in both forward and reverse directions, meaning that it can conduct under both positive and negative gate signal situations.

TRIAC Symbol

A TRIAC can be built by connecting two equivalent SCRs in inverse parallel to one another and connecting the gates of the two SCRs together to produce a single gate. The TRIAC symbol consists of three terminals: Main Terminal 1 (MT1), Main Terminal 2 (MT2), and Gate (G).

TRIACs Construction

The TRIAC structure is a four-layer device with six doping areas. The gate terminal is intended to have ohmic contact with both the N and P regions, allowing the device to be activated with both positive and negative polarities.

TRIACs VI Characteristics

As the TRIAC is a bidirectional device, its VI characteristics curve will be in the first and third quadrants of the graph, similar to a Thyristor's VI characteristics. When terminal MT2 is configured to be positive in relation to terminal MT1, the TRIAC will operate in forward blocking mode.

During the initial stage due to the resistance of the TRIAC, there will be a small leakage current flowing through the device as the applied voltage is less than the breakdown voltage. When the voltage is increased to the breakdown voltage, the TRIAC is activated and a large current flows through the device.

 
Applications of TRIAC

TRIACs are utilized in a wide range of applications, including light dimmers, speed controls for electric fans and other electric motors, and sophisticated computerized control circuits in a wide range of home small and large appliances. They may be used in both AC and DC circuits, but their initial purpose was to replace the need for two SCRs in AC circuits. BT136 and BT139 are two families of TRIACs that are mostly utilized for application purposes.

TRIAC as a Switching Circuit

This circuit works as follows: if switch one is open, the device acts as an open switch, and the light passes through zero current.

With the help of the current limiting resistor R, the device is in an ON state when the SW1 is closed. The self-latching occurs immediately after the start of each half-cycle, resulting in full switching power to the light load.

This circuit's input supply is sinusoidal alternating current, and the TRIAC automatically unlatches at the conclusion of each half-cycle. As long as the switch is closed, the instantaneous power supply voltage and load current decrease to zero, and it will re-latch it by using the opposite thyristor.

TRIACs as speed controls for electric fans

TRIACs are the components used in controlling the AC signals. They are used in a variety of applications where high-power switching in AC waveforms is required. TRIACs are commonly used in AC dimmer circuits and are extremely useful when attempting to control the speed of a fan or as a dimmer for an AC Lamp.

 

BT136 TRIAC

The BT136 is TRIAC with a 4A maximum terminal current. The gate threshold voltage of the BT136 is also very less so can be driven by digital circuits.

Since TRIACs are bi-directional switching devices they are commonly used for switching AC applications. So if you looking to switch control (dim, speed control) an AC load that consumes less than 6A with a digital device like microcontroller or microprocessor then BT136 might be the right for you.

BT136 Datasheet

Specifications

Applications

• AC Light dimmers
• AC motor speed control
• Noise coupling circuits
• Controlling AC loads using MCU/MPU
• AC/DC Power control

BT131 TRIAC

The BT131 is a TRIAC with a maximum terminal current of 1 amp. The BT131's gate threshold voltage is also very low, allowing it to be driven by digital circuits. TRIACs are commonly used for switching AC applications because they are bidirectional switching devices. The BT131 is the best choice for switching off control of an AC load that consumes less than 3 A using a digital device such as a microcontroller or microprocessor.

BT131 Pinout

Applications

• AC Light dimmers
• Strode lights
• AC motor speed control
• Noise coupling circuits
• Controlling AC loads using MCU/MPU
• Ac/DC Power control
• Light dimmers
• Washing machines
• Motor control

BTA12-600B TRIAC

The BTA12-600B Triac is suitable for general purpose mains power alternating current switching. They can be used in applications such as static relays, heating regulation, and induction motor starting circuits as an ON/OFF function. They are also recommended for phase control operations in light dimmers and speed controllers for appliance motors.

Features: 

• Medium current Triac
• Low thermal resistance with clip bonding
• Low thermal resistance insulation ceramic for insulated BTA
• High commutation (4Q) or very high commutation (3Q) capability
• Suitable for general purpose AC switching.
• Applications: Static relays, heating regulation, induction motor starting circuits, phase control operation in light dimmers, motor speed controllers.
• BTA-12 | BTA12 | BTA12-600b | BTA12-600 | BTA12 600b | 

Common TRIAC with their model number
BT131
BT139
BTA41
BTA12
BTA12-600B
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