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.
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).
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.
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.
|Repetitive peak off-state voltage||600 V|
|RMS on-state current||4A|
|Peak gate current||2A|
|Peak gate power||5W|
|Average gate power||0.5W|
|Gate trigger current||10mA|
|Junction temperature||125 °C|
- AC Light dimmers
- AC motor speed control
- Noise coupling circuits
- Controlling AC loads using MCU/MPU
- AC/DC Power control
Common TRIAC with their model number
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