TRIAC stands for Triode for Alternating Current. It is a genericized trademark for an electrical device that has 3 terminals and when triggered conducts electrical current in both directions. Its conventional name is bilateral triode thyristor or bidirectional triode thyristor. A thyristor is comparable to a relay where a small voltage induced current can control a lot bigger current and voltage.
Thyristors can be said to be the superset of TRIACs. TRIACs are also relatable to SCRs (Silicon Controlled Rectifiers). TRIACs and SCRs can be distinguished in one characteristic feature i.e. the first one is bidirectional, the flow of current is in both the direction but the later one allows the flow of current in only one direction. Generally, the TRIACs get initiated by the consequence of a positive or a negative potential to the gate but the SCR needs only a positive potential. Once activated, SCRs and TRIACs keep on conducting, regardless of whether the current in the gate ceases, until the principle current dips under a specific level called the holding current.
The GTOs or Gate Turn-Off Thyristors are the same as TRIACs but when the signal in the gate ceases, it provides much more control by turning OFF.
The bidirectional feature of this equipment makes it a good switch for AC or Alternating Current. A trigger, when applied in the main circuit at AC's controlled phase angle, permits control of the average current streaming into a load. This feature is popularly used for managing the speed of dimming lamps, electric heaters, and universal motor.
Factors that affect the working of TRIAC
TRIACS, unlike SCRs, needs appropriate enhancement for its legitimate working. There are some inherent drawbacks like TRIACs Backlash effect, Rate effect, etc. Thus designing it requires proper case.
This effect is one of the most acute Control Hysteresis that grows in the speed control or the lamp control circuits with the help of a Potentiometer for controlling the Gate current. The glowing brightness of the lamp gets a minimum when the potentiometer's resistance increases to the maximum. The lamp never gets ON when the pot is turned back until and unless the resistance of the pot drops to its lowest value. The main reason behind this is the discharging of the TRIAC's capacitor. The triggering pulse is provided to the gate by a Diac. Triac releases through the Diac, generating the Backlash effect.
The Rate effect generally takes place due to high inrush current when overwhelming inductive loads switch on and also because of a momentary variation in frequency, voltage or current in the mains.
RFI or the Radio Frequency Interference seriously influences the working of Triacs. Depending on the resistance and the supply voltage of the load, the load current is seen to sharply increase from 0 to a high value whenever the TRIAC switches on the load. This forms pulses of RFI.
This was all regarding TRIACs. Brands that manufacture it are Littelfuse, STMicroelectronics, and NXP. We hope that you liked the article. If you want to refer to the brands then just follow the links as given.
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