The firing angle of a thyristor is a crucial parameter that defines the timing of turning on the device during each AC cycle. Also known as the conduction angle or delay angle, the firing angle is measured in degrees and determines when the thyristor starts conducting current in a controlled rectifier circuit.
Thyristors are semiconductor devices with three or more terminals used for various applications, including power control in AC circuits. They operate in a switching mode, allowing current to flow when triggered and remaining in a conducting state until the current drops below a certain threshold.
In a controlled rectifier circuit, the firing angle is the delay in turning on the thyristor after the zero-crossing point of the AC waveform. The firing angle is defined from the point where the AC voltage crosses zero to the point when the thyristor is triggered to start conducting. The delay in triggering the thyristor allows for the control of power flow and enables the regulation of output voltage.
A smaller firing angle means the thyristor turns on earlier in each AC cycle, allowing more power to flow through the circuit. Conversely, a larger firing angle delays the turn-on, reducing the power delivered to the load. By adjusting the firing angle, one can control the average power delivered to the load and, consequently, control the speed, intensity, or other parameters in various applications like motor drives, heating systems, and lighting control.
In summary, the firing angle of a thyristor is a critical parameter that governs the timing of current conduction in a controlled rectifier circuit, providing a means of regulating power and achieving controlled output in AC power applications.