The composition of the dimmer
The commonly used SCR dimmer consists of main loop, trigger circuit, control loop and feedback system (Fig. 1), which is suitable for dimming of thermal radiation source.
The main circuit is a bidirectional or one-way anti parallel thyristor connected in the light source loop. After input, the sine wave is exchanged, and the sinusoidal phase shifted sinusoidal wave is output through thyristor. As seen in Figure 2, it is necessary to contain high order harmonics, which will produce radio interference; secondly, the effective value of its output voltage has a nonlinear relationship with the conduction angle.
The trigger circuit is composed of a semiconductor discrete element, a flip flop oscillator and a monolithic integrated trigger with trigger diodes. It has to produce a trigger pulse that is required to synchronize the phase shift angle of the input voltage in each cycle. It has a certain trigger power to achieve the purpose of reliability.