One of the unijunction transistor trigger circuits

A trigger circuit composed of a single-junction transistor, etc., is also called a single-junction transistor relaxation oscillator. The single-junction transistor trigger circuit is simple
and easy to adjust, has a steep pulse front edge and strong anti-interference ability. However, due to the narrow pulse, small trigger power and small phase shift range, it is
mostly used in medium and small power systems with thyristors of 50A and below.
    The circuit is shown in Figure 16-6. The phase shift range of this circuit is less than 180. , usually 150. ~160. . Adjusting the potentiometer
RP can change the charging speed of the capacitor C, thus also changing the time when the first pulse appears, thus changing
the conduction angle of the controlled thyristor to achieve the purpose of word pressure.