Non-isolated thyristor switching power supply

The picture shows a non-isolated switching power supply circuit composed of thyristor. The 220V AC voltage is directly applied to the bridge rectifier composed of VD503, WD505, VD507, and VD509. The full-wave voltage it outputs is added to the cathode of the adjusting device SCR529 through the choke. As long as the phase of the trigger pulse of SCR529 is changed, the output voltage can be adjusted to keep it stable. The output voltage becomes a smooth DC of 155V after being filtered by a two-stage RC filter composed of R544, C535 and R545, R546, and C536. VT516 is an error amplifier tube. VD518 is a Zener diode that provides the reference voltage for VT516. R531, R515 and R514 form a sampling voltage dividing circuit and together with the silicon controlled thyristor SCR528 form a control circuit. The error amplifier collector load resistor R519 and C521 form an integral delay circuit. It delays the rectified input voltage and then adds it to the anode of the silicon controlled SCR528. Assume that when the output voltage increases for some reason, the sampling voltage provided by the sampling circuit to the base of the error amplifier tube VT516 also increases, the collector current increases, and the charging current of the integrating capacitor C521 decreases, making the potential of point B lower than A. The point potential time is later, the SCR529 conduction time lags behind, the SCR529 conduction angle becomes smaller, and the output voltage decreases. When the output voltage decreases, adjust in the opposite direction according to the above process, and the conduction angle of the silicon controlled SCR529 will increase, causing the reduced output voltage to rise, thereby maintaining the stability of the output voltage.