AC stabilized power supply circuit

The AC stabilized power supply circuit is shown in the figure. It is mainly composed of several unit circuits such as power supply, reference voltage, and voltage sampling comparison.
The mains power is input from the ① and ② pins of the transformer. The ③ and ④ pins are auto-coupling voltage regulating taps. The ⑤ and ⑥ pins are the power supply and sampling taps of the control circuit. When the mains
voltage is normal, the voltage at point C is always 3V (that is, Ri step-down vs. voltage-stabilization). The voltages at points A and B are both greater than 3V, so ^J1 and AJ2 output low level
. When the mains voltage drops, the voltages at pins ⑤ and ⑥ also drop, and the voltage at point A also drops. When the voltage at point A drops When it is lower than 3V, AJ1 outputs a high level, causing the transistor VT1 to saturate and conduct, and the relay Kl' is warmly closed, adjusting the voltage regulator output to pins 1 and 3; when the mains voltage continues to drop, the voltage at point B will be the same. When it is lower than 3V (UA<UB), /U2 outputs a high level, causing VT2 to saturate and conduct, K2 pulls in, and the voltage regulator output is adjusted to pins ① and ④ to achieve the purpose of auto-coupling boost.     On the contrary, if the voltage at point B increases, the voltage at point B also increases. When the voltage at point B is higher than 3V, AJZ outputs low level, VT2 is cut off, K2-1 is released, and the output terminal is connected to pins ① and ③; when When the mains voltage continues to rise, the voltage at point A is higher than 3V, AJ1 outputs low level , 'VT1 is cut off, Kl is released, and the output end is adjusted to ① and ② pins. AJ1 and ^J2 are operational amplifiers, used as voltage comparators here; IC1 is a three-terminal integrated voltage stabilizing device. ~Provides power supply for operational amplifiers and relays; VD5 and VD6 are protection diodes.