AC voltage regulator circuit

It consists of power supply, reference voltage, voltage sampling comparison and other unit circuits.
  AC 220V is input from the ①~② end windings of the transformer , the ③~④ windings are auto-coupling voltage regulating taps, and the ⑤~⑥ windings are the power supply and sampling taps of the control circuit
. Al and A2 are operational amplifiers. It is used as a voltage comparator; IC1 is the i-side voltage stabilizing block, which provides
power supply for the operational amplifier and relay; VD5 and VD6 are protection diodes.
    When the mains voltage is normal, the voltage at point C is always 3V (stepped down by R3 and stabilized by DW). The voltages at points A and B are both greater than 3V, so Al and
A2 output low level, transistors VT1 and VT2 are cut off, relays Kl and K2 do not operate, and the voltage regulator output is adjusted to the ①~② winding.
    When the mains voltage drops, the voltage of the ⑤~⑥ windings drops, and the voltage at point A drops accordingly. When the voltage at point A is lower than 3V, Al outputs
high level, the transistor VT1 is saturated and turned on, the relay Kl is closed, and the voltage regulator output is adjusted to the ①~③ winding; when the mains voltage continues to decrease
, the voltage at point B When it drops below 3V, A2 outputs a high level, causing the transistor VT2 to saturate and conduct, and the relay K2 closes, adjusting the voltage regulator output
to the ①~④ windings. When the voltage at point B increases, the voltage at point B also increases. When the voltage at point B is higher than 3V, A2 outputs low level. VT2
is cut off, K2 is released, and the output terminal is adjusted to the ①~③ winding; when the mains voltage continues to increase. The voltage at point A is higher than 3V, and the Al output is low level.
vri is cut off, Kl is released, and the output end is adjusted to the ①~② winding .