"clairvoyance" charger circuit diagram

The "clairvoyance" charger circuit is shown in the figure. Among them, the unidirectional thyristor VS1 is the charging current tube of the battery GB, and VS2 is used to cut off the charging current when the battery is charging. When the power is turned on for charging, relay K operates, contact 3 and contact 2 are connected, the trigger terminal of VS1 obtains the trigger voltage from R1 and VD4 and is turned on, and the rectified current charges the battery GB through VS1. When battery GB is charged to the set voltage (for example, 7.2V), VS2 is turned on, causing the potential at point A of the trigger terminal of VS1 to be much lower than the cathode potential of VS2, VS1 is cut off, and battery GB stops charging. The LED of the light-emitting tube is used for charging display. When the battery charging stops and VS2 is turned on, the LED goes out. The 6V indicator light HL is used to indicate ~220V power outage.