It can Stabilize Mains voltage to around +/- 10% . It can be used for both 110V AC or 220V AC inputs with modifications. The Output is 220V AC. There is an overload, under voltage and over voltage trip circuit.
U2A and U2B are two comparators which controls relays K2 and K3 Respectively. One Boosts the voltage (Step-up) when mains supply is low. The other Bucks the voltage (Step-down) when mains voltage goes beyond a limit.
U2C and U2D work like a window comparator to trip the unit above and below certain preset limits. This circuit is clubbed with a Mains control relay K1 which can be Turned ON-OFF with two pushbuttons.
Put a 0.1uF 1KV pl cap across all relay contacts to avoid sparking. Relay current paths should be large and direct to supply, or when relay operates ground will lift and cause malfunction.All mains wiring and connections should be designed for high voltage and current, They should be isolated visually from control circuits by 10 mm or more. If input voltage is 230V put the two 110V windings in series in proper polarity.
Put one LED with resistor for boost and buck indication if required. Use Presets with series resistor as required so that you can test or calibrate. The 1M dead band or hysteresis resistor can be varied from 330K to 10M as performance demands, this resistor stops oscillation or chattering of relays.