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
This circuit is a design i did, not tested by me as yet.With some tweaks and modifications it might work.PNG-Schematic PDF-Circuit DSN-Source
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
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
20th May 2020
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