Automatic Voltage Stabiliser Circuit

Here is the circuit of automatic voltage stabiliser which solves almost all problem faced in normal available stabiliser efficiently. With the help of automatic voltage stabiliser we are able to keep constant voltage at 230V, when voltage goes low as 170V and high as 250V automatically.

Working strategy of Automatic Voltage Stabiliser

The working strategy of the circuit is very simple, this circuit energized one relay at a time from 170V AC upwards, and all relays and energized when 230V AC input is reached. Similarly, if supply input voltage decreases gradually from 230V, the relay are d-energized automatically one by one so that the output voltage remains constant at 230V AC.

Circuit Description of Automatic Voltage Stabiliser

The power supply to the circuit is given from the secondary coil of transformer X2. As the voltage between two tapping is 20V, so it is directly rectified using bridge rectifier using diode D1 through D4. The rectified output is further filtered using electrolytic capacitor C1.

automatic voltage stabiliser

relay and transformer connection diagrams

The voltage input from the source is sensed by the transformer X1 and is rectified with the help of bridge rectifier made from diode D5 through D8. The rectified output is further filtered by capacitor C2 and given to the base of transistor T1 to T4 through variable resistor VR1 to VR4. For reference voltage zener diode ZD1 to ZD4 are used.


Resistor (all ¼-watt, ± 5% Carbon)
R1 = 4.7 Ω, 3WR2, R3 = 100 Ω,0.5W

R4, R5 = 56 Ω, 0.5W

R6 – R9 = 1 KΩ

R10 = 1 KΩ, 0.5W

VR1 – VR4 = 20 KΩ Linear

C1 = 470 µF/40V (Electrolytic Capacitor)C2 = 100 µF/40V (Electrolytic Capacitor)

C3 – C6 = 10 µF/50V (Electrolytic Capacitor)

T1 – T5 = SL100 (NPN transistors)D1 – D12 = 1N4007 (Rectifier Diode)

ZD1 – ZD4 = 2V, 1 amp. Zener Diode

LED1 = Any Color LED

X1 = 230V AC primary to 0-12V, 300mA SecondaryX2 = 230V AC primary to 0-170V, 190V,210V,230V,250V Secondary

RL1 – RL4 = 12V, 300 Ω double contact relays

SW1 = ON-OFF Switch