The project “Auto Cut Circuit for Over and Under Voltage” is designed to protect electrical and electronic devices from over and under voltage which ensures a long lifespan of this device. An “Auto Cut Circuit for Over and Under Voltage” has been presented here serving multiple purposes for security; under-voltage protection, over-voltage protection, auto reset, auto cut off, and regulation.
Circuit Description of Auto Cut Circuit for Over and Under Voltage
The circuit diagram of “Auto Cut Circuit for Over and Under Voltage” is shown in figure 1. The entire circuit of the auto cut circuit is built around a two-timer 555 IC, configured in comparator mode. Although the circuit looks complex, it comprises building blocks you have been familiar with.
As seen in the left part of the circuit, input mains are connected to the primary step-down transformer which lowers the input voltage to 12V AC. A bridge rectifier made from four general-purpose rectifier diodes converts 12V AC to pulsating 12V DC which is further smoothening using capacitors as shown in the circuit diagram. The ripple-free 12V DC is obtained at this point which is further given to relay and input of 9V series voltage regulator IC. The output of the series voltage regulator is 9V DC.
Two timer IC (IC2 and IC3) are configured in comparator mode which compares the mains voltage and produces output as per our desire. The output of the 1st comparator (IC2) is given to the reset pin (pin 4) of the 2nd comparator (IC3) through the collector of transistor T1. The voltage at the input pin of IC3 (pin 2) is 1/3 of Vcc i.e. 3 volts.
Till the input voltage (voltage at pin 2) is less than 1/3 of Vcc the output of IC3 (pin 3) is high. As long as the output at pin 3 is high the LED connected to pin 7 becomes off due to high impedance. Similarly, when the input pin voltage (voltage at pin 2) is greater than 1/3 of Vcc the output becomes low as a result the LED connected to pin 7 starts to glow.
The circuit “Auto Cut Circuit for Over and Under Voltage” can only operate in a range of 160V AC to 270V AC, other than this range of voltage i.e. under 160V AC or over 270V AC the relay connected to the output of IC3 is de-energized as a result load will be off. Transistor T1 is used to drive the reset pin of IC3, similarly, transistor T2 is used to drive the relay.
Check out other Cut out projects posted on bestengineeringprojects.com
- Auto Cut for Manual Stabilisers using 741 IC
- Automatic Cut off Power Supply
- Single Phase Preventer with Under/Over Voltage Cutout
Calibration Auto Cut Circuit for Over and Under Voltage
- At first, the circuit is fabricated on a PCB board.
- Adjust variable resistor VR1 in such a way that LED1 starts to glow when the mains voltage is lower than 160V AC.
- Adjust variable resistor VR2 in such a way that LED2 start to glow when the mains voltage becomes higher than 270V AC.
PARTS LIST OF AUTO CUT CIRCUIT FOR OVER AND UNDER VOLTAGE
| Resistors (all ¼-watt, ± 5% Carbon) |
| R1, R5 = 220 Ω
R2, R3, R6, R7 = 1 KΩ R4 = 100 KΩ VR1, VR2 = 100 KΩ (Preset) |
| Capacitors |
| C1 = 0.1 µF (Ceramic Disc)
C2, C3 = 1000 µF/25V (Electrolytic Capacitor) C4, C5 = 0.01 µF (Ceramic Disc) |
| Semiconductors |
| IC1 = LM7809 (9V series voltage regulator)
IC2, IC2 = NE555 (Timer IC) T1 = BC547 (Silicon NPN transistor ) T2 = SL100 (Medium power NPN transistor) D1 – D4 = 1N4007 (Rectifier diode) D5 = 1N4001 (Rectifier diode) LED1 = Yellow Color LED LED2 = Red Color LED |
| Miscellaneous |
| X1 = 230V AC Primary to 12V, 250mA Secondary Transformer
RL1 = 12V, 200Ω Relay |
Thank you Mr. Reeko Azil for letting us know. We had updated the circuit diagram with possible modification.