Simple Over Voltage Protection Circuit: High Voltage Cut Off

Voltage fluctuation is a serious issue in every home. Due to some reasons our supply voltage may rise above 110V or 230V. Flow of this high electricity may lead to the damage of our home electrical devices. Have you thought how electrical protection is possible via a simple over voltage protection circuit? Here CG comes with an interesting over voltage protection device to protect your electrical appliances from getting damaged. Zener diode voltage regulator is the main part of this high voltage cut off circuit. You can implement this over voltage protection relay circuit in your home as a high voltage regulator.

Circuit diagram of over voltage protection circuit

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Components required

1. Transformer (110V to 12V or 230V to 12V) 
2. Diodes (1N4007 x 5) 
3. Zener diode (6.2V) 
4. Capacitor (1000µF, 25V) 
5. Resistors (5.6kΩ; 6.8kΩ; 1kΩ) 
6. Potentio meter (10kΩ) 
7. Transistors (BC187 x 2; BC547) 
8. 12V relay

Working of voltage regulator

• R1 and R2 forms a potential divider network, we can adjust the cut off voltage by varying the 10K pot (R2).

• Neutral line is directly connected to the ‘Common’ terminal of relay, then the ‘NO’ terminal and Phase lines are fed to the home appliances.

• Q3 is always in ON state, so the relay connects the electrical appliances to the mains.

• At normal condition a small amount of current will flow through the zener diode but it is insufficient to turn ON the transistor Q1.

• Sudden increase of supply voltage (over voltage) leads to the increase of zener current. This current will turn ON the transistor Q1.

• The collector voltage of Q1 is applied to the base of Q2. Thus Q2 and Q3 become OFF because  transistor acts a digital switch  here.

• Q3 is our relay driver, turning OFF of Q3 shuts down the relay too. When relay is OFF, there will be no supply of electricity to the device. Hence they are protected from over voltage. 

Pinout of components

• BC187
• BC547
• Zener diode

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