Unexpected Changes in the power supply may become the cause of many problems in homes, offices, and industries.  Voltage up and down in the electric power has a very dangerous effect on the connected load.  Fluctuations of over-voltage and under-voltage protection systems are produced to control the bad effects. Generally, these systems are used in water pumps, agriculture motors and etc. We are going to discuss the different control structures like timers and compactors of the Undervoltage & overvoltage protection system in this article.

What is an Over Voltages and Under Voltages?

When the voltages in any circuit exceed its upper limit is called over-volts and when the voltages decrease from its lower limit is called Undervoltage. Depending on the duration the over-voltage duration is like a transient, voltage spike, and power surge. The given below graph shows the variations between the time and voltage in both over-volts and under volts variations.


Circuit Using Comparator

This circuit is used to trip the mechanism to protect it from damage. Generally, in homes and industries, we observe that there is a frequent change in AC power. Due to these changes in the AC power, the electronic circuits may damage easily. To avoid this problem we implement the tripping mechanism of over-Undervoltage protection.

Components Needed

  • 12 volts transformer
  • IN 4007 (D1,D2)
  • 1k (R1, R2)
  • 5k pot (P1, P2)
  • BC 547 Transistors (T1, T2)
  • 12V relay (RL1)


How the Circuit Works

When the 220V or 120V mains supply is within the set limits, T2 (BC547 Transistor) will be conducting, rendering T1 (Transistor) in a non-conducting state.

When the Current is lower than the set limit, T2 cannot conduct, when the results relay remains off.
This adjustment is done by setting up P2.

During an overvoltage condition, T1 will get into a conducting state, de-energizing the relay. This setting is done by adjusting P1.

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