Overvoltage and undervoltage protection circuit with 1 minute line check error

Thread Starter

Dennis Tahar

Joined Mar 22, 2018
My name is Dennis and I want to design a safety circuit that should provide for household appliances for over voltage and under voltage protection based on these conditions:
1. When there is a line voltage between 115 -125 vac, the output of the protection circuit is under normal voltage. In this situation the Line is OK and a green LED will go on.

2. if the line voltage is less than 130 vac then the protection circuit will switch off the load. There will be a Line Error and a red LED will go on. At the moment when the load is switched off, a line check of 1 minute will be done.

3. If the voltage is between 115-125 Vac then is the Line OK nd the load will be switched on.
We have to simulate it on multisim and we have to calculate all the resistors and voltages.

After that we need to explain why we choose those types of components.

I use a window detector for the undervoltage and overvoltage. I still have to connect the timer at the end for 1 minute line check.

undervoltage and overvoltage schematic.PNG Dennis Tahar


Joined Mar 14, 2008
Few things:

The 7408 gate requires 5V. Where is that coming from?
You could use a 74C08 when can operate up to 15V.

The LM339 have an open collector output so they need a pullup resistor the V+.

You can eliminate the 7408 by connecting the two LM339 outputs together with one pull-up resistor (giving the AND function).
Then the output is high only when the two comparator outputs are high.