# Overvoltage protection circuit

Discussion in 'The Projects Forum' started by prescott2006, Mar 29, 2011.

1. ### prescott2006 Thread Starter Active Member

Nov 8, 2008
72
1
Based on figure attached, I would like to design an overvoltage protection circuit at the selected red rectangular area.
The voltage supply for the circuit is 230V with 50Hz. The protection circuit should somehow block the voltage when the power supply voltage reach 110% of the nominal voltage. When the voltage return to the nominal voltage, the circuit should allow the current to flow again. Any suggestion to achieve this requirements?? Thank you.

File size:
12.3 KB
Views:
78
2. ### tom66 Senior Member

May 9, 2009
2,613
214
Mains voltage is allowed to reach 110%. In fact it is typically rated 216V to 253V. You might consider changing a set point to a fixed voltage like 260V which gives some margin.

3. ### wayneh Expert

Sep 9, 2010
12,361
3,220
Not sure this is the simplest approach, but it would work: Switch a power MOSFET on/off depending on the voltage state. Determine the voltage state using a comparator. Using a resistor divider including a pot, divide down the rippling DC voltage to, say 2v at the inverting input of the comparator. Compare the divided down voltage to a reference, for instance a 2v zener or a divided-down 7805 voltage regulator (which could double as a power source for the comparator) at the non-inverting input of the comparator. Use a pot for fine adjustment of the reference voltage. Send the comparator output to the gate of the MOSFET. The comparator output must be pulled up with a 3.3K resistor. The MOSFET source is connected to the low voltage (ground) rail, the drain is at the low-voltage side of the load.

When the DC voltage is too high, the inverting input voltage will exceed the setpoint and the comparator output will go low, turning off the MOSFET.

You'll need to divide down the voltage to safely supply either a zener or the 7805.