over voltage protection circuit

Thread Starter


Joined May 28, 2008
hi every one
i have a circuit that works with 12 ~ 30 DC, 200 mA
i want to protect my circuit from voltages above 30 volt
i designed the following circuit to cut voltage when is above 30 volt,
i tested circuit, it works nicely
please consider this circuit,
if there is mistake, tell me to correct or optimize it or if you suggest better circuit tell me please

in schematic input voltage is in left side, 0 ~ 50 V DC
and out put is in right side
when input is 0~30 v, the output is 0~30 v
when input is 30~50v, the output is 0



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Joined Jul 17, 2007
You're attempting to open the ground side to the load. Very bad idea.

You need to disconnect the power side.
Consider using a "buck" regulator design instead. If your input voltage will fall below what your circuit requires to operate, consider a buck/boost or flyback design.

There are many topologies for switching DC-DC converters.
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Thread Starter


Joined May 28, 2008

i just want to disconnect over voltage to my circuit, just for preventing my circuit damage, in less voltages, my circuit doesn't work and not important.

i will install my circuit in a place that voltage is normally bitween 12 and 24,
rarely the voltage may rise up to 50 volt, i want to prevent damage my circuit


Joined Jul 2, 2008
Hi majid,
For 200mA, opening the load to ground is ok, but I have found a flaw.

You are using a 27v zener. So when your input DOES go to 50v, the first MOSFET's (left side) gate will receive 23v and will explode as most of the MOSFETs can only withstand upto 20v at the gate. You better use NPN transistors, as there would be no problem with base voltage, but be sure to limit base current. The second MOSFET will explode as well as it will receive 27v whenever input is >27v.