N Channel Mosfet Reverse Voltage Protection

Good day, I want to make a 30 volt reverse voltage protection circuit using an n-channel mosfet, but when I connect the load as follows, it shows negative voltage when I measure the load with a voltmeter. How can I get the output to be 0 volts in the wrong connection.

Can you draw the circuit correctly please - you have labelled the source of the FET as "D" and the drain as "S".

sorry i didn't pay attention

What polarity is "correct" and what polarity is "wrong" - I'd expect a p-channel in this sort of circuit and ground not to be where you've indicated.

BTW this is the sort of circuit I'd be expecting: https://electronics.stackexchange.com/questions/305425/mosfet-in-reverse-polarity-protection

I want to do it via n channels

The issue is what circuit will work, and for that we need to know the intended behaviour - so I'll ask again which polarity is "correct" and which is "incorrect" in your application - its not obvious from what you've posted. That determines if a p-channel or n-channel is needed.

Did you actually make it, or use a simulator.
Circuit seems correct, but the LED is not a resistive load. LEDs work like zener diodes.
If you don't bleed off the leakage of the fet, then you could see some zener voltage there.
Try a 10k resistor across the LED.

I have a step down voltage reducer, but this integrated has no reverse voltage protection. My problem is that when reverse connection is made to the mosfet, it gives negative voltage, I want it to be 0 volts, if p channel will solve my problem, I am ready to use p channel.
I made reverse polarity in the circuit above, but when I measure it with a voltmeter, I get a negative value. What should I do to see it as zero volts?

I just added the LED as a load. I'm going to add a voltage reducer instead of the LED, so I used the LED as I couldn't find it in the simulator. My problem is how can I reset the negative value on the voltmeter.

Hi, @mertkslkc

Have you got the polarity of V1 the input voltage the correct way around?
How do you aim to get the Gate positive with respect to the Source.

The usual polarity protection associated with switching a circuit ON/OFF is done in the positive supply wire.
Isolating gnd instead of positive supply comes with some problems if you have other separately connected circuits that use other power supplies.

Is there a reason you want to isolate and protect using the gnd connection.

Tom... :smiley: :+1: :coffee: :australia:

This is the system design. Accordingly, 30 volts dc from the transformer first passes through the mosfet, if it is not reverse polarized, it goes to the step down voltage regulator from there, and 30 volts is reduced to 5 volts and feeds the esp32 board.

I asked a very simple question, in fact, how can I see the negative voltage as 0 volts in reverse connection, there should be a simple solution to this, I thought of connecting a capacitor in parallel between Vin - Source, do you think this would work?

What sort of step down regulator?
Why are you not using a simple diode in the positive 30V to do polarity protection?

Thanks.. Tom... :smiley: :+1: :coffee: :australia:

Diode will cause heating problem. I want to do it with mosfet so that I don't have to deal with it in the future.

I think I solved the problem guys. Since the input is 30 volts, I limited the gate supply to 10 volts by making a voltage divider between Vgs and added a 10 volt zener to the output of the voltage divider. Then I added an lc circuit to the output to filter the voltage spikes originating from the transformer. What are your comments?


How much current are you aiming your project to handle?
At 600mA, I don't think you have a problem.

What does your simulation show when you connect V1 correctly?
Include in the simulation a load, such as enough to draw 600mA.
At the moment your simulation has no load.

Tom... :smiley: :+1: :coffee: :australia:

Not sure R1 is strictly necessary. The values of the resistors can be much higher as a MOSFET gate takes negligible DC current.

Tom :slight_smile: it's easiest to add diodes, I want to go the hard way and I don't want to give up on this problem now as I will be working with mosfet more often in the future.

What do you think the resistance values ​​should be?
Why shouldn't r1 be needed?
30 volts is coming from the source, how can I feed the door with 10 volts..


What door?
PLEASE tell us what your project is?

Thanks... Tom.. :smiley: :+1: :coffee: :australia:

When I said door, I spelled it wrong, I meant the gate foot of the mosfet.
My project is as follows, I am developing an iot device to be connected to the PLC's electrical panel. There is a transformer giving 30 volt dc output on the panel. The previous model I developed did not have reverse voltage protection, so I want to make a device with reverse voltage protection and lc filter circuit in this version.