How to protect circuits from reversed voltage polarity!

What people said

Recommends helloworld922 · 2013-01 · Electrical Engineering Stack Exchange · on “Is a Schottky diode appropriate for reverse polarity protection?”

The bigger problem you're likely to run into is operation under forward bias conditions. Schottky diodes still have a voltage drop under forward bias, say 0.25V. That means at 100mA, you're dissipating 25mW of power. Better than a standard silicon diode, but not great especially for a battery constrained device. A better way to get reverse bias protection is to use a P-Channel MOSFET. MOSFET's act more like a resistor when saturated, and it's possible to get MOSFETs with low on resistances. Let's assume we have a 1 ohm on resistance. At 100mA, that's a 0.1 V drop across the MOSFET and 10mW dissipation. 1 ohm on resistance is kind of lousy for a MOSFET, you can get some which have significant

Recommends KyranF · 2015-05 · Electrical Engineering Stack Exchange · on “What's the purpose of the diode in this selectable supply voltage circuit part”

There is a much better way to do this, especially if battery powered (every watt lost is a kitten lost! Or time, at least) using a PFET "backwards" from the usual high side power switch configuration, and with the gate to ground. Same behaviour as the diode shown, but almost zero lost power during normal conditions in comparison. Check this youtube video for explanation [this video]

Recommends helloworld922 · 2015-07 · Electrical Engineering Stack Exchange · on “Does my device need reverse polarity protection?”

A better solution for reverse polarity protection using a P-channel MOSFET: simulate this circuit [LINK] – Schematic created using CircuitLab [LINK] This circuit has virtually no voltage drop across the MOSFET, where-as a diode will have one (even a schottky diode might have a ~0.25V drop). Note that this circuit requires that \$V_1 > V_{th}\$, which in this case would be ~2V. Also with 2AAA batteries you might have a hard time driving some LED's, especially as the batteries drain. If you prefer, here's an equivalent circuit which uses an N-channel MOSFET. Similarly, it requires \$V_1 > V_{th}\$ simulate this circuit [LINK] For a more complete explanation on why these circuits work, I would

Recommends DSWG · 2018-10 · Electrical Engineering Stack Exchange · on “Opinions on what I've come up with for a 12 V-to-5 V automotive circuit?”

Just adding my two cents, if you care :) I've designed 3 systems which are automotive powered. They were for GE (I don't work for GE, I work for an OEM who they contract to). People have suggested a diode for reverse polarity and transient feedback protection. Instead, use a P-Channel Enhancement MOSFET on the high-side, or a N-Channel Enhancement MOSFET on the low-side. Great video on the concept here [this video] , showing how easy it is to do, and how much more efficient it is. Make sure the Vds rating on the MOSFET is over 30V. Add a common-mode choke on the two lines coming in, to remove common-mode noise. Make sure the current rating is acceptable for the current you expect. Add a ferrite o

Recommends Codebeat · 2021-09 · Electrical Engineering Stack Exchange · on “Reverse polarity protection idea”

See also afrotechmods channel video [this video] for an explanation. Quick explanation/characteristics: Less power loss/dissipation in comparison to a diode; Voltage drop of about 1V at the output. Keep in mind that if you need for example 12V at the output, you need to apply 13V at the input; The mosfet is unable to turn on at reverse polarity and protect your circuit; The zener diode is used to protect against overvoltage of the gate and to protect the mosfet against damage because of overvoltage; The resistor is to limit the current on the gate of the mosfet. [LINK] Another clever solution I found [LINK] , with a relay and no voltage drop. [LINK]

Recommends Ste Kulov · 2022-06 · Electrical Engineering Stack Exchange · on “Is there such thing as an inline ideal diode?”

I don't fully understand what you're trying to do, but if you're looking for reverse polarity protection on the battery you can use a P-channel MOSFET as described in this video: [this video]

Recommends Ste Kulov · 2025-05 · Electrical Engineering Stack Exchange · on “What is the use of this dual MOSFET in the battery section”

@Confused Not reverse current, but reverse polarity for the battery. If there's another voltage source attached to V_BATT then it can't prevent reverse current. Here's a decent video which explains this technique: [this video]

Cites skyler · 2013-04 · Electrical Engineering Stack Exchange · on “Diodes in parallel”

Use a p-channel MOSFET for reverse protection. It is much more efficient, does not drain a lot of heat, and less power is wasted. Here [this video] is a YouTube video talking about it's efficiency, and following is a picture of a schematic. Diodes aren't horrible though,and they are pretty efficient compared to the old selenium rectifiers or vacuum tubes or crystal rectifiers. For the MOSFET, an IRFp450 should suit your needs if you want to do the MOSFET strategy.

Cites Fil Nick · 2016-01 · Electrical Engineering Stack Exchange · on “Using MOSFET’s For AC Rectification”

I recently saw this video that did inspire a little bit of interest on my part. [this video] It appears that when the drain of a N channel mosfet is connect to the gate it can act as a diode. Also according to this video it can do that very efficiently. So I messed around a little bit on a very primitive inverter that I built a while back. I tried to rectify the output current of the inverter which was stepped down to 12 volts ac. So I tried to use the transistors as diodes and my results where the following. I tried an NPN and I got 8 volts of DC on my multi meter. I tried the MOSFET and got less than a volt even without the gate being connected. Simply put the Mosfet acted a lot like a wire and

Cites Tom · 2016-08 · Electrical Engineering Stack Exchange · on “Dual rail reverse voltage protection”

After watching Afrotechmod's tutorial about reverse voltage protection [this video] , I wondered if I could incorporate it in a circuit I'm working on. Unlike the circuit in the video, mine's dual supply, and there's where things get lost on me. Do I need to tie the MOSFET's gate to GND, or to the supposedly negative power rail? Is is even possible to do this with a single MOSFET, or do I need another one? If so, P-channel or N-channel? simulate this circuit [LINK] – Schematic created using CircuitLab [LINK]