# Over voltage and reverse polarity protection

I was trying to make an over voltage and reverse polarity protection circuit and create a PCB that I can easily use in some of my projects.

My level of electronics it's not so good, and that's why I'm here.

I thought one circuit, but as long as I know it's not so good:

simulate this circuit – Schematic created using CircuitLab

There's a bunch of circuits arround the internet that involves transistors, but I don't know which one I would pick (or even an IC, as it was discussed previously here, but I couldn't understand which configuration should I use).

Here's my requirements:

• It should output around 5V (if the input it's too low it can output less voltage, but if it's greater it should be limited). I want to use it with 74LS ICs, so the input voltage should be 5V, but it can go from 4.75V to 5.25V. The current used it's, at most, 1.5A.
• The input voltage can go from +40V to -40V.
• I'm using a workbench power supply, so no need to over current protection (it's already integrated).
• It should be as simple as possible (~5 components). I don't want to solder >25 components.
• I don't care if something blow up. As long as the external circuit stays safe, it's OK for me.

Is there an IC or circuit that suits my needs?

Please go nice on me, this isn't my specialty. Thanks!

• Just zenner 5.6V 10W. Set proper current limit, like 1A. Commented Jan 16, 2021 at 19:28
• @user263983 OK, or even the fuse solution seems OK to me (just in case). Can you explain me why 5.6V and not 5.1V? 5.6 it's above the maximum voltage. There's one problem with the diode, and it's that there's a small current in reverse voltage, and maybe that current can lead to the destruction of some ICs. Commented Jan 16, 2021 at 19:30

A diode reverse voltage protection in a 5 volt circuit is not ideal. Even if you use a good Schottky you are still going to loose ~ 0.5V and the reverse current in some schottky's may still damage your circuit.

Overvoltage protection with a Zener is also not ideal. You need some margin so you must use a 5,6V zener, if not it will conduct "nominally". A voltage at 5.6V may exceed your ratings. (And you need a fuse - if not the zener will overheat and blow up)

What you want is an efuse. As your voltage is similar to USB there are many types, so I am sure you can find one that fits your need. One example is NIS6150. Your biggest challenge might actually be to find one that is solderable by hand. Most of these components are tiny.

• Sorry, made a mistake when reading the datasheet. NIS6150 blocks reverse current, not reverse polarity. TPS26600 seems nice. Perhaps a bit too fancy? Commented Jan 16, 2021 at 20:54
• you can just edit your comment if you made a mistake Commented Jan 16, 2021 at 21:11
• @Arcatus Today I have received the PCB to solder the TPS26600 and it works like a charm! Thanks! Commented Jan 30, 2021 at 0:07

Zenner diode is not ideal. With nominal voltage 5.1V and applied 5V some current will go through. Cheçk datasheet to get more specific. Fuse nominal chosen to make it blow before zenner. So 10W can hold 2A. But fuse should be fast, or lesser value. Also it gives protection in case of reversed polarity because in that connection zenner works as regular diode with drop voltage 0.7V.