5V Overvoltage protection circuit

Other Hardware General Electronics
1

Hello everyone!

I am trying to build my first protection circuit for a project and I am having some issues. The project basically consumes around 0.5A and it works at 5V. I decided to make a protection circuit that cuts the voltage if gets to 6V. I did some research online and found a circuit with PNP transistors to be a good one. So I built the following circuit:

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However, it is not working. If I put a voltage higher than 6V it still goes through and after reviewing everything I can't manage to find what is failing...

Here are the parts I used:

ZENER: https://www.mouser.es/ProductDetail/Micro-Commercial-Components-MCC/SMBJ5340B-TP?qs=ZNK0BnemlqHJq1hQMWEIvQ%3D%3D

PNP Transistor: https://www.mouser.es/ProductDetail/ROHM-Semiconductor/2SAR574D3FRATL?qs=qSfuJ%252Bfl%2Fd7dUuPev%2FfRjQ%3D%3D

2

If you replace your circuit with a DC-DC converter that can take e.g., 3-12V input then it will continue to work at 6V.

3

Problem is with Vbe of Q5 (about 0.6 V). With 6 V Zener the threshold is too high. Try 5V1 Zener or even lower voltage.

1 Like
4

Here is the same circuit I found online. The resistor values are different from yours. I don't know if that matters, but it might.

Simple-Overvoltage-Protection-Circuit
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1 Like
6

Today I am getting new Zener diodes so I will do some tests to see if it works properly.

7

As the load consumes 500mA, the base of Q2 needs 50mA or so, so R3 should be 220 ohms. ZD1 can be 4V7 for more precise voltage limiting.

Q2 cannot be a BC557 (which is only rated at 100mA), so that needs fixing too.

8

Maybe you want to look into using a crowbar circuit that uses an SCR instead of a series pass transistor. It functions only on an over-voltage condition, then limits the output voltage to about 1 volt.

9

It shorts the power supply and relies on a fuse in the power supply to blow to protect the circuit and the power supply.

Tom... :grinning: :+1: :coffee: :australia:

10

I prefer FOLDBACK CURRENT LIMITING . I know what you're thinking "Foldback current limiting is practically
idiot proof so I must be an idiot to recommend it". You can say that but I have found that
when you have foldback current limiting you can pretty much stop worrying about overcurrent.

11

Am I missing something? Why not just regulate the voltage to 5V?

12

I am supplying power with a 5V adapter, and I accidentally connected a 24V and fried it... That is why I was looking for overvoltage protection. I am not an expert, could you explain what type of circuit would it be? And would the voltage regulation work with a situation like this?

13

A 5V regulator with a 36V input ?

14

OK, just learned something new! However, I have a doubt, do they heat up?

15

Do WHAT heat up ? (not sure what heat has to do with voltage)

16

Just wondering if during operation the regulator heats up a lot or not. Just googled it and, I have seen that linear regulators heat up a lot since they are very inefficient but switching regulators don't heat up as much but might generate noise.

17

FYI

Efuse

1 Like
18

You obviously didn't read the datasheet or the
info on the website. It's NOT a LINEAR regulator.
it's a Switching DC2DC CONVERTER !

Description: "Linear Regulator REPLACEMENT"

19

Sorry, you do not need "overvoltage protection".

You need something quite different, and I do not think we can really provide it for you. :thinking:

20

You really are quite ambiguous.

21

Sorry if I sound ambiguous... I will try my best to sound more precise in future posts. And thank you for all the suggestions!