Electronic – Reverse polarity protection idea

polarityprotection

I'm thinking about making a reverse polarity protection for a project, and I've came up with this idea:

schematic

simulate this circuit – Schematic created using CircuitLab

I think that if I reverse the polarity, the diode will short the supply and blow the fuse. Will it work this way?

The only weird thing is that I didn't find anything simillar when looking around the internet… so I'm assuming there is a catch.

Best Answer

What you show is fine. However, the diode needs to be able to handle the large current from the time the power supply is connected backwards until the fuse blows. That could be several 100 ms. Check the fuse datasheet. Usually you would use a beefy diode, not a zener. There are such things as power zeners, but if you're only trying to protect against reverse polarity and not overvoltage, you don't need the zener function. Just get a power diode.

Note that in the overvoltage case, the zener will dissipate much more power until the fuse blows than in the reverse voltage case when it's acting like a ordinary diode. The zener will dissipate a lot more than the fuse, so finding one that won't melt before the fuse does will be tricky, and expensive when you do.

The fuse and reverse diode is occasionally used, but nowadays the trend is to not force the user to replace a blown fuse unless something has really broken, in which case replacing the fuse isn't going to do any good anyway. This is a cheap and effective way to protect against reverse voltage that hardly gets in the way when the voltage is applied properly. However, you have to consider whether users are going to get upset when the fuse blows.

Unless this is low voltage and every last bit of efficiency matters, you're probably better off putting the diode in series and simply blocking reverse voltage. At low voltage, use a Shottky diode to reduce the voltage drop when operating normally. Roughly at 100 V or more, use a ordinary silicon diode.