Reverse Battery Protection With Mosfet (no voltage drop) – Voltlog #353

Welcome to a new Voltlog, today we’re going to be talking about reverse battery protection, I’m gonna be showing you a few methods for achieving this protection but I’m going to be focusing specifically on low power designs, where you might be using let’s say a single coin cell battery.

When we’re talking about higher input voltages, battery protection is pretty simple, you can simply add an inline Schottky diode, if the input voltage is reversed, the diode will be reversed biased and it will block the current flow. There is about 0.5V voltage drop on your diode but if you have a 9V input into a 5V regulator, there’s plenty of margin to afford losing half a volt. There is also the power dissipation to consider in that case, so you multiply the current with the voltage drop and you get your power dissipation into the diode, you pick an appropriate diode capable of dissipating that and the problem is solved.

Now when you start talking about low power devices, specifically those powered by coin cells, it gets a little tricky to get some reverse polarity protection into your circuit. Because our battery voltage is now just 3V we can’t afford losing 0.5V on our input diode, that will ruin our battery life, it will waste the little precious energy we have stored in the coin cell and might prevent our circuit from powering up.

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