To power my microcontroller (ATmega8), I am using a ~5.4V voltage source. I want to ensure that I don't accidentally connect the voltage source in reverse, and figured a diode would be a nice way to accomplish this as from what I have learned so far, a diode allows current to flow in one direction, and blocks it in the other.
But what I also learned is that diodes create drops in voltage. I have a few of the typical diodes (1N4001, 1N4148, etc.), and would like to use them to achieve the aforementioned result without dropping the voltage as it would be too low to power the IC.
My question is, is there any way to do this with a diode? Or do I need some other component (if so, what would you recommend)?
Answer
You do not want an as low as possible voltage drop. The ATmega8 is specified for 2.7 V to 5.5 V operation, and that 5.5 V is actually 5.0 V with some margin. In the datasheet you'll see many parameters specified at 5 V.
Your supply voltage is ~5.4 V. What does the "~" mean? That it may vary by a few percent? 3 % higher gives you 5.56 V, which is out of spec. It won't cause the AVR to go up in flames, but it's a good habit to stick to the specs.
So let the voltage drop. Allow a 500 mV drop. The ATmega will consume only a couple tens of mA. A 1N4148 will drop typically 900 mV at 50 mA, which I would accept gladly, but which you may find too high. In that case go for the Schottky, like also suggested in other answers. You don't want a Schottky diode with a 100 mV drop, go purposely for one with worse specs. This one will drop 450 mV at 100 mA.
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