How to protect against overvoltage and reversed voltage polarity?

How can I protect my circuitry against overvoltage and reversed voltage polarity?

With Schottky diodes? Zener diodes?

my circuitry

What kind of circuitry?

http://www.thebox.myzen.co.uk/Tutorial/Protection.html

http://www.digikey.com/us/en/techzone/microcontroller/resources/articles/protecting-inputs-in-digital-electronics.html

It would depend a lot on your particular circuit; whether or not you can live with a voltage drop on the input… but yeah, a schottky and a zener makes perfect sense. You might substitute the schottky for a FET if your voltages are critical.

syntaxterror: but yeah, a schottky and a zener makes perfect sense.

Which ones you you recommend (to protect a 5V and/or a 3,3V circuit)?

Zealot: Which ones you you recommend (to protect a 5V and/or a 3,3V circuit)?

Do we know the current draw of the circuit(s)?

syntaxterror: Do we know the current draw of the circuit(s)?

30mA typical. 500mA max.

Zealot: 30mA typical. 500mA max.

Well that's not horribly big numbers. I'd probably just stick with a 1N5817. As for the zener.. it can be a bit tricky sometimes. It really depends on the 5V you'll be supplying it with. You don't want a high 5V supply to push it past its breakdown voltage. That said, if you put the zener on the cathode end of the schottky, I'm guessing there would be no problem. In that case I'd be going with some type of 5V1 (or 3V3, although with a schottky diode, voltages this low aren't ideal). I don't really have any preference with zeners - just make sure to check your power supply's maximum current and dimension the zener accordingly.

A word about polarity reversal though. Given the voltage drop and the low voltages, a schottky diode is hardly an optimal solution. If all we're talking about is accidental reversal, I'll venture that you'll be better served keying your connectors or otherwise making sure it's just not physically possible to reverse the power and ground.