Is the function of 1N4001 before the 5V regulator reverse polarity protection?
Is this a fine method? And I sometimes see 1N4148.
Can any diode(besides zener) be used for such function?
Electronic – A question about reverse polarity protection diode
diodesreverse-polarity
Related Solutions
I'm assuming the type of circuit you are thinking of is this: -
For use on your battery powered circuit I see little to say against it. A couple of things though; you need to pick a FET with low \$V_{GS(threshold)}\$ so that the device is still offering a tiny volt drop at low battery voltages AND you'll need a FET with low \$R_{DS(on)}\$ so that at 30mA (or whatever your peak current is) the FET is dropping less than (say) 100mV.
Maybe the following FET is a decent example: -
With 1.8V gate drive it has 0.071\$\Omega\$ resistance. At 100mA drain current this device will "lose" 7.1mV.
If you have a voltage peak the TVS will clamp it by draining current. Since you don`t have a resistor your diode most likely will blow. Find the current that you need and calculate the resistance and power for your circuit. Check the maximum clamp voltage of you TVS. It should be lower than your regulator. A couple of capacitors may help to filter some noise from alternator and spark plugs. They will work as a RC low pass filter.
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Best Answer
Yes, this diode is probably for reverse polarity protection. It does its job but has the disadvantage that about 0.6 V is dropped across it. It needs to be rated for the current, both continuous and surge, as well as the reverse voltage it might encounter. 1N4148 is fine for lower current applications. A shunt diode with polyswitch/fuse is also an option. More elaborate schemes with MOSFETs are possible.