1N4148s cannot be used as protection diodes...

[shredgd]

...I mean when you put them across +9v and ground. I just did a test with a fresh 9v battery to simulate a reverse polarity situation in a pedal with such a protection and I burnt the diode, while a 1N4001 didn't get damaged.
Then I read 1N4148s are low current (signal) diodes, while 1N4001 are capable of higher current.
I'm writing because maybe there is someone else who thought 1N4001s and 1N4148s were interchangeable...!

Giulio

[Paul Perry (Frostwave)]

Surely the protection diode should be in SERIES wiht the battery, not across it??
And, in the best of all possible worlds (that is, a world where peope are prepared to pay 6 cents for protection) you would have TWO diodes, one from the battery to the power rail, then another (reversed) across the power rail, after the first diode.

[Boofhead]

A series diode will introduce an undesirable voltage drop.  The reverse diodes have no effect unless there is a fault condition.

shredgd, using a 1N914/1N4148 still protects the circuit but if you reverse the connection it can fry the diode with a fresh battery.

There's a few solutions:
- Series diode si, but this introduces voltage drops
- Series Schottky diode, still have voltage drop but it's less than Si,
  more costly however.
-  use a 1N4004 etc which won't fry with th fault current,  or
-  put a resistor in series with the line *before* the diode. The series resistor protects the diode and introduces little drop. it also limits the fault current on the battery but now you have to make sure the resistor won't fry.  Usually to cover all the bases this method works best for low current effects where the resistor can be reasonably large (say 100 ohm), which prevents it cooking, and at the same time maintaing a low voltage drop.  Power your LED circuits form the battery side of the resistor.

[Paul Marossy]

Rectifier diodes, such as a 1N4004, are virtually indestructible in a 9V battery circuit. They are pretty tough components.

[shredgd]

Thank you guys for the additional information!

[smoguzbenjamin]

Howabout 1n4002s? I used this in my breadboard power module (runoffgroove.com) and reversed the battery, no problem at all.

[Paul Marossy]

1N4001, 1N4002, 1N4003, 1N4004, 1N4005, 1N4007 are all rectifier diodes. The 4001 has a lower voltage rating, the 1N4007 is highest. Any of them will work in a circuit with a 9v battery. I don't think it's possible to fry one in this type of circuit.