Protection Diodes
- Thread starter Route14
- Start date
benny_profane
Well-known member
You can use 1n400x rectifiers for polarity protection, but they are typically used in a crowbar method—i.e., reversed biased to ground rather than forward biased in series. Note that this can be destructive. Check the data sheets to see how Vf differs for the two.
benny_profane
Well-known member
Please note that this has a potential to get destroyed with application of reversed polarity power. You also add a LPF to the power supply (i.e., beyond what is typically formed by the source impedance and the filter caps).
Robert
Reverse Engineer
I'm suggesting the resistor come before the diode, specifically to limit current and protect the diode (and nearby PCB traces) from failure in a reverse polarity situation. Like you mentioned, it will also improve the filtering quality of C1.
I say suggesting and not recommending because I would rather just avoid the diode to ground method altogether. To the average pedal user with no soldering iron a shorted protection diode is just as broken as a defective opamp or transistor.
I say suggesting and not recommending because I would rather just avoid the diode to ground method altogether. To the average pedal user with no soldering iron a shorted protection diode is just as broken as a defective opamp or transistor.
benny_profane
Well-known member
Right. The crowbar method is really only helpful if the circuit is powered by a battery and the protection is for brief polarity reversal. With PSUs, it’s best to avoid entirely.
Thanks for all the great feedback!
Is this Diode strictly for reversed polarity concerns or will it protect against other issues. i.e. using 18v instead of 9v. Does it affect the circuit at all? Not that I am advocating this approach but, if I knew I was always going to use the correct power supply is this diode really needed? Could I just jumper it? (knowing full well that if my buddy brings over his Nintendo wall wart I'll be plugging straight into the amp!)
The reason for my original question was mostly because I've seen other projects use 1N4001 and I had this surplus of 02 and 03s I never use. I thought maybe I could put them to use as substitutes. I think I'll likely save them for something else and stick with the proper diode.
Apologies for all the questions. I did read up on the "crow bar" method and I think I get the difference now and why 5817 protection is better. Thanks for that info!
Is this Diode strictly for reversed polarity concerns or will it protect against other issues. i.e. using 18v instead of 9v. Does it affect the circuit at all? Not that I am advocating this approach but, if I knew I was always going to use the correct power supply is this diode really needed? Could I just jumper it? (knowing full well that if my buddy brings over his Nintendo wall wart I'll be plugging straight into the amp!)
The reason for my original question was mostly because I've seen other projects use 1N4001 and I had this surplus of 02 and 03s I never use. I thought maybe I could put them to use as substitutes. I think I'll likely save them for something else and stick with the proper diode.
Apologies for all the questions. I did read up on the "crow bar" method and I think I get the difference now and why 5817 protection is better. Thanks for that info!
Robert
Reverse Engineer
Neither of these methods protect against overvoltage, only reverse polarity.
If you use a zener diode in the place of D1 above it will protect against overvoltage and reverse polarity simultaneously, but it still has the same shortcomings of a regular diode to ground.
You can jumper the diode when it is in series to bypass polarity protection and the circuit will work fine, but will have no protection against reverse polarity.
You can't jumper the diode to ground, but you can remove it (or omit it) completely. Again, the circuit will work fine but will have no protection against reverse polarity.
If you use a zener diode in the place of D1 above it will protect against overvoltage and reverse polarity simultaneously, but it still has the same shortcomings of a regular diode to ground.
You can jumper the diode when it is in series to bypass polarity protection and the circuit will work fine, but will have no protection against reverse polarity.
You can't jumper the diode to ground, but you can remove it (or omit it) completely. Again, the circuit will work fine but will have no protection against reverse polarity.
Awesome thanks! That all makes sense and partly what I suspected. Thanks @PedalPCB and @benny_profane!!!
fig
Village Idiot
Socket them like a fuse and tape a spare to the enclosure lid. ehh? ehh?
Feral Feline
Well-known member
Fusing different solutions together, @fig?
Sorry, I couldn't resist, I'll put a cap on it. Oops, I diode it again.
Wire we so polarised about which protection-racket to put in the circuit packet? Ohm so confused.
Kay, that's it. Now I'm trying too hard to be punny, and it's just coming across as puny. Socket ooh me.
Sorry, I couldn't resist, I'll put a cap on it. Oops, I diode it again.
Wire we so polarised about which protection-racket to put in the circuit packet? Ohm so confused.
Kay, that's it. Now I'm trying too hard to be punny, and it's just coming across as puny. Socket ooh me.
