Diode power protection - what do you use?

[Philtre]

Wondering what the thinking is on this for 9v circuits. Do you strap a diode across the +/- terminals or do you use a (Schottky) diode in series with the positive supply? The pedal I'm building doesn't have one on the board so I'm wondering whether it's best to add a 1N5817 in series. Or maybe nothing at all is OK?

[jubal81]

1N5817 in series. The other method is useless and disaster waiting to happen.

[somnif]

If its a battery, a 4001/etc across the poles is fine (can't pump enough juice to pop the diode) if rather inelegant. If its a power supply, go with the 5817 (or 5818/5819 if working higher voltages), or if you just want a cleaner/better solution.

The brute force 1n400X version has been used for so long that it pops up in a ton of circuits, and if you're careful about polarity its.... ok? But its a one-and-done "why do I smell smoke" sort of protection.

I just really wish pcb designers would make 1n5817's space on the board a little bit bigger. So many of my boards have this awkwardly jacked up diode because the pads are a wee bit too close together for its chunky leads to bend cleanly.

[stringsthings]

The brute force 1n400X version has been used for so long that it pops up in a ton of circuits, and if you're careful about polarity its.... ok? But its a one-and-done "why do I smell smoke" sort of protection.

[Max]

Probably the 1n5817 is cheaper, but wouldn't an N-channel mosfet be even more effective?

ps: Until now I relied on the "everybody-does-it-like-that" shunt diode solution, but you guys made me actually look into it, so thanks for the hint!

[somnif]

Probably the 1n5817 is cheaper, but wouldn't an N-channel mosfet be even more effective?

ps: Until now I relied on the "everybody-does-it-like-that" shunt diode solution, but you guys made me actually look into it, so thanks for the hint!

MOSFETs for protection would probably work better, yeah. But we pedal builders are a superstitious lot, and those old smokey diodes hold a certain mojo all their own.....

But seriously, its mostly a matter of inertia. Commercial builders use diodes because they're cheap and take less board real estate, DIY'ers follow suit because they work we are not the cleverest of monkeys (except when we are).

So of course, some of our best and brightest HAVE brought it up in the past 

http://www.geofex.com/Article_Folders/mosswitch/mosswitch.htm

Edit: And as a bit of historical context, recall that when he calls a diode in parallel the "cleverer arrangement", he was working in a Battery driven world. A third of a volt matters a lot more when you're on a limited tank, and a battery probably won't pump enough current to toast a 400X in any reasonable amount of time.

[Philtre]

I've chosen to go with 1N5817 in series.

I recently built a Timmy clone and it had one on the vero layout, but my latest build (Lunar Module Deluxe) didn't have one, so I simply soldered one in line with the positive 9v lead.

[Max]

So of course, some of our best and brightest HAVE brought it up in the past 

http://www.geofex.com/Article_Folders/mosswitch/mosswitch.htm

Interesting read, thank you!

[BuGG]

1N5817 in series for me.   

Like jubal said, the "classic" diode to ground method has always bugged me...  If reverse polarity is applied the diode shorts and sometimes takes out traces and/or the PSU with it.   

Maybe it saved the rest of the circuit, but to the average consumer a shorted protection diode is still just a broken pedal.

[helos]

I've chosen to go with 1N5817 in series.

I recently built a Timmy clone and it had one on the vero layout, but my latest build (Lunar Module Deluxe) didn't have one, so I simply soldered one in line with the positive 9v lead.

But Isn't there any voltage drop accross the diode?

[helos]

I've chosen to go with 1N5817 in series.

I recently built a Timmy clone and it had one on the vero layout, but my latest build (Lunar Module Deluxe) didn't have one, so I simply soldered one in line with the positive 9v lead.

But, is there any voltage drop accross the diode?

[Philtre]

A small amount. 1N5817 is a Schottky diode with minimal forward voltage drop.

[somnif]

But, is there any voltage drop accross the diode?

About half a volt. Nothing problematic on a plug-in power supply, but not great if you're living in a battery world.

[Philtre]

But, is there any voltage drop accross the diode?

About half a volt. Nothing problematic on a plug-in power supply, but not great if you're living in a battery world.

But good for a Fuzz factory!