Author Topic: Weird 1N5817G problem only in one situation. Help? [Flabluanche]  (Read 269 times)

midwayfair

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Weird 1N5817G problem only in one situation. Help? [Flabluanche]
« on: December 07, 2016, 11:40:28 PM »
Cross posting this from DIYstompboxes ...

I was building a Flabulanche, which is a circuit I ... know pretty well :P

http://www.madbeanpedals.com/projects/Flabulanche/Flabulanche_2015.pdf

Schematic page 4.

I ordered a pile of this diode, 1N5817G from Mouser:
http://www.mouser.com/search/ProductDetail.aspx?r=863%2d1N5817G

Datasheet:
http://www.mouser.com/ds/2/308/1N5817-D-103200.pdf

I've been through the datasheet and I can't find anything that tells me what the "G" suffix means, but I wouldn't have expected it to cause any issues. I mean ... it's a diode, right? In any case, I didn't give it a second thought when I was ordering it.

It works perfectly fine for the charge pump part of the circuit. I get my normal voltage at the end (17.7).

The place where I'm having trouble is the D1 rectifier. (For clarity, this rectifies the output of Q3 and puts a negative voltage on the gate, dropping the gain.)

There's some positive DC on the cathode of the diode (about 3.3V, from the gate bias for Q4). Normally that's not an issue -- I grabbed a previous build and there's no DC on the anode. But that build had a different diode.

On this build, when I flipped the switch, I've suddenly got a bunch of positive DC on the anode! Quite a bit of it, too -- about 2.3V.

So I grabbed a 1N60P out of the stash, pulled the 1n5817 and replaced it ... and the DC is gone. There's the tiniest bit of leakage across it, but that's it.

I doubled checked and none of the 1N5817 are bad or measuring something they shouldn't. My multimeter's not reading anything from cathode->anode for Fv. There shouldn't be enough current or voltage to hit any reverse breakdown or anything like that.

Just to make sure, I tested one of the 5817 in the previous build, and they cause the same problem. I tested every other diode I have at home and no other diode causes the issue. It's just this baggie of 5817Gs. I don't have any other 5817s to test, but I have 50+ other types of diodes and I can't find any others that malfunction in this way.

I popped one of the 5817 in a quick test circuit (just a load and a DC input). They block DC flipped around backwards like they're supposed to and drop .2V again like they're supposed to. So they diodes don't appear to be bad.

What am I failing to consider here? Is there something unusual about the "G" designation of the 5817 that's causing this unique problem?

Has anyone else had an issue with a 1N5817 causing their Flabulanche to malfunction?
Myself's music & things I make: http://jonpattonmusic.com. My band: http://midwayfair.org. PCBs of my designs from: http://www.1776Effects.com (Bearhug Comp & Cardinal Harmonic Trem); http://www.jmkpcbs.com (Hamlet+ delay & Blue Warbler envelope vibe); Snow Day OD/Flabulanche: www.madbeanpedals.com

midwayfair

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Re: Weird 1N5817G problem only in one situation. Help? [Flabluanche]
« Reply #1 on: December 08, 2016, 12:32:34 AM »
Rob Strand helped me track down the issue -- the leakage on a 1N5817 is through the roof. In fact, I measured a mere 47Ohms REVERSE across the diode, certainly low enough resistance to pass quite a bit of voltage.

http://www.diystompboxes.com/smfforum/index.php?topic=116264.0

Since I used a different Schottky in my prototype, I didn't consider this. I'll have Brian amend the build doc.

If you've used a 1N5817 in the Flabulanche, I highly recommend swapping it for pretty much any other Schottky. A BAT4x has extremely low leakage and the .25 Fv ones are probably the best choice. A 1N60P will also work and will have lower Fv.
Myself's music & things I make: http://jonpattonmusic.com. My band: http://midwayfair.org. PCBs of my designs from: http://www.1776Effects.com (Bearhug Comp & Cardinal Harmonic Trem); http://www.jmkpcbs.com (Hamlet+ delay & Blue Warbler envelope vibe); Snow Day OD/Flabulanche: www.madbeanpedals.com

bsoncini

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Re: Weird 1N5817G problem only in one situation. Help? [Flabluanche]
« Reply #2 on: August 20, 2017, 02:47:17 AM »
I just built one of these.  Real nice pedal.   I just stumbled upon this post and tested my voltages.  I had the same problem with the 1n5817 in D1.  Switched to Bat41 and minimal voltage.