[sdiy] Vanilla electronics question

[Mike Bryant]

Pure guess ... more like a breakdown current.  Sort of like a Zener ... but not quite.

Conversely there may be a better explanation ... just I can't think of one.
________________________________
From: Chris McDowell <declareupdate at gmail.com>
Sent: 17 February 2024 23:16
To: Mike Bryant <mbryant at futurehorizons.com>
Cc: grant musictechnologiesgroup.com <grant at musictechnologiesgroup.com>; Rutger Vlek <rutgervlek at gmail.com>; SDIY List <synth-diy at synth-diy.org>
Subject: Re: [sdiy] Vanilla electronics question

wacky. Is it the leakage current of D1 that allows C1 to do anything in the first place?

Cheers,
Chris

On Feb 17, 2024, at 4:59 PM, Mike Bryant <mbryant at futurehorizons.com> wrote:


Yes fairly sure D1 is operating in some form of avalanche mode, turning the LEDs on for a short while before it recovers and turns them off again.  Could be at 100Hz, 1Hz or even 0.1Hz though, depends on C1.

As for it not working, it's possibly because D1 is borked from being used like this.
________________________________
From: Synth-diy <synth-diy-bounces at synth-diy.org> on behalf of Rutger Vlek via Synth-diy <synth-diy at synth-diy.org>
Sent: 17 February 2024 18:35
To: grant musictechnologiesgroup.com <grant at musictechnologiesgroup.com>
Cc: SDIY List <Synth-diy at synth-diy.org>
Subject: Re: [sdiy] Vanilla electronics question

Here's a schematic of the circuit. These are really all the components. The entire PCB is really no more than twice the size of my finger tip. The capacitor value is unknown.

<image.png>


Op za 17 feb 2024 om 18:58 schreef grant musictechnologiesgroup.com<http://musictechnologiesgroup.com> <grant at musictechnologiesgroup.com<mailto:grant at musictechnologiesgroup.com>>:
Once you all get consensus on the circuit, any chance us in the peanut gallery can get some kind of schematic so we can follow along? Thanks!

GB


------ Original Message ------
From "Rutger Vlek via Synth-diy" <Synth-diy at synth-diy.org<mailto:Synth-diy at synth-diy.org>>
To "SDIY List" <Synth-diy at synth-diy.org<mailto:Synth-diy at synth-diy.org>>
Date 2/17/2024 7:48:43 AM
Subject [sdiy] Vanilla electronics question

Dear list,

Against my wishes, I'm working on repairing my eBike's rear light, instead of building something synth related. However, I'm stumbled by a seemingly simple circuit that just does not behave as I expected. Of course I considered buying a new rear light, but for the sake of the planet (and my own knowledge gathering), I'm trying to revive the original one.

The circuit is simple, I'll try to describe it. Positive voltage (appox. 12V) from the bike's battery enters two red, parallelled power LEDs (in forward direction), goes through a 150 ohm resistor, and then through what seems like a Schottky diode (SMD package labelled SS16) in reverse (!), non-conducting direction to ground. The point before the SS16 is also connected via a capacitor to the positive supply.

I replaced the LEDs and they are testing fine now (didn't before). From the start I assumed the SS16 (presumed Schottky diode) to be there for reverse voltage protection, until today... when I looked at the direction in which it's placed. Moreover, the resistance and power dissipation capacity of the resistor don't seem to fit a traditional LED circuit. In other words, the resistor would run the LEDs very close or over their maximum current rating, and would burn out due to the heat it had to dissipate while doing so.

So....can anyone tell me, what is this circuit? If I had to guess, it's either:
(1) an attempt at a traditional LED circuit by someone who messed-up badly
(2) some kind of switching voltage regulator (the rear light indicates to be capable of handling a supply anywhere between 6V to 12V). So I'm guessing it's the latter.

If moderation feels this is way off topic, I can completely understand. Although I'm interested to learn about this circuit, as it perhaps could find its way into synthesizers too.

Rutger



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