[sdiy] Vanilla electronics question

[Benjamin Tremblay]

I think it’s a subject near and dear. PWM.
Benjamin Tremblay

> On Feb 17, 2024, at 11:31 AM, Mike Bryant <mbryant at futurehorizons.com> wrote:
> 
> 
> 
> Possibly explanation is the SS16 is being used like a unijunction transistor was (as in original Moogs)
> 
> The voltage on the capacitor builds up until it reaches the breakdown voltage of the Schottky (selected for less than 12V) which then discharges the charge in the capacitor into the LEDs.  Hence the LEDs only flash so nothing actually burns out.
> 
> Just a guess but worth looking at.
> 
> 
> 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 15:48
> To: SDIY List <Synth-diy at synth-diy.org>
> 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
> 
> 
> 
> ________________________________________________________
> This is the Synth-diy mailing list
> Submit email to: Synth-diy at synth-diy.org
> View archive at: https://synth-diy.org/pipermail/synth-diy/
> Check your settings at: https://synth-diy.org/mailman/listinfo/synth-diy
> Selling or trading? Use marketplace at synth-diy.org
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://synth-diy.org/pipermail/synth-diy/attachments/20240217/c4aac3c4/attachment.htm>