<html><head><meta http-equiv="content-type" content="text/html; charset=utf-8"></head><body dir="auto">this sounds like a switching regulator to me! I use this kind of led driver a lot. there is usually a pin on the driver IC held at some voltage that sets the current through the leds. 150ohms sounds high for what I'm used to, but who knows. The direction of the schottky is consisent with buck configuration in a constant current led driver, too. I frequently use the SSxx series diodes in circuits like this cuz they're small and readily available. <div><br id="lineBreakAtBeginningOfSignature"><div dir="ltr">Cheers,<div>Chris </div></div><div dir="ltr"><br><blockquote type="cite">On Feb 17, 2024, at 10:19 AM, Mike Bryant <mbryant@futurehorizons.com> wrote:<br><br></blockquote></div><blockquote type="cite"><div dir="ltr">
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Possibly explanation is the SS16 is being used like a unijunction transistor was (as in original Moogs)</div>
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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.</div>
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Just a guess but worth looking at.</div>
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<div dir="ltr" id="divRplyFwdMsg"><span style="font-family: Calibri, sans-serif; font-size: 11pt; color: rgb(0, 0, 0);"><b>From:</b> Synth-diy <synth-diy-bounces@synth-diy.org> on behalf of Rutger Vlek via Synth-diy <synth-diy@synth-diy.org><br>
<b>Sent:</b> 17 February 2024 15:48<br>
<b>To:</b> SDIY List <Synth-diy@synth-diy.org><br>
<b>Subject:</b> [sdiy] Vanilla electronics question</span>
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<div style="direction: ltr;">Dear list,</div>
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<div style="direction: ltr;">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.</div>
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<div style="direction: ltr;">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.</div>
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<div style="direction: ltr;">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.</div>
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<div style="direction: ltr;">So....can anyone tell me, what is this circuit? If I had to guess, it's either:</div>
<div style="direction: ltr;">(1) an attempt at a traditional LED circuit by someone who messed-up badly</div>
<div style="direction: ltr;">(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.</div>
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<div style="direction: ltr;">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.</div>
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<div style="direction: ltr;">Rutger</div>
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