[sdiy] Vanilla electronics question

Tue Feb 20 13:13:09 CET 2024

Most likely a Zener diode to drop some of the excess voltage.

-Richie,

On 2024-02-19 22:34, Ben Bradley via Synth-diy wrote:
> From the schematic I'm pretty sure that one "diode" or whatever it is
> has to have a range of negative resistance for this thing to
> oscillate, which I'm sure is how it works. I've not heard of schottky
> diodes/rectifiers having negative resistance in their reverse
> direction,  but then I don't know everything. I don't see anything on
> the SS16 datasheet that looks like a negative resistance.
> 
> I wonder if this could be an SCR with an internal resistor between the
> gate and anode, so that it triggers at something below 12 volts. The
> current through the LEDs would have to be below the "turnoff" current
> of the SCR, and that seems questionable.
> 
> Decades ago (1950s-1960s)  a tunnel diode was popular as an oscillator
> in the VHF/UHF region, but apparently went obsolete when transistors
> were made to operate at those frequencies. Electrically this could be
> a tunnel diode, but looking on Digikey and Mouser shows no
> possibilities for anything called a tunnel diode.
> 
> As mentioned, a unijunction transistor is another possibility, but
> Mouser only shows a few, at over a dollar each in any quantity, and
> made by Central Semiconductor, which is apparently a source of
> otherwise-obsolete semiconductors much like Rochester.
> 
> Something like an SCR would be my best guess, but I'm not confident in 
> that.
> 
> On Mon, 19 Feb 2024 at 11:07, Tony Mowbray <tmowbray at ihug.com.au> 
> wrote:
>> 
>> Actually I think it runs as an oscillator so the operation of the LEDs 
>> is pulsed to allow high current for a short period of time.
>> 
>> But then again, I could be way off
>> 
>> 
>> 
>> Regards Tony,
>> 
>> Sent from Samsung tablet.
>> 
>> 
>> -------- Original message --------
>> From: René Schmitz <synth at schmitzbits.de>
>> Date: 19/2/24 23:41 (GMT+10:00)
>> To: synth-diy at synth-diy.org
>> Subject: Re: [sdiy] Vanilla electronics question
>> 
>> 
>> Only: SS16 has 60V reverse voltage capability. Probably with 
>> considerable slack until it actually breaks down. I can't see how it 
>> would get into a breakdown with 12V.
>> 
>> 
>> 
>> The reverse leakage current of this device would be in the order where 
>> you can see the LED light up. (0.4mA)
>> 
>> IMO it's an attempt to build a current limit.
>> 
>> 
>> Best,
>> 
>>  René
>> 
>> 
>> 
>> Am 18.02.2024 um 00:34 schrieb 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 
>> <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>
>> To "SDIY List" <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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