parallel LEDs each with on/off switch. Residual current/ faint glow issue - Page 1
Forum section: electronics / beginners

author: twingall1
author_rank: Newbie
timestamp: October 10, 2023, 08:28:35 pm
content: Hi all, I have a circuit of 7 parallel rgb leds each with two toggle switches (one ON-ON-ON for red green or blue; one ON-OFF to take that particular LED out of the circuit).It works almost perfectly, but i'm finding that an LED will faintly glow despite being turned off via the on-off toggle. It glows always with the color of the ON LED preceding it in the circuit.Is there any way to fix this? Maybe with Diodes?Any advice greatly appreciated,T

author: Benta
author_rank: Super Contributor
timestamp: October 10, 2023, 08:32:07 pm
content: Schematic needed.

author: pqass
author_rank: Super Contributor
timestamp: October 10, 2023, 08:33:35 pm
content: If I recall, you could put a high value resistor (100K) between anode and cathode of each LED.That should discharge the stray capacitance.

author: twingall1
author_rank: Newbie
timestamp: October 10, 2023, 08:55:45 pm
content: here is my schematic; the dotted red circle is repeated 6 more times down the parallel circuit

author: twingall1
author_rank: Newbie
timestamp: October 10, 2023, 08:59:24 pm
content: hmm, thanks, noted, will test on breadboard. Doable but tricky in terms of space as it's all boxed tightly in rosewood pannels now. Was hoping for a fix involving less parts/soldering/space..I should have used breadboard much more thoroughly at the start lol

author: iMo
author_rank: Super Contributor
timestamp: October 10, 2023, 09:06:16 pm
content: ..make your image smaller, it is 3MB now..The stray capacitance should not play a role unless you use a power supply with some AC on the DC.It looks like wiring issue, or some DC current leakage..

author: twingall1
author_rank: Newbie
timestamp: October 10, 2023, 09:20:18 pm
content: the power supply is from usb phone charger socket output 5v 1.5A DCthere is some naked copper wire touching the wooden housing, i assumed that wood would insulate fine, perhaps not?smaller image in the above post now..

author: pqass
author_rank: Super Contributor
timestamp: October 10, 2023, 09:28:10 pm
content: I can't find a hard reference for you but Big Clive mentioned the effect in several of his videos WRT capacitive dropper power supplies.Maybe it's easier for you to put a 100K resistor from DPDT switch pin to common anode (ie. across LED cathode+1K).

author: iMo
author_rank: Super Contributor
timestamp: October 10, 2023, 09:43:14 pm
content: Quote from: twingall1 on October 10, 2023, 09:20:18 pmThe glow may come from the charger, imho (there is a capacitive coupling of the secondary to the mains).The modern LEDs are sensitive, a couple of uAmps AC/DC is enough to make them glow.Try it with a battery, you should not see any glow then..

author: twingall1
author_rank: Newbie
timestamp: October 10, 2023, 09:54:39 pm
content: tried with 3.7v 18650 battery, still got the glow unfortunately..Also tried 3x 100K resistors anode>>cathode on one of the leds; still got the glow unfortunately..modified image orig post, 1x small filesize now

author: iMo
author_rank: Super Contributor
timestamp: October 10, 2023, 09:58:39 pm
content: Then you have a DC leakage somewhere. Parasitic resistance in your switches or wiring (solder flux or dirt in the switch??).Clean up your pcb/wiring with IPA (or alcohol), for example.

author: BeBuLamar
author_rank: Super Contributor
timestamp: October 10, 2023, 10:02:32 pm
content: This is a 3 color LED so the leakage is inside the LED perhaps. How about wire only 1 switch to 1 color. Leave the other 2 leads not connected?

author: iMo
author_rank: Super Contributor
timestamp: October 10, 2023, 10:07:56 pm
content: Quote from: twingall1 on October 10, 2023, 08:28:35 pmCould it be it is just an optical reflection??

author: twingall1
author_rank: Newbie
timestamp: October 10, 2023, 10:08:10 pm
content: Ok, it's not the neatest job and i was a bit liberal with the flux, so will have a good clean up on that front. Thanks for your help."Could it be it is just an optical reflection??" Haha, i wish; they're quite widely separated..BeBuLamar I tried that initially (switches on one color only) and didn't work out for me..Thank you all for your help and advice!

author: twingall1
author_rank: Newbie
timestamp: October 10, 2023, 10:25:41 pm
content: OMG you're right, what a dingbat i've been, It was just optical reflection!Was just getting the rubbing alcohol out to clean and had my thumb between 2 of them and no more glow..Sorry for the time taken up, Many thanks for pointing that out