Controlling multiple LED regulators with one potentiometer (Dimming) - Page 1
Forum section: electronics / beginners

author: desertgreg
author_rank: Contributor
timestamp: April 17, 2019, 02:29:25 am
content: I'm looking into making a circuit which will control several strings of LEDs. Each string of LEDs will have its own adjustable constant current regulator like this one from ON Semiconductor:https://www.onsemi.com/pub/Collateral/NSI45060JD-D.PDFThis regulator has an adjustable output which is controlled by a resistor. I would like to attach all of my regulators to a single potentiometer or digital potentiometer to allow me to control the brightness of all of the LED strings at once. My question is, will the circuit work if I attach multiple of these regulators to a single adjustment resistor?Thanks!

author: Mr.B
author_rank: Unknown
timestamp: April 17, 2019, 02:40:08 am
content: With a single adjustment resistor... I would suggest not.If you were to use individual digital pots, individually addressable by an MCU, it should work fine.A single pot can then be used as an input to one of the ADCs on the MCU.

author: Zero999
author_rank: Super Contributor
timestamp: April 17, 2019, 10:26:49 am
content: If you use digital pots, make sure it's on the low side, otherwise the voltage on the pots will be too high.Why not just use PWM?If you must use a resistor, then go for the standard op-amp+BJT current sink.

author: desertgreg
author_rank: Contributor
timestamp: April 17, 2019, 05:41:26 pm
content: Its going to be used with a vision system and I was worried that the camera might pick up the flickering LEDs. Ideally I'd like to have smoothly varying light intensity rather than flickering. Maybe if the PWM frequency is high enough it will work though. This current regulator looks promising but it will be a challenge to control multiple regulators due to board space (there's always something!)

author: grifftech
author_rank: Frequent Contributor
timestamp: April 18, 2019, 09:05:01 pm
content: https://www.amazon.com/s?k=dual+potentiometer&ref=nb_sb_noss_1

author: Zero999
author_rank: Super Contributor
timestamp: April 19, 2019, 08:38:58 am
content: I think he wants to control more than two strings.Here's what I meant. I've only shown two strings, but the op-amp and transistor part can be duplicated for as many strings as necessary.

author: desertgreg
author_rank: Contributor
timestamp: April 19, 2019, 01:37:41 pm
content: Yes this exactly! I suspect that the part I'm asking about is essentially the equivalent of your op-amp+transistor subcircuit but I'm not sure:https://www.onsemi.com/pub/Collateral/NSI45060JD-D.PDFThats why I was thinking I might be able to control multiple strings with one reisistor.

author: Mechatrommer
author_rank: Super Contributor
timestamp: April 19, 2019, 02:05:20 pm
content: currently waiting the pcb of the same purpose... but more like smps, not linear regulation.

author: Zero999
author_rank: Super Contributor
timestamp: April 19, 2019, 04:58:11 pm
content: Quote from: desertgreg on April 19, 2019, 01:37:41 pmWhy do you want to use that specific IC? A quad op-amp, such as the LM324, plus a transistor for each string, will probably work out cheaper.What's the supply voltage? If it's above the maximum rating of the LM324, run it from a voltage regulator made with a zener diode, which could also be used for the control voltage reference.