[UPDATED: PCB photo] What kind of LED driver does a ring light use? - Page 1
Forum section: electronics / general

author: eti
author_rank: Super Contributor
timestamp: January 21, 2023, 05:46:15 am
content: I’ve bought a cheap and superb clip-on ring light for a mere £7. It has cool & warm LEDs, 20 of each. I’ve noticed there is NO PWM flicker whatsoever… NONE.<Photo of PCB attached>Do you have any idea what type of LED driver these things use? Also I’d like to be able to choose how much warm LED + cool LED is mixed for the “neutral” colour temperature, as it’s just ALL cool and ALL warm LEDs on at once, and they all dim or brighten together when you hold down the button. I’d like to be able to vary and mix that myself.Ideas would be useful… many thanks.

author: Zero999
author_rank: Super Contributor
timestamp: January 21, 2023, 02:48:20 pm
content: Probably linear.It would help if you at least posted a link to the product.Have you opened it up and looked inside?

author: tom66
author_rank: Super Contributor
timestamp: January 21, 2023, 03:51:01 pm
content: Mains powered? A simple off-line switcher can maintain constant brightness if the filter cap is sufficiently sized.For the brightness control of independent channels, a buck/boost converter can control current very precisely with no PWM. This is commonly used in newer automotive products, brake lights for instance are moving away from PWM drive as it can be distracting at night.

author: themadhippy
author_rank: Super Contributor
timestamp: January 21, 2023, 05:11:17 pm
content: Don't turn it on,tear it apart.

author: eti
author_rank: Super Contributor
timestamp: January 21, 2023, 11:02:55 pm
content: Hi all.Yeah I'll take it apart and post photos, later on. Been a bit busy. Thank you for all the helpful replies

author: james_s
author_rank: Super Contributor
timestamp: January 22, 2023, 12:34:30 am
content: There's no way to say without looking. My guess is it's just a bog standard DC power supply with groups of series LEDs each with a resistor. Or it could be an LED driver with a capacitor across the LEDs, buck converter usually. It's the lack of a capacitor that results in flicker.

author: kjr18
author_rank: Regular Contributor
timestamp: January 23, 2023, 06:20:06 pm
content: Not much to do here to be honest. U1 is linear charge controller, U2 is li-ion battery protection ic with integrated mosfets, U3 is some cheap microcontroller. maybe even OTP. So it's not really possible to change how it works without changing it to something that would fit this pinout.

author: Zero999
author_rank: Super Contributor
timestamp: January 23, 2023, 06:37:31 pm
content: I can't see any current limiting or sense resistors. It relies on the resistance of the output transistors, Q1 & Q2, and wiring to limit the current, which isn't good design practise. Dimming will be accomplished with plain old PWM. If there's no flicker, it's because the frequency is too high.

author: james_s
author_rank: Super Contributor
timestamp: January 23, 2023, 08:03:28 pm
content: I suspect it has current limiting resistors on the board with the LEDs, probably the typical LED strip configuration with groups of 3 LEDs and a resistor.

author: Zero999
author_rank: Super Contributor
timestamp: January 23, 2023, 08:33:24 pm
content: Quote from: james_s on January 23, 2023, 08:03:28 pmMaybe there are resistors on the board with LEDs, but they can't be in groups of three. There are 20 warm white and 20 cool white and there's a USB connector on the board, indicating this uses a single lithium ion cell.

author: thm_w
author_rank: Super Contributor
timestamp: January 23, 2023, 09:47:53 pm
content: If you want to learn:- Draw out the schematic.- Probe the circuit in various places with your oscilloscope and add that information as notes to the schematic.If you want to customize it:- Replace U3 micro with an arduino and a few pots or buttons for inputs- or, buy a few buck modules with adjustable current limiting and connect a pot to each to have distinct LED string control- or just get a LED light with color adjust functionality already built in

author: eti
author_rank: Super Contributor
timestamp: January 23, 2023, 11:07:40 pm
content: Quote from: thm_w on January 23, 2023, 09:47:53 pmI reckon I can shoehorn an ESP32 into it somehow, and control it with BLE "GATT" commands, which I've been playing with for a few weeks. I wonder how I'd do that...