Author Topic: [UPDATED: PCB photo] What kind of LED driver does a ring light use?  (Read 1447 times)

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Offline etiTopic starter

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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.
« Last Edit: January 23, 2023, 07:29:12 am by eti »
 

Online Zero999

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Re: What kind of LED driver does a ring light use?
« Reply #1 on: January 21, 2023, 02:48:20 pm »
Probably linear.

It would help if you at least posted a link to the product.

Have you opened it up and looked inside?
 

Online tom66

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Re: What kind of LED driver does a ring light use?
« Reply #2 on: January 21, 2023, 03:51:01 pm »
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.
« Last Edit: January 21, 2023, 03:54:30 pm by tom66 »
 
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Online themadhippy

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Re: What kind of LED driver does a ring light use?
« Reply #3 on: January 21, 2023, 05:11:17 pm »
Don't turn it on,tear it apart.
 
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Offline etiTopic starter

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Re: What kind of LED driver does a ring light use?
« Reply #4 on: January 21, 2023, 11:02:55 pm »
Hi all.

Yeah I'll take it apart and post photos, later on. Been a bit busy. Thank you for all the helpful replies :)
 

Offline james_s

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Re: What kind of LED driver does a ring light use?
« Reply #5 on: January 22, 2023, 12:34:30 am »
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.
 
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Offline kjr18

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Re: [UPDATED: PCB photo] What kind of LED driver does a ring light use?
« Reply #6 on: January 23, 2023, 06:20:06 pm »
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.
 
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Online Zero999

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Re: [UPDATED: PCB photo] What kind of LED driver does a ring light use?
« Reply #7 on: January 23, 2023, 06:37:31 pm »
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.
 

Offline james_s

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Re: [UPDATED: PCB photo] What kind of LED driver does a ring light use?
« Reply #8 on: January 23, 2023, 08:03:28 pm »
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.
 

Online Zero999

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Re: [UPDATED: PCB photo] What kind of LED driver does a ring light use?
« Reply #9 on: January 23, 2023, 08:33:24 pm »
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.
Maybe 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.
« Last Edit: January 23, 2023, 08:53:55 pm by Zero999 »
 

Online thm_w

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Re: [UPDATED: PCB photo] What kind of LED driver does a ring light use?
« Reply #10 on: January 23, 2023, 09:47:53 pm »
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
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Offline etiTopic starter

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Re: [UPDATED: PCB photo] What kind of LED driver does a ring light use?
« Reply #11 on: January 23, 2023, 11:07:40 pm »
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

I 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...
 
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