Modifying a microscope ringlight - questions

Flashlight Modding and DIY Parts
1

Bonjour, Mesdames, Messieurs

I have bought myself a cheap Microscope (this) and have been upgrading it since.

At the moment I am modifying it with a 10Ah 1S Battery, 13,3" 4K Screen, 4K 60fps Camera and three different lights, one from underneath, one ringlight and one on a swans neck.
I have 3d printed a part where 3 PWM dimmers will sit in to regulate the 3 lights.

This thread is about the ringlight.

It is this one: IFixes iL16 Mikroskop Staubdicht Spiegel Ring Licht 27LED Hohe Helligkeit Handy Reparatur Spezialisierte Mikroskop Licht - AliExpress 1420
I have an assortment of ringlights, and this one delivers the best overall package. Small, bright, CRI85, good CCT.

Originally measured, the light draws around 1.4A at 4.8V which gets every of the 27 LEDs 50mA.
I need to remove the onboard dimming function.

This is the original circuit:

PXL_20260122_182033740
PXL_20260122_1820337401920Ă—1446 135 KB

On the left, positive enters the circuit, the inner ring is all negative. The circuit then switches the little mosfet so that the negative gets to the 0.15Ohm resistor and then to the LEDs.
I have removed all the parts except the 0.15Ohm resistor and put 5V directly on it.
It draws over 3 Amps and the powerbank I am using shuts down.

I tested some other resistors, but all of them get super hot and start smoking very very quickly. For 1.4A from 5V I would need a 1.1ohm Resistor, but even a 2.4Ohm resistor gets flaming hot after 2 seconds

So I put the light with no resistor on the benchtop power supply
To achieve the same Lux, I have to give the LEDs 1.7A at 3.21V - to reduce 5V down to that I would need a 2.5W resistor - when I use the Lithium Battery directly, it would still be 1W. No wonder those poor SMD resistors got so hot…

So the question is: How did the manufacturer do this with just a 0.15Ohm resistor?
It must be some heavy PWMing and overcurrenting the LEDs, right?

But the more important question is: How can I get this light to work from a lithum battery without the heavy loss of energy in a resistor or diode?

Appreciate the help!

1 Thank
2

This might do the trick

3

Have you tried running it with a flashlight driver?

4

I compewz…you removed all the other resistors and wonder why the one remaining resistor gets hot? Or does it get hot to begin with?

5

I can’t use a buck converter since I have to use a PWM dimmer somewhere in the circuit as well and that PWM Dimmer doesn’t work with 3.3V as far as I know. I will test later.

Same with a flashlight driver, must be dimmable with a potentiometer.

The circuit shows that the only resistor in front of the LEDs is the 0.15 Ohm one on the far right side, all the rest is just dimming circuit.

1 Thank
6

Ah, I read your post too quickly the first time. It makes sense now. I’m no expert on this stuff but I’ve acquired a lot of components from AE for just this sort of thing. I may have some time to try out a few ideas. Hopefully someone more knowledgeable than me can help in the meantime.

1 Thank
7

If that pwm dimmer doesn’t work with 3.3V then it won’t work with a 1S battery pack either. If it does work with a 1S battery pack then that’s all you need. Otherwise you can use the buck converter and replace the trimmer with a potentiometer and that’s it.

8

“So the question is: How did the manufacturer do this with just a 0.15Ohm resistor?”

It’s the whole circuit that does it, not just that one resistor

1 Thank
9

That’s what I was wondering about too lol

10

So…from my limited understanding of electronics, the electrons are always loaded, like a chainsaw chain. The current hits max impedence when switched on a cold start, but it quickly drops back down as the electrons start flowing. With ONLY the 0.15Ohm in the circuit, it bears the ENTIRE current/voltage. With larger resistor values LATER in the circuit, they work like control valves, while sharing the load with the lower value resistors earlier in the circuit, essentially a bottleneck at the end rather than in the beginning.

Does that sound right, @Toaster79

1 Thank
11

I just checked the dimmer, it still works under 3V. That opens up possibilities.

Since all of my devices are powered by USB, I have 3 4A 1S to 5V Boost modules here - that’s what the Dimmers will receive or at least one of them for the light underneath.

I will now have a look if I can bring the 1S Voltage to a stable 3.3V with a Buck/Boost Converter and use that to power the LEDs via a resistor.

@DC38: The circuit on the left is there to switch the mosfet on the right - so in the end there is only the 0.15Ohm resistor in the circuit of the LEDs. That’s why I think that there must be a heavy PWM use, but my understanding of this is just too small.

I will order a new one and test it a bit further. I have all the removed parts still here, but the ringlight is so cheap, I couldn’t be bothered…

12

If you get that buck regulator from ali you have it set for 1.7A to the leds and put the dimmer between the buck and the leds so you don’t exceed the 1.7A or measure the drop of the dimmer after the buck and set the buck so the dimmer fully open doesn’t supply more than 1.7A.

Battery pack → DC-DC → dimmer - LED

No need for stepping up the voltage to bring it down again