# LED Flashlight repair: constant current IC (5501)

#### stenzer

##### Full Member level 4
Hi,

I friend of mine gave me his "broken" LED flashlight. It is the BARBARIC from Martinez Albainox [1]. Unfortunately there are no informations at all, especially regarding the power and the charging voltage. My friend gave me a power supply which can be plugged into a cigarette lighter plug of an car, thus I assume it should be chargeable from a ~12 V source (which I also measured). This charger can be also partially be seen in [1].

I powered the flashlight with may laboratory bench-top power supply, and it already draws a current of about 1 A @ ~3.5 V (current increases with increasing voltage). I disassembled the flash light, here is a picture of the electronics.

It seems the IC 5501 got really hot, two cables have been melded together on top of this IC. This melting also created a short circuit of those two cables, which I have fixed. As can be seen on the attached figure, there is only a single IC.

The package is marked by KBG2z and the PCB label states 5501. After quite some time I came up with an IC called MIX5501, which seems to be a constant current source (which makes sense). The pin configuration fits with the installed IC, the following figure is taken from [2]. Unfortunately I couldn't find a dataseeht in english.

I'm measuring a short circuit between pin 4 and 6, and when I power the flashlight with the above mentioned ~3.5 V (~1 A) it is light up and the ON/OFF button has no effect. Thus, I assume the IC is damaged. According to the shown circuitry, the maximum IC supply voltage is 4.2 V.

The used LED seems to be a CREE XP-G [3], with a maximum forward current of 1.5 A.

My question is, is there an appropriate IC which can be operated at 12 V? Or is the 12 V power supply provided by my friend and also visible in [1] just not suitable? Has someone the datasheet of the MIX5501 in english?

BTW, the flashlight uses two 3.7 V 2000 mAh accumulators which are in parallel, and placed in parallel to the LED. I performed all measurements without the accumulators.

[2] https://product.ic37.com/product/759328/
[3] https://www.cree.com/led-components/products/xlamp-leds-discrete/xlamp-xp-g

Greets and thanks for any advice!

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#### stenzer

##### Full Member level 4
Hi,

I spent a couple of time and came up with a single appropriate replacement. The part number is FM2819 [1] and is also available in a SOT23-6 package. The pin out fits as well. It seems "those" ICs are not operable with 12 V, so it seems my friend destroyed the IC (5501) by a too high supply voltage. I will think about a space-saving over voltage protection (calculating power loss of a zener).

Further, I will adjust a LM2576 based cigarette-lighter supply, to enable an appropriate charging in a car.

[1] https://datasheet.lcsc.com/szlcsc/2004031005_Shenzhen-Fuman-Elec-FM2819_C88274.pdf

I will give an update when the ICs ordered at aliexpress are arrived.

greets

#### stenzer

##### Full Member level 4
Hi,

I got the mentioned FM2819 ICs and they are working fine. The first push of the button turns the flashlight fully on, the second push dims the light, after the third push the light begins to flash, and finally the flashlight is turned off by pressing the button a fourth time.

For proper operation I had to get rid of one of the three 1 $\Omega$ (parallel) resistors which can be seen in the first attached image, as the datasheet of the FM2819 states a (LED) series resistor of 0.5 $\Omega$.

As the flashlight uses two 3.7 V 2000 mAh Li-Ion (18650 ICR) accumulators in parallel, I have to get an apropriate charger, if possible fitting in a cigarette lighter plug. The charger provided by my friend is definitively the wrong one (12 V output voltage). To my knowledge charging a Li-Ion accumulators is done by first applying a constant current and than changing to a constant voltage (saturation charge). For curiosity, is there a good approach to charge Li-Ion accumulators by a bench-top power supply?

BR

#### d123

##### Advanced Member level 5
Hi,

If possible, just get a (Li-ion) charger IC, serious/safe and reliable homespun methods mean getting lost in the Tardis of ever-expanding subcircuits...

#### Relayer

##### Full Member level 4
{quote]For curiosity, is there a good approach to charge Li-Ion accumulators by a bench-top power supply?[/quote]

Yes, you could charge the batteries with a bench-top power supply.
You need to find a datasheet on the batteries to confirm the correct charge voltage.
Many Li-ion batteries can be sensitive to incorrect charge voltage.
The main thing you need to watch out for is over charging them. Or when the batteries
start to get hot.
You should be able to charge them in parallel together, since they would have the same
voltage charge.
Regards,
Realyer