Tag Archives: led driver

Jansjö Reading Light Conversion: running on 12 V, and never running out of light again, even in remote places!

How any would it be to have nice reading light at the garden house (or in the car), especially, a light without any smoke and hazard and hazzle like candle light! A light that keeps your eyes healthy. Well, at home, you can just use an IKEA Jansjö light for this purpose, which has a single 3 W LED installed.

All that is needed is a 12 V constant current board, LED driver. These are really cheap, so there is no need to build one yourself, you can just get it shipped from China directly, for a very reasonable price.

This board has a few nice components: 5 SS14 diodes (Schottky), 4 are used a bridge rectifier, 1 is used for the buck converter. There is a 47 Microhenry inductor, a 220 Mikrofarad (25 V) capacitor – and, the magic switch and regulator, a PT4115 device.

The PT4115 features a pretty straightforward design. It’s a step-down converter, can can drive over 1 Amp of current. The board I am using has a 0.22 Ohms current sense resistor, i.e., it is set to 0.1 V/0.22 Ohms = 0.46 A of current. This is plenty to drive the IKEA lamp.

The lamp itself will remain completely unmodified, just using a socket to connect to the original plug (which used to plug into a mains-powered LED driver of similar current rating). The connection to the 12 V system of the garden house is done via a “cigarette lighter” plug.

To protect the driver board, all sealed up in hot glue! It’s not perfect, but it works!

Finally, not much more to say, it works just fine!

Ultra-cheap LED Spot Lights: Failure mode analysis, and some reverse engineering, and some concerns

Something amazing about the advent of LED technology for general lighting is not only the brightness, efficiency, and so on, but also the amazingly low price. Here, 20 light fixtures, including 3 LED elements each, 34 EUR total. That’s a bargain a friend of mine could not resist. But think twice, after about 1 year of occasional usage of these lights – several failed. Brightness is gone, some lightly flashing lights remains.


Still the price is amazing – considering the price of a singe 1 W LED element, with about 1 EUR retail. Plus the case, heat sink, aluminum circuit board, heat conduction paste, external case, 3 lenses!! No idea how this is made in China, for about 1.5 a piece delivered.


The first suspect – the drivers: each lamp has their own little driver box. Type S3W-0103.



The parts, and a good quality aluminum board, named CQ-LV8072. This is a universal board, found in many kinds of Chinese LED light fixtures.


Tested the LEDs – turns out, one of the LED elements is dead, and this ruins the whole thing, as all three LEDs are arranged in a series circuit. We can fix this easily by replacing the LED elements, all three, with some good quality elements. Albeit, at almost non-economic cost. Hint – the case and be unscrewed with the heatsink turning vs. the outer case. No need to apply brute force like I did, to open it up.


Some reverse engineering reveals a rather simple, but practical circuit. Using S8050 and MJE13003 TO-92 transistors, and a little transformer.


As you can see, no protection elements, what if the input capacitor shorts out, or if some overvoltage blows the transistor. Could it set your flat on fire? Well, my guess is, yes.