Dp9502b Led Driver Hacking and Current Reduction for LED Ceiling Lamp

I bought this round flat LED Lamp on Ebay (https://www.ebay.de/itm/165058879286?mkcid=16&mkevt=1&mkrid=707-127634-2357-0&ssspo=R8Ty6J5tREu&sssrc=2047675&ssuid=&var=464608313825&widget_ver=artemis&media=COPY ). It is too bright for my taste though, so I was searching for a way to make it weaker and less glaring. In addition, reducing the power flowing through the LEDs makes them more efficient and they will last way longer, since they don’t get that hot. Unfortunately, the LED driver inside does not have a trimpot to adjust its output, so I was searching for another solution. It’s a 24W lamp running at 200 mA at 60 V - 80 V DC.

Resistors

Solder

Cables

Insulation Tape

Soldering Iron

Wire Cutters

Wire Strippers

Phillips Screwdriver

Warning:

Following this guide may involve working with high voltages that can lead to fatal injuries. I do not take any responsibility for any damage done while following this guide. You are doing this at your own risk. Please only continue if you feel comfortable working with high voltages.

Please note that power supplies are still dangerous after unplugging them, because there can be charged capacitors inside. This is also the case with this one. When shorting out the legs of the orange capacitor after unplugging the system, you may see a small spark. You do not what that energy to flow through your body. I also observed the LED light flashing for a short moment a few seconds after unplugging it, which proves how much energy is stored inside this power supply.

To open the LED driver, you need to unscrew the four screws in the orange parts. After that, you can remove the bottom part by unclipping it using a flat head screwdriver. Inside, there is a surprisingly tiny PCB.  

There are very few components on this board. In terms of things that look like chips, there’s only the full bridge rectifier with its four legs and the DP9502B. The current to the LEDs and therefore their brightness is set using a resistor, or two in this case. After bending the orange capacitor out of the way, you can see a small SMD resistor below a blue THT resistor. Those resistors are the ones we’re looking for. They are connected in parallel, maybe for fine-tuning the resulting resistor value.

Now we can modify the resistance. Removing the blue resistor already increases the resistance slightly, but the reduction in current is only about 1/6, and the LEDs were still too bright for me. So I also removed the SMD resistor and soldered two wires in its place, to make it easier to add resistors. You can solder them to the top or bottom side of the PCB. Just make sure the PSU fits back in its housing in the end. I tried different resistor values, but I was limited to what I had laying around. In the end I ended up with a resistance around 4 ohms (up from 1-2 ohms), which resulted in a current of 150-200 mA (down from 300 mA). This is much more pleasant for my eyes and will hopefully also make this light last for many years or decades.

I insulated the added resistors (two in series in my case) with some electrical tape and put everything back together.

Note:

When trying different resistor values, the lamp sometimes didn’t turn on at all. I don’t know if this was due to bad connections with my alligator clips and breadboard, or because the driver has a limit on how high of a resistance it can handle. If the LEDs didn’t turn on, the capacitors stayed charged and discharged in a flash a few seconds after unplugging the lamp.