Compaq laptop power supply for LED lighting
One day the power supply of the LED lighting
in my kitchen broke down.
As I wanted to make a warranty claim, I expected
it would take a while before I had a replacement.
So I dug in the junkbox to see if I had a suitable
small power supply to serve as a temporary replacement.
I found this 27VA Compaq power supply, dating 1994.
Probably it belonged to a laptop and has
landed in my inventory more than 10 years ago.
With a minor modification, I could use it for my LED lighting.
According to the fine print on the back, this power
supply delivers max 16V at 27VA.
The reasons why I chose this one were (1) its rated power
was not as high as most laptop power bricks (2) the case
wasn't glued together and could be opened.
Component side of the PCB.
Solder side of the PCB.
PCB with shield mounted again.
I opened the case and found a compact unit packed in
After removing the shield, I had a quick glance at
the circuit board. It contained a single transistor
for power conversion, controlled by a UC3843AN
A CQY80 optocoupler bridges the gap between mains and
output circuits to convey the control signal.
On the solder side of the PCB, there are a number
of SMD components, including an 8-pin IC carrying
the type designation “358”, so I assume
this would be an LM358 equivalent.
There is a trimpot near the output.
I tried to turn it but it was sealed with a
Using plyers, I broke the seal, but I suspected this might
damage the pot.
So I replaced it. It was a 1k pot, I had a spare or two
After this, I connected a 8 Ω resistor to
The device initially delivered 16V.
I could turn it down to 11V.
I set it to 12V and connected the LED lighthing.