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Home > Video > Video Display > Teardown of a 5W Rolson GU10 LED lamp.

Teardown of a 5W Rolson GU10 LED lamp.

I spotted this in TK Maxx today and spontaneously bought it to take to bits.  Ronson is a generic tool brand in the UK so I guessed it might be fairly typical of a  lamp even if it had the higher than usual 5W rating.
On the power meter it showed as just 3W!  If you cheat and allow for reactive power then it could theoretically be classed as 5W but that’s not an optical power rating.
The front has a bezel that seems to be a friction fit and the lens behind it turned out to be glass (as you probably heard when I dropped it on the table.)  Removal of the glass reveals a round PCB with 36 SMD LEDs wired in series on an aluminium core PCB which is glued to a concealed aluminium frame with a white rubbery thermal transfer adhesive.
The circuitry is mounted in the back and is accessed by removing two screws from the back of the lamp, which is quite unusual.
And here’s where I got a surprise!  It was a traditional capacitive dropper as opposed to the more sophisticated switching circuitry often found in the higher wattage lamps.  Here’s a breakdown of the circuitry.
Mains comes in and immediately goes through a 10 ohm resistor which limits inrush current and acts as a fuse.  There’s a MOV (Metal Oxide Varistor) for transient protection, although it appears to be rated for 470V so it’s going to have to be quite a transient before it kicks in.  One lead of the mains then goes directly to the rectifier (MB10S) while the other goes via a 560nF 400V capacitor with a 1M discharge resistor across it.  The output of the rectifier has a 2.2uF 400V capacitor, a 330K resistor a mystery component (1328 XR) and the LED series string across it.  As far as I can see the mystery component might be a high voltage zener diode, but finding data on it was not easy.  The nearest I found was a 1N1327 with the mystery component possibly being the next voltage rating up.
So a pretty basic power supply, but quite rugged and neat.  It does exhibit mild flicker though, and could have done with a higher value electrolytic on the output with maybe a series resistor between it and the LED string.
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