Teardown of yet another slightly dangerous Chinese LED lamp.
bigclivedotcom 10:36
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It's a while since I've taken a small Chinese LED lamp to bits. This one was randomly added to an ebay order from China and came in a box with a matching lamp free. I'm not sure it was supposed to be free, they may not realise there are two in each box.
The lamp has a single round circuit board with nine 5730 (5.7mm by 3mm) single chip LEDs on the front and a typical smoothed capacitive dropper on the back.
The series capacitor is a whopping 820nF and after rectification it is smoothed by a 400V 4.7uF electrolytic capacitor before driving the LEDs via a rather lightweight 1.5 ohm resistor.
I measured the current through the circuit by simply bridging one of the LEDs with a meter while the power was on (yes, live exposed solder connections again) and measured 50mA which means the lamps rating is roughly 1,5W. The listing said 3W but they often do. And to be fair they sent two 1.5W lamps which adds up to 3W....
Both the series cap and smoothing cap have 1.1 Megohm resistors across them for discharging when the power is turned off.
Pretty much a typical cheap LED lamp. Very simple and works. The quality of the LEDs may be a bit suspect as I tested them with a very current limited supply and they had the characteristic of a crappy doomed-to-failure LED. With one light one of the LEDs didn't light until it had been running for a while and "blew clear". On the other there was a dim LED. With both, when the wall switch is off the slight capacitive leakage through mains wiring causes the LEDs to glow slightly, but not all of them, even though they are in series.
The lamp has a single round circuit board with nine 5730 (5.7mm by 3mm) single chip LEDs on the front and a typical smoothed capacitive dropper on the back.
The series capacitor is a whopping 820nF and after rectification it is smoothed by a 400V 4.7uF electrolytic capacitor before driving the LEDs via a rather lightweight 1.5 ohm resistor.
I measured the current through the circuit by simply bridging one of the LEDs with a meter while the power was on (yes, live exposed solder connections again) and measured 50mA which means the lamps rating is roughly 1,5W. The listing said 3W but they often do. And to be fair they sent two 1.5W lamps which adds up to 3W....
Both the series cap and smoothing cap have 1.1 Megohm resistors across them for discharging when the power is turned off.
Pretty much a typical cheap LED lamp. Very simple and works. The quality of the LEDs may be a bit suspect as I tested them with a very current limited supply and they had the characteristic of a crappy doomed-to-failure LED. With one light one of the LEDs didn't light until it had been running for a while and "blew clear". On the other there was a dim LED. With both, when the wall switch is off the slight capacitive leakage through mains wiring causes the LEDs to glow slightly, but not all of them, even though they are in series.
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