Do You Know the Linear LED Driver?
February 13, 2020
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Disassembling electronic devices, broken or not, can be very instructive. After recovering a dead 30 W LED floodlight in the dumpster and taking it apart, an unusual circuit was uncovered. Instead of the expected basic string of LEDs in series with the main voltage and maybe a current-limiting resistor, the driver turned out to be a so-called (sequential) linear LED driver or direct AC LED driver. This clever design has a much better power factor than the classic design. Repairing the spot was surprisingly easy.
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Discussion (6 comments)
gert-ce 4 years ago
ElektorLabs 4 years ago
gert-ce 4 years ago
Treth 4 years ago
Would appear quite difficult to troubleshoot with both mains voltages and switching within the mains cycle, but very clever.
n111ckk 4 years ago
Instead, you put all the LEDs in one series chain with a constant current feed. Then you have a transistor connected to each LED pair node, shorting them to ground. So to just light one LED, you might have 9 transistors turned on, progressively turning them off to light more LEDs.
I used this technique with a quad open-collector comparator to provide a sliding LED indication to show the output power of an audio amplifier.
Jose Baars 4 years ago