These are pretty nice.
There's a bridge rectifier, a cap, and a switching regulator inside. All the 18 LEDs are in parallel, at about 2.5 volts. It uses 100 mA at
12 volts.What's interesting is that one can be run constant-current, or from 12 volts with a series resistor, and dims all the way down to 1 mA. I can apparently run all six in parallel from a 12 volt wart, and add one resistor to dim the array if it's too bright.
So they're just driving the LEDs with constant voltage? or do all the LED cathodes connect to a current sense?
A boost + series string offers better efficiency but boosts don't really like to be used as constant current sources
A Cuk converter could make a good LED driver.
They use the MT7201 LED regulator, which seems to run constant-power into the LEDs from about 10 to 24 volts in. I think it quits switching at low current, and the supply current just passes through all 18 LEDs in parallel, somehow. What's surprising is that it looks pretty good at 1 mA net supply current, which is 55 uA per LED. And that I can parallel the lamps.
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