I came across this video regarding a simple constant current linear LED Driver. The AL5809 is available in a number of current ranges from 15mA to 150mA (fixed) that can handle up to 60 volts for LED strings. Looks like a handy solution for driving 1 watt or 3 watt LEDs, a question that comes up from time to time.
The driver requires about 2.5 volts overhead, and ideally the supply voltage is not too much greater then the ΣVf of the LEDs in the string + 2.5 volts – excess voltage is converted to heat by this linear regulator. Chips (of the same current rating) may be paralleled for higher currents.
When the suppy voltage is less than ΣVf + 2.5v, the LED string will be powered by less than the chip's rated current. When the voltage exceeds that level, current is limited to the rated current.
The datsheet is attached for your convenience.
The driver requires about 2.5 volts overhead, and ideally the supply voltage is not too much greater then the ΣVf of the LEDs in the string + 2.5 volts – excess voltage is converted to heat by this linear regulator. Chips (of the same current rating) may be paralleled for higher currents.
When the suppy voltage is less than ΣVf + 2.5v, the LED string will be powered by less than the chip's rated current. When the voltage exceeds that level, current is limited to the rated current.
The datsheet is attached for your convenience.