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Efficient LED lighting? Answered

I want to power 3x 0.5W LEDs in series with 3x AA Ni-Mh batteries (input voltage will range from 2.5 to- 3.7 ). The total forward voltage is around 10volts, and the current of the LEDs is 150mA.

I've tried using a Joule thief but it's quite inefficient, even with different transistor / toroid / resistor configurations (even with fast switching Darlington transistors) the maximum current I've been able to get at the LEDs is less than 100mA, and many energy gets lost in the process, it seems the resistor between the coil and the base of the transistor slows down the switching process and limits the current.

I need a more efficient way to power the LED's, either an improved design or a LED driver chip. But trying to keep the efficiency rate around 60-70% or more.

I have found a design that claims to be more efficient (see picture), but I'm not sure about if it will deliver 150mA.



Best Answer 4 years ago

Forget the joule thief topology, buy a dedicated LED driver from Linear Technology, Nat Semi, or Maxim. Efficiencies of over 90% are commonplace.


Answer 4 years ago


They are called Joule thief for a reason.

They can suck the last ma out of a battery and light any LED.

But they are inefficient and not conducive to pushing power !


4 years ago

Sorry, I forgot the second picture: