In the early days of my LED flashlight experimentation in August of 2003 I was experimenting with LED V boost circuits and wrote up the following note. I don’t remember what the circuit was – might have been a Joule Thief.
LED V Boost, Low V
Input V = 1.503V
Input I = 16.3 mA
Total input power: 24.5 mW
Assumed LED V = 3.3 V
Meas. LED current = 4.4 mA
LED power = 14.52 mW
Efficiency = 59.3%Changed output transistor from BC337 to a BC639. It made no difference in current consumption or output current.
Apparently I was trying different transistors to see how to maximize the current and efficiency. It’s obvious that I didn’t have enough power to the LED. At that time I was using coils with a lot of turns and high resistance, probably on a toroid with low mu. That’s probably the reason why the circuit was not putting out much power.