Joule Thief Testing

I have done hundreds of tests of this circuit in various configurations.

  1. Set 1
  2. Set 2
  3. Set 3
  4. Set 4

Testing Notes

FIXME Is the following any good?

Without a zener diode in place to protect the LED, the safest way to measure the efficiency is to determine the LED and diode's voltage drop and assume their reverse current leakage losses and the capacitor's losses are negligible. Then measure the current at two places: the coil's center tap and the transistor's emitter. If you are using one multimeter, do not switch the multimeter's scale between measurements. Even so, the multimeter changes the behavior of the circuit differently when measuring the current at each point, so these numbers are unreliable.

For example, Vdiode=0.3, VLED=3.0, Vin=1.27, Icoil=30, IE=20,

  1. I_{out}=I_{coil}-I_{E} = 30-20=10 mA
  2. P_{LED}=V_{LED}*I_{out} = 3.0*10=30 mW
  3. Sigma P = V_{i n}*I_{coil} = 1.27*30=38.1 mW
  4. efficiency = {P_{LED}}/{Sigma P} = 30/38.1=79%

It would be better to measure the current through the LED instead of through the transistor, and much better to wire two meters into the circuit.