The replication following is a circuit derived from Dr. Steven E. Jones joule thief circuit outlined in Figure 1.
|Figure 1 Dr Jones Joule Thief Circuit|
The Rb chosen was 2k ohms. R0 was set to 5-10Kohms.Cb was set too approx 150pF using spare parts from a old TV set. The Transistor is a BC548 standard general use low power.
The circuit input current is measured by a 1.5ohm 1/2 watt Resistor. I measured this with the DVM at 65.5mV 65.5/1.5=43.67mA
Power is measured by Pi=VI=6x43.7=262milliWatts.
I then connected a 20-led bulb in parallel to the 10k Load Resistor. Also I attached a 10ohm current measuring resistor. With the DVM I measured this input power again 71.9mV. The current is 71.9/1.5=47.93mA. Pi2=6x48=288 milliwatts.
Finally I measured the ouput current through the lamp. A reading above of 8.04Volts. This however is an AC signal half wave rectified so this will give us the average power through which is acceptable.
The DVM reading from the sense resistor was 96mV. Current becomes 96/10=9.6mA. Po=8.04x9.6=77.2milliwatts.