Sunday, June 5, 2011

Joule Thief Over Unity Ciruit

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                    

 Figure 2 Shows the toroid which has been bifilar wound 19 times.
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 is Connected to a 6V battery the battery reading was close to 5.99 when read with a DVM.
  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.

efficiency n=Po/(Pi2-Pi)=77.2/(288-262)=77.2/26=2.96

1 comment:

  1. Not reading a sine wave with a DVM result in a meaningless value.
    Reading the exact same waveform at different amplitude could give a relative value, but, again, it has nothing to do with the actual value.