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With everything wired up, I setup
my square wave signal generator for a nice 12v peak signal and connected it to the
circuit’s input. When all was ready, I turned on the +5v supply and adjusted
the signal generator frequency up and down, until I saw a peak on the coil voltage
test point with my scope. The frequency was pretty close to 125KHz. The
voltage measured about 400 volts peak to peak. The meter on my +5v supply said
the average current was about 0.5 amps. I was hoping for more but this was not
bad for the first test. Although the DC resistance of the some 50 feet of the
24 gage wire making the coil was only about 1 ohm, the actual impedance of the wire
due to “skin effect” was much higher. There might be some tables somewhere on
the Internet, which could tell me what the high frequency resistance of the wire
might be, but I prefer to find out by experiment. I’m confident that by going
to 22 ga wire, I could gain some more power. Right now, this was an acceptable
first attempt.
To test the efficiency of the
driver circuit, I moved the frequency well off the resonant point and measured the
+5v current draw. It measured 0.08 amps. This meant that about 0.4 watts was
being dissipated in my push-pull transistor driver circuit. I can later use a
more efficient driver and get this figure down to a lower value. |
