Voltage Doubler

By Cliff Bockard and Ryan Sherry

Purpose

The purpose of this experiment is to determine the relationship of an input to its corresponding output for an unknown circuit. The circuit to be analyzed is shown in Figure-1.

Figure-1


Procedure

To determine what the circuit inFigure-1 does, we applied a 4 volt sinusoidal input and obtained a trace of the output on an oscilloscope. To build the circuit we used 1N4007 p-n diodes. The capacitor values for the circuit are C1 = C2 = 10 pF. The output of the circuit is shown in Figure-2.

Figure-2

Analysis

The circuit puts out a DC voltage equal to almost twice the peak value of the AC input voltage. The reason the output is DC and not AC is because of the capacitor C2. Once diode D2 turns on, the voltage across the capacitor is just a constant DC voltage . Notice in Figure-2, that the DC output is not quite the 8 volts expected from the 4 volt input. The explanation for this is the turn-on voltage of D2. The turn-on voltage for the Si 1N4007 is about 0.7 V, and notice that the output voltage is about 7.2 Volts, very close to 8V-.7V. From this, a better name for this circuit would be a voltage doubler.

Figure-3 is a plot of the transfer function (Vout vs. Vin) of Circuit 3. The Y-axis represents the output voltage while the X-axis is Vin. We see that as the AC input voltage sweeps from -4V to +4V the circuit produces an output of +8V DC. While experimenting with variations of the input voltage, we found that the transfer function shifted upwards on the Y-axis and widened along the X-axis as we increased the amplitude of the input AC signal.

Figure-3

Conclusion

From the experimental data that we have collected we determined that Circuit 3 of Lab 5 is a voltage doubler. The doubled voltage is, however, a DC voltage with an AC input as explained above. It is important to realize that this circuit does not solve the energy crisis because since we are doubling the voltage we reduce the current by one half as given by P=VI.

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