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Half-wave DC power supply

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This is a simulation of a simple DC power supply based on a half-wave rectifier.

Use the left slider to adjust the AC line voltage and the right slider to adjust the DC current drawn from the power supply. You can also change the filter capacitance and the transformer turns ratio. Just click on the value with the mouse pointer and edit like any text field.

The transformer steps the line voltage up or down by the "turns ratio", which can be changed. The rectifier diode allow current to flow only in one direction, allowing the filter capacitor to charge during the positive half-cycles only. The load current slightly discharges the filter capacitor in the negative half-cycles, but it is re-charged during the positive half-cycles. The resulting voltage fluctuation is called ripple. If the load current is small, the filter capacitor charges all the way to the peak voltage (1.414 times the RMS secondary voltage), minus the forward drop if the diode (about 0.6 volt). As the load current increases, the capacitor is dischared partially during the negative half-cycles and the average DC voltage drops. This causes "ripple" in the DC output, which increases as the load current increases. Using a larger filter capacitance will reduce this effect.

Student Questions

1. Launch (double-click on) "Half Wave" and inspect the screen layout.

2. This is the simplest of all the power supply simulations; it is a half-wave, unregulated power supply. Begin by setting the primary voltage to 115 vac (left-hand slider), the transformer turns ratio to 0.11, the filter capacitor to 1000 F, and the load current to zero (right-hand slider).

3. Why is the DC output voltage greater than the transformer secondary voltage?

4. Increase the load current (right-hand slider) to simulate drawing current from the power supply. Why does the DC output voltage decrease and the ripple (indicated by the figure under the output voltage) increase as the load current is increased?

5. Set the load current to 0.25 amps. Increase the value of the filter capacitor. Why does the DC output voltage increase and the ripple decrease as the filter capacitor is increased?

6. Change the primary voltage to simulate fluctuations in the line voltage (brown-outs, etc). Is there any evidence that the DC output voltage is stabilized against such fluctuations?

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This page is maintained by Prof. T. C. O'Haver , Department of Chemistry and Biochemistry, The University of Maryland at College Park. Comments, suggestions and questions should be directed to Prof. O'Haver at
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