AC DC Using a full wave diode rectifier circuit used in the music system final project The 20 1 turns ratio transformer here reduces the rms voltage from the wall outlet 120 V by a factor of 20 to in volts rms The voltage across the load resistor still has positive and negative values 120V VR 20 1 Figure 0 1 Step down transformer power supply 50 VR V Time ms Putting a single diode in the circuit eliminates the negativegoing voltages but is inefficient because of that and the output voltage is not a steady value as a function of time VR 120V 20 1 Figure 0 2 Half wave rectifier power supply 50 VR V Time ms Using four diodes connected as shown produces only positive going voltages more efficient but the voltage is not steady it has very large ripple VR 120V 50 VR V 20 1 Figure 0 3 Full wave rectifier power supply Time ms To see how the four diode full wave rectifier works look first at the voltage polarity across the load resistor When the top of the transformer secondary is positive the two diodes shown are forward biased and the current is downward through the load resistor When the top of the transformer is negative with respect to the bottom these two diodes are reverse biased and pass no current VR 120V 20 1 Figure 0 4 Positive transformer output causes the pair of diodes shown to conduct in the fullwave rectifier power supply VR V Time ms When the top terminal of the transformer is negative The other two diodes are forward biased and pass Current through the load resistor from top to bottom Filling in the missing parts of the output waveform VR 120V 20 1 Figure 0 5 Negative transformer output causes the other diode pair to conduct VR V Time ms The output can be filtered by adding a capacitor across the load resistor reducing the ripple significantly The time constant RLC needs to be large compared with the period of the AC part of the output waveform What is the frequency of that AC part And what is its period 20 1 Figure 0 6 Filtered full wave rectifier power supply VR V VR 120V Time ms To get a really steady voltage out we can add an integrated circuit regulator to the circuit 2500 F 20 1 Figure 0 7 Regulated power supply 120V MC7805 regulator 1 F
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