4.3.5 Voltage Multiplier

Chapter 4.3.5 Voltage Multiplier

Physics Lecture Notes – Phys 395 Electronics Book
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Physics Lecture Notes – Phys 395 Electronics Book

  • CHAPTER 4. DIODE CIRCUITS724.3.5Voltage MultiplierA voltage multiplier circuit is shown in figure 4.10. We can think of it as two half-waverectifier circuits in series. During the positive half-cycle one of the diodes conducts andcharges a capacitor. During the negative half-cycle the other diode conducts negatively tocharge the other capacitor. The voltage across the combination is therefore equal to twicethe peak voltage. In this type of circuit we have to assume that the load does not draw asignificant charge from the capacitors.Figure 4.10: Voltage doubler circuit.4.3.6ClampingWhen a signal drives an open-ended capacitor the average voltage level on the output termi-nal of the capacitor is determined by the initial charge on that terminal and may thereforebe quite unpredictable. Thus it is necessary to connect the output to ground or some otherreference voltage via a large resistor. This action drains any excess charge and results in anaverage or DC output voltage of zero.A simple alternative method of establishing a DC reference for the output voltage is byusing a diode clamp as shown in figure 4.11. By conducting whenever the voltage at theoutput terminal of the capacitor goes negative, this circuit builds up an average charge onthe terminal that is sufficient to prevent the output from ever going negative. Positive chargeon this terminal is effectively trapped.V0C->VsSGFigure 4.11: Diode clamp circuit and its output waveform.