Semiconductor Fundamentals Unit 3 – Full-Wave Rectification and Filtering
Exercise 3 – Voltage Doubler
EXERCISE OBJECTIVE
When you have completed this exercise, you will be able to demonstrate how to obtain a filtered
dc voltage equal to double the peak ac input voltage by using a voltage doubler circuit. You will
verify your results with a multimeter and an oscilloscope.
DISCUSSION
- Voltage doubler circuit rectifies the ac input signal and filters the output producing a dc
output voltage twice the peak ac input voltage minus the forward voltage drop of the diode. - A typical full-wave voltage doubler circuit consists of two diodes and two series filter
capacitors. - Total voltage across series capacitors is the sum of the capacitor voltage drops. The addition
of these voltage drops produce the voltage doubling effect of the circuit. - Resistors R1 and R2 are equalizing resistors that evenly divide the capacitor voltages within
the circuit. - Full-wave voltage doubler use both the positive and negative half-cycle of the ac input
signal. One diode and one capacitor are paired per half-cycle. - Diode (CR1) and capacitor (C1) function for the positive half-cycle. Diode (CR2) and
capacitor (C2) function for the negative half-cycle. - Since the discharge time constant is large, the capacitors maintain a charge close to the
maximum charged voltage between charging cycles. - Output ripple frequency of a full-wave voltage doubler is twice the ac input frequency.
- Input peak voltage is reduced during the capacitor charging period because the voltage
doubler input is supplied by an unregulated power supply.