The Voltage Multiplier is a type of diode rectifier circuit that can produce an output voltage many times greater than the applied input voltage. A voltage doubler is an electronic circuit that is used to charge the capacitors in such a way that the double voltage, in the ideal case, is produced at the output as at the input.
Voltage doublers are frequently encountered in electronic circuits. The present one is a variation that is of interest since most digital circuits already have buffered clocks (CLK) available or have a spare Schmitt trigger gate. Since in those cases no new IC is needed, the cost of the doubler is much reduced. If a buffered CLK signal is available only four components C4, C5, D1, and D2 are required to produce a voltage of 10V from a supply of 5V. If an oscillator needs to be built from a spare gate, two further components are required: R1 and C3.
As its name suggests, a Voltage Doubler is a voltage multiplier circuit that has a voltage multiplication factor of two. The circuit consists of only two diodes, two capacitors, and an oscillating AC input voltage (a PWM waveform could also be used). This simple diode-capacitor pump circuit gives a DC output voltage equal to the peak-to-peak value of the sinusoidal input. In other words, double the peak voltage value because the diodes and the capacitors work together to effectively double the voltage. The most important parameters of the circuit are in the table below. Note that owing to tolerances in the clock circuit, these data may be slightly different.
Voltage Doubler Circuit Diagram:
So how does it work? The circuit shows a half-wave voltage doubler. During the negative half cycle of the sinusoidal input waveform, diode D1 is forward biased and conducts charging up the pump capacitor, C1 to the peak value of the input voltage, (Vp). Because there is no return path for capacitor C1 to discharge into, it remains fully charged acting as a storage device in series with the voltage supply. At the same time, diode D2 conducts via D1 charging up a capacitor, C2.
During the positive half cycle, diode D1 is reverse biased blocking the discharging of C1 while diode D2 is forward biased charging up capacitor C2. But because there is a voltage across capacitor C1 already equal to the peak input voltage, capacitor C2 charges to twice the peak voltage value of the input signal.