A voltage multiplier circuit is an electronic circuit used to multiply an input voltage by a certain factor. It's often used in high-voltage applications where a higher voltage is required, such as in cathode ray tube (CRT) displays, voltage multipliers for particle accelerators, or high-voltage power supplies.
The basic principle behind a voltage multiplier circuit is to use a combination of diodes and capacitors to repeatedly charge and discharge capacitors in a specific pattern. This results in an accumulation of voltages across the capacitors, leading to an overall higher output voltage compared to the input voltage.
One of the simplest and most common types of voltage multiplier circuits is the Cockcroft-Walton voltage multiplier. It consists of a ladder-like arrangement of diodes and capacitors, and its operation can be explained as follows:
Input Voltage: The voltage multiplier circuit is connected to an AC input voltage source. This AC voltage is usually rectified into a pulsating DC voltage using diodes. The input voltage is typically a low-voltage AC signal.
Diode Charging Phase: During the positive half-cycle of the input AC voltage, the diodes in the circuit conduct and charge the capacitors in a specific manner. The first stage capacitor charges to the peak voltage of the input AC waveform. Subsequent capacitors charge to voltages that are multiples of the peak voltage due to the diode arrangement.
Diode Blocking Phase: During the negative half-cycle of the input AC voltage, the diodes block any current flow from the capacitors. This prevents the capacitors from discharging back into the input source.
Voltage Accumulation: As the AC voltage continues to alternate, each capacitor charges and retains its voltage during the diode blocking phase. Since each stage of the circuit accumulates a voltage equal to the previous stage plus the peak input voltage, the overall output voltage across the final capacitor becomes significantly higher than the input voltage.
Output Voltage: The output voltage across the last capacitor in the ladder can be calculated by multiplying the peak input voltage by the number of stages in the circuit.
It's important to note that while voltage multipliers can provide higher output voltages, they are often limited by factors such as the breakdown voltage of the diodes and the voltage ratings of the capacitors. Additionally, the voltage multiplier's output may be affected by the load connected to it and the frequency of the input AC signal.
Voltage multiplier circuits are advantageous because they eliminate the need for high-voltage transformers and can provide relatively high output voltages without complex and expensive equipment. However, they are also susceptible to issues such as voltage droop under load and increased ripple voltage due to the charging and discharging of capacitors.