A voltage multiplier is an electronic circuit used to generate a higher DC voltage from a lower input voltage. It is often used in electronic devices and systems that require higher voltages than what a conventional power supply can provide. The voltage multiplier circuit is based on the principle of charge storage and accumulation, and it typically consists of capacitors and diodes.
There are different configurations of voltage multiplier circuits, but one of the most common and basic types is the "Cockcroft-Walton voltage multiplier." Let's go through the operation of a simple 2-stage Cockcroft-Walton voltage multiplier:
Components:
Input voltage source (Vin): The lower DC voltage that needs to be multiplied.
Capacitors (C1 and C2): These are typically high-value capacitors, and their capacitance determines the output voltage ripple and current capability.
Diodes (D1, D2, D3, and D4): These are typically fast-switching diodes that allow the flow of current in one direction only.
Operation:
Charging Phase:
During the charging phase, the input voltage source (Vin) is connected to the voltage multiplier circuit.
Capacitor C1 charges to Vin during the positive half-cycle of the input voltage.
Capacitor C2 charges to 2*Vin during the negative half-cycle of the input voltage.
Doubling Phase:
During the doubling phase, the input voltage source is disconnected.
The diodes come into play to double the voltage across the capacitors.
When the input voltage is positive (Vin+), diodes D2 and D3 conduct, allowing current to flow through C1 and C2, adding their voltages together.
As a result, the voltage across C2 adds to the voltage across C1, effectively doubling the voltage at the output terminal.
Output Voltage:
The output voltage is taken across capacitor C2 and is now approximately 2 times Vin (ignoring voltage drops due to diodes).
To further increase the output voltage, more stages can be added to the voltage multiplier, with each stage doubling the voltage of the previous stage. For instance, adding a third stage would generate an output voltage of approximately 4 times Vin.
It's important to note that voltage multipliers are not very efficient, and their output voltage is subject to the input voltage and load variations. Additionally, they are sensitive to high-frequency variations and may require filtering components to reduce ripple in the output voltage.
Despite their limitations, voltage multipliers find applications in various areas, such as high-voltage power supplies for cathode-ray tubes (CRTs), electrostatic generators, and other devices that need high DC voltages.