Voltage Multipliers

A voltage multiplier is a circuit that produces a direct-current output voltage several times higher than the peak of its alternating-current input, using only diodes and capacitors rather than a high-voltage transformer. Each stage charges a capacitor during one half of the input cycle and adds its stored voltage in series with the next, so the output accumulates as a multiple of the input peak. Because the components are inexpensive and compact, multipliers are a common way to generate high voltages at low current.

The simplest example is the voltage doubler, which combines two diodes and two capacitors to roughly double the peak input voltage. Adding further stages gives a voltage tripler, quadrupler and so on. The classic ladder arrangement is the Cockcroft–Walton multiplier, a cascade of diode-capacitor stages that was historically used to generate the very high voltages needed for early particle accelerators. The same topology appears in cathode-ray television sets, photocopiers, ion generators and other equipment requiring kilovolt-level supplies.

Voltage multipliers suit applications that draw little current, because the output voltage sags noticeably under load and the ripple increases with the number of stages and the current demanded. They share a working principle with the charge pump, a related circuit that uses switched capacitors to move charge and so step a supply voltage up or down. Charge pumps are widely used inside integrated circuits to generate bias voltages without inductors or transformers.

Frequently asked questions

How does a voltage multiplier raise voltage without a transformer?

Diodes steer current so that capacitors charge on alternate half-cycles and then add their voltages in series, producing an output that is a multiple of the input peak.

What is a Cockcroft-Walton generator used for?

It is a cascaded diode-capacitor ladder that produces very high DC voltages, used historically in particle accelerators and in equipment such as television tubes and X-ray sets.

Why can multipliers only supply small currents?

The output relies on charge stored in capacitors, so drawing significant current causes the voltage to drop and the ripple to rise.