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A doubler is a device, circuit, or person designed to increase a quantity by a factor of two. In electronics, the term most commonly refers to a voltage doubler, a circuit that produces a direct current output roughly twice the peak of its input alternating current or pulsating DC.

Voltage doublers use diodes and capacitors to store and stack charge, creating a higher output voltage than the input. Common configurations include half-wave variants (Villard-type) and full-wave variants (Greinacher or Delon). The basic idea is to charge capacitors at one portion of the cycle and then add their voltages in series to yield about twice the input peak, minus diode drops. Output voltage, regulation, and ripple are influenced by load, input voltage, and frequency. Doublers are simple and inexpensive but typically supply limited current and offer no isolation from the power source.

Applications for voltage doublers include compact, transformerless power supplies, high-voltage generation for devices such as CRTs or photomultiplier tubes, and scenarios where a compact high-voltage rail is needed without a bulky transformer. They perform best at higher input frequencies, where ripple and regulation are more manageable, and are less suitable for demanding loads or where isolation is required.

Other uses of the term includ e a doubler in entertainment, referring to a performer who substitutes for another actor, such as a stunt double or body double. More generally, a doubler can describe any mechanism or process that increases a quantity by two.