What’s a charge pump?

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A charge pump is a type of converter that uses capacitors to change the input voltage of a power source. Capacitors act to store and transfer energy, allowing the electrical circuit to supply a lower or higher voltage to a part of a device, such as an LCD screen, than that provided by the main power source. A type of direct current to direct current (DC-DC) converter, it is a relatively simple circuit, but its small size and low cost make it a good option for many portable electronic devices.

How does it work
A simple charge pump increases the voltage of a power supply by charging a capacitor to the same voltage as the power supply. A switch is used to change the circuit and place the capacitor in series with the power supply, which effectively doubles the voltage, assuming no electrical leakage occurs. Additional capacitors can be added, increasing the voltage available to the output, and the fast switching speed minimizes the amount of charge each cycle has to store and discharge from the capacitor. The voltage of a charge pump is load dependent, meaning that a higher load on the circuit will produce a lower average voltage.

Charge pump switching is typically driven by an external circuit. Simple charge pumps change the voltage of the power source by an integer value, such as doubling or tripling the voltage, and other topologies can reduce the voltage instead of increasing it. Charge pumps with more sophisticated controllers and circuitry can generate a specific output voltage or range of voltages, and a regulator can keep the output voltage constant.

Where charge pumps are used
Charge pumps are found in a wide variety of electronic devices that require a relatively low voltage power input but have elements that require higher voltages. They can be used to provide short-term bursts of energy, allowing batteries to last longer in standby mode. A charge pump is typically very small and can fit into increasingly smaller portable electronic devices, and modern developments have helped make them more efficient.

A significant number of small electronic components include EEPROM (Electrily Erasable Programmable Read Only Memory) chips and flash memory. These memory chips use charge pumps to produce a high voltage pulse to purge existing data in their memory, allowing new data to be written to that memory cell. Charge pumps are also used to increase the voltage on liquid crystal displays (LCDs) in devices such as cell phones and digital cameras.

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