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A charge pump is a type of converter that uses capacitors to change the incoming voltage of a power source. The capacitors act to store and transfer energy, allowing the electrical circuit to deliver lower or higher voltage to part of a device — such as and LCD screen — than the main power source provides. A type of direct current-to-direct current (DC-to-DC) converter, it is a relatively simple circuit, but its small size and low cost makes it a good option for many portable electronics.
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 for output, and the fast switching rate minimizes the amount of charge that each cycle must store and dump from the capacitor. The voltage of a charge pump is dependent on the load, meaning that a higher load on the circuit will produce a lower average voltage.
The switching of the charge pump is typically driven by an external circuit. Simple charge pumps modify 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 increase it. Charge pumps with more sophisticated controllers and circuits can generate a specific output voltage or range of voltages, and a regulator can keep the output voltage constant.
Charge pumps are found in a wide variety of electronics that require a relatively low voltage power input but which have elements that need higher voltages. They can be used to provide short-term bursts of power, allowing the batteries to last longer when in standby mode. A charge pump is typically very small, and can be fit into increasingly tiny portable electronics, and modern developments have helped make them more efficient.
A significant number of small electronics include Electrically Erasable Programmable Read Only Memory (EEPROM) chips and flash memory. These memory chips use charge pumps to produce a pulse of high voltage to delete existing data in their memory, allowing new data to be written to that memory cell. Charge pumps are also used to help boost the voltage to liquid crystal displays (LCDs) in devices like cell phones and digital cameras.