Charge pumps are a type of electronic circuit used to generate a higher or lower DC voltage from a DC input voltage. They work by transferring charge between capacitors in a cyclic manner to achieve the desired output voltage. Charge pumps have several applications in electronic circuits, including voltage doubling, voltage inversion, voltage multiplication, and voltage regulation.
The basic concept of a charge pump involves using switches (typically transistors or diodes) to control the charge transfer between capacitors. Depending on the configuration, charge pumps can be classified into various types, such as voltage doubler, voltage tripler, voltage inverter, and voltage multiplier charge pumps.
Voltage Doubler: A voltage doubler charge pump converts a DC input voltage to a doubled DC output voltage. It employs two capacitors and two switches, and the capacitors are charged in parallel during one part of the cycle and then connected in series during the other part, effectively doubling the voltage across the load.
Voltage Tripler: A voltage tripler charge pump is an extension of the voltage doubler, which triples the input voltage.
Voltage Inverter: A voltage inverter charge pump generates the opposite polarity of the input voltage. It can be used in circuits where a negative supply voltage is required, but only a positive supply is available.
Voltage Multiplier: Voltage multiplier charge pumps can generate higher output voltages than those achievable with simple voltage doublers or triplers. They utilize multiple stages of charge pump circuits to increase the voltage further.
Applications of Charge Pumps:
Voltage Regulation: Charge pumps are often used in voltage regulators to provide a regulated output voltage, especially in low-power or battery-powered devices.
Power Supplies: Charge pumps are used in some integrated circuits (ICs) as on-chip voltage generators for internal operations, particularly when a higher voltage is required than the available supply voltage.
Display Drivers: Charge pumps are employed in some LCD (Liquid Crystal Display) drivers to generate higher voltage levels needed for biasing.
Flash Memory Programming: Charge pumps can be used in flash memory programming circuits, where high voltage levels are required to program memory cells.
Audio Amplifiers: Charge pumps are used in some audio amplifier circuits to provide a negative supply voltage for powering the operational amplifier's negative rail.
LED Drivers: Charge pumps can be utilized in LED driver circuits to generate higher voltages for driving LED strings.
Charge pumps are attractive for certain applications due to their simplicity, low component count, and ability to generate higher voltages without using inductors. However, they have limitations, such as limited current output and lower efficiency compared to switching regulators in high-power applications. Nonetheless, in low-power and portable electronic devices, charge pumps can be a cost-effective and efficient solution for voltage conversion.