A charge pump is a type of DC-DC converter used in electronics to perform voltage conversion. Its primary function is to increase (boost) or decrease (buck) the input voltage level to a desired output voltage level. Charge pumps are widely used in various applications, including power management circuits, voltage regulators, and electronic devices.
The basic operation of a charge pump involves the transfer of electric charge from one capacitor to another, hence the name "charge pump." It typically consists of a series of switches (usually implemented as transistors) and capacitors. The charge pump operates in cycles, and during each cycle, it charges and discharges capacitors to transfer charge and achieve the desired voltage conversion.
Here's a brief overview of the role of a charge pump in different types of voltage conversion:
Voltage Boosting (Step-Up Conversion):
In a step-up charge pump (boost converter), the output voltage is higher than the input voltage. During the charging phase, the charge pump switches connect the input voltage to one side of the capacitor, while the other side is connected to the output. The capacitor is charged to the input voltage level. Then, during the discharging phase, the charge pump switches disconnect the input and connect the capacitor's charged side to the output, effectively boosting the voltage to a higher level than the input voltage.
Voltage Reduction (Step-Down Conversion):
In a step-down charge pump (buck converter), the output voltage is lower than the input voltage. The charging and discharging phases are similar to the boost converter, but the output voltage is tapped from the capacitor's side that has a voltage lower than the input voltage, effectively reducing the voltage.
Inverting Voltage (Inverting Charge Pump):
An inverting charge pump converts a positive input voltage into a negative output voltage (or vice versa). This is achieved by using an intermediate voltage level, typically generated by a switched capacitor network, to create the inverted voltage.
The efficiency of charge pumps is not as high as some other DC-DC converter topologies like buck-boost or flyback converters. However, charge pumps are favored in certain low-power applications due to their simplicity, low component count, and small size. They are commonly used in scenarios where the required output current is relatively low, and where space and cost constraints are critical factors.