A switched-capacitor charge pump is a type of circuit used for AC-DC conversion, primarily to step up or step down voltage levels. It's a versatile and efficient device commonly found in various electronic applications, such as voltage converters in power management circuits, display drivers, and more.
Here's a basic overview of how a switched-capacitor charge pump operates in AC-DC conversion:
Basic Concept: A switched-capacitor charge pump operates by transferring charge between capacitors using switches and a clock signal. It doesn't require inductors like traditional voltage converters, making it suitable for integration in CMOS technology.
Switching Network: The core of the charge pump consists of a network of switches and capacitors. These switches are typically implemented using transistors (MOSFETs in CMOS technology) and are controlled by a clock signal. The switches alternate between connecting capacitors in series and in parallel.
Charge Transfer: The operation occurs in multiple stages, which involve transferring charge between capacitors. During one phase of the clock signal, the switches connect capacitors in parallel, allowing them to share charge. In the other phase, the switches connect capacitors in series, effectively doubling the voltage across them.
Voltage Doubling (Step-Up Operation): In step-up operation, a lower input voltage is converted to a higher output voltage. During the parallel phase, the input voltage charges one capacitor. Then, during the series phase, the charged capacitor is connected in series with the input voltage, effectively doubling the voltage across the output capacitor. This process can be repeated through multiple stages to achieve even higher voltage levels.
Voltage Halving (Step-Down Operation): In step-down operation, a higher input voltage is converted to a lower output voltage. The process is similar, but instead of doubling the voltage, the capacitors are connected in a way that reduces the output voltage in discrete steps.
Clock Generation: The charge pump requires a clock signal to control the switching of the capacitors. This clock signal is typically generated externally or by an integrated oscillator circuit. The frequency and duty cycle of the clock signal determine the efficiency, output voltage ripple, and maximum achievable conversion ratio of the charge pump.
Control and Regulation: Some charge pump applications might require regulation to maintain a stable output voltage despite variations in input voltage or load conditions. This can be achieved using feedback control loops that adjust the clock frequency or duty cycle based on the output voltage.
Efficiency and Considerations: The efficiency of a switched-capacitor charge pump depends on factors such as the clock frequency, duty cycle, switching losses, and component tolerances. While charge pumps can be highly efficient for certain voltage conversion ratios, they may have limitations in terms of current handling capability and overall efficiency compared to other voltage conversion techniques like switching regulators.
Overall, switched-capacitor charge pumps provide a compact and efficient solution for AC-DC voltage conversion in various electronic devices, especially in situations where size, integration, and simplicity are important factors.