Question

How does a charge-pump voltage converter work?

Answer 1

A charge-pump voltage converter is a type of DC-DC converter that uses capacitors to generate higher or lower voltages from a given input voltage without using inductors. It operates based on the principle of switched-capacitor circuits.

Working Principle of a Charge-Pump Voltage Converter

A charge pump transfers charge between capacitors using a switching network, typically driven by a clock signal. The process consists of two main phases:

1. Charge Phase (Pump Capacitor Charging)

1. A capacitor (often called the "pump capacitor") is connected to the input voltage source.
   

1. The capacitor charges up to the input voltage level.
   

2. Transfer Phase (Voltage Boost or Inversion)

1. The switch network reconfigures the connections.
   

1. Depending on the circuit design, the capacitor's charge is either added to the input voltage (boosting it) or subtracted from it (inverting it).
   

Common Charge-Pump Configurations

1. Voltage Doubler (Boost Converter)
   

   - Uses two switches and a capacitor.
   - In the first phase, the capacitor charges to the input voltage.
   - In the second phase, the capacitor is reconfigured in series with the input, doubling the output voltage.
   - Example: If input is 5V, the output becomes 10V.

1. Voltage Inverter (Negative Voltage Generator)
   

   - In the first phase, the capacitor charges to the input voltage.
   - In the second phase, the capacitor is connected in reverse, producing a negative voltage.
   - Example: If input is 5V, the output becomes -5V.

1. Fractional Voltage Conversion
   

   - By using different capacitor configurations, charge pumps can generate fractional multiples of the input voltage (e.g., 1.5×V_in, 2/3×V_in).

Advantages of Charge-Pump Converters

1. No Inductor Required → Reduces size and cost.
   

1. High Efficiency → Typically 80-95% under optimal conditions.
   

1. Low Noise → Less electromagnetic interference (EMI) compared to inductor-based converters.
   

Disadvantages

1. Limited Output Current → Typically used for low-power applications.
   

1. Output Ripple → Due to capacitor switching, additional filtering may be required.
   

Applications

1. Generating negative voltage for LCD displays.
   

1. Voltage boosting for flash memory and sensor circuits.
   

1. Powering low-power circuits in battery-operated devices.
   

Would you like a circuit diagram for a charge-pump voltage converter?