Charge Pump Output Voltage

Formula

Description

A charge pump (voltage multiplier) uses capacitors and diodes to generate a DC output voltage that is a multiple of the input voltage without using inductors. During each half cycle, capacitors are charged in parallel and then reconnected in series, stacking their voltages. Each diode in the chain drops one forward voltage Vf, reducing the ideal output. Charge pumps are used for generating gate drive voltages, EEPROM programming voltages, and in applications where magnetic components are undesirable or where very low noise is required.

Variables

• Vout — Output voltage under no load (V)
• N — Number of multiplier stages
• Vin — Input voltage per stage (V)
• Vf — Forward voltage drop per diode (V)

Practical Notes

Output impedance increases with N, limiting the available output current. Each stage adds capacitor ESR and diode drop losses. Practical charge pumps are efficient only at light loads (typically < 100 mA). Switched-capacitor voltage converters (like the ICL7660) implement a 1-stage inverter or doubler with regulated output. Use Schottky diodes (Vf = 0.2-0.3V) instead of silicon (Vf = 0.6-0.7V) for better efficiency.