Switched capacitor DC – DC power converters

Switched capacitor DC – DC power converters boost converter

Switched-Capacitor (SC) DC–DC Boost Converter

A Switched-Capacitor Boost Converter is a type of inductor-less DC–DC converter that steps up (boosts) the input voltage to a higher output voltage using only capacitors and switches. Instead of storing energy in an inductor’s magnetic field (like conventional boost converters), it relies on capacitors charged and reconfigured through controlled switching cycles.Working Principle

The operation consists of two main phases:

1. Charging Phase

• A capacitor is connected across the input supply and charges up to the input voltage.

1. Boosting/Discharging Phase

• The charged capacitor is reconfigured in series with the input source using switches.
• This effectively adds the capacitor’s voltage to the input, producing a higher output voltage.

For example, in a simple 2:1 boost topology:Vout≈2⋅VinV_{out} \approx 2 \cdot V_{in}Vout​≈2⋅Vin​

More complex configurations can provide higher multiples (e.g., 3×, 4×).

Key Features

• Inductor-less design → Only capacitors and switches are used.
• Step-up (boost) capability → Output voltage is higher than input.
• Compact and lightweight → No bulky magnetic components.
• Discrete voltage ratios → Output is an integer multiple of input (Vin, 2Vin, 3Vin…).
• Suitable for integrated circuits → On-chip voltage boosting.

Advantages

• High power density and compact design.
• Ideal for low-power ICs and portable devices.
• Low electromagnetic interference (EMI) (no inductors).
• Simple structure and control.

Limitations

• Limited to specific boost ratios (cannot continuously vary output like PWM inductive boost).
• Efficiency decreases with high load currents (due to capacitor ESR & switching losses).
• Voltage regulation is not as flexible as inductor-based converters.

Applications

• Charge pumps in integrated circuits.
• LCD biasing and camera flash circuits.
• Battery-powered devices (mobile phones, laptops, wearables).
• Energy harvesting systems (small-scale solar, RF power).
• On-chip voltage scaling in microelectronics.