Switched capacitor DC – DC power converters

Switched capacitor DC – DC power converters buck converter

Switched-Capacitor DC–DC Power Converters (Buck Converter)

A Switched-Capacitor (SC) Buck Converter is a type of DC–DC step-down converter that uses capacitors as the main energy transfer elements instead of inductors. It belongs to the family of switched-capacitor converters, which achieve voltage conversion by charging and discharging capacitors through controlled switches (MOSFETs).Working Principle

The basic operation of a switched-capacitor buck converter can be described in two phases:

1. Charging Phase

• A capacitor is connected to the input supply through MOSFET switches.
• The capacitor charges up to the input voltage (or a fraction, depending on topology).

1. Discharging Phase

• The charged capacitor is reconfigured through switching so that it delivers energy to the output load.
• By controlling the duty cycle and switching sequence, the average output voltage is stepped down from the input.

Thus, the output voltage is typically a fraction (like 1/2, 1/3, etc.) of the input voltage, depending on the switching network configuration.Key Features of Switched-Capacitor Buck Converter

• Inductor-less design → Relies only on capacitors and switches.
• Step-down (buck) capability → Output is lower than input voltage.
• High power density → Compact and lightweight.
• Integrated circuit friendly → Ideal for on-chip DC–DC conversion.
• Discrete voltage ratios → Output voltage ratios are set by topology (e.g., Vin/2, Vin/3).

Advantages

• No bulky inductors → Smaller size and cost-effective.
• Easy to integrate into ICs for portable electronics.
• High efficiency at moderate loads.
• Reduced electromagnetic interference (EMI) compared to inductive converters.

Limitations

• Limited to specific fractional conversion ratios.
• Efficiency decreases at high current loads (due to capacitor ESR & switching losses).
• Requires careful design to handle switching transients.

Applications

• Portable electronics (mobile phones, laptops, wearables).
• On-chip power management circuits.
• Low-power renewable energy systems.
• LED drivers and compact DC power supplies.