Electronic Design

Voltage Conversion Without Magnetic Components

Sponsored by: NATIONAL SEMICONDUCTOR

What are typical charge pump applications?

Charge pumps have come far in the past decade, from unregulated single-output ICs to regulated ICs with multiple output voltages. Output power and efficiency also have improved, so the charge pump can now deliver up to 250 mA at 75% efficiency (average). Most applications are in battery-based systems like cell phones, pagers, Bluetooth systems, and portable electronics. Major applications include powering white LEDs for backlighting LCDs and powering milliwatt-range digital processors.

How does a charge pump work?

Charge pump (switched-capacitor) ICs provide dc-dc voltage conversion using a switch network to charge and discharge two or more capacitors. The basic charge pump switch network toggles between the capacitors' charge and discharge states. C1 (the "flying capacitor") shuttles charge, and C2 (the "reservoir capacitor") holds charge and filters the output voltage. Additional "flying capacitors" and switch arrays enable multiple gains.

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TAGS: Components
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