STMicroelectronics AN2754 Application Note: Buck High-Brightness LED Driver Based on ST1S10

About this manual

The document details how to implement a constant current drive for high-brightness LEDs (HBLEDs) using a buck topology switching regulator. It explains that controlling forward current is essential for consistent LED brightness and efficiency, as opposed to simple voltage control which suffers from power loss and instability due to LED V-I curve variations.

The note provides a design example based on the ST1S10 monolithic power switching regulator. It covers the selection of passive components such as inductors and capacitors, describes the board layout, and includes schematic diagrams with a bill of materials for driving a single HBLED at 1 A.

What's inside

• Background
• Buck topology switching power supply
• Design example
• Power stage selection
• Current sense
• Inductor selection
• Output capacitor selection
• Input capacitor selection
• Board layout
• Typical application waveforms

Specifications

Frequently asked questions

Why is a buck converter preferred for driving high-brightness LEDs?

A standard buck converter is the best choice because only this topology has an average inductor current equal to the average load current, making constant voltage-to-current conversion easier.

What are the drawbacks of driving LEDs with a voltage source?

Using a voltage source causes large swings in forward current due to small changes in forward voltage and results in power loss across a ballast resistor.