STMicroelectronics L5991 Application Note AN1049 Minimize Power Losses of Lightly Loaded Flyback Converters

About this manual

The document details the operation of the 'Standby' function within the L5991 PWM controller, which automatically reduces the switching frequency when a converter is lightly loaded to improve energy efficiency. This feature helps meet strict energy-saving standards for office equipment like monitors and printers.

Additionally, the note provides design strategies for minimizing power losses in flyback topologies. It covers the relationship between input power, peak current, and standby thresholds, offering formulas and tips for optimizing the converter's performance under low-load conditions.

What's inside

• Introduction
• Designing with the L5991 PWM Controller
• Standby function description
• Standby Operation Analysis
• Internal Schematic and Operation
• Oscillation Frequency Calculation

Frequently asked questions

What is the primary benefit of the L5991's Standby function?

It automatically detects light load conditions and decreases the oscillator frequency to reduce power losses dependent on switching frequency.

What are the typical quiescent current values for the L5991?

The typical quiescent current is 7 mA, with a maximum of 10 mA.

Which office equipment examples are mentioned as suitable for this controller?

Monitor displays, printers, photocopiers, scanners, and fax machines.