AN1537 application note introduces the standby function of L5991, which can effectively reduce the input power consumption of offline converters at light load, making them compliant with energy saving standards such as EnergyStar, Energy2000 and others.
This document details a technique to improve the standby function of the L5991 advanced PWM controller. The L5991's standard standby function reduces oscillator frequency at light loads to meet energy standards, but this note proposes a specific circuit modification to further enhance performance.
| Normal Operation Switching Frequency | 70kHz typ. |
|---|---|
| Light Load Switching Frequency | 18kHz typ. |
The theoretical maximum ratio of fosc to fgg is 5.59, though the practical limit is likely less than 4.
It is recommended to choose fgg well above the audible range, for example fgg > 30kHz.