This application note describes a design strategy for a high- efficiency, compact flyback converter. Design considerations, mathematical equations, and guidelines for a printed circuit board layout are presented.
The document details the design strategy for a high-efficiency, compact flyback converter utilizing the SG6741 series of PWM controllers. Key features include high-voltage startup, low operating current of 4mA, and a proprietary green mode that linearly decreases the switching frequency to 22KHz at light-load conditions to meet power conservation requirements. The controller also incorporates frequency hopping to reduce EMI and peak-current-mode control with synchronized slope compensation.
| Operating Current | 4mA |
|---|---|
| Minimum PWM Frequency | 22KHz |
| Gate Output Maximum Voltage Clamp | 18V |
| Over-Voltage Protection Threshold | 26V |
| Turn-on Threshold Voltage | 16.5V |
| Turn-off Threshold Voltage | 10.5V |
| Feedback Pin Termination Voltage | 1.2V |
| Leading Edge Blanking Time | 350ns |
The SG6741 is manufactured using BiCMOS process, which allows an operating current of only 4mA.
The SG6741 integrates an internal frequency hopping function to reduce the EMI emission of a power supply with minimal line filtering.
In Green Mode, the PWM frequency decreases to 22KHz at no-load and approximately one-third of the nominal PWM frequency.
LEB avoids premature termination of the MOSFET by a spike induced by diode reverse recovery and output capacitances.