AN-6075 describes how to design a compact flyback converter. The converter uses the FSQ500L as a controller and has fixed frequency (130KHz), under-voltage lockout (UVLO) protection, soft-start time tuned by external capacitor, overload protection (OLP), leading-edge blanking (LEB), optimized gate turn-on/turn-off driver, thermal shutdown (TSD) protection with hysteresis, and temperature-compensated precision-current sources for loop compensation. The no-load power consumption can be less than 250mW (without auxiliary bias winding) or 60mW (with auxiliary bias winding) for universal AC input voltage range to meet the power conservation requirements. Compared to a linear power supply, the converter has a smaller size and weight, higher efficiency, higher productivity, and higher system reliability.
This document describes a detailed design strategy for a compact flyback converter using the FSQ500L, which combines a current-mode Pulse Width Modulator (PWM) with a single-chip 700V senseFET. The device is designed to replace linear power supplies to achieve low cost, reduced size, and increased efficiency for universal AC input voltage ranges.
| Operating Frequency | 130KHz |
|---|---|
| No-load Power Consumption | less than 250mW |
| No-load Power Consumption (with auxiliary) | down to 60mW |
| Input Voltage Range | universal AC |
| Thermal Shutdown Threshold | approximately 140°C |
| TSD Recovery Temperature | lower than 60°C |
| Output Power (Design Example) | 2.04W |
No, the FSQ500L needs no auxiliary bias winding as it uses an internal high-voltage regulator.
The typical soft-start time is around 8ms when using a 47uF capacitor for C1.
The thermal shutdown triggers when the temperature exceeds approximately 140°C.