This application note shows the step-by-step process to design a high-performance supply. The equations shown in this document can also be used for different output voltages and total power. The complete power supply circuits shown in Figures 6 and 7 demonstrate the FAN4800’s ability to manage high output power while complying with international requirements regarding AC line quality. The PFC section provides 380VDC to a dual-transistor current-mode forward converter. The output of the converter delivers +12V at up to 8.4 amps. The circuit operates from 85 to 265VAC with both power sections switching at 100kHz. The FAN4800 is initialized once C12 is charged to 13V through R27 and R28. PFC switching action boosts the voltage on C5 to 380V via L1’s inductance. T2 then supplies a well-regulated 13V for the FAN4800 from its secondary winding. T2’s primary-to-secondary turns ratio (NPRI / NSEC) is 18.8:1. For proper circuit operation, high-frequency bypassing with low-ESR ceramic or film capacitors on VCC and VREF is provided. Orderly PFC operation upon start-up is achieved when D2 quick charges the boost capacitor to the peak AC line voltage before the boost switch Q1 is turned on. This ensures the boost inductor current is zero before IEAO RAMP2.
This document is an application note for the FAN4800 Combo Controller, a device used to design high-performance power supplies. It details the step-by-step process for designing a supply that manages high output power while complying with international AC line quality requirements. The note specifically demonstrates the controller's ability to power a PFC section that boosts voltage to 380V DC for a dual-transistor current-mode forward converter.
| Input Voltage Range | 85 to 265V AC |
|---|---|
| Output Voltage (PFC) | 380V DC |
| Output Current | up to 8.4 amps |
| Switching Frequency | 100kHz |
| Turns Ratio (T2) | 18.8:1 |
It manages high output power while complying with international requirements regarding AC line quality.
The PFC stage provides 380V DC to the dual-transistor current-mode forward converter.
Both power sections should switch at 100kHz.