Update: 28 September, 2023
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.
File format: PDF
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MD5 Checksum: 38C6DE0BDBA67C0F8D19BE6A9915E30B
Publication date: 11 July, 2012
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PDF Link: FAIRCHILD FAN4800 Combo Controller Applications Manual PDF