【2010-05-17】ML4803 240W Off-Line Power Supply with PFC.pdf

March 1999 Application Note 42043 ML4803 240W Off-Line Power Supply with PFC INTRODUCTION Included in this Application Note are a reference Electrical Specifications schematic, ML4803 design equations, the circuit layout, and parts list. The reference schematic demonstrates how Line voltage 85 to 265VAC the ML4803 can meet the requirements of a PFC Line harmonic content IEC1000-3-2 corrected power supply for desktop computer Switching frequency 67kHz applications. The design features include a low-cost single POUT 240W sided PCB with 240W of output power, a form factor Regulation ±0.1% compatible with desk top computer requirements, and Ripple 30mVRMS line frequency harmonic content compliant with Efficiency @ 115VAC, 240W 85% IEC1000-3-2. THEORY OF OPERATION PFC CONTROL CIRCUIT DESIGN The ML4803 Power Factor Control section uses an input Internal Voltage Ramp current wave-shaping technique that senses the boost inductor current. It compares the inductor current The internal ramp current source is programmed by way of downslope during the off-time of the main power switch the VEAO signal voltage (see Figure 1). This current source with a ramp programmed by the PFC output voltage