Part # Application Note Power Supply And Power Management L4981 AN1606 datasheet

Part Manufacturer: ST Microelectronics

ST Microelectronics

Part Description: A bridgeless PFC configuration based on L4981 PFC controller

Part Details:

AN1606 APPLICATION NOTE A "BRIDGELESS P.F.C. CONFIGURATION" BASED ON L4981 P.F.C. CONTROLLER. by Ugo Moriconi This technical document describes an innovative topology dedicated to a medium to high power PFCstage. The originality of this topology is the absence of the bridge that usually is placed between theEMC filter and the PFC stage. The advantages of this topology can be found in terms of increased ef-ficiency and improved thermal management. L4981 PFC Controller This application features the L4981 PFC controller. It is a high performance device operating in average currentmode with many on-chip functions. The driver output stage can deliver 1.5A, which is very important for this typeof application. A detailed device description can be found in AN628. A functional block diagram is shown in Figure 1. Figure 1. Functional Diagram November 2002 1/18 AN1606 APPLICATION NOTE Description of "Bridgeless PFC Configuration" Topology The conventional boost topology is the most efficient for PFC applications. It uses a dedicated diode bridge torectify the AC input voltage to DC, which is then followed by the boost section. See Figure 2. This approach is good for a low to medium power range. As the power level increases, the diode bridge beginsto become an important part of the application and it is necessary for the designer to deal with the problem ofhow to dissipate the heat in limited surface area. The dissipated power is important from an efficiency point ofview. Figure 2. Inductor D L Load A M Mains V_Rs Rs controller The bridgeless configuration topology presented in this paper avoids the need for the rectifier input bridge yetmaintains the classic boost topology. This is easily done by making use of the intrinsic body diode connected between drain and source of PowerMOSswitches. A simplified schematic of the bridgeless PFC configuration is shown in Figure 3. Figure 3. D1 D2 Inductor Mains L O Load A D M1 M2 Controller 2/18 AN1606 APPLICATION NOTE The circuit shown from a functional point of view is similar to the common boost converter. In the traditional to-pology current flows through two of the bridge diodes in series. In the bridgeless PFC configuration, currentflows through only one diode with the PowerMOS providing the return path. To analyze the circuit operation, it is necessary to separate it into two sections. The first section operates as theboost stage and the second section operates as the return path for the AC input signal. Referring to Figure 4, the left side (Figure 4a) shows current flow during the positive half cycle and the right side(Figure 4b) shows current flow during the negative half cycle Figure 4. Positive half cycle Negative half cycle Fig4a D

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Application Note Power Supply And Power Management L4981 AN1606.pdf Datasheet