Part # Application Note Power Supply And Power Management L6561 AN1059 datasheet

Part Manufacturer: ST Microelectronics

ST Microelectronics

Part Description: Design equations of high-power-factor flyback converters based on the L6561


Part Details:

AN1059 ® APPLICATION NOTE DESIGN EQUATIONS OF HIGH-POWER-FACTOR FLYBACK CONVERTERS BASED ON THE L6561 by Claudio Adragna Despite specific for Power Factor Correction circuits using boost topology, the L6561 can be suc-cessfully used to control flyback converters. Among the various configurations that an L6561-basedflyback converter can assume, the high-PF one is particularly interesting because of both its peculiar-ity and the advantages it is able to offer. AC-DC adapters for mobile or office equipment, off-line bat-tery chargers and low-power SMPS are the most noticeable examples of application that this configu-ration can fit.This paper describes the equations governing such a kind of flyback converter with the aim of provid-ing a number of relationships useful to the system designer. INTRODUCTION Figure 1a. TM Flyback Configuration Three different configurations that an L6561-basedflyback converter can assume have been identified. Vout Vac They are illustrated in fig. 1. CBULK Configurations a) and b) are basically conventionalflyback converters. The former works in TM (Transi-tion Mode, i.e. on the boundary between continuous DISABLE and discontinuous inductor current mode), thereforeat a frequency depending on both input voltage andoutput current. The latter works at a fixed frequency, ZCD VCC imposed by the synchronisation signal, and is there- L6561 fore completely equivalent to a flyback converter GD OPTO based on a standard PWM controller. + TL431 Configuration c), which most exploits the aptitude ofthe L6561 for performing power factor correction,works in TM too but quite differently: the input ca-pacitance is so small that the input voltage is very close to a rectified sinusoid. Besides, the control loophas a narrow bandwidth so as to be little sensitive to the twice mains frequency ripple appearing at theoutput. Figure 1b. Synchronised Flyback Configuration Figure 1c. High-PF Flyback Configuration Vout Vout Vac Vac CBULK CIN SYNCH DISABLE DISABLE ZCD VCC ZCD MULT VCC L6561 L6561 GD GD COMP INV OPTO OPTO + + TL431 TL431


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Application Note Power Supply And Power Management L6561 AN1059.pdf Datasheet