Part # Application Note Television L6565 AN1729 datasheet

Part Manufacturer: ST Microelectronics

ST Microelectronics

Part Description: L6565-based low cost SMPS for TV with less then 1W standby consumption


Part Details:

AN1729 APPLICATION NOTE L6565-BASED LOW COST SMPS FOR TV WITH LESS THEN 1W STANDBY CONSUMPTION by: R.D. Stracquadaini, C. Leonardi The need for energy consumption reduction brings to the design of more and more efficient power sup-plies. High efficiency is required not only when the system supplied is fully operating but also when it isin standby condition and absorbs very little power. A common design target for many home appliancesis that their power consumption in standby mode be less than 1W. In this paper a cost-effective solution for the power supply of a 60W 14" TV, with a standby power con-sumption of less then 1W is presented. The topology used for this Switch Mode Power Supply is a Quasi-resonant Flyback Converter (SeeAN1326) in order to reduce the switching losses (ZVS at turn-on) and then to increase efficiency. In or-der to increase the performance in standby condition the start up network was designed with particularcare and the 2nd level of overcurrent protection of the L6565 QR controller is used to obtain an enhancedburst mode operation of the power supply when the system is in standby condition. The power MOSSTP7NK80 (BVDSS = 800V, RDSon = 1.5 ) is used as the power switch. QR ZVS Flyback topology In figure 1 a typical Flyback topology is illustrated. CD is the total capacitance of the drain node. It is the sum ofthe Mosfet s COSS, transformer intrawinding capacitance, stray capacitance due to the layout of the circuit aswell as other contributions reflected from the secondary side. Figure 1. Flyback topology Lm Ls Vout Lp Llk Vin Cin Rp Cd VDS D03IN1462 June 2003 1/10 AN1729 APPLICATION NOTE The Power Mos is turned off when the drain current reaches a threshold that is fixed by the controller dependingon the input and the output voltages. As the secondary winding has run dry of energy, the secondary rectifierno longer conducts and the Power Mos is still off, the tank circuit, made up LP and CD, resonates. It is an RLC circuit (considering the sum of dissipative effects concentrated in a equivalent resistor RP) and thedrain voltage follows the natural evolution of such circuit starting from the condition of CD charged at VDSs at t= 0 (see waveforms in figure 2). RP is normally by far less than the critical damping impedance of the tank circuit. At the point where the drain voltage has a valley (a minimum) we can turn on the Power MOS and we can havea zero voltage turn on (if Vin VR) or a turn on where VD is as close as possible to zero compared with a squarewave flyback (see figure 2). This is Quasi-resonant (QR) operation. Figure 2. Typical waveforms of QR operation Llk & Cd L V p & Cd DS VDSs VDS @ Vin2 >Vin V Vin2 R Vin NO ZVS! ZVS Ip t IPKs Pri Sec Is @ Vin2 >Vin IPKp Ip @ Vin2 >Vin TON TFW TV T = 1/fsw


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Application Note Television L6565 AN1729.pdf Datasheet