Part # Application Note Power Supply And Power Management L6561 AN966 datasheet

Part Manufacturer: ST Microelectronics

ST Microelectronics

Part Description: L6561, enhanced transition mode power factor corrector

Part Details:

AN966 ® APPLICATION NOTE L6561, ENHANCED TRANSITION MODE POWER FACTOR CORRECTOR by Claudio Adragna The TM (Transition Mode) technique is widely used for Power Factor Correction in low power appli-cations, such as lamp ballasts or low-end monitors. The L6561 is the latest ST s proposal for thismarket and the emerging ones that are supposed to require a low-cost Power Factor Correction.Based on a well-established architecture, the L6561 offers excellent performance that enlarges itsfield of application considerably. IntroductionThe front-end stage of conventional off-line converters, typically made up of a full wave rectifier bridgewith a capacitor filter, gets an unregulated DC bus from the AC mains. The filter capacitor must be largeenough to have a relatively low ripple superimposed on the DC level. This means that the instantaneousline voltage is below the voltage on the capacitor most of the time, thus the rectifiers conduct only for asmall portion of each line half-cycle. The current drawn from the mains is then a series of narrow pulseswhose amplitude is 5-10 times higher than the resulting DC value.Lots of drawbacks result from that: much higher peak and RMS current drawn from the line, distortion ofthe AC line voltage, overcurrents in the neutral line of the three-phase systems and, after all, a poor utili-sation of the power system s energy capability.This can be measured in terms of either harmonic contents, as norms EN61000-3-2 envisage, or PowerFactor (PF), intended as the ratio between the real power (the one transferred to the output) and the ap-parent power (RMS line voltage times RMS line current) drawn from the mains, which is more immedi-ate. A traditional input stage with capacitive filter has a low PF (0.5-0.7) and high harmonic contents. Figure 1. Internal Block Diagram of the L6561. COMP MULT CS 2 3 4 1 INV - 40K 2.5V MULTIPLIER + VOLTAGE OVER-VOLTAGE 5pF + - REGULATOR DETECTION VCC 8 V INTERNAL CC SUPPLY 7V R Q 20V R1 S 7 + GD UVLO DRIVER - R2 VREF2 ZERO CURRENT DETECTOR 2.1V + STARTER 1.6V -

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Application Note Power Supply And Power Management L6561 AN966.pdf Datasheet