AN991 AN966 NE555 AN880

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AN991 APPLICATION NOTE L6569 L6561 LIGHTING APPLICATION WITH
DESCRIPTION application been developed supply fluorescent lamps. consists sections: Power Factor Corrected preregulator (PFC), using L6561, lamp ballast stage with L6569 (see fig.1). power factor corrector section based L6561. This intended control preregulators using transition mode technique. especially dedicated electronic lamp ballast applications better understand L6561 characteristics refer AN966). Referring application circuit (see fig.1), mains voltage rectified diodes bridge delivered boost converter. converter section boosts rectified voltage controlled value. section consists boost inductor (T1), controlled power switch (Q1), boost diode (D1), output capacitor (C5) and, obviously, control circuitry. Since input time-variable supply voltage (sine wave), make input current shaped like line voltage, converter produce boost inductor average current like rectified input voltage. L6561 controls system transition mode. Transition mode approach consists "zero current turn-on" system, switching variable frequency duty cycle. output voltage value PFC, which adjusted pair resistor R7-R8, Volt. regulated voltage delivered ballast section. L6569 high voltage half-bridge driver with built-in oscillator, similar NE555 timer better understand L6569 lighting applications refer AN880). load consists series resonant circuit with lamps connected across capacitors. This topology allows operate Zero Voltage Switching, reduce transistor switching losses electromagnetic interference generated output wiring lamp. preheating lamp cathodes achieved high switching frequency, about (R14, C14), current flows filaments, without lamp ignition. preheating time defined time constant C10. After this time elapsed, switching frequency decreases moving towards resonance (L1/L2, C16/C17), thus increasing voltage across lamps causing ignition. steady state frequency reaches (R14, C13+C14). start when running, ballast controller (L6569) powered When ballast section running, current pump (C12, R13, DZ2) allows start power factor section supply overall circuit. This sequence prevents activation over voltage protection. fact starts first, loaded long ballast operating. application provided with safety circuitry that, case open load ignition failure, shuts down supply controllers. This fault condition latched until mains removed turn-on sequence repeated.
July 1998
220K 820pF 600V BYT11600 STP5NA50 1N4148 100nF 4.7V 750K 1N4148 2.2M 5.6V 470pF BS170 560pF 10µF 470nF 1.5M STP6NB50 750K 330K 2.3mH 680nF 22µF 450V 100nF 10µF P0102AA STP6NB50 180K 100nF 250V 1N4148 5.6K 6.8nF 630V 820K 820K
Figure Schematic circuit
FUSE
Bridge
AN991 APPLICATION NOTE
750K
750K
L6569
220nF 400V
L6561
8.2K
10nF 9.53K
C15A 100nF 250V
2.3mH 6.8nF 630V 1.5M 1.5M
2.2M
2.2M 1N4148
D98IN822A
AN991 APPLICATION NOTE
Information furnished believed accurate reliable. However, STMicroelectronics assumes responsibility consequences such information infringement patents other rights third parties which result from use. license granted implication otherwise under patent patent rights STMicroelectronics. Specification mentioned this publication subject change without notice. This publication supersedes replaces information previously supplied. STMicroelectronics products authorized critical components life support devices systems without express written approval STMicroelectronics. logo registered trademark STMicroelectronics 1998 STMicroelectronics Printed Italy Rights Reserved STMicroelectronics GROUP COMPANIES Australia Brazil Canada China France Germany Italy Japan Korea Malaysia Malta Mexico Morocco Netherlands Singapore Spain Sweden Switzerland Taiwan Thailand United Kingdom U.S.A.

AN991 AN966 NE555 AN880

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