application note 250w high power factor supply for tv introduction this application has been designed to provide a complete supply for colour tv. the system has been configured using a flyback dc-dc con- verter with an upstream pfc section in order to improve the characteristics of the whole supply. the architecture of the system consists of a l4981a controller with the relevant circuitry for the pfc section, and of a tea2261 synchro- nised, in master-slave configuration, with a tea5170 at 15 khz switching frequency. when the supply is in stand-by condition, the tea2261 controller operates in burst mode. system block diagram. (fig.1) system main features: input voltage range: 176 to 270 vac rated output power: 250w power factor at max. output power: 0.98 input power in stand-by mode: 3w dc preregulated voltage: 400 efficiency: > 80% operating frequency: 15khz synchronised (only fly-back section) minimum output power synchronised : 8.5 w others: short circuit, overload and open load protection. description. how to use the demoboard: the evaluation board is provided with a multi-con- tact switch (sw.1) which allows to simulate the tvc operations. the procedure is very simple: 1) put the switch (1) in s-by position and then switch on the board. in this condition no pulses are coming from the tea5170 i.c. , t1 is in on state grounding c9 (at soft start pin of l4981) and so the pfc section is not working. it is possible to test the voltage at the output of the step-up (pfc) section c23. it must be about 308 v (depending on the mains volt- age). the outputs of the converter should be measured, and the values can be adjusted with p1 placed at the primary side. here below the schematic diagram is shown in fig 2a, pcb and components layout in fig. 2b. AN826/01297 emi filter 220v pfc (l4981a) fly back dc-dc conv (tea2261- tea5170) +400v +135(b+) +15 +14 -14 +7.5 d95in236a figure 1. 1/7
c1 150nf 250v~ c2 220nf 250v~ 21 3 tr1 f1 3at d1 4 x by255 d3 d2 d4 r6 33k 1w c7 470 m f com1 176-265v~ 1,7,10 r9 120k c11 330nf r22 1.8m r23 18k 312 14 c10 220nf 400v 220pf d9 stta506m 20 4 t3 sth12 n60f1 r26 1m r27 13k r31 r 12 2w r25 18 r15 1m tr2 orega g5155-01 2 r21 3.9k 8 r8 2.7k 59 r14 27k c16 r7 2.7k 1.2nf c8 10 m f 611 c9 1 m f 12 17 r18 39k 18 c19 1nf 19 c23 150 m f 450v d11 ba157 c21 100 m f r24 1m t1 bc548 t2 bc548 d7 ba157 r10 12 10 c4 1nf 11 r8 100k 16 15 4,5,12,13 9 c3 470nf c5 1 m f 87 c6 470pf 6 r2 100k r4 10k 2 c17 470pf r19 22 l1 2.2 m h c20 47 m f d8 b2x85 c3v3 t4 buh515 r29 100 14 r1 1.8k p1 2.2k r5 6.8k d5 ba157 c12 1nf r20 1k r33 470 9w d13 byt11 1000 c25 2.2nf r34 r12 2w r34 r12 1m 1 3 tr4 t5 bc308 r40 3.3k r41 10k g5154-02 orega ic2 l4981a ic1 tea2261 r42 10m c28 4.7nf ic3 tea5170 c5 10 m f r34 1k r37 22k r38 100 d20 1n4148 c30 1 m f c29 220nf r45 330 com2 s-by sync 4 3 2 1 r55 r c42 150pf r54 6.8k r43 240k c31 470pf 2 3148 76 d19 byw80/200 5 c37 4.7nf r44 47k r52 1k p2 1k c36 2200 m f 25v r48 22k c35 2200 m f 25v r47 1.8k r51 68k 0.5w d18 byt08/400 c34 100 m f 160v r46 68k 1w d17 byt13/1000 d16 byt08/200 d15 byt08/200 c33 2200 m f 50v c39 10 m f c32 2200 m f 50v c38 10 m f r49 56k r50 56k l3 l2 1 2 3 4 5 6 7 +14v -14v +135v com3 +15v +7.5v d95in237c d7 ba157 d7 ba157 d7 ba157 1n4148 10nf 33k 10 m h figure 2a: schematic diagram. application note 2/7
figure 2b: pcb and components layout. application note 3/7
on the evaluated board (refer to con3 in fig.3) the adjusted voltage values are: voltage at out 1 = +16.5v voltage at out 3 = -16.5v voltage at out 4 = +13.7v voltage at out 1 = +15.7v voltage at out 1 = +10v as the o stand-by o output values have been set, put the switch in on position the loads are now connected and all the circuits of the application run. the tea5170 is now supplied and it sends pwm pulses from the secondary to the primary side of the converter. t2 is turned on, is t1 is cut- off, thus enabling the l4981a to start. as the pfc runs, the voltage at the bulk capacitor c23 reaches 400v. con2 s-by con3 d95in246 sound 10 20w 10 20w +14v -14v +135v +15v +7.5v rl 15v rl 135v off on sby on 1 2 3 4 5 6 7 1 2 3 4 sw1 figure 3: tvc simulation with external resistive loads. r l must be dimensioned according to the required output power test results: output voltage 405v (at 230w output power). output power 10 to 250w efficiency 85% (at max. output power) power factor 0.998 thd at max. output power: 3.5% power factor in stand-by mode: 0.3 thd in stand-by mode: 70% efficiency at min. output power: 0.5 (pi min = 17w) minimum output power = 8.5w 135v ? 18ma + 15v ? 300ma + 7.5v ? 250ma application note 4/7
in the attached photos (1 to 4 ) the essential waveforms are depicted (ref. fig. 2a). load regulation: a) 135v output (4) = 0.12% @ io4 (135v) = 0.05 to 1a io5 (15v) = 2.5a io6 (7.5v) = 2.5a io1 (14v0 = 1.3a io3 (-14v) = -1.3a b) 135v output (4) = 0.75% @ io4 (135v) = 1a io5 (15v) = 2.5a to 0a io6 (7.5v) = 2.5a io1 (14v0 = 1.3a io3 (-14v) = -1.3a c) 135v output (4) = 0.75% @ io4 (135v) = 1a io5 (15v) = 2.5a io6 (7.5v) = 2.5a to 0a io1 (14v0 = 1.3a io3 (-14v) = -1.3a d) 135v output (4) = 0.1% @ io4 (135v) = 0.05a io5 (15v) = 2.5a io6 (7.5v) = 2.5a io1 + 3 ( 14v) = -1.3a to 0a 14v output (1 + 3) = +60% for i = 1.3 to 0a photo 1: pfc section (pout = 230w; i l = 1a/div; vi = 100v/div; t = 2ms/div) 0 0 photo 2: flyback section (pout = 230w; i c = 1a/div; vce = 200v/div; t=10 m s/div) ic vce t3 d9 tr2 il vi d95in259 i c v ce t4 d95in292 application note 5/7
photo 3: stand-by mode turn-off transistor buh517 (i c = 0.5a/div; vce = 200v/div; t = 0.5 m s/div) 0 ic vce photo 4: stand-by mode pfc at bulk capacitor (i l = 0.5a/div; vi = 100v/div; t = 2ms/div) 0 0 t3 d9 tr2 il vi d95in259 i c v ce t4 d95in292 il vi application note 6/7
information furnished is believed to be accurate and reliable. however, sgs-thomson microelectronics assumes no responsibility for the consequences of use of such information nor for any infringement of patents or other rights of third parties which may result from its use. no license is granted by implication or otherwise under any patent or patent rights of sgs-thomson microelectronics. specification mentioned in this publication are subject to change without notice. this publication supersedes and replaces all information previously supplied. sgs- thomson microelectronics products are not authorized for use as critical components in life support devices or systems without express written approval of sgs-thomson microelectronics. ? 1997 sgs-thomson microelectronics printed in italy all rights reserved sgs-thomson microelectronics group of companies australia - brazil - canada - china - france - germany - italy - japan - korea - malaysia - malta - morocco - the netherlands - singapore - spain - sweden - switzerland - taiwan - thailand - united kingdom - u.s.a. application note 7/7
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