Tricomi Arrigo This note describes off-line autoranging (85Vac-26

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Tricomi Arrigo This note describes off-line autoranging (85Vac-26

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OFF-LINE AUTORANGING BATTERY CHARGER WITH L4990
Tricomi Arrigo
This note describes off-line autoranging (85Vac-264Vac) battery charger designed operate three different functional modes: constant voltage constant current constant power These requirements typical battery chargers notebook computers. resulting output characteristic system shown Figure output characteristic
From point adapter works constant current mode until output voltage reaches practice difficult have constant current characteristic below output voltage 2-3V because primary auxiliary supply voltage drops controller turn-off threshold (internally fixed 7.6V typ.) characteristic exhibit foldback zero. mandatory operate constant current mode till secondary post-regular other tricky solutions windings, primary secondary, required. shows characteristic obtained with circuit Figure Practical characteristics
D96IN439
Vin=220VAC
Vin=110VAC
D96IN437
portion characteristic constant voltage mode. This situation happen when battery pack almost completely charged. final value battery pack. From point charger operates constant power mode, reducing output voltage while increasing output current. benefit introducing constant power mode that maximum output power lower with respect power output point This reduces power managed primary circuitry consequence reduces total dissipation power. This useful improvement considering that complete system packaged plastic case with very limited capability dissipating heat.
AN889/0397
ELECTRICAL SPECIFICATION: Input voltage 85Vac 264Vac Regulated output voltage Maximum output power Switching frequency 100kHz Target efficiency full load >80% Topology discontinuouscurrent mode flyback shows electrical circuit.
50pF 120pF 470µF BYT11 470µH 330µF SB860 82µF 400V BYT11600 0.5W
THERMISTOR
FUSE
18V/2A
2.7M BC337 BC337 STP5NA80 Csen ISEN PGND 100pF VREF 22µF 22µF 22µF
4.7K
Figure AC-DC converter electrical schematic.
5.1K
VREF
5.1K
L4990A
SGND
101A
OUTPUT 220nF 220nF 100K 2.2K CCREF Crin Vrin
2.2nF
5.1K
COMP
10nF
TCDT 1101GB
2.2nF
D97IN537
realisation three different functional modes requires dedicated controls. voltage current controls located secondary side transformer, error signal transferred primary controller optocoupler order have isolated feedback. TSM101A dual op/amp, with internal 1.24V reference used. op/amp dedicated voltage mode control second constant current control. output OR-ed common point drives optocoupler. current signal taken across 40mOhm current sense resistor, R16, while potentiometer adjusts output voltage. constant power characteristic easy achieve with discontinuous mode operation, since constant primary peak current means constant output power. value programmed adding proper offset voltage, defined value (fig current sense ramp value this resistor related desired output power Pout below relationship: Pout where primary inductance, expected efficiency, switching frequency current sense resistance. L4990A introduces delay, 100ns, turn-off, current loop, this, primary peak current value increases according slope. consequence that regulated output power function input voltage. introduced order compensate this error. value calculated with following formula: Table System efficiency.
(Vac) 17.97 17.94 17.89 17.89 Iout Vout 83.9% 85.1% 84.4% 82.0% Iout Pout Vout 17.96 17.96 17.91 17.89 82.2% 83.7% 83.5% 83.0% Iout 1.8A, Pout Vout 13.82 13.86 14.31 14.41 82.6% 83.7% 83.8% 82.7%
Figure Schematic diagram output constant power.
2.7M
L4990A
100pF
D96IN438
(R30
primary auxiliary winding required supply after turn-on, designed generate voltage within limits supply voltage range. should loosely coupled with secondary winding order minimise reflected secondary-to-primary effects when output voltage going down towards short circuit. second auxiliary winding, secondary side transformer, forward coupled with principal primary winding, been added. When system constant current mode, output voltage reduced, this winding provides supply voltage TSM101A. Table summarises efficiency performance complete system, Table shows electrical system performance.
Table System performance (Pout limited 25W)
Line regulation Load regulation Maximum efficiency Output ripple Vac, Iout Iout 1.8A, Vac, Iout 1.8A Vac, Iout 1.8A 80mV 10mV 10mV 85.2% 200mV
Information furnished believed accurate reliable. However, SGS-THOMSON Microelectronics assumes responsibility consequences such information infringement patents other rights third parties which result from use. license granted implication otherwise under patent patent rights SGS-THOMSON Microelectronics. Specification mentioned this publication subject change without notice. This publication supersedes replaces information previously supplied. SGSTHOMSON Microelectronics products authorized critical components life support devices systems without express written approval SGS-THOMSON Microelectronics. 1997 SGS-THOMSON Microelectronics Printed Italy Rights Reserved SGS-THOMSON Microelectronics GROUP COMPANIES Australia Brazil Canada China France Germany Hong Kong Italy Japan Korea Malaysia Malta Morocco Netherlands Singapore Spain Sweden Switzerland Taiwan Thailand United Kingdom U.S.A.

Tricomi Arrigo This note describes off-line autoranging (85Vac-26

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