®
Design Idea DI-12
TOP S w it c h ®-GX 16 W, Universal
Input, Lead Acid Battery Charger
Application
Power Output
Input Voltage
Topology
Device
Output Voltage
Flyback
16 W
85-265 VAC
13.55 V at 25 ˚C
Battery Charger
TOP244P
TOP244P requires no external heatsink, using the PC board
instead.
Design Highlights
• Lowest cost and low component count solution
• Universal input voltage replaces the need for multiple linear
based designs
• High efficiency: >75%
• Integratedlineundervoltagedetection(UV)andovervoltage
(OV) power system surge protection
• Constant voltage / constant current (CV/CC) output
• Temperature compensated output voltage
• Monitor input to allow state of charge measurements
During the first 10 ms of operation, internal soft-start is
enabled, lowering stresses on the internal power MOSFET,
clamp and output rectifier. Built-in switching frequency jitter
reducesconductedEMI,allowingthedesigntomeetEN55022B
limits with simple input filtering. Diode D1 and Zener VR1
clamptheleadingedgedrainvoltagespikecausedbytransformer
leakage inductance.
Lead acid batteries for standby use are normally charged at
~2.3 V per cell and 0.1 A per Ah of capacity. Resistor R1, U2,
C9, Q1, R3, R4 and R5 form the current limit circuit. Resistor
R3 controls the current limit (1.2 A typical). Resistor R5
ensures sufficient voltage to drive the opto LED, even with the
output shorted. Capacitor C9 and R4 provide compensation
and limit Q1 base current. The output voltage is controlled
using a TL431 voltage reference (U3). Resistors R7, R8, R9
and RT1 program output voltage as a function of temperature
(Figure3)toapproximatethatrequiredbythelead-acidbattery.
During CV operation, DC gain is set by R6. Capacitor C8, C5
and R10 provide loop compensation. Bias for U3 is provided
by R2.
Operation
The circuit shown in Figure 1 provides a CV/CC output for
charging lead-acid batteries in applications such as fire/burglar
alarms and emergency lighting.
The design utilizes many of the features of the TOPSwitch-GX
family. Line undervoltage and overvoltage (100 V and 450 V,
respectively) are implemented using a single resistor (R13).
Line undervoltage detection eliminates power-up/down output
glitches, while overvoltage shutdown provides protection for
short line transients and longer duration power system surges,
removingtheneedforaninputMOV. TheDIP8packageofthe
C7
1 nF
Y1
D2
L2
3.3 µH
D1-D4
1N4007V
1 A, 1000 V
UG4D
+13.55 V
7,8
5,6
1
VR1
P6KE
200
C3
8T
24 AWG
Triple Insulated
C2
560 µF
35 V
220 µF
35 V
R2
1 kΩ
R7
11.8 kΩ
RT1
4.7 kΩ
R11
27 kΩ
t°
D1
UF4005
D3
R1
4.7 Ω
BAV20
4
3
2
C4
0.1 µF
50 V
8T
30 AWG
Q2
L1
22 mH
C1
47 µF
400 V
U2
2N4401
R13
PC817A
MON
U1
TOP244P
2 MΩ
R8
52.7 kΩ
TOP S w it c h -GX
R12
10 kΩ
D
M
R6
470 Ω
C6
CONTROL
0.1 µF
C
C8
0.1 µF
250 VAC
R10
S
F1
C9
6.8 Ω
3.15 A
0.47 µF
Q1
2N4401
C5
47 µF
10 V
R4
470 Ω
L
U3
TL431
R9
12.7 kΩ
85-265 VAC
N
R3
0.5 Ω
1 W
R5
0.6 Ω
1 W
RTN
PI-3404-112502
Figure 1. TOPSwitch Lead Acid Battery Charger.
DI-12
www.powerint.com
November 2002
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