Design Idea DI-12
®
TOPSwitch-GX
16 W, Universal
Input, Lead Acid Battery Charger
Application
Battery Charger
Device
TOP244P
Power Output
16 W
Input Voltage
85-265 VAC
Output Voltage
13.55 V at 25 ˚C
Topology
Flyback
®
Design Highlights
• Lowest cost and low component count solution
• Universal input voltage replaces the need for multiple linear
based designs
• High efficiency: >75%
• Integrated line undervoltage detection (UV) and overvoltage
(OV) power system surge protection
• Constant voltage / constant current (CV/CC) output
• Temperature compensated output voltage
• Monitor input to allow state of charge measurements
TOP244P requires no external heatsink, using the PC board
instead.
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
reduces conducted EMI, allowing the design to meet EN55022B
limits with simple input filtering. Diode D1 and Zener VR1
clamp the leading edge drain voltage spike caused by transformer
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
(Figure 3) to approximate that required by the lead-acid battery.
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,
removing the need for an input MOV. The DIP8 package of the
D1-D4
1N4007V
1 A, 1000 V
C7
1 nF
Y1
VR1
P6KE
200
1
7,8
D2
UG4D
8T
24 AWG
Triple Insulated
5,6
D3
BAV20
L2
3.3
µH
C2
560
µF
35 V
R2
1 kΩ
R1
4.7
Ω
C4
0.1
µF
50 V
U2
PC817A
R8
52.7 kΩ
R6
470
Ω
C8
0.1
µF
Q2
2N4401
R7
11.8 kΩ
RT1
4.7 kΩ
C3
220
µF
35 V
+13.55 V
t°
D1
UF4005
L1
22 mH
2
C1
47
µF
400 V
U1
TOP244P
D
M
CONTROL
C
R11
27 kΩ
4
8T
30 AWG
3
R13
2 MΩ
MON
R12
10 kΩ
TOPSwitch-GX
C6
0.1
µF
250 VAC
F1
3.15 A
L
S
R10
6.8
Ω
C5
47
µF
10 V
Q1
2N4401
R3
0.5
Ω
1W
C9
0.47
µF
R4
470
Ω
R5
0.6
Ω
1W
U3
TL431
85-265 VAC
N
R9
12.7 kΩ
RTN
PI-3404-112502
Figure 1. TOPSwitch Lead Acid Battery Charger.
DI-12
www.powerint.com
November 2002
POWERINT [ POWER INTEGRATIONS, INC. ]
