16 W, Universal Input, Lead Acid
85 – 265 VAC
13.55 V at 25 °C
Lowest cost and low component count solution
Universal input voltage replaces the need for multiple linear
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
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 TOP244PN
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
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.
For Battery detection and monitoring, R11, R12 and Q2 reduce the
output voltage to approximately 8 V when a 5 V signal is applied to
R12. This allows the Battery voltage to be measured, giving the
state of charge.
1 A, 1000 V
85 - 265
TOPSwitch Lead Acid Battery Charger.