Hospira LifeCare XL Series, Technical & Service Manual

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SECTION 4 THEORY OF OPERATION
430-00587-008 (Rev. 2/05) 4 - 4 Plum XL Series
4.2.1.3
BATTERY CHARGER CIRCUITRY
The primary function of the battery charger circuitry is to charge the battery.
The main component of the battery charger circuitry is a constant current source
comprised of transistors Q6 and Q8, IC U6B, resistor R33, and associated
passive devices. Q6 is the current carrying device and R33 is the sense resistor.
When AC (mains) is off, Q8 is off and Q6 is on.
The battery is charged by two current levels and trickle current (R20). Charge current
control is achieved by controlling the voltage at U6-6 by the signals LOCHG (low charge),
CHRG_OFF (charge off), and BAT2 (battery 2). The BAT2 signal is active when a short is
introduced at battery connector J26-3 and -4 (an active BAT2 signal implies battery type
2 is connected to connector J26). In this case, the charge current is lower since Q10 is on.
Table 4-1, Battery Charge Current States , lists the charge current state as a function of
the control signals.
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Note: Table 4-1 applies to all 115 VAC and 220 VAC infusion systems.
IC U7A also offers overpower protection for transistor Q6. When the voltage across Q6
generates more than +2.5 VDC at U7-4, the charge current switches to low.
The LOCHG_REQ (low charge request) signal alerts the MCU PWA of the battery voltage
level. LOCHG_REQ is generated by ICs U6A, U7B, U7C, U7D, and associated passive
components.
IC U6A, resistors R24 through R28, and capacitor C20 constitute a differential amplifier
that monitors the battery voltage as the battery is being charged. The output of the
differential amplifier is compared to a previously determined level by voltage comparator
U7C. U7C generates the LOCHG_REQ signal. The voltage level depends on whether U7-13
or -1 is low or, alternately, whether battery one or battery two is connected.
Table 4-1. Battery Charge Current States
LOCHG Signal CHRG_OFF Signal J26-3 to J26-4 Approximate Current
Low Low Short 0.8 A
Low Low Open 1.2 A
High Low Short 0.16 A
High Low Open 0.25 A
Don't care High Don't care Trickle = (11-Vbat)/475
115 V