SECTION 4 THEORY OF OPERATION
430-00587-008 (Rev. 2/05)
4 - 6
Plum XL Series
At AC (mains) power-up, capacitor C12 provides delayed timing to permit the voltage
potential at U2-14 (Vcc) to reach its minimum level. Diode CR11, and capacitors C18, C23,
and C24 rectify the transformer T2 voltage to create the main DC voltage source for the
infusion system. Diode CR10, resistor R23, IC U4, and capacitor C19 constitute a
sec12 VDC control loop for protection in case of primary loop failure. Diode CR12
and capacitor C25 create a feed-forward converted negative voltage across capacitor C25
to switch transistor Q9 on through resistor R57 and diode CR14. The Q9 output,
housekeeping DC (HKDC), provides the necessary voltage to power both the main
regulation loop and the charger circuitry. HKDC is at ground level when AC (mains) is off
and diode CR14 inhibits unnecessary battery power drain. Resistors R58 through R60,
capacitors C30 through C32, and IC U9 filter HKDC and create a 2.5 VDC reference
voltage (F2.5V). Both HKDC and F2.5V are at ground level when AC (mains) is off.
IC U8B, with resistors R7, R21, R39, R43 through R45, capacitor C27, and IC U3 constitute
the main loop control. Transistor Q7, resistor R42, and diode CR9 eliminate latch-up at
AC (mains) power-up by enabling voltage regulation only after +BUSS r9 VDC.
VMOT voltage regulator circuitry (U8A, Q5, and Q4 and associated passive
components) is at 9.35 VDC when AC (mains) is on.
Transistor Q2 remains forward-biased by HKDC through diode CR9 and resistors R11 and
R12. While transistor Q2 remains on, transistor Q3 is disabled to inhibit POWERHOLD
and SPSTIN from affecting the voltage regulator circuitry.
When AC (mains) is off, transistor Q2 is disabled. If battery operation is required, transistor
Q4 is turned on momentarily by the SPSTIN signal and permanently by POWERHOLD
through transistor Q3. Since Q2 is off, transistor Q4 switches the battery voltage through
the VMOT circuitry to supply voltage to the necessary circuits, including the +5 VDC
regulator U5. IC U5, the +5 VDC low-drop voltage regulator, powers most of the digital
circuits in the infusion system.
The primary part of the battery charger is the constant current source,
comprised of transistors Q6 and Q8, IC U6B, resistor R33, and associated
passive devices. Transistor Q6 is the current-carrying device, and resistor R33
is the sense resistor. When AC (mains) is off, transistor Q8 is off and transistor
Q6 is on.
The battery is charged by two current levels and trickle current (resistor R20). Current
level is achieved by controlling the voltage at U6-6. IC U7A, transistor Q10, and resistors
R31, R32, R34, R62, and R63 control the voltage at U6-6, and hence, the current level.
The BAT2 signal is high (not logic level) when a short is introduced at the battery connector
J26 pins 3 and 4, which implies that battery type 2 is connected to connector J26. In this
case, the battery charge current is low since transistor Q10 is on.
IC U7A also serves as an overpower protection for transistor Q6. When the voltage across
Q6 generates more than 2.5V at U7-4, the charge current switches to low.
220 V
220 V
Summary of Contents for LifeCare XL Series
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