4.2
ELECTRONICS OVERVIEW
Technical Service Manual
4 - 5
430-00587-008 (Rev. 2/05)
The power supply PWA consists of switcher circuitry, voltage regulator circuitry,
and battery charger circuitry. Refer to
Figure 9-24, Power Supply PWA Schematic
, or
Figure 9-26, Power Supply PWA Schematic (XLM
. The power supply PWA includes the following operational modes:
❏
AC (mains) off. Infusion system is not connected to mains voltage and is not operating
❏
AC (mains) off, infusion system on. Infusion system is not connected to mains voltage
and is operating
❏
AC (mains) on. Infusion system is connected to mains voltage and is not operating
❏
AC (mains) on, infusion system on. Infusion system is connected to mains voltage
and is operating
The switcher circuitry converts AC (mains) voltage to an is11 VDC power
through flyback topology.
Fuses F1 and F2, and variable resistors VR1 and VR2 provide protection against
high-line voltage spikes and abnormally high input power demands. Capacitors C1, C2,
C35, C36, C37, and C38, transformer T1, and inductor L1 are designed for attenuating
the conducted emissions. IC U1, resistor R1, inductor L1, and capacitor C3 provide the
DC voltage required for conversion by the switcher. Diodes CR1, CR2, CR4, and CR15;
resistors R22, R68, R73, and R74; capacitors C4, C9, and C34; and transistors Q11 and
Q12 provide the DC voltage for IC U2, the current mode switcher controller IC.
A UL-544 isolation barrier surrounds transistor Q1, transformer T2, IC U2, and associated
passive components to minimize radiated EMI. Optocoupler U3 is part of the main
regulation loop that provides the UL-544 isolation barrier.
IC U2 oscillates at approximately 40 kHz, a frequency dictated by the values of resistor
R4 and capacitor C5. U2 controls the duty cycle of transistor switch Q1 through resistors
R5 and R6, and diode CR16. Resistor R9 provides the current sense and resistor R8 and
capacitor C7 filter the ramp voltage across R9 and feed it back to IC U2.
U2 configuration allows DC voltage at pin 9 (ERR+) to equal the peak voltage across resistor
R9. This DC voltage controls the delivered power through transformer T2 to regulate the
output voltage. Voltage at U2 pin 9 is limited to +1.25 VDC so that peak current through
transistor Q1 is limited to 1.25 VDC divided by the value of resistor R9.
Resistors R61 and R72, diode CR5, and capacitor C6 provide transformer T2 winding short
protection by applying the higher voltage across resistor R9 to the U2 inhibit input. C6
and the input impedance at U2-4 apply the low hiccup frequency to protect transistor Q1.
Diode CR3 and the clamp winding of transformer T2 provide intermediate energy transfer
to capacitor C3 and limit the peak voltage across transistor Q1.
220 V
220 V
Summary of Contents for LifeCare XL Series
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