Hospira LifeCare XL Series, Техническое и сервисное руководство

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SECTION 4 THEORY OF OPERATION
430-00587-008 (Rev. 2/05) 4 - 12 Plum XL Series
4.2.5.4
EL PANEL DRIVER CIRCUITRY (XL)
Transistor Q1 and transformer T1 windings 1-3 (primary) and 4-2 (feedback) constitute
the main oscillator positive feedback. The T1 output winding (5, 8) provides a large-turn
ratio (to T1 primary winding) to boost the output to 300 volts peak-to-peak (Vpp). The
capacitance of EL panel EL1 and the inductance of the T1 output winding dictates the
oscillation frequency of 300 Hz to 500 Hz. As the capacitance of EL1 decreases because
of aging, the frequency increases to maintain a constant brightness.
A control loop consisting of diode CR1; capacitors C13 and C10; resistors R13, R4, R3,
and R6; IC U10B; and transistor Q2 maintains a constant output amplitude by rectifying
the output and comparing it to the ELON signal.
4.2.5.5
LED BACKLIGHT PANEL AND DRIVER (XLM)
The display backlight panel is an array of 60 LEDs arranged as parallel elements of two
series LEDs. The required drive voltage of the panel equals two LED voltage drops of
approximately 4.2 VDC. The actual forward voltage changes with temperature and varies
from panel to panel. Driving the panel with a constant current compensates for varying
voltage requirements.
The XLM backlight panel requires approximately 200 mA for optimum brightness. The
current is controlled utilizing a current mode switching technique enabling high efficiency
operation with a wide power supply range of 7 to 11 volts. The signal VMOT is the supply
voltage for the backlight constant current regulator.
Current through U5, LED panel, is regulated by Q3 operation until the voltage across
current sensing resistors R14, R23, and R24 exceeds a reference voltage of approximately
96 mV. The voltage drop is filtered by R13 and C7 and then compared to the turn-off
threshold determined by the voltage divider R11 and R12. Comparator U3, pin 1 drives
low when the current through R14, R23, and R24 exceeds the turn-off threshold,
discharging C4. U1 senses the quick discharge of C1 and then turns off Q1.
Q1 remains off while C4 charges via resistor R9. Q3 turns on when the the charge on C4
exceeds the input voltage high threshold of U3, pin 2.
4.2.5.6
RUN INDICATOR CIRCUITRY
LEDRUN, when active, turns LED1 on. IC U10A (Q8 XLM) functions as a constant current
source to LED1 by maintaining constant voltage across resistor R20. The voltage is
approxi3.33 VDC.
4.2.5.7
LINE POWER INDICATOR CIRCUITRY
HKDC is active when the infusion system is operating on AC (mains), and turns on the
line power indicator, LED2. HKDC brings transistor Q4 base voltage to VDIG + Vf through
R15 (Vf equals forward voltage of diode CR1). This base voltage change causes Q4 to
conduct and the current through LED2 equals approximately VDIG divided by the value
of resistor R14.