Physio Control LIFEPAK 9 - Page 30

LIFEPAK 9 defibrillator/monitor
Charge LED Drive The Charge LED Drive signal from the System microprocessor controls Q 14
when the energy storage capacitor is charging. Transistor Q14 drives the
front panel CHARGE LED and the paddle CHARGE LED. Resistor R128 on
the drain of Q14 limits the current to the Paddle LED. The gate of Q13 is
connected to the Charge Valid signal. When the voltage for the selected
energy level has been reached, Q 13 conducts. Transistor Q14 then clamps
the charge LEDs on continuously.
Interconnect PCB The Interconnect PCB provides electrical connection between the Main PCB
Assembly (803761) and the Power Conversion PCB. It also drives the front panel LEDs and
generates the audible tones.
The LED drive circuitry consists of Q4, QS, Q13, R14, R15, and R11. Static
protection is provided by R9, R21, R22, C6 through C8, and CRI through
CRII.
The Main PCB System microprocessor selects 1 of 8 volume levels by
writing the appropriate binary number (000 for the loudest and 111 for the
softest) on line VOLI, VOL2, and VOL3. These lines are routed to 3-to-8
decoder U1 on the Interconnect PCB. Static protection is provided by R1
through R4, Cl through C3, and CS.
The decoder U1 sets the voltage required for the volume level selected by the
System microprocessor. The decoder output turns on one of the transistors
(Q1 through Q3 or Q7 through Q10) which puts the corresponding resistor in
series with R8. The center tap of the resistor divider is routed to the input of
either U2A or U2B as determined by Q11, Q12, and Q6. The output of U2A
or U2B applies the voltage to the piezoelectric transducer, X1.
The free-running oscillator in the System microprocessor generates the
desired tone frequency. The oscillator generates a square wave, Audio Drive,
which is routed to the gate of O11. If the voltage at the gate of Q11 is low,
Q12 conducts, grounding U2A pin 3. Transistor Q6 then shuts off, applying
the selected voltage to U2B pin 5. If the voltage at the gate of Q11 is high,
Q11 switches on and Q12 switches off, applying the selected voltage to
U2A pin 3. Transistor Q6 then turns on, grounding U2B pin 5. Therefore,
the frequency of the oscillator controls transistors Q11, Q12, and Q6, which
drive the transducer. Op amps U2A and U2B provide buffering and high
current drive to X1.
1-16 All Rights Reserved © August 1993 Physio-Control