Physio Control LIFEPAK 9 - Page 151

LIFEPAK 9 shock advisory adapter Service Manual
Microcontroller
Inhibit
The
disruptive
nature
of
a
defibrillator
pulse
requires
that
the
microcontroller
(U17)
be
inactive
during
defibrillation.
The
Microcontroller
Inhibit
circuit
shuts
down
the
Power
Supply,
forcing
the
microcontroller
into
reset
until
defibrillation
is
over.
Two conditions must be met before microcontroller activity can be
inhibited: the CHARGE LED must be illuminated and BOTH discharge
pushbuttons must be pressed simultaneously.
Dual comparator U1 shuts down pulse-width modulator U2 when a
defibrillation pulse occurs. The noninverting input of U1A is controlled
by the CHG LED through resistor divider R2 and R4; the inverting input
of U1A is controlled by both XFER SW lines through resistor divider
R3, Ri, and R6.
UIA and UIB change states when the charge LED illuminates and both
discharge pushbuttons are pressed. Pressing the discharge pushbuttons
(XFER SW) switches R1 and R6 in parallel, presenting +2.1V at the
noninverting input of UIA. Illumination of the CHG LED presents
+2.5V at the inverting input of U1A, forcing the output to ground. UIB
responds to the output of U1A by switching high at pin 7 and shuts down
pulse-width modulator U2. The microcontroller then resets for the
duration of the defibrillator pulse (see Microcontroller Core, page 1-8).
RC network C3 and R5 delay the BATT voltage enough to keep from
activating the microcontroller too soon after a defibrillation pulse.
1-10 All Rights Reserved © November 1994 Physio-Control Corporation