(9) This multiple action described above is another form of safety circuit. By
virtue of the removal of drive on the main invertor for a period of time that it takes for the
SCR current to diminish to a point where the comparator flips back to nonconduction, a
certain hold-off time has been provided to ensure that the SCR current is low enough so
as not to be latched on or hung up.
(10) Another circuit in relatively the same position as the above is the low
battery shut off circuit. If the voltage on pin 3 of U12 falls low enough, the entire unit is
p. Functions of the Circuits in the Synchronizer.
(1) The synchronizer section consists primarily of Q17, Q12, U18, and K3. If
the operator chooses synchronized operation, he activates the front panel synchronizer
switch which turns on Q17. It generates a clock pulse for U18 which provides an output at
pin 1 which turns on transistor Q12.
(2) This action pulls in relay K3 which turns on the sync lamp and latches the
relay. This action creates a high at the sync output by removing the ground lead and now
one of the fire control gates is high, prohibiting the firing of the defibrillator.
(3) However, if the monitor scope outputs the sync signal during this time, the
sync output line returns to a low condition, and the fire control is again enabled, ready for
firing the defibrillator.
(4) The other components in the reset circuit of U18 are necessary in order to
ensure that the U18 chip is always in the off state each time that there is an initial power
up of the machine. Therefore, sync has not been inadvertently selected.
q. Functions of the Circuits in the Selected Energy Display and Charging
(1) Energy selector switch SW5 (isolated section) selects one of eight inputs
(energy levels) for EPROM U32. Oscillator/divider U21 continually select four inputs for
EPROM U32. This allows for four different data codes for each input selected by SW5.
Three of these codes are used to multiplex the three-level indicators U52, U53, and U54.
U21 also provides the signals for blinking (charging) of the energy indicators and the tone
and beeping of the audible charging indicator K4.
(2) U22 decodes the data from U21 to control the multiplexing transistors Q13,
Q14 and Q15. U47 and U48 are the control logic for the energy display and audible
charging indicator. Two additional inputs to U32 are used (1) an error message and (2) a
seven segment test (all on).