FUNCTIONS OF THE CIRCUITS IN THE DEFIBRILLATOR
You have just learned how to pin point malfunctions in terms of precise
voltages/signals in the ECG monitor. The following paragraphs discuss how to pin point
malfunctions in terms of precise voltages/signals in the defibrillator.
a. Functions of the Circuits in the AC Power Supply. The purpose of this
circuit is to bypass the battery completely as soon as the unit is plugged into an ac outlet.
(1) The output from this power supply allows operation of the defibrillator while
the battery is being charged. A transformer, with two identical primaries, makes the supply
switchable from 120v to 24Ov, 50/60Hz, line.
(2) The 17v secondary is rectified by a full-wave bridge (CR4) and is filtered
by C1, C2, and C3.
(3) The 24vdc output supplies the battery charger, and the regulating
transistor Q1. The output of Q1 is regulated by voltage reference CR1 (12v zener diode),
which presents any error voltage to the base of Q3.
(4) If the output voltage deviates from the nominal value (12.6v 5 percent),
this transistor alters the drive current at the base of Q2. Q2 will, in turn, control the drive
current to the base of Q1 until the nominal value is reached. Capacitors C7 and C5
improve the transient response of the supply. C5 and C6 prevent oscillation under certain
(5) The regulated output closes relay K1 removing the battery entirely from the
load, although it is still kept under normal charging conditions. Fuse Fl, located on the
supply's PC board, protects both the battery and the supply from overloads.
Before the unit is plugged into any outlet, verify the line voltage. If it is
different from the one shown at the line voltage selector switch at the rear
of the unit, set to correct value.
(6) The line fuse in the primary circuit of the transformer has to be of the
recommended value for that particular line voltage:
2 amp for 110v--126v, 50/60Hz line.
1 amp for 210v--240v, 50/60Hz line.
Failure to comply with the above may result in severe damage to the unit and
may pose a fire hazard.