(3) Through the action of the zener diode CR41, the total voltage can never
exceed 200v. This voltage, through R65, charges up C33 until the trigger device Q7
breaks down providing a pulse to the torroid T3.
(4) A pulse appears on the secondary side of the torroid and through diode
CR39 and current limiting resistor R50 and activates the dump SCR.
(5) The time constant is such that this occurs only if the high voltage lasts
beyond 40 milliseconds (adjusted by the potentiometer). This is longer than the primary
dump pulse for any energy level and any normal load condition. However, this safety
dump will terminate the output pulse while the discharge is still substantially trapezoidal.
m. Functions of the Circuits in the Selected Energy Protection.
(1) Another dump circuit is provided. It is referred to as selected energy
protection or a safety discharge circuit. This circuit is necessary in order to assure that
anytime the machine is placed in a CHARGE mode, and the operator changes the energy
select switch to another position, without first delivering the energy to the paddles, the
entire energy will be dumped internally. Furthermore, the charging system will be shut
down by providing a pulse to Q8 in the automatic off circuit just as though the machine had
(2) This now requires a restart with either panel or paddle charge button, thus
preventing the wrong energy (due to incorrect starting pulse voltage) from being delivered
to the paddles. This is accomplished with yet another section of SW5. Transistor Q6,
through R63, CR38 and CR37 would be capable of placing a high at pin 4 of U11, the
trigger for dump pulses, if it were allowed to conduct. However, SW5 keeps the base of
Q6 at floating ground potential as long as SW5 is in any energy position.
(3) If the switch is moved in any direction, this ground is momentarily
removed. Through R64 the base of Q6 rises and outputs a high to U11 generating dump
(4) The front panel disarm switch SW10 is also connected in this path and
performs the same safety discharge at any time required. An additional section of the
disarm switch also supplies ground signal to Q9 and releases the holding on the power
relay K1 which turns off all charging simultaneously with the safety discharge.
n. Functions of the Circuits in the Additional Defibrillator Components.
R68, C32, R70, and C35 are DV/DT filters for the SCR.
(2) The two high voltage diodes CR42 and CR43 between the two SCR
anodes prevent noise impulses. These impulses may be produced by contact of the
paddles to an external object. This increases the potential across the fire SCR and
prevents an AUTO FIRE mode.