ZOLL M Series Defibrillator Rev R - Manual (Page 133)

M Series Service Manual
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Defibrillator Charging and Discharging
The defibrillator charges and discharges high voltage capacitor energy. A user can initiate a charge in three ways by 1)
pressing the charge button on the front panel; or (2) pressing the charge button on the paddles; or (3) configuring unit
to charge automatically when it detects a shockable rhythm following an ECG analysis. To initiate a discharge, a user
depresses both shock buttons on the paddles or depresses a single shock button on the front panel.
The defibrillator circuit charges the high voltage capacitor to the energy level the user specifies.This circuit also
provides feedback to the main system board on the high voltage capacitor's voltage level and discharges the high
voltage capacitor energy through paddles or the universal cable. The defibrillator portion of the high voltage circuitry
is active only when the front panel selector switch is set to DEFIB.
Charging The charging process starts when the Main System Board detects a charge request. The defibrillator circuits begin
charging the high voltage capacitor to the target voltage or energy that the user selects on the front panel display. The
Main System Board continuously monitors the capacitor voltage signal to ensure that the high voltage capacitor
charges at the proper rate. When the target voltage is reached, the Main System Board initiates a continuous beeper
tone to indicate that defibrillator is ready to discharge. The target energy level displays on the display screen.
The defibrillator holds the energy for 60 seconds for manual units and 15 seconds for AED units, refreshing the energy
level as necessary. An intermittent beep tone sounds during the last ten seconds (five seconds for AED unit) of the hold
period. After the 60 second period, if the defibrillator has not been discharged, the energy is dissipated into the internal
discharge resistor by closing the safety relay (XSAFREL). The unit discharges internally and displays a warning
message if it is not functioning properly.
Unlike previous ZOLL designs that isolated the patient from defib circuitry via an electromechanical patient relay, the
M Series utilizes a bank of silicon-controlled rectifiers (SCRs). As the defibrillator capacitor is charged, the voltage is
monitored via R1 - R4, which drive differential amplifiers referred to the system ground. These resistor dividers split
the capacitor voltage more or less equally above and below ground in order that the positive capacitor terminal is
approximately 2500 volts above ground, and the negative capacitor terminal is approximately 2500 volts below ground
(at 360J setting). The voltage at the patient electrodes is set by the divider RN1 and RN2. These networks are each 5X
25 M (125 M total) whose total resistance is specified to be 125 M +\- 1%. As a result, the patient is nominally at
ground and the hot switch bank is split into a ‘positive’ side and a ‘negative’ side.