BC Biomedical DA-2006, Service Manual, Page: 144 / 171

B 5
DEFIBRILLATOR CIRCUITRY
The defibrillator circuitry consists of a voltage input measurement section as well as an
analog output section. The input circuitry is used to measure the defibrillator discharge
pulse or the pacemaker pulse. The analog output is used to generate ECG or pacemaker
test waveforms.
The input circuit begins with the power resistors R22 and R25. These are 25
Ω
, 100 W,
Non-Inductive power resistors. These resistors absorb the power from the defibrillator
discharge pulse. Connected to these power resistors is a series of 16 low power resistors
R12 through R19 and R26 through R33. The purpose of these resistors is to divide the
voltage of the defibrillator discharge pulse. U1A is the differential amplifier that is used to
measure the divided voltage. The relays RL1 and RL2 are used along with R1, R2, R3, R6,
R7, and R8 to select the gain for either Low Range Defibrillator input, High Range
Defibrillator Input, or Pacemaker input measurements.
The amplifier U1:C is used to generate the zero offset voltage for the Defibrillator input
circuitry. U1:D is used to generate the self test waveform pulse. R4, R35, and RA1 are
used to properly attenuate the self-test and input signals and provide gain adjustment. The
output of U1:B is then connected to the A/D converter. The signal is offset by ½ of the A/D
reference voltage. This gives an analog range of 0 V = -2048 counts, 1.25V = 0 counts,
and 2.5 V = 2047 counts. The output of U1:A is also connected to the multiplexer U8 to
drive the scope output circuitry.