Mallinckrodt NELLCOR NPB-4000, Service Manual

Page: 108 / 219

Section 11: Isolated Front End Functions -- Theory of Operation
11-12
11.10 ISOLATED POWER SUPPLY
The isolated power supply consists of high-current switched driver, U54,
isolation transformer T1, two full-wave rectifiers with dual diodes D11 and D10,
filter capacitors C122 and C127 and three voltage regulators. Regulators U83
and U68
p5 volts and -5 volts for analog circuitry and regulator U69
pr5 volts for digital circuitry on both Front End and SpO
2
boards.
Switched driver U54 is controlled by square wave 100 kHz signals from the CPU
and powered by the main power supply 12 volts regulator.
11.11 SPO
2
BOARD
The SpO
2
board (MP-205) plugs into the main board and uses it for power
supply and isolation. The SpO
2
input signal through D-type panel connector and
Front End connector J101 is fed to the receptacle J100; power, control, and
output signals go to the receptacle J10. Two output signals are asynchronous:
serial link RX and TX. Serial TX controls optocoupler U59, and RX is
controlled by optocoupler U58. Control signal is ECG_SYNC which comes
from the R-wave detector.
11.12 ISOLATION
The isolation barrier is provided by isolation transformer T1, linear optocoupler
U57, and digital optocouplers U59, U58, U55, and U56. Spark gap SG1 is used
to protect isolation components against over-voltage exceeding their limits.