Figure 9-4: Digital Circuitry Block Diagram; Figure 9-5: Power Supply Block Diagram - Mallinckrodt Nellcor N-20 Service Manual

Technical Supplement
9.6.1 Digital Circuitry Block Diagram (Figure 9-4)
Figure 9-4 shows the N-20/N-20P hardware and circuits, which include the CPU and system memory,
the power supply and power control circuitry, user controls, display and ambient light sensors, audio
output, thermal printer (N-20P only) and ambient temperature sensor, and the real-time clock.
Measure
Check Battery
To analog section
9.6.2 Power Supply Block Diagram (Figure 9-5)
Power supply circuitry (Figure 9-5) is located on the auxiliary PCB and consists of four subsections:
1. Four "C" size batteries that provide 4-6 VDC
2. Power control circuitry that senses a press of the Measure button and switches power on
3. Power shutoff circuit that controls power to all circuits except the power control circuit
4. Power supply circuits include a regulated power supply at 5 VDC, unregulated power supplies of
-5 VDC, 10 VDC, and 12 VDC, and a high voltage power supply of 70 VDC.
Disposable
4-6 VDC
batteries
9-4
N-20/N-20P Control buttons
Power supply AUX
& control PCB
Ambient
light sensor
CPU
Main PCB
Memory
&
software
Real-time Ambient
AUX
clock PCB temp. sensor

Figure 9-4: Digital Circuitry Block Diagram

Measure
button
Power
control
circuits
EMI protect,
ESD protect)
AUX PCB

Figure 9-5: Power Supply Block Diagram

Main
PCB
AUX PCB
Display
drivers
Audio beeper
Printer
Main
ON ADV D/D
PCB
AUX PCB
Power
shutoff
Power
circuits
supply
(fuse,
circuits
-5 +10
VDC VDC
SpO2
Analog
section
(main board)
Display
AUX PCB
(N-20 only)
Printer Control button
Main PCB
+5 VDC
Microprocessor
+70 VDC
Display drivers
AUX PCB
Display backlight
+12
VDC