Ac Input; Power Supply Pcb Theory Of Operation - Mallinckrodt NELLCOR NPB-195 Service Manual

11.5 AC INPUT

11.6 POWER SUPPLY PCB THEORY OF OPERATION

The Display module includes the Membrane Panel and the LCD Display. The
Membrane panel contains enunciators and push buttons, allowing the user to
access information and to select various available parameters. The LCD Display
PCB contains the LCD that presents the patient data.
Power
Entry
Fuses
Module
Battery
Alarm Speaker
Serial port
Figure 11-2: NPB-195 Functional Block Diagram
A selector switch on the back of the NPB-195 allows the user to connect the
monitor to AC power ranging from 100 VAC to 240 VAC. The switch has two
positions, one for 100 VAC through 120 VAC and one for 210 VAC through 240
VAC. Verify that the switch selection matches the AC power at your location
before plugging the monitor into an AC outlet.
AC power enters the NPB-195 through the Power Entry Module (PEM). A 0.5-
amp fuse is placed in both the "Hot" and "Neutral" lines. These user accessible
fuses are located in a fuse drawer, which is part of the PEM on the back of the
instrument.
The NPB-195 uses an unregulated linear power supply. This power supply
provides the DC power needed to charge the battery, run the cooling fan and to
power the User Interface PCB (UIF). Electro Static Discharge (ESD) protection
is also provided by the power supply.
AC power from the PEM is passed through a step-down transformer, T2, which
has two primary and two secondary windings. If switch SW1 on the back of the
monitor is in the 120 VAC position, the primary windings are in parallel. The
primary windings are in series if SW1 is in the 240 VAC position.
Each secondary winding is fused with a 2.0 amp fuse (F1 and F2). If a short
circuit should occur in the DC circuitry, these fuses prevent the transformer from
overheating. The output of the transformer varies, depending on load and input.
Voltage measured between the outlet of a secondary winding and ground can be
from 6 to 20 VAC. C6 and C8 filter high frequency noise from the AC line and
from the UIF PCB before passing through the bridge rectifier.
Section 11: Technical Supplement
Power Supply
Battery DC
Charger Supply
80196
ROM
CPU
RAM
UIF PCB
Membrane
Panel
LCD Display
RTC
MC68331
CPU
System RAM
32K
Flash ROM
64K
SpO Module
2 Patient
Connection
11-3