Mallinckrodt NELLCOR NPB-4000 Service Manual page 183

15.2.1 Overview
15.2.2 Flyback Principles
The AC (mains) power supply accepts 90 to 264 volts RMS at 47 to 63 Hz and
provides 18 volts DC at a maximum of 2 amps into the battery charger circuit.
The 18 volts DC overrides any supplied external DC (10-16 volts DC) and
becomes the dominant source to the charger when both external AC and DC are
present.
Figure 15-3: General Flyback Circuit Concept
See Figure 15-3. In a general flyback circuit, energy is stored in an inductor and
transferred to a load during switching cycles. In the first part of the cycle, the
switch is closed, the input voltage is applied to the inductor, and current builds
linearly. When the switch opens, the voltage at point A (which was grounded)
"flies back" up until it hits the output diode. The energy stored in the inductor
now depletes into the load.
In the NPB-4000/C power supply, the inductor is a transformer which provides
both isolation and a step-down function to reduce the output voltage as required.
Figure 15-4: AC Power Supply Block Diagram
See Figure 15-4. The NPB-4000/C AC supply runs from a universal AC input
and has EMI filtering, rectification, and capacitive storage to provide 100 to 350
Section 15: Drawings
15-3