Mindray VS-800, Service Manual

Page: 18 / 74

Principles of Operation
2-6
2.2.1.3.6 NURSE CALL connector
2.2.1.3.7 The NURSE CALL connector controls the NURSE CALL signal by using an I/O
port extended by the FPGA.
2.2.2 Power Board
2.2.2.1 General
The power board converts the power input (from AC mains or battery) to different working
voltages for other boards; it also has the function of charging the battery.
2.2.2.2 Principle diagram
According to the design requirements, the power board can be divided into three parts: AC/DC
isolation converter, DC/DC converter and charging circuit, as shown in Figure 2-5.
EMI filter Rectifer & filter
PWM
controller
Current
detection
Start-up
circuit
Rectifer
& filter
16.8
V
Coupler feeckback
& isolation circuit
AC
input
Charging
circuit
Battery
DC/DC
converter
12V
output
DC/DC
converter
3.3V output
Switch circuit
Flyback converter
OVP&OCP
OVP&OCP
OVP&OPP
LDO
circuit
5V output
Figure 5 Operation principle of the power board
2.2.2.3 Principle
After the AC input reaches the power board through the connection board, it flows through the
EMI filter circuit and rectifier and filter circuit. Then it is converted to a DC voltage, which is
further converted to the 16.8V DC voltage by the Flyback converter. The 16.8V DC voltage is
the main input of the DC/DC converter and charging circuit; it is used to charge the lithium
battery or lead-acid battery, and also converted to 12V, 5V and 3.3V DC voltages by
corresponding DC/DC converters and LDO circuit. In case the AC input is unavailable, the
battery can supplies power for the DC/DC converters to get the 12V, 5V and 3.3V DC voltages.
Meanwhile, the 12V, 5V and 3.3V DC outputs are under the control of the switch signal.