Welch Allyn PROPAQ CS - Manual (Page 115)

Service Manual Technical overview 111
Power electronics description
The power system circuits are located on the Analog, Digital, and Recharger Boards. The
power system includes the ac mains power adapter. Refer to the figure below.
The power system
• converts ac mains current to dc current (external power adapter)
• recharges the internal battery pack (Recharger Board)
• generates the high voltage drive for the cold cathode backlight in the display
• converts battery power to several regulated and unregulated power supplies for
both isolated and non-isolated electronics (Analog and Digital Boards)
• provides isolated power for RS423 communications (Digital Board)
• controls the activation and deactivation of the power system (Digital Board)
Power is delivered from ac mains to the monitor through a power adapter. The adapter
converts ac to dc current at approximately 15 Volts.
The internal battery continually supplies monitor power and is recharged while the power
adapter is plugged into ac mains and connected to the monitor. The monitor can also be
recharged from any dc power source that meets the monitor’s dc power input
specifications. An accessory cable is available from Welch Allyn to allow connection of
such a power source to the dc power input connector on the monitor’s right side panel.
This cable must be used for monitor calibration.
Thermistors in the battery compartment monitor battery temperature. As battery charging
takes place, battery temperature rises. The recharger output voltage is temperature-
compensated; as battery temperature rises, maximum recharger output voltage
decreases.
Switching power supplies generate power for recharging the battery, for powering the
display, and for other power sources throughout the monitor. Suppression devices
designed into the power system provide EMI suppression. A transformer bridges the
battery power to the isolated electronics. Voltage clamps and fuses provide secondary
protection against loss of regulation in switching supplies on the Analog, Digital, and
Recharger Boards.
Several control lines activate and deactivate the power supplies. These control lines
originate on the Digital Board and are routed to the Recharger Board and Analog Board to
activate the display power supply and the main power supply. The recharger supply is
automatically activated any time an adequate dc power source is connected to the power
input jack on the monitor’s right side panel.