Theory of Operation Power System Overview
8-10 PageWriter TC 70 Cardiograph Service Manual
Power System Overview
The PageWriter TC70 cardiograph power system consists of:
One 80-watt AC/DC medical grade power module
Two 11.1 volt, 7.2amp-hour lithium ion rechargeable batteries
Battery charging circuitry, various voltage regulators, and logic circuitry on the main
board
The PageWriter TC70 cardiograph is designed to run on AC power or battery. The main board
contains a battery charging chip that controls battery charging. The main board has an A/D
converter that monitors the voltage of the power supply, and a smart battery controller (part of
the charging chip) that monitors the battery charging status.
The major power draws within the PageWriter TC70 cardiograph are the LCD display
backlights, which can draw up to 19 watts, and the thermal printer, which can draw
approximately 35 watts. Provisions have been incorporated into the PageWriter TC70
cardiograph that allow the user to adjust the display brightness. To extend battery life, set the
display brightness to the low or medium setting. Also, activate the power save mode (entering
standby) to further extend battery life. The printer control circuitry is current-limited for
normal printing. However, if print demand is too high, the current limiter will not print the
output, resulting in a faded page. For more information on configuring power saving options
on the cardiograph, see Chapter 2 “Configuration” of the PageWriter TC70 Cardiograph
Instructions for Use, available for download from the Philips InCenter site
(
incenter.medical.philips.com).
Battery
The two 11.1V rechargable lithium ion batteries provides power to the PageWriter TC70
cardiograph and can support full cardiograph functionality without AC when properly
charged. Built-in protection circuitry in each pack prevents damage to the battery by
overcharging, over discharging, over current, and over temperature.
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