Epson PX-8 Technical Manual page 28

REV.-A
2.2 Power Supply
This computer operates with a rechargeable Ni-Cd battery and is provided with features for mini-
mizing power consumption and controlling battery charge. The power supply is summarized in
the following:
• Batteries: Two batteries; main and auxiliary, are used.
Main battery ....................... Supplies a DC voltage of 4.SV and has a capacity of 1100 mAH. It
can power all the computer circuits; backing up the commercial as
AC power when not used or unavailable. It also supplies power to
the attached option units.
Auxiliary battery ................. Also supplies the DC 4.SV power. It has a capacity of 90 mAH and
backs up the main battery when in a low voltage (discharged) con-
dition.
• Charging circuit: Supplies charging current to the main and auxiliary battery when an AC adap-
tor is connected. This circuit, which operates in either of two modes; normal and tricle (low
current) charges, under the control of a sub-CPU 750S, controls the charging current.
• Voltage detection circuit: Monitors the voltage of the main battery using an internal AD con-
verter. The result is processed by the sub-CPU 750S to cause the circuit to provide two func-
tions. One is low voltage detection which allows the computer, if it is operating, to display a
warning message "CHARGE BATTERY" on the LCD screen, when the battery power (i.e., vol-
tage) falls below a certain level. In addition, this function causes the computer to stop at an ap-
propriate point in the operation in progress. The other function determines the normal charge
restart timing; causing a switch from tricle to normal charge when AC adapter is connected.
• Backup circuit: Supplies the power required to maintain data in the RAMs when the power
switch is off or the computer is not connected to the AC power line. It also serves to normally
operate the circuits which monitor the battery voltage and detect whether power is on.
• ±
SV regulator: This voltage regulator supplies DC voltages of
±
SV required for RS-232C
operations. The voltages are generated from the battery voltage (VB) only when the RS-232C
or serial interface is used.
• -15V regulator: Supplies a -15V DC voltage used for LCD display control. This voltage is gen-
erated from the battery voltage (VB) as long as power is on.
• 5V regulator: Supplies a +5V DC voltage used for the PROM capsule. This voltage is generated
from the battery voltage (VB) only when the PROM is accessed. The regulator is provided in
order to prevent a transient due to PROM access from directly affecting the VB line.
2-4