Epson PX-8 Technical Manual page 40

REV.-A
2.2.2.5 Protection Against Charging Voltage Supply Failure
An overvoltage detection circuit and a reverse-current blocking circuit are provided in order to
protect the batteries and their charging circuits when any abnormal voltage occurs on the output
of the ac adaptor; i.e., the charging voltage. The operations of the circuits are described in the fol-
lowing:
(1) Protection against low voltage
The diode inserted in the charging circuit in series prevents reverse current if the charging vol-
tage falls below the battery voltage.
(2) Protection against overvoltage
If the voltage at the cathode of the zener diode (VCH) rises to +7.5V or above, the zener diode
breaks down, and protect the overvoltage condition for VB+ line.
VCH
Charge mode control
ZD4
R17 11<
To port 61 of
~---'--~N\r-----tt------n 4-bit sub CPU 7508
Fig. 2-10 Battery Protection Circuit
2-16