Supply Current Monitor; Charge Switches; Front Slot Switch; Rear Slot Switch - Ericsson EF738 Service Manual

Supply Current Monitor

The current distributed from the external power source to the front or rear slot
passes through the Supply Current Monitor. The CPU reads the output from the
Supply Current Monitor is order to establish whether charging or charging com-
pleted is in effect as follows:
>200mA: Charging
<200mA: Charging completed

Charge Switches

The current from the external power source to the two slots can independently be
switched On/Off by two separate CPU outputs.

Front Slot Switch

This CPU controlled switch is normally On except when the spare battery is being
charged.

Rear Slot Switch

The rear slot charging switch is controlled by the second CPU output, which will
allow charging of the spare battery only if the phone battery is fully charged or if no
phone is inserted in the front slot. This switch goes Off for a short while once every
other second for voltage reading purposes.

Voltage Monitors

The CPU controls the Voltage Monitors to enable reading of the battery voltages.

Front Slot Monitor

If the CPU input of the Front Slot Voltage Monitor suddenly detects a voltage at
DCIO when the corresponding charge switch is Off, this means that the voltage is
coming from the battery, i.e. a phone has been inserted into the slot. This will be
detected regardless of whether the phone is turned On or Off. If Off when inserted,
the auto-turn-on mode will turn it On.
However, if the phone is removed during charging, e.g. when a call is received, this
will not be detected as this input still will read a voltage, now coming from the
external power source. (See Phone On/Off Status on next page)

Rear Slot Monitor

The Rear Slot Voltage Monitor detects whether the spare battery requires charging.
During the charging the current is switched off for a short while every other second
in order to read the battery voltage and in this way establish whether the battery is
fully charged or not. The CPU is in this way also informed if the battery is removed
during the charging process.
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