Operation; Charging Indication; Charge Control - Nokia 9000i Service Manual

RAE/RAK–1N
Accessories

Operation

The device has a dc plug input connector for the ACP–3 charger and
4–pin output connector for an extra battery. Recommended charging
temperature is between 0 ... 45 degrees centigrade. Charge control of the
spare battery is done with a constant voltage controller and dissipative
transistor located in a desktop charger PCB.

Charging indication

Charge is indicated with two LEDs, red and green. They both shed their
light into same mechanical light guide.
Red LED indicates that the battery is not full. This color is shown to user
until current to battery decreases under 65mA.
Green LED indicates that the battery is full but charging of the Lithium
battery continues after green indication to ensure the maximum capacity.
Charging is stopped completely after current to battery decreases below
30mA. Green LED stays visible until battery or charger is removed.
When battery is disconnected and charger is connected, LEDs are off.
When charger is disconnected and battery is connected, LEDs are off.
Battery is not discharged so there is no harm in leaving the battery to
desktop charger for long periods. For example during trips it is a benefit to
carry both spare battery and desktop charger together in small space.
When full battery is reconnected to desktop charger, LED color is first red
and after couple of seconds it turns green. Red color is shown because
charge is started again and correct indication is given only after measured
current value settles down.

Charge Control

Charge current for the battery is supplied through a series pass transistor
in desktop charger. This transistor is fully on when voltage of the battery
is under maximum value: 8.4V or 8.2V, depending on battery chemistry.
During this condition charger is supplying a constant current to the battery.
After voltage rises to maximum value, pass transistor controller IC: N115
limits the voltage so that current to battery begins to decrease. This is the
same action as in linear regulators.
Energy equal to voltage difference over pass transistor times current
through it transforms to heat. This requires big PCB area to dissipate the
heat. Current begins to fall rapidly after highest battery voltage is reached
so heat load comes in intensive transient. Large copper area in PCB is
required to absorb the peak heat energy. Some energy losses are also
transformed to heat in diode and current measuring resistor after pass
transistor.
Battery voltage feedback to controller is taken from battery terminal so
that there is no voltage drops of series elements. Current to battery is
measured by instrumentation amplifier which outputs absolute voltage
proportional to voltage difference of its inputs.
Page 10
After Sales
Technical Documentation
Original, 08/96