Original Publication Date: 1995-Feb-01
Included in the Prior Art Database: 2005-Mar-30
Pantelkis, T: AUTHOR [+1]
Disclosed is a method of maintaining a constant charge current through a battery connected in parallel with an active load, eliminating the effect of variations in load current on battery voltage, so that battery charging can be terminated when the battery voltage reaches a predetermined level.
a method of maintaining a constant charge current
through a battery connected in parallel with an active load,
eliminating the effect of variations in load current on battery
voltage, so that battery charging can be terminated when the battery
voltage reaches a predetermined level.
The IBM* 9075
and 9075e Battery Eliminator/charger provides an
output current which is used for charging the battery within a
PCradio* and for operating the load of other circuits in the PCradio.
The battery is connected parallel to the load provided by these other
circuits, so that it can provide current to drive this load when the
Eliminator/Charger is eliminated. The Battery Eliminator/Charger
uses a voltage signal, named IBATT, generated by the PCradio, which
is proportional to the current flowing into the battery in the
PCradio device. When this signal drops below the current present
value, the output voltage of the Battery Eliminator/Charger is
increased until the desired preset current is obtained. On the other
hand, if the current into the battery exceeds the present preset
value, this output voltage is decreased. In this way, a regulated,
constant current is maintained through the battery during charging,
regardless of changes in current required to operate the load of
other PCradio circuits.
occurs at one of three rates. Initially,
current is applied to the battery until the battery reaches a
threshold voltage. Then the circuit toggles between providing a
lower charge current (185 mA) and a very low charge current (20 mA).
In this way, a trickle charge rate is maintained after the rapid
charge is completed. The threshold voltage for switching from the
rapid charge to the trickle charge is adjusted in response to
temperature changes, compensating for changes in the battery output
voltage with temperature. If the temperature is below 0C or above
44C, the present charge current is set to 20 mA.
The Figure is
a schematic view of the Eliminator/Charger
control circuit. The power supply 10 provides a positive supply
voltage on line 12, relative to a ground level at line 14. Lines 12
and 14 are directly connected to the PCradio unit 16, with the
charging current through a battery within unit 16 being controlled by
varying the power supply output voltage on line 12 in a manner to be
described. Power supply 10 is a switching power supply, having a
control node connected to control line 17, varying the voltage of
output line 12 to maintain the voltage of control line 17 at a
constant value relative to the ground level of line 14. The PCradio
unit 16 provides the IBATT signal on line 18, indicating the level of
current through the battery being charged, and a TIN signal,
indicating the temperature, on line 20.
voltage, VREG, is established from the voltage on
line 20, through voltage regulator 21, at a level of 5 volts, w...