Electricity: battery or capacitor charging or discharging – Battery or cell discharging – With charging
Reexamination Certificate
1999-04-20
2001-07-24
Riley, Shawn (Department: 2838)
Electricity: battery or capacitor charging or discharging
Battery or cell discharging
With charging
C307S066000
Reexamination Certificate
active
06265848
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a battery device (hereinafter, referred to as “battery pack”) including a circuit required to be monitored for a battery state such as a voltage or a charge/discharge current, a battery state monitoring circuit for monitoring the circuit, an external connection terminal for connection to a device outside of the battery device, a switch element, a secondary battery and a sense resistor in a battery pack for a secondary battery.
As a conventional battery state monitoring circuit, there has been known a device shown in a circuit block diagram of FIG.
2
. For example, Japanese Patent Application Laid-open No. Hei 9-312172, entitled “Battery pack, charger and charging system as well as charging method”, discloses a structure of this type. This is directed to a battery pack which is commonly called a “smart battery system” or the like. That is, this is a battery pack
100
a
having a function of monitoring a voltage and charge/discharge current of the secondary battery by use of a microcomputer
5
a,
and communicating with a load such as a charger
17
or a computer through terminals
101
,
102
.
Employing the battery pack
100
a
thus structured, it is possible to recognize a battery state by communication with the charger
17
, the microcomputer within a personal computer, a load
16
or the like. The use of this information allows an indication of the residual amount of the battery, a suspension of battery charge, etc., to be conducted accurately. In the case where a lithium ion battery is used as a secondary battery, since a self-protecting action is not provided, unlike that of a nickel cadmium battery, an over-charge protecting circuit is required. That is, the lithium ion battery is provided with a circuit for detection of a battery voltage and a switch element for suspending a charging operation from the outside.
In the battery pack
100
a
thus structured, a microcomputer
5
a
is used. The battery pack
100
a
is also equipped with an amplifier
3
a
for monitoring a battery voltage and a sense resistor
10
and an amplifier
3
b
for monitoring a charge/discharge current. To the microcomputer
5
a
is supplied electric signals from a battery voltage monitor circuit
20
a
and amplifiers
3
a
,
3
b
. Since the microcomputer
5
a
has a calculating function and an A/D converter so that it can calculate the voltage and the capacity of the secondary batteries
6
to
8
from the above-described signals, it can monitor a battery state. This makes it possible for the microcomputer
5
a
to control the on/off state of the switch elements
11
a
and
11
b,
and therefore the microcomputer
5
a
provides safety with respect to over-charging of the battery pack in which a lithium ion battery is used.
It is necessary for a constant voltage to be provided as a power supply of the microcomputer
5
a
which is a structurally important part. For example, a voltage of 3.3 V or 5.0 V is a normal value. If the supply voltage applied to the microcomputer
5
a
is unstable, the detection accuracy of the battery voltage, etc., are degraded. In the worst case, there generally occurs a phenomenon called “runaway” of the microcomputer
5
a
. This creates an environment in which the microcomputer
5
a
is not controlled at all, with the result that the safety of the battery pack
100
a
is not assured at all. In addition, it is desirable for a constant voltage to be applied to the battery voltage monitoring circuit
20
a
and the amplifiers
3
a
,
3
b
for their safe operation.
Because the power supply for the battery state monitoring circuit
18
a
within the battery pack
100
a
is made up of the secondary batteries
6
to
8
, the voltage is varied according to the load state. In the case where the battery pack
100
a
is discharged to the load, the supply voltage becomes low, whereas in the case where the battery pack
100
a
is charged, the supply voltage becomes high. In order to apply a constant voltage to the microcomputer
5
a
and the amplifier
3
a
,
3
b
equipped within the battery pack
100
a,
a voltage regulator is disposed within the battery pack. The voltage regulator serves to maintain a constant output voltage constant even if the supply voltage is varied.
SUMMARY OF THE INVENTION
However, even if the voltage regulator is disposed in this manner, the battery voltage as the power supply becomes low if the discharging continues. As the supply voltage of the voltage regulator becomes lower, the output voltage naturally becomes lower. In this state, a supply voltage required for stable operation of the microcomputer cannot be applied. Thus, there is a problem in that when the supply voltage to the microcomputer becomes low, runaway of the microcomputer may occur, thereby rendering the apparatus unable to monitor the battery state.
FIG. 4
is a diagram for explaining the operation described above. In the figure, the abscissa represents time whereas the ordinate represents voltage, and the battery voltage and the output voltage of the voltage regulator (supply voltage of the microcomputer) are shown. During a time period from time 0 to time ta, a current is supplied to a load from a battery pack, and the battery voltage drops as time elapses. At time ta, the battery voltage becomes equal to the output voltage of the voltage regulator.
After time ta, the output voltage of the voltage regulator becomes lower than a predetermined value. Although
FIG. 4
shows that the output voltage of the voltage regulator is identical with the battery voltage after the time ta, this is to simplify the description. In fact, the output voltage becomes lower than the battery voltage. At time tb, the supply of current from the battery pack to the load is suspended, and a charger is connected to the battery pack. With the charger being connected to the battery pack, the battery voltage starts to rise, and then becomes identical with the output voltage set by the voltage regulator at a time period tc. After the time period tc, the output voltage of the voltage regulator becomes constant.
In the example of
FIG. 4
, because the output voltage of the voltage regulator, that is, the supply voltage of the microcomputer, drops during the period of time from time ta to time tc, stable operation of the microcomputer is not assured, and the battery state cannot be accurately monitored.
This problem arises even in actual use. The operation of the microcomputer becomes unstable a period of time from that when the battery voltage becomes lower, with the load being connected to the battery pack, and the output voltage value of the voltage regulator is reduced to the battery supply voltage or lower; and the microcomputer stably operates when the battery voltage rises to the supply voltage or higher, where the microcomputer stably operates with the charger being connected to the battery pack. The safety of the battery pack during the period of time when the battery power is reduced below a sufficient level is not assured at all.
In view of the above, in order to solve the above-mentioned problems inherent in the prior art, an object of the present invention is to enable runaway of a microcomputer to be prevented by supplying a constant voltage of a sufficient level to the microcomputer so that the battery state can be monitored in a wide range, as well as the safety of a battery pack is enhanced.
In order to solve the above problems, according to the present invention, in a battery state monitoring circuit including an internal voltage regulator, a power supply of the voltage regulator is selected as the higher voltage of a secondary battery and an external charger. Also, when the output voltage of the voltage regulator becomes lower, a voltage detecting circuit for sending a signal to the microcomputer is further provided.
In a battery state monitoring circuit having the internal voltage regulator, the power supply of the voltage regulator is a voltage provided by a circuit that selects a higher voltage of either a battery or a charger. Also, when the
Adams & Wilks
Riley Shawn
Seiko Instruments Inc.
Toatley Gregory J.
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