Charging controller

A charging controller for charging a secondary battery by a dc source has a consumption current detector detecting a consumption current of a load; a charging current detector detecting a charging current to the secondary battery; a charging voltage detector detecting a charging voltage to the secondary battery, a function-processor to which detection outputs from the consumption current detector, the charging current detector, and the charging voltage detector are provided, respectively, and PA1 a charging control circuit controlling a charging output to the secondary battery, based on calculation results by the function-processor such that driving the load and charging are simultaneously executed within the ratings of the dc source.

BACKGROUND OF THE INVENTION
 1. Cross Reference to Related Application
 This application is one of four related applications, Ser. Nos. 09/566,445
 , 09/566,930, 09/568,720 and 09/569,938.
 2. Field of the Invention
 The present invention relates to a charging controller, and more
 particularly to a charging controller for charging a secondary battery
 used in a portable electronic device, for example.
 3. Description of the Related Art
 Portable electronic devices such as a notebook-sized computer, and so forth
 contain a secondary battery. As to a charging controller for driving a
 unit and charging the secondary battery simultaneously, the following
 techniques have been disclosed.
 According to a first technique, the rating of output power from a dc source
 is designed so as to be not less than the sum of the maximum consumption
 power of a unit and maximum charging power.
 According to a second technique, as described in Japanese Unexamined Patent
 Publication No. 5-137276, only a unit load current is detected, the
 difference between the rated current of a dc source and the unit load
 current is determined, and a charging output is controlled so that the
 charging current is equal to the difference.
 According to a third technique, as described in U.S. Pat. No. 5,723,970, an
 output current from a dc source is detected, and a charging output is
 controlled so that the output current from the dc source is prevented from
 exceeding the rated current.
 Generally, a portable electronic device can be driven by application of
 power which is considerably lower than the maximum consumption power, and
 the time period while the device is required to be driven by application
 of the maximum consumption power is very short. FIG. 5 shows the operation
 conceptual diagram. In FIG. 5, the maximum power required to drive the
 unit is 30 W, and the maximum charging power is 30 W. Accordingly, the
 supply capability of the dc source is 60 W. However, since the power
 required to drive the device is changed with time, a large part of the
 power supply capability of the dc power is surplus.
 For this reason, regarding the above-described first technique of the
 conventional example, it is needed that the power supply capability of the
 dc source is designed so as to be surplus to a unit consumption power
 required under ordinary operation. Thus, there arises the problem that the
 shape and size and the cost of the dc source are increased.
 In the above-described second technique of the conventional example, the
 charging output is controlled so that the rated current of the dc source
 is not exceeded. Therefore, the maximum supply power of the dc source can
 be reduced to the maximum consumption power of the unit. However, since
 the charging current is kept constant, irrespective of the charging
 voltage, the surplus power of the dc source can not effectively be used.
 FIG. 6 illustrates the relation between the charging voltage and the
 charging current, obtained in the second technique of the conventional
 example. The rated power of the dc source is 20V/1.5 A (30 w), the unit
 current draw is 1.2 A, and the charging voltage range is 9.0-13.0V.
 FIG. 7 shows an output power characteristic. According to the second
 technique of the conventional example, the charging current is kept
 constant, irrespective of the charging voltage as described above.
 However, the power available for charging (20 W.times.1.5-20 W
 .times.1.2=6 W) is constant, as shown in FIG. 7. Accordingly, if the
 charging is carried out in this technique, the power supply capability of
 the dc source becomes surplus when the charging voltage is low.
 Accordingly, in the second technique of the conventional example, the power
 supply capability of the dc source can not effectively be used. Thus,
 there arises the problem that the charging time is increased, in spite of
 the power supply capability of the dc source.
 FIG. 8 is a circuit block diagram of a charging controller which employs
 the above described third technique of the conventional example. In FIG.
 8, an output 15 from a dc source 1 is provided to a charging control
 circuit 2 via a dc source output current detection resistor 5 of a
 charging circuit 14, and also provided to a DC-DC converter 6 via a
 rectification element 13. The input 17 of the DC-DC converter 6 is
 connected to the anode of a secondary battery 4 via a rectification
 element 12. The output 18 of the DC-DC converter is connected to a unit
 load 7 of a portable device.
 A voltage developed across the dc source output current detection resistor
 5 is detected by a dc source output current detection circuit 10, and the
 detection signal 21 is provided to a control circuit 2 of the charging
 controller. The output of the charging control circuit 2 is connected to
 the anode of the secondary battery 4 via a charging current detection
 resistor 3. A voltage developed across the charging current detection
 resistor 3 is detected by a charging current detection circuit 8, and the
 detection signal 19 is provided to the charging control circuit 2. A
 charging voltage on the anode side of the secondary battery 4 is detected
 by a charging voltage detection circuit 9, and the detection signal 20 is
 also provided to the charging control circuit 2.
 Next, the operation of the charging circuit 14 shown in FIG. 8 will be
 described. In the case of charging while the unit stops, a voltage
 developed across the charging current detection resistor 3 is detected by
 the charging current detection circuit 8. The charging voltage detection
 circuit 9 detects a charging voltage on the anode side of the secondary
 battery 4. The output 19 from the charging current detection circuit 8 and
 the output 20 from the charging voltage detection circuit 9 are fed back
 to the charging control circuit 2, whereby constant-voltage,
 constant-current charge is carried out.
 When the unit is under operation, a voltage developed across the dc source
 output current detection resistor 5 is detected by a dc source output
 current detection circuit 10, and the detection output 21 is fed back to
 the charging control circuit 2, whereby the charging output is controlled
 so that the output current from the dc source 1 is prevented from
 exceeding a predetermined value.
 With the charging controller shown in FIG. 8, the surplus power determined
 by subtracting a practical unit consumption power from the current supply
 capability of the dc source 1 can be utilized as charging output power,
 without any surplus or shortage. Accordingly, the charging time of the
 secondary battery 4 can be reduced.
 However, it is needed that all of the current required for driving the unit
 and charging is made to flow through the dc source output current
 detection resistor 5 for detecting the output current from the dc source
 1. Therefore, a loss and heat generated in the dc source output current
 detection resistor 5 are increased, the reliability of the circuit is
 reduced, and the current detection accuracy deteriorates, caused by
 effects on the temperature characteristic of the dc source output current
 detection resistor 5. Moreover, it is needed to take heat dissipation
 measures such as attachment of a radiation plate, which causes the problem
 that the shape and size, and the cost of the charging circuit are
 increased.
 SUMMARY OF THE INVENTION
 The present invention can solve the aforementioned problem associated with
 the conventional art and provides a charging controller which can reduce
 maximum charging power and charging time, and can reduce a loss generated
 in the current detection resistor.
 The charging controller for charging a secondary battery from a dc source
 comprises a consumption current detector detecting a consumption current
 of a load, a charging current detector detecting a charging current to the
 secondary battery, a charging voltage detector detecting a charging
 voltage to the secondary battery, a function-processor to which detection
 outputs from the consumption current detector, the charging current
 detector, and the charging voltage detector are provided, respectively,
 and a charging control circuit controlling a charging output to the
 secondary battery, based on the calculation results by the
 function-processor such that driving the load and the charging are
 simultaneously executed within the ratings of the dc source.
 The function-processor may calculate a function of the consumption current,
 based on the detection output from the consumption current detector,
 calculates a function of the charging current based on the detection
 output from the charging current detector, and calculates a function of
 the charging voltage, based on the detection output from the charging
 voltage detector, and calculates the sum of the three calculated functions
 as the output rating of the dc source, and the charging control circuit
 controls the charging output to the secondary battery so that the output
 rating of the dc source, calculated by the function-processor, is
 prevented from exceeding a predetermined value.
 The function-processor may include at least one operational amplifier to
 calculate the function of the consumption current, the function of the
 charging current, and the function of the charging voltage.
 According to the present invention, the load consumption current, the
 charging current to the secondary battery, and the charging voltage to the
 secondary battery are detected, respectively. By controlling the charging
 output to the secondary battery, based on the detection results, by use of
 the function-processor, driving the load and charging the secondary
 battery can be simultaneously carried out within the ratings of the dc
 source, the loss in the resistor for detecting the consumption current can
 be suppressed, and reduction of the reliability of the circuit and the
 current detection accuracy, caused by effects on the temperature
 characteristic of the current detection resistor is eliminated. No heat
 radiation/dissipation measures such as attachment of a heat radiation
 plate or the like are needed. The size and shape and the cost of the
 charging controller can be reduced.
 For the purpose of illustrating the invention, there is shown in the
 drawings several forms which are presently preferred, it being understood,
 however, that the invention is not limited to the precise arrangements and
 instrumentalities shown.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION
 Hereinafter, the preferred embodiments of the present invention are
 explained in detail with reference to the drawings.
 FIG. 1 is a block diagram of an embodiment of the present invention. In
 FIG. 1, parts which are configured differently from the configuration
 shown in FIG. 8 will be described. In this embodiment, a unit consumption
 current detection resistor 25 is provided instead of the dc source output
 current detection circuit 5 shown in FIG. 8, a unit consumption current
 detection resistor 26 is provided instead of the dc source output current
 detection circuit 10, and an operation circuit 11 is provided. To the
 operation circuit 11, a detection output 19 from a charging current
 detection circuit 8, a detection output 20 from a charging voltage
 detection circuit 9, and a detection output 27 from the unit consumption
 current detection circuit 26 are provided. The operation circuit 11, based
 on these detection outputs, calculates the charging power and the output
 power from a dc source 1. The calculation result 22 is provided to a
 charging control circuit 2. The charging control circuit 2 controls a
 charging output to a secondary cell 4 so that the output power from the dc
 source 1 is prevented from exceeding a predetermined value.
 Next, the operation of the charging controller shown in FIG. 1 will be
 described. The charging controller has the configuration in which the
 output 15 of the dc source 1 and the anode 16 of the secondary cell 4 are
 wired OR connected through rectification elements 13 and 12, respectively,
 and the output power from the dc source 1 or the secondary cell 4 is
 converted to a voltage required for a unit load 7 by means of a DC-DC
 converter 6 for operation of the unit.
 The dc source 1 has a function of stabilizing the output at a predetermined
 voltage Vin to output. The rated power is represented by Pinmax. In the
 charging current detection resistor 3, a voltage is developed, which is
 defined as
EQU Rc.cndot.Ic (1)
 in which Rc represents the resistance of the charging current detection
 resistor 3, and Ic a charging current. The charging current detection
 circuit 8 detects the Rc.cndot.Ic, and provides an output corresponding to
 the Rc.cndot.Ic to the operation circuit 11. A charging voltage Vc is
 detected by the charging voltage detection circuit 9, and an output
 corresponding to the charging voltage Vc is provided to the operation
 circuit 11.
 In the unit consumption current detection resistor 25, a voltage is
 developed, which is defined as
EQU Rs.cndot.Is (2)
 in which Rs represents the resistance of the unit consumption current
 detection resistor 25, and Is a unit consumption current Is. The unit
 consumption current detection circuit 26 detects the Rs.cndot.Is, and an
 output 27 corresponding to the Rs.cndot.Is is provided to the operation
 circuit 11.
 The output power Pin of the dc source 1 can be expressed by the following
 equation (3) in which Ps represents the consumption power of the unit, and
 Pc the charging power.
EQU Pin=Ps+Pc (3)
 Here, the Ps and Pc can be expressed as follows, by using the unit
 consumption current Is, a dc source output voltage Vin, the charging
 current Ic, and the charging voltage Vc.
EQU Ps=Is.cndot.Vin (4)
EQU PC=IC.cndot.Vc (5)
 Thus, equation (3) can be expressed as
EQU Pin=Is.cndot.Vin+Ic.cndot.Vc (6)
 The Is represents the unit consumption current which changes successively,
 caused by the operation conditions of the unit. Further, Vc represents a
 voltage at the anode of the secondary cell 4, is stabilized, and is
 gradually increased as the charging of the secondary cell 4 progresses.
 The Vin represents the output voltage from the dc source 1, and hence, can
 be considered to be constant.
 As shown in the above-description, the output power Pin from the dc source
 1 can be kept constant by controlling the charging current Ic,
 correspondingly to the unit consumption current Is and the charging
 voltage Vc. Accordingly, the output rated-power from the dc source 1 can
 be divided for the charging output and driving the electronic unit,
 without any surplus of the power, by controlling so as to satisfy the
 following equation,
EQU Pinmax=Is.cndot.Vin+Ic.cndot.Vc (7),
 in which Pin of equation (6) is replaced by the rated power Pinmax of the
 dc source 1, whatever values the Is and the Vc may have (that is, whatever
 values the consumption current of the unit and the charging voltage may
 have) in the range of
EQU Pinmax&gt;Ps (8)
 As regards equation (6), it is necessary to calculate the product of the
 charging power Ic and the charging voltage Vc. However, generally, it is
 very difficult to realize the cost-reduction and the highly-enhanced
 precision of a multiplication integration circuit for two variables, since
 the circuit scale is large, and the temperature stability is low.
 In the charging circuit 14, the ranges of the charging voltage and the
 charging current are limited by the secondary cell 4. In equation (6), the
 charging voltage and the charging current have an inversely proportional
 relation. The characteristic of the charging voltage versus the charging
 current is depicted by a hyperbola. However, in the practical-use range
 thereof, the charging voltage range is limited, so that the characteristic
 can be approximated with a straight line.
 In this embodiment, the product of the charging voltage and the charging
 current is not calculated. The characteristic of the charging voltage and
 the charging current is approximated by a straight line by use of the
 linear function values of the charging voltage and the charging current.
 That is, pseudo-constant power control is carried out by controlling so
 that
EQU Pinmax=.alpha..cndot.Is+.beta..cndot.Ic+.gamma..cndot.Vc (9)
 holds. In the equation (9), .alpha., .beta., .gamma. and represent
 arbitrary real numbers.
 FIG. 2 shows the charging characteristic in this embodiment, and FIG. 3 the
 output power characteristic of the dc source.
 In FIGS. 2 and 3, the power supply capability of the dc source is 20V/1.5
 A, the unit current draw is 1.2 A, and the charging voltage range is
 9-13.0V. In this case, the power available for charging is
 20.times.1.5-20.times.1.2=6 W.
 As seen in FIG. 2, the power available for charging can be depicted by a
 hyperbola. As seen in FIG. 3, the power available for charging can be
 utilized most effectively in the used charging voltage range, even when
 the characteristic is approximated with a linear function as in this
 embodiment. Further, in contrast to a multiplication circuit for two
 variables, a multiplication circuit for one variable can be realized at
 high precision and stability, and is advantageous in reliability and cost
 reduction.
 The operation circuit 11 executes calculation corresponding to the
 above-described equation (9). Accordingly, the charging current can be
 controlled without any surplus or shortage in the output rated-power of
 the dc source 1 by feeding back the output corresponding to the charging
 current determined according to equation (7), to the charging control
 circuit 2.
 The charging current detection circuit 8, the charging voltage detection
 circuit 9, and the unit consumption current detection circuit 26 each can
 be formed of an operational amplifier circuit.
 FIG. 4 is an operational conceptual diagram of an embodiment of the present
 invention. As described above, charging and driving the unit can be
 simultaneously carried out by executing the calculation equivalent to
 equation (9) in the operation circuit 11 for charging control, on
 condition that the output rated-power of the dc source 1 is not less than
 the maximum consumption power of the unit, as shown in FIG. 4.
 Accordingly, in contrast to the method of designing so that the output
 power rating of the dc source 1 is not less than the sum of the maximum
 consumption power of the unit and maximum charging power, as stated in
 reference to the first technique of the conventional example, the charging
 maximum power can be reduced. Therefore, the shape and size, the weight,
 and the cost of the dc source 1 can be considerably reduced.
 Further, according to the second technique of the conventional example,
 even when the charging voltage is low, the charging is carried out by
 application of the charging current of which the value is obtained by
 subtracting the unit consumption current from the output current from the
 dc source 1. In this embodiment, as seen in equation (9), even when the
 charging voltage is low, the charging current is increased correspondingly
 to the low charging voltage. Accordingly, as compared with the
 conventional second technique, the charging time of the secondary cell 4
 can be reduced.
 Further, in this embodiment, the unit consumption current is small as
 compared with the output current from the dc source 1. Therefore, the loss
 generated in the current detection resistor can be reduced, as compared
 with that generated in the conventional third technique in which the
 output current from the dc source 1 is monitored.
 In the case that the operation of an electronic device and charging are
 simultaneously carried out, the loss generated in the unit consumption
 detection resistor 25, caused by the flow of the maximum supply current
 Iinmax of the dc source 1, is defined as
EQU Iinmax.sup.2.cndot.Rin (10)
 in which Rin represents the resistance of the unit consumption current
 detection resistor 25. Hereupon, the loss defined by equation (10) is
 invariably constant, irrespective of the charge current in the unit.
 According to the configuration of this embodiment, the loss defined as
EQU Is.sup.2.cndot.Rs (11)
 is generated, caused by the current Is flowing in the unit consumption
 current detection resistor 25. Further,
EQU Iinmax.gtoreq.Is
 holds invariably, and therefore, when the maximum values of voltage
 developed across the current detection resistor are the same, the
 following equation holds.
 Rs=Rin (12)
 Accordingly, the loss generated in the current detection resistor can be
 expressed as follows, based on equations (10), (11), and (12). It is
 understood that the loss of the conventional example shown in FIG. 8 is
 larger than that of the embodiment shown in FIG. 1.
EQU Iinmax.sup.2.cndot.Rin-Is.sup.2.cndot.Rs=Iinmax.sup.2.cndot.Rin-Is.sup.
 2.cndot.Rin=(Iinmax.sup.2 -Is.sup.2).cndot.Rin&gt;0
 If the average value of the unit consumption current is half of the maximum
 supply current of the dc source 1, for example, the loss generated in the
 unit consumption current detection resistor 25 is one-quarter of the loss
 in the dc source output current detection resistor 5 shown in FIG. 8.
 It should be understood that the embodiments disclosed here are
 illustrative and not restrictive. The scope of the present invention is
 defined by the appended claims rather than by the above description, and
 is intended to include meanings equivalent to the claims and all changes
 without departing from the claims.