JP2006204021A - Charger - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a charger for secondary batteries wherein fluctuation in battery voltage is prevented in transition from constant-current charging to constant-voltage charging. <P>SOLUTION: The charger includes a converter unit that charges a secondary battery with direct-current power obtained by rectifying and smoothing power generated when power from an input direct-current power supply is switched by a switch element and applied to an inductor; a charging current detection circuit that generates a current control signal corresponding to a charging current to the secondary battery; a voltage detection circuit that generates a voltage control signal corresponding to the battery voltage of the secondary battery; a current detection circuit that generates a current detection signal corresponding to a current passed through the inductor; and a control circuit that selects one of the lower level from the current control signal and the voltage control signal, and controls the switching operation of the switch element so that the current detection signal follows the selected control signal. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a secondary battery charger that switches from constant current charging to constant voltage charging.

Charging of secondary batteries such as mobile phones uses a converter such as a series regulator or switching power supply to charge quickly by constant current charging at the beginning of charging, and switch to constant voltage charging when the battery voltage approaches the full charge voltage. A method is used.
Japanese Patent No. 3019353 discloses an operation of constant current-constant voltage charging by a conventional charger. A conventional charger will be described with reference to FIG.

  In the charger of the conventional example, the converter unit 1 converts the input voltage Vi into an AC voltage by the switch element 10, and rectifies and smoothes the AC voltage by the diode 11, the inductor 12, and the capacitor 13. The secondary battery 2 is connected to the converter unit 1 and charged.

  The charging current detection circuit 3 includes a current detection resistor 30 that detects a charging current Ib flowing from the converter unit 1 to the secondary battery 2, a voltage source 31 that outputs a DC voltage Vs, a voltage drop at the current detection resistor 30, and a direct current. The amplifier 32 is configured to amplify a voltage difference with the voltage Vs and output a current control signal Vec.

  The voltage detection circuit 4 includes a resistor 40 and a resistor 41 that detect the voltage Vb of the secondary battery 2, a voltage source 42 that outputs a DC voltage Vr, a voltage at a connection point between the resistor 40 and the resistor 41, and a DC voltage Vr. The amplifier 43 outputs a voltage control signal Vev by amplifying the voltage difference between the two.

  The control circuit 9 includes a diode 90 whose cathode is connected to the output of the amplifier 32, a diode 91 whose cathode is connected to the output of the amplifier 43, a triangular wave generator 92 that outputs a triangular wave voltage Vt, and a diode connected to the positive input terminal. 90 and the anode of a diode 91 are connected to each other, and a comparator 93 in which a triangular wave voltage Vt is inputted to a negative input terminal is constituted. The comparator 93 outputs a drive pulse with the duty ratio δ set, and controls the on / off of the switch element 10.

  During constant current charging at the initial stage of charging, the current control signal Vec is selected by the diodes 90 and 91 and input to the comparator 93. When the battery voltage Vb of the secondary battery rises, the current control signal Vec rises, and the on-time pulse width of the switch element 10 output from the comparator 93 becomes wider. That is, the duty ratio δ increases and the output voltage Vo of the converter 1 increases.

  When the battery voltage Vb of the secondary battery approaches the full charge voltage, the voltage control signal Vev output from the amplifier 43 decreases. When the voltage value of the voltage control signal Vev becomes lower than that of the current control signal Vec, the voltage control signal Vev is selected by the diodes 90 and 91 and constant voltage charging is started.

In constant voltage charging, when the voltage control signal Vev decreases, the pulse width of the ON time of the switch element 10 output from the comparator 93 becomes narrower. That is, the duty ratio δ becomes small and the output voltage Vo of the converter 1 becomes low. The charging current flowing from the converter unit 1 to the secondary battery 2 decreases, and the battery voltage Vb is maintained at a predetermined value (for example, a fully charged voltage value).
Japanese Patent No. 3019353

  The conventional charger has the maximum duty ratio δ at the time of transition from constant current charging to constant voltage charging where the input voltage Vi is low and the output power of the converter 1 is maximum. In such a case, the current control signal Vec that has increased may cross the voltage control signal Vev that has decreased in the vicinity of the apex of the triangular wave voltage. The problem in that case will be described below with reference to FIG. FIG. 9 is an operation waveform diagram at the time of crossing of the current control signal Vec and the voltage control signal Vev in the above case, and also shows the on / off state of the switch element 10 of the converter 1 along with the triangular wave voltage Vt.

  When the intersection between the current control signal Vec and the voltage control signal Vev is near the apex of the triangular wave voltage Vt, the duty ratio δ is close to 1. In the worst case, as shown in FIG. 9, when the intersection of Vec and Vev coincides with the apex of the triangular wave voltage Vt, the duty ratio δ becomes 1, and the switch element remains on for approximately two cycles. Although it is a short time, it operates to raise the battery voltage more than necessary near the full charge voltage, and the battery voltage fluctuates. When charging a secondary battery, fluctuations in the battery voltage near the full charge voltage may cause overcharging, and thus particularly strict regulations are required.

  The present invention has been made to solve the above-described problems, and provides a battery charger for a secondary battery that prevents battery voltage fluctuation from occurring during transition from constant current charging to constant voltage charging. For the purpose.

In order to solve the above problems, the present invention has the following configuration.
The invention according to claim 1 is a converter unit that charges a secondary battery with DC power obtained by switching power applied from an input power supply by a switching element and applying the power to an inductor, and rectifying and smoothing the power generated in the inductor; A charging current detection circuit that generates a current control signal obtained by comparing and amplifying the charging current to the secondary battery with a reference current value; and a voltage that generates a voltage control signal obtained by comparing and amplifying the battery voltage of the secondary battery with a reference voltage value. A detection circuit; a current detector that generates a current detection signal according to a current flowing through the inductor; and a low-level control signal is selected from the current control signal and the voltage control signal, and the current detection signal is selected. And a control circuit that controls a switching operation of the switch element so as to follow the control signal.

  According to the present invention, since the on-time of the switch element, that is, the current flowing through the inductor is adjusted in order to make the charging current constant, the level of the current control signal hardly fluctuates even when the battery voltage rises due to charging. Therefore, when switching from constant current charging to constant voltage charging, the duty ratio also changes smoothly, and battery voltage fluctuations do not occur.

  According to a second aspect of the present invention, in the charger according to the first aspect, the control circuit selects a low level signal from the current control signal and the voltage control signal and outputs the selected signal as a control signal. A control signal switching circuit, a comparator in which the current detection signal is input to one input terminal, the control signal is input to the other input terminal, a clock generator that outputs a clock pulse, and a comparator An RS flip-flop having an output input to a reset terminal and an input of the clock pulse to a set terminal, turning on the switch element at the timing of generation of the clock pulse, and a peak value of the current detection signal being When the control signal is reached, the switch element is turned off.

  According to the present invention, since the current control signal hardly changes even when the battery voltage increases during constant current charging, the change in the duty ratio at the intersection of the current control signal and the voltage control signal changes smoothly, and the battery Voltage fluctuation can be prevented.

  According to a third aspect of the present invention, in the charger according to the first aspect, the control circuit selects a low level signal from the current control signal and the voltage control signal and outputs the selected signal as a control signal. A control signal switching circuit, a comparator in which the current detection signal is input to one input terminal and the control signal is input to the other input terminal, and a circuit for setting the switching element OFF timing. An ON time setting circuit that sets the ON time of the switch element to be shorter as the level of the control signal is lower when the control signal is less than or equal to a predetermined value, and the output of the comparator is input to a set terminal, An RS flip-flop input to a reset terminal as an output of an on-time setting circuit, and when the valley value of the current detection signal reaches the control signal, the switch element is turned on. Characterized in that it turns off the switching element based on an output of said on-time setting circuit.

  According to the present invention, the on-time of the switch element is set to a fixed value while the charging current is large, and the off-time is changed by controlling the valley value of the current flowing through the inductor. Thereby, the control circuit of a converter part can be simplified. In the region where the charging current after the transition to constant voltage charging is small, the control range of the converter part by the control circuit is expanded and the output ripple of the converter part is controlled by shortening the ON time as the control signal level is lower. Can be reduced.

  According to a fourth aspect of the present invention, in the charger according to the third aspect, the control circuit includes a switch circuit that is turned on when the control signal is equal to or lower than a predetermined value, and one end of the converter unit and the secondary battery. And a resistor connected to the other end of the switch and grounded when the switch circuit is turned on, and discharging the secondary battery when the control signal is equal to or lower than the predetermined value. And

  The present invention increases the charging current flowing from the converter section to the secondary battery by discharging the secondary battery through a path different from the path through which the current flows from the converter section to the secondary battery at the end of charging when the charging current is low. Can be made. As a result, the control range of the converter unit by the control circuit can be expanded and the charging current detection accuracy for determining the end of charging can be improved.

  According to a fifth aspect of the present invention, in the charger according to the third aspect, the charging current detection circuit is configured to charge the secondary battery at least while the control circuit selects the voltage control signal. When the small charge detection signal indicates that the charging current is equal to or less than the predetermined value, the control circuit detects the secondary battery. It is characterized by discharging.

  According to the present invention, the charging current can be increased by discharging the secondary battery at the end of charging when the charging current is low. As a result, the control range of the converter unit by the control circuit can be expanded and the charging current detection accuracy for determining the end of charging can be improved.

  According to the charger of the present invention, since the current flowing through the inductor is adjusted in order to make the charging current constant, the level of the current control signal hardly fluctuates even when the battery voltage rises due to charging. Therefore, the duty ratio changes smoothly when switching from constant current charging to constant voltage charging, and an advantageous effect is obtained that battery voltage fluctuation does not occur.

  The charger of the present invention can simplify the control circuit of the converter unit by changing the OFF time by controlling the valley value of the current flowing through the inductor while the ON time of the switch element is fixed while the charging current is large. . Also, in the region where the charging current after the transition to constant voltage charging is small, the control range of the converter unit by the control circuit can be expanded by shortening the ON time as the level of the control signal is lower, and the output of the converter unit Ripple can be reduced.

  The charger of the present invention can increase the charging current by discharging the secondary battery through a path different from the path through which the current flows from the converter unit to the secondary battery at the end of charging when the charging current is low. As a result, the control range of the converter unit by the control circuit can be expanded and the charging current detection accuracy for determining the end of charging can be improved.

  The best mode for carrying out the present invention will be described below with reference to the drawings.

Embodiment 1
The charger according to the first embodiment of the present invention will be described with reference to FIGS. FIG. 1 is a circuit configuration diagram of a charger according to Embodiment 1 of the present invention. The charger according to the first embodiment of the present invention includes a converter unit 1 that converts an input voltage Vi into a DC output voltage Vo, and a charging current detection circuit 3 that detects a charging current that flows from the output of the converter unit 1 to the secondary battery 2. , A voltage detection circuit 4 for detecting the voltage Vb of the secondary battery 2, a current detector 5 for detecting a current flowing through the inductor 12 and outputting a current detection signal Vc, and outputs of the charging current detection circuit 3 and the voltage detection circuit 4 Is provided with a control circuit 6 for controlling on / off of the switch element 10 of the converter unit 1.

  The converter unit 1 includes a switch element 10 having one end connected to an input power source that outputs an input voltage Vi, a diode 11 having a cathode connected to a connection point between the other end of the switch element 10 and the inductor 12, and an anode grounded, One end is connected to a connection point between the switch element 10 and the diode 11 and the other end is connected to the capacitor 13 via the current detector 5, and one end is connected between the inductor 12 and the current detection resistor 30. The other end of the capacitor 13 is grounded.

  For example, an output from an AC adapter or the like is input to the converter unit 1 as an input voltage Vi. The switch element 10 converts the input voltage Vi into an alternating voltage by turning it on and off at a high frequency of 1 KHz to 10 KHz, for example. This AC voltage is rectified and smoothed by the diode 11, the inductor 12, and the capacitor 13. The converter unit 1 outputs a DC output voltage Vo. The output voltage Vo of the converter unit 1 is controlled by a duty ratio δ that is a ratio of the on-time in one switching cycle of the switch element 10. The secondary battery 2 is connected to the converter unit 1 and charged.

  The charging current detection circuit 3 includes a current detection resistor 30 connected between the capacitor 13 of the converter unit 1 and the secondary battery 2, and one end connected between the current detection resistor 30 and the secondary battery 2 and the resistor 40. The voltage source 31 is connected to the point and the other end is connected to the negative input terminal of the amplifier 32. The amplifier 32 has the positive input terminal connected to the connection point of the capacitor 13 and the current detection resistor 30 and the output terminal connected to the diode 60. It consists of.

The current detection resistor 30 detects a charging current Ib flowing from the converter unit 1 to the secondary battery 2.
The voltage source 31 outputs a DC voltage Vs (referred to as a “reference current value”) that is a reference voltage for comparison with a voltage drop of the current detection resistor 30. In the first embodiment, the resistance value Rs of the current detection resistor 30 is set to 50 mΩ, and the DC voltage Vs is set to about 25 mV.
The amplifier 32 amplifies the voltage difference between the voltage drop at the current detection resistor 30 and the DC voltage Vs, and outputs a current control signal Vec.

  The voltage detection circuit 4 has one end connected to a connection point between the current detection resistor 30 and the secondary battery 2 and the other end connected to the resistor 41, and one end connected to the resistor 40 and the other end connected to ground. 41, a voltage source 42 having one end connected to the negative input terminal of the amplifier 43 and the other end grounded, an amplifier 43 to which the connection point of the resistors 40 and 41 is connected to the positive input terminal and the diode 61 is connected to the output terminal. Composed.

The resistor 40 and the resistor 41 detect the voltage Vb of the secondary battery 2.
The voltage source 42 outputs a DC voltage Vr (referred to as a “reference voltage value”) that is a reference voltage for comparison with the voltage of the secondary battery 2 detected using the ratio of the resistor 40 and the resistor 41. The value of the DC voltage Vr is set to an arbitrary value equal to or lower than the full charge voltage (4.2 V) of the secondary battery 2. Preferably, a band gap voltage (about 1.25 V) having extremely small temperature dependence is used as the DC voltage Vr in the semiconductor integrated circuit.
The amplifier 43 amplifies the voltage difference between the voltage at the connection point between the resistor 40 and the resistor 41 and the DC voltage Vr, and outputs a voltage control signal Vev.

  The current detector 5 in FIG. 1 is described equivalently. The current detector 5 has a low resistance, for example, and detects a current flowing through the inductor 12 by detecting a voltage drop of the low resistance, and outputs a current detection signal Vc. Instead of using a low resistance for the current detector 5, the switch element 10 or the diode 11 may be replaced with a MOS transistor, and the current flowing through the inductor 12 may be detected by detecting the voltage drop.

  The control circuit 6 includes a diode 60 having a cathode connected to the output terminal of the amplifier 32, a diode 61 having a cathode connected to the output terminal of the amplifier 43, and anodes of the diodes 60 and 61 connected to a negative input terminal. The comparator 63 is connected to the current detector 5, the clock generator 62 is connected to the set terminal S of the RS flip-flop 64, the output terminal Q is connected to the reset terminal R, and the output terminal Q is connected to the switch element 10. It is comprised by RS flip-flop 64 connected to. The diodes 60 and 61 constitute a control signal switching circuit.

  A low-level control signal is selected from the current control signal Vec output from the amplifier 32 and the voltage control signal Vev output from the amplifier 43 by the diode 60 and the diode 61 and input to the negative input terminal of the comparator 63. The comparator 63 outputs a high (H) signal if the current detection signal Vc input to the positive input terminal is larger than the control signal input to the negative input terminal, and outputs a low (L) signal if it is smaller.

  The RS flip-flop 64 is set by the clock pulse CK output from the clock generator 62 and is reset by the output of the high (H) signal from the comparator 63. The RS flip-flop 64 outputs a drive pulse with a duty ratio δ set from the output terminal Q, and controls on / off of the switch element 10.

  The charger according to Embodiment 1 of the present invention has a current detector 5 and a configuration of the control circuit 6 as compared with the conventional charger. The operation of the charger according to Embodiment 1 of the present invention will be described below with reference to FIGS.

  FIG. 2 is a diagram illustrating a process in which the charger according to the first embodiment of the present invention illustrated in FIG. 1 charges the secondary battery 2, and (a) illustrates the battery voltage Vb of the secondary battery 2 and the converter unit 1. FIG. 5B is an operation waveform diagram showing the change over time of the charging current Ib flowing through the secondary battery 2, and FIG. In FIG. 2A, the horizontal axis indicates time (t), and the vertical axis indicates voltage / current. In FIG.2 (b), a horizontal axis shows time (t) and a vertical axis | shaft shows a voltage.

  FIG. 3 is an enlarged view of the intersection of the current control signal Vec and the voltage control signal Vev in FIG. FIG. 3 also shows the current detection signal Vc, and shows on / off of the clock pulse CK and the switch element 10. In FIG. 3, the forward diode voltages of the diode 60 and the diode 61 are ignored.

As shown in FIG. 2, since the battery voltage Vb of the secondary battery 2 is low at the initial stage of charging, the voltage at the connection point between the resistor 40 and the resistor 41 is lower than the DC voltage Vr. Therefore, the amplifier 43 outputs a high level voltage control signal Vev.
The current control signal Vec decreases when the voltage of the current detection resistor 30 is greater than the DC voltage Vs, and conversely increases when the voltage of the current detection resistor 30 is lower than the DC voltage Vs. In the initial stage of charging, the voltage of the current detection resistor 30 tends to be higher than the DC voltage Vs. Therefore, the amplifier 32 outputs a low level current control signal Vec.
The low-level current control signal Vec is selected by the diodes 60 and 61 and input to the comparator 63.

  The comparator 63 compares the current detection signal Vc with the current control signal Vec, and outputs a high (H) level signal when the current detection signal Vc exceeds the current control signal Vec. The RS flip-flop 64 is reset by this H level signal.

  As shown in FIG. 3, the switch element 10 whose on / off operation is controlled by the output of the RS flip-flop 64 is turned on at a predetermined switching period according to the clock signal CK, and then a current detection signal indicating an inductor current that increases. When Vc reaches the current control signal Vec, it is turned off. With such an operation, the current control signal Vec directly controls the inductor current.

Next, it will be described that the charging current flowing in the secondary battery 2 works to be stabilized to a constant current when the circuit of FIG. 1 is used.
When the battery voltage Vb increases due to the charging of the secondary battery 2, the voltage difference between the output voltage Vo of the converter unit 1 and the battery voltage Vb, that is, the voltage of the current detection resistor 30 decreases. Then, the difference between the voltage of the current detection resistor 30 and the DC voltage Vs increases, and the current control signal Vec increases. When the current control signal Vec rises, the time until the current detection signal Vc reaches the current control signal Vec, that is, the pulse width of the ON time of the switch element 10 is widened. As the duty ratio δ increases, the output voltage Vo of the converter unit 1 increases. Thus, when the battery voltage Vb rises, feedback works so that the output voltage Vo of the converter unit 1 increases accordingly. Therefore, the voltage difference between the output voltage Vo of the converter unit 1 and the battery voltage Vb, that is, the voltage of the current detection resistor 30 is kept constant (DC voltage Vs). From the above, when the resistance value of the current detection resistor 30 is Rs, the charging current Ib to the secondary battery 2 is stabilized to a constant current (Vs / Rs).

As described above, the charging current Ib is stabilized at a constant current. As a result, the level of the current control signal Vec output from the amplifier 32 hardly changes during constant current charging as shown in FIGS.
That is, when the constant current charging advances and the battery voltage Vb increases, the duty ratio δ increases and the output voltage Vo of the converter unit 1 increases, but the output voltage Vo increases (the charge current Ib is made constant). The change of the current control signal Vec for the
Since the current control signal Vec hardly changes, the level of the current flowing through the inductor 12 hardly changes. Since the average value of the current flowing through the inductor 12 becomes the charging current Ib flowing through the secondary battery 2, the charging current Ib is made constant.

  In FIG. 2, when the battery voltage Vb of the secondary battery 2 rises and approaches a predetermined value (for example, a full charge voltage value), the voltage difference between the voltage at the connection point between the resistor 40 and the resistor 41 and the DC voltage Vr is increased. The voltage control signal Vev decreases as the voltage decreases. When the voltage control signal Vev becomes equal to or lower than the current control signal Vec, the voltage control signal Vev is selected by the diodes 60 and 61 and is input to the comparator 63.

  The comparator 63 compares the voltage control signal Vev with the current detection signal Vc, and outputs an H level signal when the current detection signal Vc exceeds the voltage control signal Vev. The RS flip-flop 64 is reset by this H level signal.

  As shown in FIG. 3, the switch element 10 that is turned on and off by the output of the RS flip-flop 64 is turned on at a predetermined switching period according to the clock signal CK, and then the current detection signal Vc indicating the inductor current that increases is a voltage. When the control signal Vev is reached, it is turned off.

  When the battery voltage Vb of the secondary battery 2 increases and the voltage at the connection point between the resistor 40 and the resistor 41 tends to be higher than the DC voltage Vr, the voltage control signal Vev decreases. Thereby, the pulse width of the ON time of the switch element 10 becomes narrow. That is, as the duty ratio δ decreases, the output voltage Vo of the converter unit 1 decreases. As the output voltage Vo decreases, the charging current Ib decreases, and the battery voltage Vb of the secondary battery 2 is maintained at a predetermined value.

  From the above, when the resistance values of the resistor 40 and the resistor 41 are R1 and R2, respectively, the battery voltage Vb of the secondary battery 2 is stabilized at a constant voltage: Vr × (1 + R1 / R2). This constant voltage value is generally set to the fully charged voltage of the secondary battery 2.

  The secondary battery 2 has an internal resistance in series, and the constant battery voltage Vb is obtained by adding the voltage drop of the internal resistance due to the charging current to the net battery voltage. Therefore, the battery voltage Vb is made constant, but the net battery voltage increases due to charging. Along with this, the voltage control signal Vev decreases and the charging current Ib decreases.

  As described above, in the charger according to Embodiment 1 of the present invention, the peak value of the inductor current is controlled to follow the smaller one of the current control signal Vec and the voltage control signal Vev. During constant current charging, the current control signal Vec hardly changes even if the duty ratio δ increases as the battery voltage Vb increases. Therefore, at the intersection of the current control signal Vec and the voltage control signal Vev, the change of the duty ratio δ changes smoothly and the fluctuation of the battery voltage Vb can be prevented.

  A control method for obtaining a desired output by controlling the inductor current is called a current mode control method, and the peak value of the inductor current is controlled while being turned on and off at a constant switching frequency as described above. There are many other current mode control methods, such as a method for controlling the valley value of the inductor current, a valley value control in which the switching frequency is not constant but the on time is constant, or a peak value control in which the off time is constant. Regardless of which system is applied to the converter unit 1 of the charger, there is almost no change in the control signal during the constant current charging, and the effect of the present invention that the transition to the constant voltage charging is smoothly performed can be obtained.

The charger according to the first embodiment of the present invention uses the diode 60 and the diode 61 as a circuit (control signal switching circuit) that selects and outputs the lower one of the current control signal Vec and the voltage control signal Vev. It was. The present invention is not limited to this configuration, and may be configured as shown in FIG. 4, for example.
In FIG. 4, the control circuit 6 includes a comparator 64 having a positive input terminal connected to the charging current detection circuit 3 and a negative input terminal connected to the voltage detection circuit 4, and a gate connected to the output terminal of the comparator 64 and a drain. Is connected to the charging current detection circuit 3 and the source is connected to the negative input terminal of the comparator 63. The switch 65 is a P-channel FET, and one end is connected to the connection point between the output terminal of the comparator 64 and the switch 65. And an inverter 66 connected to the gate of the switch 67, and a switch 67 comprising a P-channel FET whose drain is connected to the voltage detection circuit 4 and whose source is connected to the negative input terminal of the comparator 63. In addition, the control circuit 6 includes a clock generator 62 that generates a clock, a current detector 5 that outputs a current detection signal Vc, a comparator 63 that is connected to a positive input terminal, and a comparator 63 as in FIG. An RS flip-flop 64 having an output terminal connected to the reset terminal R and a clock generator 62 connected to the set terminal S is provided.

The comparator 64 compares the current control signal Vec and the voltage control signal Vev. The switch 65 is driven by the output of the comparator 64. The switch 67 is driven by the output of the comparator 64 via the inverter 66. The switches 65 and 67 are connected at their output ends, the switch 65 turns on and off the current control signal Vec, and the switch 67 turns on and off the voltage control signal Vev.
When the current control signal Vec is lower than the voltage control signal Vev, the comparator 64 outputs a low (L) level, so that the switch 65 is turned on, the switch 66 is turned off, and the current control signal Vec is output.
Conversely, when the voltage control signal Vev is at a lower level than the current control signal Vec, the comparator 64 outputs an H level, so that the switch 65 is turned off, the switch 66 is turned on, and the voltage control signal Vev is output.

  In the following embodiments, a circuit using a diode similar to that in FIG. 1 is presented as a circuit for selecting and outputting the lower one of the current control signal Vec and the voltage control signal Vev. Needless to say, the present invention is not limited to the configuration, and may be configured as shown in FIG. 4, for example.

<< Embodiment 2 >>
A charger according to Embodiment 2 of the present invention will be described with reference to FIGS. 5 and 6. FIG. 5 is a circuit configuration diagram of a charger according to Embodiment 2 of the present invention. In FIG. 5, the same components as those of the charger according to the first embodiment of the present invention shown in FIG. In FIG. 5 of the second embodiment, the difference from FIG. 1 is the configuration of the control circuit. In order to distinguish from the control circuit 6 in FIG. 1, the control circuit 7 is shown in FIG. The control circuit 7 according to the second embodiment will be described.

  The cathode of the diode 70 is connected to the output terminal of the amplifier 32. The cathode of the diode 71 is connected to the output terminal of the amplifier 43. The anodes of the diode 70 and the diode 71 are connected to the positive input terminal of the comparator 72. The comparator 72 has a negative input terminal connected to the current detector 5 and receives the current detection signal Vc.

  The set terminal S of the RS flip-flop 73 is connected to the output terminal of the comparator 72, and the reset terminal R is connected to the output terminal of the comparator 78. The output terminal Q of the RS flip-flop 73 is connected to the switch element 10 and outputs a drive pulse from the output terminal Q to turn on and off the switch element 10.

  Inverter 74 is connected to output terminal Q of RS flip-flop 73. The switch 75 receives the output of the RS flip-flop 73 via the inverter 74. The switch 75 and the capacitor 76 are connected in parallel between the constant current source circuit 77 and the ground potential. The capacitor 76 is charged by the constant current source circuit 77 and is short-circuited when the switch 75 is turned on.

The positive input terminal of the comparator 78 is connected to the connection point between the capacitor 76 and the constant current source circuit 77 and inputs the voltage of the capacitor 76. The negative input terminal of the comparator 78 is connected to a resistor 79 connected to the reference voltage Vr.
The anode of the diode 80 is connected to the negative input terminal of the comparator 78, and the cathode of the diode 80 is connected to the positive input terminal of the comparator 72.

  In the second embodiment, the inverter 74, the switch 75, the capacitor 76, the constant current source circuit 77, the comparator 78, the resistor 79, and the diode 80 constitute an on-time setting circuit.

  FIG. 6 is an operation waveform diagram at the intersection of the current control signal Vec and the voltage control signal Vev in the second embodiment. FIG. 6 also shows the current detection signal Vc, and shows the voltage Vcon of the capacitor 76, the reference voltage Vr, and the on / off state of the switch element 10. In FIG. 6, the forward diode voltages of the diode 70 and the diode 71 are ignored. Hereinafter, the operation of the charger according to the second embodiment of the present invention will be described with reference to FIG.

First, in constant current charging with a low battery voltage Vb, the voltage control signal Vev is at a high level, and the current control signal Vec is selected by the diodes 70 and 71 and input to the comparator 72.
The comparator 72 compares the current control signal Vec and the current detection signal Vc, and outputs an H level signal when the current detection signal Vc falls below the current control signal Vec. The RS flip-flop 73 is set by this H level signal.
The switch element 10 that is turned on / off by the output of the RS flip-flop 73 is turned on when the set RS flip-flop 73 outputs an H level. When the switch element 10 is turned on, the inductor current and the current detection signal Vc increase.

  On the other hand, when the RS flip-flop 73 outputs an H level, the switch 75 is turned off by the inverter 74. The capacitor 76 is charged by the constant current source circuit 77, and the voltage Vcon of the capacitor 76 increases. When the voltage of the capacitor 76 exceeds the reference voltage Vr, the comparator 78 outputs an H level and resets the RS flip-flop 73. When the RS flip-flop 73 is reset, the switch element 10 is turned off. At the same time, the switch 75 is turned on and the capacitor 76 is grounded.

  That is, the ON time of the switch element 10 is set to the time until the voltage Vcon of the capacitor 76 is released from the ground fault state and charged to the reference voltage Vr. When the capacitance of the capacitor 76 is Con and the current value output from the constant current source circuit 77 is Ion, the on time Ton of the switch element 10 is approximately Ton = Con × Vr / Ion.

  When the battery voltage Vb increases due to the charging of the secondary battery 2, the voltage difference between the output voltage Vo of the converter unit 1 and the battery voltage Vb, that is, the voltage of the current detection resistor 30 decreases. For this reason, the current control signal Vec rises and the off time of the switch element 10 is shortened. That is, as the duty ratio δ increases, the output voltage Vo of the converter unit 1 increases. As the output voltage Vo increases, the voltage of the current detection resistor 30 is maintained at the DC voltage Vs. From the above, when the resistance value of the current detection resistor 30 is Rs, the charging current to the secondary battery 2 is stabilized to a constant current (Vs / Rs).

  As the constant current charging proceeds, the duty ratio δ increases, and the output voltage Vo of the converter unit 1 increases. On the other hand, the level of the current control signal Vec for making a constant current hardly changes. In the charger of the first embodiment, the peak value of the inductor current follows the level of the current control signal Vec, whereas in the charger of the second embodiment, the valley value of the inductor current has the level of the current control signal Vec. Follow. However, as in the first embodiment, the current control signal Vec during constant current charging hardly changes as a result.

  When the voltage control signal Vev becomes equal to or lower than the current control signal Vec, the voltage control signal Vev is selected and input to the comparator 72. As shown in FIG. 6, when the current detection signal Vc falls below the voltage control signal Vev, the switch element 10 is turned on and turned off after a predetermined time. When the resistance values of the resistor 40 and the resistor 41 are R1 and R2, respectively, the battery voltage Vb of the secondary battery 2 is stabilized at a constant voltage Vr × (1 + R1 / R2). This is the same as in the first embodiment. The battery voltage Vb is made constant, but the net battery voltage increases due to charging. Along with this, the voltage control signal Vev decreases and the charging current Ib decreases.

  In the charger according to the second embodiment of the present invention, the on-time of the switch element 10 is fixed as described above, and the valley value of the inductor current follows the lower one of the current control signal Vec and the voltage control signal Vev. Control to do. For this reason, when the charging current Ib decreases and the valley value of the inductor current reaches zero, further control becomes impossible. Therefore, when the current control signal Vec and the voltage control signal Vev input to the positive input terminal of the comparator 72 via the diodes 70 and 71 are equal to or lower than a predetermined value, the diode 80 is turned on, thereby causing the negative input of the comparator 78. The voltage applied to the terminal is lowered, and the ON time of the switch element 10 is shortened.

  Since the voltage applied to the negative input terminal of the comparator 78 decreases according to the current control signal Vec or the voltage control signal Vev, the ON time of the switch element 10 becomes shorter as the charging current decreases. When the forward diode voltage of the diode 80 is Vd, the on-time Ton of the switch element 10 when the charging current Ib decreases during constant voltage charging is Ton = Con × (Vev + 2Vd) / Ion. Therefore, the ON time Ton of the switch element 10 is shortened in the region of Vev <Vr−2Vd.

  As described above, the charger according to the second embodiment controls the valley value of the inductor current while the on-time of the switch element 10 is constant during constant current charging. As in the first embodiment, the charger according to the second embodiment has almost no change in the current control signal Vec, and the effect of the present invention that a smooth transition to constant voltage charging can be obtained. When the charging current is reduced to a predetermined value or less during constant voltage charging, the on-time of the switch element 10 is shortened as the charging current is decreased, so that the control range can be expanded.

  Although a detailed description is omitted, when the switching frequency is constant, the current mode control type converter has a phenomenon that the operation becomes unstable when the duty ratio δ is 0.5 or more. In order to counter this unstable operation phenomenon, a slope compensation circuit is required. However, in the method in which the switching frequency is not constant as in the charger of the second embodiment, this unstable operation phenomenon does not occur, so that the slave compensation circuit is unnecessary and the circuit is simplified.

<< Embodiment 3 >>
A charger according to the third embodiment of the present invention will be described with reference to FIG. FIG. 7 is a circuit configuration diagram of a charger according to Embodiment 3 of the present invention. In FIG. 7, the same components as those of the charger according to the second embodiment of the present invention shown in FIG. The charger in FIG. 7 of the third embodiment is different from that in FIG. 5 in the configuration of the control circuit. In order to distinguish from the control circuit 7 of FIG.

The control circuit 8 of the third embodiment has a PNP transistor 81, an NPN transistor 82, a resistor 83, and a dummy resistor 84 instead of the diode 80 of the control circuit 7 of FIG. The PNP transistor 81 and the NPN transistor 82 of the third embodiment constitute a switch circuit.
The PNP transistor 81 has a base connected to the positive input terminal of the comparator 72, an emitter connected to the negative input terminal of the comparator 78, and a collector connected to one end of the resistor 83. The other end of the resistor 83 is grounded.
The NPN transistor 82 has a base connected to a connection point between the collector of the PNP transistor 81 and the resistor 83, an emitter grounded, and a collector connected to one end of the dummy resistor 84. The other end of the dummy resistor 84 is connected to the secondary battery 2.

The charger according to the third embodiment has the same operation as that of the second embodiment shown in FIG. 5 when the charging current decreases during constant voltage charging and the on-time of the switch element 10 becomes shorter than a predetermined value. Different.
When the ON time of the switch element 10 becomes shorter than a predetermined value (set to a time longer than the minimum ON time of the switch element 10), the PNP transistor 81 becomes active and supplies the base current to the NPN transistor 82. The collector voltage of the NPN transistor 82 decreases, and the secondary battery 2 is discharged via the dummy resistor 84. Therefore, the amount of discharge current to dummy resistor 84 is added to the substantial charge current to secondary battery 2, and charge current Ib flowing from converter unit 1 to secondary battery 2 increases.

  In other words, since the current obtained by subtracting the discharge current to the dummy resistor 84 from the charging current Ib flowing from the converter unit 1 to the secondary battery 2 flows to the secondary battery 2 as a substantial charging current, The charger can expand the control range to a charging current smaller than that of the charger of the second embodiment. Moreover, an effect of facilitating detection of the charging current Ib for detecting the full charge of the secondary battery 2 is also obtained.

  Although not shown in the above charger, when the charging current is reduced to a predetermined current value due to constant voltage charging, the control circuit determines that the battery is fully charged and stops the operation of the converter unit 1. It may have a function of terminating charging. The charging current at the end of the charging is very small compared to the constant current charging. According to the charger of the third embodiment, since charging current Ib is increased, a minute charging current at the end of charging can be easily detected.

  In the charger of the third embodiment, the start of discharging to the dummy resistor 84 is linked with the shortening of the on-time of the switch element 10, but it is not necessarily linked. The present invention is not limited to this method. One of the current control signal and the voltage control signal, or the voltage control signal at the time of constant voltage charging may be compared with a predetermined value determined separately, and discharge may be started when the predetermined value or less is reached.

  In addition to referring to the level of the control signal for the start of discharge to the dummy resistor 84, the discharge may be started when the charge current becomes a predetermined value or less. For example, the charging current detection circuit 3 generates a small charge detection signal indicating a comparison result between the charging current Ib to the secondary battery 2 and a predetermined value at least while the control circuit 6 selects the voltage control signal Vev. The control circuit 6 may be configured to discharge the secondary battery when the small charge detection signal indicates that the charging current Ib has become a predetermined value or less.

  The charger of the present invention is useful for charging a secondary battery such as a lithium ion battery.

FIG. 3 is a circuit configuration diagram of a charger according to Embodiment 1 of the present invention. Operational waveform diagram of charger in embodiment 1 of the present invention The elements on larger scale of the operation waveform of the charger in Embodiment 1 of this invention Another circuit configuration diagram of a part of the charger of the present invention Circuit configuration diagram of a charger in Embodiment 2 of the present invention Partial enlarged view of the operation waveform of the charger in the second embodiment of the present invention Circuit configuration diagram of a charger according to Embodiment 3 of the present invention Circuit diagram of conventional charger Partial enlarged view of the operation waveform of a conventional charger

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Converter part 2 Secondary battery 3 Charging current detection circuit 4 Voltage detection circuit 5 Current detector 6, 7, 8 Control circuit 10 Switch element 11 Diode 12 Inductor 13 Capacitor 30 Current detection resistance 31, 42 Voltage source 32, 43 Amplifier 40 , 41, 79, 83, 84 Resistor 60, 61, 70, 71, 80 Diode 62 Clock generator 63, 72, 78 Comparator 64, 73 RS flip-flop 74 Inverter 75 Switch 76 Capacitor 77 Constant current source circuit 81 PNP transistor 82 NPN transistor

Claims (5)

A converter unit that charges the secondary battery with direct current power that is rectified and smoothed by applying power to the inductor by switching the power from the input power source to the inductor,
A charging current detection circuit that generates a current control signal obtained by comparing and amplifying the charging current to the secondary battery with a reference current value;
A voltage detection circuit that generates a voltage control signal obtained by comparing and amplifying the battery voltage of the secondary battery with a reference voltage value;
A current detector that generates a current detection signal corresponding to the current flowing through the inductor;
A control circuit that selects a low-level control signal from the current control signal and the voltage control signal, and controls the switching operation of the switch element so that the current detection signal follows the selected control signal;
A charger characterized by comprising: The control circuit includes:
A control signal switching circuit for selecting a low level signal from the current control signal and the voltage control signal and outputting the selected signal as a control signal;
A comparator in which the current detection signal is input to one input terminal and the control signal is input to the other input terminal;
A clock generator for outputting clock pulses;
An RS flip-flop in which the output of the comparator is input to a reset terminal and the clock pulse is input to a set terminal;
Have
2. The charger according to claim 1, wherein the switch element is turned on at the timing of generation of the clock pulse, and the switch element is turned off when a peak value of the current detection signal reaches the control signal. The control circuit includes:
A control signal switching circuit for selecting a low level signal from the current control signal and the voltage control signal and outputting the selected signal as a control signal;
A comparator in which the current detection signal is input to one input terminal and the control signal is input to the other input terminal;
An on-time setting circuit configured to set an on-time of the switch element to be shorter as a level of the control signal is lower when the control signal is equal to or lower than a predetermined value; ,
An RS flip-flop, in which the output of the comparator is input to a set terminal, and the output of the on-time setting circuit is input to a reset terminal;
Have
2. The charging according to claim 1, wherein when the trough value of the current detection signal reaches the control signal, the switch element is turned on, and the switch element is turned off based on an output of the on-time setting circuit. vessel. The control circuit includes:
A switch circuit that is turned on when the control signal falls below a predetermined value;
One end is connected to a connection point between the converter unit and the secondary battery, and the other end is grounded when the switch circuit is turned on, and
Further comprising
The charger according to claim 3, wherein the secondary battery is discharged when the control signal becomes equal to or less than the predetermined value. The charging current detection circuit generates a small charge detection signal indicating a comparison result between a charging current to the secondary battery and a predetermined value at least while the control circuit selects the voltage control signal,
4. The charger according to claim 3, wherein the control circuit discharges the secondary battery when the small charge detection signal indicates that the charging current is equal to or less than the predetermined value. 5.

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