JP3929454B2 - Charger and charge control method - Google Patents

Description

  The present invention relates to a charger that is provided in various electronic devices driven by a battery, and that is supplied with electric power from an external power source having a current limiting function to charge the battery.

In recent years, a charger provided in an electronic device such as a portable device having a battery is required to have a rapid and high-rate charging function.
Conventionally, as a charger, an apparatus having a circuit configuration as shown in FIG. 3 has been used. In FIG. 3, the charger 12 is supplied with power from the external power supply 1, and includes a backflow prevention switch 4 made of a P-channel MOSFET, a control element 13 made of a P-channel MOSFET, a constant current control detection resistor 9, and a control circuit 14. Is provided.

  The direct current supplied from the external power source 1 charges the battery 3 via the switch 4, the control element 13, and the resistor 9. The backflow prevention switch 4 is controlled by the control circuit 14 and is turned on during the charging operation to the battery 3 by being supplied with power from the external power source 1, and from the battery 3 when there is no power supply from the external power source 1. The discharge current is turned off so as not to flow backward. In the following description of the charging operation of the charger 12, the backflow prevention switch 4 is in an on state.

  FIG. 4 shows the output characteristics of the external power source 1 and the output characteristics of the charger 12. As shown in FIG. 4, the external power supply 1 has a constant voltage output function for outputting a predetermined voltage Va and a current limiting function for limiting the output current to a predetermined value Ia. Further, the control element 13 is controlled in the impedance between the source and the drain by the gate voltage from the control circuit 14, and takes the following three states.

The first state of the control element 13 is an on state. The second state is a constant current state in which the voltage drop at the constant current control detection resistor 9 due to the charging current Ib to the battery 3 is controlled to be a constant value. The constant current value in this case is Ic. The third state is a constant voltage state that is controlled so as to stabilize the voltage Vb of the battery 3 to a predetermined value Vc. FIG. 4 shows a constant current state and a constant voltage state of the charger.

Figure 5 is an operation waveform diagram representing the time variation of the charging current Ib to the voltage Vb and battery 3 of the battery 3 that by the charging operation of the charger. The operation of the conventional charger shown in FIG. 3 will be briefly described below with reference to the charging operation waveform diagram of FIG.

First, “charging 1” is a period in which the battery 3 is rapidly charged, and the battery 3 is charged with a constant current Ia using the current limiting function of the external power source 1. At this time, the control element 13 made of a P-channel MOSFET is in the first state, that is, the on state.

  “Charging 2” is a period in which the control element 13 is in the second state and the battery 3 is charged with the constant current Ic. For overvoltage protection of the battery 3, the battery 3 is charged with a constant current with a current Ic set smaller than the constant current value Ia from the external power supply 1 in “charging 1”.

  Finally, “charging 3” is a period in which the control element 13 is in the third state. During this period, since the battery 3 is almost fully charged, the voltage Vb of the battery 3 is held at a constant voltage Vc. And the charging current gradually decreases. That is, the charger 12 operates as a series regulator during the period of “charge 2” and “charge 3”.

Patent Document 1 discloses a charging device using a switching type DC-DC converter, and high-efficiency charging is realized by constant current control of the DC-DC converter.
JP-A-9-238432

  In the conventional charger as described above, there is a problem that power loss occurs due to the series regulator and conversion efficiency is poor. In particular, during the “charging 2” period, a difference voltage (Va−Vb) between a predetermined output voltage value Va of the external power supply 1 and the battery voltage Vb is applied to the control element 13, and at the same time, the control element 13 is controlled. A constant current Ic set by the circuit 14 flows. The product (Va−Vb) · Ic of the differential voltage and the constant current value becomes a power loss, which deteriorates the conversion efficiency. For this reason, the amount of heat generated during charging increases, and the surface temperature of the electronic device rises, so that the constant current value Ic cannot be set large, resulting in a problem that the charging time of the battery becomes long.

  Moreover, the charger using the switching type DC-DC converter as in Patent Document 1 is not a configuration using an external power source. For this reason, since the charging time depends only on the constant current characteristics of the DC-DC converter, there is a problem that rapid charging is difficult.

  SUMMARY OF THE INVENTION An object of the present invention is to provide a charger that uses an external power source having a current limiting function to the maximum, has high efficiency, does not increase in temperature, and has a short charging time.

Charger according to claim 1 of the present invention is supplied with power from an external power supply having a function of limiting the supply current to the first current value, charge the battery, via a step-down converter is controlled by a control circuit a charger, wherein the control circuit, by detecting the voltage of the charging current and the battery to the battery, when the voltage of the battery reaches a first voltage value, the voltage of the battery is turned on and off the buck converter at a time ratio that limits the the first voltage value, wherein when the battery voltage is equal to or greater than the first and lower than the voltage value of the second voltage value is, the charging current It is turned on and off the buck converter at a time ratio that limits the second current value, if the voltage of the battery is lower than the second voltage value, conduction between the input and output of the buck converter Characterized by being configured to cause.

According to a second aspect of the present invention, in the charger according to the first aspect, the step-down converter includes a switch element having one end connected to an input end of the step-down converter and one end connected to the other end of the switch element. A rectifier having the other end grounded, an inductor having one end connected to the other end of the switch element, and smoothing means having one end connected to the other end of the inductor and the other end grounded. The control circuit is configured to supply the charging current from the means to the battery, and the control circuit periodically turns on and off the switch element, and detects and controls the battery voltage and the charging current. The switch element is configured to adjust an on time and an off time.
The charger according to claim 3 of the present invention is characterized in that, in claim 1, the second current value is set smaller than the first current value.
According to a fourth aspect of the present invention, in the charger according to the first aspect, the step-down converter includes a through switch that short-circuits between the input and output of the step-down converter by the control circuit. When the voltage is less than the second voltage value, the through switch is turned on.

The charger according to claim 5 of the present invention is characterized in that, in claim 4 , at least the through switch and the control circuit are mounted in an integrated circuit.
According to a sixth aspect of the present invention, there is provided a charge control method for charging a battery via a step-down converter that is supplied with electric power from an external power source having a function of limiting a supply current to a first current value and is controlled by a control circuit. upon charging the battery by the charger, by detecting the voltage of the charging current and the battery to the battery, when the voltage of the battery reaches a first voltage value, the voltage of the battery When the step-down converter is turned on and off at a time ratio limited to the first voltage value, and the battery voltage is lower than the first voltage value and greater than or equal to the second voltage value, the charging current is changed to the first voltage value. It is turned on and off the buck converter at a time ratio that limits the second current value, if the voltage of the battery is lower than the second voltage value, the buck converter And characterized in that conduction between input and output.

Charging control method according to claim 7 of the present invention, in claim 6, when the voltage of the battery is lower than the second voltage value, the through-switched-on state to short-circuit between the input and output of the buck converter It is characterized by doing.

  The charger of the present invention has an excellent effect of high efficiency and low calorific value by using a switching step-down converter for charge control. In addition, by using the current limiting function of the external power source, there is an excellent effect that the heat generation amount of the electronic device main body is reduced and the charging time is short.

Hereinafter, the charge control method of the present invention will be described based on specific embodiments.
(First embodiment)
FIG. 1 shows a charger according to a first embodiment of the present invention.

  In FIG. 1, a charger 2 is supplied with electric power from an external power supply 1, and includes a backflow prevention switch 4 made of a P-channel MOSFET, a switch 5 made of a P-channel MOSFET, a synchronous rectifier 6 made of an N-channel MOSFET, An inductor 7, a capacitor 8, a constant current control detection resistor 9, and a control circuit 10 are provided.

  In the charger 2, a series circuit of a backflow prevention switch 4, a switch 5, an inductor 7, and a constant current control detection resistor 9 is interposed between the external power source 1 and the battery 3. And a capacitor 8 is connected between the connection point between the constant current control detection resistor 9 and the reference power source. The synchronous rectifier 6 is connected between a connection point between the switch 5 and the inductor 7 and a reference power source.

  The backflow prevention switch 4 is controlled by the control circuit 10 and is turned on during the charging operation to the battery 3 by being supplied with power from the external power source 1, and from the battery 3 when there is no power supply from the external power source 1. The discharge current is turned off so as not to flow backward. In the following description of the charging operation of the charger 2, the backflow prevention switch 4 is in the on state.

  The switch 5 made of P-channel MOSFET, the synchronous rectifier 6 made of N-channel MOSFET, the inductor 7 and the capacitor 8 constitute a switching step-down converter 15. The step-down converter 15 outputs DC power from the capacitor 8 via the inductor 7 when the switch 5 and the rectifier 6 are alternately turned on and off by the control circuit 10. When the ON / OFF operation of the switch 5 and the synchronous rectifier 6 is periodically repeated, the ratio of the ON time of the switch 5 to one cycle (hereinafter, this ratio is described as a duty ratio) is adjusted. The DC power output from the step-down converter 15 can be controlled.

  FIG. 4 shows the output characteristics of the external power source 1 and the output characteristics of the charger 2. As shown in FIG. 4, the external power supply 1 has a constant voltage output function for outputting a predetermined voltage Va and a current limiting function for limiting the output current with the first current value Ia. The switch 5 is turned on and off alternately with the synchronous rectifier 6 by the control circuit 10, and takes the following three states.

  In the first state, the switch 5 is steadily turned on, and the rectifier 6 is steadily turned off. That is, the aforementioned duty ratio is 1. In this state, it can be said that the repetition of the on / off operation of the step-down converter 15 is stopped.

  The second state is a constant current state in which the duty ratio of the switch 5 is adjusted so that the voltage drop at the constant current control detection resistor 9 due to the charging current Ib to the battery 3 becomes a constant value. The constant current value in this case is defined as a second current value Ic. The second current value Ic is set smaller than the first current value Ia of the external power source 1.

  The third state is a constant voltage state in which the duty ratio of the switch 5 is adjusted so that the voltage Vb of the battery 3 is stabilized at the first voltage value Vc. FIG. 4 shows a constant current state and a constant voltage state of the charger.

Figure 5 is an operation waveform diagram representing the time variation of the charging current Ib to the voltage Vb and battery 3 of the battery 3 that by the charging operation of the charger.
Hereinafter, the charging operation of the charger 2 according to the first embodiment will be described with reference to the operation waveform diagram shown in FIG.

  “Charging 1” in FIG. 5 is a period in which the switch 5 is in the first state, that is, the on state. At this time, the battery 3 is charged with a constant current from the external power source 1 with the first current value Ia via the backflow prevention switch 4, the switch 5, the inductor 7, and the constant current control detection resistor 9. That is, by using the external power source 1 as the heat source, the temperature rise of the electronic device is prevented, and the charging time is shortened by the large current value Ia. This period of “charging 1” is until charging proceeds and the voltage Vb of the battery 3 reaches the second voltage value Va, and when the battery voltage Vb reaches the second voltage value Va, the process shifts to “charging 2”. To do.

  “Charging 2” in FIG. 5 is a period in which the switch 5 is in the above-described second state, that is, the charger 2 is in the constant current state, and the battery 3 is constant-current charged with the second current value Ic. Charging using the step-down converter 15 enables highly efficient power conversion and suppresses heat generation. The reason why the period of “charging 2” is provided for “charging 1” is that if the charging is performed too rapidly, a voltage exceeding the overvoltage characteristic of the battery 3 may be applied. For this reason, the second current value Ic is set to be smaller than the first current value Ia of the external power supply 1.

  On the other hand, in order to shorten the charging time, it is desirable to set the second current value Ic large within the allowable range of the thermal burden on the charger 2. By using the step-down converter 15 having highly efficient power conversion characteristics, the second current value Ic can be set large and the charging time can be shortened. This period of “charging 2” is until charging proceeds and the voltage Vb of the battery 3 reaches the first voltage value Vc, and when the battery voltage Vb reaches the first voltage value Vc, the process shifts to “charging 3”. To do.

  In “Charging 3” of FIG. 5, the switch 5 is charged in the third state described above, that is, the charger 2 is in a constant voltage state, and the battery voltage Vb is charged while being limited to the first voltage value Vc. The first voltage value Vc is set to a value close to the fully charged voltage of the battery 3, and the charging current Ib decreases as the charging proceeds. The charging is terminated when the fully charged voltage is reached.

(Second Embodiment)
FIG. 2 shows a charger according to a second embodiment of the present invention.
In FIG. 2, the charger 2 has a through switch 11 made of a P-channel MOSFET, and the control circuit 10 has a function of driving the through switch 11 as shown in FIG. Different from the charger 2 of the first embodiment.

  In FIG. 2, the through switch 11 is inserted between the output of the backflow prevention switch 4 and the battery 3. A switch 5 made of a P-channel MOSFET, a synchronous rectifier 6 made of an N-channel MOSFET, an inductor 7 and a capacitor 8 constitute a step-down converter 15. The structure and operation of the step-down converter of the charger 2 of the first embodiment are as follows. 15 is the same.

  The charging operation is performed as shown in the charging operation waveform diagram shown in FIG. 5 as in the first embodiment. In the charging operation, the charger 2 according to the second embodiment of the present invention operates differently from the charger 2 according to the first embodiment during the “charging 1” period. During the periods of “Charge 2” and “Charge 3”, the through switch 11 is in an off state, which is the same as in the first embodiment.

  In “charging 1”, the switch 5 is turned on, and a charging current flows from the external power source 1 to the battery 3 through the backflow prevention switch 4, the switch 5, the inductor 7, and the constant current control detection resistor 9. At the same time, the through switch 11 is also in the on state, and the battery 3 is charged via the through switch 11. The sum of the charging currents flowing through both the paths is a first current value Ia supplied from the external power source 1 and charging the battery 3. By bypassing the charging current of the through switch 11, the charging current flowing through the switch 5, the inductor 7, and the constant current control detection resistor 9 is reduced. Therefore, power loss due to the charging current can be reduced.

  The through switch 11 does not perform a high-frequency switching operation like the switch 5 or the synchronous rectifier 6, and does not flow the full charge current unlike the backflow prevention switch 4, and is different from other components. There is little electric power burden. Therefore, since the heat capacity can be designed to be relatively small, the charger can be reduced in size by being integrated with the control circuit 10.

  The charger according to the present invention is useful as a charger with high efficiency and a short charging time by selectively using a current limiting function of an external power supply and a constant current output function using a switching step-down converter according to the battery voltage.

The circuit block diagram which shows the charger of 1st Embodiment which concerns on this invention The circuit block diagram which shows the charger of 2nd Embodiment which concerns on this invention Circuit diagram showing a conventional charger Characteristic diagram showing output characteristics of external power supply and charger Charging current and charging voltage operation waveform diagram showing charger operation

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 External power supply 2 Charger 3 Battery 4 Switch for backflow prevention 5 Switch 6 Synchronous rectifier 7 Inductor 8 Capacitor 9 Detection resistor 10 for constant current control Control circuit 15 Step-down converter

Claims (7)

The supply current is supplied power from an external power supply having a function of limiting the first current value, a charger charge the battery, via a step-down converter is controlled by a control circuit,
The control circuit includes :
By detecting the voltage of the charging current to the battery battery,
When the voltage of the battery reaches a first voltage value, to on-off operation of the buck converter in a time ratio that limits the voltage of the battery to the first voltage value,
When the voltage of the battery is lower than the first voltage value and greater than or equal to the second voltage value, the step-down converter is turned on / off at a time ratio that limits the charging current to the second current value,
When the voltage of the battery is lower than the second voltage value, the charger configured so as to conduct between the input and output of the buck converter. The step-down converter
A switching element having one end connected to the input end of the step-down converter;
A rectifier having one end connected to the other end of the switch element and the other end grounded;
An inductor having one end connected to the other end of the switch element;
Smoothing means having one end connected to the other end of the inductor and the other end grounded, and configured to supply the charging current from the smoothing means to the battery,
The control circuit is configured to periodically turn on and off the switch element and adjust an on time and an off time of the switch element to detect and control the battery voltage and the charging current.
The charger according to claim 1. The charger according to claim 1, wherein the second current value is set smaller than the first current value. The step-down converter has a through switch that short-circuits the input and output of the step-down converter by the control circuit,
The control circuit is configured to turn on the through switch when the voltage of the battery is less than the second voltage value.
The charger according to claim 1. At least the through switch and the control circuit are mounted in an integrated circuit.
The charger according to claim 4. When charging the battery by a charger that is supplied with electric power from an external power source having a function of limiting the supply current to the first current value and charges the battery via a step-down converter controlled by a control circuit;
By detecting the charging current to the battery and the voltage of the battery,
When the voltage of the battery reaches a first voltage value, the step-down converter is turned on / off at a time ratio that limits the voltage of the battery to the first voltage value,
When the voltage of the battery is lower than the first voltage value and greater than or equal to the second voltage value, the step-down converter is turned on / off at a time ratio that limits the charging current to the second current value,
When the voltage of the battery is less than the second voltage value, the input / output of the step-down converter is made conductive.
Charge control method. When the voltage of the battery is less than the second voltage value, a through switch that short-circuits the input and output of the step-down converter is turned on.
The charge control method according to claim 6.

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