JP2006174612A - Charger - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a charger applied to various external power supply, efficiently suppressing a temperature rise, and drastically reducing a charging time. <P>SOLUTION: The charger 2 supplied with DC power from the external power supply 1, is provided with a reverse current preventing switch 4, a switching voltage drop converter comprising a switch 5, a rectifier 6, an inductor 7 and a capacitor 8, a constant current controlling detection resistor 9, a control circuit 10 and a temperature detecting circuit 11. A charging current is controlled by the control circuit 10 in response to a voltage of a battery 3, and the temperature rise is suppressed in the charger 2 by adding a control by the temperature detecting circuit 11 to a constant voltage charging control by the voltage drop converter. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a charger that is provided in various battery-driven electronic devices and that is charged with power from an external power supply.

  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 highly efficient 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 source 1, and includes a backflow prevention switch 4, a P-channel MOSFET, a control element 13, a constant-current control detection resistor 9, and the like. 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 switch 4 is controlled by the control element 13 and is turned on during the charging operation to the battery 3 by being supplied with power from the external power source 1, and when there is no power supply from the external power source 1, the discharge current from the battery 3. Is turned off to prevent reverse flow.

  Therefore, 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 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 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 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.

  FIG. 5 is an operation waveform diagram showing temporal changes in the voltage Vb of the battery 3 and the charging current Ib to the battery 3 due to the charging operation of the charger.

  Hereinafter, the operation of the conventional charger shown in FIG. 3 will be briefly described with reference to the charging operation waveform diagram of FIG.

  Charging (1) in FIG. 3 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. In order to protect the overvoltage of the battery 3, the battery 3 is charged with a constant current by a current Ic set smaller than the constant current value Ia from the external power source 1 in the charge (1).

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

Patent Document 1 discloses a charging device using a switching type DC-DC converter, and the DC-DC converter is controlled at a constant current to realize high-efficiency charging. Therefore, it is difficult to perform rapid charging because it is not possible to perform optimal charging current control according to the characteristics of the external power supply.
Japanese Patent Laid-Open No. 9-238432

  The conventional charger has 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 source 1 and the battery voltage Vb is applied to the control element 13, and at the same time, the control element 13 is controlled. The constant current Ic set by the circuit 14 flows, and the product (Va−Vb) · Ic of this 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.

  In addition, since charging is performed using the current limiting function of the external power supply 1, there is a problem that it is impossible to use other than a specific external power supply.

  An object of the present invention is to solve the problems of the prior art and to provide a charger that is highly efficient, has no temperature rise, and has a very fast charging time regardless of the type and configuration of the external power supply.

  In order to achieve the above object, a charger according to the present invention includes an external power source, a step-down converter including a switch, a rectifier, an inductor, and a control circuit, and a temperature detection circuit that detects the temperature of the charger. A charger that outputs a charging current from the step-down converter to the battery, wherein the control circuit receives the detection signal of the temperature detection circuit and the voltage detection signal of the battery, and the temperature of the charger and the battery In order to limit the voltage of the battery to a predetermined temperature and a predetermined voltage value, the switch is turned on / off at a predetermined on / off time ratio, and when the battery voltage is lower than the predetermined voltage value, The charging current is limited so that the temperature of the charger is maintained at the predetermined temperature.

  The charger according to the present invention uses a switching type step-down converter for charge control, thereby achieving an effect of high efficiency and low calorific value, and using a temperature detection circuit that keeps the temperature of the charger at a predetermined value. By suppressing the temperature rise and using it together with the step-down converter, it becomes possible to control the optimum charging current in accordance with the characteristics of various external power supplies, and extremely rapid charging is possible without accompanying the temperature rise.

  Hereinafter, a preferred embodiment according to the charger of the present invention will be described with reference to the drawings.

  FIG. 1 is a circuit diagram showing a configuration of a charger according to an 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, a control circuit 10, and a temperature detection circuit 11 are provided.

  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 when there is no power supply from the external power source 1, The battery 3 is turned off so that the discharge current from the battery 3 does not flow backward.

  Therefore, in the following description of the charging operation of the charger 2, the backflow prevention switch 4 is in the on state. 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 switching step-down converter.

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

  FIG. 2 is an operation waveform diagram showing the time change of the voltage Vb of the battery 3 and the charging current Ib to the battery 3 due to the charging operation of the charger, and the temperature change of the charger at that time.

  Hereinafter, the charging operation of the charger 2 according to the present embodiment will be described with reference to the operation waveform diagram shown in FIG.

  Charging (1) in FIG. 2 is a period for charging the battery 3 by limiting the charging current so that the temperature of the charger 2 is maintained at a predetermined Ta while the charger 2 is in the set temperature holding state. . Charging using the step-down converter enables highly efficient power conversion, and charging can be performed with an optimal charging current according to the characteristics of the external power supply, so that very rapid charging is possible.

  Moreover, since the temperature of the charger 2 is kept constant, it has an effect of preventing a temperature rise. In order to shorten the charging time, it is desirable to set the charging current value large within the allowable range of the thermal burden on the charger 2. By using a step-down converter having high-efficiency power conversion characteristics, a charging current value can be set large and the charging time can be shortened.

  The period of this charging (1) is until charging proceeds and the voltage Vb of the battery 3 reaches the first voltage value Va. When the battery voltage Vb reaches the first voltage value Va, the process proceeds to charging (2). To do.

  In charging (2) in FIG. 5, the charger 2 is in a constant voltage state, and the battery voltage Vb is charged while being limited to the first voltage value Va. The first voltage value Va 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, and the charging is finished when the fully charged voltage is eventually reached. To do.

  The charger according to the present invention uses a switching step-down converter and adds a function of maintaining a constant temperature of the charger to the control of the step-down converter, so that the charger temperature control and the battery voltage control are performed according to the battery voltage. It is useful as a charger that can use various external power sources with high efficiency and very short charging time.

The circuit block diagram which shows the charger of embodiment which concerns on this invention Operation waveform diagram of charging current, charging voltage, and charger temperature showing the operation of the charger of this embodiment Circuit diagram showing a conventional charger Characteristic diagram showing output characteristics of conventional external power supply and charger Operating waveform diagram of charging current and charging voltage showing the operation of a conventional charger

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 External power supply 2 Charger 3 Battery 4 Backflow prevention switch 5 Switch 6 Rectifier 7 Inductor 8 Capacitor 9 Constant current control detection resistor 10 Control circuit

Claims (1)

A charger that includes an external power source, a step-down converter including a switch, a rectifier, an inductor, and a control circuit, and a temperature detection circuit that detects a temperature of the charger, and outputs a charging current from the step-down converter to a battery. There,
The control circuit receives the detection signal of the temperature detection circuit and the voltage detection signal of the battery, and limits the temperature of the charger and the voltage of the battery to a predetermined temperature and a predetermined voltage value. When the battery voltage is lower than the predetermined voltage value, the charging current is limited so that the temperature of the charger is maintained at the predetermined temperature. A charger characterized by having a configuration to perform.

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