JP3430283B2 - Battery charger - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a battery charger, and more particularly to a battery charger suitable for charging a storage battery such as a lithium ion battery in a short time.

[0002]

2. Description of the Related Art FIG. 3 is a diagram showing a configuration example of a conventional battery charger. As shown, the conventional battery charger 100 includes a power supply terminal 1, a rectifier circuit 2, a PWM control unit 3, a pulse power supply unit 4, a diode 5, a voltage detection unit 7,
Reference voltage generator 8, resistor 9, resistor 10, switch 1
1. The charging terminal 14 is provided. The battery 200 has a configuration in which the battery element 21 is housed in the casing 22,
The casing 22 is provided with terminals 23, 23 for charging and discharging,
The electrodes of the battery element 21 are connected by electric wires 24 and 25, respectively. Charging terminal 1 of the battery charger 100
Connect the terminals 23, 23 of the battery 200 to 4, 14,
It is supposed to charge.

The PWM control unit 3 of the battery charger 100 comprises a PWM control circuit 3-1 and a photocoupler 3-2, and the pulse power supply unit 4 comprises an output transformer 4-1 and a transistor 4-2. The AC power supplied to the power supply terminal 1 is converted into direct current by the rectifier circuit 2 and supplied to the pulse power supply unit 4. The transistor 4-2 is turned on / off by the pulse signal from the PWM control circuit 3-1 of the PWM control unit 3.
It controls and turns on and off the direct current output from the rectifier circuit 2. The PWM control unit 3 controls the ON / OFF time of the pulse power supply unit 4 by controlling the pulse width of the pulse signal of the PWM control circuit 3-1.
The N / OFF output is supplied to the charging terminal 14 via the high frequency rectifying diode 5 and the switch 11.

The output voltage V ₁ is divided by the resistors 9 and 10, and the divided voltage is compared with the reference voltage V _r1 by the voltage detection unit 7, and the difference voltage is amplified and PWM control unit 3 is input to the photocoupler 3-2. In the PWM control unit 3, the photo coupler 3-2 receives the signal, and the PWM control circuit 3
The pulse width of the output signal of −1 is controlled to output the output voltage V ₁
The voltage difference between the _divided voltage and the reference voltage V _r1 is controlled to be zero. Similarly, at the initial stage of charging, the charging current I is controlled to be constant by the constant current control circuit, but illustration of the circuit is omitted here.

FIG. 4 is a diagram showing the charging characteristics of a conventional battery charger. In the constant current charging region at the initial stage of charging, the charging current I is controlled to be constant, and after the output voltage V ₁ reaches the set voltage, it is controlled to the constant voltage as described above (constant voltage charging region). When the charging current I decays to the full current I _0, it is determined that charging is completed, and the switch 11 is turned off.

[0006]

However, in the battery charger 100 having the above-mentioned conventional structure, the diode 5 for high frequency rectification generates a large amount of heat, and even when the Schottky diode is used, the forward voltage is 0.4 V, and the charging current is, for example, the charging current. When is 3 A, the power (heat) loss is 1.2 W. In addition, the battery 200 has a resistance (contact resistance) value Rs of the switch 11, a resistance value Rf of the substrate pattern, and a charging terminal 1.
Since the resistance value Rc of the contact resistance of No. 4 is inserted in series, the charging voltage Vb applied between the terminals 23 of the battery 200 is a voltage drop due to the resistance value from the output voltage V ₁ {I (Rs + Rf + Rc). } Minutes, and Vb in FIG.
As shown in, Vb = V ₁ −I (Rs + Rf + Rc). That is, in the constant voltage region, the charging voltage Vb gradually rises and approaches the output voltage V _1. Therefore, there is a problem that the decay of the charging current I is slow and the charging completion time t becomes long.

The present invention has been made in view of the above points, and an object of the present invention is to provide a battery charger which eliminates the above problems, has a small heat loss, and can significantly reduce the charging time.

[0008]

In order to solve the above problems, the invention according to claim 1 is directed to a rectifier circuit for converting alternating current into direct current, a pulse power supply section for turning on / off a direct current output of the rectifier circuit, and the pulse. PWM control unit for controlling the power supply unit, high-frequency rectifier circuit for rectifying the output of the pulse power supply unit, output voltage V
_{A first} feedback circuit that compares ₁ with the first reference voltage V _r1 and feeds back the difference V ₁ −V _r1 to the PWM control unit, and determines the pulse width of the pulse signal from the PWM control unit. Control, control the ON / OFF time of the pulse power supply, control the output voltage V _1, and charge through the switch.
Configured to output to a battery connected to the terminals
In the battery charger, the battery
Remove the battery voltage Vb and from the vicinity of the electrode of the battery on the side, a second feedback circuit for feeding back the difference compared with the the battery voltage Vb and the second reference voltage V _r2 to the voltage Vb-V _r2 to the PWM controller It is characterized in that it is provided separately from the first feedback circuit.

The invention described in claim 2 is the same as claim 1.
In the battery charger described in the above item 1, an FET is used in the high frequency rectification circuit, and the FET is turned on and off by the output of the pulse power supply unit.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 is a diagram showing a configuration example of a battery charger of the present invention. As shown,
The battery charger 100 of the present invention uses a FET (Field Effect Transistor) 30 as a high frequency rectifier circuit to suppress heat generation, and further, to reduce the influence of voltage drop, the battery voltage V is higher than that of a portion closer to the electrode of the battery element 21.
The voltage terminals 26, 26 for taking out b are provided.
Battery voltage Vb taken out between 6 and 26 and reference voltage V
A means for feeding back the difference in _r2 (detailed later) is provided. In the figure, the same reference numerals as those in FIG. 3 have the same functions, and a description thereof will be omitted.

The pulse power supply unit 4 outputs a pulse voltage and F
ET30 drain D, diode 32 and resistor 31
It is applied to the gate G through the circuit of. The FET 30 conducts between the drain D and the source S only when the pulse output voltage is a positive voltage, and opens when the pulse output is 0, and thus has the same rectifying function as the diode 5 in FIG. During conduction between the drain D and the source S, the voltage drop between the drain D and the source S is 0.1 V or less, and if the charging current is 3 A, the power loss in the FET 30 is 0.3 W or less.

The casing 22 of the battery 200 is newly provided with voltage terminals 26, 26, and the battery voltage Vb is introduced from the vicinity of both electrodes of the battery element 21 in order to reduce the influence of the voltage drop. The resistor 27 is connected to the terminal 26,
It is a short-circuit current limiting resistor for limiting the short-circuit current when 26 is short-circuited.

On the other hand, the battery charger 100 is provided with voltage terminals 19, 19 connected to the voltage terminals 26, 26 of the battery 200 at the time of charging and a voltage detection unit 15, and a battery applied to the voltage terminals 19, 19 at the time of charging. Voltage Vb
The pressure through the resistor 17 and the resistor 18 minutes, apply voltage and the reference voltage V _r2 obtained by dividing該分to the voltage detection unit 15, and a voltage with a reference voltage V _r2 obtained by dividing the amount the voltage detecting section 15 The difference voltage e is compared, amplified, and fed back to the PWM control unit 3.

FIG. 2 is a diagram showing the charging characteristics of the battery charger of the present invention. In the constant current charging area at the initial stage of charging, the charging current I is controlled to be constant, and after the battery voltage Vb reaches the set voltage, it is controlled to a constant voltage (constant voltage charging area). Hereinafter, description will be given using mathematical expressions.

The voltage of the reference voltage generator 8 is V _r1 and the resistor 9
When the charging terminals 14 and 14 are opened, that is, when the battery 200 is disconnected from the battery charger 100, the output voltage V ₁ of the battery charger 100 is V ₁ = V _r1 (1 + R1 / R2) is controlled.

The set voltage of the reference voltage generator 16 is set to V
_{When r2} is the resistance value of the resistor 17, R4 is the resistance value of the resistor 18, and R5 is the resistance value of the resistor 27, the battery voltage Vb when the battery 200 is connected to the battery charger 100 is The difference voltage e between the voltage obtained by dividing Vb by the resistors 17 and 18 and the set voltage V _r2 of the reference voltage generator 16 becomes small, that is, Vb = V _r2 (1+ (R3 + R5) / R4) Controlled to approach. Incidentally, the resistor 17 and the resistor 1
8. Since the resistor 27 is a voltage circuit, the influence of contact resistance between the voltage terminals 19 and 19 and the voltage terminals 26 and 26 can be reduced by increasing the resistance value.

When the charging current is I, the (contact) resistance value of the switch 11 is Rs, the resistance value of the substrate pattern is Rf, and the contact resistance value of the charging terminal 14 is Rc, the output voltage V ₁ is V ₁ = Vb + I (Rs + Rf + Rc), and if the setting of the voltage detection unit 7 (setting of V ₁ ) and the setting of the voltage detection unit 15 (setting of Vb) are set to V ₁ −I (Rs + Rf + Rc) ≧ Vb, PWM The control unit 3 controls the output voltage Vb by the voltage detector 15. Therefore, the battery voltage Vb rises as shown in FIG. 2 and is controlled by the set value in the constant voltage charging region, so that the decay of the charging current is accelerated and the charging completion time (time to decrease to the full current I ₀ ) is short. Become. Then, as shown in the figure, the output voltage V ₁ is increased by a voltage drop of the set voltage, that is, {I (Rs + Rf + Rc)}.

As described above, according to this embodiment, since the FET 30 is used for the high frequency output of the pulse power source section 4,
The power loss is reduced from 1.2 W in the case of using the conventional diode to 0.3 W or less, and heat generation is also reduced.
In addition, from the vicinity of both electrodes of the battery element 21, the voltage terminal 2
Since the battery voltage Vb is taken out to 6 and 26, and the battery voltage Vb is controlled as the output voltage, the influence of the charging current due to a voltage drop or the like is eliminated, the charging completion time t is shortened, and the voltage / current is accurately and properly controlled. Therefore, overcharging or undercharging of the battery element 21 is eliminated.

[0019]

As described above, according to the invention described in each claim , the following excellent effects can be obtained .

According to the invention described in claim 1, the switch
From the battery side and near the battery electrodes
The voltage Vb is taken out and the battery voltage Vb and the second reference
The voltage _Vr2 is compared and the difference voltage Vb- _Vr2 is applied to the PWM control unit.
The second feedback circuit for feeding back the first feedback circuit
Since it is provided separately from the feedback circuit,
Immediately when the battery is not installed in the
The battery is not installed and the switch is in the OFF state.
Control the output voltage V ₁ with the first feedback circuit.
Output voltage V ₁ becomes abnormally high.
It is safe and secure. Also the battery char
When the battery is installed in the
When it is installed and the switch is in the ON state,
It is necessary to control the battery voltage Vb with the feedback circuit.
Therefore, the influence of the voltage drop due to the contact resistance and the resistance of the substrate pattern is eliminated, and the charging completion time can be shortened.

[0021] According to the invention of claim 2, the above-mentioned claim
In addition to the effect of the invention described in Item 1, the high frequency rectifier circuit has an FE.
T is used and the FET is turned on by the output of the pulse power supply unit.
・ As it is configured to turn off, the loss of the high frequency rectifier circuit
Loss is reduced and the amount of heat generated is also reduced.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration example of a battery charger of the present invention.

FIG. 2 is a diagram showing charging characteristics of the battery charger of the present invention.

FIG. 3 is a diagram showing a configuration example of a conventional battery charger.

FIG. 4 is a diagram showing charging characteristics of a conventional battery charger.

[Explanation of symbols]

100 battery charger 1 power supply terminal 2 rectifier circuit 3 PWM control unit 3-1 PWM control circuit 3-2 Photo coupler 4 pulse power supply 4-1 Output transformer 4-2 Transistor 7 Voltage detector 8 Reference voltage generator 9 resistors 10 resistors 11 switch 14 charging terminals 15 Voltage detector 16 Reference voltage generator 17 resistor 18 resistors 19 voltage terminals 200 batteries 21 Battery element 22 casing 23 terminals 26 voltage terminals 30 FET 31 resistor 32 diodes

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Claims (2)

(57) [Claims] 1. A rectifier circuit for converting alternating current into direct current, a pulse power supply section for turning on / off a direct current output of the rectifier circuit, a PWM control section for controlling the pulse power supply section, and a high frequency for rectifying the output of the pulse power supply section. A rectifier circuit, and a first feedback circuit for comparing the output voltage V ₁ with the first reference voltage V _r1 and feeding back the difference V ₁ −V _r1 to the PWM control unit. The pulse width of the pulse signal is controlled, the ON / OFF time of the pulse power source is controlled to control the output voltage V _1, and the charging terminal is connected through the switch.
In a battery charger configured to output to a continuous battery, the battery voltage Vb is taken out from the switch on the battery side and in the vicinity of the electrode of the battery, and the battery voltage
Vb and the second reference voltage V _r2 are compared to _obtain a difference voltage Vb−V _r2
And a second feedback circuit for feeding back to the PWM control unit separately from the first feedback circuit. 2. An FET is used in the high frequency rectification circuit,
The FET is turned on / off by the output of the pulse power supply unit.
The battery charger according to claim 1, wherein the battery charger is configured to: