JPH10150732A - Battery charger - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a battery charger where the charging time is shortened while reducing heat loss. SOLUTION: The battery charger BC is constituted such that output voltage and current are compared, respectively, with reference levels and an error signal is fed back to a control section 1 so that a constant current charging operation is performed in the early charging stage and a constant voltage charging operation is performed after the battery voltage is settled. The battery charger BC comprises an amplifier 9 for amplifying the voltage in proportion to the charging current of a batter B, and an adder 4 for adding the output signal from the amplifier 9 to a reference voltage. Output voltage from the battery charger BC is controlled by feeding a differential voltage (e), obtained by comparing the output voltage from the adder 4 with the output voltage V from the battery charger BC divided through resistors 5, 6, back to the control section 1.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a battery charger for charging a lithium ion battery or the like, and more particularly to a battery charger having a short charging time and low heat loss.

[0002]

2. Description of the Related Art FIG. 2 is a diagram showing an example of a circuit configuration of a conventional battery charger. As shown in the figure, a conventional battery charger BC has a control unit 1 for controlling a voltage and a current, compares a voltage obtained by dividing an output voltage V by a resistor 5 and a resistor 6 with a reference voltage Vr, and outputs a control signal. Output voltage detector 2,
It comprises a current detection section 3 for detecting an output current from the shunt resistor 10 and outputting a control signal, and a charging terminal 8 for connecting the battery B, and supplies a charging current to the battery B via the charging terminal 8.

FIG. 3 is a diagram showing charging characteristics of the above-mentioned conventional battery charger. When the battery B is connected to the charging terminal 8 and charging is started, the control unit 1 controls the charging current Ic 'to be constant at the beginning of charging by feedback of the output signal of the current detecting unit 3. During that time, the charging voltage Vb 'of the battery B rises from the start voltage Vs as shown (constant current charging region). The control unit 1 minus the voltage drop V'the charging voltage Vb 'from the set voltage V ₀ (voltage drop due to the resistance of the contact resistance and the electric wire or the like of the charging terminals 8 and Switches) value (Vb' = V ₀ -V' ), The voltage detector 2
The output voltage is controlled to be constant by feedback of the output signal. Accordingly, attenuated in accordance with the charging current Ic' the elapsed time, the charging voltage Vb' approaches the constant voltage set value V ₀ (constant voltage charging region). When the control unit 1 detects the current I ₀ at the time of full charge t ₂ , it determines that the battery is fully charged and completes the charging.

However, in the charging by the battery charger having the above-described circuit configuration, the charging is performed at a constant voltage in the latter half of the charging time, so that the charging current Ic 'gradually decreases and the time until the battery B is fully charged, that is, the time. work in inconvenient efficiency a longer charging completion time t ₂ also there is a problem that becomes worse.

A battery charger BC having a circuit configuration shown in FIG. 4 has been proposed in order to address the above problem and to shorten the charging completion time t ₂ . In the battery charger BC, the voltage detector 2 detects a voltage V proportional to the charging current Ic.
g and the reference voltage Vr are added by the adder 4, the added voltage is compared with a voltage obtained by dividing the output voltage V by the resistors 5 and 6, and a signal corresponding to the difference voltage e is sent to the control unit 1. And the voltage is controlled by feedback.

FIG. 5 is a diagram showing charging characteristics of the battery charger BC having the configuration shown in FIG. When the battery B is connected to the charging terminal 8 and charging is started, the control unit 1 controls the charging current Ic to be constant at the beginning of charging by feedback of the output signal of the current detecting unit 3. Meanwhile, the charging voltage Vb of the battery B rises from the start voltage Vs as shown in the figure.

Here, assuming that the charging voltage of the battery B is Vb, the voltage proportional to the charging current is Vg, and the voltage drop is V ', the output voltage V = Vb + Vg + V'.
-It becomes (1). On the other hand, the control unit 1 performs feedback control such that the input voltage (difference voltage e) of the voltage detection unit 2 becomes zero in the constant voltage charging region, so that the output voltage V is set to the reference voltage Vr and the resistor 5 The output voltage V is represented by the following equation when represented by the resistance value R1 and the resistance value R2 of the resistor 6. V = (Vr + Vg) ( 1 + R1 / R2) = Vr (1 + R1 / R2) + Vg + Vg · R1 / R2 = V 0 + Vg + Vg · R1 / R2 ············· (2) where, V ₀ is the output voltage when the charging current = 0.

From the equations (1) and (2), the charging voltage Vb of the battery B is as follows: Vb = V ₀ + Vg · R1 / R2-V ′ (3) That is, if the resistance value Rg of the resistor 7 is properly selected (if the value of the voltage Vg proportional to the charging current is appropriately selected), the charging current Ic is in the constant current charging region, and the charging voltage Vb is equal to the charging current = 0. set voltage V _0, greater reached Vp of, since the constant voltage charging region charging current Ic decreases, the charging voltage V
b decreases according to equation (3) and approaches V ₀ (curve V in the figure).
b).

As can be seen from FIG. 5, the resistance value R of the resistor 7 is
If g is adjusted so as to appropriately generate a voltage Vg proportional to the charging current Ic, the open voltage of the battery B does not exceed the set voltage, does not overcharge, and does not shorten the life of the battery B. and, charging at a constant current charging region is prolonged, constant-voltage charging region is shortened charging completion time is greatly shortened full charge time t ₁ in FIG. 5 from the full charge time t ₂ in FIG.

[0010]

However, in the battery charger BC having the charging characteristic shown in FIG. 5 and having the configuration shown in FIG. 4, the maximum voltage Vp is increased within the allowable range to extend the constant current charging area. In order to increase the charging current, it is necessary to increase the resistance value Rg of the resistor 7. When the resistance value Rg is increased, the heat loss Ic ² · Rg is increased, the efficiency is reduced, and there is a problem that downsizing is difficult due to an increase in temperature.

SUMMARY OF THE INVENTION The present invention has been made in consideration of the above problems, and has as its object to provide a battery charger which has a short charging time and a small heat loss.

[0012]

In order to solve the above-mentioned problems, the present invention compares the output voltage and the output current of a battery charger with reference values and feeds back the difference value to a control unit. Amplifying means for amplifying a voltage value proportional to the charging current of a battery in a battery charger for performing constant current charging at the beginning of charging and performing constant voltage charging after the battery voltage reaches a constant value; Adding means for adding the voltage value amplified by the step (a) and the reference voltage value, comparing the voltage value added by the adding means with a voltage value corresponding to the output voltage value of the battery charger, and controlling the difference value In the part
And controlling the output voltage of the battery charger.

[0013]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 is a diagram showing an example of a circuit configuration of a battery charger of the present invention. As shown in the figure, the battery charger BC of the present invention comprises a control unit 1, a voltage detection unit 2, a current detection unit 3, an adder 4, a resistor 5, a resistor 6, a resistor 7, a charging terminal 8, an amplifier 9 It is a structure provided with. The main point of this battery charger BC is that an amplifier 9 for amplifying a voltage Vg proportional to the charging current Ic is provided, and the other points are the same as the circuit configuration of FIG. In the same drawing, the portions denoted by the same reference numerals as those in FIG. 2 have the same functions, and thus the description thereof is omitted here.

The charging characteristics of the battery charger of the present invention are the same as the charging characteristics shown in FIG. The operation of the battery charger of the present invention will be described with the amplification degree of the amplifier 9 as K. Assuming that the charging voltage of the battery B is Vb, the voltage proportional to the charging current is Vg, and the voltage drop (the voltage drop due to the contact resistance of the charging terminal 8 and the switch or the resistance of the electric wire or the like) is V ′, the output voltage V V = Vb + Vg + V '(4) On the other hand, in the constant voltage charging region, the control unit 1 divides the input voltage (the voltage obtained by adding the voltage Vg proportional to the charging current Ic and the reference voltage Vr) and the output voltage V into the resistor 5 and the resistor 6. Since the feedback control is performed so that the difference voltage e) from the compressed voltage becomes zero, the output voltage V is the reference voltage Vr, the resistance of the resistor 5 is R1, the resistance of the resistor 6 is R2, and the amplifier is When the amplification degree of No. 9 is represented by K, the output voltage V is represented by the following equation. V = (Vr + K · Vg) (1 + R1 / R2) (5) From the equations (4) and (5), the charging voltage Vb is: Vb = V ₀ + ((1 + R1 / R2) ) K-1) Vg-V '(6) Here, V ₀ is the output voltage when the charging current = 0.

If the resistance value of the resistor 7 is Rg, Vg = I
c · Rg, and Ic attenuates rapidly with time, so that the charging voltage Vb has the characteristics shown in FIG. By appropriately selecting the amplification degree K of the amplifier 9 from the equation (6), the charging voltage Vb becomes the set voltage V ₀ (the output voltage when the charging current = 0).
Can be set as high as possible (Vp). The heat loss due to the resistor 7 is given by the following equation: Heat loss = Ic ^2.
Rg, and the calorific value can be sufficiently reduced by reducing the resistance value Rg.

As described above, according to this embodiment, the voltage proportional to the charging current Ic is amplified by the amplifier 9 and the reference voltage V
r and the output voltage V are applied to the resistors 5 and 6
And the output voltage is controlled by feedback of the difference voltage e through the control unit 1. If the amplification K of the amplifier 9 is properly selected, the charging voltage Vb is The charging time can be shortened by setting as high as possible and the resistance value Rg of the resistor 7 for detecting the charging current Ic can be sufficiently reduced to reduce the heat loss and suppress the heat generation.

[0017]

As described above, according to the present invention, the amplifying means for amplifying the voltage value proportional to the charging current of the battery and the adding means for adding the voltage value amplified by the amplifying means and the reference voltage value are provided. The voltage value added by the adding means is compared with a voltage value corresponding to the output voltage value of the battery charger, and the difference voltage value is fed back to the control unit to output the output voltage of the battery charger. Therefore, by appropriately selecting the amplification degree of the amplifier, the output voltage of the battery charger in the constant current region is increased within an allowable range to shorten the charging time, and a resistor for detecting the charging current is used. By making the resistance value sufficiently small, it is possible to provide a battery charger capable of suppressing the amount of heat generation and downsizing.

[Brief description of the drawings]

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

FIG. 2 is a diagram showing a circuit configuration example of a conventional battery charger.

FIG. 3 is a diagram showing charging characteristics of the battery charger shown in FIG.

FIG. 4 is a diagram showing an example of a circuit configuration of a conventional battery charger.

5 is a diagram showing charging characteristics of the battery charger shown in FIG.

[Explanation of symbols]

 BC Battery Charger 1 Controller 2 Voltage Detector 3 Current Detector 4 Adder 5 Resistor 6 Resistor 7 Resistor 8 Charging Terminal 9 Amplifier B Battery

Claims (1)

[Claims] An output voltage and an output current of a battery charger are each compared with a reference value, and a difference value is fed back to a control unit. The control unit performs constant current charging at an initial stage of charging.
Amplifying means for amplifying a voltage value proportional to the charging current of the battery, a voltage value amplified by the amplifying means, and a reference voltage value in a battery charger for performing constant voltage charging after the battery voltage reaches a constant value. The voltage value added by the adding means is compared with a voltage value corresponding to the output voltage value of the battery charger, and the difference value is fed back to the control unit to provide a battery. A battery charger for controlling an output voltage of the charger.