JP3156585B2 - Charging device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a charging device used for charging a rechargeable battery of a personal computer or a video-integrated camera.

[0002]

2. Description of the Related Art A conventional technique will be described with reference to a circuit diagram of a charging device shown in FIG. According to the drawing, reference numeral 3 denotes a DC / DC converter for converting a voltage provided with a positive input power terminal 1 and a negative input power terminal 2, and 8 denotes an emitter connected to the positive output terminal of the converter 3. And the collector side is connected via a diode 15 to the positive charging terminal 12.
And a first transistor having a base connected to a plus output terminal of the converter 3 via a resistor 7.

[0003] 16 and 17 are detachable batteries 1
4 is a voltage dividing resistor connected in series between a positive charging terminal 12 and a negative charging terminal 13, and 11 is a voltage dividing resistor having an emitter connected to the base of the first transistor 8 and a collector connected to the charging terminal. 13 is a transistor whose base side is connected to the control circuit 9.

The control circuit 9 is connected between the voltage dividing resistors 16 and 17, detects the voltage divided between the voltage dividing resistors 16 and 17, turns off the transistor 11, and turns the first transistor 8 on. At the same time, the voltage of the resistor 10 connected between the charging terminal 13 and the negative output terminal of the converter 3 is detected to keep the voltage of the resistor 10 constant (that is, the charging current flowing through the resistor 10 is reduced). And a built-in timer circuit (not shown). After charging for a certain period of time, the transistor 11 is driven to turn on / off the first transistor 8 to stop charging the battery 14. It also has the function of performing

Next, the operation will be described. The power is supplied from the input power supply terminals 1 and 2 (for example, 15 V), and the converter 3 converts the power to a voltage (0 V to 13 V) suitable for charging the battery 14. Output, the emitter and collector of the first transistor 8 and the positive charging terminal 1
2 for charging the battery 14.

In order to control the charging voltage to the battery 14 optimally, it is necessary to keep the charging current constant when the battery 14 is a nickel-cadmium battery or a nickel-metal hydride battery. The converter 3 controls the converter 3 in comparison with a prescribed voltage to make the charging current constant.

Further, the voltage of the battery 14 is
6 and the voltage divided by the voltage dividing resistor 17 are input to an A / D converter (not shown) of the microcomputer in the control circuit 9 to monitor the state of charge of the battery 14, and when the charge of the battery 14 is completed. , The first transistor 8 is turned off by turning off the transistor 11, and the charging current is stopped.

Since the above state is a state in which a DC voltage is being output from converter 3, transistor 11
Even if the base voltage is lowered and turned off, the minute current i flows through the collector of the transistor 11 and the first transistor 8 is turned on by the current i.
Through the resistor 7 so that the first transistor 8 is not unnecessarily turned on. That is, if the voltage between the base and the emitter at which the transistor 8 is turned on is Vbe, and the resistance value of the resistor 7 is R7, then i × R7 <Vbe (about 0.6 V)... Is set.

When the battery 15 is mounted on the charging device in a state where power is not supplied from the input power supply terminals 1 and 2, the voltage of the battery 14 is applied to the collector of the first transistor 8. That is, the emitter and the resistor 7 of the first transistor 8 connected to the converter 3 are at 0 V because there is no power supply to the input, so that the base of the first transistor 8 from the collector to the base is a PN junction. Therefore, the base current flows through the resistor 7 connected to the base, preventing a large current from flowing from the collector to the emitter of the first transistor 8, and preventing the converter 3 and the control circuit 9 from consuming the current of the battery 14. It is to prevent.

[0010]

However, in the above configuration, the diode 15 needs to be of a large current type in which a charging current of 1-2 A flows during charging, and such a large current type is required. Since the device generates a large amount of heat, it is necessary to provide a heat radiating plate, the voltage drop is 0.7 V, the power loss is as large as about 0.7 to 1.4 W, and the diode 15
However, there is a problem that the cost is high and the heat sink and its mounting cost are required.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned conventional problems, and has as its object to provide a cost-effective charging device which can obtain the same effect as the conventional one by using a low-current diode. is there.

[0012]

In order to solve the above-mentioned problems, a charging device according to the present invention comprises: a converter having a DC input; a first transistor having an emitter connected to a positive output terminal of the converter; A first series circuit including a first resistor and a first diode connected between the emitter and a positive input terminal of the converter;
A second series circuit composed of a second resistor and a second diode connected between the intersection of the resistor and the first diode and the base of the first transistor, and a base voltage of the first transistor. And a control circuit for controlling.

According to the above configuration, most of the charging current in the normal charging state flows from the positive output terminal of the converter to the positive charging terminal via the emitter and the collector of the transistor. The second diode may correspond to an extremely small current, and the second diode allows the connection of the battery from the base of the first transistor to the second resistor even when the battery is mounted in the charging device without power supply. Since the flowing current is blocked, the current does not flow from the collector to the emitter, so that the discharging that occurs when the battery is attached to the charging device with the battery turned off can be prevented and can be performed at very low cost.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The invention according to claim 1 of the present invention is directed to a converter having a DC input, a first transistor having an emitter connected to a positive output terminal of the converter, A first series circuit consisting of a first resistor and a first diode connected between a positive input terminal of the converter, an intersection of the first resistor and the first diode, and a first transistor connected to the first transistor; A second resistor and a second diode connected between the bases;
And a control circuit for controlling the base voltage of the first transistor, and a second diode for preventing discharge of a battery mounted when the charging device is turned off is provided for an extremely low current. Therefore, it is possible to provide a charging device which is excellent in cost performance by using an inexpensive diode and eliminating the need for a heat sink.

According to a second aspect of the present invention, there is provided a converter having a direct current as input, two first transistors having respective emitters connected to a positive output terminal of the converter, the respective emitters and the converter. A first series circuit composed of a first resistor and a first diode connected between the positive input terminals of the first and second transistors, an intersection of the first resistor and the first diode, and the two first transistors And a control circuit for controlling the base voltage of each of the two first transistors, and a second series circuit composed of two sets of second resistors and second diodes connected between the respective bases. In a charging device in which two batteries can be mounted, the same effect as the first aspect of the invention can be obtained.

An embodiment of the present invention will be described below with reference to FIG. In the description, the same parts as those in the related art are denoted by the same reference numerals, and description will be omitted.

(Embodiment 1) FIG. 1 is a circuit diagram of an embodiment of a charging device according to the present invention. Differences from the prior art are as follows. (1) The collector of the first transistor 8 and the charging terminal 12
A point where the diode 15 inserted between them is deleted and directly connected. (2) A first resistor 4 provided on the input power supply terminal 1 side between the input power supply terminal 1 of the converter 3 and the emitter of the first transistor 8 and a first diode 5 provided on the emitter side of the first transistor 8 A first series circuit consisting of (3) The conventional resistor 7 connected between the emitter and the base of the first transistor 8 is deleted, the emitter and the base of the first transistor 8 are opened, and the first series transistor 8 is opened. The second diode 6 connected to the intersection of the first resistor 4 and the first diode 5 of the circuit and the second resistor 1 connected to the base of the first transistor 8
8 is provided with a second series circuit. It is.

The operation of the charging device configured as described above will be described below, focusing on the first transistor 8 and the first and second series circuit portions, which are essential parts of the present invention.

First, the second series circuit includes the battery 14
At the end of charging, even if the base voltage of the transistor 11 is lowered and turned off by the control circuit 9, since the DC voltage is output from the converter 3, the minute current i flows through the collector of the transistor 11. The small current i flows through the diode 6 and the resistor 18 so that the first transistor 8 does not turn on, so that the first transistor 8 does not turn on unnecessarily.

That is, the base-emitter voltage at which the first transistor 8 starts to turn on is Vbe, the resistance value of the resistor 18 is R18, and the forward voltages of the first diode 5 and the second diode 6 are Vd5 and Vd6. Then, the second resistor 18 is set such that (i × R18 + Vd6) <(Vbe + Vd5) (2)

Specifically, Vd6 and Vd5 are appropriately set in the first resistor 4, and a current close to the minute current i is supplied to the diode 5
By eliminating Vd6 and Vd5 from the above equation 2 by flowing through equation (2), equation 2 satisfies i × R18 <Vbe, and can be handled in the same manner as equation 1 of the prior art.

Next, a case will be described in which the battery 14 is mounted on the charging device in a state where there is no power supply from the input power supply terminals 1 and 2 (the power is supplied by converting the voltage from a home AC power supply).

The voltage of the battery 14 is applied to the collector of the first transistor 8, and the converter 3
, The emitter of the first transistor 8 and the resistor 4 are at 0 V because there is no input power supply. First
Although the base from the collector to the base of the transistor 8 is a PN junction, the base current does not flow from the base via the resistor 18 because the second diode 6 is connected in the reverse direction.

As a result, the current does not flow from the collector to the emitter of the first transistor 8, so that the converter 3 and the control circuit 9 do not consume the current of the battery 14.

Further, the first and second diodes 5 and 6 do not directly handle the charging current unlike the conventional diode 15, so that there is no power loss due to the diodes. In this case, a low-capacity and inexpensive device can be used, and a heat radiating plate is not required, which can contribute to miniaturization and cost reduction of the charging device.

(Embodiment 2) FIG. 2 is a circuit diagram of another embodiment of the charging device according to the present invention.
4, 14a. As is clear from FIG. 2, two charging circuits of FIG. 1 after the converter 3a are provided in parallel. The same circuit parts as those of FIG. 1 are given the same reference numerals as those of the circuit part, and the description is the same. Therefore, the description is omitted and only the differences from FIG.
Reference numeral a denotes a control circuit for detecting the divided voltages of the voltages at both ends of the batteries 14 and 14a to detect the first transistors 8 and 8a, respectively.

In the present embodiment, the first series circuit connects the first resistor 4 to the input power supply terminal 1 side of the converter 3a, and connects the first diode to the intersection of the first transistors 8, 8a. Side, so the first series circuit is 1
A circuit may be used, and in a charging device for charging two batteries, an increase in the number of components can be suppressed.

[0028]

As described above, the charging device according to the present invention comprises a converter having a DC input, a transistor having an emitter connected to the positive output terminal of the converter, the emitter and the positive input of the converter. A first series circuit including a first resistor and a first diode connected between the terminals; and a second series circuit connected between an intersection of the first resistor and the first diode and a base of the transistor. By comprising a second series circuit comprising a resistor and a second diode and a control circuit for controlling the base voltage of the transistor, the first and second diodes may correspond to an extremely small current. Also, the second diode prevents the current flowing from the base of the transistor to the resistor even if the battery is mounted in the charging device without power supply. Since the, it does not flow a current from the collector to the emitter, the discharge from the battery occurring when mounted to the battery off by charging apparatus may be capable of performing this extremely low cost is possible prevented.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of a charging device according to an embodiment of the present invention.

FIG. 2 is a circuit diagram of another embodiment.

FIG. 3 is a circuit diagram of a conventional charging device.

[Explanation of symbols]

 1, 2 input power supply terminal 3, 3a converter 4 first resistor 5 first diode 6, 6a second diode 8, 8a first transistor 9, 9a control circuit 18, 18a second resistor

Claims (2)

(57) [Claims] 1. A converter having a DC input and a first output terminal having an emitter connected to a positive output terminal of the converter.
A first series circuit consisting of a first resistor and a first diode connected between the emitter and the positive input terminal of the converter; and a first series circuit of the first resistor and the first diode. A second series circuit including a second resistor and a second diode connected between the intersection and the base of the first transistor, and a control circuit for controlling a base voltage of the first transistor. Charging device. 2. A converter having a DC input, two first transistors having respective emitters connected to a positive output terminal of the converter, and a first transistor connected between the respective emitters and a positive input terminal of the converter. The first connected to
A first series circuit consisting of a resistor and a first diode;
The intersection of the first resistor and the first diode and the 2
A second series circuit consisting of two sets of second resistors and a second diode connected between the respective bases of the first transistors, and controlling the respective base voltages of the two first transistors; A charging device including a control circuit.