JP2001238359A - Power supply circuit device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce a battery in size and weight, and to manufacture the battery at a low cost. SOLUTION: A power supply circuit in the main circuit 1 of a of a portable information terminal comprises an IC circuit 4, a diode D3 for preventing reverse current, and a pnp bipolar transistor Q2 connected between the diode D3 and a battery 2. When the circuit 4 failes, the transistor Q2 is turned on, a current flowing in the diode D3 is increased, and the voltage drop in the diode D3 is increased, to prevent application of limit voltage to the battery 2.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power supply circuit device for charging a battery, and more particularly to a power supply circuit device installed in a main body circuit of a portable information terminal.

[0002]

2. Description of the Related Art In recent years, portable information terminals such as portable telephones, notebook computers, and video cameras have become widespread.
These portable information terminals use batteries for supplying power. Generally, a rechargeable secondary battery is used as this battery.

On the other hand, a power supply circuit for charging a battery is installed in a main body circuit of the portable information terminal. FIG. 3 shows an example of a power supply circuit in a main body of a conventional portable information terminal.

[0004] As shown in FIG. 3, the power supply circuit is installed in the main body circuit 1 of the portable information terminal, and is connected to the battery 2 via the protection circuit 8. The protection circuit 8 is provided to protect the battery from overcharging or the like, and is generally formed on a separately provided protection circuit board.

The power supply circuit is connected to the outside via terminals 5 to 7, is connected to an electronic circuit 3 and an integrated circuit (IC) circuit 4, and has diodes D1, D2, D3, resistors R1, R2, and a MOS ( Metal Oxide Semiconductor) transistor Q1.

The diodes D 1 and D 2 supply current to the electronic circuit 3 or the battery 2. The diode D3 is connected to the battery 2
From flowing to the electronic circuit 3 through the resistor R2 and the MOS transistor Q1 (backflow). The resistor R1 applies a predetermined voltage to the node N2 when no current flows into the IC circuit 4.

The IC circuit 4 includes a node N on both sides of the resistor R2.
The voltage between one and the other, or one of the voltages, is detected by an electronic circuit such as a microcomputer, and a predetermined voltage is applied to the gate of the MOS transistor Q1 via the node N2. As a result, MO
The gate voltage of the S transistor Q1 is changed to control the current / voltage to the terminal 7.

The terminal 5 is, for example, a desktop adapter output terminal, the terminal 6 is, for example, an AC adapter output terminal, and the terminal 7 is a terminal for connection to the battery 2.

When charging the battery 2, a voltage of, for example, 5.5 V is applied to the terminal 6. At this time, the IC circuit 4
Detects the voltage between the nodes N3 and N4 and also detects the current flowing through the resistor R2. Based on the detection result, the IC circuit 4 sets the voltage of the node N3 to, for example, 4.2.
The voltage of the node N2 is controlled to be V. Thereby, it is possible to prevent a voltage higher than the specified voltage of 4.3 V from being applied to the battery 2.

However, the IC circuit 4 fails for some reason, and the node N2 goes to a low level.
When MOS transistor Q1 is a p-channel MOS transistor, MOS transistor Q1 turns on.

At this time, for example, the output of terminal 6 is 5.5
V, there is a voltage drop of 0.6 V due to the diode D1 and 0.1 V due to the MOS transistor Q1.
There is a voltage drop of 0.1 V or less due to the diode D3. (If the IC circuit 4 breaks down and the current to the battery 2 is small, the voltage drop due to the diode D3 may be 0.1 V or less. is there). Therefore, about 4.
A voltage of 8 V will be applied to the battery 2.

That is, a voltage higher than the limit voltage is applied to the battery 2. Thereby, there is a concern that the battery 2 is broken. In order to solve such a problem, the above-described protection circuit 8 is separately provided. By providing the protection circuit 8, even if the IC circuit 4 breaks down, the battery 2 can be protected.

[0013]

As described above, in the conventional power supply circuit, a circuit section for compensating for a failure of the IC circuit 4 is not provided on the power supply circuit side of the portable information terminal main body. It had to be provided separately on the battery 2 side.
This makes it difficult to reduce the size and weight of the battery 2,
There is also a problem that the manufacturing cost increases.

The present invention has been made to solve the above problems. An object of the present invention is to reduce the size and weight of a battery and make it possible to manufacture the battery at low cost by using a configuration of a power supply circuit in which a conventional protection circuit can be omitted.

[0015]

A power supply circuit device according to the present invention is for charging a battery, and includes a reverse current preventing element for preventing a reverse current from the battery and a voltage generated by the reverse current preventing element. Voltage drop control means for controlling the drop to protect the battery.

With the provision of the voltage drop control means, the voltage drop in the reverse current preventing element can be increased. Thereby, it is possible to prevent an overvoltage from being applied to the battery.

The power supply circuit device has a MOS (Metal Oxide Semiconductor) transistor for controlling the supply of current to the battery, and the reverse current preventing element includes a diode and is provided between the MOS transistor and the battery. . At this time, the voltage drop amount control means is connected between the reverse current preventing element and the battery.

As described above, by increasing the amount of voltage drop in the reverse current preventing element provided between the MOS transistor as a switching element and the battery, it is possible to reliably prevent the battery from being over-voltage applied.

As the voltage drop amount control means, for example, a bipolar transistor can be used. When the bipolar transistor is a pnp-type bipolar transistor, the MOS transistor is preferably a p-channel MOS transistor. When the bipolar transistor is an npn-type bipolar transistor, the MOS transistor is an n-channel MOS transistor.
It is preferably an S transistor.

Thus, by installing the bipolar transistor as described above, a desired amount of current can be drawn from between the reverse current preventing element and the battery as necessary, and the reverse current preventing element flows. The amount of current can be increased.

[0021]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS.

(Embodiment 1) FIG. 1 is a circuit diagram showing a power supply circuit according to Embodiment 1 of the present invention. This power supply circuit is for charging a battery, and is provided in the main body circuit 1 of a portable information terminal such as a mobile phone.

As shown in FIG. 1, the power supply circuit has terminals 5 to 5.
7, and connected to the electronic circuit 3 and the IC circuit 4, the diodes D1, D2, D3 and the resistor R
1, R2, R3, MOS transistor Q1, pnp
Type bipolar transistor Q2. Note that FIG.
The same components as those of the conventional example shown in FIG.

In the power supply circuit according to the present invention, a voltage drop amount control means for protecting the battery 2 by controlling a voltage drop amount by a reverse current preventing element for preventing a reverse current from the battery 2 such as a lithium ion battery. Is an important feature.

With the provision of the voltage drop control means as described above, the voltage drop in the reverse current preventing element can be increased, and the application of an excessive voltage exceeding the limit voltage to the battery 2 can be prevented. .

In the embodiment shown in FIG. 1, a diode D3 is provided as a reverse current preventing element, and a pnp bipolar transistor Q2 is provided as voltage drop amount control means. The diode D3 is a p-channel MO as a switch element.
It is provided between the S transistor Q1 and the battery 2. pn
The p-type bipolar transistor Q2 is connected between the diode D3 and the battery 2.

When the IC circuit 4 fails and the node N2 goes to a low level, the MOS transistor Q
1 turns on. At this time, since the node N2 is connected to the base of the pnp bipolar transistor Q2,
The low-level potential is applied to the base, and the emitter of the bipolar transistor Q2 is connected to the node N.
5, a potential higher than the potential applied to the base is applied.

As a result, the pnp bipolar transistor Q2 is turned on, a current flows through the pnp bipolar transistor Q2, and a desired amount of current can be extracted from the node N5. At this time, by providing the resistor R3, a constant current can flow through the pnp bipolar transistor Q2.

As a result, the amount of current flowing through the diode D3 can be increased, and the amount of voltage drop in the diode D3 can be increased. Specifically, when the output of the terminal 6 is 5.5V, the voltage drop amount of the diode D3 can be increased to about 0.6V.

Here, as in the case of the conventional example, the diode D1 has a voltage drop of 0.6 V, and the MOS transistor Q1 has a voltage drop of 0.1 V. Will join. Thus, it is possible to prevent a voltage higher than the specified voltage from being applied to the battery 2 and to protect the battery 2 from an overvoltage. As a result, the protection circuit provided conventionally can be omitted.

When pnp type bipolar transistor Q2 is employed as described above, MOS transistor Q1 is preferably a p-channel MOS transistor as described above. Thereby, when IC circuit 4 fails, pnp bipolar transistor Q2 can be turned on, and a desired current can be drawn from node N5.

(Embodiment 2) Next, Embodiment 2 of the present invention will be described with reference to FIG. FIG. 2 is a circuit diagram showing a power supply circuit according to Embodiment 2 of the present invention.

As shown in FIG. 2, in the second embodiment,
An npn-type bipolar transistor Q3 is employed instead of the pnp-type bipolar transistor Q2. In this case, the MOS transistor Q1 is an n-channel MOS transistor.

The MOS transistor Q1 is an n-channel MO
In the case of the S transistor, the output of the IC circuit 4 at the time of abnormality is at a high level. Therefore, by providing npn-type bipolar transistor Q3,
The n-type bipolar transistor Q3 can be turned on.

Thus, as in the first embodiment, a desired amount of current can be extracted from node N5, and the amount of voltage drop in diode D3 can be increased. As a result, application of overvoltage to the battery 2 can be prevented, and the battery 2 can be protected.

The npn type bipolar transistor Q
When using No. 3, it is preferable to install diodes D4 and D5 and a resistor R4 as shown in FIG.

Although the embodiment of the present invention has been described above, the above embodiment is merely an example, and the present invention is not limited to the above embodiment.

For example, any element or circuit other than the diode D3 can be used as long as a reverse current from the battery 2 can be prevented. Although a bipolar transistor has been described as an example of the voltage drop amount control means, the voltage drop amount of the reverse current preventing element may be controlled using other elements or circuits.

[0039]

As described above, according to the power supply circuit device of the present invention, it is possible to prevent the limit voltage from being applied to the battery even if the intermediate stage circuit in the power supply circuit is broken. A separately provided conventional protection circuit can be omitted. Thereby, not only the size and weight of the battery can be reduced, but also the manufacturing cost can be reduced.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of a power supply circuit according to Embodiment 1 of the present invention.

FIG. 2 is a circuit diagram of a power supply circuit according to a second embodiment of the present invention.

FIG. 3 is a circuit diagram of a conventional power supply circuit.

[Explanation of symbols]

1 body circuit, 2 batteries, 3 electronic circuits, 4 IC circuits, 5 to 7 terminals, D1 to D5 diodes, N1 to N
5 nodes, Q1 MOS transistor, Q2pnp bipolar transistor, Q3 npn bipolar transistor, R1 to R4 resistors.

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) H02J 7/00 H02J 7/00 S (72) Inventor Hirokazu Ishida 2-3-2 Marunouchi, Chiyoda-ku, Tokyo No. Mitsubishi Electric Co., Ltd. (72) Inventor Hirotoshi Morishita 2-3-2 Marunouchi, Chiyoda-ku, Tokyo Mitsui Electric Co., Ltd. (72) Tomie Tanaka 2-5-2, Otemachi, Chiyoda-ku, Tokyo F term (reference) in Mitsubishi Electric Engineering Co., Ltd.

Claims (5)

[Claims] 1. A power supply circuit device for charging a battery, wherein the power supply circuit device includes a reverse current prevention element for preventing a reverse current from the battery, and a voltage drop caused by the reverse current prevention element. Power supply circuit device, comprising: a voltage drop amount control unit for controlling the battery to protect the battery. 2. The power supply circuit device includes a metal oxide semiconductor (MOS) for controlling supply of current to the battery.
A transistor, wherein the reverse current preventing element includes a diode;
The power supply circuit device according to claim 1, wherein the power supply circuit device is provided between an S transistor and the battery, and the voltage drop amount control means is connected between the reverse current preventing element and the battery. 3. The power supply circuit device according to claim 2, wherein said voltage drop amount control means includes a bipolar transistor. 4. The method according to claim 1, wherein the bipolar transistor is a pnp.
The power supply circuit device according to claim 3, wherein the power supply circuit device is a type bipolar transistor, and the MOS transistor is a p-channel MOS transistor. 5. The device according to claim 1, wherein the bipolar transistor is npn.
The power supply circuit device according to claim 3, wherein the power supply circuit device is a type bipolar transistor, and the MOS transistor is an n-channel MOS transistor.