JPH1048264A - Current detector for electronic apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To detect relationship of connection through a simple arrangement by detecting a voltage drop across a resistor due to connection of a terminal and turning a latch circuit on, and turning the latch circuit off when disconnection of the terminal is detected thereby controlling a transistor with the output from the latch circuit and feeding power to the terminal. SOLUTION: When a terminal is connected with a main unit, an FET 3 is initially turned off and a current flows from a power supply terminal 1 through a resistor 4. A latch circuit 6 is turned on when a voltage drop across the resistor 4 is detected by a voltage detection circuit 5 and a detected signal is latched. The FET 3 is turned on with an output from the latch circuit 6 and a source power is fed through a power supply terminal 2 to the terminal. When a detection switch 7 detects disconnection of the terminal, the latch circuit 6 is turned off to interrupt power supply to the power supply terminal 2. In other words, current variation is detected over a wide range through simple circuitry and the mounting and the relationship of connection of an electronic apparatus can be detected.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a current detecting device for electronic equipment, and more particularly to a current detecting device capable of detecting a change in current over a wide range with a simple structure.

[0002]

2. Description of the Related Art In recent years, portable electronic devices (hereinafter, represented by portable terminals) such as portable information processing terminals have become widespread in business and other fields. Since such a portable terminal is portable, it is operated with a secondary battery that can be repeatedly used by charging as a power source. When data is transmitted / received to / from a main device such as a host computer or a personal computer, the data is transmitted / received by being mounted on a concentrator / distributor unit connected to these main devices, that is, a so-called concentrator / distributor. In this case, in consideration of the fact that the portable terminal uses a secondary battery as a power source, a measure for charging the secondary battery at the same time that the portable terminal is attached to the collecting and distributing apparatus and data is transmitted and received. Is adopted. Therefore, usually, a detection switch for mechanically detecting the attachment of the portable terminal is provided in the collecting and distributing device, and when the portable terminal is properly attached, the data transmitting / receiving unit and the charging circuit are closed to perform both operations. Like that.

[0003]

However, in the above-described conventional current detecting device for electronic equipment, since the attachment of a terminal device such as a portable terminal to a main device is mechanically detected, the portable terminal is not used. There is a possibility that even if it is slightly shifted from the collecting / distributing device, the attachment of the portable terminal is detected, and a situation may occur in which data transmission / reception is not actually performed or a charging operation is not performed. is there.

In order to eliminate such a problem, there is a method of detecting in the power supply circuit section that a current has actually flowed from the main device to the portable terminal. However, depending on the situation when the mobile terminal is connected, several mA to several hundred mA
Current detection must be performed with respect to the current, and the existing current detection device has a disadvantage in that it is costly just to detect the current.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and an object of the present invention is to provide a current detecting device for an electronic device which can detect the mounting and connection of the electronic device with a simple circuit configuration.

[0006]

In order to achieve the above object, the present invention provides a current detecting device for an electronic device, comprising a power input terminal, a power supply terminal connected to the power input terminal and supplying power to the terminal device. A transistor member connected between the power input terminal and the power supply terminal for switching the power supply terminal, a resistor connected in parallel to the transistor member, and detecting a voltage drop across the resistor. A voltage detecting means, a latch circuit for latching a voltage value detected by the voltage detecting means and operating a transistor member at an output thereof, and a terminal device connected to a circuit branched from a circuit connecting a power input terminal and a power supply terminal to mount a terminal device. And a detection switch for detecting the

According to the present invention, current flows first through the resistor due to the connection of the terminal equipment, thereby causing a voltage drop. This voltage drop is detected by the voltage detecting means, and the latch circuit is turned on to latch the detection signal.
Then, the transistor member is turned on by the latch output to supply power to the terminal device. When the detection switch detects the detachment of the terminal device, the latch circuit is turned off.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The invention according to claim 1 of the present invention is directed to a power supply input terminal, a power supply terminal connected to the power supply input terminal and supplying power to terminal equipment, and a power supply terminal between the power supply input terminal and the power supply terminal. , A resistor connected in parallel to the transistor, a resistor connected in parallel to the transistor, voltage detecting means for detecting a voltage drop across the resistor, and voltage detecting means. A latch circuit for latching the applied voltage value and activating the transistor member with its output, and a detection switch connected to a circuit branched from a circuit connecting the power input terminal and the power supply terminal and detecting the mounting of the terminal device The voltage drop in the resistor is latched and used as an operation signal of the transistor member, and the detection switch detects the disconnection of the terminal device and latches it. So as to turn off the operation of the circuit, it detects a change in current over a wide range with a simple circuit configuration, an effect that allows detecting the mounting and connection of electronic devices.

An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram illustrating a schematic configuration of a current detection device for an electronic device according to an embodiment of the present invention.
In FIG. 1, reference numeral 1 denotes a power input terminal, and 2 denotes a power supply terminal connected to the power input terminal, and supplies power to a terminal device such as a mobile terminal. Reference numeral 3 denotes an FET which is connected between the power input terminal 1 and the power supply terminal 2 and performs a switching operation for transmitting power to the power supply terminal 2. A resistor 4 is connected in parallel to the FET 3. 5 is a voltage detection circuit for detecting a voltage drop caused by the resistor 4 when the current is conducted, 6 is a latch circuit for latching the voltage value detected by the voltage detection circuit and operating the FET 3 with its output,
Reference numeral 7 denotes a detection switch which is connected to a circuit branched from a circuit connecting the power input terminal 1 and the power supply terminal 2 and detects attachment and detachment of a terminal device. A relatively large resistance value is set for resistor 4, and in this embodiment, for example, a resistor of Rs = 2.7 (KΩ) is used.

The latch circuit 6 comprises a NAND gate 6a to which a detection signal of the detection switch 7 is input, and a NAND gate 6b for performing a logical OR operation of the output of the NAND gate 6a and the output of the voltage detection circuit 5. . The latch circuit 6 and the FET 3 are connected so that the output of the latch circuit 6 is transmitted to the FET 3.

The operation of the current detecting device for an electronic device having such a configuration will be described. When a terminal device is attached to a main device, for example, a portable terminal is attached to a concentrator / distributor, whether or not the terminal device has been attached correctly is determined by whether or not a current flows through a circuit. obtain. When the terminal device is properly mounted, the FET 3 is initially turned off, so that a current flows through the resistor 4 by the power from the power supply terminal 1 and the resistor 4 A voltage drop occurs. The voltage detection circuit 5 determines whether or not this voltage drop has occurred.
When the voltage drop in the resistor 4 is detected, the latch circuit 6 is turned on to latch the detection signal. Then, the FET 3 is turned on by the output of the latch circuit 6, the power supply is conducted to the power supply terminal 2, and the power is supplied to the portable terminal. When the detection switch 7 detects the detachment of the portable terminal, the latch circuit 6 is turned off to stop supplying power to the power supply terminal.

FIG. 2 is a truth table showing the signal levels of the input section (latch input section) and the output section in the current detection device during the above operation. As the latch input unit, NAND
The input side of the gate 6a is an input section A, the input side of the NAND gate 6b is an input section B, and the output section is Y. In the current detection operation, when the power is turned on, the input section A is set to Lo.
It takes a w level (ie, “0”) and takes a Hi level (ie, “1”) when the detection switch 7 is turned on. It takes "1" for the load connection, and takes "0" when the detection switch 7 is turned off. The input section B takes "1" when the power is turned on, and takes "1" when the detection switch 7 is turned on. It takes "0" for the load connection, and takes "0" when the detection switch 7 is turned off. The output section Y takes "1" when the power is turned on, and takes "1" when the detection switch 7 is turned on. It takes "0" for the load connection and takes "1" when the detection switch 7 is turned off.

With the above operation, the attachment of the portable terminal is detected by current detection, and the power supply is supplied to the portable terminal.

[0014]

As described above, according to the present invention,
A power supply input terminal, a power supply terminal connected to the power supply input terminal, and supplying power to the terminal device;
A transistor member connected between the power input terminal and the power supply terminal for switching the power supply terminal; a resistor connected in parallel to the transistor member; and a voltage for detecting a voltage drop across the resistor. Detecting means, a latch circuit for latching the voltage value detected by the voltage detecting means and activating the transistor member with its output, and a terminal connected to a circuit branched from a circuit connecting the power input terminal and the power supply terminal to mount the terminal device. Since the detection device is constituted by the detection switch for detecting, it is possible to realize a current detection device capable of detecting a change in current over a wide range with a simple circuit configuration and detecting the mounting and connection of the electronic device.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a configuration of a current detection device of an electronic device according to an embodiment of the present invention.

FIG. 2 is a truth table showing signal levels of an input unit and an output unit in the current detection device during operation of the embodiment.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Power supply input terminal 2 Power supply terminal 3 FET (transistor member) 4 Resistor 5 Voltage detection circuit 6 Latch circuit 7 Detection switch

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[Procedure amendment]

[Submission date] October 21, 1996

[Procedure amendment 1]

[Document name to be amended] Drawing

[Correction target item name] All figures

[Correction method] Change

[Correction contents]

FIG.

FIG. 2

Claims (1)

[Claims] 1. A power supply terminal, a power supply terminal connected to the power supply input terminal for supplying power to terminal equipment, and a transistor member connected between the power supply input terminal and the power supply terminal for switching the power supply terminal. A resistor connected in parallel to the transistor member, voltage detecting means for detecting a voltage drop at both ends of the resistor, and latching the voltage value detected by the voltage detecting means to operate the transistor member at its output. And a detection switch connected to a circuit branched from a circuit connecting the power supply input terminal and the power supply terminal to detect the attachment of the terminal device. The detection circuit detects the detachment of the terminal device and activates the latch circuit. A current detection device for an electronic device, wherein the current detection device is turned off.