JP2000014036A - Power source unit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To eliminate consumption of a car battery at a time when a load with charge function is removed. SOLUTION: A capacitor 4 is charged when power is supplied to a load. When the load is removed, a voltage between terminals of a resistor 5 becomes zero, the output of a comparator 6 turns to a low level, a transistor 3 is turned off, and a current flowing into a DC/DC converter 1 is cut off. Thereby consumption of a battery is prevented when the load is removed. When the load is connected, charges of the capacitor 4 flows in the load, a potential difference is generated across the resistor 5, and the output of the comparator 6 turns to a high level. Thereby the transistor 3 turns on, the battery is connected with the DC/DC converter 1, and a state of power supply is set.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power supply device, and more particularly, to a power supply device having a function of supplying and charging power to a portable telephone.

[0002]

2. Description of the Related Art FIG. 2 shows a schematic configuration of a vehicle-mounted power supply device of a portable telephone, in which a DC input from a car battery is converted into a voltage by a DC / DC converter 1, and the portable telephone is charged via a charge control circuit 2. Supply power to The charge control circuit 2 controls so that a current corresponding to the degree of consumption of the battery of the mobile phone is output.

[0003]

In a conventional on-vehicle power supply device, the output current is controlled in accordance with the battery consumption state of the mobile phone as a load, and the mobile phone is disconnected from the power supply device or mounted. Even if the power switch of the mobile phone is turned off, that is, even when there is no load, only the output current is zero, and the DC / DC converter is provided with a DC input and is in an operating state. Had become. For this reason, even when there is no load, a current of about 10 to 20 mA is consumed by the power supply device, and there is a problem that the power of the car battery is wastefully consumed especially when the engine is stopped.

[0004] It is an object of the present invention to provide a power supply device that prevents unnecessary power consumption when the load is removed.

[0005]

In order to achieve the above object, the present invention provides a DC / DC converter for converting a DC voltage applied to an input terminal, and a DC / DC converter for converting the DC / DC voltage.
A charge control circuit for controlling an output current of a DC converter in accordance with a load, wherein a capacitor connected between positive and negative output terminals of the charge control circuit; A resistor connected between a terminal and a load connection terminal corresponding to the terminal, and an ON signal when a potential difference between both ends of the resistor becomes a predetermined value or more, and an OFF signal when the potential difference becomes less than a predetermined value. A comparator for outputting a DC voltage input when the ON signal is supplied to the DC / DC converter, and applying the DC voltage to the DC / DC converter when the OFF signal is supplied.
And a switching means for interrupting application to the DC converter.

Further, according to the present invention, the input terminal and the output terminal of the comparator are connected by a resistor, and the output of the comparator is supplied from when the operation power is supplied to the comparator until the output is determined. A power supply device characterized in that a level is set to the ON signal.

[0007]

Embodiments of the present invention will be described below. FIG. 1 is a circuit diagram showing a configuration example of a power supply device according to the present invention. An npn transistor 3 for switching is provided on the input side of a DC / DC converter 1, and a charge control circuit 2 is provided.
Is connected to a capacitor 4 and a resistor 5, and a comparator 6 controls on / off of the transistor 3 by its output.

In the circuit shown in FIG. 1, a DC input is a car battery power supply from, for example, a cigar plug of an automobile. When this DC input is first supplied, power is supplied to the comparator 6 and other circuits. Two input terminals 6
The operation of comparing the voltages 1 and 62 is performed, but for a while immediately after the power is turned on, the level of the output terminal 63 is in an undetermined state.
High impedance. Therefore, in this state, the output terminal 63 is forcibly set to the high level via the resistor 7 and the base of the npn transistor 3 is set to the high level via the resistor 8, so that the transistor 3 is turned on.
Thereby, irrespective of whether the device to be charged as a load, that is, the mobile phone is in a connected state, a DC input is supplied to the DC / DC converter 1 and a current is output from the charge control circuit 2 to charge the capacitor 4. Is done.

When the operation of the comparator 6 is stabilized, the two input terminals 61 and 62 inputted through the resistors 9 and 10 are provided.
Are compared, and when the voltage at the input terminal 61 becomes larger than the voltage at the input terminal 62 by a predetermined value or more, the output terminal of the comparator 6 outputs a high level, otherwise, outputs a low level. When this operation is started, if a load (device to be charged) is connected, a current flows to the resistor 5 and a potential difference is generated between the input terminals 61 and 62,
Therefore, at this time, the transistor 3 maintains the ON state,
A normal power supply state is set. If the load is not connected when the operation of the comparator is started, there is no current in the resistor 5 and there is no potential difference between the input terminals 61 and 62, so that the transistor 3 is turned off. Is shut off. This means that the transistor 3 is similarly turned off when the connection is turned off from the state where the load is connected and the power is supplied, that is, when the load is disconnected from the power supply device or when the power switch is turned off, and the DC 3 / DC
The current to converter 1 is cut off. Therefore, when no load is connected, no power is consumed by the DC / DC converter, and the load on the car battery during a stop or the like can be greatly reduced.

On the other hand, the capacitor 4 is charged when the power is supplied to the load. Further, when the power supply device is disconnected from the DC input and is input, the transistor 3 is turned on and the current is output from the charge control circuit 2 until the operation of the comparator is determined as described above. As a result, the capacitor 4 is charged as well. Therefore, when the load changes from the unconnected state to the connected state, the transistor 3 is off but the charge of the capacitor 4 flows to the load. This current causes a potential difference between two inputs of the comparator 6, turning on the transistor 3. This time, the current supply from the DC / DC converter 1 to the load is started. Then, the terminal potential difference of the resistor 5 remains generated, the on state of the transistor 3 is maintained, and the current can be supplied to the load. That is, when a load that has been disconnected is connected, the DC / DC converter can be automatically started by a simple circuit operation.

In order to reliably perform the above operation, the capacitor 4 needs to be sufficiently charged between the time when the DC input is connected and the time when the operation of the comparator 6 is established. For this purpose, the comparator 6 needs a certain amount of time during which its operating power is supplied and the output is in an indefinite state. If this time is insufficient with a normal comparator circuit, a circuit for delaying the comparator output is required. Provide. In addition, if the capacitor 4 discharges spontaneously after the load is not connected for a long time, the load cannot be started. To this end, the discharge current of the capacitor when the load is not connected should be minimized, and the charged charge should be maintained for a necessary time by using a capacitor having a large capacity.

[0012]

According to the present invention, it is possible to reliably prevent the car battery from being consumed when the load is not connected.
In addition, when the load is connected, the operation can be automatically started, and a power supply device that is easy to use can be realized.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing a configuration example of a power supply device according to the present invention.

FIG. 2 is an explanatory diagram of a conventional power supply device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 DC / DC converter 2 Charge control circuit 3 Transistor 4 Capacitor 5 Resistor 6 Comparator

Claims (2)

[Claims] 1. A DC / DC converter for converting a DC voltage applied to an input terminal, and a DC / D converter
A power supply device comprising: a charge control circuit that controls an output current of a C converter according to a load; a capacitor connected between a positive output terminal and a negative output terminal of the charge control circuit; A resistor connected between the terminal and a load connection terminal corresponding to the terminal; an ON signal when a potential difference between both ends of the resistor becomes a predetermined value or more, and an OFF signal when the potential difference becomes less than a predetermined value. A comparator for outputting the DC voltage input when the ON signal is supplied to the DC / DC converter, and applying the DC voltage input when the OFF signal is supplied to the DC / DC converter And a switching means for shutting off the power supply. 2. An input terminal and an output terminal of the comparator are connected by a resistor, and the output level of the comparator is turned on from the time when the operation power is supplied to the comparator until the output is determined. The power supply device according to claim 1, wherein the power supply device is a signal.