JP2008052629A - Load current controller and load current control method and the like - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a load current controller which can maintain current flowing in a source cable at a fixed value or below with a simple circuit structure without increasing a cable diameter or using a component of a large allowable current value, and to provide a load current control method and the like. <P>SOLUTION: The load current controller S1 is connected to a power source B and controls load current to be supplied to the load. The controller is provided with a source voltage detection part 2 for detecting a change in source voltage input from the power source B and an LED control unit 4 for changing the load current linearly in accordance with the change in source voltage. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present application relates to a technical field such as a load current control device that is connected to a power source and controls a load current supplied to a load, and a method thereof.

  2. Description of the Related Art Conventionally, a display (rear seat display) that displays characters, images, and the like may be installed at a predetermined position in a vehicle for an occupant sitting on a rear seat of the vehicle. In such a case, the power for the display is supplied through, for example, a power cable extended from the front of the vehicle.

  However, since the current value increases due to a drop in the power supply voltage due to the extended power cable, it is necessary to increase the cable diameter to be used or to increase the allowable current value of the components to be used (for example, an inductor).

  Further, when the amount of power supply voltage drop due to the extended power cable is large, it becomes difficult to operate the display drive circuit (for example, DC / AC inverter, DC / DC inverter), and thus a separate booster circuit is provided.

On the other hand, in Patent Document 1, a constant load is provided in the apparatus power supply in parallel with the load, a voltage of the constant load is detected, an adjustment voltage value is calculated from the voltage, and the adjustment voltage value is added to the output voltage. There is disclosed a library device that performs control and adjusts a voltage applied to a load to a constant voltage.
JP 2003-22596 A

  However, if the cable diameter to be used is increased as described above, it becomes difficult for the user to handle. Further, when the cable diameter is increased or a part having a large allowable current value is used, the cost is increased (the material cost is increased), and when the booster circuit is provided, the cost is further increased.

  Further, in Patent Document 1, since a constant voltage is applied to the load, an adder circuit or the like is required for the constant load circuit or the voltage output circuit, which increases the number of components.

  Therefore, in this application, the solution of such a problem is an example of the problem, and it is not necessary to increase the cable diameter or use parts with a large allowable current value, and the current flowing in the power cable with a simple circuit configuration. An object of the present invention is to provide a load current control device, a load current control method, and the like that can keep the voltage below a certain value.

  In order to solve the above-mentioned problem, the invention according to claim 1 is a load current control device for controlling a load current supplied to a load connected to a power supply, wherein a change in power supply voltage input from the power supply is achieved. And a load current control means for linearly changing the load current in accordance with a change in the power supply voltage.

  The invention according to claim 5 is a load current control method for controlling a load current connected to a power source and supplied to a load, the step of detecting a change in a power source voltage input from the power source, and And a step of linearly changing the load current in accordance with a change in power supply voltage.

  According to a sixth aspect of the present invention, there is provided a computer program that controls a load current that is connected to a power source and that is supplied to the load, wherein the load current is controlled according to a change in the power source voltage input from the power source. It is characterized by functioning so as to change linearly.

  The invention of the recording medium according to claim 7 is characterized in that the load current control program according to claim 6 is recorded so as to be readable by a computer.

  Hereinafter, the best embodiment of the present application will be described with reference to the accompanying drawings.

(First embodiment)
First, in the first embodiment, referring to FIG. 1, an LED (light emitting diode) (an example of a display unit) constituting a display (for example, a rear seat display) is used as a load, and a load current supplied to the load is calculated. The configuration and function of the load current control device to be controlled will be described. Note that the load current control device is incorporated in a display device mounted on a vehicle, for example.

  FIG. 1 is a diagram illustrating a schematic configuration example of a load current control device S1 according to the first embodiment.

  The load current control device S1 according to the first embodiment includes a power input unit (for example, a power input terminal) 1 for inputting a power voltage from a power source (for example, a battery) B, as shown in FIG. The power supply voltage detection unit 2 (an example of a power supply voltage detection unit), a resistance value determination unit 3, and an LED control unit 4 (an example of a load current control unit) are configured.

  For example, as shown in FIG. 1B, the power supply voltage detector 2 includes a Zener diode D, a transistor (for example, an NPN-type bipolar transistor) Tr, a resistor R1 (a resistance value is, for example, about several kilohms), And a change in the power supply voltage input from the power supply B is detected. The base of the transistor Tr is connected to the power supply input unit 1 via the Zener diode D, and is grounded via the resistor R1, and the emitter of the transistor Tr is grounded. The transistor Tr has a characteristic that changes linearly (in other words, gradually changes) from on (ON) to off (OFF) or from off to on (that is, gradually changes). The resistance value of linearly changes).

  In addition, the resistance value determining unit 3 includes, for example, as shown in FIG. 1B, resistors R2 (resistance value is about several hundred ohms, for example) and R3 (resistance value is about several hundred ohms, for example) One ends of the resistor R2 and the resistor R3 are connected to each other and connected to the input terminal T1 of the LED control unit 4, the other end of the resistor R2 is connected to the collector of the transistor Tr, and the other end of the resistor 3 is grounded. . The resistance value connected to the input terminal T1 of the LED control unit 4 (in other words, the voltage applied to the input terminal T1) changes according to the on / off operation of the transistor Tr (that is, the parallel resistance value of the resistors R2 and R3). And the resistance value of only the resistor R3).

Moreover, since the resistance value of the transistor Tr changes linearly, the resistance value connected to the input terminal T1 also changes linearly. As a result, the voltage applied to the input terminal T1 of the LED control unit 4 also changes. It will change linearly.
The LED control unit 4 is configured by, for example, a control IC, and controls supply of load current to the LED 5 according to a voltage (voltage applied to the input terminal T1) corresponding to the resistance value determined by the resistance value determination unit 3. Since the voltage applied to the input terminal T1 changes linearly according to the change of the power supply voltage, the LED control unit 4 changes the load current amount supplied to the LED 5 linearly accordingly. . Note that the LED control unit 4 may include DC / DC inverter control.

  Next, the operation in the load current control device S1 configured as described above will be described.

  When the power supply voltage from the power supply input unit 1 is larger than the voltage as the threshold of the Zener diode D (base-emitter voltage VBE of the transistor Tr, for example, +0.6 V), the transistor Tr is turned on in the saturation region. Therefore, the resistance value connected to the input terminal T1 of the LED control unit 4 is a parallel resistance value of the resistors R2 and R3.

  Subsequently, when the power supply voltage becomes lower than the voltage (VBE, for example, +0.6 V) of the Zener diode D, the transistor Tr moves out of the saturation region and gradually changes its operation in the off direction. Thereby, the resistance value connected to the input terminal T1 of the LED control unit 4 gradually approaches the resistance value of the resistor R3, and thus increases linearly.

  The LED control unit 4 controls the load current supplied to the LED 5 to decrease linearly (gradually) according to the resistance value that changes linearly in this way (the LED control unit 4 decreases its output). In this way, the load current amount is linearly reduced. At this time, by setting the resistor R3 to an appropriate value, it is possible to avoid giving a sense of incongruity to the amount of decrease in luminance in the display as viewed from the user (because it is not controlled below the value set by the resistor R3). ).

  In the above operation, when the power supply voltage becomes larger than the threshold value, the load current is controlled to gradually increase.

(Second embodiment)
Next, in the second embodiment, referring to FIG. 2, a configuration of a load current control device that controls a load current supplied to the load using a fluorescent tube (an example of a display unit) constituting the display as a load. The function will be described.

  FIG. 2 is a diagram illustrating a schematic configuration example of the load current control device S2 according to the second embodiment.

  The load current control device S2 according to the second embodiment includes a power input unit (for example, a power input terminal) 11 for inputting a power voltage from a power source (for example, a battery) B, as shown in FIG. The power supply voltage detection unit 12 (an example of a power supply voltage detection unit), a resistance value determination unit 13, and a fluorescent tube control unit 14 (an example of a load current control unit) are configured.

The configuration of the power supply voltage detection unit 12 is the same as that of the power supply voltage detection unit 2 in the first embodiment, for example, as shown in FIG.
The configuration and the like of the resistance value determining unit 13 are basically the same as the resistance value determining unit 3 in the first embodiment, for example, as shown in FIG. They are connected to each other and to the input terminal T2 of the fluorescent tube control unit 14, and are also connected to the fluorescent tube 16 via the diode D1.

  The fluorescent tube control unit 14 is configured by, for example, a control IC (DC / AC inverter control IC), and an inverter according to a voltage (voltage applied to the input terminal T2) corresponding to the resistance value determined by the resistance value determination unit 13 The supply control of the load current to the fluorescent tube 16 is performed via the transformer 15, and the voltage applied to the input terminal T2 changes linearly according to the change of the power supply voltage. Accordingly, the load current supplied to the fluorescent tube 16 via the inverter transformer 15 is linearly changed.

  Since the operation in the load current control device S2 configured as described above is the same as that in the first embodiment, a duplicate description is omitted.

  As described above, according to the above-described embodiment, a change in the power supply voltage input from the power supply B is detected, and the load current supplied to the load is linearly changed according to the change in the power supply voltage (for example, Since the load current is gradually decreased (or increased) when the power supply voltage becomes smaller (or larger) than the threshold value, for example, the extended power cable diameter is increased or allowed. It is not necessary to use a component having a large current value, and the current flowing through the power cable can be kept below a certain value with a simple circuit configuration. In addition, even if the power supply voltage changes (increases / decreases), the load current changes linearly, so that it is possible to prevent the user from feeling uncomfortable with the change in luminance on the display.

  In addition, by using the transistor Tr having a characteristic that changes linearly from on to off or from off to on, control is realized in which the load current supplied to the load is linearly changed with a simpler circuit configuration. be able to.

  In the above-described embodiment, an LED or a fluorescent tube is applied as an example of the display unit. However, the present invention is not limited to this. For example, an organic EL (electroluminescence) element may be applied.

  In the above embodiment, a load current control program is stored in a recording medium such as a ROM, a non-volatile memory, or a hard disk provided in a load current control device mainly composed of a CPU as a computer. By reading and executing the load current control program (software) from the recording medium, as described above, the load current supplied to the load is linearly changed according to the change of the power supply voltage input from the power supply. You may comprise so that it may control.

  Moreover, although it is more effective that the said embodiment is applied with respect to the display for vehicle-mounted rear seats, with respect to the display for general vehicle-mounted displays and portable terminals (for example, a mobile phone, PDA etc.). It is also possible to apply.

It is a figure showing an example of outline composition of load current control device S1 concerning a first embodiment. It is a figure which shows the schematic structural example of load current control apparatus S2 which concerns on 2nd embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1,11 ... Power supply input part 2,12 ... Power supply voltage detection part 3,13 ... Resistance value determination part 4 ... LED control part 5 ... LED
DESCRIPTION OF SYMBOLS 14 ... Fluorescent tube control part 15 ... Inverter transformer 16 ... Fluorescent tube S1, S2 ... Load current control apparatus

Claims (7)

A load current control device that is connected to a power source and controls a load current supplied to a load,
Power supply voltage detection means for detecting a change in power supply voltage input from the power supply;
Load current control means for linearly changing the load current according to a change in the power supply voltage;
A load current control device comprising: In the load current control device according to claim 1,
The load current control device, wherein the load current control means gradually decreases the load current when the power supply voltage becomes smaller than a threshold value. In the load current control device according to claim 1 or 2,
The power supply voltage detection means includes a transistor, and the transistor has a characteristic that changes linearly from on to off or from off to on. In the load current control device according to claim 1,
The load current control device is characterized in that the load is a display means constituting a display. A load current control method for controlling a load current supplied to a load connected to a power source,
Detecting a change in power supply voltage input from the power supply;
Changing the load current linearly in response to a change in the power supply voltage;
A load current control method comprising: A computer connected to a power source and controlling the load current supplied to the load,
A load current control program for causing a function to linearly change the load current in accordance with a change in power supply voltage input from the power supply.   7. A recording medium in which the load current control program according to claim 6 is recorded so as to be readable by a computer.

Images