JP6399345B2 - Vehicle display device - Google Patents

Description

  The present invention relates to a vehicle display device, and is particularly suitable for a vehicle display device that supplies power for driving a load circuit from a backup power source.

  As a conventional vehicle display device, in order to display time and maintenance information, there is one that is subjected to arithmetic processing such as counting time of various conditions such as time, vehicle operating time, and parts replacement time. It is disclosed in Patent Document 1.

  In addition, in a vehicle display device, even when power is not supplied from an in-vehicle battery or the like, a backup power source is used to perform operations such as timekeeping or to retain the storage contents of a storage medium. Is disclosed in, for example, Patent Document 2.

  This backup power source is composed of an electric double layer capacitor, a diode that prevents backflow of current from the electric double layer capacitor, and a power source connected to the anode of the diode. The electric double layer capacitor is charged at the time of supply), and becomes a backup power source during a period when the power source is off.

JP-A-5-319139 JP 2002-95185 A

  However, since the diode used for this backup power supply has a forward voltage drop, it cannot give a sufficient potential to the capacitor during charging, and in particular, in a low-voltage circuit system, a longer backup is required. There was a problem that it was a hindrance to get time.

  Accordingly, an object of the present invention is to provide a vehicle display device that can obtain a longer backup time by paying attention to the above-described problems.

The vehicle display device of the present invention includes:
A step-down circuit connected to a power source and outputting a predetermined voltage;
A capacitor that can be charged based on the power from the step-down circuit;
A switch circuit provided between the capacitor and the step-down circuit;
A load circuit that operates by supplying power from the power source or the capacitor;
With
The switch circuit switches an energization state depending on whether or not power is supplied from the power source, and switches an energization state between the step-down circuit and the capacitor based on a potential between the step-down circuit and the power source. A vehicle display device.

  The load circuit may be a real time clock circuit.

  The present invention relates to a display device for a vehicle, and can obtain a longer backup time.

The figure which shows the circuit structure in embodiment of this invention. The time chart which shows the operation state of embodiment same as the above. The model figure which shows the backup time extension of embodiment same as the above. The figure which shows the circuit structure in another example of embodiment same as the above. The time chart which shows the operation state of embodiment same as the above (another example).

  Hereinafter, an embodiment in which the vehicle display device is applied to a monitor device mounted on a work vehicle will be described as an embodiment of the present invention with reference to the drawings.

  The vehicle display device A includes a first power supply unit 1, a second power supply unit (step-down circuit) 2, a control unit 3, a real-time clock circuit unit (load circuit) 4, a switch element (switch circuit) 5, An electric double layer capacitor (capacitor) 6, a switch control circuit unit 7, and a display 8 are provided and connected to a battery power supply unit 9 provided with an in-vehicle battery B and a switch S. The battery power supply unit 9 is connected to supply power to the first power supply unit 1 when the vehicle display device A is in operation.

  The first power supply unit 1 includes a circuit that clamps or steps down a high voltage (for example, 72V) applied to the primary side based on the power supply from the battery power supply unit 9 and outputs the voltage to the secondary side. A predetermined voltage is supplied to the power supply unit 2. Moreover, the 1st power supply part 1 contains a surge cut circuit. As this predetermined voltage, for example, Vb in the figure is 10V.

  The second power supply unit 2 can apply a step-down circuit that steps down the primary side potential and generates a system voltage (system power supply) for operating the control unit 3 and the real-time clock circuit unit 4 on the secondary side. Then, this system power is emitted to the real-time clock circuit unit 4 via the switch element 5. For example, the Vreg location in the figure is a system voltage of 3.3V.

  The control unit 3 can be applied with a microcomputer, operates for a period when the system power from the second power supply unit 2 is supplied, and displays a clock on the display 8 based on the clock data acquired from the real-time clock circuit unit 4 (time Display) or maintenance information display of the vehicle based on elapsed time or the like.

  The real-time clock circuit unit 4 can be applied with a clock count circuit with low current consumption, and counts the clock when system power is supplied or when a backup power source described later from the electric double layer capacitor 6 is valid.

  The switch element 5 can be an n-channel FET (field effect transistor), is controlled by a gate signal input from the switch control circuit unit 7, and is connected to the drain side by creating a conduction or cutoff state between the source and drain. The system power supply from the second power supply unit 2 is supplied to or stopped from the electric double layer capacitor 6 and the real-time clock circuit unit 4.

  The electric double layer capacitor 6 is connected to the switch element 5 and the real-time clock circuit unit 4 and is charged when the switch element 5 is conductive, and when the switch element 5 is cut off, the charged power is supplied to the real-time clock circuit unit 4 as a backup power source. Supply as.

  The switch control circuit unit 7 includes a resistor that divides the primary side potential of the second power supply unit 2. As shown in FIG. 2, when the output potential exceeds the ON threshold of the switch element 5 with respect to the gate-source voltage of the switch element 5, the switch control circuit unit 7 The connection between the drain and the drain of the switch element 5 is interrupted when the ON state of the switch element 5 is not exceeded. The resistance ratio of the voltage dividing resistor is set so that the switch element 5 is cut off before the system power supply is reduced, thereby preventing a backflow of current from the electric double layer capacitor 6.

  The display 8 can be a liquid crystal display panel provided with a backlight, and displays and outputs various vehicle information based on a control signal from the control unit 3 when the vehicle display device A is in a normal operation.

  As described above, by using the switching element 5 to switch charging / discharging of the electric double layer capacitor 6, it is possible to prevent back-up of the backup power source from the electric double layer capacitor 6 during discharge. In addition, as shown in FIG. 3, when charged through a diode with a conventional voltage drop (for example, 0.7 V), that is, from the state of being charged at 2.6 V, the minimum value of the real-time clock circuit unit 4 is reached. The time tb to reach the minimum operating voltage from the state charged with the system voltage (3.3 V) from the second power supply unit 2 is longer than the time ta to reach the operating voltage (for example, 1.6 V). Therefore, the function of counting time can be maintained for a long time even when the vehicle display device A is not in an operating state.

  In the above-described embodiment, the switch control circuit unit 7 uses a resistor voltage divider. However, as shown in FIG. 4, the switch control circuit unit 7 is configured by a switch control circuit unit 71 that sets a threshold voltage value. You can also. For example, as shown in FIG. 5, by setting a low potential detection threshold value for the Vb value, the influence of errors such as variations in the ON threshold value of the switch element 5 can be reduced, and the switch element 5 can be shielded more accurately. The circuit can set conditions.

  Such a vehicle display device A includes a second power supply unit 2 that is connected to a power source and outputs a predetermined voltage, an electric double layer capacitor 6 that can be charged based on electric power from the second power supply unit 2, and the electric double layer. A switch element 5 provided between the capacitor 6 and the second power supply unit 2; and a real-time clock circuit unit 4 that operates by supplying power from the power source or the electric double layer capacitor 6. The switch element 5 includes: The energization state is switched according to whether or not power is supplied from the power source.

  Therefore, when the vehicle display device A does not operate and the real-time clock circuit unit 4 is driven by the backup power source, the above-described switch element 5 is used in the circuit configuration provided for backflow prevention. When the display device A is in operation, a potential close to the system voltage can be applied to the electric double layer capacitor 6 for charging, and loss of charging capacity can be suppressed. In particular, a 3.3V system power supply is advantageous in that the system voltage can be effectively used to increase the backup time.

  The switch element 5 uses a complicated circuit configuration by switching the energization state between the second power supply unit 2 and the electric double layer capacitor 6 based on the potential between the second power supply unit 2 and the power supply. Even if this is not the case, a sufficient potential difference is provided between the gate and the source of the switch element (field effect transistor) 5.

  In addition, although the power supply circuit of the vehicle display device of the present invention has been described as an example in the configuration of the above-described embodiment, the present invention is not limited to this, and the present invention is also applied to other configurations. It goes without saying that various improvements and display changes can be made without departing from the gist of the invention.

  The present invention can be applied to a power supply circuit of a display device for a vehicle mounted on a moving object including an automobile, a motorcycle, an agricultural machine, or a construction machine, for example, regarding the display device for a vehicle.

1 1st power supply part 2 2nd power supply part (step-down circuit)
3 Control unit 4 Real-time clock circuit unit (load circuit)
5 Switch element (switch circuit)
6 Electric double layer capacitor (capacitor)
7 Switch control circuit unit 8 Display unit 9 Battery power supply unit A Display device for vehicle

Claims (2)

A step-down circuit connected to a power source and outputting a predetermined voltage;
A capacitor that can be charged based on the power from the step-down circuit;
A switch circuit provided between the capacitor and the step-down circuit;
A load circuit that operates by supplying power from the power source or the capacitor;
With
The switch circuit switches an energization state depending on whether or not power is supplied from the power source, and switches an energization state between the step-down circuit and the capacitor based on a potential between the step-down circuit and the power source. A vehicle display device. The vehicle display device according to claim 1, wherein the load circuit includes a real-time clock circuit.

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