JPH10166902A - Power supply for vehicle meter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a power unit of a vehicular meter whose integrated distance will not change at all even if ignition on-off operations are repeated in a state that a dome fuse is removed off. SOLUTION: Two transisters 27 and 28 are operated by way of utilizing a residual voltage after an ignition being turned off in a DC-DC converter 11 for lighting a fluorescent character display tube, and when voltage VDD of a vehicular meter 1 is lowered up to voltage Vt1 being slightly higher than the data holding voltage Vh of a random access memory 18, the voltage VDD is forcibly turned to zero volt, and thereby data of the random access memory 18 of the vehicular meter 1 are cleared.

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 for a vehicle meter.

[0002]

2. Description of the Related Art Conventionally, electronic vehicle meters include:
The integrated distance value is stored in a volatile memory such as a RAM, and the contents of the volatile memory are stored in an EEPROM when the ignition is turned on.
For example, the data is transferred to a non-volatile memory.
This type of vehicle meter checks the content of the volatile memory once when transferring the content of the volatile memory to the nonvolatile memory, and determines whether or not the content has reached a check criterion. . Also, this vehicle meter
The vehicle is provided with a power supply device for operating the volatile memory, the nonvolatile memory, and the CPU for controlling the nonvolatile memory and the like.

FIG. 3 shows a conventional vehicle meter 1 and a power supply device 2.
FIG. 3 is a circuit diagram showing the configuration of FIG. In this figure, a voltage from a battery 3 is supplied to a power supply 2 via a dome fuse 4.
At the same time, and is applied to the IG + terminal of the power supply device 2 via the meter fuse 5 and the ignition switch 6.

The battery voltage applied to the + B terminal of the power supply 2 is supplied to a 5 V power supply I through a diode 7 for preventing backflow.
The voltage is applied to C8, and a stabilized output of 5 V is obtained. On the other hand,
The battery voltage applied to the IG + terminal of the power supply device 2 is applied to the 5V power supply IC 10 through the backflow preventing diode 9 to obtain a stabilized output of 5V, and the DC-D
An output which is applied to the C converter 11 and turns on a fluorescent display tube (not shown) is obtained. Further, the battery voltage applied to the IG + terminal of the power supply device 2 is controlled by a diode 1 for backflow prevention.
2 is also applied to the 5V power supply IC8.

Electrolytic capacitors 13 and 14 are interposed between the input and output sides of the 5V power supply IC 8 and the ground. The 5V voltage obtained by the 5V power supply IC 8 is supplied to the CPU 17, the RAM 18, and the like of the vehicle meter 1.

[0006]

In the above-mentioned conventional power supply device for a vehicle meter, the dome fuse 4 is removed in order to prevent the battery 3 from rising in a line or transportation of an automobile manufacturer. However, there has been a problem that the repeated distance may be changed when the ignition is turned on / off repeatedly with the dome fuse 4 removed.

That is, when the ignition is turned off with the dome fuse 4 removed, the power is naturally not supplied to the vehicle meter 1, and as shown in the waveform diagram of FIG. It gradually decreases. Then, when the voltage drops below the data holding voltage Vh of the RAM 18, the data of the RAM 18 starts to be broken and finally becomes a cleared state. However, if the ignition is turned on when the data in the RAM 18 starts to be corrupted, the CPU 17 checks the data in the RAM 18 but may pass the check depending on how the data in the RAM 18 is corrupted. In that case, the CPU 17
It is determined that the data of the AM 18 is correct, and this data is written to a non-volatile memory such as an EEPROM (not shown). As a result, there occurs a problem that the current integrated distance is changed to the data of the RAM 18 whose data is almost destroyed. This phenomenon also occurs when the time required for removing and reconnecting the battery 3 for repairing the vehicle is short.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a power supply device for a vehicle meter in which the integrated distance does not change even when the ignition is turned on / off repeatedly with the dome fuse removed.

[0009]

The concept of the present invention will be described below.

According to the present invention, when the voltage VDD of the vehicle meter falls below the data holding voltage of the volatile memory, the voltage VDD is forcibly set to 0 V to clear the data of the volatile memory.

[0011] In the case of a vehicle meter provided with a light source such as a fluorescent display tube, a DC-DC converter for generating a voltage for lighting the fluorescent display tube or the like is provided. When the ignition is turned off, since the fluorescent display tube and the like are turned off, the voltage gradually decreases due to circuit wraparound, element leakage current, and the like. Since this decreasing tendency is slower than the decreasing tendency of the voltage VDD (5 V) of the vehicle meter, the switch means is operated using the remaining voltage, so that the voltage VDD of the vehicle meter is reduced.
Can be forcibly set to 0 V before the voltage falls below the data holding voltage of the volatile memory.

As described above, before the voltage VDD of the vehicle meter falls below the data holding voltage of the volatile memory, the voltage is forced to 0V.
By doing so, even when the ignition is turned on / off repeatedly with the dome fuse removed, the phenomenon in which the integrated distance changes does not occur.

According to the first aspect of the invention based on the above concept, data of a volatile memory for storing data such as an integrated distance is checked at the time of ignition-on, and if the data reaches a standard for clearing the check, the data is authenticated. First voltage generating means for generating a voltage to be supplied to an electronic circuit used as data by reducing a battery voltage, and second voltage generating means for generating a voltage to be supplied to a fluorescent display tube or the like by increasing a battery voltage In a power supply device for a vehicle meter having
A third voltage generating means for generating the same voltage as the voltage generated by the first voltage generating means from the voltage generated by the second voltage generating means; Switch means set to be turned on by a difference between a voltage slightly higher than a data holding voltage of the volatile memory and a voltage generated by the third voltage generation means; Ground means for forcibly grounding the output side of the first voltage generating means when the means is turned on.

According to a second aspect of the present invention, the data in the volatile memory for storing data such as the integrated distance is checked when the ignition is turned on, and if the data reaches a reference for clearing the check, the data is used as regular data. A vehicle meter comprising: a power supply circuit for an electronic circuit that generates a voltage to be supplied to an electronic circuit by reducing a battery voltage; and a DC-DC converter that generates a voltage to be supplied to a fluorescent display tube or the like by increasing the battery voltage. A constant-voltage diode for generating the same voltage as the voltage generated by the electronic circuit power supply circuit from the voltage generated by the DC-DC converter, and the power supply circuit generated by the electronic circuit power supply circuit. To be turned on by a difference between a voltage slightly higher than a data holding voltage of the volatile memory and a voltage generated by the constant voltage diode. A first transistor Subaiasu is set, the first transistor is turned on by turning on, is provided with a second transistor for grounding the output side of the power supply circuit for the electronic circuit.

[0015]

Embodiments of the present invention will be described below with reference to the drawings.

<Structure of Power Supply Device for Vehicle Meter> FIG. 1 is a circuit diagram showing a structure of an embodiment of a power supply device for a vehicle meter according to the present invention. Note that, in this figure, the same parts as those in FIG. 3 described above are denoted by the same reference numerals. In this figure, the battery 3, the dome fuse 4, the meter fuse 5, and the ignition switch 6 shown in FIG. 3 are omitted.

In the vehicle meter power supply device 23 of this embodiment, a voltage VDD of 5 V is applied to the RAM 1 of the vehicle meter 1.
In the case where the voltage is lower than the data holding voltage of 8, a shutoff circuit 24 for forcing the voltage VDD to 0V is provided. The shutoff circuit 24 includes resistors 25, 28, 29, 30, 3
1, constant voltage diode 26, PNP transistor 2
7. It comprises an NPN transistor 32.

The resistor 25 has one end connected to the output terminal T 2 of the DC-DC converter 11 and the other end connected to the cathode of the constant voltage diode 26. The anode of the constant voltage diode 26 is grounded. The PNP transistor 27 has a voltage diode 26 as an emitter.
, And connected to the base via a resistor 28, and further connected to one end of a resistor 30 and the output side of a 5V power supply IC 8 via a resistor 29. The collector of the transistor 27 is connected to the NPN
It is connected to the base of the type transistor 32. The transistor 32 has an emitter grounded and a collector connected to the other end of the resistor 30.

The constant voltage diode 26 is a DC-DC
It generates a voltage VzD of 5 V from the output voltage V2 (51 V) of the converter 11. The resistors 28 and 29 determine the base bias of the transistor 27.
When the voltage VDD of V is lower than the voltage Vth1 slightly higher than the data holding voltage of the RAM 18 of the vehicle meter 1, the transistor 2
The respective resistance values are determined so that 7 turns on. The resistors 30 and 31 limit the base current and the collector current of the transistor 32 and protect the transistor 32.

Here, FIG. 2 shows a DC-DC converter 1
FIG. 6 is a waveform diagram showing changes in the output voltage V2, the voltage VDD from the 5V power supply IC 8 and the voltage VzD of the constant voltage diode 26 when the ignition is turned on / off. When the ignition is turned off, the DC-DC converter 1
Since the output voltage V2 of the constant voltage diode 2 gradually decreases, the voltage VzD of the constant voltage diode 26 keeps constant at about 5V. 5V
The voltage VDD from the power supply IC 8 is a DC-DC converter 11
Of the output voltage V2 decreases faster than the output voltage V2 decreases. When the voltage VDD drops to a voltage Vth1 slightly higher than the data holding voltage of the RAM 18, the transistor 27 is turned on, and the transistor 32 is turned on. At this point, the data in the RAM 18 is completely cleared.

<Operation of Power Supply Device for Vehicle Meter>
The operation of the power supply device 23 for a vehicle meter having the above configuration will be described. << Ignition ON >> When the ignition is turned on with the dome fuse 4 removed, the battery voltage is applied to the IG + terminal of the power supply device 23, and the stabilized 5V voltage VDD from the power supply device 23 is applied to the vehicle. Meter 1
Supplied to

While a voltage of 5 V is being output from the power supply 23, this voltage is supplied to the cutoff circuit 24.
The transistor 27 is off without a base bias applied. Of course, the transistor 32 is also off.

<< Ignition Off >> When the ignition is turned off with the dome fuse 4 removed, the voltage VDD of 5 V decreases. The voltage V slightly higher than the data holding voltage of the RAM 18 of the vehicle meter 1
When the voltage drops below th1, the voltage VDD and DC
The difference between the output voltage V2 of the DC converter 11 and the voltage of VzD obtained by the constant voltage diode 26 provides a base bias enough to turn on the transistor 27, thereby turning on the transistor 27. When the transistor 27 is turned on, a base current flows through the transistor 32, and the transistor 32 is also turned on. When the transistor 32 is turned on, the output side of the 5V power supply IC 8 is grounded via the resistor 30, and the voltage VDD suddenly becomes 0V.
Thereby, the data in the RAM 18 of the vehicle meter 1 is cleared.

As described above, in this embodiment, the transistors 27 and 32 are operated using the remaining voltage after the ignition of the DC-DC converter 11 for turning on the fluorescent display tube, and the vehicle meter 1 is turned on. Is slightly higher than the data holding voltage Vh of the RAM 7.
When the voltage drops to th1, the voltage VDD is forcibly set to 0V,
The data in the RAM 18 of the vehicle meter 1 is cleared.

Therefore, even if the ignition is turned on / off repeatedly with the dome fuse removed, the data in the RAM 18 of the vehicle meter 1 does not remain in a broken state, and the accumulated distance changes. Occurrence can be prevented.

[0026]

As described above, according to the power supply device for a vehicle meter according to the first and second aspects, when the voltage of the vehicle meter is lower than the data holding voltage of the volatile memory, the voltage is controlled. Is forced to 0V to clear the data in the volatile memory, so that even if the ignition is turned on / off repeatedly with the dome fuse removed, the cumulative distance may change. Nothing. In addition, the reliability as a product can be improved.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing a configuration of an embodiment of a power supply device for a vehicle meter according to the present invention.

FIG. 2 is a waveform chart for explaining an operation of the power supply device for the vehicle meter according to the embodiment.

FIG. 3 is a circuit diagram showing a configuration of a conventional power supply device for a vehicle meter.

FIG. 4 is a waveform diagram for explaining the operation of a conventional power supply device for a vehicle meter.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 vehicle meter 3 battery 4 dome fuse 6 ignition switch 8 5V power supply IC 11 DC-DC converter 17 CPU 18 RAM 24 delay circuit 25, 28, 29, 30, 31 resistor 26 constant voltage diode 27 PNP transistor 32 NPN transistor

Claims (2)

[Claims] 1. An ignition circuit checks data in a volatile memory for storing data such as an integrated distance when the ignition is turned on, and supplies the data to an electronic circuit used as regular data if the data reaches a reference for clearing the check. A first voltage generating means for generating a voltage by lowering a battery voltage; and a second voltage generating means for generating a voltage supplied to a light source such as a fluorescent display tube by boosting the battery voltage. A power supply device for a vehicle meter, comprising: a third voltage generation unit configured to generate, from the voltage generated by the second voltage generation unit, the same voltage as the voltage generated by the first voltage generation unit; The semiconductor memory device is turned on by a difference between a voltage generated by the first voltage generator and a voltage slightly higher than a data holding voltage of the volatile memory and a voltage generated by the third voltage generator. A set switch means, power supply device for a vehicle meter, characterized in that the grounding means, the provided for grounding the output side of the forcing said first voltage generating means by the switching means is turned on. 2. Checking data in a volatile memory for storing data such as an integrated distance when the ignition is turned on, and supplying the data to an electronic circuit used as regular data if the data reaches a reference for clearing the check. A power supply circuit for an electronic circuit that generates a voltage by stepping down a battery voltage; and a DC-DC converter that generates a voltage to be supplied to a light source such as a fluorescent display tube by stepping up a battery voltage. In the power supply device, a constant voltage diode that generates the same voltage as a voltage generated by the electronic circuit power supply circuit from a voltage generated by the DC-DC converter, and a voltage generated by the electronic circuit power supply circuit. To turn on with a difference between a voltage slightly higher than the data holding voltage of the volatile memory and a voltage generated by the constant voltage diode. A first transistor to which a bias is set; and a second transistor which is turned on when the first transistor is turned on and grounds an output side of the electronic circuit power supply circuit. Power supply for vehicle meters.