JP2004302829A - Power switch circuit of on-vehicle information terminal, and on-vehicle information terminal - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a power switch circuit of an on-vehicle information terminal which synchronizes a reduction in power consumption with switching to a backup power supply without being affected by parts characteristics when the voltage of a main power supply drops. <P>SOLUTION: The voltage of the main power supply input to a terminal 22 from an on-vehicle battery 3 shown in Figure 1 is monitored by a reset IC 21. At or below a predetermined voltage, the output voltage of the reset IC 21 changes from H to L. This turns off transistors Q2 and Q1 and the main power supply from the on-vehicle battery 3 is no longer output from a terminal 24 to a microcomputer 10 shown in Figure 1. A backup power supply 15 in Figure 1, input to a terminal 23, is then output to the microcomputer 10 via a terminal 24. Further, the output voltage of the reset IC 21 changes from H to L, so that the microcomputer 10 is set in its sleep mode to reduce its own power consumption. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a power supply switching circuit of an in-vehicle information terminal that switches to a backup power supply when the voltage of a supplied main power supply decreases in an in-vehicle information terminal such as a navigation device.
[0002]
[Prior art]
Normally, an in-vehicle information terminal such as a navigation device operates with a power supplied from an in-vehicle battery. Therefore, when the ignition switch of the vehicle is turned off or the battery is discharged, the voltage of the supplied power is reduced, and the vehicle cannot operate. In particular, in an in-vehicle information terminal that stores information in a volatile storage device, for example, a communication navigation device that stores various information such as distributed map data in a RAM in a microcomputer, the information is stored due to the decrease in the power supply voltage. Information may be lost. In order to avoid such a situation, there is an in-vehicle information terminal provided with a microcomputer having a function of switching to a backup power supply when the power supply voltage drops.
[0003]
As a microcomputer having such a power supply switching function, for example, a microcomputer device of Patent Document 1 is known. This microcomputer device has the configuration shown in FIG. 3, and a power supply circuit 40 and a backup power supply 45 are both connected to a power supply circuit 52. As a result, when the voltage of the power supply circuit 40 that is normally used decreases, power is supplied from the backup power supply 45 to the power supply circuit 52 instead. Further, the voltage of the power supply circuit 40 is detected by the power supply voltage detection circuit 61, and when the voltage falls below a predetermined voltage, the CPU 51 is set to a sleep mode to reduce power consumption. According to the microcomputer device of Patent Literature 1, by switching the power supply circuit 40 to the backup power supply 45 and synchronizing the sleep mode setting of the CPU 51, the loss of stored information is avoided for a while even when the power supply voltage is reduced. be able to. In the in-vehicle information terminal, the power supply circuit 40 in FIG. 3 corresponds to an in-vehicle battery, and the backup power supply 45 corresponds to a backup battery or the like.
[0004]
[Patent Document 1]
JP-A-07-271754
In the microcomputer device of Patent Literature 1, the output of the power supply circuit 40 is output to a point A in the drawing via the diode 59, and when the voltage is lower than the voltage of the backup power supply 45, the output is switched to the backup power supply 45. Further, the output of the power supply circuit 40 is also output to the power supply voltage detection circuit 61 via the diode 60, and when the voltage falls below a predetermined value, the CPU 51 is set to the sleep mode. Therefore, the power supply voltage for switching to the backup power supply 45 does not match the power supply voltage for setting the sleep mode due to variations in the characteristics of the diodes 59 and 60, and they may not be synchronized. In this case, the CPU 51 is not set to the sleep mode, and the power is supplied from the backup power supply 45, and the backup power supply 45 may be consumed immediately.
[0006]
The present invention relates to an in-vehicle information terminal in which, when the voltage of a supplied main power supply decreases, power consumption is reduced and switching to a backup power supply is performed synchronously without being affected by component characteristics. Is provided.
[0007]
[Means for Solving the Problems]
A power supply switching circuit for an in-vehicle information terminal according to claim 1 is a main power supply input terminal for inputting main power from an external main power supply means, and a backup power input terminal for inputting backup power from an external backup power supply means. Power supply means for selecting either the input main power supply or backup power supply and supplying it to the outside, and signal output means for outputting a signal when the voltage of the input main power supply becomes equal to or lower than a predetermined voltage. Reset means for outputting the signal to the outside. The power supply means switches the power supply to the outside from the main power supply to the backup power supply when the signal is output from the signal output means.
According to a second aspect of the present invention, there is provided an in-vehicle information terminal including the power supply switching circuit according to the first aspect, backup power supply means for outputting a backup power supply to the power supply switching circuit, and a microcomputer device supplied with power from the power supply switching circuit. The microcomputer device sets itself to the sleep mode when a signal is output from the power supply switching circuit.
The invention of claim 3 is applied to the on-vehicle information terminal of claim 2, wherein the backup power supply means is constituted by a primary battery.
[0008]
BEST MODE FOR CARRYING OUT THE INVENTION
FIG. 1 shows a navigation device which is an embodiment of a vehicle-mounted information terminal according to the present invention. The navigation device 1 of FIG. 1 receives various information such as map data transmitted from an information distribution center by a communication terminal 2 and provides the information to a user. The navigation device 1 is normally operated by the power supplied from the vehicle-mounted battery 3, and switches the power supply to the backup power supply 15 when the voltage decreases. The navigation device 1 includes a microcomputer 10, a power supply switching circuit 14, a backup power supply 15, a current position detection device 16, an image memory 17, a display monitor 18, and an input device 19.
[0009]
The microcomputer 10 has a control circuit 11, a ROM 12, and a RAM 13. The control circuit 11 includes a microprocessor and its peripheral circuits, and performs various controls by executing a control program stored in the ROM 12 using the RAM 13 as a work area. Note that various information such as map data received by the communication terminal 2 is stored in the RAM 13. The RAM 13 can store the information only when power is supplied to the microcomputer 10. That is, when power is not supplied to the microcomputer 10, the information stored in the RAM 13 is lost.
[0010]
The power supply switching circuit 14 selects one of the backup power supply 15 and the power supply supplied from the vehicle-mounted battery 3 and supplies one of the power supplies to the microcomputer 10. At this time, the power is supplied from the vehicle-mounted battery 3 in a normal state, and when the power supply voltage from the vehicle-mounted battery 3 decreases, that is, when the ignition switch of the vehicle is turned off or when the battery discharge proceeds, etc. Supplies power from the backup power supply 15. Details of the operation of the power supply switching circuit 14 will be described later. In addition, as the backup power supply 15, for example, a primary battery such as an alkaline battery is used.
[0011]
The power supply switching circuit 14 outputs a reset signal to the microcomputer 10 when switching the power supply to the microcomputer 10 from the vehicle-mounted battery 3 to the backup power supply 15. When the reset signal is output, the microcomputer 10 sets itself to the sleep mode. When the sleep mode is set, the microcomputer 10 does not accept an external input, executes only the minimum processing required to hold the information stored in the RAM 13, and reduces its own power consumption. When the power supply voltage from the vehicle-mounted battery 3 recovers, the power supply switching circuit 14 returns the power supply to the microcomputer 10 from the backup power supply 15 to the vehicle-mounted battery 3 and outputs a reset release signal. Upon receiving the reset release signal, the microcomputer 10 releases the setting of the sleep mode.
[0012]
The current position detecting device 16 is a device that detects the current position of the vehicle, and includes, for example, a direction sensor 16a that detects the traveling direction of the vehicle, a vehicle speed sensor 16b that detects the vehicle speed, a GPS sensor 16c that detects a GPS signal from a GPS satellite, and the like. Become. The navigation device 1 requests a map of an area including the current position of the vehicle detected by the current position detection device 16 to an information distribution center (not shown) via the communication terminal 2. Further, on the map data transmitted from the information distribution center in response to the request, the current position of the vehicle detected by the current position detection device 16, that is, the position of the own vehicle, is displayed on the display monitor 18.
[0013]
The image memory 17 stores image data to be displayed on the display monitor 18. The image data includes road map drawing data, various graphic data, and the like, and these are appropriately selected based on the map data transmitted from the information distribution center. By displaying the selected image data on the display monitor 18, the navigation device 1 can provide the user with the information of the transmitted map data.
[0014]
The input device 19 has various switches for inputting a destination of the vehicle and the like. When the destination of the vehicle is input by the input device 19, the navigation device 1 requests map data from the current position of the vehicle detected by the current position detection device 16 to the destination to the information distribution center. The map data transmitted from the map information distribution center in response to this request is received by the communication terminal 2 and stored in the RAM 13 as described above.
[0015]
FIG. 2 shows a circuit example of the power supply switching circuit 14. The power supply switching circuit 14 has a reset IC 21, transistors Q1 and Q2, resistors R1 and R2, and a diode D1. The terminal 22 receives the main power from the vehicle-mounted battery 3, and the terminal 23 receives the backup power from the backup power supply 15, selects one of them and outputs it to the microcomputer 10 from the terminal 24. At this time, the main power input to the terminal 22 is output to the microcomputer 10 via the transistor Q1, and the backup power input to the terminal 23 is output to the microcomputer 10 via the diode D1. The switching of the power supply is controlled by the reset IC 21 as described below.
[0016]
The reset IC 21 monitors the voltage of the main power supply from the vehicle-mounted battery 3 input to the terminal 22, and when the main power supply voltage falls below a predetermined voltage, the reset IC 21 changes its output voltage from H (high) to L (low). Changes to This output is connected to B (base) of the transistor Q2 via the resistor R2, and changes from H to L to turn off the transistor Q2. Then, the transistor Q1 connected to C (collector) of the transistor Q2 is turned off, and the main power from the vehicle battery 3 is not output to the microcomputer 10. At this time, the backup power input to the terminal 23 is output via the diode D1.
[0017]
Thereafter, when the main power supply voltage recovers to a voltage higher than the predetermined voltage, the reset IC 21 changes its output voltage from L to H. Then, the transistor Q2 is turned on, whereby the transistor Q1 is turned on, and the main power input to the terminal 22 is output to the microcomputer 10. At this time, since the voltage of the backup power supply at point P is lower than the main power supply voltage (a voltage drop by the diode D1; about 0.7 V), the backup power supply is not output.
[0018]
The output from the reset IC 21 is also connected from a terminal 25 to a reset terminal (not shown) of the microcomputer 10. The microcomputer 10 recognizes that the reset signal has been output by changing the output voltage from H to L, and sets the sleep mode. Conversely, when the output voltage from the reset IC 21 changes from L to H, the microcomputer 10 recognizes that the reset release signal has been output, and releases the setting of the sleep mode.
[0019]
As described above, the power supply switching circuit 14 of the navigation device 1 monitors the main power supply voltage from the vehicle-mounted battery 3 by the reset IC 21 and changes the output voltage from H to L when the voltage becomes lower than the predetermined voltage. As a result, the power supply to the microcomputer 10 is switched from the main power supply to the backup power supply, and the microcomputer 10 is set to the sleep mode.
[0020]
According to the navigation device 1 described above, the following operational effects can be obtained.
(1) When the main power supply voltage from the vehicle-mounted battery 3 falls below a predetermined voltage, a reset signal is output from the reset IC 21, and the power supply to the microcomputer 10 is switched from the main power supply to the backup power supply by this reset signal. The microcomputer 10 is set to the sleep mode. With this configuration, when the voltage of the supplied main power supply decreases, the power consumption can be reduced and the switching to the backup power supply can be performed in synchronization without being affected by the component characteristics. In addition, since reduction in power consumption and switching to a backup power supply can be realized by the same circuit, the size and cost of the circuit can be reduced.
(2) Since the backup power supply 15 for supplying the backup power supply is constituted by a primary battery, a charging circuit for the backup power supply is not required, and the circuit size and cost can be further reduced.
[0021]
In the embodiment described above, a communication navigation device that receives various information such as map data distributed from an information distribution center and provides the information to a user has been described as an example of an in-vehicle information terminal. It is not limited to. The present invention can be applied to any in-vehicle information terminal that is supplied with main power from the outside.
[0022]
In the embodiment described above, when the main power supply voltage falls below the predetermined voltage, a reset signal is output from the reset IC 21 of the power supply switching circuit 14, and the reset signal causes the transistors Q1 and Q2 to switch from the main power supply to the backup power supply. Has been described, and the sleep mode of the microcomputer 10 is set, but the present invention is not limited to this. The present invention can be applied as long as a specific signal is output when the main power supply voltage becomes equal to or lower than a predetermined voltage, and the switching from the main power supply to the backup power supply and the setting of the sleep mode are performed by the signal.
[0023]
In the embodiment described above, the main power supply means is realized by the vehicle-mounted battery 3, the backup power supply means is realized by the backup power supply 15, and the power supply means is realized by the power supply switching circuit 14, and the signal output means and the reset means are realized by the power supply switching circuit. 14 reset ICs 21 and terminals 25 respectively. The microcomputer device is realized by the microcomputer 10. However, these are merely examples, and each component is not limited to the above-described embodiment as long as the features of the present invention are not impaired.
[0024]
【The invention's effect】
According to the present invention, a reset signal is output when the main power supply voltage becomes equal to or lower than a predetermined voltage, and the reset signal switches the power supply to the microcomputer from the main power supply to the backup power supply and sets the microcomputer to the sleep mode. I did it. With this configuration, reduction in power consumption and switching to the backup power supply can be performed in synchronization without being affected by component characteristics.
[Brief description of the drawings]
FIG. 1 is a diagram showing an embodiment of an in-vehicle information terminal according to the present invention; FIG. 2 is a diagram showing a circuit example of a power supply switching circuit according to the present invention; FIG. 3 is a diagram showing a configuration of a microcomputer device of Patent Document 1; Explanation of code]
1: Navigation device 2: Communication terminal 3: In-vehicle battery 10: Microcomputer 11: Control circuit 12: ROM
13: RAM 14: Power supply switching circuit 15: Backup power supply 16: Current location detecting device 17: Image memory 18: Display monitor 19: Input device 21: Reset IC
22-25: Terminal

Claims (3)

A main power input terminal for inputting main power from an external main power supply means,
A backup power input terminal for inputting backup power from an external backup power supply means,
Power supply means for selecting any of the input main power supply or backup power supply and supplying it to the outside,
Signal output means for outputting a signal when the input voltage of the main power supply is equal to or lower than a predetermined voltage,
Reset means for outputting the signal to the outside,
The power supply switching circuit for an in-vehicle information terminal, wherein the power supply means switches the power supply to the outside from the main power supply to the backup power supply when the signal is output from the signal output means. A power supply switching circuit according to claim 1,
Backup power supply means for outputting backup power to the power supply switching circuit;
A microcomputer device supplied with power from the power supply switching circuit,
The in-vehicle information terminal, wherein the microcomputer device sets itself to a sleep mode when the signal is output from the power supply switching circuit. The in-vehicle information terminal according to claim 2,
The in-vehicle information terminal, wherein the backup power supply unit includes a primary battery.

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