JP2000089866A - Circuit for preventing leak of computer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent leak current from a display device from flowing to a display control part by interrupting a signal path between the display control part and the display device by a switching means when the power of a computer is in an off state. SOLUTION: The drain/source of a field effect transistor 13 is inserted into and connected to a signal path between the synchronizing signal output terminal of a display control part 11 and a connection terminal for synchronizing signal output 12. When the power of a computer 10 is turned off, the supply of power to the display control part 11 is cut and the supply of power to a control circuit 34 is also cut. Thus, the field effect transistor 13 becomes an off state and impedance between the drain and the source becomes considerably large. Thus, current from the display device 17, namely, leak current is prevented from flowing to the display control part 11 of the computer 10 even in the state where power is supplied to the display device 17.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a circuit for preventing a leak current from a display device connected to a computer to the computer.

[0002]

2. Description of the Related Art In general, electronic equipment called a computer has been widely used. However, a computer called a desktop type has a display device provided outside.
A terminal for connecting a display device is provided.

FIG. 2 shows a connection relationship between a conventional computer and a display device. Reference numeral 1 denotes a computer, and 2 a display control unit incorporated in the computer 1, which performs an output operation of a video signal, a synchronization signal, and the like. Reference numeral 3 denotes a synchronization signal output connection terminal provided in the computer 1, and is connected to the display control unit 2.

[0004] Reference numeral 4 denotes a display device having a display for display, and a control unit 5 for controlling the operation of the display is provided. Reference numeral 6 denotes a synchronization signal input connection terminal connected to the synchronization signal output terminal 3 of the computer 1 by a cable 7, and is connected to a synchronization signal input terminal of the control unit 5. Reference numerals 8 and 9 denote pull-up resistors connected between the synchronization signal path of the computer 1 and the display device 4 and the power supply, respectively.

In such a configuration, a synchronization signal and a video signal output from the display control unit 2 are input to the display device 4 through respective signal paths, and an image is displayed on a display by the control operation of the control unit 5.

[0006]

A computer and a display device connected to the computer are configured so that power on / off operations are individually performed. When each process is performed by the computer, the power is turned off. In this case, the user may forget to turn off the power of the display device. In such a case, a leak current flows from the display device in the energized state to the display control unit 2 on the computer side via the pull-up resistor 9 and the cable.
Problems such as deterioration of C and malfunction of the computer when the power of the computer is turned on may occur.

An object of the present invention is to provide a computer leak prevention circuit which solves such a problem.

[0008]

According to the present invention, switching means is inserted into a signal path of a display control section which is incorporated in a computer main body and outputs a display signal to a display device, so that the power supply of the computer is turned off. At this time, the signal path between the display control unit and the display device is cut off by the switching means.

[0009]

FIG. 1 is a circuit diagram showing an embodiment of the present invention. In FIG. 1, reference numeral 10 denotes a computer, and 11 denotes a display control unit incorporated in the computer 10 for outputting video signals, synchronization signals, and the like. 12
Is a connection terminal for synchronizing signal output provided in the computer 10, 13 is a signal path between the synchronizing signal output terminal of the display control unit 11 and the connecting terminal 12 for synchronizing signal output, and a drain and source are inserted and connected. Field-effect transistor. Further, a pull-up resistor R1 is connected between the synchronization signal output terminal of the display control unit 11 and the power supply.

Reference numeral 14 denotes a control circuit for controlling the operation of the field-effect transistor 13. The control circuit 14 has a drain and a source connected in series between a power supply and a ground, has a gate connected to each other, and is grounded. Field-effect transistors 15 and 16. In such a control circuit 14, the field-effect transistor 1
The connection points of the source and the drain, which are commonly connected, are connected to the gate of the field effect transistor 13.

Reference numeral 17 denotes a display device having a display for display, and a control unit 18 for controlling the operation of the display.
Is provided. Reference numeral 19 denotes a synchronization signal input connection terminal which is connected to the synchronization signal output connection terminal 12 of the computer 10 by a cable 20.
8 and to the power supply via a pull-up resistor R2. The video signal and the like output from the display control unit 11 are configured to be input to the control unit 18 via a plurality of cables (not shown).

The present invention is configured as described above. Next, the operation will be described. Turning on a power switch (not shown) provided on the computer 10 and the display device 17 puts the computer 10 and the display device 17 into an operating state.

When the computer 10 is turned on, the field effect transistor 15 constituting the control circuit 14 is turned on, so that the field effect transistor 13 is biased and turned on. In such a state, the synchronization signal output from the synchronization signal output terminal of the display control unit 11 is:
The signal is input to the synchronization signal input terminal of the control unit 18 between the drain and source of the field-effect transistor 13, the synchronization signal output connection terminal 12, the cable 20, and the synchronization signal input connection terminal 19. Further, a video signal and the like output from the display control unit 11 are also input to the control unit 18 via a cable (not shown).

As a result of the input of the synchronizing signal and the video signal to the control unit 18 in this manner, the control operation by the control unit 18 is performed, and the video data signal is displayed on the display.

As described above, the display operation of the video data output from the computer 10 by the display device 17 is performed. Next, the case where only the power of the computer 10 is turned off will be described. When the power of the computer 10 is turned off, the power supply to the display control unit 11 is cut off and the power supply to the control circuit 14 is also cut off.

As a result, the field effect transistor 13 is turned off, and the impedance between the drain and the source becomes extremely large. Therefore, even when the power is supplied to the display device 17, the current from the display device 17, that is, the leak current, is generated by the display controller 1 of the computer 10.
It does not flow into 1.

In this embodiment, a field effect transistor is used as the switching means connected to the signal path. However, other switching elements can be used.

[0018]

According to the present invention, a switching means is inserted into a signal path of a display control section which is incorporated in a computer main body and outputs a display signal to a display device. Since the signal path between the display control unit and the display device is cut off by the means, it is possible to prevent a leak current from the display device from flowing into the display control unit. Therefore, according to the present invention, I
C can be reliably prevented from deteriorating and abnormal operation when the computer is turned on.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing one embodiment of the present invention.

FIG. 2 is a circuit diagram showing a conventional example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Computer 11 Display control part 12 Connection terminal for synchronizing signal output 13 Field effect transistor 14 Control circuit 17 Display device 18 Control part

Claims (2)

[Claims] 1. A computer provided with a connection terminal for connecting a display device to a main body, wherein a switching means is inserted into a signal path of a display control unit incorporated in the main body and outputting a display signal to the display device. A leakage prevention circuit for a computer, wherein the signal path between the display control unit and the display device is cut off by the switching means when the power supply of the computer is off. 2. The leak preventing circuit according to claim 1, wherein the switching means is constituted by a field effect transistor.