JP2012003631A - Protection circuit and display unit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To protect a circuit from excess current possibly generated when external equipment is connected to a USB connection terminal and immediately restore the circuit to normal state when the cause of the excess current generation is eliminated.SOLUTION: A protection circuit comprises: a first supply path capable of supplying current from a power source to a USB connection terminal via a first resistor and a first switch; and a second supply path capable of supplying current from the power source to the USB connection terminal via a second resistor, of which resistance value is higher than that of the first resistor, and a second switch. A control section monitors current supplied from the power source to the USB connection terminal via the first resistor. If the current is excess current, the first switch is turned off while the second switch is turned on. Current supplied from the power source to the USB connection terminal via the second resistor is monitored by the control section, and if excess current is eliminated, the second switch is turned off while the first switch is turned on.

Description

  The present invention relates to a protection circuit and a display device.

  FIG. 4 shows a conventional protection circuit 100. The protection circuit 100 is a circuit mounted on an electronic device (for example, a digital television) including a USB connection terminal 101 for connecting a USB device 200 such as a USB (Universal Serial Bus) memory from the outside. In the protection circuit 100, normally, a power supply can be supplied from a 5V power source 102 to the USB connection terminal 101 via a resistor R having a predetermined resistance value and an FET (Field Effect Transistor) 103 as a switch element. Thus, when the user connects the USB device 200 to the USB connection terminal 101, a current flows through the USB device 200. As shown in FIG. 4, the microcomputer 104 inputs a current supplied to the USB connection terminal 101 via a resistor R at a predetermined input port 104a, and monitors the current value.

  The user uses a USB device 200 connected to the USB connection terminal 101 as a USB device 200, for example, a USB memory whose internal is short-circuited, or a device that consumes more power than a device originally supposed to be connected to the USB connection terminal 101 (for example, a hard disk drive ) Or the like is connected, an excessively large current (overcurrent) flows into the USB connection terminal 101. Therefore, when the current value to be monitored exceeds a predetermined reference, the microcomputer 104 determines that the current is an overcurrent, outputs a control signal from the control port 104b to the FET 103, turns the FET 103 off, and sets the overcurrent. Was prohibited from flowing.

  Also, from the viewpoint of preventing overcurrent, a means for detecting the voltage / current supplied to the USB port, and when the detected voltage / current is overvoltage / overcurrent, supply the power from the USB port to the internal circuit. When a protection circuit having a switch means for disconnection (see Patent Document 1) or a microprocessor detects that the divided potential obtained by dividing the voltage of the output line of the HDMI power supply is lower than the set potential, the output A power supply control device that cuts off a line and cuts off supply of power supply voltage to an external device is known (see Patent Document 2).

Japanese Patent Laid-Open No. 2008-9898 JP 2008-305314 A

  In the protection circuit 100 as described above, after the FET 103 is turned off once as described above, the FET 103 is turned on again after a predetermined time has elapsed, and the current supply function of the circuit is restored. However, the protection circuit 100 cannot detect whether or not the USB device 200 serving as a load is disconnected from the USB connection terminal 101. For this reason, if the USB device 200 is still connected to the USB connection terminal 101 when the FET 103 is turned on again, an overcurrent state occurs again, and the FET 103 is turned on and off unless the USB device 200 is removed by the user. May be repeated. In such a state, it cannot be said that the circuit is appropriately protected from overcurrent.

  The present invention has been made to solve the above-described problems, and accurately protects a circuit from an overcurrent that may occur when an external device is connected to a USB connection terminal, and eliminates the cause of the occurrence of an overcurrent. Provided is a protection circuit and a display device that can immediately return the circuit to a normal state in the event of a failure.

  One aspect of the present invention is a protection circuit including a control unit capable of executing a process of cutting off the current supply to the USB connection terminal when the current supplied from the power source to the USB connection terminal is a predetermined overcurrent. A first supply path capable of supplying a current from the power source to the USB connection terminal via the first resistor and the first switch, and a second having a resistance value larger than that of the first resistor from the power source. And a second supply path capable of supplying a current to the USB connection terminal via the second switch, and the controller supplies a current supplied from the power source to the USB connection terminal via the first resistance. In the case of a predetermined overcurrent, the first switch is turned off to cut off the current supply to the USB connection terminal through the first supply path and turn the second switch on. Second by Start supplying current to the USB connection terminal through the supply path, monitor the current supplied from the power source to the USB connection terminal via the second resistor, and if the predetermined overcurrent is resolved, By turning off the switch, the current supply to the USB connection terminal through the second supply path is interrupted and the first switch is turned on.

  According to the above configuration, the control unit supplies the current supplied from the power source to the USB connection terminal via the first resistor in a normal state (a state in which current can be supplied to the USB connection terminal through the first supply path). When an overcurrent is detected, the first switch is turned off and the second switch is turned on. Therefore, an overcurrent is prevented from flowing from the USB connection terminal to the USB device, and a current (not an overcurrent) whose value is reduced by passing through the second resistor (higher resistance than the first resistor) is prevented. It flows from the USB connection terminal to the USB device. The control unit also monitors the current supplied from the power supply to the USB connection terminal via the second resistor, and the USB device that caused the overcurrent is removed from the USB connection terminal and the overcurrent state is released. If this is detected, the second switch is turned off and the first switch is turned on, so that the circuit can be returned to the normal state.

It is a figure which shows schematic structure of a display apparatus. It is a figure which shows the structure of a protection circuit. It is a flowchart which shows the control process of an electric current supply. It is a figure which shows the structure of the conventional protection circuit.

The protection circuit according to the present invention can be mounted on any device as long as it is an electronic device having a USB connection terminal.
As an embodiment of the present invention, for example, when the control unit determines that the predetermined overcurrent is present, it notifies the outside that the overcurrent state is present, and the control unit has resolved the predetermined overcurrent. It is possible to employ a configuration that further includes notification means for notifying the outside that the overcurrent state has been resolved when it is determined.
Further, as an embodiment of the present invention, for example, a protection provided with a microcomputer capable of executing a process of cutting off the current supply to the USB connection terminal when the current supplied from the power source to the USB connection terminal is a predetermined overcurrent. A display device including a circuit, wherein the protection circuit includes a first supply path through which a current can be supplied from the power source to the USB connection terminal via the first resistor and the first FET, and the power source A second supply path capable of supplying a current to the USB connection terminal via the second resistor having a resistance value larger than that of the first resistor and the second FET, and the microcomputer has a first resistor from the power supply. The current supplied to the USB connection terminal via the first supply path is monitored, and if it is a predetermined overcurrent, the first FET is turned off to turn off the power to the USB connection terminal via the first supply path. The supply of current to the USB connection terminal via the second supply path is started by cutting off the supply and turning on the second FET, and supplied from the power source to the USB connection terminal via the second resistor. When the predetermined overcurrent is resolved, the current supply to the USB connection terminal through the second supply path is cut off and the first FET is turned on by turning off the second FET. And when the microcomputer determines that the predetermined overcurrent is present, an OSD display is displayed on the predetermined screen indicating that the microcomputer is in the overcurrent state, and the microcomputer determines that the predetermined overcurrent has been eliminated. In such a case, it is possible to employ a configuration including OSD display means for OSD displaying on the predetermined screen that the overcurrent state has been eliminated.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 shows a schematic configuration of a display device 10 equipped with a protection circuit 11. The display device 10 is a television, for example. In addition to the protection circuit 11, the display device 10 includes a main control unit 12, a tuner circuit 13, a video processing circuit 14, a panel drive circuit 15, a liquid crystal panel 16, a power supply circuit 17, and the like. Further, the display device 10 includes a USB connection terminal 11a for connecting an external USB device 20 on the surface of the housing. In this embodiment, the USB device 20 is assumed to be a USB memory or the like with relatively low power consumption, and the USB memory is connected by a user for the purpose of updating firmware installed in the display device 10 or the like.

  The main control unit 12 is a microcomputer, and is connected to each unit constituting the display device 10 via a bus. The CPU 12a executes processing according to a program stored in the ROM 12b while using the RAM 12c as a work area. 10 overall control. The tuner circuit 13 receives a broadcast signal through an antenna under the control of the main control unit 12, and the video processing circuit 14 performs video demodulation, image quality adjustment, scaling processing, and the like from the broadcast signal, thereby displaying a video for one screen. A signal is generated and stored in a frame memory (not shown). The panel drive circuit 15 drives the liquid crystal panel 16 based on the video signal stored in the frame memory, and displays the video based on the video signal on the liquid crystal panel 16. The power supply circuit 17 supplies a necessary power supply voltage to each unit of the display device 10 under the control of the main control unit 12. A part of the power supply voltage is also supplied to the protection circuit 11.

  The main control unit 12 includes an OSD (On Screen Display) unit 12d. The OSD unit 12 d can generate still images such as characters and characters and display them on the screen of the liquid crystal panel 16. The OSD unit 12d can generate image data for performing OSD display, and can output the image data to the panel drive circuit 15 after being superimposed on the video signal recorded in the frame memory. Of course, in addition to the configuration shown in FIG. 1, the display device 10 can include various known configurations required for functioning as a television, such as an audio processing circuit, a speaker, and a backlight of a liquid crystal panel. It is. Further, the panel for displaying an image does not need to be a liquid crystal panel, and may be a plasma display panel or any other display panel. In addition, the display device according to the present invention is not limited to the television as long as it has an image display function.

  FIG. 2 shows a circuit configuration of the protection circuit 11. The protection circuit 11 has a configuration capable of supplying current from the 5V power supply 11b to the USB connection terminal 11a through two supply paths. The first supply path is a path connected from the power source 11b to the USB connection terminal 11a via the resistor R1 (first resistor) and the FET 11c (first switch), and the second supply path is a resistor from the power source 11b. This is a path connected to the USB connection terminal 11a via R2 (second resistor) and the FET 11d (second switch). The resistance value of the resistor R1 is the same as that of the resistor R shown in the conventional protection circuit 100 (FIG. 4). The resistance value of the resistor R2 is higher than the resistance value of the resistor R1. Therefore, the value of the current flowing through the second supply path to the USB connection terminal 11a is smaller than the current flowing through the first supply path to the USB connection terminal 11a.

  In the protection circuit 11, the control part 11e is arrange | positioned as a part of structure. The control unit 11e is also a microcomputer, like the main control unit 12, and executes a current supply control process described later. The control unit 11e and the main control unit 12 are connected to be communicable with each other. However, the main control unit 12 and the control unit 11e are not necessarily configured separately, and one microcomputer may realize the roles and functions of the main control unit 12 and the control unit 11e. In the present embodiment, the description will be continued by taking as an example a configuration in which the control unit 11e and the main control unit 12 are separated.

  The control unit 11e inputs the current (current after passing through the resistor R1) supplied from the power source 11b through the resistor R1 to the USB connection terminal 11a through the input port 11e1, and performs A / D conversion. Monitor the current value. Similarly, the control unit 11e inputs the current (current after passing through the resistor R2) supplied from the power source 11b through the resistor R2 to the USB connection terminal 11a through the input port 11e2 and performs A / D conversion. The current value is monitored above. Further, the control unit 11e controls the gate voltage of the FET 11c with the control voltage output from the control port 11e3 to the FET 11c, so that the current flows between the source and the drain of the FET 11c (the FET 11c is in the on state) and does not flow. The state (the FET 11c is in an off state) can be switched. Similarly, the control unit 11e controls the gate voltage of the FET 11d by the control voltage output from the control port 11e4 to the FET 11d, so that a current flows between the source and the drain of the FET 11d (the FET 11d is in an on state). It is possible to switch to a state where the FET 11d is in an off state.

  FIG. 3 is a flowchart showing a current supply control process executed by the controller 11e. In the normal state of the protection circuit 11 (the state where the FET 11c is on and the FET 11d is off), the control unit 11e monitors the current input via the input port 11e1 and determines whether or not it is in an overcurrent state ( Step S100). Whether or not it is an overcurrent state is determined by whether or not the current value to be monitored exceeds a predetermined reference value. If the USB device 20 is not connected to the USB connection terminal 11a, or if a USB memory that functions normally for firmware update is connected as the USB device 20, the overcurrent state does not occur and step S100 is performed. Then, “No” is determined. If “No” is determined in step S100, the determination in step S100 is repeatedly performed (monitoring of the current input via the input port 11e1 is continued).

  On the other hand, when the USB device 20 is connected to the USB connection terminal 11a, for example, a short-circuited USB memory or a device with high power consumption (for example, a hard disk drive) that is not originally supposed to be connected. The overcurrent tends to flow into the USB connection terminal 11a through the first supply path, and it is easy to determine the overcurrent state in step S100. If the control unit 11e determines in step S100 that the current is in the overcurrent state ("Yes" in step S100), the control unit 11e proceeds to step S110.

  In step S110, the control unit 11e switches the FET 11c to the OFF state via the control port 11e3 and switches the FET 11d to the ON state via the control port 11e4. At the same time, the main control unit 12 is notified of the overcurrent state. As a result of step S110, the current supply to the USB connection terminal 11a via the first supply path is interrupted, while the current is supplied to the USB connection terminal 11a via the second supply path. That is, by passing through the resistor R2 in the second supply path, a current (not an overcurrent) whose value is lower than that through the resistor R1 flows to the USB connection terminal 11a. Even if the USB device that causes the overcurrent as described above remains connected to the terminal 11a, the overcurrent state does not occur, and the circuit or the like is prevented from being destroyed.

  In step S120, in a state where the FET 11c is off and the FET 11d is on, the control unit 11e monitors the current input via the input port 11e2, and determines whether or not the overcurrent state has been eliminated. When the USB device 20 is disconnected from the USB connection terminal 11a, the current value monitored via the input port 11e2 changes. Therefore, when such a predetermined change is detected, the control unit 11e is in an overcurrent state. Is resolved (“Yes” in step S120), and the process proceeds to step S130. That is, in step S120, it is detected whether or not the user has removed the USB device causing the overcurrent from the USB connection terminal 11a. If “No” is determined in step S120, the determination in step S120 is repeated.

  In step S130, the control unit 11e switches the FET 11d to the off state via the control port 11e4 and switches the FET 11c to the on state via the control port 11e3. At the same time, the main control unit 12 is notified that the overcurrent state has been eliminated. As a result of step S130, the current supply to the USB connection terminal 11a through the second supply path is cut off, and the normal state is restored (return to step S100).

  In FIG. 2, signal lines related to current supply to the USB connection terminal 11a side (USB device 20 side) and control thereof are shown, but of course, signals used for data communication for firmware update and the like described above. A line also exists between the USB connection terminal 11 a and the control unit 11 e or the main control unit 12.

  The main control unit 12 that has received the notification that it is in the overcurrent state in step S110 issues a command to the OSD unit 12d, thereby giving a message to the OSD unit 12d that the overcurrent state is present in the USB connection terminal 11a. The OSD is displayed on the screen of the panel 16. As a result, the message is displayed on the screen, and the user who sees the message recognizes that it is in an overcurrent state, and can then disconnect the USB device 20 connected to the USB connection terminal 11a. Further, the main control unit 12 that has received the notification that the overcurrent state has been eliminated in step S130 issues a message to the OSD unit 12d that the overcurrent state has been eliminated by issuing a command to the OSD unit 12d. The OSD display process is performed on the screen of the liquid crystal panel 16. As a result, the message is displayed on the screen, and the user who sees the message recognizes that the overcurrent state has been eliminated. The control unit 11e, the main control unit 12 (particularly the OSD unit 12d), and the like correspond to the notification unit and the OSD display unit of the present invention.

  As described above, according to the present embodiment, in the protection circuit 11, the first supply path connected to the USB connection terminal 11a from the power source 11b through the predetermined resistor R1, which is the original current supply path to the USB connection terminal 11a. In addition, a second supply path is provided from the power source 11b to the USB connection terminal 11a through the resistor R2 that is higher in resistance than the resistor R1, and a switch is provided in the middle of each of the first and second supply paths. By turning on and off each switch, current can be supplied and cut off in the first and second supply paths. Then, the current value of the first supply path is monitored in the normal state, and in the case of an overcurrent, the current supply of the first supply path is cut off to interrupt the circuit of the circuit due to the overcurrent flowing into the USB connection terminal 11a. The load and breakage were alleviated and prevented accurately, and at the same time the current supply through the second supply path was allowed. Then, by monitoring the current value of the second supply path, when it is detected that the USB device that has caused the overcurrent is disconnected from the USB connection terminal 11a, the normal state is immediately restored. Therefore, since it is not known on the device side whether or not the user has removed the USB device that caused the overcurrent from the USB connection terminal as in the past, the current supply line until such a USB device is removed by the user. It is possible to avoid the situation where the interruption and return of the operation are repeated.

DESCRIPTION OF SYMBOLS 10 ... Display apparatus, 11 ... Protection circuit, 11a ... USB connection terminal, 11b ... Power supply, 11c, 11d ... FET, 11e ... Control part, 12d ... OSD part, 16 ... Liquid crystal panel, 20 ... USB device

Claims (3)

A protection circuit including a control unit capable of executing a process of cutting off the current supply to the USB connection terminal when the current supplied from the power source to the USB connection terminal is a predetermined overcurrent,
A first supply path capable of supplying current from the power source to the USB connection terminal via the first resistor and the first switch;
A second supply path capable of supplying a current from the power source to the USB connection terminal via a second resistor having a resistance value larger than that of the first resistor and a second switch;
The control unit
The current supplied from the power supply to the USB connection terminal via the first resistor is monitored, and if there is a predetermined overcurrent, the first switch is turned off to make the USB connection through the first supply path. The current supply to the USB connection terminal by the second supply path is started by cutting off the current supply to the terminal and turning on the second switch,
The current supplied from the power source to the USB connection terminal via the second resistor is monitored, and when the predetermined overcurrent is resolved, the second switch is turned off to turn off the second switch. A protection circuit that cuts off current supply to a USB connection terminal and turns on a first switch.   When the control unit determines that the predetermined overcurrent is present, it notifies the outside that the overcurrent state is present, and when the control unit determines that the predetermined overcurrent is resolved, the overcurrent state is resolved. The protection circuit according to claim 1, further comprising notification means for notifying the outside of the fact. A display device including a protection circuit including a microcomputer capable of executing a process of cutting off current supply to the USB connection terminal when the current supplied from the power source to the USB connection terminal is a predetermined overcurrent,
The protection circuit is
A first supply path capable of supplying current from the power source to the USB connection terminal via the first resistor and the first FET;
A second supply path capable of supplying current from the power source to the USB connection terminal via a second resistor having a resistance value larger than that of the first resistor and a second FET;
The microcomputer is
The current supplied from the power supply to the USB connection terminal via the first resistor is monitored, and if it is a predetermined overcurrent, the first FET is turned off to make the USB connection through the first supply path. The current supply to the USB connection terminal by the second supply path is started by shutting off the current supply to the terminal and turning on the second FET,
The current supplied from the power supply to the USB connection terminal via the second resistor is monitored, and when the predetermined overcurrent is eliminated, the second FET is turned off by the second supply path. Cut off the current supply to the USB connection terminal and turn on the first FET,
When the microcomputer determines that the predetermined overcurrent is present, an OSD display is displayed on the predetermined screen indicating that the microcomputer is in an overcurrent state, and the microcomputer determines that the predetermined overcurrent has been eliminated. A display device comprising OSD display means for OSD-displaying on the predetermined screen that the overcurrent state has been eliminated.

Images