TWI729853B - Spare line system for flexible display panel and automatic switching method of spare line system thereof - Google Patents

Abstract

A spare line system for a flexible display panel and an automatic switching method of a spare line system thereof are provided. The spare line system includes a main line, a disconnect switch, a spare line, a control switch and a comparison circuit. The disconnect switch and the main line are connected in series between a first node and a second node, are preset to be on, and are turned off in response to a control voltage. The control switch and the spare line are connected in series between the first node and the second node, are preset to be off, and are turned on in response to the control voltage. The comparison circuit compares a first voltage of the first node and a second voltage of the second node, and provides the control voltage according to the comparison result.

Description

Standby circuit system for flexible display panel and automatic switching method of standby circuit system

The present invention relates to a backup circuit technology, and more particularly to a backup circuit system for a flexible display panel and an automatic switching method of the backup circuit system.

The development trend of display panel technology is a narrow frame design, and the use of flexible substrate bending technology can make the circuit bend below the panel to narrow the frame. However, the use of flexible substrate bending technology may cause the phenomenon of metal wiring disconnection, which affects the circuit operation. Therefore, a new type of circuit system is required to overcome the disconnection problem.

The invention provides a standby circuit system for a flexible display panel and an automatic switching method of the standby circuit system, which can automatically disconnect the abnormal main circuit and activate the normal control standby circuit.

The backup circuit system for a flexible display panel of the present invention includes a main circuit, a disconnect switch, a backup circuit, a control switch and a comparison circuit. The disconnect switch and the main circuit are connected in series between the first node and the second node, and are preset to be turned on and turned off in response to the control voltage. The control switch and the backup circuit are connected in series between the first node and the second node, are preset to be off, and are turned on in response to the control voltage. The comparison circuit compares the first voltage of the first node and the second voltage of the second node, and provides a control voltage according to the comparison result.

The automatic switching method for the standby circuit system of the flexible display panel of the present invention includes the following steps. The control voltage is initialized through the comparison circuit to turn on the disconnect switch and turn off the control switch. The interrupt switch and the main circuit are connected in series between the first node and the second node, and the control switch and the backup circuit are connected in series between the first node and the second node. Between nodes. The comparison circuit compares the first voltage of the first node and the second voltage of the second node. When a voltage difference between the first voltage and the second voltage is less than or equal to the preset voltage, a control voltage is provided to the disconnect switch and the control switch through the comparison circuit to maintain the disconnection switch and turn off the control switch. When the voltage difference between the first voltage and the second voltage is greater than the preset voltage, a control voltage is provided to the disconnect switch and the control switch through the comparison circuit to keep the disconnect switch off and turn on the control switch.

Based on the above, the standby circuit system for flexible display panels and the automatic switching method of the standby circuit system of the embodiment of the present invention can monitor the pressure of the main circuit at both ends of the bending area through the comparison circuit in real time, so as to reflect the main circuit Set/switch the control voltage according to the line status of the line to automatically disconnect the abnormal main line and activate the normal control backup line. Therefore, manual judgment or other maintenance methods are not required, and the maintenance cost is reduced.

In order to make the above-mentioned features and advantages of the present invention more comprehensible, the following specific embodiments are described in detail in conjunction with the accompanying drawings.

Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by those of ordinary skill in the art to which the present invention belongs. It will be further understood that terms such as those defined in commonly used dictionaries should be interpreted as having meanings consistent with their meanings in the context of related technologies and the present invention, and will not be interpreted as idealized or excessive The formal meaning, unless explicitly defined as such in this article.

It should be understood that although the terms "first", "second", "third", etc. may be used herein to describe various elements, components, regions, layers and/or parts, these elements, components, regions, and/or Or part should not be restricted by these terms. These terms are only used to distinguish one element, component, region, layer or section from another element, component, region, layer or section. Therefore, the "first element", "component", "region", "layer" or "portion" discussed below may be referred to as a second element, component, region, layer or section without departing from the teachings herein.

The terminology used here is only for the purpose of describing specific embodiments and is not restrictive. As used herein, unless the content clearly indicates otherwise, the singular forms "a", "an" and "the" are intended to include the plural forms, including "at least one." "Or" means "and/or". As used herein, the term "and/or" includes any and all combinations of one or more of the related listed items. It should also be understood that when used in this specification, the terms "including" and/or "including" designate the presence of the features, regions, wholes, steps, operations, elements, and/or components, but do not exclude one or more The existence or addition of other features, regions as a whole, steps, operations, elements, components, and/or combinations thereof.

FIG. 1 is a schematic diagram of a system of a flexible display panel according to an embodiment of the present invention. Please refer to FIG. 1, in this embodiment, the flexible display panel FDP is equipped with at least a display area ADP and a backup line system 100, and the backup line system 100 includes a main line TRA, a disconnect switch SWA, a backup line TRB, and a control switch SWB, comparison circuit CMP, detection circuit CDT and controller CT1. In the display area ADP, for example, a pixel array (not shown), a source driver (not shown), a gate driver (not shown), etc. can be configured.

The disconnect switch SWA and the main line TRA are connected in series between the first node a and the second node b. The disconnect switch SWA is turned on in response to the initial level of the control voltage Vc (that is, it is preset to be turned on), and is turned off in response to the transition of the control voltage Vc. The control switch SWB and the backup line TRB are connected in series between the first node a and the second node b, and are turned off in response to the initial level of the control voltage Vc (that is, by default to be turned off), and in response to the transition of the control voltage Vc State and conduction.

The comparison circuit CMP is coupled to the first node a, the second node b, and the control node c, and the control node c is coupled to the disconnect switch SWA and the control switch SWB. The bending area RBL of the flexible display panel FDP is located in the first node. Between node a and second node b. The comparison circuit CMP receives the first voltage Va of the first node a and the second voltage Vb of the second node b, and compares the first voltage Va and the second voltage Vb to provide the control voltage Vc to the control node c according to the comparison result.

When the main line TRA has no break or the break is slight, the line impedance of the main line TRA will be lower, that is, the pressure difference between the first node a and the second node b will be smaller. At this time, the comparison circuit CMP can maintain the control voltage Vc at the initial level (for example, a low voltage level) to maintain the turn-on of the disconnect switch SWA and turn-off of the control switch SWB. Conversely, when the main line TRA is severely or completely broken, the line impedance of the main line TRA will be very high, that is, the pressure difference between the first node a and the second node b will become very high. At this time, the comparison circuit CMP can switch the control voltage Vc (for example, switch to a high voltage level), so as to intercept the disconnect switch SWA and turn on the control switch SWB.

In this way, through the real-time monitoring of the comparison circuit CMP, the control voltage Vc can be set/switched in response to the line status of the main line TRA. Therefore, the display panel can automatically disconnect the abnormal main line TRA without manual judgment or other maintenance methods. , And use the backup line TRB to supply the signals required for driving the flexible display panel FDP.

In the embodiment of the present invention, the detection circuit CDT is coupled to the control node c to detect the control voltage Vc, and provides the detection signal SDT to the controller CT1 according to the detection result. After receiving the detection signal SDT, the controller CT1 provides a line status signal Sst to the outside of the flexible display panel FDP according to the detection signal SDT to indicate the line impedance and/or line status of the main line TRA. In this way, the detection circuit CDT can return the detection signal SDT to the controller CT1 to know the line impedance and/or line status of the current main line TRA.

In the embodiment of the present invention, the controller CT1 can provide the driving signal Sdr or the detection voltage Vdt to the first node a. In the spot mode, the controller CT1 can provide the driving signal Sdr, and in the detection mode, Before receiving the detection signal SDT, the controller CT1 provides the detection voltage Vdt. In the embodiment of the present invention, the detection voltage Vdt may be equal to the black display voltage (that is, the voltage at which no image is displayed in the display area APD).

In the embodiment of the present invention, the error range value of the comparison circuit CMP is set to be within ±10mV (that is, the preset voltage) as a normal error, and the impedance of the abnormal main line TRA (slightly damaged or broken line) is set to be greater than 10k ohms (Ohm) Even higher. In other words, when the current of the main line TRA is greater than 1uA, abnormal wiring can be judged. Generally speaking, the impedance of the normal main line TRA should be less than 1 Ohm, which will not affect the judgment of the line.

In addition, in the spot mode, the actuation time of the comparison circuit CMP is limited to within 6 microseconds (us), for example. In other words, in a display panel with a frame refresh rate of 60 Hz and a resolution of QHD (that is, 2560×1440), the comparison circuit CMP must complete the comparison within the time length of one horizontal scan line.

In addition, in spot mode, the turn-on time of the control switch must be less than 0.5 us. In other words, in a display panel with a screen refresh rate of 60Hz and a resolution of QHD (that is, 2560×1440), the time length of a horizontal scan line is 6.5 us, and more than 5 us will be used in the pixel circuit of the display area ADP ( Not shown) compensation. If the control switch SWB is turned on for longer than 0.5 us, the compensation of the pixel circuit (not shown) will be affected.

2A to 2C are flowcharts of an automatic switching method of a backup circuit system of a flexible display panel according to an embodiment of the present invention. Please refer to FIG. 1 and FIGS. 2A to 2C. In this embodiment, the controller CT1 is used to determine the backup circuit system 100 to operate in the spotting mode or the detection mode (step S201), wherein the spotting mode is shown in FIG. 2B , And the detection mode is shown in Figure 2C.

As shown in FIG. 2B, in the spot mode, the drive signal Sdr is provided to the first node a through the controller CT1 (step S210), and the control voltage Vc is initialized through the comparison circuit CMP to turn on the disconnect switch SWA and turn off the control switch SWB (Step S211). In step S212, the first voltage Va of the first node a and the second voltage Vb of the second node are compared through the comparison circuit CMP. When the voltage difference between the first voltage Va and the second voltage Vb is less than or equal to the preset voltage, that is, the first voltage Va is approximately equal to the second voltage Vb, the control voltage Vc is provided to the disconnect switch SWA and the control switch SWB through the comparison circuit CMP. The cut-off switch SWA is kept on and the control switch SWB is turned off (step S213). In addition, the drive signal Sdr is transmitted through the disconnect switch SWA, but no signal is transmitted from the backup line TRB (step S214). Finally, the driving signal Sdr is transmitted to the flexible display panel FDP, so that the flexible display panel FDP is normally chipped (step S215).

When the voltage difference between the first voltage Va and the second voltage Vb is greater than the preset voltage, that is, the first voltage Va is not equal to the second voltage Vb, the comparison circuit CMP provides the control voltage Vc to the disconnect switch SWA and the control switch SWB to maintain The disconnect switch SWA is turned off and the control switch SWB is turned on (step S216). In addition, the main line TRA is disconnected, and the backup line TRB is activated for transmission of the driving signal Sdr (step S217). Furthermore, the driving signal Sdr can also be transmitted to the flexible display panel FDP, so that the flexible display panel FDP can be normally chipped (step S215).

As shown in FIG. 2C, in the detection mode, the detection voltage Vdt is provided to the first node a through the controller CT1 (step S220), and the control voltage Vc is initialized through the comparison circuit CMP to turn on the disconnect switch SWA and turn off the control switch SWB (step S221). In step S222, the first voltage Va of the first node a and the second voltage Vb of the second node are compared through the comparison circuit CMP. When the voltage difference between the first voltage Va and the second voltage Vb is less than or equal to the predetermined voltage, that is, the first voltage Va is approximately equal to the second voltage Vb, the comparison circuit CMP provides a first level (such as a low voltage level) The control voltage Vc (step S223). Then, the detection circuit CDT detects the control voltage Vc to provide the detection signal SDT to the controller CT1, and the controller CT1 determines whether the main line TRA is disconnected and provides the line status signal Sst to the outside of the flexible display panel FDP .

FIG. 3 is a schematic diagram of a driving sequence of a flexible display panel according to an embodiment of the present invention. 3, in this embodiment, the picture period Pframe is roughly divided into a vertical space period and a picture display period. The vertical space period includes at least a vertical sync pulse period VW, a vertical back porch period VBP, and a vertical front porch period VFP. Among them, a frame period Pframe can be defined by the vertical synchronization signal VSYNC, the vertical synchronization pulse period VW, the vertical back porch period VBP, the vertical front porch period VFP and the horizontal scanning period can be defined by the horizontal synchronization signal HSYNC. The data signal DATA is used to indicate the transmission sequence of the display data.

In the embodiment of the present invention, when the flexible display panel FDP is operated in the vertical blanking period of the frame period Pframe, the controller CT1 can determine the backup circuit system 100 to operate in the detection mode; on the contrary, when the flexible display panel FDP is operated During the screen display period of the screen period, the controller CT1 can determine the backup circuit system 100 to operate in the spot mode. Among them, the vertical blank period is the period during which the flexible display panel FDP is between different screens and the flexible display panel FDP outputs a black screen. At this time, no signal may be transmitted.

In the embodiment of the present invention, if the wire is severely disconnected, the second node b will be in a floating state, and the first node a should be given a black screen voltage (for example, 2V). During the vertical blanking period, if the output result of the control node c is equal to 2V, it can be determined that the main line TRA is obviously disconnected.

In the method of detecting disconnection during the vertical blanking period, if the detection voltage Vdt output by the controller CT1 is 0V, it is no different from floating. Therefore, the detection voltage Vdt output by the controller CT1 must not be 0V. If the black screen voltage is not 0V, the controller CT1 can first set the threshold voltage for judging disconnection, and if it is greater than the threshold, it will be judged as disconnection.

In the method of detecting disconnection during the vertical blanking period, the controller CT1 can send a fixed voltage detection voltage Vdt during the vertical blanking period for measurement. Among them, the vertical blank period must be at least 50 us. In other words, in a display panel with a frame refresh rate of 60 Hz and a resolution of QHD (that is, 2560×1440), at least 8 horizontal scanning lines are required. And, if the screen refresh rate is higher or the resolution is higher, the time length of the required horizontal scanning lines is more. However, the vertical blanking period should be less than 200 us so that it will not cause other effects on the screen display.

In the embodiment of the present invention, the detection circuit CDT can simply determine the digital voltage value of the control voltage Vc output by the comparison circuit CMP. The controller CT1 can confirm whether the main line TRA is disconnected according to the returned digital voltage value. That is, the controller CT1 can read back the voltage values of different control nodes c and make judgments.

In the embodiment of the present invention, a subtractor can be used as the design of the comparison circuit CMP to output the subtracted digital voltage of the control node c, and then return the digital voltage of the control node c to the controller CT1 for resistance judgment .

In the embodiment of the present invention, different judgment standards can be set to distinguish the resistance status of the main line TRA. The assumption conditions are as follows: the current of the main line TRA is 10uA, the readback voltage of the control node c is 1V, the impedance of the main line TRA is 0.1M Ohm, and the main line TRA is obviously disconnected; the main line TRA current is 10uA, and the control node c returns If the reading voltage is 10mV, the impedance of the main line TRA is 1k Ohm, and the main line TRA is slightly disconnected; the main line TRA current is 10uA, and the readback voltage of the control node c is less than 1mV, then the impedance of the main line TRA is 100 Ohm. TRA is normal.

4 is a schematic circuit diagram of a backup circuit system of a flexible display panel according to an embodiment of the present invention. 1 and 4, in this embodiment, the disconnect switch SWA includes a first transistor T1, wherein the first transistor T1 has a first terminal electrically connected to the first node a, and electrically connected to the second node b The second terminal of, and the control terminal receiving the control voltage Vc.

The control switch SWB includes an inverter INT and a second transistor T2. The inverter INT receives the control voltage Vc to provide an inverted voltage of the control voltage Vc. The second transistor T2 has a first end electrically connected to the first node a, a second end electrically connected to the second node b, and a control end receiving the inverted voltage of the control voltage Vc.

The comparison circuit CMP includes a comparator CP, a first resistor R1, a second resistor R2, a third resistor R3, and a fourth resistor R4, and a comparator CP, a first resistor R1, a second resistor R2, a third resistor R3, and a fourth resistor. R4 can be operated as an analog subtractor. The comparator CP has a first input terminal, a second input terminal, and an output terminal for providing a control voltage Vc. The first resistor R1 is coupled between the second node b and the first input terminal of the comparator CP. The second resistor R2 is coupled between the first input terminal of the comparator CP and the output terminal of the comparator CP. The third resistor R3 is coupled between the first node a and the second input terminal of the comparator CP. The fourth resistor R4 is coupled to the second input terminal of the comparator CP and the ground terminal.

The detection circuit CDT includes a third transistor T3 and a fifth resistor R5. The third transistor T3 has a first terminal electrically connected to the first node a, a second terminal receiving the control voltage Vc, and a control terminal receiving the sensing signal S_Sensing, wherein the sensing signal S_Sensing can be from the flexible display panel FDP However, the embodiment of the present invention is not limited to this. The fifth resistor R5 is coupled between the second terminal of the third transistor T3 and the ground terminal.

FIG. 5 is a schematic diagram of the configuration of a backup circuit system of a flexible display panel according to an embodiment of the present invention. Please refer to FIG. 1 and FIG. 5. In this embodiment, the same or similar components use the same or similar reference numerals. For the first group of lines formed by the main line TRA1 and the backup line TRB1, the main line TRA1 is close to the first edge EDG1 of the flexible display panel FDP, and the backup line TRB1 is close to the first edge of the flexible display panel FDP. The second edge of EDG1 is EDG2. For the second group of lines formed by the main line TRA2 and the backup line TRB2, the main line TRA2 is close to the second edge EDG2 of the flexible display panel FDP, and the backup line TRB2 is close to the second edge of the flexible display panel FDP. The first edge of EDG2 is EDG1. Thereby, the possibility of simultaneous damage of the main line TRA1 and the backup line TRB1 can be reduced, and the possibility of the main line TRA2 and the backup line TRB2 being damaged at the same time can be reduced.

On the other hand, the main lines TRA1 and TRA2 are closer to the edges EDG1 and EDG2 of the flexible display panel FDP than the backup lines TRB1 and TRB2, and the backup lines TRB1 and TRB2 are closer to the center line of the flexible display panel FDP than the main lines TRA1 and TRA2. LCM. In this way, the possibility of damage to the backup lines TRB1 and TRB2 can be reduced.

In summary, the standby circuit system for flexible display panels and the automatic switching method of the standby circuit system according to the embodiments of the present invention can monitor the pressure of the main circuit at both ends of the bending area through the comparison circuit in real time, so as to ensure Set/switch the control voltage in response to the line status of the main line to automatically disconnect the abnormal main line and activate the normal control backup line. Therefore, manual judgment or other maintenance methods are not required, and the maintenance cost is reduced. In addition, by supplying the signals required for driving the flexible display panel through the backup circuit, the service life of the flexible display panel can be prolonged.

Although the present invention has been disclosed in the above embodiments, it is not intended to limit the present invention. Anyone with ordinary knowledge in the relevant technical field can make some changes and modifications without departing from the spirit and scope of the present invention. The protection scope of the present invention shall be subject to those defined by the attached patent application scope.

FDP: Flexible display panel ADP: display area 100: Standby line system TRA, TRA1, TRA2: main routes SWA: disconnect switch TRB, TRB1, TRB2: standby line SWB: control switch CMP: Comparison circuit CDT: Detection circuit CT1: Controller a: the first node Va: first voltage Vb: second voltage b: second node Vc: Control voltage c: control node RBL: bending zone SDT: detect signal Sst: Line status signal Sdr: drive signal CP: Comparator DATA: data signal EDG1, EDG2: Edge HSYNC: horizontal synchronization signal INT: inverter LCM: Midline Pframe: during the frame R1: first resistance R2: second resistor R3: third resistor R4: Fourth resistor R5: Fifth resistor S_Sensing: sensing signal T1: The first transistor T2: second transistor T3: third transistor VBP: During the vertical back porch Vdt: Detection voltage VFP: During the vertical front porch VSYNC: vertical synchronization signal VW: vertical sync pulse period S201, S210~S217, S220~S226: steps

FIG. 1 is a schematic diagram of a system of a flexible display panel according to an embodiment of the present invention. 2A to 2C are flowcharts of an automatic switching method of a backup circuit system of a flexible display panel according to an embodiment of the present invention. FIG. 3 is a schematic diagram of a driving sequence of a flexible display panel according to an embodiment of the present invention. 4 is a schematic circuit diagram of a backup circuit system of a flexible display panel according to an embodiment of the present invention. FIG. 5 is a schematic diagram of the configuration of a backup circuit system of a flexible display panel according to an embodiment of the present invention.

100: Standby line system

a: the first node

ADP: display area

b: second node

c: control node

CDT: Detection circuit

CMP: Comparison circuit

CT1: Controller

FDP: Flexible display panel

RBL: bending zone

Sdr: drive signal

SDT: detect signal

Sst: Line status signal

SWA: disconnect switch

SWB: control switch

TRA: main route

TRB: Standby line

Va: first voltage

Vb: second voltage

Vc: Control voltage

Vdt: Detection voltage

Claims (19)

A backup circuit system for flexible display panels, including: A main line; A disconnect switch, connected in series with the main circuit between a first node and a second node, is preset to be turned on and turned off in response to a control voltage; A spare line; A control switch, connected in series with the backup line between the first node and the second node, is preset to be off, and is turned on in response to the control voltage; A comparison circuit compares a first voltage of the first node and a second voltage of the second node, and provides the control voltage according to the comparison result. The backup circuit system according to claim 1, wherein a bending area of the flexible display panel is located between the first node and the second node. The backup line system according to claim 1, wherein the disconnect switch includes a first transistor having a first end electrically connected to the first node, a second end electrically connected to the second node, and A control terminal that receives the control voltage. The backup line system according to claim 1, wherein the control switch includes: An inverter that receives the control voltage to provide an inverted voltage of the control voltage; and A second transistor has a first terminal electrically connected to the first node, a second terminal electrically connected to the second node, and a control terminal receiving the inverted voltage. The backup line system according to claim 1, wherein the comparison circuit includes: A comparator having a first input terminal, a second input terminal and an output terminal for providing the control voltage; A first resistor, coupled between the second node and the first input terminal; A second resistor, coupled between the first input terminal and the output terminal; A third resistor, coupled between the first node and the second input terminal; and A fourth resistor is coupled between the second input terminal and a ground terminal. The backup circuit system according to claim 1, further comprising a detection circuit for detecting the control voltage to provide a detection signal. The backup line system according to claim 6, wherein the detection circuit includes: A third transistor having a first terminal electrically connected to the first node, a second terminal receiving the control voltage, and a control terminal receiving a sensing signal; and A fifth resistor is coupled between the second terminal and a ground terminal. The backup circuit system according to claim 6, further comprising a controller that provides a driving signal to the first node, and after receiving the detection signal, provides a circuit state signal to the outside of the flexible display panel. The backup line system according to claim 8, wherein the controller provides a detection voltage to the first node before receiving the detection signal. The backup circuit system according to claim 9, wherein the detection voltage is equal to a black display voltage. The standby circuit system according to claim 1, wherein the main circuit is close to a first edge of the flexible display panel, and the standby circuit is close to a second edge of the flexible display panel relative to the first edge. edge. The standby circuit system according to claim 1, wherein the main circuit is closer to an edge of the flexible display panel than the standby circuit, and the standby circuit is closer to a center line of the flexible display panel than the main circuit. An automatic switching method for the standby line system of a flexible display panel, including: A control voltage is initialized through a comparison circuit to turn on a disconnect switch and turn off a control switch, wherein the disconnect switch and a main circuit are connected in series between a first node and a second node, and the control switch and a standby The line is connected in series between the first node and the second node; Comparing a first voltage of the first node and a second voltage of the second node through the comparison circuit; When a voltage difference between the first voltage and the second voltage is less than or equal to a predetermined voltage, providing a control voltage to the disconnect switch and the control switch through the comparison circuit to maintain the disconnection switch and turn off the control switch; as well as When the voltage difference between the first voltage and the second voltage is greater than the predetermined voltage, the control voltage is provided to the disconnect switch and the control switch through the comparison circuit to maintain the disconnection switch and turn on the control switch. The automatic switching method according to claim 13, wherein a bending area of the flexible display panel is located between the first node and the second node. The automatic switching method described in claim 13 further includes: A controller is used to determine whether the backup circuit system is operated in a one-chip mode or a detection mode; When the backup circuit system is operating in the spot mode, provide a driving signal to the first node through the controller; and When the backup circuit system is operated in the detection mode, a detection voltage is provided to the first node through the controller. The automatic switching method described in claim 15 further includes: When the backup circuit system is operating in the detection mode, the control voltage is detected by a detection circuit to provide a detection signal to the controller, and a circuit status signal is provided to the flexible display panel through the controller Outside. The automatic switching method according to claim 15, wherein determining, through the controller, that the backup line system is operated in the spot mode or the detection mode includes: When the flexible display panel is operated in a vertical blank period of a screen period, the controller determines that the backup circuit system is operated in the detection mode; and When the flexible display panel is operated in a screen display period of the screen period, the controller determines that the backup circuit system is operated in the spot mode. The automatic switching method according to claim 15, wherein the detection voltage is equal to a black display voltage. The automatic switching method described in claim 13 further includes: When the voltage difference between the first voltage and the second voltage is less than or equal to the predetermined voltage, the control voltage having a first level is provided through the comparison circuit; and When the voltage difference between the first voltage and the second voltage is greater than the predetermined voltage, the control voltage having a second level relative to the first level is provided through the comparison circuit.

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