Start-up timing control circuit and control chip

Abstract

The application is suitable for the technical field of LED backlight driving, and provides a starting timing control circuit and a control chip. The starting timing control circuit comprises a switching module, a comparison module, a threshold adjusting module and a switching module. The comparison module is electrically connected with the switching module, the threshold adjusting module and the switching module. The switching module is electrically connected with a detection selection module and an error amplification module. The comparison module is electrically connected with a feedback module. The threshold adjusting module is electrically connected with a logic driving module. The switching module is electrically connected with the logic driving module and a control module. The starting timing control circuit provided by the application embodiment configures the error amplification module as a unit gain buffer in the starting stage, and connects the error amplification module and the control module into a closed loop circuit when the output voltage approaches the target value, and gradually increases the overcurrent protection threshold through the threshold adjusting module to relax the phased cooperative control logic of current limitation, so that the output voltage is smoothly raised.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of LED backlight driving, and particularly relates to a starting timing control circuit and a control chip. BACKGROUND

[0002] Light-Emitting Diode (LED) has become the core device of the Liquid Crystal Display (LCD) backlight system due to its characteristics of high brightness, low power consumption and long service life, and the starting control performance of the driving circuit directly affects the safety and stability of the system. The existing starting timing control circuit usually adopts the ways of limiting the switching current of the power tube, gradually releasing the current limit or controlling the charging rate of the compensation capacitor, but such methods may cause overcharging of the inductor current in the Boost starting process. SUMMARY

[0003] The application provides a starting timing control circuit and a control chip, which can solve the problem of overcharging of the inductor current in the Boost starting process.

[0004] In a first aspect, the application provides a starting timing control circuit, comprising a switching module, a comparison module, a threshold adjustment module and a switching module, the comparison module is electrically connected with the switching module, the threshold adjustment module and the switching module, the switching module is electrically connected with a detection selection module and an error amplification module, the comparison module is electrically connected with a feedback module, the threshold adjustment module is electrically connected with a logic drive module, and the switching module is electrically connected with the logic drive module and a control module.

[0005] When the feedback voltage output by the feedback module is less than a preset voltage, the comparison module outputs a first comparison signal to the switching module, the threshold adjustment module and the switching module; the switching module is used for turning on the first input end of the error amplification module and the output end of the error amplification module according to the first comparison signal; the switching module is used for turning off and disconnecting the control module and the logic drive module according to the first comparison signal; and the threshold adjustment module is used for outputting an overcurrent protection signal to the logic drive module according to the first comparison signal, a reference signal and a sampling signal.

[0006] When the feedback voltage is greater than or equal to the preset voltage, the comparison module outputs a second comparison signal to the switching module, the threshold adjustment module and the switch module; the switching module is configured to turn on the first input end of the error amplifier module and the detection selection module according to the second comparison signal; the switch module is configured to connect the control module and the logic drive module according to the second comparison signal; the threshold adjustment module is configured to gradually increase the threshold of the overcurrent protection signal according to the second comparison signal, the reference signal and the sampling signal.

[0007] In a possible implementation manner of the first aspect, the switching module comprises a first transmission gate, a first end of the first transmission gate is electrically connected with the first input end of the error amplifier module, a second end of the first transmission gate is electrically connected with the detection selection module, a third end of the first transmission gate is electrically connected with the output end of the error amplifier module, and a control end of the first transmission gate is electrically connected with the comparison module.

[0008] In a possible implementation manner of the first aspect, the comparison module comprises a first comparator, a first input end of the first comparator is configured to be electrically connected with the feedback module, a second input end of the first comparator is configured to receive the preset voltage, and an output end of the first comparator is electrically connected with the switching module, the threshold adjustment module and the switch module respectively.

[0009] In a possible implementation manner of the first aspect, the threshold adjustment module comprises a reference voltage generation unit, a current mirror unit, a first switch unit, a second switch unit, a third switch unit, an energy storage unit and a comparison output unit, the current mirror unit is electrically connected with the reference voltage generation unit, the first switch unit, the third switch unit, the energy storage unit and the comparison output unit respectively, and the comparison output unit is electrically connected with the second switch unit and the third switch unit respectively.

[0010] The reference voltage generation unit is configured to provide a reference voltage signal to the current mirror unit; when the feedback voltage output by the feedback module is less than the preset voltage, the first switch unit is turned on, the second switch unit is turned on, the third switch unit is turned off, and the current mirror unit is configured to output a first current to the comparison output unit according to the reference voltage signal; the comparison output unit is configured to output an overcurrent protection signal to the logic drive module according to the first current, a node voltage, the reference signal and the sampling signal, the node voltage being a voltage of a common end of the comparison output unit and the second switch unit.

[0011] When the feedback voltage is greater than or equal to a preset voltage, the first switch unit is turned off, the second switch unit is turned off, the third switch unit is turned on, the current mirror unit is configured to output a charging current to the energy storage unit according to the reference voltage signal, and the energy storage unit is configured to store energy according to the charging current, so that the node voltage gradually increases.

[0012] In a possible implementation of the first aspect, the reference voltage generation unit comprises a first resistor and a current source, a first end of the first resistor is electrically connected to the current mirror unit, and a first end of the current source is electrically connected to a second end of the first resistor and the current mirror unit respectively.

[0013] The current mirror unit comprises a first transistor, a second transistor, a third transistor, a fourth transistor, a fifth transistor and a sixth transistor, a gate of the first transistor is electrically connected to a drain of the second transistor, the reference voltage generation unit, a gate of the third transistor and a gate of the fifth transistor respectively, a source of the first transistor, a source of the third transistor and a source of the fifth transistor are configured to be electrically connected to a power supply, a drain of the first transistor is electrically connected to a source of the second transistor, a gate of the fourth transistor is electrically connected to a gate of the second transistor, the reference voltage generation unit and a gate of the sixth transistor respectively, a source of the fourth transistor is electrically connected to a drain of the third transistor, a drain of the fourth transistor is electrically connected to the first switch unit, the third switch unit and the energy storage unit respectively, a source of the sixth transistor is electrically connected to a drain of the fifth transistor, and a drain of the sixth transistor is electrically connected to the comparison output unit.

[0014] In a possible implementation of the first aspect, the first switch unit comprises a first switch tube, a gate of the first switch tube is electrically connected to the comparison module, a drain of the first switch tube is electrically connected to the current mirror unit, the third switch unit and the energy storage unit respectively, and a source of the first switch tube is grounded.

[0015] The second switch unit comprises a second switch tube, a gate of the second switch tube is electrically connected to the comparison module, a source of the second switch tube is configured to be electrically connected to a power supply, and a drain of the second switch tube is electrically connected to the third switch unit and the comparison output unit respectively.

[0016] The third switch unit includes a third switch tube and a fourth switch tube, a gate of the third switch tube and a gate of the fourth switch tube are electrically connected with the comparison module, a drain of the third switch tube is electrically connected with a drain of the fourth switch tube, the current mirror unit, the first switch unit and the energy storage unit respectively, and a source of the third switch tube is electrically connected with a source of the fourth switch tube, the second switch unit and the comparison output unit respectively.

[0017] In a possible implementation manner of the first aspect, the energy storage unit includes a first capacitor, a first end of the first capacitor is electrically connected with the first switch unit, the third switch unit and the current mirror unit respectively, and a second end of the first capacitor is grounded.

[0018] In a possible implementation manner of the first aspect, the comparison output unit includes a fifth switch tube, a seventh transistor, an eighth transistor, a second resistor, a third resistor and a second comparator, a gate of the fifth switch tube is electrically connected with the second switch unit and the third switch unit respectively, a source of the fifth switch tube is electrically connected with a source of the seventh transistor, a source of the eighth transistor and the current mirror unit respectively, a drain of the fifth switch tube is electrically connected with a drain of the seventh transistor, a first end of the second resistor and a first input end of the second comparator respectively, a gate of the seventh transistor is used for receiving the reference signal, a gate of the eighth transistor is used for receiving the sampling signal, a drain of the eighth transistor is electrically connected with a first end of the third resistor and a second input end of the second comparator respectively, an output end of the second comparator is used for being electrically connected with the logic driving module, and a second end of the second resistor and a second end of the third resistor are grounded.

[0019] In a possible implementation manner of the first aspect, the switch module includes a control switch, a control end of the control switch is electrically connected with the comparison module, a first end of the control switch is used for being electrically connected with the control module, and a second end of the control switch is used for being electrically connected with the logic driving module.

[0020] In a second aspect, the embodiments of the present application provide a control chip, comprising a detection selection module, an error amplification module, a feedback module, a logic drive module, a first switch module, a control module and the start timing control circuit of any one of the first aspect, the detection selection module and the error amplification module are electrically connected with the switching module in the start timing control circuit, the control module is electrically connected with the error amplification module, the first switch module and the switching module in the start timing control circuit respectively, the logic drive module is electrically connected with the first switch module, the feedback module and the threshold adjustment module and the switching module in the start timing control circuit respectively, and the feedback module is electrically connected with the comparison module in the start timing control circuit.

[0021] Compared with the prior art, the embodiments of the present application have the following beneficial effects:

[0022] The start timing control circuit provided by the embodiments of the present application comprises a switching module, a comparison module, a threshold adjustment module and a switching module. When the feedback voltage is less than the preset voltage, it indicates that the output voltage is low. At this time, the comparison module outputs a first comparison signal. The switching module turns on the first input end and the output end of the error amplification module according to the first comparison signal, that is, the error amplification module is configured in the form of a unit gain buffer, and the first reference voltage received by the second input end of the error amplification module can be used to charge the compensation capacitor. Since the first reference voltage is less than the steady-state reference voltage at the steady state, the voltage at the output end of the error amplification module (i.e. the COMP voltage) can be ensured to start from a lower voltage, thereby indirectly realizing the soft start effect. In this process, the switching module is turned off, the threshold adjustment module outputs an overcurrent protection signal and transmits it to the logic drive module, the first switch module is turned off by the logic drive module, and then the output voltage of the Boost is increased, driving the feedback voltage to gradually increase.

[0023] As the feedback voltage gradually increases, when the feedback voltage is greater than or equal to the preset voltage, it indicates that the output voltage of the Boost has approached the target voltage. At this time, the comparison module outputs a second comparison signal. The switching module turns on the first input end of the error amplifier and the detection selection module according to the second comparison signal, that is, the error amplification module is connected to the loop, and starts to work in the form of a closed loop. In this process, the switching module is turned on, the control module is also connected to the loop, the threshold adjustment module gradually increases the threshold of the overcurrent protection signal, and the current limit is gradually relaxed as the circuit stabilizes. This design can effectively avoid the sudden change of the COMP voltage caused by the charging and discharging characteristics of the compensation capacitor when the error amplification module is connected to the loop, and the problems of sudden increase of duty ratio and inductance current impact caused thereby, thereby ensuring the synchronous and smooth rise of voltage and current.

[0024] Therefore, the startup timing control circuit provided in this application embodiment configures the error amplification module as a unity-gain buffer during the startup phase, uses a lower first reference voltage to charge the compensation capacitor to achieve COMP voltage soft start, combines a low threshold overcurrent protection signal to limit the current, and connects both the error amplification module and the control module to the closed loop when the output voltage approaches the target value. The phased collaborative control logic, which gradually increases the overcurrent protection threshold through the threshold adjustment module to relax the current limit, effectively solves the problem of inductor current overcharging that may occur during Boost startup and achieves a smooth rise in output voltage. Attached Figure Description

[0025] To more clearly illustrate the technical solutions in the embodiments of this application, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0026] Figure 1 This is a schematic diagram of the application circuit of an existing LED backlight driver start-up control scheme;

[0027] Figure 2 This is a schematic diagram of the chip circuit for an existing LED backlight driver startup control scheme.

[0028] Figure 3 This is the internal block diagram of the existing adaptive control Boost;

[0029] Figure 4 This is a schematic diagram of a startup timing control circuit provided in an embodiment of this application;

[0030] Figure 5 This is a circuit connection diagram of a startup timing control circuit provided in an embodiment of this application;

[0031] Figure 6 This is a schematic diagram of a threshold adjustment module provided in an embodiment of this application;

[0032] Figure 7 This is a circuit connection diagram of a threshold adjustment module provided in an embodiment of this application;

[0033] Figure 8 This is a schematic flowchart of the startup timing control provided in an embodiment of this application.

[0034] In the figure: 101, switching module; 102, comparison module; 103, threshold adjustment module; 1031, reference voltage generating unit; 1032, current mirror unit; 1033, first switch unit; 1034, second switch unit, 1035, third switch unit; 1036, energy storage unit; 1037, comparison output unit; 104, switching module; 100, detection selection module; 200, error amplification module; 300, feedback module; 400, logic drive module; 500, control module; 600, first switch module. DETAILED DESCRIPTION

[0035] In the following description, for the purpose of explanation and not limitation, specific details are set forth, such as particular system configurations, techniques, etc., in order to provide a thorough understanding of the embodiments of the present application. However, it will be apparent to those skilled in the art that the present application can be practiced in other embodiments that depart from these specific details. In other instances, detailed descriptions of well-known systems, devices, circuits, and methods are omitted so as not to obscure the description of the present application with unnecessary detail.

[0036] It should be understood that the term "comprises" as used in the specification and the appended claims indicates the presence of the described features, integers, steps, operations, elements, and / or components, but does not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or groups thereof.

[0037] It should also be understood that the term "and / or" as used herein refers to any combination of one or more of the associated listed items, and all possible combinations, and includes these combinations.

[0038] As used in the specification and the appended claims, the term "if' can be interpreted as meaning "when" or "once" or "in response to a determination" or "in response to a detection" depending on the context. Similarly, the phrase "if determined" or "if detected [the described condition or event]" can be interpreted as meaning "once determined" or "in response to a determination" or "once detected [the described condition or event]" or "in response to a detection [the described condition or event]" depending on the context.

[0039] In addition, in the description of the present application and the appended claims, the terms "first", "second", "third", etc. are only used for differentiation of description, and cannot be understood as indicating or implying relative importance.

[0040] Reference throughout this application to "one embodiment" or "an embodiment" means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment. The appearances of the phrase "in one embodiment" or "in some embodiments" in various places in the specification are not necessarily all referring to the same embodiment, however, but can refer to one or more but not all embodiments. The terms "including," "comprising," "carrying," "having," "containing," and variations thereof are meant to encompass the item listed thereafter, but do not exclude additional, unrecited items. The terms "a" or "an," as used herein in the disclosure, mean "one or more." The term "another," as used herein in the disclosure, means "at least one."

[0041] As shown in FIG. 1, a common application circuit is to drive LED lamp strings by Boosting the input voltage. The number of lamp strings varies from 1 to 6, and each string contains 6-10 LED lamps. Figure 1 As shown in FIG. 2, a conventional LED backlight drive startup scheme usually sends the minimum value of the headroom voltage (CH1-CH6) of the LED to the input of the error amplifier of the Boost, and then adjusts the output voltage of the Boost. The Boost usually adopts a non-synchronous rectification form, uses a Schottky diode externally, and integrates an N-type pull-down tube internally. Due to the characteristics of the LED load, when the output voltage of the Boost is insufficient to turn on the LED, the voltages of CH1-CH6 are all substantially equal to the ground level. At this time, if the Boost loop is not controlled, it will always work at the maximum duty cycle, thereby causing an excessive inductor current, leading to whistling or device burnout. Figure 2 Another common control method of the LED CH1-CH6 voltage is to internally set two threshold voltages LOW_REF and MID_REF. A comparator is used to compare the sizes of CH1-CH6 and LOW_REF, MID_REF. If only one voltage of CH1-CH6 is lower than LOW_REF, the output voltage of the Boost is adjusted upward. The step size and the time of each adjustment are set by internal registers. When all voltages of CH1-CH6 are higher than MID_REF, the output voltage of the Boost is adjusted downward. The final result is to limit the lowest CH1-CH6 value between LOW_REF and MID_REF. The internal implementation of the Boost is shown in FIG. 3.

[0042] As shown in FIG. 4, a resistance string is used to detect the voltage of VBOOST internally, and the size of the active load current is adjusted to adjust the rising and falling of the VBOOST voltage. Figure 3

[0043] ​In summary, the existing start timing control circuit usually adopts the ways of limiting the switching current of the power tube, gradually releasing the current limit or controlling the charging rate of the compensation capacitor, but such methods may cause overcharging of the inductor current during the Boost startup process.

[0044] Based on the above problems, the start timing control circuit provided by the embodiments of the present application includes a switching module, a comparison module, a threshold adjustment module and a switching module. When the feedback voltage is less than the preset voltage, it indicates that the output voltage is low. At this time, the comparison module outputs a first comparison signal. The switching module turns on the first input terminal and the output terminal of the error amplifier module according to the first comparison signal, that is, the error amplifier module is configured in the form of a unity gain buffer, and the first reference voltage received by the second input terminal of the error amplifier module can be used to charge the compensation capacitor. Since the first reference voltage is less than the steady-state reference voltage, the voltage at the output terminal of the error amplifier module (i.e. the COMP voltage) can be ensured to start from a lower voltage, thereby indirectly achieving the effect of soft start. During this process, the switching module is turned off, the threshold adjustment module outputs an overcurrent protection signal and transmits it to the logic drive module, the first switch module is driven to be turned off by the logic drive module, and then the output voltage of the Boost is increased, driving the feedback voltage to gradually increase.

[0045] As the feedback voltage gradually increases, when the feedback voltage is greater than or equal to the preset voltage, it indicates that the output voltage of the Boost has approached the target voltage. At this time, the comparison module outputs a second comparison signal. The switching module turns on the first input terminal of the error amplifier and the detection selection module according to the second comparison signal, that is, the error amplifier module is connected to the loop, and it starts to work in the form of a closed loop. During this process, the switching module is turned on, the control module is also connected to the loop, and the threshold adjustment module gradually increases the threshold of the overcurrent protection signal, so that the current limit is gradually relaxed as the circuit stabilizes. This design can effectively avoid the sudden change of the COMP voltage caused by the charging and discharging characteristics of the compensation capacitor when the error amplifier module is connected to the loop, as well as the problems of sudden increase of duty cycle and inductor current impact, thereby ensuring the synchronous and smooth rise of voltage and current.

[0046] Therefore, the start timing control circuit provided by the embodiments of the present application can configure the error amplifier module as a unity gain buffer during the startup phase, realize soft start of the COMP voltage by charging the compensation capacitor with a lower first reference voltage, combine the low threshold overcurrent protection signal to limit the current, and connect the error amplifier module and the control module to the closed loop when the output voltage approaches the target value, and gradually increase the overcurrent protection threshold by the threshold adjustment module to relax the current limit. The phased cooperative control logic effectively solves the problem of overcharging of the inductor current during the Boost startup process, and realizes the smooth rise of the output voltage.

[0047] In order to illustrate the technical solutions described in the present application, the following will be described by specific embodiments.

[0048] Figure 4 The principle diagram of the start timing control circuit provided by an embodiment of the present application is shown. Referring to Figure 4 As shown, the start timing control circuit includes a switching module 101, a comparison module 102, a threshold adjustment module 103 and a switch module 104, the comparison module 102 is electrically connected with the switching module 101, the threshold adjustment module 103 and the switch module 104 respectively, the switching module 101 is electrically connected with the detection selection module 100 and the error amplification module 200 respectively, the comparison module 102 is electrically connected with the feedback module 300, the threshold adjustment module 103 is electrically connected with the logic drive module 400, and the switch module 104 is electrically connected with the logic drive module 400 and the control module 500 respectively.

[0049] Specifically, when the feedback voltage VFB is less than the preset voltage Vref2, it indicates that the output voltage VOUT is relatively low. At this time, the comparison module 102 outputs a first comparison signal. The switching module 101 turns on the first input end and the output end of the error amplification module 200 according to the first comparison signal, that is, the error amplification module 200 is configured in the form of a unit gain buffer, and the compensation capacitor can be charged by the first reference voltage Vref1 received by the second input end of the error amplification module 200. Since the first reference voltage Vref1 is less than the steady-state reference voltage at steady state, it can be ensured that the voltage at the output end of the error amplification module 200 (i.e. the COMP voltage) starts to build from a lower voltage, thereby indirectly achieving the soft start effect. In this process, the switch module 104 is turned off, the threshold adjustment module 103 outputs an overcurrent protection signal OCP and transmits it to the logic drive module 400, the first switch module 600 is turned off by the logic drive module 400, and the output voltage VOUT of the Boost is thus increased, driving the feedback voltage VFB to gradually increase.

[0050] As the feedback voltage VFB gradually increases, when the feedback voltage VFB is greater than or equal to the preset voltage Vref2, it can be represented that the output voltage VOUT of the Boost has approached the target voltage (for example, the output voltage VOUT is 2.5V lower than the target voltage). At this time, the comparison module 102 outputs a second comparison signal. The switching module 101 turns on the first input end of the error amplifier EA and the detection selection module 100 according to the second comparison signal, that is, the error amplification module 200 is connected to the loop, so that it starts to work in the form of a closed loop. In this process, the switch module 104 is turned on, the control module 500 is also connected to the loop, and the threshold adjusting module 103 gradually increases the threshold of the overcurrent protection signal OCP, so that the current limit gradually relaxes as the circuit stabilizes. This design can effectively avoid the sudden change of the COMP voltage caused by the charging and discharging characteristics of the compensation capacitor when the error amplification module 200 is connected to the loop, and the resulting sudden increase in duty ratio and inductance current impact, thereby ensuring that the voltage and current rise smoothly and synchronously.

[0051] Therefore, the start timing control circuit provided by the embodiments of the present application can effectively solve the problem of overcharging of inductance current during the start of the Boost, and realize the smooth rise of the output voltage VOUT, by configuring the error amplification module 200 as a unit gain buffer in the start phase, charging the compensation capacitor with a lower first reference voltage Vref1 to realize soft start of the COMP voltage, combining the low threshold overcurrent protection signal OCP to limit the current, and connecting the error amplification module 200 and the control module 500 to the closed loop when the output voltage VOUT approaches the target value, and gradually increasing the overcurrent protection threshold by the threshold adjusting module 103 to relax the current limit.

[0052] It should be noted that in the start phase, the error amplification module 200 is configured as a unit gain buffer, and the compensation capacitor is charged by the first reference voltage Vref1 with a lower voltage, so that the voltage at the output end of the error amplification module 200 (i.e. the COMP voltage) can be established from a lower voltage (since the bandwidth of the Boost is usually not very large, the COMP end is connected to a large capacitor, and the transconductance of the error amplification module 200 is also not large), thereby indirectly realizing the soft start effect. However, soft start is not always effective, especially when a large resistance is connected in series with the compensation capacitor (in order to obtain faster response speed). When the error amplification module 200 is connected to the Boost loop from the unit buffer, the current generated by the error amplification module 200 flowing through the compensation resistor will cause a sudden change in the COMP voltage, thereby causing a sharp increase in the duty ratio of the Boost, and then causing a rapid increase in the inductance current. Therefore, the threshold adjusting module 103 is added to gradually increase the threshold of the overcurrent protection signal OCP when the output voltage VOUT approaches the target voltage, so that the current limit gradually relaxes as the circuit stabilizes.

[0053] It should be noted that when the circuit is actually used for control, the control module 500 is also electrically connected with the error amplification module 200 and the first switch module 600, and the logic drive module 400 is electrically connected with the first switch module 600 and the feedback module 300. The detection selection module 100 can detect the voltage of the output end of the plurality of LED lamp strings and output the detection voltage to the switching module 101. Whether the value of the first voltage is in the preset range can be determined to confirm the connection state of each LED lamp string. If the voltage of the output end of each LED lamp string is in the preset range, it indicates that all the LED lamp strings are connected normally. At this time, the switching module 101 turns on the first input end and the output end of the error amplification module 200, that is, the error amplification module 200 is configured in the form of a unity gain buffer, and the first reference voltage Vref1 received by the second input end of the error amplification module 200 is used to charge the compensation capacitor to obtain the COMP voltage. The feedback module 300 outputs the feedback voltage VFB to the comparison module 102 according to the output voltage VOUT, and when the feedback voltage VFB is less than the preset voltage Vref2, the logic drive module 400 outputs the drive signal to the first switch module 600 according to the oscillation signal OSC, the feedback signal and the overcurrent protection signal OCP, so that the first switch module 600 is turned off, and then the output voltage VOUT of the Boost is increased, and the feedback voltage VFB is gradually increased.

[0054] Because in the starting stage, the switch module 104 is turned off, and the control module 500 is not connected with the logic drive module 400, the control module 500 will not output the control signal to the logic drive module 400, and then control the turn-on and turn-off timing of the first switch module 600.

[0055] It should be noted that the detection selection module 100 can include LED open circuit detection and minimum LED selection. The LED open circuit detection is used to monitor the connection state of each LED lamp string in real time, that is, by detecting the abnormal change of the voltage of the output end of the LED lamp string (such as the voltage of a certain road suddenly rising to close to the output voltage VOUT of the Boost), it is judged whether the corresponding LED lamp string has an open circuit or a short circuit fault, which provides a basis for subsequent fault protection and avoids the abnormality of the circuit caused by the open circuit or the short circuit. The minimum LED selection is used to select the minimum value from the voltages of the output ends of the plurality of LED lamp strings and transmit the minimum value to the error amplification module 200. Because the voltage of the output end of the minimum LED lamp string directly reflects the state of the lamp string which needs the output voltage VOUT of the Boost to be improved most. If the minimum value is greater than the set value, it means that the voltage of all the LED lamp strings is greater than the set value.

[0056] It's important to note that due to the large size of the compensation capacitor, the design must ensure that the charging completion time of COMP is less than the rise time of the output voltage VOUT. This can be achieved by increasing the charging current capability of the error amplifier module 200, or by waiting for a period of time after the Boost output voltage VOUT rises, to ensure that the COMP voltage reaches the design target. That is, after ensuring that the Boost output voltage VOUT is sufficient to activate the current ramp of the LED string (the LED string current increases from zero to the target value), the voltage may have just reached the threshold and is not yet fully stable. Therefore, it is necessary to wait for a preset time (e.g., 4 milliseconds) to ensure that the Boost output voltage VOUT further stabilizes under closed-loop control and that the charge distribution of the compensation capacitor tends to be balanced. Only then can the current ramp be activated, allowing the Boost to more stably support the LED current demand and preventing the current output from deviating from the preset pattern (such as linear or exponential characteristics) due to voltage fluctuations.

[0057] The following is combined with Figure 5 The specific implementation methods of the error amplification module 200, control module 500, logic drive module 400, first switch module 600, feedback module 300 and comparison module 102 are described in detail.

[0058] like Figure 5 As shown, the error amplification module 200 includes an error amplifier EA. The first input terminal of the error amplifier EA is electrically connected to the switching module 101. The second input terminal of the error amplifier EA is used to receive the first reference voltage Vref1. The output terminal of the error amplifier EA is electrically connected to the control module 500 and the switching module 101, respectively.

[0059] Specifically, the inverting input of error amplifier EA serves as the first input, and the non-inverting input serves as the second input, used to receive the first reference voltage Vref1. During the Boost enable phase, switching module 101 directly connects the inverting input of error amplifier EA to its output (COMP terminal), configuring error amplifier EA as a unity-gain buffer. At this time, the first reference voltage Vref1 received by the non-inverting input directly drives the compensation capacitor to charge through the buffer. Upon entering the switching phase, switching module 101 disconnects the inverting input from the COMP terminal and connects it to the output of detection selection module 100. At this time, both error amplifier EA and control module 500 are connected to a closed-loop control circuit. The non-inverting input of error amplifier EA still receives the first reference voltage Vref1, while the inverting input receives the detection voltage. Error amplifier EA adjusts the COMP voltage by comparing the difference between the two. Control module 500 outputs a control signal to logic drive module 400 based on the COMP voltage, ultimately achieving the goal of controlling the Boost output voltage VOUT to match the changes in LED string current in real time.

[0060] As shown in Figure 5 , the control module 500 includes a first operational amplifier, a PWM (Pulse Width Modulation) controller, an accumulator, and a slope compensation. The negative input terminal of the first operational amplifier is electrically connected with the output terminal of the accumulator, the positive input terminal of the first operational amplifier is electrically connected with the output terminal of the error amplifier EA for receiving a reference voltage, and the output terminal of the first operational amplifier is electrically connected with the PWM controller. The first input terminal of the accumulator is electrically connected with the first switch module 600, and the second input terminal of the accumulator is electrically connected with the slope compensation. The slope compensation is used for receiving an oscillation signal OSC output by an oscillator.

[0061] Specifically, the accumulator is used for accumulating the compensation signal output by the slope compensation and the current signal flowing through the first switch module 600, and outputting an accumulated signal to the negative input terminal of the first operational amplifier. The first operational amplifier outputs a first operational amplifier signal to the PWM controller according to the accumulated signal and the reference signal. The PWM controller outputs a PWM signal according to the first operational amplifier signal.

[0062] It should be noted that since the design of the control module 500 is a conventional design architecture of a switching power supply, such design is relatively mature in the field of switching power supply, and the related principles all conform to the conventional design logic in the industry, so no more details are given here.

[0063] As shown in Figure 5 , the logic drive module 400 includes an OR gate and a first flip-flop. The first input terminal of the OR gate is electrically connected with the threshold adjustment module 103, the second input terminal of the OR gate is electrically connected with the feedback module 300, the third input terminal of the OR gate is electrically connected with the switch module 104, the output terminal of the OR gate is electrically connected with the first input terminal of the first flip-flop, the second input terminal of the first flip-flop is used for receiving an oscillation signal OSC, and the output terminal of the first flip-flop is electrically connected with the first switch module 600.

[0064] Specifically, in the Boost start-up phase, the first input terminal of the OR gate is used for receiving an overcurrent protection signal OCP, the second input terminal of the OR gate is used for receiving a feedback signal, and the OR gate outputs a first logic signal to the first input terminal of the first flip-flop according to the overcurrent protection signal OCP and the feedback signal. The first flip-flop outputs a first drive signal according to the first logic signal and the oscillation signal OSC, so as to make the first switch module 600 turn off. In the switching phase, the first input terminal of the OR gate is used for receiving a PWM signal output by the PWM controller, and the OR gate outputs a second logic signal to the first input terminal of the first flip-flop according to the PWM signal, the feedback signal, and the overcurrent protection signal OCP. The first flip-flop outputs a second drive signal according to the second logic signal and the oscillation signal OSC, so as to make the first switch module 600 turn on or turn off.

[0065] It should be noted that a driver is further arranged between the first flip-flop and the first switch module 600 to improve the driving capability of the first switch module 600.

[0066] For example, the first flip-flop can be an RS flip-flop.

[0067] As shown in Figure 5 the first switch module 600 includes a lower switch tube Q1, a gate of the lower switch tube Q1 is electrically connected with the logic driving module 400, a drain of the lower switch tube Q1 is electrically connected with an inductor and an anode of a diode in the Boost respectively, and a source of the lower switch tube Q1 is grounded through a resistor.

[0068] Specifically, the lower switch tube Q1 is used as a switching device to turn on or turn off according to the driving signal received by the gate. In the Boost starting stage, the lower switch tube Q1 is turned off according to the first driving signal, so that the output voltage VOUT of the Boost is increased. In the switching stage, the lower switch tube Q1 is turned on or turned off according to the second driving signal, so as to adjust the output voltage VOUT of the Boost to match the requirement of the current ramp of the LED lamp string.

[0069] For example, the designer can select the type of the lower switch tube Q1 according to the actual situation, that is, a full-controlled power device such as a metal oxide field effect transistor or an insulated gate bipolar transistor can be used. For example, the lower switch tube Q1 can be an NMOS tube.

[0070] As shown in Figure 5 the feedback module 300 includes two voltage dividing resistors and a feedback comparator, a positive input terminal of the feedback comparator is connected to a common terminal of the two voltage dividing resistors, a negative input terminal of the feedback comparator is used to receive a reference value (1.2V), and an output terminal of the feedback comparator is used to output a feedback signal.

[0071] Specifically, the two voltage dividing resistors are used to divide the output voltage VOUT, and transmit the divided voltage (feedback voltage VFB) to the feedback comparator. The feedback comparator compares the divided voltage with the 1.2V voltage and outputs the feedback signal.

[0072] As shown in Figure 5 the comparison module 102 includes a first comparator CMP1, a first input terminal of the first comparator CMP1 is electrically connected with the feedback module 300, a second input terminal of the first comparator CMP1 is used to receive a preset voltage Vref2, and an output terminal of the first comparator CMP1 is electrically connected with the switching module 101, the threshold adjusting module 103 and the switch module 104 respectively.

[0073] Specifically, the positive input terminal of the first comparator CMP1 is configured to receive the feedback voltage VFB, and the negative input terminal of the first comparator CMP1 is configured to receive the preset voltage Vref2. The first comparator CMP1 is configured to compare the feedback voltage VFB with the preset voltage Vref2. When the feedback voltage VFB is less than the preset voltage Vref2, it indicates that the output voltage VOUT is relatively low, and the first comparator CMP1 outputs a first comparison signal, i.e., VBOOST_OK=0. When the feedback voltage VFB is greater than or equal to the preset voltage Vref2, it indicates that the output voltage VOUT has approached the target voltage, and the first comparator CMP1 outputs a second comparison signal, i.e., VBOOST_OK=1.

[0074] In an embodiment of the present application, the switching module 101 comprises a first transmission gate, a first end of the first transmission gate is electrically connected with the first input terminal of the error amplifier module 200, a second end of the first transmission gate is electrically connected with the detection selection module 100, a third end of the first transmission gate is electrically connected with the output terminal of the error amplifier module 200, and a control end of the first transmission gate is electrically connected with the comparison module 102.

[0075] Specifically, by receiving the first comparison signal and the second comparison signal, the first transmission gate can switch between two states. Specifically, in the Boost starting phase, the first transmission gate receives the first comparison signal, the first transmission gate turns on between the output terminal and the inverting input terminal of the error amplifier EA, forms a unity-gain buffer, and makes the error amplifier EA establish the COMP voltage at a lower voltage in an open-loop mode. In the switching phase, the first transmission gate receives the second comparison signal, the first transmission gate connects the detection selection module 100 to the inverting input terminal of the error amplifier EA, so that the error amplifier EA enters a closed-loop control state, and adjusts the COMP voltage based on the detection voltage and the first reference voltage Vref1.

[0076] In an embodiment of the present application, the switching module 104 comprises a control switch, a control end of the control switch is electrically connected with the comparison module 102, a first end of the control switch is configured to be electrically connected with the control module 500, and a second end of the control switch is configured to be electrically connected with the logic drive module 400.

[0077] Specifically, the control switch can be turned on or turned off according to the received first comparison signal and second comparison signal. Specifically, in the Boost starting stage, the control switch receives the first comparison signal, the control switch is turned off, the PWM signal cannot be transmitted to the logic driving module 400, and the logic driving module 400 drives the first switch module 600 to be turned off. In the switching stage, the control switch receives the second comparison signal, the control switch is turned on, the PWM signal can be transmitted to the logic driving module 400 to dominate the switching sequence of the first switch module 600, so that the Boost output voltage VOUT can be dynamically adjusted according to the LED lamp string current slope requirement, and the precise control of the LED lamp string current is realized. Through this switching, the system realizes the overcurrent protection in the starting stage, and restores the normal control loop in the switching stage, ensuring the safety and stability of the Boost circuit in different working states.

[0078] The working principle of the threshold adjustment module 103 will be described in detail below. Figure 6 And Figure 7 The working principle of the threshold adjustment module 103 will be described in detail below.

[0079] In an embodiment of the present application, as shown in Figure 6 , the threshold adjustment module 103 includes a reference voltage generating unit 1031, a current mirror unit 1032, a first switch unit 1033, a second switch unit 1034, a third switch unit 1035, an energy storage unit 1036, and a comparison output unit 1037. The current mirror unit 1032 is electrically connected with the reference voltage generating unit 1031, the first switch unit 1033, the third switch unit 1035, the energy storage unit 1036, and the comparison output unit 1037 respectively. The comparison output unit 1037 is electrically connected with the second switch unit 1034 and the third switch unit 1035 respectively.

[0080] Specifically, the reference voltage generating unit 1031 is configured to provide a reference voltage signal to the current mirror unit 1032. When the feedback voltage VFB is less than the preset voltage Vref2, the comparison module 102 outputs a first comparison signal, i.e., VBOOST_OK=0, and correspondingly, At this time, the first switch unit 1033 is turned on, the second switch unit 1034 is turned on, and the third switch unit 1035 is turned off. The current mirror unit 1032 is configured to output a first current to the comparison output unit 1037 according to the reference voltage signal. The comparison output unit 1037 is configured to output an overcurrent protection signal OCP to the logic driving module 400 according to the first current, the node voltage (the P-point voltage), the reference signal VREF, and the sampling signal Vs. When the feedback voltage VFB is greater than or equal to the preset voltage Vref2, the comparison module 102 outputs a second comparison signal, i.e., VBOOST_OK=1, and correspondingly, At this time, the first switch unit 1033 is off, the second switch unit 1034 is off, the third switch unit 1035 is on, the current mirror unit 1032 is used for outputting a charging current to the energy storage unit 1036 according to the reference voltage signal, and the energy storage unit 1036 is used for storing energy according to the charging current, so that the node voltage gradually increases.

[0081] In one embodiment of the present application, as shown in the figure, the reference voltage generating unit 1031 includes a first resistor R1 and a current source, a first end of the first resistor R1 is electrically connected with the current mirror unit 1032, a first end of the current source is electrically connected with a second end of the first resistor R1 and the current mirror unit 1032 respectively, and a second end of the current source is grounded. Figure 7

[0082] Specifically, the current source can provide a stable current, the current output by the current source flows through the first resistor R1, and based on Ohm's law, a certain voltage drop will be generated across the first resistor R1, which is used as the reference voltage signal and is transmitted to the current mirror unit 1032.

[0083] In one embodiment of the present application, as shown in the figure, the current mirror unit 1032 includes a first transistor M20, a second transistor M21, a third transistor M22, a fourth transistor M23, a fifth transistor M24 and a sixth transistor M25, a gate of the first transistor M20 is electrically connected with a drain of the second transistor M21, the reference voltage generating unit 1031, a gate of the third transistor M22 and a gate of the fifth transistor M24 respectively, a source of the first transistor M20, a source of the third transistor M22 and a source of the fifth transistor M24 are all used for being electrically connected with a power supply VDD, a drain of the first transistor M20 is electrically connected with a source of the second transistor M21, a gate of the fourth transistor M23 is electrically connected with a gate of the second transistor M21, the reference voltage generating unit 1031 and a gate of the sixth transistor M25 respectively, a source of the fourth transistor M23 is electrically connected with a drain of the third transistor M22, a drain of the fourth transistor M23 is electrically connected with the first switch unit 1033, the third switch unit 1035 and the energy storage unit 1036 respectively, a source of the sixth transistor M25 is electrically connected with a drain of the fifth transistor M24, and a drain of the sixth transistor M25 is electrically connected with the comparison output unit 1037. Figure 7

[0084] ​​Specifically, the first transistor M20, the third transistor M22 and the fifth transistor M24 constitute a group of current mirrors, the gates of which are connected and connected with the drain of the second transistor M21 and the reference voltage generating unit 1031, and the sources of which are connected with the power supply VDD. Through the unified control of the gate voltage, the third transistor M22 and the fifth transistor M24 mirror the current characteristics of the first transistor M20 respectively, and provide the subsequent circuit with working current proportional to the reference current. The second transistor M21, the fourth transistor M23 and the sixth transistor M25 constitute another group of current mirrors, and the fourth transistor M23 and the sixth transistor M25 are synchronously controlled by the gate voltage, so that the fourth transistor M23 and the sixth transistor M25 mirror the current characteristics of the second transistor M21.

[0085] The third transistor M22 and the fourth transistor M23 are used to output a charging current to the energy storage unit 1036 when the first switch unit 1033 is off, the second switch unit 1034 is off and the third switch unit 1035 is on, so that the energy storage unit 1036 is charged and the node voltage gradually increases. The fifth transistor M24 and the sixth transistor M25 are used to output a first current to the comparison output unit 1037 when the first switch unit 1033 is on, the second switch unit 1034 is on and the third switch unit 1035 is off, so as to provide a current reference for the generation of the overcurrent protection signal OCP. Through the precise matching of the current mirror structure, the stability of the reference current is ensured, and the current control of the threshold adjustment module 103 in different working stages is reliably supported.

[0086] For example, the designer can select the types of the first transistor M20, the second transistor M21, the third transistor M22, the fourth transistor M23, the fifth transistor M24 and the sixth transistor M25 according to the actual situation, that is, all full-controlled power devices such as metal oxide field effect transistors or insulated gate bipolar transistors can be used. For example, the first transistor M20, the second transistor M21, the third transistor M22, the fourth transistor M23, the fifth transistor M24 and the sixth transistor M25 can all be PMOS tubes.

[0087] In an embodiment of the present application, as shown in Figure 7 The first switch unit 1033 includes a first switch tube M29, the gate of the first switch tube M29 is connected with the comparison module 102, the drain of the first switch tube M29 is connected with the current mirror unit 1032, the third switch unit 1035 and the energy storage unit 1036 respectively, and the source of the first switch tube M29 is grounded.

[0088] Specifically, the first switch tube M29 is used as a switching device, and is turned on or turned off according to the comparison signal (the first comparison signal or the second comparison signal) received by the gate. When the feedback voltage VFB is less than the preset voltage Vref2, the comparison module 102 outputs the first comparison signal, that is, VBOOST_OK=0, and accordingly, the first switch tube M29 is turned on. When the feedback voltage VFB is greater than or equal to the preset voltage Vref2, the comparison module 102 outputs the second comparison signal, that is, VBOOST_OK=1, and accordingly, the first switch tube M29 is turned off.

[0089] In an embodiment of the present application, as shown in Figure 7 the second switch unit 1034 includes a second switch tube M30, the gate of the second switch tube M30 is electrically connected with the comparison module 102, the source of the second switch tube M30 is electrically connected with the power supply VDD, and the drain of the second switch tube M30 is electrically connected with the third switch unit 1035 and the comparison output unit 1037 respectively.

[0090] Specifically, the second switch tube M30 is used as a switching device, and is turned on or turned off according to the comparison signal (the first comparison signal or the second comparison signal) received by the gate. When the feedback voltage VFB is less than the preset voltage Vref2, the comparison module 102 outputs the first comparison signal, that is, VBOOST_OK=0, and accordingly, the second switch tube M30 is turned on, and the node voltage is pulled up to the power supply VDD voltage. When the feedback voltage VFB is greater than or equal to the preset voltage Vref2, the comparison module 102 outputs the second comparison signal, that is, VBOOST_OK=1, and accordingly, the second switch tube M30 is turned off.

[0091] In an embodiment of the present application, as shown in Figure 7 the third switch unit 1035 includes a third switch tube M31 and a fourth switch tube M32, the gate of the third switch tube M31 and the gate of the fourth switch tube M32 are electrically connected with the comparison module 102, the drain of the third switch tube M31 is electrically connected with the drain of the fourth switch tube M32, the current mirror unit 1032, the first switch unit 1033 and the energy storage unit 1036 respectively, and the source of the third switch tube M31 is electrically connected with the source of the fourth switch tube M32, the second switch unit 1034 and the comparison output unit 1037 respectively.

[0092] Specifically, the third switch tube M31 and the fourth switch tube M32 are both used as switching devices, and are turned on or turned off according to the comparison signal (the first comparison signal or the second comparison signal) received by the gate. When the feedback voltage VFB is less than the preset voltage Vref2, the comparison module 102 outputs the first comparison signal, that is, VBOOST_OK=0, and correspondingly, , the third switch tube M31 and the fourth switch tube M32 are both turned off. When the feedback voltage VFB is greater than or equal to the preset voltage Vref2, the comparison module 102 outputs the second comparison signal, that is, VBOOST_OK=1, and correspondingly, , the third switch tube M31 and the fourth switch tube M32 are both turned on, and the node voltage is determined by the voltage at the first end of the energy storage unit 1036.

[0093] In summary, through the linkage with the comparison module 102, the four switch tubes accurately control the on-off of the current path, ensure that the threshold adjustment module 103 works according to the expected logic under different feedback states, and realize the dynamic switching of the overcurrent protection threshold.

[0094] For example, the designer can select the types of the first switch tube M29, the second switch tube M30, the third switch tube M31 and the fourth switch tube M32 according to the actual situation, that is, all full-controlled power devices such as metal oxide field effect transistors or insulated gate bipolar transistors can be used. For example, the first switch tube M29 and the fourth switch tube M32 can be selected as NMOS tubes, and the second switch tube M30 and the third switch tube M31 can be selected as PMOS tubes.

[0095] In an embodiment of the present application, as shown in Figure 7 , the energy storage unit 1036 includes a first capacitor C0, the first end of the first capacitor C0 is electrically connected with the first switch unit 1033, the third switch unit 1035 and the current mirror unit 1032 respectively, and the second end of the first capacitor C0 is grounded.

[0096] Specifically, the first capacitor C0 as the core element of the energy storage unit 1036 mainly undertakes the functions of charge storage and voltage ramping. When the feedback voltage VFB is less than the preset voltage Vref2, the first switch tube M29 and the second switch tube M30 are both turned on, the third switch tube M31 and the fourth switch tube M32 are both turned off, the voltage at the first end of the first capacitor C0 is pulled down to the ground, the node voltage is pulled up to the voltage of the power supply VDD, and is maintained at a high level, so as not to affect the output of the overcurrent protection signal OCP by the comparison output unit 1037 in the starting stage. When the feedback voltage VFB is greater than or equal to the preset voltage Vref2, the first switch tube M29 and the second switch tube M30 are both turned off, the third switch tube M31 and the fourth switch tube M32 are both turned on, and the small current (charging current) flowing through the third transistor M22 and the fourth transistor M23 can charge the first capacitor C0, so that the first capacitor C0 is gradually charged and stored with energy, and the node voltage slowly rises with the accumulation of the charge amount. The gradual rising characteristic of the voltage is directly converted into the gradual increase of the overcurrent protection threshold value through cooperation with the comparison output unit 1037, a smooth transition from the starting stage to the steady state stage is realized, the current impact caused by the sudden change of the threshold value is avoided, and key timing buffering is provided for stable starting of the circuit.

[0097] In an embodiment of the present application, as shown in Figure 4 to Figure 8 The comparison output unit 1037 includes a fifth switch tube M26, a seventh transistor M27, an eighth transistor M28, a second resistor R2, a third resistor R3 and a second comparator CMP2. The gate of the fifth switch tube M26 is electrically connected with the second switch unit 1034 and the third switch unit 1035 respectively, the source of the fifth switch tube M26 is electrically connected with the source of the seventh transistor M27, the source of the eighth transistor M28 and the current mirror unit 1032 respectively, the drain of the fifth switch tube M26 is electrically connected with the drain of the seventh transistor M27, the first end of the second resistor R2 and the first input end of the second comparator CMP2 respectively, the gate of the seventh transistor M27 is used for receiving a reference signal VREF, the gate of the eighth transistor M28 is used for receiving a sampling signal Vs, the drain of the eighth transistor M28 is electrically connected with the first end of the third resistor R3 and the second input end of the second comparator CMP2 respectively, the output end of the second comparator CMP2 is electrically connected with the logic driving module 400, and the second end of the second resistor R2 and the second end of the third resistor R3 are both grounded.

[0098] Specifically, the fifth switch tube M26 is taken as a switching device, and is turned on or turned off according to the node voltage received by the gate. When the feedback voltage VFB is less than the preset voltage Vref2, the first switch tube M29 and the second switch tube M30 are both turned on, the third switch tube M31 and the fourth switch tube M32 are both turned off, the node voltage is pulled up to the voltage of the power supply VDD, and is maintained at a high level, so as not to affect the output of the over-current protection signal OCP by the comparison output unit 1037 in the starting stage. When the feedback voltage VFB is greater than or equal to the preset voltage Vref2, the first switch tube M29 and the second switch tube M30 are both turned off, the third switch tube M31 and the fourth switch tube M32 are both turned on, and a small current (charging current) flowing through the third transistor M22 and the fourth transistor M23 can charge the first capacitor C0, so that the first capacitor C0 is gradually charged and stored, and the node voltage slowly rises with the accumulation of the charge, thereby gradually increasing the threshold of the over-current protection signal OCP.

[0099] The gate of the seventh transistor M27 receives the reference signal VREF (the reference signal VREF is a reference voltage when the OCP normally works), and the gate of the eighth transistor M28 receives the sampling signal Vs (a voltage converted by the resistance through which the sampling current of the power tube flows). The sources of the seventh transistor M27 and the eighth transistor M28 are connected and connected with the sixth transistor M25, to form a current comparison branch based on the reference signal VREF and the sampling signal Vs, wherein the current of the seventh transistor M27 corresponds to the reference signal VREF, and the current of the eighth transistor M28 corresponds to the sampling signal Vs. The second resistor R2 and the third resistor R3 are connected with the drains of the seventh transistor M27 and the eighth transistor M28 respectively and grounded at the other end, to convert the current of the transistor into a voltage signal. The second comparator CMP2 outputs the over-current protection signal OCP to the logic drive module 400 by comparing the sampling signal Vs and the reference signal VREF / node voltage (if the voltage of the reference signal VREF is less than the node voltage, the second comparator CMP2 compares the sampling signal Vs and the reference signal VREF; if the voltage of the reference signal VREF is greater than the node voltage, the second comparator CMP2 compares the sampling signal Vs and the node voltage). The small current of the third transistor M22 and the fourth transistor M23 charges the first capacitor C0, and the gradual increase of the node voltage can realize that the reference input end of the second comparator CMP2 gradually increases from 0.

[0100] For example, the designer can select the types of the fifth switch tube M26, the seventh transistor M27 and the eighth transistor M28 according to the actual situation, that is, all of them can be full-controlled power devices such as metal oxide field effect transistors or insulated gate bipolar transistors. For example, the fifth switch tube M26, the seventh transistor M27 and the eighth transistor M28 can all be PMOS tubes.

[0101] It should be noted that, compared with the scheme of gradually increasing the OCP threshold from the beginning, the application does not need to limit the OCP threshold for too long time, because the output voltage VOUT has been very close to the target voltage. In this way, the requirements for the value of the first capacitor C0 and the current size of the third transistor M22 become very relaxed.

[0102] The principles and starting processes of the starting timing control provided by the embodiments of the application will be described in detail below. ​ The principles and starting processes of the starting timing control provided by the embodiments of the application will be described in detail below.

[0103] First stage: detection and protection before starting (Boost is not started, state preparation)

[0104] After the LED backlight is powered on, the value of Efuse or MTP is loaded first, and after the loading is completed (i.e., LOAD_OK), the IDLE state is entered.

[0105] Second stage: Boost starting and COMP voltage pre-charging (voltage establishment, preparation for slope)

[0106] The system enters the Boost starting stage (i.e., EN_BST=1). When the feedback voltage VFB is less than the preset voltage Vref2, that is, the voltage of VBOOST is lower than the threshold set internally, at this time the comparison module 102 outputs the first comparison signal, that is, VBOOST_OK=0, and the switching module 101 connects the inverting input end of the error amplifier EA with its output end through the first transmission gate under the action of the first comparison signal, so that the error amplifier EA is configured as a unity-gain buffer; at this time, the non-inverting input end of the error amplifier EA receives the first reference voltage Vref1 (lower than the steady-state reference voltage), and the compensation capacitor is charged through the low reference voltage, so as to ensure that the COMP voltage starts to establish from a lower voltage, thereby indirectly realizing the soft starting effect. At the same time, the switching module 104 is turned off, the threshold adjusting module 103 outputs the overcurrent protection signal OCP and transmits it to the logic driving module 400, which drives the first switching module 600 to be turned off through the logic driving module 400, thereby making the output voltage VOUT of Boost rise and gradually driving the feedback voltage VFB to rise.

[0107] Third stage: loop switching and current slope starting (LED lamp string is turned on, current slope)

[0108] As the boost output voltage VOUT and the feedback voltage VFB increase, when the feedback voltage VFB is greater than or equal to the preset voltage Vref2, it can be characterized that the output voltage VOUT of the boost has approached the target voltage (for example, the output voltage VOUT is 2.5V lower than the target voltage). At this time, the comparison module 102 outputs a second comparison signal, that is, VBOOST_OK=1, and the switching module 101 is connected to the output end of the detection selection module 100 under the action of the second comparison signal, that is, the error amplifier EA is switched from the unit gain buffer mode to the closed-loop control mode. At the same time, the switch module 104 is turned on, the control module 500 is also connected to the loop, and the threshold adjustment module 103 gradually increases the threshold of the overcurrent protection signal OCP, so that the current limit is gradually relaxed as the circuit stabilizes. After waiting for a fixed time (for example, 4ms), the LED current ramp is started.

[0109] The fourth stage: steady-state switching and normal operation (current meets the standard, stable output)

[0110] When the LED lamp string current reaches the target current, the redundant amount of the boost output voltage VOUT is reduced, and the power consumption is reduced (that is, the ACTIVE state). The error amplifier module 200 maintains closed-loop control, so that the boost output voltage VOUT is stable at the level that meets the target current of the LED. The control module 500 maintains the stability of the PWM signal through a conventional mechanism, ensures the long-term stable output of the LED current, and starts the control process.

[0111] In addition, real-time detection of the LED lamp string connection is required in the third and fourth stages to ensure system safety and reliability.

[0112] The entire startup process realizes the smooth rise of the boost output voltage VOUT through the timing cooperation and mode switching of each module, and avoids the sudden change of the inductor current during the startup process.

[0113] The application further discloses a control chip, which comprises a detection selection module 100, an error amplification module 200, a feedback module 300, a logic drive module 400, a first switch module 600, a control module 500 and the start timing control circuit, the detection selection module 100 and the error amplification module 200 are electrically connected with a switch module 101 in the start timing control circuit, the control module 500 is electrically connected with the error amplification module 200, the first switch module 600 and a switch module 104 in the start timing control circuit respectively, the logic drive module 400 is electrically connected with the first switch module 600, the feedback module 300, a threshold adjustment module 103 and the switch module 104 in the start timing control circuit respectively, and the feedback module 300 is electrically connected with a comparison module 102 in the start timing control circuit. The control chip adopts the start timing control circuit, can dynamically adjust the overcurrent protection threshold value and the working mode of the error amplification module 200 in stages, realizes smooth establishment of the output voltage VOUT and the current, effectively avoids device damage or voltage fluctuation caused by inductance current overcharge in the starting process, simultaneously simplifies external element configuration, and improves starting reliability, adaptability and overall working efficiency of the control chip in the scene of LED backlight driving.

[0114] The application further discloses a power supply system, which comprises a plurality of LED lamp strings and the control chip, and the plurality of LED lamp strings are electrically connected with the control chip. The power supply system can provide smooth and accurate power supply support for the plurality of LED lamp strings by means of the start timing control circuit built in the control chip, can ensure that the LED lamp string current rises stably and synchronously, and realizes smooth transition of brightness. Therefore, the power supply system can meet the high dynamic dimming demand of the large-size liquid crystal display screen, and can also adapt to the scene sensitive to starting speed, such as the vehicle-mounted screen and the VR equipment. The power supply system deeply integrates the intelligent control chip and the plurality of LED lamp strings, optimizes the starting timing and the dynamic response in cooperation, and provides a complete solution for display applications with high image quality and high energy efficiency.

[0115] Since the processing and functions realized by the power supply system and the control chip in the embodiment are basically corresponding to the embodiments, principles and examples of the start timing control circuit, the description of the embodiment is not described in detail, and the related description in the foregoing embodiments can be referred to, and is not described here.

[0116] The foregoing embodiments are only used to illustrate the technical solutions of the application, rather than limit them; although the application is described in detail with reference to the foregoing embodiments, those skilled in the art should understand that the technical solutions recorded in the foregoing embodiments can be modified, or some technical features can be replaced equivalently; and the modification or replacement does not make the essence of the corresponding technical solution deviate from the spirit and scope of the technical solutions of the embodiments of the application, and should be included in the protection scope of the application.

Claims

1. A start-up timing control circuit, characterized by comprising: The switching module, the comparison module, the threshold adjustment module and the switch module are electrically connected, the switching module is electrically connected with the detection selection module and the error amplification module, the comparison module is electrically connected with the feedback module, the threshold adjustment module is electrically connected with the logic drive module, and the switch module is electrically connected with the logic drive module and the control module; When the feedback voltage output by the feedback module is less than the preset voltage, the comparison module outputs the first comparison signal to the switching module, the threshold adjustment module and the switch module; the switching module is used for turning on the first input end of the error amplification module and the output end of the error amplification module according to the first comparison signal; the switch module is used for turning off and disconnecting the control module and the logic drive module according to the first comparison signal; The threshold adjustment module is used for outputting the overcurrent protection signal to the logic drive module according to the first comparison signal, the reference signal and the sampling signal; When the feedback voltage is greater than or equal to the preset voltage, the comparison module outputs the second comparison signal to the switching module, the threshold adjustment module and the switch module; the switching module is used for turning on the first input end of the error amplification module and the detection selection module according to the second comparison signal; the switch module is used for turning on and connecting the control module and the logic drive module according to the second comparison signal; and the threshold adjustment module is used for gradually increasing the threshold value of the overcurrent protection signal according to the second comparison signal, the reference signal and the sampling signal; The threshold adjustment module comprises a reference voltage generating unit, a current mirror unit, a first switch unit, a second switch unit, a third switch unit, an energy storage unit and a comparison output unit, the current mirror unit is electrically connected with the reference voltage generating unit, the first switch unit, the third switch unit, the energy storage unit and the comparison output unit, and the comparison output unit is electrically connected with the second switch unit and the third switch unit; The reference voltage generating unit is used for providing the reference voltage signal to the current mirror unit; When the feedback voltage output by the feedback module is less than the preset voltage, the first switch unit is turned on, the second switch unit is turned on, the third switch unit is turned off, and the current mirror unit is used for outputting the first current to the comparison output unit according to the reference voltage signal; the comparison output unit is used for outputting the overcurrent protection signal to the logic drive module according to the first current, a node voltage, the reference signal and the sampling signal, and the node voltage is the voltage of the common end of the comparison output unit and the second switch unit; When the feedback voltage is greater than or equal to the preset voltage, the first switch unit is turned off, the second switch unit is turned off, the third switch unit is turned on, the current mirror unit is used for outputting a charging current to the energy storage unit according to the reference voltage signal, and the energy storage unit is used for storing energy according to the charging current, so that the node voltage gradually increases.

2. The start-up timing control circuit of claim 1, wherein, The switching module comprises a first transmission gate, a first end of the first transmission gate is electrically connected with a first input end of the error amplification module, a second end of the first transmission gate is electrically connected with the detection selection module, a third end of the first transmission gate is electrically connected with an output end of the error amplification module, and a control end of the first transmission gate is electrically connected with the comparison module.

3. The start-up timing control circuit of claim 1, wherein, The comparison module comprises a first comparator, a first input end of the first comparator is used for being electrically connected with the feedback module, a second input end of the first comparator is used for receiving the preset voltage, and an output end of the first comparator is electrically connected with the switching module, the threshold adjustment module and the switch module respectively.

4. The start-up timing control circuit of claim 1, wherein, The reference voltage generation unit comprises a first resistor and a current source, a first end of the first resistor is electrically connected with the current mirror unit, a first end of the current source is electrically connected with a second end of the first resistor and the current mirror unit respectively, and a second end of the current source is grounded. The current mirror unit comprises a first transistor, a second transistor, a third transistor, a fourth transistor, a fifth transistor and a sixth transistor, a gate of the first transistor is electrically connected with a drain of the second transistor, the reference voltage generation unit, a gate of the third transistor and a gate of the fifth transistor respectively, a source of the first transistor, a source of the third transistor and a source of the fifth transistor are all used for being electrically connected with a power supply, a drain of the first transistor is electrically connected with a source of the second transistor, a gate of the fourth transistor is electrically connected with a gate of the second transistor, the reference voltage generation unit and a gate of the sixth transistor respectively, a source of the fourth transistor is electrically connected with a drain of the third transistor, a drain of the fourth transistor is electrically connected with the first switch unit, the third switch unit and the energy storage unit respectively, a source of the sixth transistor is electrically connected with a drain of the fifth transistor, and a drain of the sixth transistor is electrically connected with the comparison output unit.

5. The start-up timing control circuit of claim 1, wherein, The first switch unit comprises a first switch tube, a gate of the first switch tube is electrically connected with the comparison module, a drain of the first switch tube is electrically connected with the current mirror unit, the third switch unit and the energy storage unit respectively, and a source of the first switch tube is grounded. The second switch unit comprises a second switch tube, a gate of the second switch tube is electrically connected with the comparison module, a source of the second switch tube is used for being electrically connected with a power supply, and a drain of the second switch tube is electrically connected with the third switch unit and the comparison output unit respectively. The third switch unit comprises a third switch tube and a fourth switch tube, the gate of the third switch tube and the gate of the fourth switch tube are electrically connected with the comparison module, the drain of the third switch tube is electrically connected with the drain of the fourth switch tube, the current mirror unit, the first switch unit and the energy storage unit respectively, and the source of the third switch tube is electrically connected with the source of the fourth switch tube, the second switch unit and the comparison output unit respectively.

6. The start-up timing control circuit of claim 1, wherein, The energy storage unit comprises a first capacitor, the first end of the first capacitor is electrically connected with the first switch unit, the third switch unit and the current mirror unit respectively, and the second end of the first capacitor is grounded.

7. The start-up timing control circuit of claim 1, wherein, The comparison output unit comprises a fifth switch tube, a seventh transistor, an eighth transistor, a second resistor, a third resistor and a second comparator, the gate of the fifth switch tube is electrically connected with the second switch unit and the third switch unit respectively, the source of the fifth switch tube is electrically connected with the source of the seventh transistor, the source of the eighth transistor and the current mirror unit respectively, the drain of the fifth switch tube is electrically connected with the drain of the seventh transistor, the first end of the second resistor and the first input end of the second comparator respectively, the gate of the seventh transistor is used for receiving the reference signal, the gate of the eighth transistor is used for receiving the sampling signal, the drain of the eighth transistor is electrically connected with the first end of the third resistor and the second input end of the second comparator respectively, the output end of the second comparator is used for being electrically connected with the logic driving module, and the second end of the second resistor and the second end of the third resistor are grounded.

8. The start-up timing control circuit of claim 1, wherein, The switch module comprises a control switch, the control end of the control switch is electrically connected with the comparison module, the first end of the control switch is used for being electrically connected with the control module, and the second end of the control switch is used for being electrically connected with the logic driving module.

9. A control chip, characterized by The starting timing control circuit comprises a detection selection module, an error amplification module, a feedback module, a logic driving module, a first switch module, a control module and the starting timing control circuit in any one of claims 1-8, the detection selection module and the error amplification module are electrically connected with the switching module in the starting timing control circuit, the control module is electrically connected with the error amplification module, the first switch module and the switch module in the starting timing control circuit respectively, the logic driving module is electrically connected with the first switch module, the feedback module, the threshold adjustment module and the switch module in the starting timing control circuit respectively, and the feedback module is electrically connected with the comparison module in the starting timing control circuit.

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