CN108055718B

CN108055718B - LED parallel current-sharing control method, system and circuit

Info

Publication number: CN108055718B
Application number: CN201711147565.2A
Authority: CN
Inventors: 廖胜峰
Original assignee: Guangzhou Shiyuan Electronics Thecnology Co Ltd
Current assignee: Guangzhou Shiyuan Electronics Thecnology Co Ltd
Priority date: 2017-11-17
Filing date: 2017-11-17
Publication date: 2021-02-02
Anticipated expiration: 2037-11-17
Also published as: CN108055718A

Abstract

The invention discloses a method, a system and a circuit for controlling parallel current sharing of an LED (light emitting diode), wherein the method is applied to an LED parallel current sharing circuit, the LED parallel current sharing circuit comprises an output end and a plurality of paths of LED lamp strings connected with the output end in parallel, and each path of LED lamp string can be connected with different numbers of LED lamps in series; controlling the total current flowing through the output end according to the number of the circuits of the working LED lamp strings and the rated current value of the working LED lamp strings; when the collected current value of the current working LED lamp string is judged to be unequal to the rated current value, the duty ratio of the PWM control signal output to the current working LED lamp string is adjusted according to the current value of the current working LED lamp string and the rated current value so as to drive the current value on the current working LED lamp string to be equal to the rated current value. The LED parallel current-sharing control method provided by the invention solves the problem that the current-sharing control of the existing multi-path LED is not convenient.

Description

LED parallel current-sharing control method, system and circuit

Technical Field

The invention relates to the technical field of LED control, in particular to a parallel current sharing control method, a system and a circuit for LEDs.

Background

A Light Emitting Diode (LED), which is a solid-state semiconductor device capable of converting electric energy into visible light, can directly convert electricity into light, and has been widely used because of its advantages of high luminous efficiency, easy control, low-voltage direct current driving, and long service life.

The applications of LEDs can be mainly divided into three main categories: LCD screen backlight, LED illumination and LED display. At present, the existing LCD screen backlight usually adopts a parallel connection mode, but because the impedance of a single LED is different, and the current between different LED lamp strings is unequal, the LED lamp strings emit different lights, which affects the backlight effect, and even damages the LED lamp string with large current, so the LED lamp strings need to be controlled in parallel current sharing.

As shown in fig. 10, the conventional scheme for current-sharing control of multiple LEDs consists of three parts, namely a TV hardware module, a power supply module, and a constant current output module. The constant current output module mainly controls all LEDs to realize current sharing, and comprises a multi-path dimming control chip, a current sharing module, a sampling/protection module and LED backlight 1-4. In the current-sharing control scheme, the control of current sharing of multiple paths of LEDs needs to be implemented by independent multiple paths of dimming control chips, and the control chips need a core controller of a TV hardware module to independently send a starting signal and a driving signal to drive constant-current output, so that the implementation is more complicated and the cost is higher, and because pins of the multiple paths of dimming control chips are limited, the expansion of a system is greatly limited. Meanwhile, in the prior art, when the sampling current value of the LED lamp group is not less than the predetermined current value, the total time of the on and off of the switching tube is controlled to make the average current on the LED lamp group equal to the predetermined current value, and when there is an open circuit in the parallel LED lamp group, all the parallel LED lamp groups are turned off, which results in low constant current precision and poor control effect.

Disclosure of Invention

Based on this, the embodiment of the invention provides a method, a system and a circuit for LED parallel current sharing control, which solve the problem that the current sharing control of the existing multi-path LEDs is inconvenient.

The embodiment of the invention provides an LED parallel current sharing control method, which comprises the following specific technical scheme:

an LED parallel current-sharing control method is applied to an LED parallel current-sharing circuit, the LED parallel current-sharing circuit comprises an output end and a plurality of LED lamp strings connected with the output end in parallel, and each LED lamp string can be connected with different numbers of LED lamps in series, and the method comprises the following steps:

collecting the current value of each path of LED lamp string, and determining the number of paths of working LED lamp strings according to the current value of each path of LED lamp string;

controlling the total current flowing through the output end according to the number of the circuits of the working LED lamp strings and the rated current value of the working LED lamp strings;

when the collected current value of the current working LED lamp string is judged to be unequal to the rated current value, the duty ratio of the PWM control signal output to the current working LED lamp string is adjusted according to the current value of the current working LED lamp string and the rated current value so as to drive the current value on the current working LED lamp string to be equal to the rated current value.

The embodiment of the invention collects the actual current of each path of LED lamp string through the sampling circuit and sends the actual current to the control circuit, the control circuit determines the number of the paths of working LED lamp strings according to the current of each path of LED lamp string collected by the sampling circuit and sends the first PWM control signal to the drive circuit, so that the drive circuit drives the total current output to each path of LED lamp string to be correspondingly changed, the current re-distributed to each path of LED lamp string is unchanged from the original maintenance, the current output required to be closed at the output end in the prior art is avoided, and the influence of overcurrent damage to each path of LED lamp string caused by overlarge current distributed to each path of LED lamp string branch circuit due to the unchanged constant total current in the prior art is avoided. Meanwhile, the control circuit adjusts the duty ratio of the second PWM control signal to be sent to the second driving circuit according to the actual current of each path of LED lamp string collected by the sampling circuit, so that the current of each path of LED lamp string can be dynamically adjusted, the current equalizing work is kept, and the problem that the current equalizing control of the existing multiple paths of LEDs is inconvenient is solved.

Further, before the step of collecting the current value of each of the LED light strings, the method further includes:

collecting the current value of the output end, and judging whether the current value of the output end is larger than a protection current value, wherein the protection current value is larger than the sum of the rated current values of the plurality of paths of LED lamp strings;

and if so, disconnecting the output end from the multiple paths of LED lamp strings.

Further, the step of adjusting the duty ratio of the PWM control signal output to the currently operating LED light string according to the current value of the currently operating LED light string and the rated current value includes:

when the current value of the current working LED lamp string is larger than the rated current value, reducing the duty ratio of the PWM control signal output to the current working LED lamp string;

and when the current value of the current working LED lamp string is smaller than the rated current value, increasing the duty ratio of the PWM control signal output to the current working LED lamp string.

Another embodiment of the present invention provides an LED parallel current sharing control system, which is applied to an LED parallel current sharing circuit, where the LED parallel current sharing circuit includes an output end and multiple LED lamp strings connected to the output end in parallel, and each of the multiple LED lamp strings can be connected to different numbers of LED lamps in series, and the system includes:

the determining module is used for acquiring the current value of each path of LED lamp string and determining the number of paths of working LED lamp strings according to the current value of each path of LED lamp string;

the first control module is used for controlling the total current flowing through the output end according to the number of the working LED lamp strings and the rated current value of the working LED lamp strings;

and the second control module is used for adjusting the duty ratio of a PWM control signal output to the current working LED lamp string according to the current value of the current working LED lamp string and the rated current value when the collected current value of the current working LED lamp string is judged to be unequal to the rated current value so as to drive the current value on the current working LED lamp string to be equal to the rated current value.

Further, the system further comprises:

the judging module is used for acquiring the current value of the output end and judging whether the current value of the output end is larger than a protection current value, wherein the protection current value is larger than the sum of the rated current values of the multiple paths of LED lamp strings;

and the third control module is used for disconnecting the output end from the multiple paths of LED lamp strings when the judgment module judges that the current value of the output end is greater than the protection current value.

Further, the second control module includes:

the first control unit is used for reducing the duty ratio of the PWM control signal output to the current working LED lamp string when the current value of the current working LED lamp string is larger than the rated current value;

and the second control unit is used for increasing the duty ratio of the PWM control signal output to the current working LED lamp string when the current value of the current working LED lamp string is smaller than the rated current value.

The invention provides an LED parallel current-sharing circuit, which comprises a sampling circuit, a control circuit, a drive circuit and a plurality of LED lamp strings, wherein the output end of the drive circuit is connected with the plurality of LED lamp strings connected in parallel;

the sampling circuit is respectively connected with the LED lamp strings and the control circuit and is used for collecting the current value of each path of LED lamp string;

the control circuit is respectively connected with the sampling circuit and the driving circuit, and comprises a first control circuit and a second control circuit; the first control circuit is used for determining the number of circuits of working LED lamp strings according to the current value of each circuit of LED lamp strings acquired by the sampling circuit, and determining to send a first PWM control signal to the drive circuit according to the number of circuits of the working LED lamp strings and the rated current value of the working LED lamp strings; the second control circuit is used for adjusting the duty ratio of a second PWM control signal output to the driving circuit according to the current value of each path of working LED lamp string and the rated current value;

the driving circuit is respectively connected with the control circuit and each path of LED lamp string, and comprises a first driving circuit and a second driving circuit; the first driving circuit is used for controlling the total current flowing through the output end according to the first PWM control signal sent by the first control circuit; the second driving circuit is used for driving the current value of each path of working LED lamp string to be equal to the rated current value according to the second PWM control signal sent by the second control circuit.

Furthermore, the LED parallel current-sharing circuit further comprises a power supply circuit, and the power supply circuit is respectively connected with the control circuit and the driving circuit;

the power supply circuit comprises an alternating current input power supply, a filter circuit connected with the alternating current input power supply and a flyback circuit connected with the filter circuit;

the flyback circuit comprises a flyback primary circuit, a flyback transformer connected with the flyback primary circuit, and a constant-current power supply circuit and a constant-voltage power supply circuit which are respectively connected with the flyback transformer;

the flyback transformer consists of a primary coil, a first secondary coil and a second secondary coil, the flyback primary circuit is respectively connected with one end of the primary coil and the filter circuit, and the other end of the primary coil is also connected with the first field-effect tube; the first secondary side coil is connected with the constant current supply circuit and used for outputting constant current; and the second secondary coil is connected with the constant voltage power supply circuit and used for outputting constant voltage.

Further, the first driving circuit comprises a first triode connected with the constant-voltage power supply circuit, a second triode and a second resistor respectively connected with the first triode, a voltage stabilizing diode and a second field-effect tube respectively connected with the second resistor, and a third resistor and a third diode respectively connected with the second field-effect tube;

the second driving circuit comprises a third field effect transistor, the grid electrode of the third field effect transistor is connected with the second control circuit, the source electrode of the third field effect transistor is grounded, and the drain electrode of the third field effect transistor is connected with the corresponding LED lamp string.

Furthermore, the sampling circuit comprises an operational amplifier, a first input circuit connected with a positive phase input end of the operational amplifier, a second input circuit connected with a negative phase input end of the operational amplifier, a compensation circuit respectively connected between the negative phase input end of the operational amplifier and an output end thereof, and a clamping circuit connected with an output end of the operational amplifier, wherein the second input circuit is connected with the LED lamp string, the clamping circuit is connected with the control circuit, and the sampling circuit is used for outputting a current flowing through the LED lamp string to the control circuit after differential amplification, amplitude limiting and clamping.

Drawings

Fig. 1 is a flowchart of a method for controlling current sharing among LEDs connected in parallel according to a first embodiment of the present invention.

Fig. 2 is a flowchart of a method for controlling current sharing among LEDs connected in parallel according to a second embodiment of the present invention.

Fig. 3 is a block diagram of a parallel LED current sharing control system according to an embodiment of the present invention.

Fig. 4 is a block diagram of a parallel LED current sharing control system according to another embodiment of the present invention.

Fig. 5 is a block diagram of a parallel current sharing circuit for LEDs according to an embodiment of the present invention.

Fig. 6 is a schematic structural diagram of an LED parallel current sharing circuit according to an embodiment of the present invention.

Fig. 7 is a schematic circuit structure diagram of an LED parallel current sharing circuit according to an embodiment of the present invention.

Fig. 8 is a schematic circuit structure diagram of a power supply circuit in an LED parallel current sharing circuit according to an embodiment of the present invention.

Fig. 9 is a schematic circuit diagram of a connection environment of a sampling circuit in an LED parallel current sharing circuit according to an embodiment of the present invention.

Fig. 10 is a schematic structural diagram of a parallel current sharing circuit of an LED in the prior art.

Fig. 11 is a diagram showing a relationship between a conventional PWM control signal and an output current.

Detailed Description

In order to make the aforementioned objects, features and advantages of the present invention comprehensible, embodiments accompanied with figures are described in detail below. In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present invention. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein, but rather should be construed as broadly as the present invention is capable of modification in various respects, all without departing from the spirit and scope of the present invention.

Referring to fig. 1, a flowchart of an LED parallel current sharing control method according to a first embodiment of the present invention is shown, where the method is applied to an LED parallel current sharing circuit, where the LED parallel current sharing circuit includes an output terminal and multiple parallel LED strings connected to the output terminal, and each of the multiple LED strings may be connected to different numbers of LED lamps in series, and the method includes:

step S101, collecting the current value of each path of LED lamp string, and determining the number of paths of working LED lamp strings according to the current value of each path of LED lamp string;

the LED parallel current-sharing circuit is provided with a plurality of sampling circuits, a control circuit and a driving circuit, wherein the control circuit is used for acquiring information acquired by the sampling circuits and sending a control signal to the driving circuit according to the information so as to enable the driving circuit to control the current value of each LED lamp string connected with the driving circuit, and each LED lamp string connected in parallel can achieve the effects of current sharing and constant current.

In the prior art, when one or more paths of the LED parallel current sharing circuits are in an open circuit state, the output end needs to be closed to output the current of all the parallel LED lamp strings, because when a constant total current is input to the multiple paths of LED lamps through the output end, each path of LED lamp string realizes a shunt function on the constant total current because the multiple paths of LED lamp strings are in a parallel state. At this time, the number of the LED lamp strings and the magnitude of the constant total current are set so that each LED lamp string can work in a normal mode, and when one or more LED lamp strings are in an open circuit state, the current flowing through the branch circuit of the LED lamp string is 0, so that the current shunted to other branch circuits of the LED lamp string by the constant total current is increased, and the other normally working LED lamp strings may have a damage problem due to an excessively large current, and therefore the current output of the output end needs to be turned off, so as to ensure that other LED lamp strings in the open-circuit multiple LED lamp strings are prevented from being damaged.

In the embodiment, each sampling circuit is connected with the corresponding LED lamp string respectively, and is used for collecting the current value of each corresponding LED lamp string respectively, at this time, the sampling circuit sends the collected current value information of each LED lamp string to the control circuit, and the control circuit determines the number of the working LED lamp strings according to the current value of each LED lamp string. The method for specifically judging the number of the working LED lamp strings comprises the steps that if one or more LED lamp strings in the multiple paths of LED lamp strings connected in parallel do not work, the LED lamp strings are in an open circuit state, the current value flowing through the LED lamp strings is 0, the voltage value flowing through the LED lamp strings is larger than the preset rated voltage, and the number of the working LED lamp strings in the multiple paths of LED lamp strings can be determined by judging the current value of each LED lamp string.

Step S102, controlling the total current flowing through the output end according to the number of the working LED lamp strings and the rated current value of the working LED lamp strings;

when the number of the working LED lamp strings is less than that of all the LED lamp strings connected in parallel, the branch circuits of the LED lamp strings are open, the current constant total current cannot be continuously maintained and input from the output end to the multiple LED lamp strings connected in parallel, and the constant total current needs to be reduced to ensure the normal work of other LED lamp strings. At the moment, the constant total current input from the output end to the parallel-connected multiple LED lamp strings can be determined and controlled according to the number of the working LED lamp strings and the rated current value of the working LED lamp strings. For example, when the number of the LED strings in the multiple paths is M, and the rated current of each LED string is I, the constant total current to be output is M × I. When the control circuit determines that N LED lamp strings are in a working state according to the acquired current value collected by the sampling circuit, that is, the number of the working LED lamp strings is N, and the number of the open-circuit LED lamp strings is M-N, the constant total current output by the output end needs to be reduced to N × I, that is, the current amount needs to be reduced is (M-N) × I. At this time, the control circuit sends the control information to the driving circuit, and the driving circuit correspondingly reduces the output current value of the output end according to the obtained control information, in this embodiment, specifically, the control circuit sends a first PWM control signal to the driving circuit, a relation graph of the PWM control signal and the output current is shown in fig. 11, when the duty ratio of the PWM control signal is 1, that is, when the current is always output, the output current is the total circuit Iomax thereof; when the duty ratio of the PWM control signal is 50%, that is, the current is output 50% of the time in one period, and the current is not output 50% of the time, the output current is half of the total current, that is, 50% Iomax. Therefore, in this embodiment, the duty ratio of the first PWM control signal is specifically adjusted to adjust the magnitude of the output current, at this time, after the magnitude of the constant total current to be output is determined according to the number of the LED lamp strings in operation, the output constant total current is made to be the required target current by correspondingly reducing the duty ratio of the output first PWM control signal, and the current shunted to each LED lamp string is unchanged from the original current maintained after the current is reduced, so that the current output required to be turned off in the prior art is avoided, and the influence of overcurrent damage to each LED lamp string due to the fact that the current shunted to each LED lamp string branch is too large because the constant total current is unchanged in the prior art is avoided.

Step S103, when the collected current value of the current working LED lamp string is judged to be unequal to the rated current value, adjusting the duty ratio of a PWM control signal output to the current working LED lamp string according to the current value of the current working LED lamp string and the rated current value so as to drive the current value on the current working LED lamp string to be equal to the rated current value;

wherein, it is pointed out that, because the quantity and specification of the LEDs in each path of LED light string are different, the current flowing through the parallel branches of each LED light string may not be equal, at this time, because the current of each LED light string is not equal, the problem of uneven brightness of each LED light in the LCD screen backlight is generated, which affects the use effect, therefore, current-sharing control needs to be implemented for each path of LED light string, at this time, the control circuit compares the current value of each path of working LED light string collected by the sampling circuit with the rated current value of the LED light string, when it is determined that the current value of any path of working LED light string is not equal to the rated current value, the current flowing through the branch of LED light string is determined to be adjusted according to the current value and the rated current value of the LED light string, for example, when the collected current value of the current working LED light string is greater than the rated current value, in this embodiment, the specific method for adjusting the current of each of the LED lamp string branches is to adjust the duty ratio of the second PWM control signal, so that the driving circuit controls the current of each of the currently operating LED lamp string branches to be equal to the rated current.

The embodiment of the invention collects the actual current of each path of LED lamp string through the sampling circuit and sends the actual current to the control circuit, the control circuit determines the number of the paths of working LED lamp strings according to the current of each path of LED lamp string collected by the sampling circuit and sends the first PWM control signal to the drive circuit, so that the drive circuit drives the total current output to each path of LED lamp string to be correspondingly changed, the current re-distributed to each path of LED lamp string is unchanged from the original maintenance, the current output required to be closed at the output end in the prior art is avoided, and the influence of overcurrent damage to each path of LED lamp string caused by overlarge current distributed to each path of LED lamp string branch circuit due to the unchanged constant total current in the prior art is avoided. The control circuit adjusts the duty ratio of the second PWM control signal to be sent to the second driving circuit according to the actual current of each path of LED lamp string collected by the sampling circuit, so that the current of each path of LED lamp string can be dynamically adjusted, and the current equalizing work is kept. The problem of current multichannel LED current-sharing control inconvenient is solved.

Referring to fig. 2, a flowchart of a LED parallel current sharing control method according to a second embodiment of the present invention is applied to an LED parallel current sharing circuit, where the LED parallel current sharing circuit includes an output terminal and multiple LED strings connected to the output terminal in parallel, and each of the multiple LED strings may be connected to different numbers of LED lamps in series, and the method includes:

step S111, collecting the current value of the output end, and judging whether the current value of the output end is larger than a protection current value;

when the current value of the output end is judged to be larger than the protection current value, step S112 is executed;

otherwise, step S113 is performed.

Before the LED parallel current-sharing circuit starts to operate, the protection current value flowing through the output end and the rated voltage value of each parallel LED lamp string need to be determined. The protection current value is used for judging the current flowing through each path of LED lamp string so as to prevent the damage of each path of LED lamp string caused by overlarge current input to each path of LED lamp string branch circuit by the output end. The rated voltage value is the maximum voltage which can be borne by the LED lamp strings in each path. Further, the protection current value is greater than the sum of the rated current values of the multiple LED light strings, for example, the rated current value of each LED light string is I, and there are M LED light strings in total, and then the total current input from the output end to each LED light string needs M × I, and then the protection current value is greater than M × I.

Step S112, disconnecting the output end from the multiple paths of LED lamp strings;

when the sampling circuit acquires that the constant total current of the output end is greater than the protection current value, the LED parallel current-sharing circuit has an overcurrent phenomenon, and if the output of each path of LED lamp string is not closed, each path of LED lamp string can be damaged. Therefore, when the control circuit obtains that the total current value of the output end acquired by the sampling circuit is greater than the protection current value, the control circuit sends the first PWM control signal to the driving circuit so as to enable the driving circuit to close the current output of the output end, specifically, the duty ratio of the first PWM control signal is set to 0, and the control circuit realizes overcurrent protection of each path of LED lamp string.

Step S113, collecting the current value of each path of LED lamp string, and determining the number of paths of working LED lamp strings according to the current value of each path of LED lamp string;

when the total current value of the output end acquired by the sampling circuit is smaller than the protection current value, the sampling circuit acquires the current value of each branch of the LED lamp strings and sends the current value to the control circuit, so that the control circuit determines the number of the working LED lamp strings and the number of the open-circuit LED lamp strings according to the current value of each branch of the LED lamp strings.

Step S114, controlling the total current flowing through the output end according to the number of the working LED lamp strings and the rated current value of the working LED lamp strings;

when the number of the working LED lamp strings is smaller than the total number of all the LED lamp strings, the total current input to each working LED lamp string from the output end is adjusted, so that the current shunted to each working LED lamp string is kept unchanged, the working LED lamp strings are kept unchanged from the original current, and the normal brightness is kept for light emission.

Step S115, when the collected current value of the current working LED lamp string is judged to be unequal to the rated current value, adjusting the duty ratio of the PWM control signal output to the current working LED lamp string according to the current value of the current working LED lamp string and the rated current value;

the number and the specification of the LED lamps in each LED lamp string are different, so that the current flowing through each LED lamp string branch in parallel connection may not be equal, and at the moment, the brightness of each LED lamp in the LCD screen backlight is uneven due to the fact that each LED lamp string is not equal, and the using effect is affected. Therefore, the control circuit compares the current value of each path of working LED lamp string collected by the sampling circuit with the rated current value of the LED lamp string, and when the current value of any path of working LED lamp string is determined to be not equal to the rated current value, the current flowing through the branch circuit of the LED lamp string is determined to be adjusted according to the current value and the rated current value of the LED lamp string.

Step S116, when the current value of the current working LED lamp string is larger than the rated current value, reducing the duty ratio of the PWM control signal output to the current working LED lamp string so as to drive the current value on the current working LED lamp string to be equal to the rated current value;

when the collected current of the current working LED lamp string is larger than the rated current value, the duty ratio of a second PWM control signal sent to the driving circuit is reduced by the control circuit, so that the current of the current working LED lamp string is reduced by the driving circuit, the work of a PID current loop is realized, the current value of each LED string is collected by the sampling circuit in real time at the moment, the dynamic compensation of the current of each LED lamp is realized through the second PWM control signal sent by the control circuit, and the current equalizing work of each LED lamp string can be realized.

Step S117, when the current value of the currently operating LED light string is smaller than the rated current value, increasing the duty ratio of the PWM control signal output to the currently operating LED light string to drive the current value on the currently operating LED light string to be equal to the rated current value.

The embodiment of the invention inputs the total current of each path of LED lamp string through the output end of the sampling current collection and sends the total current to the control circuit, the control circuit judges whether the port output end is connected with each path of LED lamp string according to the total current, so that when the total current is overlarge, the connection with each path of LED lamp string can be disconnected, the influence of overcurrent damage on each path of LED lamp string is avoided, each path of LED lamp string current signal is further collected in real time through the collection circuit, and the duty ratio of the output second PWM signal is adjusted in real time according to the collected current signal by the control circuit, so that a PID current loop is formed, dynamic regulation can be realized on each path of LED lamp string, and current equalizing work is kept.

Referring to fig. 3, a block diagram of a parallel LED current sharing control system according to an embodiment of the present invention is shown, where the system 100 is applied to a parallel LED current sharing circuit, where the parallel LED current sharing circuit includes an output terminal and multiple parallel LED strings connected to the output terminal, and each of the multiple parallel LED strings may be connected to different numbers of LED lamps in series, and the system 100 includes:

the determining module 101 is configured to collect a current value of each path of the LED lamp string, and determine the number of paths of the working LED lamp strings according to the current value of each path of the LED lamp string;

the first control module 102 is configured to control a total current flowing through the output terminal according to the number of the working LED lamp strings and a rated current value of the working LED lamp strings;

and the second control module 103 is configured to, when it is determined that the acquired current value of the current working LED light string is not equal to the rated current value, adjust a duty ratio of a PWM control signal output to the current working LED light string according to the current value of the current working LED light string and the rated current value, so as to drive the current value on the current working LED light string to be equal to the rated current value.

Referring to fig. 4, a block diagram of a parallel LED current sharing control system according to another embodiment of the present invention is shown, where the system 110 is applied to a parallel LED current sharing circuit, where the parallel LED current sharing circuit includes an output terminal and multiple parallel LED strings connected to the output terminal, and each of the multiple parallel LED strings may be connected to different numbers of LED lamps in series, and the system 110 includes:

the judging module 111 is used for acquiring the current value of the output end and judging whether the current value of the output end is greater than a protection current value, wherein the protection current value is greater than the sum of the rated current values of the multiple paths of LED lamp strings;

and a third control module 112, configured to disconnect the output end from multiple LED light strings when the determining module 111 determines that the current value of the output end is greater than the protection current value.

A determining module 113, configured to collect a current value of each path of the LED light string when the determining module 111 determines that the current value of the output end is smaller than the protection current value, and determine the number of paths of the working LED light strings according to the current value of each path of the LED light string;

a first control module 114, configured to control a total current flowing through the output terminal according to the number of circuits of the working LED light strings determined by the determination module 113 and the rated current value of the working LED light strings;

and the second control module 115 is configured to, when it is determined that the acquired current value of the current working LED light string is not equal to the rated current value, adjust a duty ratio of a PWM control signal output to the current working LED light string according to the current value of the current working LED light string and the rated current value, so as to drive the current value on the current working LED light string to be equal to the rated current value.

Wherein the second control module 115 comprises:

the first control unit 1151 is configured to reduce a duty ratio of the PWM control signal output to the currently operating LED lamp string when the current value of the currently operating LED lamp string is greater than the rated current value;

and a second control unit 1152, configured to increase a duty ratio of the PWM control signal output to the currently operating LED light string when the current value of the currently operating LED light string is smaller than the rated current value.

Technical features and technical effects of the LED parallel current sharing control system provided in the embodiment of the present invention are the same as those of the method provided in the embodiment of the present invention, and are not described herein again.

Referring to fig. 5 to 9, the LED parallel current sharing circuit 10 according to another embodiment of the present invention includes a power supply circuit 20, a control circuit 30 and a driving circuit 40 connected to the power supply circuit 20, a plurality of LED strings 50 connected to the driving circuit 40, and a sampling circuit 60 respectively connected to the control circuit 30 and the LED strings 50. Wherein, the LED lamp strings 50 are connected in parallel. The power supply circuit 20 is used for providing a required constant power supply voltage for the control circuit 30, the driving circuit 40 and the LED light string 50, and providing a constant current for the driving circuit 40.

The sampling circuit 60 is connected to the LED lamp strings 50 and the control circuit 30, respectively, and is configured to collect a current value of each LED lamp string 50; the control circuit 30 determines to send out a PWM control signal to the driving circuit 40 according to the actual current of each LED string 50 collected by the sampling circuit 60, so that the driving circuit 40 controls the current flowing through each LED string 50 to be maintained unchanged. It should be noted that, in this embodiment, the LED parallel current-sharing circuit 10 is applied to a television, and is used for performing current-sharing dimming on each LED lamp in the LCD screen backlight in a TV, so that the LCD screen backlight in the TV can achieve uniform brightness. Among them, the control circuit 30 is integrated in a hardware circuit in the TV.

Further, the power supply circuit 20 is connected to the drive circuit 40 and the control circuit 30, respectively. Wherein the driving circuit 40 includes a first driving circuit 41 and a plurality of second driving circuits 42, and the control circuit 30 includes a first control circuit 31 and a plurality of second control circuits 32. Wherein the power supply circuit 20 includes an alternating current input power AC, a filter circuit 21 connected to the alternating current input power AC, and a flyback circuit 22 connected to the filter circuit 21. Wherein the AC input power AC is connected to the filter circuit 21, in the present embodiment, the filter circuit 21 at least includes an EMI filter for suppressing high frequency interference in the AC input power AC. The ac power with the high frequency noise filtered out is processed by the flyback circuit 22 and then outputs a dc power.

Further, the flyback circuit 22 at least includes a flyback primary circuit 23, a flyback transformer TC, a first fet Q1, a first resistor R1, a first diode T1, a second diode T2, a first capacitor C1, a second capacitor C2, and a constant current inductor L. Wherein the output terminal of the flyback circuit 22 includes a constant current supply circuit 24 and a constant voltage supply circuit 25. The flyback transformer TC is composed of a primary coil and a secondary coil, and is used for transmitting energy of the primary coil to the secondary coil and isolating the primary coil from the secondary coil. The flyback primary circuit 23 is respectively connected to the filter circuit 21 and the primary coil, and is configured to process the ac power and transmit the processed ac power to the primary coil. The primary coil is an input stage of the flyback transformer TC, and the secondary coil is an output stage of the flyback transformer TC, and is configured to output energy of the primary coil.

One end of the primary coil is connected with the flyback primary circuit 23, and the other end is connected with the drain d of the first field effect transistor Q1. The source s of the first fet Q1 is connected to one end of the first resistor R1, the gate g of the first fet Q1 receives a PWM signal, and the other end of the first resistor R1 is connected to the digital ground SGND. In this embodiment, the first fet Q1 is an N-channel enhancement MOS transistor, and the PWM signal is used to control the amount of energy transmitted from the primary winding to the secondary winding. When the PWM signal is at high level, the first field effect transistor Q1 is switched on, and the primary coil starts to store energy. When the PWM signal is at a low level, the first field effect transistor Q1 is cut off, and the primary coil transmits energy to the secondary coil. Therefore, the first fet Q1 can control the conduction time in each period according to the duty ratio of the PWM signal, so as to control the primary winding to transmit a certain amount of energy to the secondary winding, wherein the first resistor R1 can collect the current of the first fet Q1 to prevent the over-current of the flyback circuit 22.

The constant current supply circuit 24 includes a first diode T1, a first capacitor C1, and a constant current inductor L. The positive electrode of the first diode T1 Is connected to one end of the first secondary winding, the other end of the first secondary winding Is grounded, the negative electrode of the first diode T1 Is connected to one end of the first capacitor C1 and one end of the constant current inductor L, respectively, the other end of the first capacitor C1 Is grounded, and the other end of the constant current inductor L Is a constant current output end Is of the constant current supply circuit 24 and Is used for outputting a constant current. In this embodiment, the first diode T1 is a constant current rectifying diode, which rectifies the ac power at the output end of the first secondary coil into dc power for output, and outputs a constant current after passing through the constant current inductor L.

The constant voltage power supply circuit 25 includes a second diode T2 and a second capacitor C2. The anode of the second diode T2 is connected to one end of the second secondary winding, the other end of the second secondary winding is grounded, the cathode of the second diode T2 is connected to one end of the second capacitor C2, and the other end of the second capacitor C2 is grounded. The first capacitor C1 and the second capacitor C2 are used for reducing ripples in the output direct current, and the cathode of the second diode T2 is the constant voltage output end Us of the constant voltage power supply circuit 25. In this embodiment, the second diode T2 is a constant voltage rectifying diode, which rectifies the ac power at the output end of the first secondary coil into a dc power for output, and the voltage of the dc power is stabilized to 12V, which is used to provide the required power supply voltage for the control circuit 30, the driving circuit 40, and the LED light string 50.

Further, the power supply circuit 20 is connected to the drive circuit 40 and the control circuit 30, respectively. Wherein the driving circuit 40 includes a first driving circuit 41 and a plurality of second driving circuits 42, and the control circuit 30 includes a first control circuit 31 and a plurality of second control circuits 32. The control circuit 30 is integrated in a TV hardware circuit in a TV, and the input end of the control circuit 30 is connected with the multiple sampling circuits 60 respectively, wherein each sampling circuit 60 is connected with a corresponding LED light string 50 and is used for collecting the actual current value of the LED light string 50 connected with the sampling circuit. The output end of the first control circuit 31 is connected to the first driving circuit 41, and is configured to determine the number of circuits of the working LED lamp strings according to the current value of each circuit of LED lamp strings 50 collected by the sampling circuit 60, and determine to send a first PWM control signal to the first driving circuit 41 according to the number of circuits of the working LED lamp strings and the rated current value of the working LED lamp strings, so that the first driving circuit 41 controls the total current input to the multiple circuits of LED lamp strings 50. Each second control circuit 32 is connected to each corresponding second driving circuit 42, and is configured to adjust a duty ratio of a corresponding second PWM control signal sent to the corresponding second driving circuit 42 according to the actual current value and the rated current value of the corresponding LED light string 50 acquired by the corresponding sampling circuit 60, so that the current value of the corresponding LED light string 50 controlled and driven by the second driving circuit 42 is equal to the rated current value.

Further, the driving circuit 40 is respectively connected to the power supply circuit 20, the control circuit 30 and the multiple LED lamp strings 50, wherein the driving circuit 40 includes a first driving circuit 41 and a second driving circuit 42, the first driving circuit 41 is configured to control the total current input to the multiple LED lamp strings 50 according to a first PWM control signal sent by the first control circuit 31, and each second driving circuit 42 is configured to control the current of the corresponding LED lamp string 50 branch according to a second PWM control signal sent by the corresponding second control circuit 32.

The first driving circuit 41 includes a first transistor T1 connected to the constant voltage supply circuit 25, a second transistor T2 and a second resistor R2 respectively connected to the first transistor T1, a zener diode D1 and a second fet Q2 respectively connected to the second resistor R2, and a third resistor R3 and a third diode T3 respectively connected to the second fet Q2. Wherein the collector c of the first triode T1 Is connected with the constant voltage output end Us of the constant voltage power supply circuit 25, the emitter e of the first triode T1 Is respectively connected with the emitter e of the second triode T2 and one end of the second resistor R2, the base b of the first triode T1 Is respectively connected with the base b of the second triode T2 and the control circuit 30, the collector c of the second triode T2 Is respectively connected with the digital SGND and the anode of the zener diode D1, the other end of the second resistor R2 Is respectively connected with the cathode of the zener diode D1 and the gate g of the second diode Q2, the source s of the second effect tube Is connected with one end of the third resistor R3, the other end of the third resistor R3 Is grounded, the drain D of the second diode Q2 Is respectively connected with the output end Is of the constant current power supply circuit 24 and the anode of the third diode T3, the cathode of the third diode T3 Is respectively connected with the anodes of the respective LED strings 50, the third diode T3 is connected in parallel with a third capacitor C3.

The first triode T1 is an NPN type triode, the second triode T2 is a PNP type triode, the first triode T1 and the second triode T2 form a push-pull circuit, the push-pull circuit is powered by the constant voltage power supply circuit 25, and is used for amplifying a first PWM control signal sent by the control circuit 30 to form a first PWM driving signal with large driving capability, and the first PWM driving signal is output by the emitter e, at this time, the first PWM driving signal is transmitted to the gate g of the second field-effect transistor Q2 through the second resistor R2, and the output end of the constant current power supply circuit 24 is connected with the source s of the second field-effect transistor Q2, and is used for outputting constant current to the second field-effect transistor Q2 and then flowing into the third diode T3 to supply the LED light strings 50 of each path to work. In this embodiment, the second field-effect transistor Q2 is an N-channel enhancement MOS transistor, and at this time, when the first PWM control signal sent by the first control circuit 31 is at a high level, the second field-effect transistor Q2 is turned on, so that the current output by the constant-current power supply circuit 24 flows through the second field-effect transistor Q2, so that the third diode T3 is short-circuited, and at this time, the current is discharged to each LED string 50 through the third capacitor C3; when the first PWM control signal is at a low level, the second fet Q2 is turned off, and all the current flowing through the drain d of the second fet Q2 in the constant current supply circuit 24 flows into the third diode T3. Therefore, by controlling the duty ratio of the first PWM control signal, the on-time of the second fet Q2 in each period can be controlled, so that the total current output to each LED string 50 can be adjusted, and at this time, the total current flows through the third diode T3 and then flows into each LED string 50, so that each LED string 50 can work. However, it cannot be ensured that the current flowing through each LED string 50 is kept constant throughout. Therefore, the second driving circuit 42 is configured to control the current in each LED string 50, so that each LED string 50 can be maintained unchanged after being dynamically compensated.

Each of the second driving circuits 42 is connected to the corresponding second control circuit 32 and the LED light string 50, wherein each of the second driving circuits 42 includes a third fet Q3, a gate g of the third fet Q3 is connected to the second control circuit 32, a source s of the third fet Q3 is grounded, and a drain d of the third fet Q3 is connected to the LED light string 50. When the second PWM control signal sent by the second control circuit 32 is at a high level, the third field effect transistor Q3 is turned on, and the LED light string 50 is on; when the second PWM control signal is at a low level, the third fet Q3 is turned off, and the LED string 50 is off, so that the duty cycle of the second PWM control signal can adjust the on/off time of the current of the LED string 50 in each period, thereby controlling the brightness of the LED string 50. At this time, the second control circuit 32 may send a second PWM control signal to the second driving circuit 42 according to the obtained actual current value of the LED light string 50 collected by the sampling circuit 60, so that the second driving circuit 42 controls the LED light string 50 to perform current-sharing dimming. For example, a rated current I1 is set for each LED string 50, when a certain sampling circuit 60 collects an actual current of the LED string 50 and sends a control circuit 30, where the actual current collected by the control circuit 30 and obtained by the sampling circuit 60 is I2, and I2 is greater than I1, the second control circuit 32 sends a new second PWM control signal to the second driving circuit 42 corresponding to the LED, where the second PWM control signal is adjusted to be lower than the original duty ratio, and at this time, after being driven by the second driving circuit 42, the current value flowing through the LED string 50 is reduced, and at this time, the current value flowing through each LED string 50 can be dynamically adjusted by PID current loop adjustment to maintain current sharing.

Further, the sampling circuit 60 is connected to the control circuit 30 and the LED string 50, respectively. The sampling circuit 60 includes an operational amplifier U, a first input circuit 61 connected to a positive input terminal of the operational amplifier U, a second input circuit 62 connected to a negative input terminal of the operational amplifier U, a compensation circuit 63 respectively connected between the negative input terminal of the operational amplifier U and an output terminal thereof, and a clamp circuit 64 connected to an output terminal of the operational amplifier U. The first input circuit 61 includes a fourth resistor R4, a fourth capacitor C4, and a fifth resistor R5 respectively connected to the non-inverting input terminal of the operational amplifier U, wherein the other ends of the fourth resistor R4, the fourth capacitor C4, and the fifth resistor R5 are grounded. The fourth resistor R4 and the fourth capacitor C4 form a low-pass filter. Wherein the second input circuit 62 includes a sixth resistor R6 connected to the negative phase input terminal of the operational amplifier U, and a seventh resistor R7, an eighth resistor R8, and a ninth resistor R9 connected to the sixth resistor R6. The end of the sixth resistor R6 connected to the seventh resistor R7 is also connected to the LED light string 50, wherein the seventh resistor R7, the eighth resistor R8 and the ninth resistor R9 are connected in parallel, and the other end is grounded. The compensation circuit 63 includes a tenth resistor R10 and a fifth capacitor C5. Wherein the tenth resistor R10 and the fifth capacitor C5 are connected in parallel between the negative phase input terminal and the output terminal of the operational amplifier U. The clamp circuit 64 comprises an eleventh resistor R11 connected to the output terminal of the operational amplifier U, a sixth capacitor C6 and a double diode D2 respectively connected to the eleventh resistor R11, wherein the other end of the sixth capacitor C6 is grounded, the anode of one diode of the double diode D2 is grounded, and the cathode of the other diode is connected to a power supply pin VCC, wherein the power supply pin VCC is 3.3V, and is used for clamping the output signal between 0 and 3.3V. The output end of the clamping circuit 64 is connected to the control circuit 30, and the end of the eleventh resistor R11 connected to the sixth capacitor C6 is connected to the control circuit 30. The sampling circuit 60 is specifically configured such that the current of the LED string 50 flows through the seventh resistor R7, the eighth resistor R8, and the ninth resistor R9, and then the current signal is converted into a voltage signal, which is input to the negative input terminal of the operational amplifier U, and output from the output terminal thereof after being differentially amplified by the operational amplifier U, wherein the output signal is amplitude limited by the clamp circuit 64 to clamp the signal between 0V and 3.3V. And outputs the current to the control circuit 30, so that the control circuit 30 can obtain the actual current value of each LED string 50.

Further, the specific work of the LED parallel current sharing circuit 10 is that the power supply circuit 20 supplies power to the control circuit 30 and the driving circuit 40, the driving circuit 40 drives the total current flowing through each LED string 50 and the current of each branch of the LED string 50, at this time, the sampling circuit 60 collects the actual circuit of each LED string 50 and the number of working circuits of the LED string 50, and sent to the control circuit 30, the control circuit 30 controls the total current flowing through each of the LED lamp strings 50 according to the obtained number of the working paths of the LED lamp strings 50, for example, the LED string 50 has N total paths, and when M paths of LED strings 50 are collected by the sampling circuit 60 to operate, that is, there are N-M LED strings 50 in an open circuit and non-operating state, and at this time, the control circuit 30 correspondingly adjusts the duty ratio of the first PWM control signal according to the reduced ratio of the LED strings 50, so that the total current flowing into each LED string 50 is correspondingly reduced. And the control circuit 30 correspondingly and dynamically adjusts the duty ratio of the output second PWM control signal according to the obtained actual current value of each LED light string 50, so that the current flowing into each LED light string 50 maintains a uniform and unchangeable state, and the LCD screen in the TV is uniformly backlit.

The embodiment of the invention collects the actual current of each path of LED lamp string through the sampling circuit and sends the actual current to the control circuit, the control circuit determines the number of the paths of working LED lamp strings according to the current of each path of LED lamp string collected by the sampling circuit and sends the first PWM control signal to the drive circuit, so that the drive circuit drives the total current output to each path of LED lamp string to be correspondingly changed, the current re-distributed to each path of LED lamp string is unchanged from the original maintenance, the current output required to be closed at the output end in the prior art is avoided, and the influence of overcurrent damage to each path of LED lamp string caused by overlarge current distributed to each path of LED lamp string branch circuit due to the unchanged constant total current in the prior art is avoided. The control circuit adjusts the duty ratio of the second PWM control signal to be sent to the second driving circuit according to the actual current of each path of LED lamp string collected by the sampling circuit, so that the current of each path of LED lamp string can be dynamically adjusted, and the current equalizing work is kept. The control circuit is integrated in the TV hardware circuit, so that the TV hardware circuit can efficiently realize LED current sharing control. And the driving signal and the starting signal do not need to be frequently sent to the multipath dimming control chip arranged outside the TV hardware module in the prior art, so that the multipath dimming control chip in the prior art is reduced, and the cost is reduced. When multiple paths of LED lamp strings are connected in an expanding mode, only pins of the control circuit need to be expanded, compatibility of the LED parallel current-sharing circuit is improved, and the problem that current-sharing control of the multiple paths of LEDs is inconvenient is solved.

The logic and/or steps represented in the flowcharts or otherwise described herein, e.g., an ordered listing of executable instructions that can be considered to implement logical functions, can be embodied in any computer-readable medium for use by or in connection with an instruction execution system, apparatus, or device, such as a computer-based system, processor-containing system, or other system that can fetch the instructions from the instruction execution system, apparatus, or device and execute the instructions. For the purposes of this description, a "computer-readable medium" can be any means that can contain, store, communicate, propagate, or transport the program for use by or in connection with the instruction execution system, apparatus, or device.

More specific examples (a non-exhaustive list) of the computer-readable medium would include the following: an electrical connection (electronic device) having one or more wires, a portable computer diskette (magnetic device), a Random Access Memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM or flash memory), an optical fiber device, and a portable compact disc read-only memory (CDROM). Additionally, the computer-readable medium could even be paper or another suitable medium upon which the program is printed, as the program can be electronically captured, via for instance optical scanning of the paper or other medium, then compiled, interpreted or otherwise processed in a suitable manner if necessary, and then stored in a computer memory.

It should be understood that portions of the present invention may be implemented in hardware, software, firmware, or a combination thereof. In the above embodiments, the various steps or methods may be implemented in software or firmware stored in memory and executed by a suitable instruction execution system. For example, if implemented in hardware, as in another embodiment, any one or combination of the following techniques, which are known in the art, may be used: a discrete logic circuit having a logic gate circuit for implementing a logic function on a data signal, an application specific integrated circuit having an appropriate combinational logic gate circuit, a Programmable Gate Array (PGA), a Field Programmable Gate Array (FPGA), or the like.

In the description herein, references to the description of the term "one embodiment," "some embodiments," "an example," "a specific example," or "some examples," etc., mean that a particular feature, structure, material, or characteristic described in connection with the embodiment or example is included in at least one embodiment or example of the invention. In this specification, the schematic representations of the terms used above do not necessarily refer to the same embodiment or example. Furthermore, the particular features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples.

The above-mentioned embodiments only express several embodiments of the present invention, and the description thereof is more specific and detailed, but not construed as limiting the scope of the present invention. It should be noted that, for a person skilled in the art, several variations and modifications can be made without departing from the inventive concept, which falls within the scope of the present invention. Therefore, the protection scope of the present patent shall be subject to the appended claims.

Claims

1. An LED parallel current-sharing control method is applied to an LED parallel current-sharing circuit, the LED parallel current-sharing circuit comprises an output end and a plurality of LED lamp strings connected with the output end in parallel, and each LED lamp string can be connected with different numbers of LED lamps in series, and the method is characterized by comprising the following steps:

the method for judging the number of the working LED lamp strings comprises the steps that if one or more LED lamp strings in the multiple paths of LED lamp strings connected in parallel do not work, the LED lamp strings are in an open-circuit state, the current value flowing through the LED lamp strings is 0, the voltage value flowing through the LED lamp strings is larger than the preset rated voltage, and the number of the working LED lamp strings in the multiple paths of LED lamp strings can be determined by judging the current value of each LED lamp string;

when the collected current value of the current working LED lamp string is judged to be unequal to the rated current value, the duty ratio of a PWM control signal output to the current working LED lamp string is adjusted according to the current value of the current working LED lamp string and the rated current value so as to drive the current value on the current working LED lamp string to be equal to the rated current value;

the parallel current-sharing circuit comprises a sampling circuit, a control circuit, a driving circuit and a plurality of paths of LED lamp strings, wherein the output end of the driving circuit is connected with the plurality of paths of LED lamp strings connected in parallel;

the driving circuit is respectively connected with the control circuit and each path of LED lamp string, and comprises a first driving circuit and a second driving circuit; the first driving circuit is used for controlling the total current flowing through the output end according to the first PWM control signal sent by the first control circuit; the second driving circuit is used for driving the current value of each path of working LED lamp string to be equal to the rated current value according to the second PWM control signal sent by the second control circuit;

the sampling circuit comprises an operational amplifier, a first input circuit connected with a positive phase input end of the operational amplifier, a second input circuit connected with a negative phase input end of the operational amplifier, a compensation circuit respectively connected between the negative phase input end of the operational amplifier and an output end of the operational amplifier, and a clamping circuit connected with the output end of the operational amplifier, wherein the second input circuit is connected with the LED lamp string, the clamping circuit is connected with the control circuit, and the sampling circuit is used for outputting a current flowing through the LED lamp string to the control circuit after differential amplification, amplitude limiting and clamping;

the step of adjusting the duty ratio of the PWM control signal output to the current working LED lamp string according to the current value of the current working LED lamp string and the rated current value comprises the following steps:

2. The LED parallel current sharing control method according to claim 1, wherein before the step of collecting the current value of each LED light string, the method further comprises:

3. The LED parallel current-sharing control method according to claim 1, wherein the LED parallel current-sharing circuit further comprises a power supply circuit, and the power supply circuit is respectively connected with the control circuit and the driving circuit;

4. The LED parallel current sharing control method according to claim 3,

the first driving circuit comprises a first triode connected with the constant-voltage power supply circuit, a second triode and a second resistor which are respectively connected with the first triode, a voltage stabilizing diode and a second field-effect tube which are respectively connected with the second resistor, and a third resistor and a third diode which are respectively connected with the second field-effect tube;

5. An LED parallel current sharing control system using the LED parallel current sharing control method of claim 1, applied to an LED parallel current sharing circuit, the LED parallel current sharing circuit comprising an output terminal and a plurality of LED strings connected in parallel to the output terminal, each of the LED strings being capable of connecting different numbers of LED lamps in series, the system comprising:

6. The LED parallel current sharing control system according to claim 5, further comprising:

7. The LED parallel current sharing control system according to claim 5, wherein the second control module comprises: