CN211792154U

CN211792154U - Backlight control circuit, television and intelligent panel

Info

Publication number: CN211792154U
Application number: CN201921805464.4U
Authority: CN
Inventors: 吴永芳
Original assignee: Guangzhou Shiyuan Electronics Thecnology Co Ltd
Current assignee: Guangzhou Shiyuan Electronics Thecnology Co Ltd
Priority date: 2019-10-25
Filing date: 2019-10-25
Publication date: 2020-10-27
Anticipated expiration: 2029-10-25

Abstract

The utility model relates to a backlight control circuit, a television and an intelligent panel, wherein the backlight control circuit comprises a front-end power circuit, a LED constant current circuit, a power consumption control circuit and a feedback control circuit; the front-end power supply circuit comprises a power supply output end which is used for supplying power to the LED constant current circuit; the LED lamp comprises a plurality of LED lamp strings, a plurality of switch tubes, a constant current control circuit and a sampling resistor; the input end of the power consumption control circuit is connected with the cathode of the LED lamp string, and the output end of the power consumption control circuit is connected with the feedback control circuit and used for outputting a PWM power adjusting signal to the control end of the feedback control circuit according to the maximum output voltage and the reference voltage of the LED lamp string; the feedback control circuit is used for adjusting the output voltage value of the power supply output end, so that the switching tube is controlled to work in an amplification state. The utility model discloses a control circuit is shaded has independent control, is applicable to jumbo size TV, prevents that the switch tube from generating heat seriously and damaging and the advantage of practicing thrift the cost.

Description

Backlight control circuit, television and intelligent panel

Technical Field

The utility model relates to a power control technical field especially relates to a control circuit, TV set and intelligence are dull and stereotyped in a poor light.

Background

In the technical field of television power control, a primary constant current modulation circuit is often adopted to realize power supply to a main board and an LED backlight at the same time.

The constant current modulation circuit is a unit circuit widely used in an analog integrated circuit, and can be used as a power supply circuit. A multi-output transformer is usually arranged in the LED backlight module, one output is LED out through the multi-output transformer to be used as an LED backlight power supply output end, and the other output is LED out to be used as a power supply output end of a mainboard. In the process of integrating television components, the main board and the backlight light bars are usually produced in a matching manner, and the backlight LED light bars with different quantities need to be adaptively output with different voltage values by the power supply circuit. In the prior art, a feedback loop connected with a power supply output end of a television main board is adopted to monitor the voltage change of the power supply output end of the television main board in time. The transformer volume is in direct proportion to the output power energy, and the adoption of the multi-output transformer is only suitable for small-size televisions but not suitable for large-size televisions. In addition, when a multi-output transformer is adopted, only one LED lamp string is usually used, so that the existing constant current modulation circuit is further limited to be suitable for small-size televisions but not suitable for large-size televisions.

On the other hand, in order to realize constant current, the constant current modulation circuit must keep the voltage drop of the middle lamp of the LED lamp string unchanged, and when the input voltage input to the LED lamp string is higher than the voltage of the LED lamp string, the voltage higher than the voltage of the LED lamp string needs to be borne by the switching tube in the constant current modulation circuit. When the power consumption at two ends of a switching tube in the constant current modulation circuit exceeds the self dissipation power, the switching tube has the possibility of serious heating and damage.

SUMMERY OF THE UTILITY MODEL

Based on this, the utility model aims at providing a control circuit, TV set and intelligence are dull and stereotyped in a poor light, it has independent control, is applicable to jumbo size TV, prevents that the switch tube from generating heat seriously and damaging and the advantage of practicing thrift the cost.

In a first aspect, an embodiment of the present application provides a backlight control circuit, which includes a plurality of LED constant current circuits connected in parallel, a power consumption control circuit, and a feedback control circuit;

the front-end power supply circuit comprises a power supply output end which is used for supplying power to the LED constant current circuit;

the LED constant current circuit comprises a plurality of LED lamp strings, a switch tube, a constant current control circuit and a sampling resistor; the anode of each LED lamp string is connected to the power supply output end in parallel, the cathode of each LED lamp string is connected with one end of a switching tube, the other end of each switching tube is grounded through the sampling resistor, and the control end of each switching tube is connected with the output end of the constant current control circuit; the constant current control circuit is used for controlling the current flowing through the sampling resistor to be a constant current signal;

the input end of the power consumption control circuit is connected to the cathodes of the LED lamp strings of the LED constant current circuit, and the output end of the power consumption control circuit is connected with the feedback control circuit and used for outputting PWM power adjusting signals to the control end of the feedback control circuit according to the maximum output voltage and the reference voltage of the LED lamp strings of the LED constant current circuit;

the input end of the feedback control circuit is connected to the power supply output end, and the output end of the feedback control circuit is connected with the front-end power circuit and used for controlling the front-end power circuit through the PWM power adjusting signal and adjusting the output voltage value of the power supply output end, so that the switching tube is controlled to work in an amplifying state.

Further, the switch tube is a triode or a field effect transistor;

when the switching tube is a triode, the collector electrode of the triode is connected with the cathode of the LED lamp string, the emitter electrode of the triode is grounded through a sampling resistor, and the base electrode of the triode is the control end of the switching tube;

when the switching tube is a field effect transistor, the drain electrode of the field effect transistor is connected with the cathode of the LED lamp string, and the source electrode of the field effect transistor is grounded through the sampling resistor; and the grid electrode of the field effect transistor is the control end of the switch tube.

Further, the constant current control circuit comprises a first operational amplifier and a plurality of switch control circuits; the inverting input end of the first operational amplifier is used for inputting a dimming signal; the dimming signal is a PWM dimming signal or an analog dimming signal; the non-inverting input end of the first operational amplifier is connected between the switching tube and the sampling resistor and used for collecting the voltage of the sampling resistor;

each switch control circuit comprises a triode; the output end of the operational amplifier is connected to the base electrode of the triode through a base electrode resistor, an interelectrode resistor is connected between the base electrode and the emitting electrode of the triode, and the emitting electrode of the triode is grounded; the collector of triode is connected with the input of power supply through two parallel divider resistors, and the control end of each switch tube is respectively connected between two divider resistors of each switch control circuit.

The power consumption control circuit further comprises a single chip microcomputer or a control main chip and a comparison voltage input end, wherein a reference voltage is arranged in the single chip microcomputer or the control main chip, and the power consumption control circuit further comprises an ADC (analog-to-digital converter) detection pin; cathodes of a plurality of LED lamp strings of the LED constant current circuit are sequentially connected with cathodes and anodes of diodes in parallel and the ADC analog-to-digital conversion detection pin; the comparison voltage input end is grounded through two voltage dividing resistors R11 and R12, and the anode of the diode is connected between the voltage dividing resistors R11 and R12; the comparison voltage input end is used for inputting comparison voltage, and the comparison voltage is compared with the maximum voltage LED out from the cathodes of the LED lamp strings of the LED constant current circuit to obtain a signal input to the ADC analog-to-digital conversion detection pin;

and the single chip microcomputer or the control main chip compares the signal input to the ADC analog-to-digital conversion detection pin with a reference voltage and outputs a PWM power adjustment signal to the control end of the feedback control circuit.

Further, the power consumption control circuit further comprises a second operational amplifier and a comparison voltage input end, wherein the inverting input end of the second operational amplifier is used for inputting a reference voltage; the non-inverting input end of the second operational amplifier is sequentially connected with the anodes of the diodes, and the cathodes of the diodes are connected with the cathodes of the LED lamp strings of the LED constant current circuit;

the comparison voltage input end is grounded through two voltage dividing resistors R11 and R12, and the anode of the diode is connected between the voltage dividing resistors R11 and R12; the comparison voltage input end is used for inputting comparison voltage, and the comparison voltage is compared with the maximum voltage LED out from the cathodes of the LED lamp strings of the LED constant current circuit to obtain a signal input to the in-phase input end;

and the second operational amplifier compares the signal input to the non-inverting input end with the reference voltage input to the inverting input end and outputs a PWM power adjusting signal to the control end of the feedback control circuit.

Further, an RC filter circuit is connected in series between the inverting input end and the output end of the first operational amplifier and the second operational amplifier.

Further, the feedback control circuit is also provided with an optocoupler PCB101 and a voltage regulator UB 102; the optocoupler PCB101 comprises a light emitting diode positioned on a primary side and an optical signal converter positioned on a secondary side;

the voltage stabilizer UB102 adopts a debuggeable precision parallel voltage stabilizer, comprises a cathode K, an anode A and a reference input end R, and is internally provided with a reference voltage; the anode A of the adjustable precision shunt regulator is grounded, and the cathode K of the adjustable precision shunt regulator is connected with a Light Emitting Diode (LED) positioned on the primary side of the optocoupler PCB 101; the reference input end R is used for accessing the PWM power adjusting signal;

the power supply output end is grounded through series-connected voltage-dividing resistors RB134 and RB135, and the working voltage of the voltage stabilizer UB102 is taken out from the connection position of the voltage-dividing resistors RB134 and RB135 and is input into a reference input end R of the voltage stabilizer UB 102;

the voltage stabilizer UB102 is used for connecting the PWM power adjusting signal to a primary side light emitting diode of the optocoupler PCB 101; the light emitting diode converts the PWM power adjustment signal into an optical signal and transmits the optical signal to an optical signal converter which is positioned on the secondary side of the optical coupler PCB 101; the optical signal converter converts an optical signal into an electric signal and outputs the electric signal to the feedback signal output end.

In a second aspect, an embodiment of the present application further provides a television set, including the backlight control circuit as described above.

In a third aspect, an embodiment of the present application further provides a smart tablet, including the backlight control circuit as described above.

In the technical scheme of the embodiment of the application, on one hand, the front-end power circuit only provides one path of power supply output end and is only used for supplying power to the LED backlight, the power supply of the LED backlight and the power supply of the television main board are independently switched on, and the independent control of the backlight is realized, so that the power of the transformer in the front-end power circuit is completely supplied to the LED backlight, each path of the transformer is independent, the power can be increased according to the requirement of the television specification and is not limited by the size of the transformer, the front-end power circuit is suitable for a large-size television, and the LED constant-current circuits are multiple and connected in parallel at the power supply output end. On the other hand, a plurality of LED lamp strings in the LED constant current circuit share one constant current control circuit, so that the current passing through the sampling resistor is constant, and the cost is saved. On the other hand, the power consumption control circuit samples voltage from the cathode of the LED lamp string, the voltage is input voltage of the switching tube, the voltage and the reference voltage generate a PWM power adjustment signal for adjusting the voltage or the power of the switching tube, the PWM power adjustment signal is fed back to the front-end power circuit through the feedback loop, the switching tube is controlled to work in an amplification state all the time, the power of the switching tube is controlled within a power consumption range, the power cannot exceed the dissipation power of the switching tube, and the switching tube is prevented from being heated seriously and damaged.

For a better understanding and practice, the embodiments of the present application are described in detail below with reference to the accompanying drawings.

Drawings

Fig. 1 is a circuit block diagram of a backlight control circuit according to an embodiment of the present application;

FIG. 2 is a circuit diagram of a first implementation of a backlight control circuit according to an embodiment of the present disclosure;

FIG. 3 is a circuit diagram of a second implementation of a backlight control circuit according to an embodiment of the present application;

FIG. 4 is a circuit diagram of an operational amplifier circuit of a backlight control circuit according to an embodiment of the present disclosure;

FIG. 5 is a circuit diagram of a switch control circuit of the backlight control circuit according to an embodiment of the present disclosure;

FIG. 6 is a circuit diagram of a feedback control circuit according to an embodiment of the present application;

FIG. 7 is a circuit diagram of a first implementation of a power control circuit according to an embodiment of the present application;

fig. 8 is a circuit diagram of a second implementation of a power control circuit according to an embodiment of the present application.

Detailed Description

Embodiments of the present application will now be described more fully hereinafter with reference to the accompanying drawings, in which embodiments of the application are shown. The embodiments of the present application may, however, be embodied in many different forms and should not be construed as limited to the specific embodiments set forth herein. Rather, these embodiments are provided to convey the scope of the embodiments of the application to those skilled in the art.

Unless otherwise defined, terms (including technical and scientific terms) used herein should be understood to have the same meaning as commonly understood by one of ordinary skill in the art to which the embodiments of the present application belong. Moreover, it will be understood that terms used herein should be interpreted as having a meaning that is consistent with their meaning in the context of this specification and the relevant art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein.

In order to overcome the defects of the prior art, please refer to fig. 1-3, a backlight control circuit includes a front-end power circuit 10, a plurality of parallel LED constant current circuits 20, a power consumption control circuit 30 and a feedback control circuit 40;

the front-end power circuit 10 comprises a power supply output end for supplying power to the LED constant current circuit 20;

the front-end power supply circuit 10 adopts a linear constant-current AC input circuit in the prior art, and is not described in detail here.

The LED constant current circuit comprises a plurality of LED lamp strings, switching tubes Q1 and QB1 … …, a constant current control circuit and a sampling resistor; the anode of each LED lamp string is connected to the power supply output end in parallel, the cathode of each LED lamp string is connected with one end of a switching tube, the other end of each switching tube is grounded through the sampling resistor, and the control end (grid G) of each switching tube (if a field effect transistor) is connected with the output end of the constant current control circuit; the constant current control circuit is used for controlling the current flowing through the sampling resistor to be a constant current signal;

the input end of the power consumption control circuit 30 is connected to the cathodes of the plurality of LED light strings of the LED constant current circuit 20, and the output end is connected to the feedback control circuit 40, and is configured to output a PWM power adjustment signal to the control end of the feedback control circuit 40 according to the maximum output voltage and the reference voltage of the plurality of LED light strings of the LED constant current circuit;

the input end of the feedback control circuit 40 is connected to the power supply output end, and the output end of the feedback control circuit 40 is connected to the front-end power supply circuit 10, so that the front-end power supply circuit 10 is controlled by the PWM power adjustment signal, the output voltage value of the power supply output end is adjusted, and the switching tube Q1 is controlled to work in an amplification state.

In specific implementation, the switching tube Q1 is a triode or a field effect transistor;

when the switching tubes Q1 and QB1 … … are triodes, the collector electrodes of the triodes are connected with the cathodes of the LED light strings, the emitter electrodes of the triodes are grounded through a sampling resistor R7, and the base electrodes of the triodes are the control ends of the switching tubes Q1 and QB1 … …;

when the switching tubes Q1 and QB1 … … are field effect transistors, the drain electrodes of the field effect transistors are connected with the cathodes of the LED lamp strings, and the source electrodes of the field effect transistors are grounded through a sampling resistor R7; the grid of the field effect transistor is the control end of the switching tubes Q1 and QB1 … …. It is understood that a gate-source resistance R10 is provided between the gate and the source of the field effect transistor to set the quiescent operating point.

Please refer to fig. 3-5, which are specific circuit diagrams of an implementation manner of the backlight control circuit according to an embodiment of the present application. In this embodiment, the switching transistors Q1 and QB1 … … are field effect transistors.

In a specific embodiment, the backlight control circuit includes two LED constant current circuits 20, and in practical application, the number of the LED constant current circuits 20 can be freely set by the backlight control circuit according to the size of the television. Each of the constant current control circuits of the LED constant current circuit 20 includes an operational amplifier circuit 21 and a switch control circuit 22. The circuit configuration of one of the constant current control circuits will be described below. Please refer to fig. 4, which is a circuit diagram of an operational amplifier circuit of a backlight control circuit according to an embodiment of the present disclosure. In the constant current control circuit, the operational amplifier circuit 21 includes a first operational amplifier U1A, and an inverting input terminal 2 of the first operational amplifier U1A is used for inputting a dimming signal; the dimming signal is a PWM dimming signal or an analog dimming signal; when the dimming signal is a PWM dimming signal, the PWM dimming signal is input to the non-inverting input terminal 2 of the first operational amplifier U1A through the voltage dividing resistors R9 and R8; when the dimming signal is an analog dimming signal, a dc level or a PWM dimming signal is input to the non-inverting input terminal 2 of the first operational amplifier U1A, but a capacitor is connected in parallel to the non-inverting input terminal 2 of the first operational amplifier U1A for filtering the PWM dimming signal into a dc voltage. The non-inverting input terminal 3 of the first operational amplifier U1A is connected between the switching tube Q1 and the sampling resistor R7 through a resistor R6, and is used for collecting the voltage of the sampling resistor R7.

Please refer to fig. 5, which is a circuit diagram of a switch control circuit of a backlight control circuit according to an embodiment of the present application. The switch control circuit 22 comprises transistors Q2, QB2 … …; the output end 1 of the first operational amplifier U1A is connected to the bases of the triodes Q2 and QB2 … … through a base resistor R4, an inter-electrode resistor R3 is connected between the bases and the emitters of the triodes Q2 and QB2 … …, and the emitters of the triodes Q2 and QB2 … … are grounded; the collectors of the triodes Q2 and QB2 … … are connected with the power supply input through two voltage-dividing resistors R1 and R2(RB1 and RB2 … …) which are connected in parallel, and the control ends (grid electrodes G) of the switch tubes Q1 and QB1 … … are connected between the two voltage-dividing resistors R1 and R2(RB1 and RB2 … …).

In the present application, a plurality of LED strings share one operational amplifier circuit 21, and a switch control circuit 22 is separately provided to receive and convert an output signal of the operational amplifier circuit 21.

The operation principle of the present embodiment will be described below by taking the operational amplifier circuit 21 and the switch control circuit 22 in which the transistor Q2 is located as an example. When the power-on operation is performed, when the PWM dimming signal is high, the PWM dimming signal is divided into 0.35V (the voltage can be set as required) by the voltage dividing resistors R9 and R8 and then supplied to the inverting input terminal (pin 2) of the first operational amplifier U1A, the level of the inverting input terminal (pin 2) is higher than the level of the non-inverting input terminal (pin 3) by 0V, the output terminal (pin 1) of the first operational amplifier U1A outputs a low level, and the base of the triode Q2 does not operate at a driving level. 5V-VCC provides drive voltage for the grid (G pin) of switch tube Q1 through resistance R1 to make it turn on, switch tube Q1 turns on and then forms a return circuit with LED +, LED lamp cluster, R7 to ground, sampling resistance R7 because of having the electric current to flow through, both ends can produce the pressure differential, send the pressure differential to the non inverting input end (3 pins) of operational amplifier through resistance R6. When the voltage difference reaches 0.35V, the output end (pin 1) of the first operational amplifier U1A stops outputting or reduces the output quantity, so as to control the working state of the switching tube Q1 through the resistor R4 (Q1 may be a triode or a MOS transistor), thereby realizing the constant current of the sampling resistor. The switching tube Q1 is turned on and off along with the change of the PWM dimming signal, that is, the constant current of the sampling resistor is realized while the PWM dimming is realized.

It should be noted that, since the plurality of LED strings are connected in parallel and share one operational amplifier circuit 21, the embodiment of the present application can implement the constant current of the sampling resistor but cannot implement the constant current of the plurality of LED strings.

Referring to fig. 6, the feedback control circuit further includes an optocoupler PCB101 and a voltage regulator UB 102; the optocoupler PCB101 comprises a light emitting diode positioned on a primary side and an optical signal converter positioned on a secondary side;

the voltage stabilizer UB102 is a debuggeable precision parallel voltage stabilizer including a cathode K, an anode a and a reference input terminal R, and has a built-in reference voltage of 2.5V (V), and may be implemented by a voltage stabilizer of model TL 431. The anode A of the adjustable precision shunt regulator is grounded, and the cathode K of the adjustable precision shunt regulator is connected with a Light Emitting Diode (LED) positioned on the primary side of the optocoupler PCB 101; and the reference input end R is used for accessing the PWM power adjusting signal.

Further, the feedback control circuit 40 is further provided with a resistor RB131 and a resistor RB 132; one end of the resistor RB131 is connected with the 5V-VCC, and the other end of the resistor RB131 is connected with the anode of the light emitting diode, positioned on the primary side, of the optocoupler PCB 101; one end of the resistor RB132 is connected to the anode of the light emitting diode, and the other end is connected to the cathode of the light emitting diode. Note that the resistor RB132 is not an essential electronic component in the feedback circuit in this embodiment.

Further, the feedback control circuit 40 is further provided with a voltage stabilization feedback circuit. In one implementation, the regulated feedback circuit includes a capacitor CB109 and a resistor RB 133; one end of the capacitor CB109 is connected to the cathode K of the debuggeable precision parallel voltage stabilizer, and the other end of the capacitor CB is connected with one end of the resistor RB133 in series; the other end of the resistor RB133 is connected to a reference input end R of the debuggeable precision parallel voltage regulator.

In another implementation, the regulated feedback circuit includes a capacitor CB 110; one end of the capacitor CB110 is connected to the cathode K of the debuggeable precision shunt regulator, and the other end of the capacitor CB is connected to the reference input end R of the debuggeable precision shunt regulator. Further, the present embodiment may combine the above two implementation manners to implement the voltage stabilization feedback circuit. Namely, the voltage stabilizing feedback circuit is simultaneously provided with a capacitor CB109, a resistor RB133 and a capacitor CB 110.

The cathode K of the voltage stabilizer UB102 is connected with a pin 2 of a light emitting diode on the primary side of the optocoupler PCB101, and the anode A of the voltage stabilizer UB102 is grounded; one end of resistor RB134 is connected with reference input end R of voltage regulator UB102, and the other end is grounded; one end of a capacitor CB109 is connected to the cathode K of the debuggeable precision parallel voltage stabilizer, and the other end of the capacitor CB is connected with one end of a resistor RB133 in series; the other end of the resistor RB133 is connected to a reference input end R of the debuggeable precision parallel voltage stabilizer; one end of the capacitor CB110 is connected to the cathode K of the debuggeable precision shunt regulator, and the other end of the capacitor CB is connected to the reference input end R of the debuggeable precision shunt regulator.

When the LED + input voltage is higher than the voltage of the LED lamp string, the constant current control circuit keeps the voltage at the two ends of the sampling R7 constant so as to realize the constant current in the loop. At this time, the voltage drop of the LED string is also unchanged, so the voltage higher than the LED needs to be borne by the switching tubes Q1 and QB1 … …, and when the power consumption of the voltage at the two ends of the drain D and source S pins of the switching tubes Q1 and QB1 … … multiplied by the current in the loop exceeds the power consumption of Q1, the possibility of serious heating and damage occurs.

Under the condition that a plurality of LED lamp strings are connected in parallel in the LED constant current circuit, the LED-voltage extracted from the cathodes of the LED lamp strings is possibly divided into high and low, the current flowing through the LED lamp strings is also uniform and constant, and therefore the power consumption of the switch tube is determined by the LED-voltage. The LED-voltage of a plurality of LED lamp strings of the LED constant current circuit is input to the power control circuit in parallel, the maximum value of the LED-voltage is selected to be adjusted, so that the switching tube with the maximum value of the LED-voltage (the maximum voltage drop of the switching tube) can work in an amplification state, all the switching tubes can work in a controllable power range, the power consumption of the switching tube Q1 is controlled in a controllable range, and the power consumption of the switching tube Q1 cannot exceed the dissipation power of the switching tube.

Therefore, on the basis of the above embodiments, in order to prevent the switching tubes Q1 and QB1 … … from being heated and damaged seriously, referring to fig. 2 and 7, the power consumption control circuit 30 further includes a single chip or a control main chip and a comparison voltage input end, the single chip or the control main chip is provided with a reference voltage therein, and further includes an ADC analog-to-digital conversion detection pin ADC 1; the cathodes and the anodes of the diodes D1 and the ADC analog-to-digital conversion detection pin ADC1 are sequentially connected in parallel with the cathodes and the anodes of the LED lamp strings of the multi-path LED constant current circuit; the comparison voltage input end is grounded through two voltage dividing resistors R11 and R12, and the anode of the diode D1 is connected between the voltage dividing resistors R11 and R12; the comparison voltage input end is used for inputting a comparison voltage (in the embodiment, 2.5V-REF), and the comparison voltage 2.5V-REF is compared with the voltage LED out from the cathode of the LED string to obtain a signal input to the ADC analog-to-digital conversion detection pin.

In this embodiment, a 4-way LED constant current circuit is taken as an example to specifically describe, when the voltage drops across the 4 ways of LED light strings are different, it is first ensured that the LED + voltage (the anode voltage of the LED light strings) output by the power supply output end is greater than the voltage drops across all the LED light strings, so that no undercurrent occurs, that is, the way with the highest light bar is taken as the target rod for setting the output voltage.

For example, the actual voltage of the lamp strip is that the voltage of an LED1 is 100V, LED2, 98 is 98V, LED3, 96 is 96V, LED4, 94V, the voltage of the LED + is always more than 100V to ensure the constant current of all the LED lamp strips, the switching tubes Q1 to Q4 of each LED constant current circuit are always ensured to work in an amplification state, and the drain-source voltage (DS pin voltage difference) is more than 0.1V. For example, when the voltage of the DS pin of the switching tube Q1 of the LED1 is 1V, the voltage of the DS pin of the switching tube Q4 of the LED4 with the lowest voltage drop is 101V-94-7V, and then the power consumption of the switching tube Q4 of the LED4 is a voltage difference of 7V to output current, which is very large, and the actual backlight deviation of the whole machine is not so large, but a heat sink needs to be added in the design to ensure the reliability of the power supply.

In order to realize current sharing under the condition of minimum power consumption, as shown in fig. 7, diodes are connected to pins D of the switching tubes Q1-Q4 (namely, cathodes of the LED light strings), 2.5V-REF comparison voltage is input from a comparison voltage input end and flows through the diodes D1-D4 respectively after passing through the resistor R11. If the voltage of the LED 1-LED 4-is larger than 2.5V, the diode is cut off in the reverse direction, and the voltage of the signal input to the ADC1 is 2.5V; if the voltage of the LED 1-LED 4-is lower than 2.5V, the diode is conducted in the forward direction, and any one of the LED 1-LED 4-is the lowest, the 2.5V reference voltage is only divided by the lowest voltage, and the divided voltage is the signal voltage input to the ADC 1.

For example, assuming that the LED1 ═ 1V, LED2 ═ 3V, LED3 ═ 5V, LED4 ═ 7V, and the voltage is to be compared with the LED1 —, the voltage of the signal input to the ADC analog-to-digital conversion detection pin ADC1 is divided into 2.5V — 1V ═ 1.5V (for understanding that the voltage drop across the diode D1 is omitted).

Further, the single chip microcomputer or the control main chip compares a signal input to the ADC analog-to-digital conversion detection pin with a reference voltage, and outputs a PWM power adjustment signal to the control terminal of the feedback control circuit. The reference voltage is set by the single chip or the control main chip, and in a specific embodiment, the reference voltage can be 1.25V, and the reference voltage is compared with a signal input to the ADC analog-to-digital conversion detection pin to output a PWM power adjustment signal. When the voltage collected by the ADC analog-to-digital conversion detection pin (ADC1) is greater than or less than the reference voltage, the single chip microcomputer outputs a PWM _ FB signal to the feedback control circuit through the output end (PWM1), and the anode LED + output voltage of the LED lamp string can be adjusted along with the change of the PWM _ FB duty ratio. When the voltage of the LED + is adjusted downwards, the dissipation power consumption of the switching tube Q1 is reduced, and in order to meet the requirement that the voltage at the two ends of the R7 is unchanged and the current in the loop is unchanged, the voltage difference exists in the pin Q1DS all the time, so that the pin Q1 works in an amplification state, but the pin Q1 is controlled within a controllable power consumption.

Referring to fig. 3 and 8, as an alternative embodiment of the present application, a second operational amplifier U2B may be selected to output the PWM power adjustment signal. The power consumption control circuit further comprises a second operational amplifier and a comparison voltage input end, wherein the inverting input end of the second operational amplifier is used for inputting reference voltage; the non-inverting input end of the second operational amplifier is sequentially connected with the anodes of the diodes, and the cathodes of the diodes are connected with the cathodes of the LED lamp strings of the LED constant current circuit;

In this embodiment, the cathode LED-voltages of the LED strings of the LED constant current circuit are fed to the non-inverting input terminal (pin 5) of the second operational amplifier U2B through R11, R12 and the diode, the comparison voltage is input from the comparison voltage input terminal, the conduction of the diode is determined according to the magnitude relationship between the comparison voltage and the LED-voltages, the voltage collected by the non-inverting input terminal (pin 5) is controlled, and the voltage collected by the non-inverting input terminal (pin 5) is compared with the reference voltage input by the inverting input terminal (pin 6). When the voltage collected by the non-inverting input end (pin 5) is greater than or less than the reference voltage input by the inverting input end (pin 6), then the high level is output to the pin UB102TL431R of the voltage loop control chip UB102 of the LED + power supply through the output end (pin 7), and the voltage level of the pin TL431R is changed along with the change of the level of the pin 7, so that the voltage level of the LED + output voltage can be adjusted. (the TL431UB102, the optical coupling PCB101A, the sampling resistor RB135RB134 and other devices form an output detection feedback control circuit of a power supply, the magnitude of the sampling resistor is changed, namely the magnitude of the output voltage can be adjusted, or the magnitude of the voltage of the TL431R pin can also be changed.) when the voltage of an LED + is adjusted downwards, the dissipation power consumption of the Q1 is reduced, in order to meet the condition that the voltage at two ends of the R7 is unchanged, the current in the loop is unchanged, the voltage difference exists at the Q1DS pin all the time, the Q1DS pin works in an amplification state, but the power consumption can be controlled in a controllable power consumption.

Further, an RC filter circuit is connected in series between the inverting input end and the output end of the first operational amplifier and the second operational amplifier. The RC filter circuit plays a role of smoothing filtering.

The invention is applied to power supply topologies with output voltage control, such as flyback, forward, BOOST, LLC and the like

The embodiment of the application also provides a television, which comprises the backlight control circuit.

The embodiment of the application also provides an intelligent tablet which comprises the backlight control circuit.

The television and the intelligent panel in the embodiment of the application have corresponding beneficial effects because the television and the intelligent panel comprise the backlight driving circuit in any embodiment.

The above-mentioned embodiments only represent some embodiments of the present invention, and the description thereof is specific and detailed, but not to be construed as limiting the scope of the present invention. It should be noted that, for those skilled in the art, without departing from the spirit of the present invention, several variations and modifications can be made, which are within the scope of the present invention.

Claims

1. A backlight control circuit, characterized by: the LED constant current circuit comprises a front-end power circuit, an LED constant current circuit, a power consumption control circuit and a feedback control circuit;

2. The backlight control circuit of claim 1, wherein: the switch tube is a triode or a field effect transistor;

3. The backlight control circuit of claim 2, wherein: the constant current control circuit comprises a first operational amplifier and a plurality of switch control circuits; the inverting input end of the first operational amplifier is used for inputting a dimming signal; the dimming signal is a PWM dimming signal or an analog dimming signal; the non-inverting input end of the first operational amplifier is connected between the switching tube and the sampling resistor and used for collecting the voltage of the sampling resistor;

4. The backlight control circuit of claim 1, wherein: the power consumption control circuit also comprises a single chip microcomputer or a control main chip and a comparison voltage input end, wherein the single chip microcomputer or the control main chip is internally provided with a reference voltage and also comprises an ADC analog-to-digital conversion detection pin; cathodes of a plurality of LED lamp strings of the LED constant current circuit are sequentially connected with cathodes and anodes of diodes in parallel and the ADC analog-to-digital conversion detection pin; the comparison voltage input end is grounded through two voltage dividing resistors R11 and R12, and the anode of the diode is connected between the voltage dividing resistors R11 and R12; the comparison voltage input end is used for inputting comparison voltage, and the comparison voltage is compared with the maximum voltage LED out from the cathodes of the LED lamp strings of the LED constant current circuit to obtain a signal input to the ADC analog-to-digital conversion detection pin;

5. The backlight control circuit of claim 3, wherein: the power consumption control circuit further comprises a second operational amplifier and a comparison voltage input end, wherein the inverting input end of the second operational amplifier is used for inputting reference voltage; the non-inverting input end of the second operational amplifier is sequentially connected with the anodes of the diodes, and the cathodes of the diodes are connected with the cathodes of the LED lamp strings of the LED constant current circuit;

6. The backlight control circuit of claim 5, wherein: RC filter circuits are connected in series between the inverting input ends and the output ends of the first operational amplifier and the second operational amplifier.

7. The backlight control circuit of claim 1, wherein: the feedback control circuit is also provided with an optocoupler PCB101 and a voltage stabilizer UB 102; the optocoupler PCB101 comprises a light emitting diode positioned on a primary side and an optical signal converter positioned on a secondary side;

8. A television set comprising the backlight control circuit as claimed in any one of claims 1 to 7.

9. A smart tablet comprising the backlight control circuit of any one of claims 1-7.