LED drive circuit and display system

Abstract

The present application provides an LED drive circuit and a display system. The LED drive circuit comprises a first operational amplifier, a second operational amplifier, a first power transistor, and a second power transistor, wherein the first operational amplifier and the second operational amplifier are respectively used for controlling gate voltages of the first power transistor and the second power transistor. A non-inverting input end of the first operational amplifier is used for receiving a first reference voltage, an inverting input end of the first operational amplifier is connected to a source of the first power transistor, and an output end of the first operational amplifier is connected to a gate of the first power transistor; a non-inverting input end of the second operational amplifier is used for receiving a second reference voltage, an inverting input end of the second operational amplifier is connected to a source of the second power transistor, and an output end of the second operational amplifier is connected to a gate of the second power transistor; and the first power transistor and the second power transistor are used for jointly driving an external LED light-emitting unit. The present application can realize diversified and controllable regulation of an output current of the LED light-emitting unit.

Description

LED driving circuit and display system Cross-reference to related applications

[0001] This patent application claims priority to the Chinese patent application with the application number 202411339858.0 and the invention name of “LED driving circuit and display system”, which was filed on September 24, 2024, and is incorporated herein by reference in its entirety. TECHNICAL FIELD

[0002] The present application relates to the technical field of electronic circuits, in particular to an LED driving circuit and display system. BACKGROUND

[0003] LED (Light Emitting Diode) has been widely used in indicator lights, displays and lighting fields due to its advantages of high efficiency, long service life, not easy to break, high switching speed, high reliability and other advantages that traditional light sources cannot match. In actual use, multiple LED light emitting elements are usually connected in series with each other to form an LED light emitting unit, and the LED light emitting unit is driven by an LED driving circuit. SUMMARY

[0004] The purpose of the embodiments of the present application is to provide an LED driving circuit and display system.

[0005] One aspect of the present application provides an LED driving circuit. The LED driving circuit includes a first operational amplifier, a second operational amplifier, a first power tube and a second power tube, the first operational amplifier and the second operational amplifier are respectively used to control the gate voltage of the first power tube and the second power tube, wherein the non-inverting input terminal of the first operational amplifier is used to receive a first reference voltage, the inverting input terminal of the first operational amplifier is connected to the source of the first power tube, and the output terminal of the first operational amplifier is connected to the gate of the first power tube; the non-inverting input terminal of the second operational amplifier is used to receive a second reference voltage, the inverting input terminal of the second operational amplifier is connected to the source of the second power tube, and the output terminal of the second operational amplifier is connected to the gate of the second power tube; the first power tube and the second power tube are used to jointly drive an external LED light emitting unit.

[0006] Further, the LED driving circuit further includes a first resistor and a second resistor, wherein the first power tube, the first resistor and the LED light emitting unit are connected in series between a power supply voltage and ground; the second power tube, the second resistor and the LED light emitting unit are connected in series between the power supply voltage and ground.

[0007] Further, the first power tube comprises a first NMOS tube, the second power tube comprises a second NMOS tube, a drain of the first NMOS tube is connected to a negative terminal of the LED light-emitting unit, and a source of the first NMOS tube is connected to ground through the first resistor; a drain of the second NMOS tube is connected to the negative terminal of the LED light-emitting unit, and a source of the second NMOS tube is connected to ground through the second resistor.

[0008] Further, the LED driving circuit further comprises a first reference setting module, the first reference setting module is configured to generate the first reference voltage, an input end of the first reference setting module is connected to a first current setting pin, the first current setting pin is connected to ground through a first current setting resistor, and an output end of the first reference setting module is connected to a non-inverting input end of the first operational amplifier, and a voltage value of the first reference voltage is adjusted by a resistance value of the first current setting resistor.

[0009] Further, the LED driving circuit further comprises a second reference setting module, the second reference setting module is configured to generate the second reference voltage, an input end of the second reference setting module is connected to a second current setting pin, the second current setting pin is connected to ground through a second current setting resistor, and an output end of the second reference setting module is connected to a non-inverting input end of the second operational amplifier, and a voltage value of the second reference voltage is adjusted by a resistance value of the second current setting resistor.

[0010] Further, the LED driving circuit further comprises an overvoltage protection module, the overvoltage protection module is configured to provide the second reference voltage, an input end of the overvoltage protection module is connected to the power supply voltage, and an output end of the overvoltage protection module is connected to a non-inverting input end of the second operational amplifier, wherein when the power supply voltage is higher than an overvoltage protection threshold of the overvoltage protection module, the second reference voltage increases with an increase of the power supply voltage.

[0011] Further, the first power tube comprises a first PMOS tube, the second power tube comprises a second PMOS tube, a source of the first PMOS tube is connected to the power supply voltage through the first resistor, and a drain of the first PMOS tube is connected to a positive terminal of the LED light-emitting unit; a source of the second PMOS tube is connected to the power supply voltage through the second resistor, and a drain of the second PMOS tube is connected to the positive terminal of the LED light-emitting unit.

[0012] Further, the LED driving circuit further comprises a first reference setting module, the first reference setting module is configured to generate the first reference voltage, wherein an input end of the first reference setting module is connected to a first current setting pin, the first current setting pin is connected to the power supply voltage through a first current setting resistor, and an output end of the first reference setting module is connected to a non-inverting input end of the first operational amplifier, and a resistance value of the first current setting resistor is used to adjust a voltage value of the first reference voltage.

[0013] Further, the LED driving circuit further comprises a second reference setting module, the second reference setting module is configured to generate the second reference voltage, wherein an input end of the second reference setting module is connected to a second current setting pin, the second current setting pin is connected to the power supply voltage through a second current setting resistor, and an output end of the second reference setting module is connected to a non-inverting input end of the second operational amplifier, and a resistance value of the second current setting resistor is used to adjust a voltage value of the second reference voltage.

[0014] Further, the LED driving circuit further comprises an overvoltage protection module, the overvoltage protection module is configured to provide the second reference voltage, an input end of the overvoltage protection module is connected to the power supply voltage, and an output end of the overvoltage protection module is connected to a non-inverting input end of the second operational amplifier, wherein when the power supply voltage is higher than an overvoltage protection threshold of the overvoltage protection module, a difference value of the second reference voltage relative to the power supply voltage increases with an increase of the power supply voltage.

[0015] Further, the LED driving circuit further comprises a first series resistor and a second series resistor, the first series resistor is connected between an inverting input end of the first operational amplifier and the first resistor, and the second series resistor is connected between the inverting input end of the first operational amplifier and an inverting input end of the second operational amplifier.

[0016] Further, a resistance value of the first series resistor is equal to a resistance value of the second series resistor, and a resistance value of the first resistor is equal to a resistance value of the second resistor.

[0017] Further, the LED driving circuit further comprises a heat sharing resistor, the heat sharing resistor is connected between a drain of the second power transistor and the LED light emitting unit.

[0018] Another aspect of the present application provides a display system. The display system comprises an LED light emitting unit and an LED driving circuit as described above, the LED driving circuit is configured to drive the LED light emitting unit.

[0019] The LED driving circuit and display system of one or more embodiments of the present application can drive the external LED light emitting unit through the first power tube in the main path and the second power tube in the branch path, so as to more flexibly adjust the output current of the LED light emitting unit, realize diversified controllable adjustment of the output current of the LED light emitting unit, and meet the diversified requirements of users for the output current of the LED light emitting unit.

[0020] The LED driving circuit and display system of one or more embodiments of the present application can realize that the sum of the drain current of the first power tube and the drain current of the second power tube is a fixed value, so as to achieve the purpose of constant current of the output current of the LED light emitting unit.

[0021] The LED driving circuit and display system of one or more embodiments of the present application can realize that the sum of the drain current of the first power tube and the drain current of the second power tube is a fixed value, so as to achieve the purpose of constant current of the output current of the LED light emitting unit. BRIEF DESCRIPTION OF DRAWINGS

[0022] FIG. 1 is a schematic diagram of a linear constant current LED driving circuit in the related art.

[0023] FIG. 2 is a schematic diagram of the LED driving circuit of the first embodiment of the present application.

[0024] FIG. 3 is a schematic diagram of the drain current of each power tube in FIG. 2 when the voltage of the power supply gradually increases.

[0025] FIG. 4 is a schematic diagram of a specific implementation of the voltage stabilizing module, the first reference setting module and the overvoltage protection module.

[0026] FIG. 5 is a schematic diagram of the first stage input end circuit of the first operational amplifier.

[0027] FIG. 6 is a schematic diagram of the first stage input end circuit of the second operational amplifier.

[0028] FIG. 7 is a schematic diagram of the LED driving circuit of the second embodiment of the present application.

[0029] Figure 8 is a schematic diagram of the drain current on each power transistor in Figure 7 when the power supply voltage gradually increases according to an embodiment of this application.

[0030] Figure 9 is a schematic diagram of the LED driving circuit according to the third embodiment of this application. Detailed Implementation

[0031] Exemplary embodiments will now be described in detail, examples of which are illustrated in the accompanying drawings. When the following description relates to the drawings, unless otherwise indicated, the same numerals in different drawings denote the same or similar elements. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with this application. Rather, they are merely examples of apparatuses consistent with some aspects of this application as detailed in the appended claims.

[0032] Figure 1 shows a schematic diagram of a linear constant current LED driver circuit 100 in the related art. As shown in Figure 1, the linear constant current LED driver circuit 100 includes an operational amplifier (OPA) and a power transistor (HVMN). An external sampling resistor Rsense is connected between the sampling input terminal CS and ground. The non-inverting input terminal of the OPA receives a reference voltage VREF, the inverting input terminal is connected to the sampling input terminal CS to receive the sampling voltage VCS, and the output terminal is connected to the gate of the power transistor HVMN. The OPA compares the sampling voltage VCS with the reference voltage VREF and outputs a gate drive voltage V. GATE Gate drive voltage V GATE Control the gate and source voltages V of the power transistor HVMN GS It is responsible for providing the necessary current to the external LED light-emitting unit 200. The source of the power transistor HVMN is connected to the sampling resistor Rsense, and the drain is the output voltage V. DRV The negative terminal of the LED light-emitting unit 200 is connected to the negative terminal of the LED light-emitting unit 200, which is composed of multiple LED light-emitting elements connected in series. The positive terminal of the LED light-emitting unit 200 is connected to the power supply voltage V. SUPPLY .

[0033] Power supply voltage V SUPPLY It is a high voltage, the power supply voltage is V SUPPLY The internal voltage regulator module 140 can generate an internal low-voltage power supply VDD for an LDO (Low Dropout Regulator), which powers the operational amplifier OPA. The voltage value of VDD is greater than or equal to the gate drive voltage V. GATE (i.e., the gate and source voltage VGS of the power transistor HVMN). When the power transistor HVMN is a thin-gate high-voltage transistor, its gate and source voltage VGS has a withstand voltage of 5V.

[0034] When the operational amplifier OPA starts to work, the operational amplifier OPA adjusts the gate drive voltage V GATE of the power transistor HVMN through a loop when the gate drive voltage V GATE of the power transistor HVMN is greater than its threshold voltage, the power transistor HVMN is turned on, and the current flows through the LED lighting unit 200, wherein the output current I LED of the LED lighting unit 200 is a constant value.

[0035] When the sampling resistor Rsense is a fixed resistance, the output current I LED of the LED lighting unit 200 can be a constant value. When the sampling resistor Rsense is a variable resistance, the output current I LED of the LED lighting unit 200 can be variable.

[0036] However, as can be seen from the above formula, the change of the output current I LED of the LED lighting unit 200 is very limited. Therefore, it is difficult to meet the diversified needs of users for the output current I LED of the LED lighting unit 200.

[0037] In addition, in the case of achieving the output current I LED of the LED lighting unit 200, the LED driving circuit 100 also has the following problems: as the voltage value of the power supply voltage V SUPPLY increases, when the voltage value of the power supply voltage V SUPPLY is relatively high compared with the lamp voltage V LED required by the LED lighting unit 200, the voltage value of the output voltage V DRV of the LED driving circuit 100 will also gradually increase, because V DRV = V SUPPLY -V LED , at this time the power P of the power transistor HVMN = V DRV × I LED , thereby causing the power consumption of the LED driving circuit 100 to gradually increase, resulting in that the power transistor HVMN generates a lot of heat, especially when the LED driving circuit 100 is a chip-level LED driving circuit, the phenomenon of "chip overheating" is prone to occur. The peripheral PCB board where the LED driving circuit 100 is located needs to use a larger area of heat sink with higher cost to ensure that the temperature rise of the LED driving circuit 100 (especially the chip-level LED driving circuit) is within a reasonable working range.

[0038] Therefore, the present application provides an improved LED driving circuit, which can solve at least one of the technical problems existing in the related art.

[0039] The LED driving circuit and display system of the present application will be described in detail below with reference to the accompanying drawings. The features in the following embodiments and implementation can be combined with each other without conflict.

[0040] First embodiment

[0041] FIG. 2 discloses a schematic diagram of the LED driving circuit 300 of the first embodiment of the present application. As shown in FIG. 2, the LED driving circuit 300 comprises a first operational amplifier OPA1, a second operational amplifier OPA2, a first power transistor 311 and a second power transistor 312. The first operational amplifier OPA1 and the second operational amplifier OPA2 can be used to control the gate voltage of the first power transistor 311 and the second power transistor 312 respectively. The non-inverting input terminal of the first operational amplifier OPA1 can receive a first reference voltage VREF1, the inverting input terminal of the first operational amplifier OPA1 is connected to the source of the first power transistor 311, and the output terminal of the first operational amplifier OPA1 is connected to the gate of the first power transistor 311; the non-inverting input terminal of the second operational amplifier OPA2 can receive a second reference voltage VREF2, the inverting input terminal of the second operational amplifier OPA2 is connected to the source of the second power transistor 312, and the output terminal of the second operational amplifier OPA2 is connected to the gate of the second power transistor 312.

[0042] The first power transistor 311 and the second power transistor 312 can be used to jointly drive the external LED lighting unit 200, and are jointly responsible for providing the required output current I LED .

[0043] Compared with FIG. 1, the LED driving circuit 300 of the present application has a main path controlled by the first operational amplifier OPA1, and also has a branch path controlled by the second operational amplifier OPA2. The first power transistor 311 in the main path and the second power transistor 312 in the branch path can be used to jointly drive the external LED lighting unit 200, so that the output current I LED of the LED lighting unit 200 can be more flexibly adjusted, the diversified controllable adjustment of the output current I LED of the LED lighting unit 200 is realized, and the diversified needs of users for the output current I LED of the LED lighting unit 200 are met.

[0044] In some embodiments, the LED driving circuit 300 of the present application can further comprise a first resistor RS1 and a second resistor RS2. The first power transistor 311, the first resistor RS1 and the LED lighting unit 200 are connected in series between the power supply voltage V SUPPLY and the ground; the second power transistor 312, the second resistor RS2 and the LED lighting unit 200 are connected in series between the power supply voltage V SUPPLY and the ground.

[0045] In the first embodiment shown in FIG. 2, the first power tube 311 and the second power tube 312 are both NMOS (N-Metal-Oxide-Semiconductor) tubes, i.e., the first power tube 311 includes a first NMOS tube HVMN1, and the second power tube 312 includes a second NMOS tube HVMN2. The LED driving circuit 300 is connected between the negative terminal of the LED light-emitting unit 200 and the ground, and the LED driving circuit 300 adopts low-side driving.

[0046] As shown in FIG. 2, the drain of the first NMOS tube HVMN1 is connected to the negative terminal of the LED light-emitting unit 200, the positive terminal of the LED light-emitting unit 200 is connected to the power supply voltage V SUPPLY , and the source of the first NMOS tube HVMN1 is connected to the ground through the first resistor RS1. The drain of the second NMOS tube HVMN2 is connected to the negative terminal of the LED light-emitting unit 200, and the source of the second NMOS tube HVMN2 is connected to the ground through the second resistor RS2.

[0047] Therefore, the drain current of the first NMOS tube HVMN1 can be controlled by the first resistor RS1, and the drain current of the second NMOS tube HVMN2 can be controlled by the second resistor RS2, and the first resistor RS1 and the second resistor RS2 can play a role of current limiting.

[0048] In some embodiments, the LED driving circuit 300 of the present application can further include a voltage stabilizing module 340. The voltage stabilizing module 340 is connected to the power supply voltage V SUPPLY , the power supply voltage V SUPPLY is high voltage, and the voltage stabilizing module 340 can convert the power supply voltage V SUPPLY into an internal power supply voltage VDD required by the LED driving circuit 300, the internal power supply voltage VDD is low voltage, and the internal power supply voltage VDD is supplied to the power supply end of the first operational amplifier OPA1 and the second operational amplifier OPA2.

[0049] In some embodiments, the LED driving circuit 300 of the present application can further include a first reference setting module 321, which can be used to generate a first reference voltage VREF1. Wherein, the input end of the first reference setting module 321 is connected to a first current setting pin SET1, and the first current setting pin SET1 is connected to the ground through an externally connected first current setting resistor Rsense1, and the output end of the first reference setting module 321 is connected to the non-inverting input end of the first operational amplifier OPA1.

[0050] The first reference voltage VREF1 varying with the first current setting resistor Rsense1 can be generated by the first current setting resistor Rsense1 externally connected. It should be noted that the upper and lower limits of the voltage range of the first reference voltage VREF1 are set internally to prevent the voltage value of the first reference voltage VREF1 from being too low or too high when the first current setting resistor Rsense1 externally connected is short-circuited or open-circuited, so that the output current controlled by the first operational amplifier OPA1 is out of control. Therefore, the voltage value of the first reference voltage VREF1 can be adjusted by the resistance value of the first current setting resistor Rsense1 externally connected, so that the drain current I D1 .

[0051] In some embodiments, the LED driving circuit 300 of the present application can further comprise an overvoltage protection module 330, which can be used to provide a second reference voltage VREF2. The input terminal of the overvoltage protection module 330 is connected to the power supply voltage V SUPPLY , and the output terminal of the overvoltage protection module 330 is connected to the non-inverting input terminal of the second operational amplifier OPA2. The overvoltage protection module 330 can provide a corresponding second reference voltage VREF2 according to the actual application requirements. In one embodiment, the overvoltage protection module 330 can provide a second reference voltage VREF2 varying with the power supply voltage V SUPPLY , so as to adjust the drain current I D2 .

[0052] Since the output current I LED of the LED lighting unit 200 is equal to the sum of the drain current I D1 of the first power transistor 311 and the drain current I D2 of the second power transistor 312, by adjusting the first reference voltage VREF1 and the second reference voltage VREF2, the drain current I D1 of the first power transistor 311 and the drain current I D2 of the second power transistor 312 can be adjusted respectively, so as to control the output current I LED of the LED lighting unit 200, and the output current I LED of the LED lighting unit 200 can be diversified.

[0053] When the output current I LED of the LED lighting unit 200 is constant, when the power supply voltage V SUPPLY is higher than the overvoltage protection threshold of the overvoltage protection module 330, the second reference voltage VREF2 provided by the overvoltage protection module 330 can vary with the power supply voltage V SUPPLYincreases, so that the drain current I D2 of the second power tube 312 gradually increases with the increase of the power supply voltage V SUPPLY . Since the LED light unit 200 outputs the current I LED in constant current, when the drain current I D2 of the second power tube 312 gradually increases with the increase of the power supply voltage V SUPPLY , the drain current of the first power tube 311 can gradually decrease, so that the load of the first power tube 311 can be reduced and the power consumption of the first power tube 311 can be lowered.

[0054] In some embodiments, the LED driving circuit 300 of the present application can further include a first series resistance RA and a second series resistance RB. The first series resistance RA is connected between the inverting input terminal of the first operational amplifier OPA1 and the first resistance RS1; and the second series resistance RB is connected between the inverting input terminal INN1 of the first operational amplifier OPA1 and the inverting input terminal INN2 of the second operational amplifier OPA2.

[0055] The following will give a typical application of the output current I LED in constant current of the LED driving circuit 300 of the present application.

[0056] The resistance value of the first series resistance RA and the resistance value of the second series resistance RB are set to be equal, and the resistance value of the first resistance RS1 and the resistance value of the second resistance RS2 are set to be equal. The A node voltage VA and the B node voltage VB, the voltage V INN2 of the inverting input terminal INN2 of the second operational amplifier OPA2, the drain current I D1 of the first power tube 311 and the drain current I D2 of the second power tube 312 are respectively as follows: VA=I D1 ×RS1 VB=V INN2 =VREF2=I D2 ×RS2

[0057] Since the sum of the node currents of the negative phase input terminal of the first operational amplifier OPA1 is 0, the current flowing through the first series resistance RA and the current flowing through the second series resistance RB are equal, and the voltage of the inverting input terminal INN1 of the first operational amplifier OPA1 is V INN1 , so that the following can be obtained:

[0058] When R A =R B , the above formula can be transformed as follows: VA+VB=2×V INN1 =2×VREF1

[0059] Therefore, it can be further obtained that I D1×RS1+I D2 ×RS2=2×VREF1

[0060] Since the output current I LED of the LED light unit 200 is D1 +I D2 , when RS1=RS2=RS is set, RS is a fixed resistance value, and the following can be obtained: LED =I D1 +I D2 =2×VREF1 / RS

[0061] As shown in FIG. 2, when the first current setting resistance Rsense1 is set to a certain fixed value, the voltage value of the first reference setting voltage VREF1 generated by the first reference setting module 321 is also a fixed value. Thus, the purpose of constant current of the output current I LED of the LED light unit 200 can be achieved.

[0062] The LED driving module 300 of the present application can achieve the purpose of constant current of the output current I D1 of the LED light unit 200 by setting the first series resistance RA and the second series resistance RB, so that the sum of the drain current I D2 of the second power tube 312 is a fixed value. LED

[0063] In some embodiments, the LED driving circuit 300 of the present application can further include a heat sharing resistance Rshare connected between the drain of the second power tube 312 and the LED light unit 200.

[0064] The following will further combine FIG. 3 to give an application of the LED driving circuit 300 of the present application, which can achieve the purpose of constant current of the output current I LED and solve the problem of chip overheating.

[0065] FIG. 3 discloses a schematic diagram of the drain current of each power tube in FIG. 2 when the voltage of the power supply voltage V SUPPLY gradually increases. As shown in FIG. 3, the initial value of the second reference voltage VREF2 is zero. When the overvoltage protection module 330 finds that the power supply voltage V SUPPLY is higher than the overvoltage protection threshold of the overvoltage protection module 330, the voltage value of the second reference voltage VREF2 will gradually increase, so that the drain current I D2 of the second power tube 312 gradually increases. Since the output current I LED of the LED light unit 200 is fixed, at this time, the drain current I D1 ​will gradually decrease.

[0066] It is worth noting that the I D1 +I D2 =2×VREF1 / RS, it can be found that the maximum value of the drain current I D1 of the first power tube 311 and the maximum value of the drain current I D2 of the second power tube 312 will not exceed 2×VREF1 / RS, which means that VREF2 cannot be higher than 2×VREF1.

[0067] When the voltage value of the power supply voltage V SUPPLY gradually increases, the drain voltage V DRV1 of the first power tube 311 gradually increases, but the drain current I D1 on the first power tube 311 gradually decreases, so the power consumption of the first power tube 311 can be guaranteed within a reasonable range.

[0068] The drain current I D2 of the second power tube 312 gradually increases under the influence of the second reference voltage VREF2, but the voltage value of the drain voltage V DRV2 gradually decreases with the increase of the pressure drop on the heat sharing resistance Rshare, because V DRV2 =V DRV1 -V Rshare =V DRV1 -Rshare×I D2 , so the power consumption of the second power tube 312 can also be guaranteed within a reasonable range. The power consumption on the heat sharing resistance Rshare is: P Rshare =Rshare×I D2 2 .

[0069] If the losses of the first operational amplifier OPA1, the second operational amplifier OPA2, and the voltage stabilizing module 340 are ignored, the main power consumption on the LED driving circuit 300 at this time is divided into three parts: the power consumption P1 of the first power tube 311, the power consumption P2 of the second power tube 312, and the power consumption P Rshare on the heat sharing resistance Rshare. The total power consumption P total on the LED driving circuit 300 is as follows: P total =P1+P2+P Rshare =V DRV1 ×I D1 +V DRV2 ×I D2 +Rshare×I D2 2

[0070] If the LED driver circuit 300 is integrated into the chip, and a thermally shared resistor Rshare of appropriate resistance value is placed outside the chip, some power consumption can be shared, reducing the power consumption P1+P2 that falls within the chip, while also ensuring the output current I on the external LED light-emitting unit 200. LED Constant current.

[0071] As can be seen from Figure 3, in this application, in order to ensure the output current I of the LED light-emitting unit 200... LED At power supply voltage V SUPPLY Constant current under different voltage values, with the power supply voltage V SUPPLY As the current gradually increases, the drain current I of the first power transistor 311... D1 It will gradually decrease from 2×VREF1 / RS, and the minimum value can approach zero current, while the drain current I of the second power transistor 312 D2 The maximum value of will be equal to 2×VREF1 / RS, which means that the maximum value of VREF2 cannot be higher than 2×VREF1.

[0072] The LED driver circuit 300 of this application is connected to an external heat-sharing circuit Rshare via the drain of the second power transistor 312 controlled by the second operational amplifier OPA2. When the power supply voltage V SUPPLY When the voltage is higher than a certain value, the drain current I on the second power transistor 312 D2 The drain current I on the first power transistor 311 gradually increases. D1 As the voltage gradually decreases, the main power consumption of the LED driver circuit 300 consists of three parts: the power consumption of the first power transistor 311, the power consumption of the second power transistor 312, and the power consumption on the external thermally shared resistor Rshare. With the power supply voltage V... SUPPLY The increased temperature of the LED driver circuit (especially the LED driver integrated into the chip) is largely absorbed by the thermally shared resistor Rshare, thus reducing the internal power consumption of the LED driver circuit 300 and ensuring its normal operation. Meanwhile, at the power supply voltage V... SUPPLY As the current gradually increases, the output current I on the external LED light-emitting unit 200 can also be controlled. LED Maintain constant current.

[0073] Figure 4 illustrates a specific implementation diagram of a voltage regulator module 340, a first reference setting module 321, and an overvoltage protection module 330 according to an embodiment of this application. As shown in Figure 4, the voltage regulator module 340 includes an operational amplifier OP3, a Zener diode HVMP, and voltage divider resistors Rdiv3 and Rdiv4. Power supply voltage V SUPPLY The low-voltage power supply VDD is generated through operational amplifier OP3, Zener diode HVMP, and voltage divider resistors Rdiv3 and Rdiv4.

[0074] The first reference setting module 321 includes a bandgap reference module 3210 and resistors Rdiv5 and Rdiv6. The bandgap reference VBG generated by the bandgap reference module 3210 is divided by resistors Rdiv5 and Rdiv6 and an external first current setting resistor Rsense1 to generate a first reference voltage VREF1.

[0075] The overvoltage protection module 330 includes a transconductance operational amplifier OP4 and resistors Rdiv1, Rdiv2, and Rleak. Power supply voltage V SUPPLY The power supply voltage V is obtained by voltage division using two resistors, Rdiv1 and Rdiv2. SUPPLY When the voltage value of the voltage divider signal VIN_DIV exceeds the overvoltage protection threshold of the overvoltage protection module 330 (which can be the bandgap reference voltage VBG or a voltage divider of the bandgap reference voltage VBG), the output of the transconductance operational amplifier OP4 begins to generate a leakage current I. leak And the leakage current I leak It changes linearly with the difference between the voltage divider signal VIN_DIV and the bandgap reference voltage VBG. Leakage current I leak The formula is as follows: I leak = gm × (VIN_DIV - VBG) where gm is the transconductance of the transconductance operational amplifier OP4.

[0076] The second reference voltage VREF2 is transmitted through the leakage current I. leak The voltage drop generated by resistor Rleak is used to obtain the second reference voltage VREF2. The formula for VREF2 is as follows: VREF2 = I leak ×Rleak=gm×(VIN_DIV-VBG)×Rleak

[0077] It can be observed that the second reference voltage VREF2 also changes linearly with the difference between the voltage divider signal VIN_DIV and the bandgap reference voltage VBG.

[0078] To ensure the output current I of the LED light-emitting unit 200 LED At power supply voltage V SUPPLY The voltage value of the second reference voltage VREF2 shall not exceed 2×VREF1, and the constant current shall be maintained under different voltage values.

[0079] Figure 5 illustrates a schematic diagram of the first stage input circuit of the first operational amplifier OPA1 according to an embodiment of this application, and Figure 6 illustrates a schematic diagram of the first stage input circuit of the second operational amplifier OPA2 according to an embodiment of this application. As shown in Figures 5 and 6, both the first operational amplifier OPA1 and the second operational amplifier OPA2 adopt a differential pair input architecture.

[0080] The input differential pair of the first operational amplifier OPA1 includes a PMOS transistor mp1 and a PMOS transistor mp2. The inverting input terminal of the first operational amplifier OPA1 includes the PMOS transistor mp1, and the non-inverting input terminal of the first operational amplifier OPA1 includes the PMOS transistor mp2.

[0081] It is worth noting that if the second reference voltage VREF2 output by the overvoltage protection module 330 changes with the power supply voltage V SUPPLY When the voltage value of the second reference voltage VREF2 is greater than twice the voltage value of the first reference voltage VREF1, i.e., VREF2>2×VREF1, as shown in FIG. 4, a clamping voltage whose voltage value is twice the voltage value of the first reference voltage VREF1 (i.e., 2×VREF1) can be generated by the first reference setting module 321. As shown in FIG. 6, the input differential pair of the second operational amplifier OPA2 can adopt a three-input differential pair, and the non-inverting input terminal of the input differential pair has a PMOS transistor mp4 and a PMOS transistor mp5. The input terminal of the PMOS transistor mp4 is connected to the second reference voltage VREF2, and the input terminal of the PMOS transistor mp5 is connected to 2×VREF1. In combination with FIG. 2, during normal operation, the size of the second reference voltage VREF2 at the non-inverting input terminal INN2 and the non-inverting input terminal of the second operational amplifier OPA2 is determined. When VREF2>2×VREF1, the PMOS transistor mp5 can be clamped to 2×VREF1, and at this time, the maximum voltage at the inverting input terminal INN2 of the operational amplifier will not exceed 2×VREF1.

[0082] The first reference voltage VREF1 and the second reference voltage VREF2 are sent to the input terminals of the first operational amplifier OPA1 and the second operational amplifier OPA2, respectively, to affect the output. It can be understood that the generation circuit of the second reference voltage VREF2 is not limited to the implementation circuit architecture shown in FIG. 6, and other circuits can also be used, as long as 0≤VREF2≤2×VREF1 is satisfied.

[0083] Second embodiment

[0084] FIG. 7 discloses a schematic diagram of an LED driving circuit 400 according to the second embodiment of the present application. As shown in FIG. 7, different from the LED driving circuit 300 of the first embodiment shown in FIG. 2, in the LED driving circuit 400 of the second embodiment, the first power transistor 311 and the second power transistor 312 both adopt PMOS transistors, i.e., the first power transistor 311 includes a first PMOS transistor HVMP1, and the second power transistor 312 includes a second PMOS transistor HVMP2. The LED driving circuit 400 is connected between the positive terminal of the LED light-emitting unit 200 and the positive terminal of the power supply voltage V SUPPLY The LED driving circuit 400 adopts high-side driving.

[0085] The source of the first PMOS transistor HVMP1 is connected to the power supply voltage V through the first resistor RS1. SUPPLY The drain of the first PMOS transistor HVMP1 is connected to the positive terminal of the LED light-emitting unit 200. The source of the second PMOS transistor HVMP2 is connected to the power supply voltage V through the second resistor RS2. SUPPLY The drain of the second PMOS transistor HVMP2 is connected to the positive terminal of the LED light-emitting unit 200.

[0086] Furthermore, since both the first power transistor 311 and the second power transistor 312 are PMOS transistors, in the LED driving circuit 400 of the second embodiment, the power supply terminals of the first operational amplifier OPA1 and the second operational amplifier OPA2 are connected to the power supply voltage V. SUPPLY Therefore, a voltage regulator module 340 is needed to generate a voltage relative to the power supply voltage V. SUPPLY The floating ground power supply voltage is supplied to the other power supply terminal of the first op-amp OPA1 and the second op-amp OPA2. The floating ground power supply voltage is equal to the power supply voltage V. SUPPLY Subtract the predetermined voltage value, for example, the floating ground power supply voltage equals V. SUPPLY -5V, thereby ensuring the source and gate voltages V of the first power transistor 311 and the second power transistor 312. SG ≤5V. Similarly, when the first power transistor 311 is a thin-gate high-voltage transistor, its source and gate voltages V SG Its withstand voltage is 5V.

[0087] Similar to the LED driving circuit 300 of the first embodiment shown in FIG2, the LED driving circuit 400 of the second embodiment may also include a first reference setting module 321. The first reference setting module 321 is used to generate a first reference voltage VREF1. The input terminal of the first reference setting module 321 is connected to the first current setting pin SET1, and the output terminal of the first reference setting module 321 is connected to the non-inverting input terminal of the first operational amplifier OPA1.

[0088] However, unlike the LED driver circuit 300 of the first embodiment shown in Figure 2, in the LED driver circuit 400 of the second embodiment, the first current setting pin SET1 is connected to the power supply voltage V through an external first current setting resistor Rsense1. SUPPLY .

[0089] Similarly, the voltage value of the first reference voltage VREF1 can be adjusted by changing the resistance value of the external first current setting resistor Rsense1, thereby changing the drain current I of the first power transistor 311. D1 .

[0090] Similar to the LED driving circuit 300 of the first embodiment shown in FIG2, the LED driving circuit 400 of the second embodiment may also include an overvoltage protection module 330. The overvoltage protection module 330 is used to provide a second reference voltage VREF2, and the input terminal of the overvoltage protection module 330 is connected to the power supply voltage V. SUPPLY The output of the overvoltage protection module 330 is connected to the non-inverting input of the second operational amplifier OPA2.

[0091] Similarly, the overvoltage protection module 330 can provide a second reference voltage VREF2 that varies with the power supply voltage V. SUPPLY The drain current I of the second power transistor 312 can be adjusted by changing the voltage. D2 .

[0092] However, unlike the LED driver circuit 300 of the first embodiment shown in FIG2, in the LED driver circuit 400 of the second embodiment, the output current I of the LED driver circuit 400 is... LED In constant current applications, when the power supply voltage V SUPPLY When the voltage exceeds the overvoltage protection threshold of the overvoltage protection module 330, the second reference voltage VREF2 provided by the overvoltage protection module 330 is relative to the power supply voltage V. SUPPLY The difference varies with the power supply voltage V SUPPLY It increases as the value increases.

[0093] Figure 8 illustrates an embodiment of this application when the power supply voltage V SUPPLY As the voltage value gradually increases, the drain current on each power transistor in Figure 7 is shown in the schematic diagram. As shown in Figure 8, in the LED driver circuit 400 of the second embodiment, when the power supply voltage V... SUPPLY As the voltage value gradually increases, the first reference voltage VREF1 of the first operational amplifier OPA1 and the second reference voltage VREF2 of the second operational amplifier OPA2 are respectively relative to the power supply voltage V. SUPPLY The difference. Therefore, the output current I on the LED light-emitting unit 200. LED = 2 × ΔVREF1 / RS, while the voltage value of VREF2 needs to be guaranteed to be: V SUPPLY -2×△VREF1≤V SUPPLY -△VREF2≤V SUPPLY In other words, the second reference voltage VREF2 is relative to the supply voltage V. SUPPLY The difference shall not exceed the first reference voltage VREF1 relative to the supply voltage V. SUPPLY Twice the difference.

[0094] The LED driving circuit 400 of the second embodiment has other same parts as the LED driving circuit 300 of the first embodiment shown in FIG. 2, which will not be repeated here.

[0095] Third embodiment

[0096] FIG. 9 discloses a schematic diagram of the LED driving circuit 500 of the third embodiment of the present application. As shown in FIG. 9, different from the LED driving circuit 300 of the first embodiment shown in FIG. 2, the LED driving circuit 500 of the third embodiment replaces the overvoltage protection module 330 in the LED driving circuit 300 of the first embodiment shown in FIG. 2 by adding a second reference setting module 322.

[0097] The second reference setting module 322 can be used to generate a second reference voltage VREF2, wherein the input end of the second reference setting module 322 is connected to a second current setting pin SET2, the second current setting pin SET2 is connected to the ground through an externally connected second current setting resistor Rsense2, and the output end of the second reference setting module 322 is connected to the non-inverting input end of a second operational amplifier OP A2.

[0098] The voltage value of the second reference voltage VREF2 can be adjusted by the resistance value of the externally connected second current setting resistor Rsense2, so that the drain current I D2 of the second power tube 312 can be changed.

[0099] The LED driving circuit 500 of the third embodiment has other same parts as the LED driving circuit 300 of the first embodiment shown in FIG. 2, which will not be repeated here.

[0100] The LED driving circuit 300 / 400 / 500 of one or more embodiments of the present application can flexibly adjust the output current I D1 of the external LED lighting unit by controlling the drain current I D2 of the first power tube 311 and the drain current I LED of the second power tube 312, realize diversified controllable adjustment of the output current I LED , and meet the diversified needs of users for the output current I LED .

[0101] The LED driving circuit 300 / 400 / 500 of one or more embodiments of the present application can additionally connect a heat sharing resistor Rshare in parallel. When the power supply voltage V SUPPLY is high, the heat sharing resistor Rshare can be used to share the power consumption, which can effectively improve the heat dissipation performance, reduce the cost, and better meet the customer needs.

[0102] The application also provides a display system. The display system comprises the LED light emitting unit 200 and the LED driving circuit 300 / 400 / 500 as described in the above embodiments, and the LED driving circuit 300 / 400 / 500 can be used to drive the LED light emitting unit 200.

[0103] The display system of the application can have the similar beneficial technical effects as the LED driving circuit 300 / 400 / 500 described above, and thus will not be described herein.

[0104] The LED driving circuit and the display system provided by the embodiments of the application are described in detail above. The LED driving circuit and the display system of the embodiments of the application are described by applying specific examples in this paper, and the above embodiment descriptions are only used to help understand the core idea of the application and not to limit the application. It should be pointed out that, for those skilled in the art, without departing from the spirit and principles of the application, some improvements and modifications can be made to the application, and these improvements and modifications should also fall within the protection scope of the appended claims of the application.

Claims

1. An LED driving circuit, characterized by, The first operational amplifier, the second operational amplifier, the first power tube and the second power tube, The first operational amplifier and the second operational amplifier are respectively used for controlling the gate voltage of the first power tube and the second power tube, wherein the non-inverting input terminal of the first operational amplifier is used for receiving a first reference voltage, the inverting input terminal of the first operational amplifier is connected to the source electrode of the first power tube, and the output terminal of the first operational amplifier is connected to the gate electrode of the first power tube; the non-inverting input terminal of the second operational amplifier is used for receiving a second reference voltage, the inverting input terminal of the second operational amplifier is connected to the source electrode of the second power tube, and the output terminal of the second operational amplifier is connected to the gate electrode of the second power tube. The first power tube and the second power tube are used for jointly driving an external LED light-emitting unit.

2. The LED driving circuit of claim 1, wherein, The first resistance and the second resistance are further included, wherein The first power tube, the first resistance and the LED light-emitting unit are connected in series between a power supply voltage and the ground; The second power tube, the second resistance and the LED light-emitting unit are connected in series between the power supply voltage and the ground.

3. The LED driving circuit of claim 2, wherein, The first power tube includes a first NMOS tube, and the second power tube includes a second NMOS tube, The drain electrode of the first NMOS tube is connected to the negative terminal of the LED light-emitting unit, and the source electrode of the first NMOS tube is connected to the ground through the first resistance; The drain electrode of the second NMOS tube is connected to the negative terminal of the LED light-emitting unit, and the source electrode of the second NMOS tube is connected to the ground through the second resistance.

4. The LED driving circuit of claim 3, wherein, A first reference setting module is further included, and the first reference setting module is used for generating the first reference voltage, wherein The input terminal of the first reference setting module is connected to a first current setting pin, the first current setting pin is connected to the ground through a first current setting resistance, the output terminal of the first reference setting module is connected to the non-inverting input terminal of the first operational amplifier, and the voltage value of the first reference voltage is adjusted through the resistance value of the first current setting resistance.

5. The LED driving circuit of claim 3, wherein, A second reference setting module is further included, and the second reference setting module is used for generating the second reference voltage, wherein The input terminal of the second reference setting module is connected to a second current setting pin, the second current setting pin is connected to the ground through a second current setting resistance, the output terminal of the second reference setting module is connected to the non-inverting input terminal of the second operational amplifier, and the voltage value of the second reference voltage is adjusted through the resistance value of the second current setting resistance.

6. The LED driving circuit of claim 3, wherein, An overvoltage protection module is further included, the overvoltage protection module is used for providing the second reference voltage, the input terminal of the overvoltage protection module is connected to the power supply voltage, and the output terminal of the overvoltage protection module is connected to the non-inverting input terminal of the second operational amplifier, wherein When the power supply voltage is higher than the overvoltage protection threshold of the overvoltage protection module, the second reference voltage increases with the increase of the power supply voltage.

7. The LED driving circuit of claim 2, wherein, The first power tube includes a first PMOS tube, and the second power tube includes a second PMOS tube, The source of the first PMOS tube is connected to the power supply voltage through the first resistor, and the drain of the first PMOS tube is connected to the positive terminal of the LED light unit. The source of the second PMOS tube is connected to the power supply voltage through the second resistor, and the drain of the second PMOS tube is connected to the positive terminal of the LED light unit.

8. The LED driving circuit of claim 7, wherein, Further comprising a first reference setting module, the first reference setting module is used to generate the first reference voltage, wherein, The input end of the first reference setting module is connected to a first current setting pin, and the first current setting pin is connected to the power supply voltage through a first current setting resistor, and the output end of the first reference setting module is connected to the non-inverting input end of the first operational amplifier, and the voltage value of the first reference voltage is adjusted by the resistance value of the first current setting resistor.

9. The LED driving circuit of claim 7, wherein, Further comprising a second reference setting module, the second reference setting module is used to generate the second reference voltage, wherein, The input end of the second reference setting module is connected to a second current setting pin, and the second current setting pin is connected to the power supply voltage through a second current setting resistor, and the output end of the second reference setting module is connected to the non-inverting input end of the second operational amplifier, and the voltage value of the second reference voltage is adjusted by the resistance value of the second current setting resistor.

10. The LED driving circuit of claim 7, wherein, Further comprising an overvoltage protection module, the overvoltage protection module is used to provide the second reference voltage, the input end of the overvoltage protection module is connected to the power supply voltage, and the output end of the overvoltage protection module is connected to the non-inverting input end of the second operational amplifier, wherein, When the power supply voltage is higher than the overvoltage protection threshold of the overvoltage protection module, the difference between the second reference voltage and the power supply voltage increases with the increase of the power supply voltage.

11. The LED driving circuit of any one of claims 2 to 10, wherein, Further comprising a first series resistor and a second series resistor, The first series resistor is connected between the inverting input end of the first operational amplifier and the first resistor. The second series resistor is connected between the inverting input end of the first operational amplifier and the inverting input end of the second operational amplifier.

12. The LED driving circuit of claim 11, wherein, The resistance value of the first series resistor is equal to the resistance value of the second series resistor, and the resistance value of the first resistor is equal to the resistance value of the second resistor.

13. The LED driving circuit of any one of claims 1 to 12, wherein, Further comprising a heat sharing resistor, the heat sharing resistor is connected between the drain of the second power tube and the LED light unit.

14. A display system characterized by, An LED light unit and an LED driving circuit according to any one of claims 1 to 13 are included, and the LED driving circuit is used to drive the LED light unit.

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