LED drive controller and system

Abstract

The present application discloses an LED drive controller and system, wherein the LED drive controller includes a zero-crossing detection circuit, which detects the inductor current in the drive system to generate a mode control signal and a zero-crossing detection signal; a reference generation circuit, which generates a peak reference voltage and an average reference voltage according to a dimming signal; a constant current control circuit, which linearly compensates the current sampling signal according to the mode control signal and the drive signal to generate a compensation voltage, and generates a conduction control signal according to the compensation voltage, the zero-crossing detection signal, the mode control signal, the drive signal and the average reference voltage; a drive circuit, which generates a drive signal according to the conduction control signal and the shutdown control signal, and the drive signal is used to control a power switch. The present application performs dimming through a hysteresis-like control method, and will not cause a long period of inductor current-free state, and can keep the output current constant, achieving a better screen flicker coefficient and current ripple rate.

Description

Technical Field

[0001] The present invention relates to the field of LED driving technology, and in particular to an LED driving controller and system. Background Art

[0002] LED (Light Emitting Diode) has the characteristics of energy saving, environmental protection, high efficiency and long life, and is widely used in lighting, display and other fields. In order to obtain better display visual effects, the accuracy requirements for LED dimming and color adjustment are becoming higher and higher. Because the forward voltage drop of LED is affected by the discrete process, the constant voltage drive method may cause differences in the brightness of the LED, so the constant current drive method is generally used to drive the LED, and the brightness of the LED is determined by the average current passing through itself.

[0003] In the phase-cut dimming method currently used, the dimming control pin inputs a low-frequency (200Hz-2kHz) PWM1 signal; an internal high-frequency (200kHz) PWM2 signal controls the power tube switch to achieve constant current. When PWM1 is low, the internal drive is turned off and the inductor current decreases. When PWM1 is high, the internal PWM2 signal controls the drive switch to work; therefore, when the dimming operation is performed and the brightness of the LED becomes weaker, when the PWM1 duty cycle gradually decreases, the PWM1 signal will be low for a longer time, the inductor current will drop to 0, and the maintenance time will become longer and longer, which will cause the output current to slowly decrease, resulting in a larger output ripple, and its screen flicker coefficient will exceed the standard.

[0004] As the lighting market's demand for health and intelligence continues to increase, smart lighting has become the future development direction. Generally, a stable constant current is provided to achieve the required LED luminous intensity and dimming accuracy. Therefore, providing an LED driver controller that can control the main circuit to output a stable current is extremely important for the development of LEDs. Summary of the invention

[0005] In view of the above problems, the object of the present invention is to provide an LED drive controller and an LED drive system to meet the requirements of screen flicker coefficient and achieve the purpose of deep dimming and color adjustment.

[0006] According to one aspect of the present invention, there is provided an LED driving controller, comprising:

[0007] A zero-crossing detection circuit detects the inductor current in the drive system to generate a mode control signal and a zero-crossing detection signal;

[0008] A reference generation circuit generates a peak reference voltage and an average reference voltage according to a dimming signal;

[0009] a constant current control circuit, which performs linear compensation on the current sampling signal according to the mode control signal and the drive signal to generate a compensation voltage, and generates a conduction control signal according to the compensation voltage, the zero-crossing detection signal, the mode control signal, the drive signal and the average value reference voltage;

[0010] The driving circuit generates a driving signal according to the on-control signal and the off-control signal, wherein the driving signal is used to control the power switch.

[0011] Optionally, the constant current control circuit further generates the shutdown control signal based on the compensation voltage and the peak reference voltage.

[0012] Optionally, the current sampling signal represents a current flowing through a power switch in the drive system.

[0013] Optionally, when the mode control signal is at a valid level, the inductor in the drive system is in a discontinuous mode; when the mode control signal is at an invalid level, the inductor in the drive system is in a continuous mode.

[0014] Optionally, the constant current control circuit includes:

[0015] The compensation module provides different compensation amounts according to the working mode of the inductor in the driving system, and generates the compensation voltage according to the current sampling signal and the corresponding compensation amount.

[0016] Optionally, the compensation amount provided by the compensation module when the inductor is in a continuous mode is smaller than the compensation amount provided when the inductor is in a discontinuous mode.

[0017] Optionally, the compensation module is used to obtain a first current sampling signal and a second current sampling signal of the current sampling signal at different times according to the driving signal, and generate a compensation current according to the first current sampling signal and the second current sampling signal.

[0018] Optionally, the compensation current is applied to resistors with different equivalent resistance values ​​according to a working mode of the inductor in the drive system to obtain different compensation amounts, and the compensation amount is superimposed on the current sampling signal to generate the compensation voltage.

[0019] Optionally, the compensation module includes:

[0020] a logic processor, receiving the driving signal, and generating a first pulse signal after a rising edge of the driving signal is delayed for a first time, and generating a second pulse signal after a falling edge of the first pulse signal is delayed for a second time, wherein the second pulse signal is generated before the falling edge of the driving signal arrives;

[0021] a first sampling and holding unit connected to the logic processor, sampling and holding the current sampling signal within the pulse time of the first pulse signal to generate the first current sampling signal;

[0022] a second sampling and holding unit connected to the logic processor, sampling and holding the current sampling signal within the pulse time of the second pulse signal to generate the second current sampling signal;

[0023] A first transconductance amplifier, wherein a first input terminal receives the first current sampling signal, a second input terminal receives the second current sampling signal, and an output terminal provides the compensation current;

[0024] A first compensation resistor, a first end of which receives the current sampling signal, and a second end of which is connected to the output end of the first transconductance amplifier;

[0025] A second compensation resistor, a first end of which receives the current sampling signal; and

[0026] The first switch has a first end connected to the second end of the second compensation resistor, a second end connected to the second end of the first compensation resistor, and a control end receiving the mode control signal.

[0027] Optionally, the constant current control circuit further includes a conduction control module, including:

[0028] A reference voltage generating unit, providing a reference voltage;

[0029] a simulation unit, which selects one of the compensation voltage, the ground voltage, and the reference voltage as the simulation voltage at different time periods in the entire control cycle according to the level states of the drive signal and the zero-crossing detection signal; and

[0030] A conduction control unit generates the conduction control signal according to the analog voltage, the average value reference voltage and the driving signal.

[0031] Optionally, the simulation unit includes:

[0032] A second switch, a first end receiving the compensation voltage, and a control end receiving the driving signal;

[0033] A third switch, a first end of which is grounded and a control end of which receives the zero-crossing detection signal;

[0034] A NAND gate, a first end of which receives the driving signal, and a second end of which receives the zero-crossing detection signal;

[0035] a fourth switch, wherein a first end receives the reference voltage, and a control end is connected to the output end of the NAND gate,

[0036] The second end of the second switch is connected to the second end of the third switch and the second end of the fourth switch to output the analog voltage.

[0037] Optionally, when the inductor is in a continuous mode, the reference voltage generated by the reference voltage generating unit is the average value reference voltage; when the inductor is in a discontinuous mode, the reference voltage is half of the peak voltage of the compensation voltage.

[0038] Optionally, the reference voltage generating unit includes:

[0039] a third sampling and holding unit, sampling and holding the peak value of the compensation voltage and outputting the peak voltage;

[0040] A voltage processing unit, connected to the third sampling and holding unit, generating a half peak voltage;

[0041] a fifth switch, a first end of which is connected to the voltage processing unit, and a control end of which receives a mode control signal;

[0042] a sixth switch, having a first end receiving the average value reference voltage, a control end receiving a mode control signal, a second end connected to the second end of the fifth switch and outputting the reference voltage; and

[0043] a first capacitor, a first end of which is connected to the second end of the sixth switch and the second end of the fifth switch, and a second end of which is grounded;

[0044] Wherein, when the mode control signal is in a first level state, the fifth switch is turned on, and when the mode control signal is in a second level state, the sixth switch is turned on.

[0045] Optionally, the conduction control unit includes:

[0046] A second transconductance amplifier, a first terminal of which receives the average value reference voltage, and a second terminal of which receives the analog voltage;

[0047] A second capacitor, a first end of which is connected to the output end of the second transconductance amplifier, and a second end of which is grounded;

[0048] A third transconductance amplifier, having a first end connected to the output end of the second transconductance amplifier and a second end grounded;

[0049] A third capacitor, a first end of which is connected to the output end of the third transconductance amplifier, and a second end of which is grounded;

[0050] a seventh switch, a first end of which is connected to the first end of the third capacitor, a second end of which is connected to the second end of the third capacitor, and a control end of which receives the driving signal;

[0051] The first comparator has a first terminal connected to the output terminal of the third transconductance amplifier, a second terminal receiving a set threshold voltage, and an output terminal outputting the conduction control signal.

[0052] Optionally, the reference voltage generating unit obtains an intermediate voltage according to the average value reference voltage, and generates the reference voltage according to the average value reference voltage and the intermediate voltage.

[0053] Optionally, the reference voltage generating unit includes:

[0054] A scaling unit, performing scaling processing on the average value reference voltage;

[0055] A subtraction unit connected to the scaling unit, performing subtraction processing on the scaled average value reference voltage and the intermediate reference voltage;

[0056] A clamping unit, connected to the subtraction unit, and clamping the subtraction result;

[0057] An adding unit is respectively connected to the clamping unit and the average value reference voltage to generate the reference voltage.

[0058] Optionally, the constant current control circuit further includes a shutdown control module, including:

[0059] a leading edge blanking unit, receiving the compensation voltage and outputting it after a third time; and

[0060] The second comparator has a first end connected to the leading edge blanking unit, a second end receiving the peak reference voltage, and an output end outputting the shutdown control signal.

[0061] Optionally, the peak reference voltage is proportional to the duty cycle of the dimming signal, and the slope between the peak reference voltage and the duty cycle of the dimming signal when the duty cycle of the dimming signal is lower than a set value is higher than the slope between the peak reference voltage and the duty cycle of the dimming signal when the duty cycle of the dimming signal is higher than the set value.

[0062] Optionally, it also includes:

[0063] The protection circuit performs over-current detection and / or over-temperature detection and outputs a protection signal to the drive circuit. The drive circuit generates the drive signal according to the protection signal to control the power switch of the drive system to turn off.

[0064] According to a second aspect of the present invention, there is provided an LED driving system, comprising:

[0065] A diode, a first end of which receives an input voltage and a second end of which is connected to the first node;

[0066] an inductor, a first end of which is connected to the first node, and a load is connected between the second end and the first end of the diode;

[0067] a power switch, having a first terminal connected to the first node, a second terminal grounded, a control terminal receiving a driving signal, and being turned on to charge the inductor and turned off to discharge the inductor in response to the driving signal; and

[0068] The LED driver controller as described above.

[0069] Optionally, the current sampling signal is connected to the second end of the power switch via a first resistor.

[0070] Optionally, the detection voltage is connected to the first end of the inductor via a fourth capacitor.

[0071] The LED drive controller and LED drive system provided by the present invention, wherein the constant current control circuit in the LED drive controller obtains a compensation voltage by linearly compensating the current sampling signal of the main circuit, and generates a conduction control signal according to the compensation voltage, the zero-crossing detection signal, the mode control signal, the drive signal and the average value reference voltage, and generates a shutdown control signal based on the compensation voltage and the peak value reference voltage. Then, the drive circuit controls the power switch during the dimming process based on the drive signal generated by the shutdown control signal and the conduction control signal, and the inductor will not be in a state of no current for a long time, thereby reducing the current ripple rate and achieving a relatively excellent screen flicker coefficient.

[0072] Furthermore, the compensation module in the constant current control circuit of the present application obtains a first current sampling signal and a second current sampling signal by sampling the current sampling signal at different times, and generates a corresponding compensation current based on the first current sampling signal and the second current sampling signal, thereby obtaining a corresponding compensation amount compensation current sampling signal, thereby maintaining the output current stable and improving the load and linear adjustment rate.

[0073] Furthermore, the reference voltage generating unit and the analog unit in the constant current control circuit of the present application output an analog voltage to the conduction control unit. The analog voltage represents the inductor current in the continuous mode and the discontinuous mode, which is equivalent to realizing current sampling in the full cycle of the power switch on and off. In this way, constant current output in the continuous mode and the discontinuous mode is realized, and deep dimming can be achieved while meeting the screen flicker coefficient.

[0074] Furthermore, the peak reference voltage generated by the reference generation circuit has an inflection point when the dimming brightness is low (for example, when the duty cycle of the dimming signal is lower than the set value), which can prevent the operating frequency of the LED driving system from being too low to enter the audio and thus generate audio noise. BRIEF DESCRIPTION OF THE DRAWINGS

[0075] The above and other objects, features and advantages of the present invention will become more apparent through the following description of the embodiments of the present invention with reference to the accompanying drawings, in which:

[0076] Figure 1 A schematic diagram of an LED driving system provided according to an embodiment of the present invention is shown;

[0077] Figure 2 A schematic diagram of the structure of an LED driving controller provided in an embodiment of the present invention is shown;

[0078] Figure 3 A schematic diagram of the structure of a constant current control circuit in an LED drive controller provided in an embodiment of the present invention is shown;

[0079] Figure 4 A circuit schematic diagram of a constant current control circuit in an LED drive controller provided according to an embodiment of the present invention is shown;

[0080] Figure 5 A timing diagram of a constant current control circuit in an LED drive controller provided according to an embodiment of the present invention is shown;

[0081] Figure 6 A schematic diagram of a dimming reference curve of a reference generating circuit in an LED driving controller provided in an embodiment of the present invention is shown;

[0082] Figure 7 Another structural schematic diagram of a reference voltage generating unit in a constant current control circuit of an LED driving controller provided according to an embodiment of the present invention is shown;

[0083] Figure 8 Show Figure 7 Schematic diagram of the waveform of the reference voltage generating unit. DETAILED DESCRIPTION

[0084] Various embodiments of the present invention will be described in more detail below with reference to the accompanying drawings. In each of the accompanying drawings, the same elements are represented by the same or similar reference numerals. For the sake of clarity, the various parts in the accompanying drawings are not drawn to scale.

[0085] The current sampling of the traditional buck constant current drive system is placed at the low end, which is not only simple and accurate, but also more efficient than high-end sampling. The common mode voltage of low-end current detection is low, and low-cost ordinary operational amplifiers can be used, but the detection resistor will introduce low-level interference, and the larger the sampling circuit, the more obvious the interference from the ground potential, and even affect the load. In addition, the phase-cut dimming method combined with dimming cannot meet the screen flicker coefficient requirements.

[0086] Figure 1 A schematic diagram of an LED driving system provided according to an embodiment of the present invention is shown. Figure 2 A schematic structural diagram of an LED driving controller provided according to an embodiment of the present invention is shown. Figure 3 A structural schematic diagram of a constant current control circuit in an LED drive controller provided according to an embodiment of the present invention is shown. Figure 4 A circuit schematic diagram of a constant current control circuit in an LED drive controller provided according to an embodiment of the present invention is shown. Figure 5 A timing diagram of a constant current control circuit in an LED drive controller provided according to an embodiment of the present invention is shown.

[0087] like Figure 1 As shown, the LED driving system 1000 includes a main circuit 1100 and an LED driving controller 1200 .

[0088] The main circuit 1100 is, for example, a BUCK type topology structure, including a diode D1, an inductor Lm, and a power switch Q1. The first end (for example, the cathode) of the diode D1 receives the input voltage VIN, and the second end (for example, the anode) of the diode D1 is connected to the first node d. The first end of the inductor Lm is connected to the first node d, and a load is connected between the second end of the inductor Lm and the first end of the diode D1. The first end of the power switch Q1 is connected to the first node d, and the second end of the power switch Q1 is connected to the ground end. The control end of the power switch Q1 receives a driving signal, and is turned on in response to the driving signal to charge the inductor Lm, and is turned off to discharge the inductor Lm.

[0089] Furthermore, the main circuit 1100 also includes an output capacitor Cout, a resistor R3 and an input module 1110. The output capacitor Cout is connected between the first end of the diode D1 and the second end of the inductor Lm, and is connected in parallel with the load. The load is, for example, a plurality of light-emitting diodes LED connected in series. The resistor R3 is connected between the second end of the power switch Q1 and the ground terminal. The input module 1110 includes a direct current power supply DC and an input filter capacitor Cin, the positive end of the direct current power supply DC outputs an input voltage VIN, and the negative end of the direct current power supply DC is grounded. The input filter capacitor Cin is connected in parallel with the direct current power supply DC.

[0090] The LED driving controller 1200 includes a zero-crossing detection pin zcd, a driving pin dr, a sampling pin cs, a ground terminal gnd, a power pin vdd, a temperature detection pin otp, a dimming pin dim, and an input pin vin. The LED driving system 1000 also includes some external components. Specifically, the zero-crossing detection pin zcd of the LED driving controller 1200 is connected to the first node d in the main circuit 1100 via a capacitor C4 to receive a detection voltage, and the received voltage is used to characterize the current of the inductor Lm. The driving pin dr of the LED driving controller 1200 is connected to the control end of the power switch Q1 via a resistor R2 to transmit a driving signal. The sampling pin cs of the LED driving controller 1200 is connected to the second end of the power switch Q1 via a resistor R1 to obtain a current sampling signal. The power pin vdd of the LED driving controller 1200 is grounded, for example, via a capacitor C5. The temperature detection pin otp of the LED driving controller 1200 is grounded, for example, via a resistor R4. The dimming pin dim of the LED driving controller 1200 receives the dimming signal DIM via a filtering network, for example. The filtering network includes a resistor Rdim and a capacitor Cdim. The first end of the resistor Rdim receives the dimming signal DIM, and the second end of the resistor Rdim is connected to the dimming pin dim. The capacitor Cdim is connected between the second end of the resistor Rdim and the ground terminal. The ground terminal gnd of the LED driving controller 1200 is connected to one end of the resistor R3 and grounded. The input pin vin of the LED driving controller 1200 is connected to the positive end of the DC source DC in the main circuit 110 to receive the input voltage VIN.

[0091] It should be noted that the above LED driving system is only an example, and the implementation of the LED driving system in the present application is not limited thereto. The main circuit 1100 in the LED driving system also includes other shutdown circuits in the prior art.

[0092] like Figure 2 As shown, the LED driving controller 1200 at least includes a constant current driving circuit 1210 , a reference generating circuit 1220 , and a zero-crossing detecting circuit 1250 , wherein the constant current driving circuit 1210 includes a constant current control circuit 1230 and a driving circuit 1240 .

[0093] The zero-crossing detection circuit 1250 is used to perform zero-crossing detection on the detection voltage Vzcd of the main circuit to generate a mode control signal Vg_DCM and a zero-crossing detection signal Vg_ZCD. The detection voltage represents the current of the inductor in the main circuit 1100. Further, the mode control signal Vg_DCM represents whether the inductor operates in a discontinuous mode or a continuous mode. When the mode control signal Vg_DCM is at an effective level, the inductor in the main circuit 1100 is in the discontinuous mode; when the mode control signal Vg_DCM is at an invalid level, the inductor in the main circuit 1100 is in the continuous mode. The zero-crossing detection signal Vg_ZCD represents whether the inductor current crosses zero. Further, the zero-crossing detection circuit 1250 is connected to the zero-crossing detection pin zcd to receive the detection voltage Vzcd.

[0094] The reference generation circuit 1220 generates a peak reference voltage Vpk_ref and an average reference voltage Vav_ref according to the dimming signal DIM. Further, the reference generation circuit 1220 is connected to the dimming pin dim to receive the dimming signal DIM.

[0095] The driving circuit 1240 is used to provide a driving signal DR to control the power switch Q1 of the main circuit 1100 to be turned on or off, so that the main circuit 1100 provides a constant output current to the load. Further, the driving circuit 1240 is connected to the driving pin dr to provide the driving signal DR.

[0096] The constant current control circuit 1230 is used to linearly compensate the current sampling signal Vcs of the main circuit 1100 to obtain a compensation voltage, and is connected to the reference generation circuit 1220, the zero-crossing detection circuit 1250, and the drive circuit 1240, and generates a conduction control signal Vg_S based on the compensation voltage, the mode control signal Vg_DCM, the zero-crossing detection signal Vg_ZCD, the drive signal DR, and the average value reference voltage Vav_ref. Further, the constant current control circuit 1230 also generates a shutdown control signal Vg_R based on the compensation voltage and the peak reference voltage Vpk_ref. Further, the constant current control circuit 1230 is connected to the dimming pin dim to receive the current sampling signal Vcs, and the current sampling signal Vcs represents the current flowing through the power switch Q1, which reflects the relationship between the input voltage, the output voltage and the inductance in the main circuit 1100. Among them, the drive circuit also generates a drive signal DR according to the conduction control signal Vg_S and the shutdown control signal Vg_R.

[0097] Furthermore, combined with Figure 3, the constant current control circuit 1230 includes a compensation module 1231, which is used to provide different compensation amounts according to the working mode of the inductor in the main circuit 1100, and generate a compensation voltage Vcsc according to the current sampling signal Vcs and the corresponding compensation amount. The output current is compensated by the change information of the sampling current, thereby ensuring an excellent adjustment rate under wide voltage input and wide voltage output. Further, the compensation amount provided by the compensation module 1231 when the inductor is in the continuous mode is less than the compensation amount provided when the inductor is in the discontinuous mode. Further, the compensation module 1231 is used to obtain the first current sampling signal V_h1 and the second current sampling signal V_h2 of the current sampling signal Vcs at different times according to the drive signal DR, and generate a compensation current according to the first current sampling signal V_h1 and the second current sampling signal V_h2, and apply the compensation current to resistors with different equivalent resistance values ​​according to the working mode of the inductor in the main circuit 1100 to obtain different compensation amounts, and superimpose the compensation amount with the current sampling signal Vcs to generate a compensation voltage Vcsc.

[0098] Specifically, combined Figure 4The compensation module 1231 includes a logic processor 12311, a first sampling and holding unit 12312, a second sampling and holding unit 12313, a first transconductance amplifier Gm1, a first compensation resistor Rc1, a second compensation resistor Rc2, and a first switch K1. The logic processor 12311 receives the driving signal DR output by the driving circuit 1240, and generates a first pulse signal Vg_sh1 after the rising edge of the driving signal DR is delayed for a first time, and generates a second pulse signal Vg_sh2 after the falling edge of the first pulse signal Vg_sh1 is delayed for a second time, wherein the second pulse signal Vg_sh2 is generated before the falling edge of the driving signal DR arrives. The first sampling and holding unit 12312 is connected to the logic processor 12311, and samples and holds the current sampling signal Vcs within the pulse time of the first pulse signal Vg_sh1 to generate the first current sampling signal V_h1. The second sampling and holding unit 12313 is connected to the logic processor 12311, and samples and holds the current sampling signal Vcs within the pulse time of the second pulse signal Vg_sh2 to generate a second current sampling signal V_h2. The first input end of the first transconductance amplifier Gm1 receives the first current sampling signal V_h1, the second input end receives the second current sampling signal V_h2, and the output end provides a compensation current. The first end of the first compensation resistor Rc1 receives the current sampling signal Vcs, and the second end is connected to the output end of the first transconductance amplifier Gm1. The first end of the second compensation resistor Rc2 receives the current sampling signal Vcs. The first end of the first switch K1 is connected to the second end of the second compensation resistor Rc2, the second end is connected to the second end of the first compensation resistor Rc1, and the control end receives the mode control signal Vg_DCM. Among them, the first switch K1 is, for example, a low conduction switch, and when the mode control signal Vg_DCM is low (invalid level, indicating that the inductor works in continuous mode), the first switch K1 is turned on. That is to say, the first switch K1 is turned on in the continuous mode, so that the compensation amount in the continuous mode is smaller than the compensation amount in the discontinuous mode. The compensation current Gm1*(V_h1-V_h2) is generated by sampling the first current sampling signal V_h1 and the second current sampling signal V_h2 at different times in the current sampling signal Vcs, and then the corresponding compensation amount is obtained, so that the load and linear regulation rate can be improved.

[0099] Furthermore, combined with Figure 3The constant current control circuit 1230 also includes a conduction control module 1236, including a reference voltage generating unit 1232, an analog unit 1233, and a conduction control unit 1234. The reference voltage generating unit 1232 is used to provide a reference voltage Voff. The analog unit 1233 selects one of the compensation voltage Vcsc, the ground voltage, and the reference voltage Voff as the analog voltage VL in different periods of the entire control cycle according to the level state of the drive signal DR and the zero-crossing detection signal Vg_ZCD. The conduction control unit 1234 generates the conduction control signal Vg_S according to the analog voltage VL, the average value reference voltage Vav_ref, and the drive signal DR.

[0100] Specifically, combined Figure 4 , the analog unit 1233 includes a second switch K2, a third switch K3, a fourth switch K4, and a NAND gate U1. The first end of the second switch K2 receives the compensation voltage Vcsc, and the control end receives the drive signal DR. The first end of the third switch K3 is grounded, and the control end receives the zero-crossing detection signal Vg_ZCD. The first end of the NAND gate U1 receives the drive signal DR, and the second end receives the zero-crossing detection signal Vg_ZCD. The first end of the fourth switch K4 receives the reference voltage Voff, and the control end is connected to the output end of the NAND gate U1. The second end of the second switch K2 is connected to the second end of the third switch K3 and the second end of the fourth switch K4 to output the analog voltage VL. Further, Figure 4A reference voltage generating unit 1232 is shown. When the inductor is in continuous mode, the reference voltage Voff is an average value reference voltage Vav_ref. When the inductor is in discontinuous mode, the reference voltage Voff is half of the peak voltage Vpk_h of the compensation voltage. Specifically, the reference voltage generating unit 1232 includes a third sampling and holding unit 12321, a voltage processing unit 12322, a fifth switch K5, a sixth switch K6, and a capacitor C1. The third sampling and holding unit 12321 is used to sample and hold the peak value of the compensation voltage Vcsc and output the peak voltage Vpk_h. The voltage processing unit 12322 is connected to the third sampling and holding unit 12321 to generate half of the peak voltage. The first end of the fifth switch K5 is connected to the voltage processing unit 12322, and the control end receives the mode control signal Vg_DCM. The first end of the sixth switch K6 receives the average value reference voltage Vav_ref, the control end receives the mode control signal Vg_DCM, and the second end is connected to the second end of the fifth switch K5 and outputs the reference voltage Voff. The first end of the first capacitor C1 is connected to the second end of the sixth switch K6 and the second end of the fifth switch K5, and the second end is grounded, and the reference voltage Voff is output. Among them, the fifth switch K5 is turned on when the mode control signal Vg_DCM is in the first level state, and the sixth switch K6 is turned on when the mode control signal Vg_DCM is in the second level state. For example, when the inductor is in the discontinuous mode, the fifth switch K5 is turned on, the value of the reference voltage Voff is Vpk_h*1 / 2, and it is output through the capacitor C1 for voltage stabilization. When the inductor is in the continuous mode, the fifth switch K6 is turned on, the value of the reference voltage Voff is the average value reference voltage Vav_ref, and it is output through the capacitor C1 for voltage stabilization. Further, for example, when the drive signal DR is at a high level, the second switch K2 is turned on, and the analog voltage VL is the compensation voltage Vcsc. When the driving signal DR is at a low level and the zero-crossing detection signal Vg_ZCD is at a low level, the fourth switch K4 is turned on. Further, when the mode control signal Vg_DCM is at a low level (the inductor is in a continuous mode), the sixth switch K6 is turned on, and the analog voltage VL is the average value reference voltage Vav_ref; when the mode control signal Vg_DCM is at a high level (the inductor is in a discontinuous mode), the fifth switch K5 is turned on, and the analog voltage VL is Vpk_h*1 / 2. When the driving signal DR is at a low level, and when the inductor is in a discontinuous mode, the inductor current drops to zero, the zero-crossing detection signal Vg_ZCD is at a high level, and the third switch is turned on, then the analog voltage VL is a ground voltage. Further, the conduction control unit 1234 includes a second transconductance amplifier Gm2, a third transconductance amplifier Gm3, a capacitor C3, a seventh switch K7, and a first comparator CMP1. The first end of the second transconductance amplifier Gm2 receives the average value reference voltage Vav_ref, and the second end receives the analog voltage VL.The first end of the capacitor C2 is connected to the output end of the second transconductance amplifier Gm2 and provides a voltage Vcomp, and the second end is grounded. The first end of the third transconductance amplifier Gm3 is connected to the output end of the second transconductance amplifier Gm2, and the second end is grounded. The first end of the capacitor C3 is connected to the output end of the third transconductance amplifier Gm3 and provides a voltage Vramp, and the second end is grounded. The first end of the seventh switch K7 is connected to the first end of the capacitor C3, the second end is connected to the second end of the capacitor C3, and the control end receives the drive signal DR. The first end of the first comparator CMP1 is connected to the output end of the third transconductance amplifier Gm3, the second end receives the set threshold voltage Vr_1, and the output end outputs the conduction control signal Vg_S. Further, the conduction control unit 1234 is used to calculate the turn-off time of the corresponding power switch Q1 according to the analog voltage VL of the entire cycle and the average value reference voltage Vav_ref to control the stability of the output current. Furthermore, when the driving signal DR is at a low level, the current output by the third transconductance amplifier Gm3 charges the capacitor C3. When the voltage Vramp on the capacitor C3 is greater than the set threshold voltage Vr_1, the conduction control signal Vg_S is generated.

[0101] Because the operating frequency of the switch tube is reduced under deep dimming, the peak reference and the average reference are also reduced, and the inductor current will enter the discontinuous mode. If the traditional control method is used, only the current signal of the switch tube during the conduction phase is sampled, which cannot meet the requirements of the flicker coefficient.

[0102] In order to meet the requirements of screen flicker coefficient under deep dimming, it is also necessary to sample the current signal of the power switch shutdown stage. The present invention designs an analog unit to output an analog voltage VL, which characterizes the inductor current in continuous mode and discontinuous mode, which is equivalent to realizing current sampling in the full cycle of power switch on and off. The conduction control unit outputs a conduction control signal according to the analog voltage, the average value reference voltage and the drive signal, so as to control the conduction and shutdown of the power switch and realize constant current output in continuous mode and discontinuous mode.

[0103] Combination Figure 3 , Figure 4, the constant current control circuit 1230 also includes a shutdown control module 1235, which generates a shutdown control signal Vg_R according to the compensation voltage Vcsc and the peak reference voltage Vpk_ref. Further, the shutdown control module 1235 includes a leading edge blanking unit 12351 and a second comparator CMP2. The leading edge blanking unit 12351 receives the compensation voltage Vcsc and outputs it after a third time. The first end of the second comparator CMP2 is connected to the leading edge blanking unit 12351, the second end receives the peak reference voltage Vpk_ref, and the output end outputs the shutdown control signal Vg_R. Specifically, for example, when the compensation voltage Vcsc is greater than the peak reference voltage Vpk_ref after the third time, the shutdown control signal Vg_R will be generated.

[0104] In other embodiments, the LED driving controller 1200 further includes a power supply circuit 1260. The power supply circuit 1260 is connected to the input pin vin and receives the input voltage VIN. The power supply circuit 1260 provides a power supply voltage to the power pin vdd and the driving circuit 1240 to power the LED driving controller 1200.

[0105] In other embodiments, the LED driving controller 1200 further includes a protection circuit 1270. The protection circuit 1270 performs over-current detection and / or over-temperature detection, and outputs a protection signal Vg_shut to the driving circuit 1240. The driving circuit 1240 generates a driving signal DR according to the protection signal Vg_shut to control the power switch Q1 of the main circuit 1100 to turn off. The resistance value of the resistor R4 varies with temperature.

[0106] Furthermore, combined with Figure 5. At time t0, the drive signal DR changes from low to high, the power switch Q1 is turned on, the inductor current IL starts to rise slowly, and the voltage value of the current sampling signal Vcs gradually rises. After the first time, at time t1, the logic processor 12311 in the compensation module 1231 generates a first pulse signal Vg_sh1 with a certain pulse width. At time t1, the first sampling and holding unit 12312 samples and holds the current sampling signal Vcs to generate a first current sampling signal V_h1. At time t2 when the falling edge of the first pulse signal Vg_sh1 arrives, the logic processor 12311 in the compensation module 1231 generates a second pulse signal Vg_sh2 with a certain pulse width. At time t2, the second sampling and holding unit 12313 samples and holds the current sampling signal Vcs to generate a second current sampling signal V_h2. At time t3, the drive signal DR changes from high to low, the power switch Q1 is turned off, the inductor current IL decreases, and the voltage Vramp starts to charge from 0; at time t4, the drive signal DR changes from low to high, and the voltage Vramp reaches the set threshold voltage Vr_1 and then clears to zero. During t0-t4, the zero-crossing detection signal Vg_ZCD is always at a low level, and the mode control signal Vg_DCM is always at a low level. The above is a complete cycle, which describes the working timing of the constant current control circuit 1230 when the inductor works in the continuous mode. And between t4-t5, the inductor still works in the continuous mode, and the value of the analog voltage VL changes with the state of the mode control signal Vg_DCM, the zero-crossing detection signal Vg_ZCD, and the drive signal DR. For specific values, please refer to Figure 3 Related description of simulation unit 1233.

[0107] Then at time t5, the drive signal DR changes from low to high, the power switch Q1 is turned on, the inductor current IL starts to rise slowly from 0, and the voltage value of the current sampling signal Vcs gradually rises; at time t6, the drive signal DR changes from high to low, the power switch Q1 is turned off, the inductor current IL drops, and the voltage Vramp starts to charge from 0; at time t7, the inductor current IL drops to 0, and the zero-crossing detection signal Vg_ZCD changes from low to high; at time t8, the drive signal DR changes from low to high, the zero-crossing detection signal Vg_ZCD changes from high to low, and the voltage Vramp reaches the set threshold voltage Vr_1 and clears to zero. That is, during the period t5-t8, the mode control signal Vg_DCM is always at a high level, which describes the working timing of the constant current control circuit 1230 when the inductor works in the discontinuous mode.

[0108] Figure 6 A schematic diagram of a dimming reference curve of a reference generating circuit in an LED driving controller provided according to an embodiment of the present invention is shown.

[0109] like Figure 6As shown, the corresponding peak reference voltage Vpk_ref and average reference voltage Vav_ref generated by the reference generation circuit 1220 according to the dimming signal DIM with different duty cycles D. Further, the average reference voltage Vav_ref increases at a certain ratio as the duty cycle D increases. The peak reference voltage Vpk_ref is proportional to the duty cycle D, and the slope between the peak reference voltage Vpk_ref and the duty cycle D of the dimming signal DIM when the duty cycle D of the dimming signal DIM is lower than the set value is higher than the slope between the peak reference voltage Vpk_ref and the duty cycle D of the dimming signal DIM when the duty cycle D of the dimming signal DIM is higher than the set value. That is, the peak reference voltage Vpk_ref has an inflection point when the dimming brightness is low (for example, when the duty cycle D of the dimming signal DIM is lower than the set value), which can prevent the operating frequency of the LED driving system from being too low to enter the audio and thus cause audio noise.

[0110] Figure 7 Another structural schematic diagram of a reference voltage generating unit in a constant current control circuit of an LED driving controller provided according to an embodiment of the present invention is shown. Figure 7 Show Figure 8 Schematic diagram of the waveform of the reference voltage generating unit.

[0111] In an alternative embodiment, if Figure 7 As shown, another reference voltage generating unit 2232 in the constant current control circuit 1230 is used to obtain an intermediate voltage according to the average value reference voltage Vav_ref, and to generate a reference voltage V_3 according to the average value reference voltage Vav_ref and the intermediate voltage. Specifically, the reference voltage generating unit 2232 includes a scaling unit 22321, a subtraction unit 22322, a clamping unit 22323, and an adding unit 22324. The scaling unit 22321 performs scaling processing on the average value reference voltage Vav_ref. The subtraction unit 22322 is connected to the scaling unit 22321, and performs subtraction processing on the scaled average value reference voltage and the intermediate reference voltage Vref_4. The clamping unit 22323 is connected to the subtraction unit 22322, and clamps the subtraction result. The adding unit 22324 is respectively connected to the clamping unit 22323 and the average value reference voltage Vav_ref to generate a reference voltage V_3.

[0112] Combination Figure 8 When the duty cycle D of the dimming signal DIM is higher than the set value, the reference voltage V_3 provided by the reference voltage generating unit 2232 is the average reference voltage Vav_ref. When the duty cycle D of the dimming signal DIM is lower than the set value, the reference voltage V_3 provided by the reference voltage generating unit 2232 is between the average reference voltage Vav_ref and the peak reference voltage Vpk_ref.

[0113] The LED drive system provided by the present application, which includes an LED drive controller, uses a hysteresis-like control method for dimming, and does not cause a long period of inductor current-free state, and can keep the output current constant, thereby achieving a relatively excellent screen flicker coefficient and current ripple rate. Furthermore, the present application achieves a higher load and linear regulation rate by compensating the current sampling signal, and the compensation amount is related to the input and output voltages.

[0114] Furthermore, the reference voltage generating unit and the analog unit in the constant current control circuit of the present application output an analog voltage to the conduction control unit. The analog voltage represents the inductor current in the continuous mode and the discontinuous mode, which is equivalent to realizing current sampling in the full cycle of the power switch on and off. In this way, constant current output in the continuous mode and the discontinuous mode is realized, and deep dimming can be achieved while meeting the screen flicker coefficient.

[0115] Furthermore, the present application adjusts the slope between the peak reference voltage and the duty cycle under dimming conditions at a low duty cycle, so that the operating frequency of the LED driving system is still controlled above the audio frequency to avoid audio noise.

[0116] According to the embodiments of the present invention as described above, these embodiments do not describe all the details in detail, nor do they limit the invention to the specific embodiments described. Obviously, many modifications and changes can be made based on the above description. This specification selects and specifically describes these embodiments in order to better explain the principles and practical applications of the present invention, so that those skilled in the art can make good use of the present invention and the modified use based on the present invention. The present invention is limited only by the claims and their full scope and equivalents.

Claims

1. An LED drive controller, wherein: include: A zero-crossing detection circuit detects the inductor current in the drive system to generate a mode control signal and a zero-crossing detection signal; A reference generation circuit generates a peak reference voltage and an average reference voltage according to a dimming signal; a constant current control circuit, which performs linear compensation on the current sampling signal according to the mode control signal and the drive signal to generate a compensation voltage, and generates a conduction control signal according to the compensation voltage, the zero-crossing detection signal, the mode control signal, the drive signal and the average value reference voltage; A driving circuit generates the driving signal according to the on-control signal and the off-control signal, wherein the driving signal is used to control the power switch, The constant current control circuit further includes a conduction control module, and the conduction control module includes: A reference voltage generating unit, providing a reference voltage; a simulation unit, which selects one of the compensation voltage, the ground voltage, and the reference voltage as the simulation voltage at different time periods in the entire control cycle according to the level states of the drive signal and the zero-crossing detection signal; and A conduction control unit generates the conduction control signal according to the analog voltage, the average value reference voltage and the driving signal.

2. The LED driving controller according to claim 1, wherein: The constant current control circuit also generates the shutdown control signal based on the compensation voltage and the peak reference voltage.

3. The LED driving controller according to claim 1, wherein: The current sampling signal represents the current flowing through the power switch in the drive system.

4. The LED driving controller according to claim 1, wherein: When the mode control signal is at a valid level, the inductor in the drive system is in a discontinuous mode; when the mode control signal is at an invalid level, the inductor in the drive system is in a continuous mode.

5. The LED driving controller according to claim 1, wherein: The constant current control circuit comprises: The compensation module provides different compensation amounts according to the working mode of the inductor in the driving system, and generates the compensation voltage according to the current sampling signal and the corresponding compensation amount.

6. The LED driving controller according to claim 5, wherein: The compensation amount provided by the compensation module when the inductor is in a continuous mode is smaller than the compensation amount provided by the compensation module when the inductor is in a discontinuous mode.

7. The LED driving controller according to claim 5, wherein: The compensation module is used to obtain a first current sampling signal and a second current sampling signal of the current sampling signal at different times according to the driving signal, and generate a compensation current according to the first current sampling signal and the second current sampling signal.

8. The LED driving controller according to claim 7, wherein: The compensation current is applied to resistors with different equivalent resistance values ​​according to the working mode of the inductor in the drive system to obtain different compensation amounts, and the compensation amount is superimposed on the current sampling signal to generate the compensation voltage.

9. The LED driving controller according to claim 8, wherein: The compensation module comprises: a logic processor, receiving the driving signal, and generating a first pulse signal after a rising edge of the driving signal is delayed for a first time, and generating a second pulse signal after a falling edge of the first pulse signal is delayed for a second time, wherein the second pulse signal is generated before the falling edge of the driving signal arrives; a first sampling and holding unit connected to the logic processor, sampling and holding the current sampling signal within the pulse time of the first pulse signal to generate the first current sampling signal; a second sampling and holding unit connected to the logic processor, sampling and holding the current sampling signal within the pulse time of the second pulse signal to generate the second current sampling signal; A first transconductance amplifier, wherein a first input terminal receives the first current sampling signal, a second input terminal receives the second current sampling signal, and an output terminal provides the compensation current; A first compensation resistor, a first end of which receives the current sampling signal, and a second end of which is connected to the output end of the first transconductance amplifier; A second compensation resistor, a first end of which receives the current sampling signal; and The first switch has a first end connected to the second end of the second compensation resistor, a second end connected to the second end of the first compensation resistor, and a control end receiving the mode control signal.

10. The LED driving controller according to claim 1, wherein: The simulation unit comprises: A second switch, a first end receiving the compensation voltage, and a control end receiving the driving signal; A third switch, a first end of which is grounded and a control end of which receives the zero-crossing detection signal; A NAND gate, a first end of which receives the driving signal, and a second end of which receives the zero-crossing detection signal; a fourth switch, wherein a first end receives the reference voltage, and a control end is connected to the output end of the NAND gate, The second end of the second switch is connected to the second end of the third switch and the second end of the fourth switch to output the analog voltage.

11. The LED driving controller according to claim 1, wherein: The reference voltage generating unit generates the reference voltage as the average value reference voltage when the inductor is in a continuous mode, and generates the reference voltage as half of the peak voltage of the compensation voltage when the inductor is in a discontinuous mode.

12. The LED driving controller according to claim 11, wherein: The reference voltage generating unit comprises: a third sampling and holding unit, sampling and holding the peak value of the compensation voltage and outputting the peak voltage; A voltage processing unit, connected to the third sampling and holding unit, generating a half peak voltage; a fifth switch, a first end of which is connected to the voltage processing unit, and a control end of which receives a mode control signal; a sixth switch, having a first end receiving the average value reference voltage, a control end receiving a mode control signal, a second end connected to the second end of the fifth switch and outputting the reference voltage; and a first capacitor, a first end of which is connected to the second end of the sixth switch and the second end of the fifth switch, and a second end of which is grounded; Wherein, when the mode control signal is in a first level state, the fifth switch is turned on, and when the mode control signal is in a second level state, the sixth switch is turned on.

13. The LED driving controller according to claim 1, wherein: The conduction control unit comprises: A second transconductance amplifier, a first terminal of which receives the average value reference voltage, and a second terminal of which receives the analog voltage; A second capacitor, a first end of which is connected to the output end of the second transconductance amplifier, and a second end of which is grounded; A third transconductance amplifier, having a first end connected to the output end of the second transconductance amplifier and a second end grounded; A third capacitor, a first end of which is connected to the output end of the third transconductance amplifier, and a second end of which is grounded; a seventh switch, a first end of which is connected to the first end of the third capacitor, a second end of which is connected to the second end of the third capacitor, and a control end of which receives the driving signal; The first comparator has a first terminal connected to the output terminal of the third transconductance amplifier, a second terminal receiving a set threshold voltage, and an output terminal outputting the conduction control signal.

14. The LED driving controller according to claim 1, wherein: The reference voltage generating unit obtains an intermediate voltage according to the average value reference voltage, and generates the reference voltage according to the average value reference voltage and the intermediate voltage.

15. The LED driving controller according to claim 14, wherein: The reference voltage generating unit comprises: A scaling unit, performing scaling processing on the average value reference voltage; A subtraction unit connected to the scaling unit, performing subtraction processing on the scaled average value reference voltage and the intermediate reference voltage; A clamping unit, connected to the subtraction unit, and clamping the subtraction result; An adding unit is respectively connected to the clamping unit and the average value reference voltage to generate the reference voltage.

16. The LED driving controller according to claim 1, wherein: The constant current control circuit also includes a shutdown control module, including: a leading edge blanking unit, receiving the compensation voltage and outputting it after a third time; and The second comparator has a first end connected to the leading edge blanking unit, a second end receiving the peak reference voltage, and an output end outputting the shutdown control signal.

17. The LED driving controller according to claim 1, wherein: The peak reference voltage is proportional to the duty cycle of the dimming signal, and the slope between the peak reference voltage and the duty cycle of the dimming signal when the duty cycle of the dimming signal is lower than a set value is higher than the slope between the peak reference voltage and the duty cycle of the dimming signal when the duty cycle of the dimming signal is higher than the set value.

18. The LED driving controller according to claim 1, wherein: Also includes: The protection circuit performs over-current detection and / or over-temperature detection and outputs a protection signal to the drive circuit. The drive circuit generates the drive signal according to the protection signal to control the power switch of the drive system to turn off.

19. An LED driving system, wherein: include: A diode, a first end of which receives an input voltage and a second end of which is connected to the first node; an inductor, a first end of which is connected to the first node, and a load is connected between the second end and the first end of the diode; A power switch, having a first terminal connected to the first node, a second terminal grounded, a control terminal receiving a driving signal, and being turned on to charge the inductor and turned off to discharge the inductor in response to the driving signal; as well as An LED drive controller as claimed in any one of claims 1 to 18.

20. The LED driving system according to claim 19, wherein: The current sampling signal is connected to the second end of the power switch via a first resistor.

21. The LED driving system according to claim 19, wherein: The detection voltage is connected to the first end of the inductor via the fourth capacitor.

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