CN115334716A - LED drive controller and system - Google Patents

Abstract

The application discloses an LED drive controller and a system, wherein the LED drive controller comprises a zero-crossing detection circuit, and is used for detecting an inductive current in a drive system to generate a mode control signal and a zero-crossing detection signal; a reference generating circuit generating a peak reference voltage and a mean reference voltage according to the dimming signal; the constant current control circuit is used for carrying out linear compensation on the current sampling signal according to the mode control signal and the driving signal so as to generate compensation voltage, and generating a conduction control signal according to the compensation voltage, the zero-crossing detection signal, the mode control signal, the driving signal and the average value reference voltage; and the driving circuit generates a driving signal according to the on control signal and the off control signal, and the driving signal is used for controlling the power switch. This application adjusts luminance through the control mode of class hysteresis loop, and the long time inductance current-free state can not appear, can keep output current invariable, reaches better screen flashing coefficient and electric current ripple rate.

Description

LED drive controller and system

technical field

The present invention relates to the technical field of LED driving, in particular, to an LED driving controller and system.

Background technique

LED (Light Emitting Diode, Light Emitting Diode) has the characteristics of energy saving, environmental protection, high efficiency, long life, etc., 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 matching are getting higher and higher. Because the forward voltage drop of the LED is affected by the discrete process, the brightness of the LED may be different if the constant voltage driving method is used, so the LED is usually driven by the constant current driving method, and the brightness of the LED is determined by the average current passing through itself.

In the current phase-cut dimming method, 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 drops. 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 is weakened, when PWM1 is duty When the ratio gradually becomes smaller, the time for the PWM1 signal to be low will become longer, and the inductor current will drop to 0, and the maintenance time will be longer and longer, which will cause the output current to drop slowly, resulting in a larger output ripple, and its screen The flicker factor will exceed the standard.

With the ever-increasing demand for health and intelligence in the lighting market, smart lighting has become the direction of future development. Generally, a stable constant current is provided to achieve the required LED luminous intensity and dimming accuracy. Therefore, it is extremely important for the development of LED to provide an LED drive controller that can control the output of a stable current from the main circuit.

Contents of the invention

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 the screen flicker coefficient and achieve the purpose of deep dimming and color adjustment.

According to one aspect of the present invention, there is provided a LED drive controller, comprising:

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 generating circuit, which generates a peak reference voltage and an average reference voltage according to the dimming signal;

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

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.

Optionally, the constant current control circuit also generates the shutdown control signal based on the compensation voltage and the peak reference voltage.

Optionally, the current sampling signal represents the current flowing through the power switch in the driving system.

Optionally, when the mode control signal is at an active level, the inductor in the main circuit is in a discontinuous mode; when the mode control signal is at an inactive level, the inductor in the main circuit is in a continuous mode.

Optionally, the constant current control circuit includes:

The compensation module provides different compensation amounts according to the working mode of the inductor in the main circuit, and generates the compensation voltage according to the current sampling signal and the corresponding compensation amount.

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

Optionally, the compensation module is configured 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 obtain the first current sampling signal and the second current sampling signal according to the first current sampling signal and the second current sampling signal. The second current sampling signal generates a compensation current.

Optionally, applying the compensation current 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 superimposing the compensation amount with the current sampling signal to generate the compensation voltage.

Optionally, the compensation module includes:

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 first pulse signal after a falling edge of the first pulse signal is delayed for a second time Two pulse signals, wherein the second pulse signal is generated before the falling edge of the driving signal arrives;

a first sample and hold unit, connected to the logic processor, to sample and hold the current sampling signal within the pulse time of the first pulse signal, so as to generate the first current sampling signal;

a second sample and hold unit, connected to the logic processor, to sample and hold the current sampling signal within the pulse time of the second pulse signal, to generate the second current sampling signal;

The first transconductance operational amplifier, the first input end receives the first current sampling signal, the second input end receives the second current sampling signal, and the output end provides the compensation current;

The first compensation resistor, the first end receives the current sampling signal, and the second end is connected to the output end of the first transconductance amplifier;

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

The first switch has a first terminal connected to the second terminal of the second compensation resistor, a second terminal connected to the second terminal of the first compensation resistor, and a control terminal receiving the mode control signal.

Optionally, the constant current control circuit also includes a conduction control module, including:

a reference voltage generation unit, providing a reference voltage;

The analog unit selects one of the compensation voltage, ground voltage, and reference voltage as the analog voltage at different periods of the entire control cycle according to the level states of the drive signal and the zero-crossing detection signal; and

The conduction control unit generates the conduction control signal according to the analog voltage, the average value reference voltage and the driving signal.

Optionally, the simulation unit includes:

a second switch, the first end of which receives the compensation voltage, and the control end receives the driving signal;

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

A NAND gate, the first end of which receives the drive signal, and the second end receives the zero-crossing detection signal;

A fourth switch, the first end of which receives the reference voltage, the control end of which 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.

Optionally, when the reference voltage generating unit is in the continuous mode, the reference voltage is the average value reference voltage, and when the inductor is in the discontinuous mode, the reference voltage is the peak value of the compensation voltage half of the voltage.

Optionally, the reference voltage generation unit includes:

a third sample and hold unit, which samples and holds the peak value of the compensation voltage and outputs the peak voltage;

a voltage processing unit, connected to the third sample and hold unit, to generate half of the peak voltage;

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

The sixth switch has 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, the first end of which is connected to the second end of the sixth switch and the second end of the fifth switch, and the second end is grounded,

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

Optionally, the conduction control unit includes:

The second transconductance operational amplifier, the first end receives the average value reference voltage, and the second end receives the analog voltage;

The second capacitor, the first end is connected to the output end of the second transconductance operational amplifier, and the second end is grounded;

The third transconductance operational amplifier, the first terminal is connected to the output terminal of the second transconductance operational amplifier, and the second terminal is grounded;

a third capacitor, the first end of which is connected to the output end of the third transconductance operational amplifier, and the second end is grounded;

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

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

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

Optionally, the reference voltage generation unit includes:

a scaling unit, configured to perform scaling processing on the average value reference voltage;

a subtraction unit, connected to the scaling unit, and subtracting the scaled average reference voltage from 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.

Optionally, 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 terminal connected to the leading edge blanking unit, a second terminal receiving the peak reference voltage, and an output terminal outputting the shutdown control signal.

Optionally, the peak reference voltage is proportional to the duty cycle of the dimming signal, and when the duty cycle of the dimming signal is lower than a set value, the peak reference voltage is proportional to the dimming signal. The slope between the duty ratios of the signals is higher than the slope between the peak reference voltage and the duty ratio of the dimming signals when the duty ratio of the dimming signal is higher than a set value.

Optionally, also include:

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

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

a diode, the first end of which receives the input voltage, and the second end is connected to the first node;

an inductor, the 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, the first end of which is connected to the first node, the second end of which is grounded, the control end receives a driving signal, and is turned on to charge the inductance and turned off to discharge the inductance in response to the driving signal; and

LED driver controller as above.

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

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

In the LED drive controller and LED drive system provided by the present invention, the constant current control circuit in the LED drive controller obtains the compensation voltage by linearly compensating the current sampling signal of the main circuit, and according to the compensation voltage, zero-crossing detection signal, mode The control signal, the driving signal and the average reference voltage generate a turn-on control signal, and generate a turn-off control signal based on the compensation voltage and the peak reference voltage. Furthermore, the drive circuit generates a drive signal based on the turn-off control signal and the turn-on control signal to control the power switch during the dimming process, so that there will be no long-term no-current state of the inductor, and the current ripple rate is reduced to achieve a relatively excellent screen flicker coefficient.

Further, the compensation module in the constant current control circuit of the present application obtains the first current sampling signal and the second current sampling signal by sampling the current sampling signals at different times, and generates the current sampling signal based on the first current sampling signal and the second current sampling signal The corresponding compensation current, and then obtain the corresponding compensation amount to compensate the current sampling signal, keep the output current stable, and improve the load and linear adjustment rate.

Further, 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, and the analog voltage represents the inductor current in the continuous mode and the discontinuous mode, which is equivalent to the power switch conduction The full cycle of on and off realizes current sampling, so as to realize constant current output in continuous mode and discontinuous mode, and realize deep dimming under the screen flicker coefficient.

Further, 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 drive system from being too low to enter the audio frequency. This results in audio noise.

Description of drawings

Through the following description of the embodiments of the present invention with reference to the accompanying drawings, the above-mentioned and other objects, features and advantages of the present invention will be more clear, in the accompanying drawings:

FIG. 1 shows a schematic diagram of an LED driving system provided according to an embodiment of the present invention;

FIG. 2 shows a schematic structural diagram of an LED drive controller provided according to an embodiment of the present invention;

FIG. 3 shows a schematic structural diagram of a constant current control circuit in an LED drive controller provided according to an embodiment of the present invention;

FIG. 4 shows a schematic circuit diagram of a constant current control circuit in an LED drive controller provided according to an embodiment of the present invention;

FIG. 5 shows a timing diagram of a constant current control circuit in an LED drive controller according to an embodiment of the present invention;

6 shows a schematic diagram of a dimming reference curve of a reference generating circuit in an LED drive controller according to an embodiment of the present invention;

FIG. 7 shows another schematic structural diagram of the reference voltage generation unit in the constant current control circuit of the LED drive controller provided according to an embodiment of the present invention;

FIG. 8 shows a schematic waveform diagram of the reference voltage generating unit in FIG. 7 .

Detailed ways

Various embodiments of the invention will be described in more detail below with reference to the accompanying drawings. In the various drawings, the same elements are denoted by the same or similar reference numerals. For the sake of clarity, various parts in the drawings have not been drawn to scale.

The current sampling of the traditional step-down constant current drive system will be placed at the low end, so that not only the sampling method is simple and accurate, but also the efficiency is higher than that of the high-end sampling. The common-mode voltage of low-side current detection is low, and low-cost common operational amplifiers can be used, but the detection resistor will introduce low-level interference, and the larger the sampling circuit, the more obvious the ground potential interference, and even affect the load. And the phase-cut dimming method combined with dimming cannot meet the screen flicker coefficient requirement.

Fig. 1 shows a schematic diagram of an LED driving system provided according to an embodiment of the present invention. Fig. 2 shows a schematic structural diagram of an LED driving controller provided according to an embodiment of the present invention. Fig. 3 shows a schematic structural diagram of a constant current control circuit in an LED drive controller according to an embodiment of the present invention. Fig. 4 shows a schematic circuit diagram of a constant current control circuit in an LED drive controller according to an embodiment of the present invention. Fig. 5 shows a timing diagram of a constant current control circuit in an LED drive controller according to an embodiment of the present invention.

As shown in FIG. 1 , the LED driving system 1000 includes a main circuit 1100 and an LED driving controller 1200 .

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

Further, 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 terminal of the diode D1 and the second terminal of the inductor Lm, and is connected in parallel with the load. Wherein, the load is, for example, a plurality of LEDs connected in series. The resistor R3 is connected between the second terminal of the power switch Q1 and the ground terminal. The input module 1110 includes a DC power supply DC and an input filter capacitor Cin. The positive terminal of the DC power supply DC outputs the input voltage VIN, and the negative terminal of the DC power supply DC is grounded. The input filter capacitor Cin is connected in parallel with the direct current power supply DC.

The LED drive controller 1200 includes a zero-cross detection pin zcd, a drive pin dr, a sampling pin cs, a ground terminal gnd, a power supply 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, for example, a capacitor C4 to receive a detection voltage, which is used to represent the current of the inductor Lm. The driving pin dr of the LED driving controller 1200 is connected to the control terminal of the power switch Q1 via a resistor R2 for transmitting 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, for example, a resistor R1 to obtain a current sampling signal. The power supply pin vdd of the LED driving controller 1200 is grounded via the capacitor C5, for example. The temperature detection pin otp of the LED drive controller 1200 is grounded, for example, via a resistor R4. The dimming pin dim of the LED drive controller 1200 receives the dimming signal DIM through a filter network, for example, the filter 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 signal DIM. Optical pin dim connection. The capacitor Cdim is connected between the second terminal of the resistor Rdim and the ground terminal. The ground terminal gnd of the LED driving controller 1200 is, for example, connected to one end of the resistor R3 and grounded. The input pin vin of the LED driving controller 1200 is, for example, connected to the positive terminal of the direct current source DC in the main circuit 110 to receive the input voltage VIN.

It should be noted that the above-mentioned LED driving system is only one example, and the implementation of the LED driving system in this application is not limited thereto. The main circuit 1100 in the LED driving system also includes other shutdown circuits in the prior art.

As shown in FIG. 2 , the LED drive controller 1200 at least includes a constant current drive circuit 1210 , a reference generation circuit 1220 , and a zero-crossing detection circuit 1250 , wherein the constant current drive circuit 1210 includes a constant current control circuit 1230 and a drive circuit 1240 .

The zero-crossing detection circuit 1250 is used to detect the zero-crossing of the detection voltage Vzcd of the main circuit to generate the mode control signal Vg_DCM and the 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 indicates that the inductor works in discontinuous mode or continuous mode. When the mode control signal Vg_DCM is at an active level, the inductor in the main circuit 1100 is in the discontinuous mode; when the mode control signal Vg_DCM is at an inactive level, the main circuit 1100 The inductor is in continuous mode. The zero-crossing detection signal Vg_ZCD indicates 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.

The reference generating 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 generating circuit 1220 is connected to the dimming pin dim to receive the dimming signal DIM.

The driving circuit 1240 is used to provide a driving signal DR to control the power switch Q1 of the main circuit 1100 to turn 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.

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, based on the compensation voltage and 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 generate a conduction control signal Vg_S. Further, the constant current control circuit 1230 also generates the 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, the current sampling signal Vcs represents the current flowing through the power switch Q1, which reflects the difference between the input voltage, the output voltage and the inductor in the main circuit 1100. Relationship. Wherein, the driving circuit also generates the driving signal DR according to the on control signal Vg_S and the off control signal Vg_R.

Further, referring to FIG. 3 , the constant current control circuit 1230 includes a compensation module 1231 for providing different compensation amounts according to the working mode of the inductor in the main circuit 1100 , and generating a compensation voltage Vcsc according to the current sampling signal Vcs and the corresponding compensation amount. The output current is compensated by sampling the change information of the current, so as to ensure 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 smaller 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 driving signal DR, and obtain the current sampling signal V_h1 and the second current sampling signal according to the first current sampling signal V_h1 and the second current sampling signal V_h2 generates a compensation current, and applies 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 superimposes the compensation amount with the current sampling signal Vcs to generate a compensation voltage Vcsc.

Specifically, referring to FIG. 4 , the 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 operational amplifier Gm1, a first compensation resistor Rc1, and a second compensation resistor Rc2 , and the first switch K1. The logic processor 12311 receives the driving signal DR output by the driving circuit 1240, and generates the first pulse signal Vg_sh1 after the rising edge of the driving signal DR is delayed for the first time, and delays the second time at the falling edge of the first pulse signal Vg_sh1 Then the second pulse signal Vg_sh2 is generated, 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 during 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 during the pulse time of the second pulse signal Vg_sh2 to generate the second current sampling signal V_h2. The first input terminal of the first transconductance operational amplifier Gm1 receives the first current sampling signal V_h1, the second input terminal receives the second current sampling signal V_h2, and the output terminal provides compensation current. The first terminal of the first compensation resistor Rc1 receives the current sampling signal Vcs, and the second terminal is connected to the output terminal 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. Wherein, the first switch K1 is, for example, a low conduction switch, and when the mode control signal Vg_DCM is low (inactive level, indicating that the inductor works in a 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 that in the discontinuous mode. Among them, 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 can be obtained to improve the load and Linear adjustment rate.

Further, referring to FIG. 3 , the constant current control circuit 1230 further 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 for providing 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 at different periods of the entire control cycle according to the level states of the driving 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 reference voltage Vav_ref and the driving signal DR.

Specifically, referring to FIG. 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 terminal of the second switch K2 receives the compensation voltage Vcsc, and the control terminal receives the driving signal DR. The first end of the third switch K3 is grounded, and the control end receives the zero-crossing detection signal Vg_ZCD. A first terminal of the NAND gate U1 receives a driving signal DR, and a second terminal receives a zero-crossing detection signal Vg_ZCD. The first terminal of the fourth switch K4 receives the reference voltage Voff, and the control terminal is connected to the output terminal of the NAND gate U1. The second terminal of the second switch K2 is connected with the second terminal of the third switch K3 and the second terminal of the fourth switch K4 to output the analog voltage VL. Further, FIG. 4 shows a reference voltage generation unit 1232. When the inductor is in continuous mode, the reference voltage Voff is the average reference voltage Vav_ref, and when the inductor is in discontinuous mode, the reference voltage Voff is the peak voltage Vpk_h of the compensation voltage. Half. 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 sample and hold 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 with the third sampling and holding unit 12321 for generating half of the peak voltage. The first terminal of the fifth switch K5 is connected to the voltage processing unit 12322, and the control terminal receives the mode control signal Vg_DCM. The first end of the sixth switch K6 receives the average 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 to output the reference voltage Voff. The first terminal of the first capacitor C1 is connected to the second terminal of the sixth switch K6 and the second terminal of the fifth switch K5, the second terminal is grounded, and outputs the reference voltage Voff. Wherein, 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 is regulated and output by the capacitor C1. 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 reference voltage Vav_ref, and is regulated and output by the capacitor C1. Further, for example, when the driving 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 drive signal DR is at low level and the zero-crossing detection signal Vg_ZCD is at low level, the fourth switch K4 is turned on. Further, when the mode control signal Vg_DCM is at low level (the inductor is in continuous mode), the sixth switch K6 is turned on, and the analog voltage VL is the average reference voltage Vav_ref; when the mode control signal Vg_DCM is at a high level (the inductor is in 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 low level and the inductor is in discontinuous mode, the inductor current drops to zero, the zero-crossing detection signal Vg_ZCD is at high level, and the third switch is turned on, then the analog voltage VL is the ground voltage. Further, the conduction control signal generating unit 1234 includes a second transconductance operational amplifier Gm2, a third transconductance operational amplifier Gm3, a capacitor C3, a seventh switch K7, and a first comparator CMP1. The first terminal of the second transconductance operational amplifier Gm2 receives the average reference voltage Vav_ref, and the second terminal receives the analog voltage VL. A first end of the capacitor C2 is connected to the output end of the second transconductance operational amplifier Gm2 to provide a voltage Vcomp, and a second end of the capacitor C2 is grounded. The first terminal of the third transconductance operational amplifier Gm3 is connected to the output terminal of the second transconductance operational amplifier Gm2, and the second terminal is grounded. The first end of the capacitor C3 is connected to the output end of the third transconductance operational amplifier Gm3 to provide a voltage Vramp, and the second end of the capacitor C3 is grounded. The first terminal of the seventh switch K7 is connected to the first terminal of the capacitor C3, the second terminal is connected to the second terminal of the capacitor C3, and the control terminal receives the driving signal DR. The first end of the first comparator CMP1 is connected to the output end of the third transconductance operational 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 turn-on control signal generation unit 1234 is used to calculate the turn-off time of the corresponding power switch Q1 according to the analog voltage VL of the whole period and the average reference voltage Vav_ref to control the stability of the output current. Further, when the driving signal DR is at low level, the current output by the third transconductance operational amplifier Gm3 charges the capacitor C3, and when the voltage Vramp on the capacitor C3 is greater than the preset threshold voltage Vr_1, the conduction control signal Vg_S is generated.

Because under deep dimming, the operating frequency of the switch tube is reduced, the peak value reference and the average value reference will also be 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 in the conduction stage is sampled, which cannot Meet the requirements of stroboscopic coefficient.

In order to meet the requirements of screen flicker coefficient under deep dimming, it is also necessary to sample the current signal in the turn-off phase of the power switch. The invention designs an analog unit to output an analog voltage VL, and the analog voltage characterizes 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 being turned on and off. The conduction control unit outputs a conduction control signal according to the analog voltage, the average reference voltage and the driving signal, so as to control the conduction and shutdown of the power switch, and realize the constant current output in the continuous mode and the discontinuous mode.

Referring to FIG. 3 and FIG. 4 , the constant current control circuit 1230 further includes a shutdown control module 1235 that generates a shutdown control signal Vg_R according to the compensation voltage Vcsc and the peak reference voltage Vpk_ref. Further, the shutdown control signal generating unit 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 is generated.

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 supply power to the LED driving controller 1200 .

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, and 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. Wherein, the resistance value of the resistor R4 changes with the temperature.

Further, in conjunction with FIG. 5 . At time t0, the driving 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. At time t1 after the first time elapses, 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, and at time t2 the second sampling and holding unit 12313 samples and sums the current sampling signal Vcs Hold to generate the second current sampling signal V_h2. At t3, 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 t4, the drive signal DR changes from low to high, and the voltage Vramp reaches the set threshold voltage Vr_1 cleared. During the period from t0 to t4, the zero-crossing detection signal Vg_ZCD is always at low level, and the mode control signal Vg_DCM is always at low level. The above is a complete cycle, which describes the working sequence of the constant current control circuit 1100 when the inductor works in continuous mode. And between t4-t5, the inductor still works in the continuous mode, and the value of the analog voltage VL changes according to the state of the mode control signal Vg_DCM, the zero-crossing detection signal Vg_ZCD, and the driving signal DR. For the specific value, please refer to the diagram The relevant description of the simulation unit 1233 in 3.

Then at time t5, the drive signal DR changes from low to high, the power switch Q1 is turned on, the inductor current IL rises 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 charging from 0; at the time t7, the inductor current IL drops to 0, and the zero-crossing detection signal Vg_ZCD signal changes from low to high; at the time t8, the driving signal DR changes from low to High, the zero-crossing detection signal Vg_ZCD signal changes from high to low, and the voltage Vramp is cleared to zero after reaching the set threshold voltage Vr_1. That is, during the period from t5 to t8, the mode control signal Vg_DCM is always at a high level, which describes the working sequence of the constant current control circuit 1100 when the inductor works in the discontinuous mode.

Fig. 6 shows a schematic diagram of a dimming reference curve of a reference generating circuit in an LED drive controller according to an embodiment of the present invention.

As shown in FIG. 6 , it is the corresponding peak reference voltage Vpk_ref and average value reference voltage Vav_ref generated by the reference generation circuit 1220 according to the dimming signal DIM with different duty ratios D. Further, the average value reference voltage Vav_ref increases in a certain proportion 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, high 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 to say, 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 frequency and then appear Audio noise.

Fig. 7 shows another schematic structural diagram of the reference voltage generation unit in the constant current control circuit of the LED drive controller provided according to the embodiment of the present invention. FIG. 7 shows a schematic waveform diagram of the reference voltage generating unit in FIG. 8 .

In an alternative embodiment, as shown in FIG. 7, it is another reference voltage generation unit 2232 in the constant current control circuit 1230, which obtains the intermediate voltage according to the average reference voltage Vav_ref, and obtains the intermediate voltage according to the average reference voltage Vav_ref and the intermediate voltage A reference voltage V_3 is generated. Specifically, the reference voltage generating unit 2232 includes a scaling unit 22321 , a subtracting 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 subtracts the scaled average reference voltage from the intermediate reference voltage Vref_4. The clamping unit 22323 is connected to the subtracting 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 the reference voltage V_3.

Referring to FIG. 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 value reference voltage Vav_ref. When the duty cycle D of the dimming signal DIM is lower than the set value, the value of the reference voltage V_3 provided by the reference voltage generation unit 2232 is between the average value reference voltage Vav_ref and the peak reference voltage Vpk_ref.

The LED drive system provided by this application, which includes an LED drive controller, adopts a hysteresis-like control method for dimming, and there will be no long-term inductive no-current state, and the output current can be kept constant, so as to achieve a more excellent Screen flicker factor and current ripple rate. Further, the present application realizes a higher load and linear adjustment rate by compensating the current sampling signal, and the compensation amount is related to the input and output voltages.

Further, 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, and the analog voltage represents the inductor current in the continuous mode and the discontinuous mode, which is equivalent to the power switch conduction The full cycle of on and off realizes current sampling, so as to realize constant current output in continuous mode and discontinuous mode, and realize deep dimming under the screen flicker coefficient.

Furthermore, the present application adjusts the slope between the peak reference voltage and the duty cycle under the dimming condition 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.

Embodiments according to the present invention are described above, and these embodiments do not describe all details in detail, nor do they limit the invention to only the specific embodiments described. Obviously many modifications and variations are possible in light of the above description. This description 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 its modification on the basis of the present invention. The invention is to be limited only by the claims, along with their full scope and equivalents.

Claims (22)

1. An LED driving controller, comprising:

the zero-crossing detection circuit detects the inductive current in the driving system to generate a mode control signal and a zero-crossing detection signal;

a reference generation circuit that generates a peak reference voltage and a mean reference voltage according to the dimming signal;

the constant current control circuit is used for carrying out linear compensation on a current sampling signal according to the mode control signal and the driving signal so as to generate compensation voltage, and generating a conduction control signal according to the compensation voltage, the zero-crossing detection signal, the mode control signal, the driving signal and the average value reference voltage;

and the driving circuit generates a driving signal according to the on control signal and the off control signal, wherein the driving signal is used for controlling the power switch.

2. The LED drive controller of claim 1, wherein the constant current control circuit further generates the turn-off control signal based on the compensation voltage, the peak reference voltage.

3. The LED drive controller of claim 1, wherein the current sampling signal is representative of a current flowing through a power switch in the drive system.

4. The LED drive controller of claim 1, wherein when the mode control signal is active level, the main circuit in-inductor is in discontinuous mode; when the mode control signal is at an invalid level, the inductor in the main circuit is in a continuous mode.

5. The LED drive controller of claim 1, wherein the constant current control circuit comprises:

and the compensation module provides different compensation quantities according to the working modes of the inductor in the main circuit and generates the compensation voltage according to the current sampling signal and the corresponding compensation quantities.

6. The LED drive controller of claim 5, wherein the compensation module provides a smaller amount of compensation when the inductance is in continuous mode than when the inductance is in discontinuous mode.

7. The LED drive controller of claim 5, wherein the compensation module is configured to obtain a first current sample signal and a second current sample signal of the current sample signal at different time instants according to the driving signal, and generate a compensation current according to the first current sample signal and the second current sample signal.

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

9. The LED drive controller of claim 8, wherein the compensation module comprises:

the logic processor receives the driving signal, and generates a first pulse signal after the rising edge of the driving signal is delayed for a first time, and generates a second pulse signal after the 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 comes;

a first sample-and-hold unit connected to the logic processor, for sampling and holding the current sample signal during a pulse time of the first pulse signal to generate the first current sample signal;

the second sampling and holding unit is connected with the logic processor and is used for sampling and holding the current sampling signal in the pulse time of the second pulse signal so as to generate the second current sampling signal;

a first transconductance amplifier, a first input end receiving the first current sampling signal, a second input end receiving the second current sampling signal, and an output end providing the compensation current;

the first end of the first compensation resistor receives the current sampling signal, and the second end of the first compensation resistor is connected with the output end of the first transconductance amplifier;

the first end of the second compensation resistor receives the current sampling signal; and

and a first end of the first switch is connected with a second end of the second compensation resistor, a second end of the first switch is connected with a second end of the first compensation resistor, and a control end of the first switch receives the mode control signal.

10. The LED drive controller of claim 1, wherein the constant current control circuit further comprises a conduction control module comprising:

a reference voltage generating unit providing a reference voltage;

an analog unit selecting one of the compensation voltage, a ground voltage, a reference voltage as the analog voltage at different periods of an entire control cycle according to level states of the driving signal and a zero-crossing detection signal; and

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

11. The LED drive controller of claim 10, wherein the analog unit comprises:

a first end of the second switch receives the compensation voltage, and a control end of the second switch receives the driving signal;

a first end of the third switch is grounded, and a control end of the third switch receives the zero-crossing detection signal;

the first end of the NAND gate receives the driving signal, and the second end of the NAND gate receives the zero-crossing detection signal;

a fourth switch, a first end of which receives the reference voltage, a control end of which is connected with the output end of the NAND gate,

a second terminal of the second switch is connected to a second terminal of the third switch and a second terminal of the fourth switch to output the analog voltage.

12. The LED driving controller according to claim 10, wherein the reference voltage generating unit is the average reference voltage when the inductor is in a continuous mode, and is one-half of a peak voltage of the compensation voltage when the inductor is in a discontinuous mode.

13. The LED driving controller according to claim 12, wherein the reference voltage generating unit includes:

a third sample-and-hold unit that samples and holds a peak value of the compensation voltage and outputs the peak voltage;

the voltage processing unit is connected with the third sampling and holding unit and generates half of peak voltage;

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

a sixth switch, a first end of which receives the average reference voltage, a control end of which receives a mode control signal, and a second end of which is connected with a second end of the fifth switch and outputs the reference voltage; and

a first capacitor, a first end of which is connected with the second end of the sixth switch and the second end of the fifth switch, and a second end of which is grounded,

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

14. The LED driving controller of claim 10, wherein the turn-on control unit comprises:

a first end of the second transconductance operational amplifier receives the average value reference voltage, and a second end of the second transconductance operational amplifier receives the analog voltage;

a first end of the second capacitor is connected with the output end of the second transconductance operational amplifier, and a second end of the second capacitor is grounded;

a third transconductance operational amplifier, wherein the first end is connected with the output end of the second transconductance operational amplifier, and the second end is grounded;

a first end of the third capacitor is connected with the output end of the third transconductance amplifier, and a second end of the third capacitor is grounded;

a first end of the seventh switch is connected with a first end of the third capacitor, a second end of the seventh switch is connected with a second end of the third capacitor, and a control end of the seventh switch receives the driving signal;

and a first end of the first comparator is connected with the output end of the third transconductance amplifier, a second end of the first comparator receives a set threshold voltage, and the output end of the first comparator outputs the conduction control signal.

15. The LED driving controller according to claim 10, wherein the reference voltage generating unit derives an intermediate voltage from the average reference voltage, and generates the reference voltage from the average reference voltage and the intermediate voltage.

16. The LED driving controller according to claim 15, wherein the reference voltage generating unit includes:

a scaling unit which performs scaling processing on the average value reference voltage;

the subtracting unit is connected with the scaling unit and is used for subtracting the scaled average value reference voltage and the intermediate reference voltage;

the clamping unit is connected with the subtracting unit and clamps the subtraction result;

and an adding unit respectively connected with the clamping unit and the average value reference voltage to generate the reference voltage.

17. The LED drive controller of claim 1, wherein the constant current control circuit further comprises a turn-off control module comprising:

the leading edge blanking unit receives the compensation voltage and outputs the compensation voltage after a third time; and

and a first end of the second comparator is connected with the leading edge blanking unit, a second end of the second comparator receives the peak reference voltage, and an output end of the second comparator outputs the turn-off control signal.

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

19. The LED drive controller of claim 1, further comprising:

and the protection circuit is used for carrying out overcurrent detection and/or overtemperature detection and outputting a protection signal to the drive circuit, and the drive circuit generates the drive signal according to the protection signal so as to control the power switch of the main circuit to be switched off.

20. An LED driving system, comprising:

a diode having a first terminal receiving an input voltage and a second terminal connected to the first node;

the first end of the inductor is connected with the first node, and a load is connected between the second end of the inductor and the first end of the diode;

a power switch, a first end of which is connected with the first node, a second end of which is grounded, and a control end of which receives a driving signal and is switched on in response to the driving signal to charge the inductor and switched off to discharge the inductor; and

an LED drive controller as claimed in any one of claims 1 to 19.

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

22. The LED driving system according to claim 20, wherein a detection voltage is connected to the first end of the inductance via a fourth capacitance.

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