Hysteresis voltage generation circuit, hysteresis current controller, hysteresis current generation method and LED driving system

Abstract

The invention provides a hysteresis voltage generation circuit, a hysteresis current controller, a hysteresis current control method and an LED driving system, and the circuit comprises a PWM dimming signal frequency detection unit which is used for generating a first clock signal, the frequency of which is in direct proportion to the frequency of a PWM dimming signal; the PWM dimming signal duty ratio counting unit is used for increasing counting based on the first clock signal, outputting a duty ratio counting value and keeping the duty ratio counting value after the duty ratio reaches a threshold value; the hysteresis voltage output unit is used for generating a hysteresis voltage and adjusting the lower limit of the hysteresis voltage based on the duty ratio count value; the lower limit of the hysteresis voltage decreases with the increase of the duty ratio count value, and the upper limit of the hysteresis voltage is a fixed value. According to the invention, the proportion of D is reduced, and the high efficiency of the system in a large dimming duty ratio and the dimming precision in a low dimming duty ratio can be considered at the same time.

Description

Technical Field

[0001] The present invention relates to the field of integrated circuit design, and in particular to a hysteresis voltage generating circuit, a hysteresis current controller, a method and an LED driving system. Background Art

[0002] According to the light-emitting principle and characteristics of LED, constant current source is selected to drive LED lamp beads. Constant current source is usually divided into linear constant current source and switch mode constant current source. Switch mode constant current source stands out for its high efficiency and small size. Among them, hysteresis current control mode Buck driver is widely used in medium and high power LED driving occasions because of its simple structure and strong versatility.

[0003] In current client applications, dimming function is a very typical requirement; there are two types of dimming methods, linear dimming and PWM dimming. Among them, the advantages of PWM dimming are high precision and no color difference, and PWM dimming is more suitable for intelligent dimming applications, so constant current drivers with integrated PWM dimming function are widely used. With the development of intelligent dimming technology, customers' demand for PWM dimming depth has further increased; currently conventional PWM dimming cannot meet the high-depth PWM dimming requirements, and there is jitter at low brightness.

[0004] like Figure 1 As shown, in the PWM dimming method of the hysteresis current control mode, the inductor current detection signal Vcs is compared with the upper limit VH of the hysteresis voltage and the lower limit VL of the hysteresis voltage respectively. When the PWM dimming signal is at a high level, the power switch tube in the LED switching power supply is periodically controlled to be turned on or off, and the average value of the inductor current detection signal Vcs is controlled to be (VH+VL) / 2 when the PWM dimming signal is at a high level. Then, the inductor current is also proportionally controlled to IL. When the PWM dimming signal is at a low level, the power switch tube remains in the off state and the inductor current is 0.

[0005] Since the inductor current is IL when the PWM dimming signal is high and 0 when the PWM is low, the average value of the inductor current is IL_AVG=IL*D, where D is the duty cycle of the PWM dimming signal. Since the LED is connected in series with the inductor, the average value of the inductor current is the average value of the LED. Therefore, by changing the duty cycle D of the PWM dimming signal, the LED current can be controlled, thereby achieving the dimming function.

[0006] based on Figure 1 It can be seen that when the duty cycle of the PWM dimming signal ranges from 0 to 100%, the upper and lower limits of the hysteresis voltage are both composed of fixed voltages, so the hysteresis voltage width remains unchanged, such as Figure 2 As shown. Figure 1 As shown in the figure, when the duty cycle D of the PWM dimming signal is within the range of △D between PWM1 and PWM2, the average current of the LED is the same, which means that within the range of △D, changing the duty cycle D of the PWM dimming signal cannot change the average current of the LED. Therefore, when the duty cycle D of the PWM dimming signal increases linearly, the LED brightness will not change within the range of △D. When the duty cycle D of the PWM dimming signal is greater than the duty cycle of PWM2, the LED brightness will change suddenly, thus affecting the linearity and continuity of dimming. When the duty cycle D of the PWM dimming signal is large, △D / D is small. Since the average current of the LED is large and the brightness of the LED is high at this time, the human eye is not sensitive to small brightness changes. In terms of the visual perception of the human eye, the impact can be ignored. However, in the case of high-depth dimming, the duty cycle D of the PWM dimming signal is extremely small, while △D remains unchanged, resulting in a large △D / D. Since the average current of the LED is small at this time, the brightness of the LED is low, and the same △D causes a more significant problem of discontinuous brightness changes, which makes the human eye feel the jitter of the light source. The impact cannot be ignored and the customer experience is deteriorated.

[0007] Therefore, how to meet the high-depth PWM dimming requirements in the hysteresis current control mode, avoid jitter at low brightness, and improve customer experience has become one of the technical problems that technical personnel in this field need to solve urgently.

[0008] It should be noted that the above introduction to the technical background is only for the convenience of providing a clear and complete description of the technical solutions of the present invention and for the convenience of understanding by those skilled in the art. It cannot be considered that the above technical solutions are well known to those skilled in the art simply because these solutions are described in the background technology section of the present invention. Summary of the invention

[0009] In view of the shortcomings of the prior art mentioned above, the object of the present invention is to provide a hysteresis voltage generating circuit, a hysteresis current controller, a method and an LED driving system, which are used to solve the problems in the prior art that PWM dimming cannot meet the high-depth PWM dimming requirements, there is jitter at low brightness, and the customer experience is poor.

[0010] To achieve the above-mentioned object and other related objects, the present invention provides a hysteresis voltage generating circuit, which is applied to a hysteresis current controller, wherein the hysteresis voltage generating circuit at least comprises: a PWM dimming signal frequency detecting unit, a PWM dimming signal duty cycle counting unit and a hysteresis voltage output unit;

[0011] The PWM dimming signal frequency detection unit receives the PWM dimming signal and is used to generate a first clock signal, wherein the frequency of the first clock signal is proportional to the frequency of the PWM dimming signal;

[0012] The PWM dimming signal duty cycle counting unit is connected to the output end of the PWM dimming signal frequency detection unit, counts up the duty cycle of the PWM dimming signal based on the first clock signal, outputs a duty cycle count value, and maintains the duty cycle count value after the duty cycle reaches a threshold value;

[0013] The hysteresis voltage output unit is connected to the output end of the PWM dimming signal duty cycle counting unit, and is used to generate a hysteresis voltage and adjust the lower limit of the hysteresis voltage based on the duty cycle count value; the lower limit of the hysteresis voltage decreases as the duty cycle count value increases, and the upper limit of the hysteresis voltage is a fixed value.

[0014] Optionally, the PWM dimming signal frequency detection unit includes: a PWM dimming signal frequency measurement module and a clock signal generation module;

[0015] The PWM dimming signal frequency measurement module counts the time when the PWM dimming signal is at a high level based on the second clock signal, and outputs a frequency count value after completing the counting, wherein the frequency count value is proportional to the frequency of the PWM dimming signal;

[0016] The clock signal generating module is connected to the output end of the PWM dimming signal frequency measuring module, and generates the first clock signal based on the frequency count value.

[0017] More optionally, the PWM dimming signal frequency measurement module includes: a delay unit, a first counter, a register and a first subtractor;

[0018] The delay unit receives the PWM dimming signal, delays the PWM dimming signal and then outputs a delayed signal, wherein the delay time is no more than two cycles of the second clock signal;

[0019] The first counter is connected to the output end of the delay unit and receives the second clock signal, and is reset and starts counting up at the rising edge of the delay signal;

[0020] The register is connected to the output end of the first counter, stores the value output by the first counter, and reads out the latched value at the rising edge of the PWM dimming signal;

[0021] The first subtractor is connected to the output end of the register, and subtracts the value output by the register from the preset value to obtain the frequency count value.

[0022] More optionally, the clock signal generating module comprises: a digital-to-analog converter and an oscillator;

[0023] The digital-to-analog converter is connected to the output end of the PWM dimming signal frequency measurement module to convert the frequency count value into an analog signal;

[0024] The oscillator is connected to the output terminal of the digital-to-analog converter, and generates the first clock signal based on the output signal of the digital-to-analog converter.

[0025] Optionally, the PWM dimming signal duty cycle counting unit includes a second counter;

[0026] The second counter is connected to the PWM dimming signal, the first clock signal and the latch signal. When the PWM dimming signal is at a high level, the second counter starts counting from an initial value based on the first clock signal, and latches the count value based on the latch signal after counting to a pre-designed value; when the PWM dimming signal is at a low level, the count value is reset to the initial value.

[0027] Optionally, the hysteresis voltage output unit includes: a current source, a resistor, a switch and a second subtractor;

[0028] The current source is controlled by the duty cycle count value, and the larger the duty cycle count value is, the larger the current flowing through the current source is;

[0029] One end of the resistor is connected to the current source, and the other end is grounded; the switch is connected in parallel to both ends of the resistor and is controlled by a driving signal of the power switch tube. When the power switch tube is turned on, the switch is turned on, and when the power switch tube is turned off, the switch is turned off;

[0030] The second subtractor subtracts a voltage at a connection node between the current source and the resistor from an upper limit voltage of the hysteresis voltage to obtain the hysteresis voltage.

[0031] In order to achieve the above-mentioned object and other related objects, the present invention further provides a hysteresis current controller, wherein the hysteresis current controller at least comprises:

[0032] A driving signal generating circuit and the above hysteresis voltage generating circuit;

[0033] The hysteresis voltage generating circuit is used to provide a hysteresis voltage;

[0034] The drive signal generating circuit is connected to the output end of the hysteresis voltage generating circuit and receives the inductor current detection signal; when the PWM dimming signal is at a high level, the drive signal is generated based on the comparison result between the inductor current detection signal and the hysteresis voltage, and when the PWM dimming signal is at a low level, the drive signal remains at a low level.

[0035] To achieve the above-mentioned object and other related objects, the present invention further provides an LED driving system, the LED driving system at least comprising:

[0036] Switching power supply module, LED load, sampling module and the above hysteresis current controller;

[0037] The sampling module detects the current of the inductor;

[0038] The LED load is connected to the switching power module and operates based on the output current of the switching power module;

[0039] The output end of the hysteresis current controller is connected to the gate of the power switch tube in the switching power supply module to provide a driving signal.

[0040] Optionally, the switching power supply module is a BUCK topology structure.

[0041] In order to achieve the above-mentioned object and other related objects, the present invention further provides a hysteresis current control method, which at least includes:

[0042] When the PWM dimming signal is at a high level, a hysteresis voltage is generated based on the PWM dimming signal, and hysteresis current control is implemented based on the hysteresis voltage; wherein the upper limit of the hysteresis voltage is fixed; the lower limit decreases linearly as the duty cycle of the PWM dimming signal increases, and remains unchanged when the duty cycle of the PWM dimming signal is greater than or equal to a threshold;

[0043] When the PWM dimming signal is at a low level, the power switch tube in the switching power supply module is turned off.

[0044] Optionally, the method for generating the hysteresis voltage includes:

[0045] Measuring the frequency of the PWM dimming signal and generating a first clock signal, wherein the frequency of the first clock signal is proportional to the frequency of the PWM dimming signal;

[0046] Based on the first clock signal, the duty cycle of the PWM dimming signal is counted to obtain a duty cycle count value, wherein the duty cycle count value increases linearly and is maintained when the duty cycle of the PWM dimming signal is greater than or equal to a threshold value;

[0047] The hysteresis voltage is generated, and a lower limit of the hysteresis voltage is adjusted based on the duty cycle count value.

[0048] More optionally, the method for implementing hysteresis current control based on the hysteresis voltage includes:

[0049] The detection signal of the inductor current in the switching power supply module is compared with the hysteresis voltage. If the inductor current detection signal rises to the upper limit of the hysteresis voltage, the power switch tube in the switching power supply module is turned off. If the inductor current detection signal drops to the lower limit of the hysteresis voltage, the power switch tube is turned on.

[0050] As described above, the hysteresis voltage generating circuit, hysteresis current controller, method and LED driving system of the present invention have the following beneficial effects:

[0051] The hysteresis voltage generating circuit, hysteresis current controller, method and LED driving system of the present invention adjust the lower limit of the hysteresis voltage based on the duty cycle of the PWM dimming signal. The lower limit of the hysteresis voltage decreases linearly with the increase of the duty cycle within the range where the duty cycle of the PWM dimming signal is less than the threshold, and maintains the minimum value when the duty cycle of the PWM dimming signal is greater than or equal to the threshold. In this way, a higher system efficiency can be obtained when the PWM dimming depth is shallow, and a linear and stable dimming effect can be obtained when the PWM dimming depth is deep, thereby eliminating the defect of light source jitter during high-depth PWM dimming and improving customer experience. BRIEF DESCRIPTION OF THE DRAWINGS

[0052] Figure 1 Shown is a schematic diagram of the principle of a PWM dimming method.

[0053] Figure 2 Display as Figure 1 Schematic diagram of the hysteresis voltage width in the PWM dimming method.

[0054] Figure 3 It is a schematic structural diagram of the hysteresis voltage generating circuit of the present invention.

[0055] Figure 4 It is a schematic diagram showing the structure of the PWM dimming signal frequency detection unit of the present invention.

[0056] Figure 5 It is a schematic diagram showing the structure of the PWM dimming signal duty cycle counting unit of the present invention.

[0057] Figure 6 It is a schematic structural diagram of the hysteresis voltage output unit of the present invention.

[0058] Figure 7 Shown is a schematic structural diagram of the hysteresis current controller of the present invention.

[0059] Figure 8 Shown is a schematic structural diagram of the LED driving system of the present invention.

[0060] Fig. 9 It is a schematic flow chart of the hysteresis current control method of the present invention.

[0061] Fig.10 It is a schematic diagram showing the principle of the hysteresis current control method of the present invention.

[0062] Component number description

[0063] 1 Hysteresis Current Controller

[0064] 1a Hysteresis voltage generation circuit

[0065] 11 PWM dimming signal frequency detection unit

[0066] 111 PWM dimming signal frequency measurement module

[0067] 112 Clock signal generation module

[0068] 11a Delay section

[0069] 11b First counter

[0070] 11c Registers

[0071] 11d First subtractor

[0072] 11e Digital to Analog Converter

[0073] 11f Oscillator

[0074] 12 PWM dimming signal duty cycle counting unit

[0075] 13 Hysteresis voltage output unit

[0076] 131 Current Source

[0077] 132 Second subtractor

[0078] 1b Driving signal generation circuit

[0079] 2 Switching power supply module

[0080] 3 Sampling module DETAILED DESCRIPTION

[0081] The following describes the embodiments of the present invention through specific examples, and those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present invention.

[0082] See also Figures 3 to 10It should be noted that the illustrations provided in this embodiment are only used to illustrate the basic concept of the present invention in a schematic manner, and the drawings only show components related to the present invention rather than being drawn according to the number, shape and size of components in actual implementation. In actual implementation, the type, quantity and proportion of each component may be changed arbitrarily, and the component layout may also be more complicated.

[0083] The present invention provides a hysteresis voltage generating circuit, a hysteresis current controller, a method and an LED driving system. Aiming at the defects of the PWM dimming method under the high-depth dimming situation, the lower limit of the hysteresis voltage is increased to reduce the value of △D / D, thereby improving the accuracy of PWM dimming and avoiding the light source jitter problem that occurs during high-depth PWM dimming. The specific scheme is as follows.

[0084] like Figure 3 As shown, the present invention provides a hysteresis voltage generating circuit 1a, and the hysteresis voltage generating circuit 1a includes:

[0085] The PWM dimming signal frequency detection unit 11 , the PWM dimming signal duty cycle counting unit 12 and the hysteresis voltage output unit 13 .

[0086] like Figure 3 As shown, the PWM dimming signal frequency detection unit 11 receives the PWM dimming signal PWM and generates a first clock signal Clock1 , and the frequency of the first clock signal Clock1 is proportional to the frequency of the PWM dimming signal PWM.

[0087] Specifically, any circuit structure capable of generating a clock signal having a frequency proportional to the frequency of the PWM dimming signal is applicable to the present invention, such as Figure 4 As shown, in this embodiment, the PWM dimming signal frequency detection unit 11 includes: a PWM dimming signal frequency measurement module 111 and a clock signal generation module 112. The PWM dimming signal frequency measurement module 111 counts the time of the high level of the PWM dimming signal PWM based on the second clock signal Clock2, and outputs a frequency count value after completing the counting, and the frequency count value is proportional to the frequency of the PWM dimming signal PWM. The clock signal generation module 112 is connected to the output end of the PWM dimming signal frequency measurement module 111, and generates the first clock signal Clock1 based on the frequency count value.

[0088] More specifically, if Figure 4As shown, as an example, the PWM dimming signal frequency measurement module 111 includes a delay unit 11a, a first counter 11b, a register 11c and a first subtractor 11d. The delay unit 11a receives the PWM dimming signal PWM, delays the PWM dimming signal PWM and outputs a delayed signal PWMD. As an example, the delay time is not greater than two cycles of the second clock signal Clock2. Further in this embodiment, the delay time is one clock cycle of the second clock signal Clock2. The first counter 11b is connected to the output end of the delay unit 11a, and receives the second clock signal Clock2. It resets and starts counting up at the rising edge of the delay signal PWMD; that is, the first counter 11b continuously counts the frequency of the delay signal PWMD. The smaller the frequency of the delay signal PWMD (the larger the cycle), the larger the count value of the first counter 11b. The register 11c is connected to the output end of the first counter 11b, registers the value output by the first counter 11b, and reads out the latched value at the rising edge of the PWM dimming signal PWM, that is, the output value is the count value from the rising edge of the delay signal PWMD to the rising edge of the PWM dimming signal PWM. The first subtractor 11d is connected to the output end of the register 11c, and subtracts the value output by the register 11c from the preset value to obtain the frequency count value, so that the frequency count value is proportional to the frequency of the PWM dimming signal PWM (linear change); in this embodiment, the preset value is the maximum value corresponding to the number of bits of the output value of the register 11c. In actual use, the preset value can be set as needed to adjust the relationship between the count value and the PWM dimming signal from inverse proportion to direct proportion, which is not limited to this embodiment.

[0089] It should be noted that the delay time is to prevent the first counter 11b from being reset when reading the data in the register 11c, and the count value cannot be read from the register 11c; by setting the delay time, the count value can be read out and then the reset step can be performed to ensure that the count value can be read smoothly. At this time, due to the existence of the delay time, the numerical value output from the register 11 is approximately considered to represent the frequency of the PWM dimming signal, and the accuracy of the PWM dimming signal frequency will be lost. Therefore, the smaller the delay time, the more accurate the frequency of the measured PWM dimming signal. In this example, there will be a loss of 1-2 clock cycles. In actual use, the delay time can be set as needed to ensure that the count value is read out while meeting the accuracy requirements. In addition, any circuit structure that can detect the frequency of the PWM dimming signal is applicable to the present invention, and is not limited to this embodiment.

[0090] More specifically, if Figure 4As shown, as an example, the clock signal generating module 112 includes a digital-to-analog converter 11e and an oscillator 11f. The digital-to-analog converter 11e is connected to the output end of the PWM dimming signal frequency measuring module 111, and converts the frequency count value into an analog signal. Any circuit structure that can realize digital-to-analog conversion is applicable, and it is not described in detail here. The oscillator 11f is connected to the output end of the digital-to-analog converter 11e, and generates the first clock signal Clock1 based on the output signal of the digital-to-analog converter 11e. In this example, the oscillator 11f is a voltage-controlled oscillator structure. In actual use, an RC oscillation structure or an LC oscillation structure can also be used, which is not described in detail here.

[0091] It should be noted that any circuit structure that can generate the first clock signal based on the frequency count value is applicable to the present invention, including but not limited to directly using a digital oscillator to generate the first clock signal, and is not limited to this embodiment.

[0092] like Figure 3 As shown, the PWM dimming signal duty cycle counting unit 12 is connected to the output end of the PWM dimming signal frequency detection unit 11, and counts the duty cycle of the PWM dimming signal PWM based on the first clock signal Clock1, outputs the duty cycle count value Dn...D0, and maintains the duty cycle count value after the duty cycle reaches a threshold.

[0093] Specifically, Figure 5 As shown, in this embodiment, the PWM dimming signal duty cycle counting unit 12 includes a second counter. The second counter is connected to the PWM dimming signal PWM, the first clock signal Clock1 and the latch signal Latch. When the PWM dimming signal PWM is at a high level, the duty cycle count value Dn…D0 is obtained based on the first clock signal Clock1 from the initial value, where n is the number of bits of the second counter; after counting to a pre-designed value (corresponding to the duty cycle threshold D1), the count value is latched based on the latch signal Latch; that is, within the duty cycle threshold range, the duty cycle count value increases with the increase of the duty cycle, and after being greater than or equal to the duty cycle threshold, the duty cycle count value remains constant. When the PWM dimming signal PWM is at a low level, the count value is reset to the initial value.

[0094] It should be noted that, in this embodiment, the preset count value is the full-scale maximum count value (11...111) of the second counter. The preset value can be set as needed during use, and will not be described in detail here. The initial value is used to determine the lower limit maximum value of the hysteresis voltage and can be set as needed. Any circuit structure that can achieve the above functions is applicable to the PWM dimming signal duty cycle counting unit of the present invention, not limited to this embodiment.

[0095] It should be noted that the frequency of the first clock signal Clock1 is recorded as f1=K*f PWM , K is a constant and needs to be set by the PWM dimming signal frequency detection unit 11. In this embodiment, the time T1 corresponding to the second counter being full is (2 n -initial value) / f1, then D1=T1*f PWM , substituting the expression of T1 into D1=f PWM *(2 n -initial value) / f1, since f1=K*f PWM , D1=(2 n -initial value) / K, then the value of K is designed to be K=(2 n -initial value) / D1 can satisfy the function of adjusting the lower limit of the hysteresis voltage when the duty cycle of the PWM dimming signal is lower than the threshold D1. In actual use, 2 n It can also be replaced by a count value corresponding to a duty cycle threshold D1, which will not be described in detail here. The duty cycle threshold D1 can be set according to specific process parameters as long as it can solve the light source jitter problem.

[0096] like Figure 3 As shown, the hysteresis voltage output unit 13 is connected to the output end of the PWM dimming signal duty cycle counting unit 12 to generate a hysteresis voltage Vhys; and the lower limit of the hysteresis voltage Vhys is adjusted based on the duty cycle counting value, and the lower limit of the hysteresis voltage Vhys decreases as the duty cycle counting value increases; the upper limit of the hysteresis voltage Vhys is a fixed value.

[0097] Specifically, Figure 6 As shown, in this embodiment, the hysteresis voltage output unit 13 includes: a current source 131, a resistor R1, a switch and a second subtractor 132. The current source 131 is controlled by the duty cycle count value. The larger the duty cycle count value, the larger the current flowing through the current source 131. One end of the resistor R1 is connected to the current source 131, and the other end is grounded. The switch is connected in parallel to both ends of the resistor R1 and is controlled by the drive signal Drv of the power switch tube. When the power switch tube is turned on, the switch is turned on, and when the power switch tube is turned off, the switch is turned off. The second subtractor 132 subtracts the voltage V1 of the connection node between the current source 131 and the resistor R1 from the upper limit voltage VH of the hysteresis voltage to obtain the hysteresis voltage Vhys.

[0098] More specifically, if Figure 6As shown, as an example, the current source 131 includes n current branches connected in parallel, each current branch is connected in series with a selection switch (S0~Sn), and the control end of each selection switch is respectively connected to the corresponding bit signal of the duty cycle count value (as an example, S0 corresponds to D0, S1 corresponds to D1, ... Sn corresponds to Dn), and when the corresponding bit signal is at a high level, the current branch is turned on; in the initial state, the current source 131 outputs a minimum current Imin based on the initial value of the duty cycle count value. As the second counter counts up, the number of selection switches turned on increases, and the current flowing through the current source 131 gradually increases. When the duty cycle count value reaches a pre-designed value (that is, the duty cycle D of the PWM dimming signal is greater than or equal to the threshold D1), the current source 131 outputs a maximum current Imax; in this example, the current in each current branch satisfies: In=2*In-1=4*In-2=…=2 n-1 *I1=2 n *I0, in actual use, the magnitude of the current in each current branch can be set as needed, not limited to this embodiment. The number of current branches is not limited to n (corresponding to the number of bits of the second counter), and can be set as needed, not less than 2, and the control relationship is adjusted accordingly, which is not described here one by one.

[0099] More specifically, if Figure 6 As shown, in this example, the switch is implemented by an NMOS tube M1, the drain is connected to the current source 131, the source is grounded, and the gate is connected to the drive signal Drv. In actual use, any switch structure is applicable, not limited to this embodiment.

[0100] More specifically, if Figure 6 As shown, the upper limit voltage of the hysteresis voltage is connected to the non-inverting input terminal of the second subtractor 132, and the connection node between the current source 131 and the resistor R1 is connected to the inverting input terminal of the second subtractor 132. When the driving signal Drv is at a high level, the inductor current is in a rising stage and needs to be compared with the upper limit of the hysteresis voltage Vhys. The switch is turned on, the node voltage V1=0, and the hysteresis voltage Vhys=VH-V1=VH. When the driving signal Drv is at a low level, the inductor current is in a decreasing stage and needs to be compared with the lower limit of the hysteresis voltage Vhys. The switch is turned off, and the node voltage V1 gradually rises from V1_min (=Imin*R1), and the hysteresis voltage Vhys=VH-V1=VL gradually decreases; if the duty cycle D of the PWM dimming signal is greater than or equal to the threshold D1, the lower limit of the hysteresis voltage gradually decreases from VL_max=VH-V1_min to VL_min=VH-V1_max, and then maintains VL_min=VH-V1_max.

[0101] It should be noted that any circuit structure that can generate the hysteresis voltage based on the duty cycle count value is applicable to the present invention and will not be described in detail here.

[0102] In summary, the hysteresis voltage generating circuit 1a of the present invention can generate a voltage with an upper limit that remains fixed, and a lower limit that decreases linearly with the increase of the duty cycle within the range where the duty cycle of the PWM dimming signal is less than the threshold value D1, and maintains at the value (minimum value) corresponding to the duty cycle D1 when the duty cycle of the PWM dimming signal is greater than or equal to the threshold value D1.

[0103] like Figure 7 As shown, the present invention further provides a hysteresis current controller 1, and the hysteresis current controller 1 includes: a hysteresis voltage generating circuit 1a and a driving signal generating circuit 1b.

[0104] like Figure 7 As shown, the hysteresis voltage generating circuit 1a is used to provide a hysteresis voltage Vhys. The structure and working principle of the hysteresis voltage generating circuit 1a are as mentioned above and will not be described in detail here.

[0105] like Figure 7 As shown, the drive signal generating circuit 1b is connected to the output end of the hysteresis voltage generating circuit 1a and receives the inductor current detection signal Vcs. When the PWM dimming signal PWM is at a high level, the drive signal Drv is generated based on the comparison result between the inductor current detection signal Vcs and the hysteresis voltage Vhys. When the PWM dimming signal PWM is at a low level, the drive signal Drv remains at a low level.

[0106] Specifically, the drive signal generating circuit 1b is used to control the power switch tube in the LED switching power supply, thereby realizing hysteresis current control. When the PWM dimming signal PWM is at a high level, the inductor current detection signal Vcs is compared with the hysteresis voltage Vhys; if the inductor current detection signal Vcs is greater than or equal to the hysteresis voltage Vhys, the drive signal Drv jumps to a low level to turn off the power switch tube; if the inductor current detection signal Vcs is less than or equal to the hysteresis voltage Vhys, the drive signal Drv jumps to a high level to turn on the power switch tube; and repeats. As an example, the drive signal generating circuit 1b includes but is not limited to a comparator and a logic module. The comparator is used to compare the inductor current detection signal Vcs with the hysteresis voltage Vhys, and the logic module is used to generate the drive signal Drv based on the comparison result and the PWM dimming signal, which are not described one by one here.

[0107] Since the lower limit of the hysteresis voltage Vhys is raised, during the period of high level of the PWM dimming signal, the number of times that the inductor current detection signal Vcs changes back and forth between the upper limit and the lower limit of the hysteresis voltage increases. Accordingly, the proportion of △D (the time for the last drop from VH to VL) decreases, which can take into account both the high efficiency of the system at a large dimming duty cycle and the dimming accuracy at a low dimming duty cycle.

[0108] like Figure 8 As shown, the present invention further provides an LED driving system, which includes: the hysteresis current controller 1, a switching power supply module 2, and an LED load and sampling module 3.

[0109] like Figure 8 As shown, as an example, the switching power supply module 2 adopts a BUCK topology structure, including an input capacitor Cin, a freewheeling diode D, an inductor L, an output capacitor Cout and a power switch tube M2, and the specific connection relationships are not described here one by one.

[0110] like Figure 8 As shown, the sampling module 3 detects the current of the inductor L to obtain an inductor current detection signal Vcs.

[0111] Specifically, in the present embodiment, the sampling module 3 is implemented by a sampling resistor Rcs, and the sampling resistor Rcs is connected in series with the inductor L in the switching power supply module 2. As an example, the sampling resistor Rcs is connected in series between the cathode of the freewheeling diode D and the upper plate of the output capacitor Cout. In actual use, the sampling module 3 can be set at any position where the current on the inductor L can be detected, and any method that can detect the current on the inductor L is applicable to the present invention, and is not limited to the present embodiment.

[0112] like Figure 8 As shown, the LED load is connected to the switching power module 2 and operates based on the output current of the switching power module 2. Specifically, the positive electrode of the LED load is connected to the upper plate of the output capacitor Cout, and the negative electrode is connected to the lower plate of the output capacitor Cout.

[0113] like Figure 8 As shown, the output end of the hysteresis current controller 1 is connected to the gate of the power switch tube M2 in the switching power supply module 2 to provide a driving signal Drv. The specific structure and principle are as mentioned above and will not be described here one by one.

[0114] like Fig. 9 and Fig.10As shown, the present invention further provides a hysteresis current control method. In this embodiment, the hysteresis current control method is implemented by using the hysteresis current controller 1 of the present invention. In actual use, any method that can implement the method is applicable. The hysteresis current control method includes:

[0115] When the PWM dimming signal PWM is at a high level, a hysteresis voltage Vhys is generated based on the PWM dimming signal PWM, and hysteresis current control is implemented based on the hysteresis voltage Vhys; wherein the upper limit of the hysteresis voltage Vhys is fixed, and the lower limit decreases linearly with the increase of the duty cycle of the PWM dimming signal PWM and remains unchanged when the duty cycle D of the PWM dimming signal PWM is greater than a threshold value D1;

[0116] When the PWM dimming signal PWM is at a low level, the power switch tube in the switching power supply is turned off.

[0117] The specific steps are as follows:

[0118] 11) When the rising edge of the PWM dimming signal PWM arrives, the frequency of the PWM dimming signal PWM is measured to generate a first clock signal Clock1 proportional to the frequency of the PWM dimming signal PWM. The first clock signal Clock1 is a high-frequency clock, and its frequency is greater than the frequency of the PWM dimming signal.

[0119] 12) Then, based on the first clock signal Clock1, the duty cycle of the PWM dimming signal PWM is counted up on the basis of the initial value to obtain a duty cycle count value, and the duty cycle count value increases linearly with the increase of the duty cycle of the PWM dimming signal.

[0120] 13) adjusting a lower limit of a hysteresis voltage according to the duty cycle count value, wherein the lower limit of the hysteresis voltage decreases linearly with an increase in the duty cycle of the PWM dimming signal, and the upper limit of the hysteresis voltage remains unchanged.

[0121] 14) Determine whether the duty cycle count value reaches a pre-designed value (in this example, the corresponding counter is full), that is, whether the duty cycle D of the PWM dimming signal is greater than or equal to the threshold D1; if not, continue to execute steps 12) and 13) to linearly reduce the lower limit of the hysteresis voltage; if yes, keep the lower limit of the hysteresis voltage at the minimum value.

[0122] 15) At the same time, during the process of the PWM dimming signal PWM being at a high level, the switch power module implements hysteresis current control based on the adjusted hysteresis voltage Vhys. Specifically, the process includes: comparing the inductor current detection signal Vcs in the switch power module with the hysteresis voltage Vhys, and if the inductor current detection signal Vcs rises to the upper limit of the hysteresis voltage Vhys, turning off the power switch tube M2 in the switch power module; if the inductor current detection signal Vcs drops to the lower limit of the hysteresis voltage Vhys, turning on the power switch tube M2; when the power switch tube M2 is between the upper and lower limits of the hysteresis voltage Vhys, the power switch tube M2 maintains the previous state.

[0123] 16) When the falling edge of the PWM dimming signal PWM arrives, the duty cycle count value is reset to the initial value, the switching power supply module turns off the output current, and the dimming ends.

[0124] It should be noted that any method that can adjust the hysteresis voltage based on the duty cycle of the PWM dimming signal so that the upper limit of the hysteresis voltage is fixed, and the lower limit decreases linearly with the increase of the duty cycle within the range where the duty cycle of the PWM dimming signal is less than the threshold D1, and maintains at the minimum value when the duty cycle of the PWM dimming signal is greater than or equal to the threshold D1; and any method that can realize hysteresis current control based on the hysteresis voltage is applicable to the present method, and is not limited to the present embodiment.

[0125] In summary, the present invention provides a hysteresis voltage generating circuit, a hysteresis current controller, a method and an LED driving system, comprising: a PWM dimming signal frequency detection unit, a PWM dimming signal duty cycle counting unit and a hysteresis voltage output unit; the PWM dimming signal frequency detection unit receives a PWM dimming signal and is used to generate a first clock signal, the frequency of the first clock signal is proportional to the frequency of the PWM dimming signal; the PWM dimming signal duty cycle counting unit is connected to the output end of the PWM dimming signal frequency detection unit, counts up the duty cycle of the PWM dimming signal based on the first clock signal, outputs a duty cycle count value, and maintains the duty cycle count value after the duty cycle reaches a threshold value; the hysteresis voltage output unit is connected to the output end of the PWM dimming signal duty cycle counting unit, is used to generate a hysteresis voltage, and adjusts the lower limit of the hysteresis voltage based on the duty cycle count value; the lower limit of the hysteresis voltage decreases as the duty cycle count value increases, and the upper limit of the hysteresis voltage is a fixed value. The hysteresis voltage generating circuit, hysteresis current controller, method and LED driving system of the present invention reduce the proportion of ΔD, and can simultaneously take into account the high efficiency of the system at a large dimming duty cycle and the dimming accuracy at a low dimming duty cycle. Therefore, the present invention effectively overcomes various shortcomings in the prior art and has a high industrial utilization value.

[0126] The above embodiments are merely illustrative of the principles and effects of the present invention, and are not intended to limit the present invention. Anyone familiar with the art may modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by a person of ordinary skill in the art without departing from the spirit and technical concept disclosed by the present invention shall still be covered by the claims of the present invention.

Claims

1. A hysteresis voltage generating circuit, applied to a hysteresis current controller, characterized in that: The hysteresis voltage generating circuit at least comprises: a PWM dimming signal frequency detecting unit, a PWM dimming signal duty cycle counting unit and a hysteresis voltage output unit; The PWM dimming signal frequency detection unit receives the PWM dimming signal and is used to generate a first clock signal, wherein the frequency of the first clock signal is proportional to the frequency of the PWM dimming signal; The PWM dimming signal duty cycle counting unit is connected to the output end of the PWM dimming signal frequency detection unit, counts up the duty cycle of the PWM dimming signal based on the first clock signal, outputs a duty cycle count value, and maintains the duty cycle count value after the duty cycle reaches a threshold value; The hysteresis voltage output unit is connected to the output end of the PWM dimming signal duty cycle counting unit, and is used to generate a hysteresis voltage and adjust the lower limit of the hysteresis voltage based on the duty cycle count value; the lower limit of the hysteresis voltage decreases as the duty cycle count value increases, and the upper limit of the hysteresis voltage is a fixed value.

2. The hysteresis voltage generating circuit according to claim 1, characterized in that: The PWM dimming signal frequency detection unit includes: a PWM dimming signal frequency measurement module and a clock signal generation module; The PWM dimming signal frequency measurement module counts the time when the PWM dimming signal is at a high level based on the second clock signal, and outputs a frequency count value after completing the counting, wherein the frequency count value is proportional to the frequency of the PWM dimming signal; The clock signal generating module is connected to the output end of the PWM dimming signal frequency measuring module, and generates the first clock signal based on the frequency count value.

3. The hysteresis voltage generating circuit according to claim 2, characterized in that: The PWM dimming signal frequency measurement module includes: a delay unit, a first counter, a register and a first subtractor; The delay unit receives the PWM dimming signal, delays the PWM dimming signal and then outputs a delayed signal, wherein the delay time is no more than two cycles of the second clock signal; The first counter is connected to the output end of the delay unit and receives the second clock signal, and is reset and starts counting up at the rising edge of the delay signal; The register is connected to the output end of the first counter, stores the value output by the first counter, and reads out the latched value at the rising edge of the PWM dimming signal; The first subtractor is connected to the output end of the register, and subtracts the value output by the register from the preset value to obtain the frequency count value.

4. The hysteresis voltage generating circuit according to claim 2 or 3, characterized in that: The clock signal generating module comprises: a digital-to-analog converter and an oscillator; The digital-to-analog converter is connected to the output end of the PWM dimming signal frequency measurement module to convert the frequency count value into an analog signal; The oscillator is connected to the output terminal of the digital-to-analog converter, and generates the first clock signal based on the output signal of the digital-to-analog converter.

5. The hysteresis voltage generating circuit according to claim 1, characterized in that: The PWM dimming signal duty cycle counting unit includes a second counter; The second counter is connected to the PWM dimming signal, the first clock signal and the latch signal. When the PWM dimming signal is at a high level, the second counter starts counting from an initial value based on the first clock signal, and latches the count value based on the latch signal after counting to a pre-designed value; when the PWM dimming signal is at a low level, the count value is reset to the initial value.

6. The hysteresis voltage generating circuit according to claim 1, characterized in that: The hysteresis voltage output unit includes: a current source, a resistor, a switch and a second subtractor; The current source is controlled by the duty cycle count value, and the larger the duty cycle count value is, the larger the current flowing through the current source is; One end of the resistor is connected to the current source, and the other end is grounded; the switch is connected in parallel to both ends of the resistor and is controlled by a driving signal of the power switch tube. When the power switch tube is turned on, the switch is turned on, and when the power switch tube is turned off, the switch is turned off; The second subtractor subtracts a voltage at a connection node between the current source and the resistor from an upper limit voltage of the hysteresis voltage to obtain the hysteresis voltage.

7. A hysteresis current controller, characterized in that: The hysteresis current controller at least comprises: A driving signal generating circuit and a hysteresis voltage generating circuit as claimed in any one of claims 1 to 6; The hysteresis voltage generating circuit is used to provide a hysteresis voltage; The drive signal generating circuit is connected to the output end of the hysteresis voltage generating circuit and receives the inductor current detection signal; when the PWM dimming signal is at a high level, the drive signal is generated based on the comparison result between the inductor current detection signal and the hysteresis voltage, and when the PWM dimming signal is at a low level, the drive signal remains at a low level.

8. An LED driving system, characterized in that: The LED driving system at least comprises: A switching power supply module, an LED load, a sampling module and a hysteresis current controller as claimed in claim 7; The sampling module detects the current of the inductor; The LED load is connected to the switching power module and operates based on the output current of the switching power module; The output end of the hysteresis current controller is connected to the gate of the power switch tube in the switching power supply module to provide a driving signal.

9. The LED driving system according to claim 8, characterized in that: The switching power supply module has a BUCK topology.

10. A hysteresis current control method, characterized in that: The hysteresis current control method at least comprises: When the PWM dimming signal is at a high level, a hysteresis voltage is generated based on the PWM dimming signal, and hysteresis current control is implemented based on the hysteresis voltage; wherein the upper limit of the hysteresis voltage is fixed; the lower limit decreases linearly as the duty cycle of the PWM dimming signal increases, and remains unchanged when the duty cycle of the PWM dimming signal is greater than or equal to a threshold; When the PWM dimming signal is at a low level, the power switch tube in the switching power supply module is turned off.

11. The hysteresis current control method according to claim 10, characterized in that: The method of generating the hysteresis voltage comprises: Measuring the frequency of the PWM dimming signal and generating a first clock signal, wherein the frequency of the first clock signal is proportional to the frequency of the PWM dimming signal; Based on the first clock signal, the duty cycle of the PWM dimming signal is counted to obtain a duty cycle count value, wherein the duty cycle count value increases linearly and is maintained when the duty cycle of the PWM dimming signal is greater than or equal to a threshold value; The hysteresis voltage is generated, and a lower limit of the hysteresis voltage is adjusted based on the duty cycle count value.

12. The hysteresis current control method according to claim 10 or 11, characterized in that: The method for implementing hysteresis current control based on the hysteresis voltage includes: The detection signal of the inductor current in the switching power supply module is compared with the hysteresis voltage. If the inductor current detection signal rises to the upper limit of the hysteresis voltage, the power switch tube in the switching power supply module is turned off. If the inductor current detection signal drops to the lower limit of the hysteresis voltage, the power switch tube is turned on.

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