CN114205952A

CN114205952A - LED dimming control system and method

Info

Publication number: CN114205952A
Application number: CN202111414731.7A
Authority: CN
Inventors: 李萌; 方倩; 朱力强
Original assignee: On Bright Electronics Shanghai Co Ltd
Current assignee: On Bright Electronics Shanghai Co Ltd
Priority date: 2021-11-25
Filing date: 2021-11-25
Publication date: 2022-03-18
Also published as: TW202322662A; TWI801131B

Abstract

The embodiment of the invention provides an LED dimming control system and method. According to the LED dimming control system provided by the embodiment of the present invention, the LED dimming control system may include: a switching tube; the valley bottom control module is used for generating a first control signal based on the drain voltage of the switching tube, the sensing voltage representing the output current flowing through the LED load and a dimming signal for controlling the brightness of the LED load; the voltage-current conversion module is used for converting the dimming reference voltage representing the dimming signal into delay current; and a delay module for generating a second control signal based on the delay current and the first control signal. According to the system provided by the embodiment of the invention, the valley bottom control module can lock the number of the valley bottoms during working, the possibility of current fluctuation is reduced, the time delay module can delay the first control signal according to the dimming depth to obtain the second control signal, and the dimming depth can be further reduced.

Description

LED dimming control system and method

Technical Field

Embodiments of the present invention generally relate to the field of integrated circuits, and in particular, to a system and method for controlling dimming of an LED.

Background

With the development of switching power supply technology, quasi-resonant (QR) dimming control technology is widely used. In LED lighting and backlighting applications, a quasi-resonant buck (buck) system is a common architecture. The quasi-resonance control utilizes a parasitic device, and the core of the quasi-resonance control is an LC resonant cavity consisting of a parasitic capacitor Cds and an inductor L1 of a metal-oxide-semiconductor field effect transistor (MOSFET). After each MOSFET is turned off, the control chip detects the voltage at the drain end of the MOSFET through a ZVS (zero voltage switch) pin, and when the demagnetization of the main inductor L1 is finished, the ZVS pin falls to a low level. After the demagnetization of the main inductor L1 is finished and the capacitor Cds enters a free resonance state, the system can open a new switching period in the valley of the waveform of the drain resonance voltage of the MOSFET, so that the switching loss and EMI of the system can be greatly reduced. The resonant period formed by main inductance L1 and parasitic capacitance Cds is small relative to the switching period, so the system operates approximately in critical conduction mode.

However, in the prior art, when the output current of the LED load is reduced to a certain level, the on-time of the switching tube cannot be further reduced, the current can only be kept unchanged, and further deep dimming cannot be performed.

Disclosure of Invention

The embodiment of the invention provides an LED dimming control system and method, the number of the operating valley bottoms can be determined and locked by a valley bottom control module under the condition that the output current of an LED load is greater than the preset current so as to obtain a first control signal for controlling the conduction of a switch tube, the possibility of current fluctuation can be reduced by locking, the first control signal can be delayed according to the dimming depth under the condition that the output current of the LED load is less than the preset current by a delay module so as to obtain a second control signal for controlling the conduction of the switch tube, and the dimming depth can be further reduced by delaying.

In one aspect, an embodiment of the present invention provides an LED dimming control system, including a switching tube, further including: the valley bottom control module is used for generating a first control signal for controlling the conduction of the switch tube based on the drain voltage of the switch tube, a sensing voltage representing the output current flowing through the LED load and a dimming signal for controlling the brightness of the LED load; a first voltage-to-current conversion module, configured to convert a dimming reference voltage representing the dimming signal into a delay current; and a delay module, configured to generate a second control signal for controlling conduction of the switching tube based on the delay current and the first control signal, where the second control signal is a delayed signal with respect to the first control signal

In another aspect, an embodiment of the present invention provides an LED dimming control method, which is used in an LED dimming control system, where the LED dimming control system includes a switching tube, and the method includes: generating a first control signal for controlling the conduction of the switching tube based on a drain voltage of the switching tube, a sensing voltage representing an output current flowing through an LED load, and a dimming signal for controlling the brightness of the LED load; converting a dimming reference voltage representative of the dimming signal into a delay current; and generating a second control signal for controlling the conduction of the switch tube based on the delay current and the first control signal, wherein the second control signal is a delay signal relative to the first control signal.

According to the LED dimming control system and method provided by the embodiment of the invention, when the dimming brightness is greater than the preset threshold, the number of the valley bottoms is locked, the valley bottom detection signals are counted, when the number of the locked valley bottoms is equal to the detected valley bottom number, the switch tube is controlled to be conducted by using the first control signal, and when the dimming circuit is smaller than the preset threshold, the first control signal is delayed to obtain the second control signal, so that the conduction of the switch tube is controlled by using the second control signal.

Drawings

In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required to be used in the embodiments of the present invention will be briefly described below, and for those skilled in the art, other drawings can be obtained according to the drawings without creative efforts.

Fig. 1 shows a schematic structure diagram of an LED dimming control system of a BUCK architecture provided in the prior art;

fig. 2 shows a timing diagram of a switching control unit for the LED dimming control system shown in fig. 1;

fig. 3 is a schematic structural diagram of an LED dimming control system according to an embodiment of the present invention;

FIG. 4 is a diagram illustrating the relationship between the compensation voltage and the upper and lower clamping frequencies provided by an embodiment of the present invention;

fig. 5 is a timing diagram illustrating the operation of the LED dimming control system according to the embodiment of the present invention during analog dimming;

FIG. 6 is a schematic structural diagram of a valley bottom control module provided by the embodiment of the invention;

FIG. 7 is a schematic structural diagram of the valley bottom locking module of FIG. 6 according to an embodiment of the present invention;

fig. 8 is a schematic structural diagram illustrating a voltage-current conversion module in an LED dimming control system according to an embodiment of the present invention;

fig. 9 is a schematic diagram illustrating a relationship between QR _ delay time and DIM _ ref voltage of the voltage-current conversion module provided by the embodiment of the present invention; and

fig. 10 is a flowchart illustrating an LED dimming control method according to an embodiment of the present invention.

Detailed Description

Features and exemplary embodiments of various aspects of the present invention will be described in detail below, and in order to make objects, technical solutions and advantages of the present invention more apparent, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not to be construed as limiting the invention. It will be apparent to one skilled in the art that the present invention may be practiced without some of these specific details. The following description of the embodiments is merely intended to provide a better understanding of the present invention by illustrating examples of the present invention.

It is noted that, herein, relational terms such as first and second, and the like may be used solely to distinguish one entity or action from another entity or action without necessarily requiring or implying any actual such relationship or order between such entities or actions. Also, the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. Without further limitation, an element defined by the phrase "comprising … …" does not exclude the presence of other identical elements in a process, method, article, or apparatus that comprises the element.

For better understanding of the LED dimming control system provided by the embodiment of the present invention, the LED dimming control system provided by the prior art is first described below, for example, referring to fig. 1, fig. 1 shows a schematic structural diagram of the LED dimming control system of the BUCK architecture provided by the prior art.

As shown in fig. 1, the system includes: the BUCK architecture quasi-resonant switch transformation unit 102, the demagnetization feedback unit 104, and the switch control unit 106. The BUCK-architecture quasi-resonant switching converter circuit 102 may include a main inductor L1, an output capacitor C1, a freewheeling diode D1, a switching tube (e.g., MOS tube) M1, and is configured to provide a desired voltage or current output to the LED load by controlling the switching tube M1 to be turned on and off, for example, to control dimming of the LED load. The demagnetization feedback circuit 104 may include a capacitor C2 and voltage dividing resistors R1 and R2. The demagnetization feedback circuit 104 obtains the drain voltage of the switching tube M1 by the non-abrupt change of the voltage across the capacitor C2, and after the voltage is divided by the voltage dividing circuit (e.g., the resistors R1 and R2) to generate the lower demagnetization feedback voltage ZVS, the switch control unit 106 detects the demagnetization feedback voltage, thus the demagnetization feedback voltage can represent the drain voltage of the switching tube.

The switching control unit 106 may include a demagnetization sensing module 1061, a peak sampling module 1062, an Error Amplifier (EA)1063, a PWM comparator 1064, a switching flip-flop 1065, a gate driver 1066, and an output feedback (CS) amplifier 1067.

Referring to fig. 1, an input terminal of the demagnetization sensing module 1061 receives the demagnetization feedback voltage ZVS, and an output terminal thereof is connected to the switch trigger 1065. In one embodiment, the switch trigger 1065 is an RS trigger, and the output terminal of the demagnetization sensing module 1061 is connected to the S terminal of the RS trigger. The input terminal of the peak sampling module 1062 receives the output feedback signal VCS, and the output terminal thereof is connected to the inverting input terminal of the EA 1063, wherein the connection of the peak sampling module 1062 to the inverting input terminal of the EA 1063 is based on the demagnetization signal output by the demagnetization sensing module 1061 and the Gate signal output by the Gate driver 1066 (for example, a switch is connected between the inverting input terminals of the peak sampling module 1062 and the EA 1063, and the on and off of the switch depends on the demagnetization signal and the Gate signal). A non-inverting input terminal of EA 1063 is configured to receive the reference voltage Vref, and an output terminal of EA 1063 is connected to an inverting input terminal of the PWM comparator 1064, wherein the output terminal of EA 1063 is further externally connected to a compensation capacitor c _ comp to compensate the output signal of EA 1063. A non-inverting input of the PWM comparator 1064 is connected to an output of the CS amplifier 1067, wherein an input of the CS amplifier 1067 is configured to receive the output feedback signal VCS. The output of PWM comparator 1064 is connected to a flip-flop 1065. For example, the output terminal of the PWM comparator 1064 is connected to the R terminal of an RS flip-flop, for example. An output terminal (e.g., a Q terminal of the RS flip-flop) of the switch flip-flop 1065 is connected to an input terminal of the Gate driver 1066, and the Gate driver 1066 is used for outputting a Gate driving signal, such as a Gate On or Gate Off signal, for controlling the On and Off of the switch tube M1.

Specifically, when the switch tube M1 is turned on, the current flowing through the load (e.g., LED load) generates a sensing voltage V across the resistor R3 connected in series with the source terminal of the switch tube M1_CSThe sensing voltage V_CSIs input to the peak sampling module 1062 to obtain an output sampled signal related to the output current flowing through the LED load, which is input to the error amplifier 1063 and operated with the reference voltage Vref at the other input terminal of the error amplifier 1063 to generate an output signal, which is compensated by the external capacitor c _ comp and compared with the output of the output feedback amplifier 1067 by the PWM comparator 1064, wherein the output feedback (CS) amplifier 1067 is configured to amplify the sensing voltage Vcs. The output signal of the PWM comparator 1064 is input to the switch trigger 1065 to control the turn-off of the switching tube M1. When the switching tube M1 is turned off, the demagnetization sensing module 1061 of the switching control unit 106 generates a demagnetization signal based on the demagnetization feedback voltage ZVS representing the drain voltage of the switching tube, and the demagnetization signal is inputted to the switching flip-flop 1065 to control the switching tube M1 to be turned on. The system controls the output peak current by controlling the on and off of the switching tube M1, thereby realizing the adjustment of the output current.

As shown in fig. 1, the switch control unit 106 may be integrated on a control chip. The control chip may include the following pins: a ZVS pin, configured to detect a demagnetization feedback signal (e.g., a demagnetization feedback voltage) for characterizing a drain voltage of the switching tube M1; the VCS pin is used for detecting an output feedback signal for feeding back the output current flowing through the LED load; a Gate pin for outputting a driving signal output by the Gate driver 1066; and a COMP pin for connecting an external compensation capacitor c _ COMP to provide compensation to the output voltage of EA 1063.

Fig. 2 shows a timing diagram of a switching control unit for the LED dimming control system shown in fig. 1. As shown in fig. 2, in the off-state of the switching tube M1, as the voltage Vds of the switching tube M1 decreases, the ZVS signal also decreases, when the ZVS signal decreases to zero, a demagnetization (dem) signal is generated, the demagnetization signal controls the generation of a Gate signal at a high level to control the conduction of the switching tube, and the sensing voltage V after the switching tube is turned on_CSThe voltage rises and after rising to the CS peak of the closed loop control, a Gate signal at a low level is generated to control the switching transistor M1 to turn off again.

In dimming applications, as the load decreases, the operating frequency of the system gradually increases, resulting in a decrease in the operating efficiency of the system. In some systems, a frequency reduction curve is added while the load is reduced, and the working frequency of an upper clamp frequency is reduced along with the reduction of the load, but the Gate is not turned on at the valley bottom at the moment, so that the working frequency of the system is reduced while the frequency is greatly changed, and the flicker of an LED lamp can occur in the dimming process.

In view of the above problems, embodiments of the present invention provide an LED dimming control system and method. For example, the valley locking technology can be added to the dimming quasi-resonant system, the working efficiency of the system can be improved, and the problem of frequency fluctuation back and forth can be solved, so that the output current of the LED load is stable during dimming, and the phenomenon of flashing is prevented.

Further, when the dimming depth is high, the ZVS signal is weak, and therefore there is a problem that detection of the bottom of the valley is impossible, and at this time, the dimming brightness is limited, and the magnitude of the output current flowing through the LED load (for example, LED lamp) cannot be further reduced. According to the technical scheme provided by the embodiment of the invention, when deep dimming is carried out, the valley bottom locking is controlled, and meanwhile, the quasi-resonance time delay can be increased according to the dimming depth, so that the turn-off time of the switch tube is further increased, and the higher dimming depth control can be realized while the efficiency of the LED dimming control system is improved.

The LED dimming control system provided by the embodiment of the present invention is described in detail below by way of specific examples, and as shown in fig. 3, fig. 3 shows a schematic structural diagram of the LED dimming control system provided by the embodiment of the present invention. It should be noted that fig. 3 is illustrated with a BUCK architecture quasi-resonant analog dimming control system as an example, which is provided as an example only and should not be construed as limiting.

As shown in fig. 3, the system may include: the BUCK architecture quasi-resonant switch transformation unit 302, the demagnetization feedback unit 304, and the switch control unit 306. The BUCK-based quasi-resonant switch transformation circuit 302 and the demagnetization feedback circuit 304 may have similar structures and functions to the BUCK-based quasi-resonant switch transformation circuit 102 and the demagnetization feedback circuit 104 shown in fig. 1, and for convenience of description, they are not described herein again.

The main difference between the LED dimming control system provided in the embodiment of the present invention and the LED dimming control system provided in the prior art is the switch control unit, and therefore, the following mainly describes the switch control unit 306 in the LED dimming control system provided in the embodiment of the present invention in detail.

As shown in fig. 3, the switching control unit 306 may include a demagnetization detection module 3061, a valley control module 3062, a peak value sampling module 3063, a dimming control module 3064, an Error Amplifier (EA)3065, an output feedback (CS) amplifier 3066, a PWM comparator 3067, a delay module 3068, a voltage-current conversion module 3069, a switch trigger 3070, a gate driver 3071, and the like. The switch control unit 306 may include ZVS, VCS, and HPWM pins, among others.

As an example, the valley control module 3062 may be configured to generate the first control signal IN for controlling the conduction of the switching transistor M1 based on a demagnetization feedback voltage (a signal from the ZVS pin, which may be referred to as a ZVS signal) characterizing the drain voltage of the switching transistor M1, a sensing voltage (a signal from the VCS pin, which may be referred to as a VCS signal) characterizing the output current flowing through the LED load, and a dimming signal (a signal from the HPWM pin, which may be referred to as an HPWM signal) for controlling the brightness of the LED load. In one embodiment, the HPWM pin can be used to receive a high frequency dimming signal input and can also be used to receive a DC voltage signal input.

In some embodiments, the dimming signal may be an analog signal. In other embodiments, the dimming signal may be a pulse width modulation signal.

As an example, the voltage-current conversion module 3069 may be configured to convert the dimming reference voltage DIM _ ref, which characterizes the dimming signal HPWM, into the delay current I _ delay.

As an example, the time delay module 3068 may be configured to delay the first control signal IN based ON the delay current I _ delay, and generate the second control signal ON for controlling the conduction of the switching tube, where the second control signal ON is a time delay signal relative to the first control signal IN.

Specifically, the input reference voltage DIM _ ref of the error amplifier EA may be changed by adjusting the duty ratio of the dimming signal, while the delay current I _ delay may be generated by the voltage current conversion module 3069 based on the reference voltage DIM _ ref, thereby controlling the time of QR _ delay.

As one example, the compensation capacitor may be provided inside the chip, so that the number of peripheral devices may be saved, and thus the cost of the system may be saved.

Specifically, the demagnetization detection module 3061 may receive a demagnetization feedback voltage (e.g., ZVS signal) characterizing the drain voltage of the switching tube, and may be configured to generate a valley detection signal valley in response to the received demagnetization feedback voltage dropping to zero, and provide the generated valley detection signal to the valley control module 3062. The valley control module 3062 also receives a compensation voltage Vcomp, which is compensated for the error amplified voltage from the error amplifier 3065, and the valley control module 3062 may be configured to generate the first control signal IN for controlling the conduction of the switching tube M1 based on the valley detection signal valley received from the demagnetization sensing module 3061 and the compensation voltage Vcomp received from the error amplifier 3065.

As one example, the peak sampling module 3063 may receive a sensed voltage (e.g., a VCS signal) characterizing an output current flowing through the LED load and configured to generate an output sampled signal based on the received sensed voltage, the dimming control module 3064 may receive a dimming signal (e.g., an HPWM signal) for controlling the brightness of the LED load and configured to generate a dimming reference voltage DIM _ ref based on the dimming signal and a reference signal Vref, and one input (e.g., a negative phase input) of the error amplifier 3065 may receive the output sampled signal from the peak sampling module 3063, the other input (e.g., a positive phase input) may receive the dimming reference voltage DIM _ ref from the dimming control module 3064 and configured to generate an error amplified voltage based on the output sampled signal and the dimming reference voltage, the error amplified voltage being compensated by a compensation capacitance of the system to obtain a compensation voltage comp, wherein the upper clamping frequency and the lower clamping frequency are related to the compensation voltage.

As an example, the connection of the output of the peak sample module 3063 to the inverting input of the error amplifier 3065 may be based on the demagnetization signal output by the valley control module 3062 and/or the Gate signal output by the Gate driver 3071.

In one embodiment, the analog dimming may include high frequency PWM to analog dimming or direct current DC analog dimming. In an embodiment of high frequency PWM dimming, the dimming reference voltage DIM _ ref may be generated by, for example, the high frequency PWM dimming control module 3064 based on the received reference signal Vref and the high frequency PWM dimming control signal HPWM. In the DC dimming embodiment, the dimming reference voltage DIM _ ref may be a DC dimming control signal. Although fig. 3 shows only an example of high frequency PWM to analog dimming, it should be understood that the non-inverting input of the error amplifier may also receive the DC dimming control signal directly.

As an example, the output of the error amplifier 3065 can also be connected to an input (e.g., an inverting input) of the PWM comparator 3067, wherein the output of the error amplifier 3065 can also be connected to a compensation capacitor to compensate for the error amplified voltage to produce the compensation voltage Vcomp. Another input (e.g., a non-inverting input) of the PWM comparator 3067 may be connected to an output of the CS amplifier 3066, where the input of the CS amplifier 3066 may be used to receive the output feedback signal VCS. The output of the PWM comparator 3067 may be connected to a switch trigger 3070 to provide a signal thereto for controlling the turn-off of the switching tube M1. The valley control module 3062 and the time delay module 3068 may generate signals for controlling the conduction of the switching tube M1. An input terminal of the switch flip-flop 3070 may be connected to the delay module 3068 and an output terminal of the PWM comparator 3067, and an output terminal of the switch flip-flop 3070 may be connected to an input terminal of the Gate driver 3071, so that the Gate driver 3071 may generate the driving signal Gate On or Off based On an output signal of the switch flip-flop 3070 to control the On and Off of the switch tube M1.

In one embodiment, the switch flip-flop 3070 may be an RS flip-flop, wherein the S terminal may be connected to the output terminal of the delay module 3068, the R terminal may be connected to the output terminal of the PWM comparator 3067, and the Q terminal may be connected to the input terminal of the gate driver 3071.

As shown in fig. 3, the switch control unit 306 may be integrated on the control chip. The control chip can comprise a ZVS pin and can be used for detecting demagnetization feedback voltage representing the drain voltage of the switching tube; a VCS pin, which may be used to detect a sense voltage that feeds back an output current flowing through an LED load; and a Gate pin for outputting the driving signal output by the Gate driver. In the embodiment shown in fig. 3, the control chip may further include an HPWM pin for providing a high frequency dimming signal input HPWM to change the reference voltage of the error amplifier by adjusting the duty cycle. In one embodiment, the control chip may further include a DC pin for providing a DC dimming signal input.

In one embodiment, the COMP pin for connecting external capacitors to provide compensation to the error amplifier EA may be eliminated, and the compensation capacitors of the error amplifier EA may be optimized to the inside of the chip to facilitate saving system cost, as shown in fig. 3.

Compared to the embodiment shown IN fig. 1, IN the embodiment shown IN fig. 3, a valley control module 3062 that can be used for the valley lock control, a delay module 3068 for delaying the first control signal IN from the valley control module 3062, and a voltage-current conversion module 3069 for converting the dimming reference voltage DIM _ ref into a delay current and providing it to the delay module 3068 are mainly added. The valley control module 3062 and the time delay module 3068 shown in FIG. 3 are described in detail below.

As an example, referring to fig. 3, when the output current of the LED load is greater than the preset current, the second control signal ON has no delay with respect to the first control signal IN, so that the conduction of the switching tube can be controlled directly by using the first control signal; when the output current of the LED load is less than the preset current, the second control signal ON is delayed with respect to the first control signal IN, so that the second control signal can be used to control the conduction of the switching tube, thereby further reducing the dimming depth.

As an example, the valley control module 3062 may be configured to lock the target locking valley number if the output current of the LED load is greater than the preset current, for example, the error amplifier 3065 may generate an error amplification signal based on the sensing voltage VCS and the dimming signal HPWM, the error amplification signal may be compensated for obtaining a compensation voltage COMP, the valley control module 3062 may determine an upper clamp frequency for increasing the number of valleys and a lower clamp frequency for decreasing the number of valleys based on the compensation voltage COMP, and then may determine a target locking valley number for the drain voltage of the switching tube based on a relationship between the switching frequency of the switching tube (e.g., the operating frequency of the system) and the upper clamp frequency and the lower clamp frequency (which will be described in detail below in connection with fig. 4), the target locking valley number may represent if the output current of the LED load is greater than the preset current, the drain voltage of the switching tube is reduced to the target number of times of valley voltage when the switching tube is in an off state; and generating a first control signal IN which can be used for controlling the conduction of the switch tube when the target locking valley bottom quantity is consistent with the actual locking valley bottom quantity, wherein the actual locking valley bottom quantity is the quantity of the generated valley, and the actual locking valley bottom quantity can represent the actual times that the drain voltage of the switch tube is reduced to the valley bottom voltage during the period that the switch tube is IN the off state under the condition that the output current of the LED load is greater than the preset current, so that the conduction of the switch tube can be controlled by directly utilizing the first control signal IN.

As an example, IN order to further reduce the dimming depth, the embodiment of the present invention further provides the above-mentioned delay module, which can further perform deep dimming by increasing the turn-off time of the switching tube, for example, the delay module can be further configured to delay the first control signal IN to obtain the second control signal ON when the output current of the LED load is smaller than the preset current, so that the conduction of the switching tube can be controlled by using the second control signal ON.

Therefore, when the output current of the LED load is greater than the preset current, the switching ON of the switching tube can be controlled by directly using the first control signal IN, and when the output current of the LED load is less than the preset current, the switching ON of the switching tube can be controlled by using the second control signal ON.

To better understand the operation of the valley control module 3062 shown in FIG. 3, it is described below in conjunction with FIG. 4, where FIG. 4 shows a schematic diagram of the relationship between the compensation voltage and the upper and lower clamp frequencies provided by an embodiment of the present invention.

As shown in fig. 4, Fup represents an upper clamp frequency for increasing the number of valleys, and Fdown represents a lower clamp frequency for decreasing the number of valleys, and the magnitudes of the upper clamp frequency and the lower clamp frequency are related to the compensation voltage, i.e., the corresponding upper clamp frequency and the lower clamp frequency can be obtained based on the compensation voltage, wherein Fup _ max is the maximum switching frequency for increasing the number of valleys, and Fup _ min is the minimum switching frequency for increasing the number of valleys; fdown _ max is the maximum switching frequency for decreasing the number of valleys, and Fdown _ min is the minimum switching frequency for decreasing the number of valleys

Referring to fig. 3 and 4, as the duty ratio of the high frequency PWM is decreased (in other embodiments, as the input DC voltage is decreased), the dimming reference voltage DIM _ ref of the error amplifier 3065 is also gradually decreased, and the demagnetization time is gradually decreased to gradually increase the operating frequency of the system (e.g., the switching frequency of the switching tube), and when the operating frequency is increased to the Fup curve as shown in fig. 4, the controller may increase the number of valleys to decrease the operating frequency, and after the number of valleys is increased, the operating frequency of the system may be between the frequency of the Fup and the frequency of Fdown until the load is decreased again, and the operating frequency is increased, and when the operating frequency is greater than the Fup, the number of valleys is increased again. Therefore, the duty ratio of the high-frequency PWM signal is increased, the load is increased, the working frequency of the system is reduced, and when the working frequency is reduced to be lower than Fdown, the working frequency of the chip can be improved by reducing the number of the valley bottoms. After the valley bottom number is determined, the valley bottom number information is latched, so that the target locking valley bottom number is obtained, and each switching period can be accurately controlled according to the current latching state.

For better understanding of the dimming principle of the LED dimming control system provided by the embodiment of the present invention, reference is made to fig. 5, and fig. 5 shows a timing chart of the operation of the LED dimming control system provided by the embodiment of the present invention in analog dimming. In one embodiment, the analog dimming may be HPWM to analog dimming. In another embodiment, the analog dimming may be DC analog dimming.

As an example, IN the case that the output current of the LED load is greater than the preset current, the valley bottom control module may determine and lock the target locking valley bottom number, so as to generate the first control signal IN when the target locking valley bottom number is equal to the actual locking valley bottom number, and control the conduction of the switching tube by using the first control signal IN.

Specifically, referring to fig. 5, when the dimming brightness is greater than the preset deep dimming threshold vth1, the dimming reference voltage DIM _ ref follows a decrease, and the output current ILED of the LED load also follows a corresponding decrease, and the number of valleys of the demagnetization feedback current ZCS increases as the output current decreases, for example, gradually increases from 1 valley to N (for example, N ═ 7) valleys, and finally may stabilize at N (for example, N ═ 7) valleys in the case where the current ILED is low, that is, the target lock valley number may be 7. At this time, the number of occurrences of the valley signal in fig. 5 is the number of actual locking valleys, and when the number of target locking valleys is the same as the number of actual locking valleys, a dem signal is generated to control the conduction of the switch tube.

It should be noted that when the load current is reduced to a certain level, the number of the valley bottoms is maintained at N (for example, N is 7), and the on-time of the switching tube is continuously reduced.

IN order to solve the above problem, IN the delay module IN the LED dimming control system according to the embodiment of the present invention, when the output current of the LED load is smaller than the preset current, the first control signal IN may be delayed to obtain the second control signal ON, so that the second control signal ON can be used to control the conduction of the switching tube.

Specifically, when the dimming reference voltage DIM _ ref is decreased to be lower than the preset deep dimming threshold Vth1 (e.g., 5%), the voltage-current conversion module 3069 may generate the delay current I _ delay based ON the dimming reference voltage DIM _ ref, and the delay module 3068 delays the first control signal IN by the delay current I _ delay for a time T2, so that the second control signal ON having a delay T2 with respect to the first control signal IN may be obtained, and the dimming depth may be further decreased by increasing the turn-off time (T1+ T2) of the switching tube.

In summary, the LED dimming control system provided by the embodiment of the present invention can be optimized in terms of system efficiency and dimming depth compared to the conventional system, and further reduces the possibility of current fluctuation due to locking of the valley during dimming.

The valley control module 3062 in fig. 3 provided by the embodiment of the present invention is described in detail below by way of specific example, and referring to fig. 6, fig. 6 shows a schematic structural diagram of the valley control module provided by the embodiment of the present invention.

As an example, the valley control module 3062 may include the voltage current conversion module 101, the current precision control module 102, the frequency comparator 103, the valley lock module 104, and the like.

Specifically, the voltage-current conversion module 101 may receive the compensation voltage comp, convert the compensation voltage into the compensation current I _ comp, and pass through the current precision control module 102 after the conversion, where the current precision control module 102 may be configured to ensure that the corresponding relationship between the compensation voltage and the upper and lower clamp frequencies as shown in fig. 4 is maintained within a certain range, so as to ensure the precision of the upper and lower clamp frequency determination. The frequency comparator 103 may receive the current I _ trim from the current precision control module, may detect the switching frequency of the switching tube, and compare the detected switching frequency with the upper and lower clamp frequency curves as shown in fig. 4, and generate a first comparison result F _ up if the switching frequency of the switching tube of the current cycle is higher than the upper clamp frequency, and generate a second comparison result F _ down if the switching frequency of the switching tube of the current cycle is lower than the lower clamp frequency. The valley bottom locking module 104 may determine the number of valley bottoms that need to be locked, i.e., the number of target locking valley bottoms, according to the numbers of F _ up and F _ down, and when a valley bottom signal valley is detected IN real time, may obtain the number of actual locking valley bottoms, and generate the first control signal IN when the number of target locking valley bottoms is equal to the number of actual locking valley bottoms.

As an example, the voltage-current conversion module 3069 may receive and convert the dimming reference voltage DIM _ ref, generate the delay current I _ delay, and provide the delay current I _ delay to the delay module 3068, so that the delay module 3068 controls the delay based ON the delay current I _ delay to generate the ON signal determining the ON time of the switching tube after delaying the first control signal IN.

The valley locking module 104 in fig. 6 provided by the embodiment of the present invention is described in detail below by way of specific examples, and fig. 7 is a schematic structural diagram of the valley locking module in fig. 6 provided by the embodiment of the present invention.

As an example, the valley lock module 104 may include a counter 1041, a counter 1042, a up-down counter 1043, a valley counter 1044, a data comparator 1045, and the like. The counter 1041 may be configured to count the first comparison result F _ up, and generate an Acc _ eff signal indicating that 1 valley is increased when the count result satisfies a preset condition, the counter 1042 may be configured to count the second comparison result F _ down, and generate a Dec _ eff signal indicating that 1 valley is decreased when the count result satisfies the preset condition, and the bidirectional counter 1043 may receive the Acc _ eff signal and the Dec _ eff signal from the counter 1041 and the counter 1042, and lock the current number of valleys when no Acc _ eff signal and Dec _ eff signal are generated, so as to obtain the target number of locked valleys (the number of valleys is represented by B0, B1, and Bn).

As an example, the valley counter 1044 may generate a pulse IN the valley signal after the ZVS pin detects the zero crossing signal, and count the number of the valley signals to obtain the above-mentioned actual locking valley number (the valley number is represented by Q0, Q1, Qn), and the data comparator 1045 may be configured to compare B0, B1, Bn with Q0, Q1, Qn, and generate the first control signal IN to control the switch-on of the switch tube when the two are consistent, so as to achieve the purpose of locking the valley.

When the output current of the LED load is smaller than the preset current, the delay module 3068 may delay the first control signal IN according to the DIM _ ref after the first control signal IN arrives, so as to obtain a second control signal ON, and control the switching of the switching tube by using the second control signal ON.

The voltage-current conversion module (for example, 3069 in fig. 3) in the LED dimming control system provided by the embodiment of the present invention is described in detail below by way of specific example, referring to fig. 8, and fig. 8 shows a schematic structural diagram of the voltage-current conversion module in the LED dimming control system provided by the embodiment of the present invention.

As an example, the voltage-current conversion module 3069 may include an operational amplifier OP1, a resistor R1, and a current mirror, and particularly, one input terminal (e.g., a positive phase input terminal) of the operational amplifier may receive the dimming reference voltage DIM _ ref, another input terminal (e.g., a negative phase input terminal) may be connected to the source of the transistor NM5 and the common terminal of the resistor R1, the other terminal of the resistor R1 may be grounded, and the drain of the transistor NM5 may be connected to the current source I1.

Wherein the dimming reference voltage DIM _ ref is converted into a current I2 by using an operational amplifier OP1 and a resistor R1, the current I1 is a fixed current, the current I3 can be generated by subtracting the current I1 and I2 (when the dimming reference voltage DIM _ ref is higher than Vth1, I3 is 0), the current I3 is mirrored by a current mirror to generate a delay current I _ delay, the current I _ delay flows through a resistor R2, and a comparison voltage Vc1 is generated on a resistor R2, the current I4 is a fixed current, after 7 valley bottoms are detected, the delay _ enable signal becomes zero, the current I4 charges a capacitor C1, and a voltage Vc1 is generated across the capacitor C1, one input terminal (e.g., a non-phase input terminal) of the comparator can receive the voltage Vc2, the other input terminal (e.g., a negative phase input terminal) can receive the voltage Vc1, when the voltage Vc2 across the capacitor C1 is larger than the reference voltage Vc1, and then the comparator is inverted, and generates a QR _ delay signal to turn on the switching tube.

As an example, fig. 9 shows a schematic diagram of a relationship between QR _ delay time and DIM _ ref voltage of a voltage-current conversion module provided by an embodiment of the present invention.

For example, the QR _ delay time starts to increase when the DIM _ ref voltage is lower than V2, and reaches the maximum value T2 and remains unchanged when the DIM _ ref voltage is lower than V1.

In addition, an embodiment of the present invention further provides an LED dimming control method, which is used in the LED dimming control system described above, for example, fig. 10 shows a schematic flow chart of the LED dimming control method provided in the embodiment of the present invention, and the method may include the following steps: s1010, generating a first control signal IN for controlling the conduction of the switch tube based on the drain voltage of the switch tube, the sensing voltage representing the output current flowing through the LED load and a dimming signal for controlling the brightness of the LED load; s1020, converting the dimming reference voltage representing the dimming signal into a delay current; and S1030, generating a second control signal ON for controlling the conduction of the switching tube based ON the delay current and the first control signal, wherein the second control signal ON is a delayed signal with respect to the first control signal IN.

When the output current of the LED load is larger than the preset current, the second control signal has no time delay relative to the first control signal, so that the conduction of the switch tube can be controlled by directly utilizing the first control signal; under the condition that the output current of the LED load is smaller than the preset current, the second control signal is delayed relative to the first control signal, so that the conduction of the switch tube can be controlled by the second control signal.

As an example, the method further comprises: when the output current of the LED load is greater than the preset current: firstly, determining an upper clamping frequency for increasing the number of the valley bottoms and a lower clamping frequency for decreasing the number of the valley bottoms based on the sensing voltage and the dimming signal, specifically comprising: determining a compensation voltage based on the sensing voltage VCS and the dimming signal HPWM, an upper clamp frequency increasing the number of valleys and a lower clamp frequency decreasing the number of valleys based on the compensation voltage; secondly, determining a target locking valley bottom number aiming at the drain voltage of the switching tube based on the switching frequency of the switching tube, the upper clamping frequency and the lower clamping frequency, wherein the target locking valley bottom number represents a target number of times that the drain voltage of the switching tube is reduced to the valley bottom voltage during the switching tube is in an off state; finally, the first control signal is generated based on the target number of locking valleys and an actual number of locking valleys, the actual number of locking valleys representing an actual number of times the drain voltage of the switching tube drops to the valley voltage during the off-state of the switching tube, so that the switching tube can be controlled to conduct by the first control signal.

As an example, the method further comprises: when the output current of the LED load is less than the preset current: and delaying the first control signal to obtain the second control signal, so that the conduction of the switch tube can be controlled by utilizing the second control signal.

As an example, the method further comprises: generating an output sampling signal based on the sense voltage VCS; generating the dimming reference voltage DIM _ ref based on the dimming signal hpmm; and generating the error amplification voltage based on the output sampling signal and the dimming reference voltage, wherein the error amplification signal is compensated by a compensation capacitor of the system to obtain a compensation voltage comp, and the upper clamping frequency and the lower clamping frequency are related to the compensation voltage.

As an example, generating the first control signal IN for controlling the conduction of the switching tube based on the drain voltage of the switching tube, the sensing voltage VCS representing the output current flowing through the LED load, and the dimming signal HPWM for controlling the brightness of the LED load comprises: obtaining a compensation voltage COMP based on a sensing voltage VCS and a dimming signal HPWM, obtaining an upper clamp frequency and a lower clamp frequency based on the compensation voltage to generate a first comparison result when the switching frequency of the switching tube is higher than the upper clamp frequency, and generating a second comparison result when the switching frequency of the switching tube is lower than the lower clamp frequency; and generating the first control signal based on the first comparison result, the second comparison result and the drain voltage of the switching tube.

As an example, generating the first control signal based on the first comparison result, the second comparison result, and the drain voltage of the switching tube includes: counting the first comparison result, and generating a first counting result indicating that 1 valley bottom is added when the counting result meets a preset condition; counting the second comparison result, and generating a second counting result indicating that 1 valley bottom is reduced when the counting result meets a preset condition; when the first counting result and the second counting result are not generated, locking the current number of the valley bottoms to obtain the target locking valley bottom number; counting the actual times that the drain voltage of the switching tube is reduced to the valley bottom voltage when the switching tube is in an off state to obtain the actual locking valley bottom quantity; and generating the first control signal when the target locking valley bottom number is equal to the actual locking valley bottom number.

As an example, the dimming signal may be an analog signal or a pulse width modulation signal.

It should be noted that, for the sake of brevity, only some steps of the LED dimming control method provided by the embodiment of the present invention are described above, because specific details included in the method are described in detail in the above description of the LED dimming control system provided by the embodiment of the present invention, and are not described herein again.

To sum up, the embodiment of the present invention provides an LED dimming control system and method, which generates a dimming reference voltage based on a dimming signal HPWM for controlling the brightness of an LED load when an output current of analog dimming is greater than a preset current, generates an error amplification signal based on a sensing voltage VCS representing the output current flowing through the LED load and the dimming reference voltage, and compensates the error amplification signal to obtain a compensation voltage, and can obtain an upper clamping frequency and a lower clamping frequency based on the compensation voltage, compare the operating frequency of the system with the upper clamping frequency and the lower clamping frequency, determine the number of valley bottoms during operation and lock the operating state, and generate a control signal IN when the number of valley bottoms actually detected is equal to the number of locked valley bottoms, so that the conduction of a switching tube can be controlled by using the control signal IN; when the dimming depth is increased and the output current is reduced to the preset current, the fixed number of the valley bottoms is the preset valley bottoms, and along with the reduction of the output current, the control signal IN is delayed based ON the dimming reference voltage to obtain the control signal ON, so that the conduction of the switch tube can be controlled by utilizing the control signal ON.

Therefore, the LED dimming control system and the LED dimming control method provided by the embodiment of the invention can improve the efficiency and solve the problem of flickering of the LED lamp in the dimming process by adding the valley bottom locking technology, and can further increase the time for turning off the grid by adding the quasi-resonance time delay technology, thereby realizing higher dimming depth control while improving the efficiency of the LED system.

It should be noted that the present invention is described by taking a quasi-resonant dimming system of a buck (buck) architecture as an example, however, this is provided as an example only and should not be construed as limiting, and may also be applied to a quasi-resonant dimming system of a flyback (flyback) architecture and a quasi-resonant dimming system of a boost (boost) architecture.

It is to be understood that the invention is not limited to the specific arrangements and instrumentality described above and shown in the drawings. A detailed description of known methods is omitted herein for the sake of brevity. In the above embodiments, several specific steps are described and shown as examples. However, the method processes of the present invention are not limited to the specific steps described and illustrated, and those skilled in the art can make various changes, modifications and additions or change the order between the steps after comprehending the spirit of the present invention.

The functional blocks shown in the above-described structural block diagrams may be implemented as hardware, software, firmware, or a combination thereof. When implemented in hardware, it may be, for example, an electronic circuit, an Application Specific Integrated Circuit (ASIC), suitable firmware, plug-in, function card, or the like. When implemented in software, the elements of the invention are the programs or code segments used to perform the required tasks. The program or code segments may be stored in a machine-readable medium or transmitted by a data signal carried in a carrier wave over a transmission medium or a communication link. A "machine-readable medium" may include any medium that can store or transfer information. Examples of a machine-readable medium include electronic circuits, semiconductor memory devices, ROM, flash memory, Erasable ROM (EROM), floppy disks, CD-ROMs, optical disks, hard disks, fiber optic media, Radio Frequency (RF) links, and so forth. The code segments may be downloaded via computer networks such as the internet, intranet, etc.

It should also be noted that the exemplary embodiments mentioned in this patent describe some methods or systems based on a series of steps or devices. However, the present invention is not limited to the order of the above-described steps, that is, the steps may be performed in the order mentioned in the embodiments, may be performed in an order different from the order in the embodiments, or may be performed simultaneously.

As described above, only the specific embodiments of the present invention are provided, and it can be clearly understood by those skilled in the art that, for convenience and brevity of description, the specific working processes of the system, the module and the unit described above may refer to the corresponding processes in the foregoing method embodiments, and are not described herein again. It should be understood that the scope of the present invention is not limited thereto, and any person skilled in the art can easily conceive various equivalent modifications or substitutions within the technical scope of the present invention, and these modifications or substitutions should be covered within the scope of the present invention.

Claims

1. The utility model provides a LED dimming control system, includes the switch tube, its characterized in that still includes:

the valley bottom control module is used for generating a first control signal for controlling the conduction of the switch tube based on the drain voltage of the switch tube, a sensing voltage representing the output current flowing through the LED load and a dimming signal for controlling the brightness of the LED load;

a first voltage-to-current conversion module, configured to convert a dimming reference voltage representing the dimming signal into a delay current; and

and the time delay module is used for generating a second control signal for controlling the conduction of the switch tube based on the delay current and the first control signal, wherein the second control signal is a time delay signal relative to the first control signal.

2. The LED dimming control system of claim 1,

when the output current of the LED load is larger than the preset current, the second control signal is not delayed relative to the first control signal;

and when the output current of the LED load is smaller than the preset current, the second control signal has time delay relative to the first control signal.

3. The LED dimming control system of claim 2, wherein the valley control module is further configured to, if the output current of the LED load is greater than the preset current:

determining an upper clamp frequency for increasing the number of the valley bottoms and a lower clamp frequency for decreasing the number of the valley bottoms based on the sensing voltage and the dimming signal;

determining a target number of locking valleys for the drain voltage of the switching tube based on the switching frequency of the switching tube, the upper clamping frequency and the lower clamping frequency, the target number of locking valleys representing a target number of times the drain voltage of the switching tube drops to a valley voltage during an off state of the switching tube;

generating the first control signal based on the target number of locking valleys and an actual number of locking valleys, the actual number of locking valleys representing an actual number of times a drain voltage of the switching tube drops to the valley voltage during an off state of the switching tube, so that the switching tube can be controlled to be turned on by the first control signal.

4. The LED dimming control system of claim 3, wherein the time delay module is further configured to, if the output current of the LED load is less than the preset current:

and delaying the first control signal to obtain the second control signal, so that the conduction of the switch tube can be controlled by utilizing the second control signal.

5. The LED dimming control system of claim 3, further comprising:

a peak sampling module to generate an output sampled signal based on the sense voltage;

a dimming control module configured to generate the dimming reference voltage based on the dimming signal; and

an error amplifier configured to generate an error amplified voltage based on the output sampling signal and the dimming reference voltage, wherein the error amplified signal is compensated by a compensation capacitor of the system to obtain a compensation voltage, and the upper clamping frequency and the lower clamping frequency are related to the compensation voltage.

6. The LED dimming control system of claim 5, wherein the valley control module comprises:

the frequency comparator is used for generating a first comparison result when the switching frequency of the switching tube is higher than the upper clamping frequency and generating a second comparison result when the switching frequency of the switching tube is lower than the lower clamping frequency; and

a valley locking module for generating the first control signal based on the first comparison result, the second comparison result and the drain voltage of the switching tube.

7. The LED dimming control system of claim 6, wherein the valley lock module comprises:

the first counter is used for counting the first comparison result and generating a first counting result indicating that 1 valley bottom is added when the counting result meets a preset condition;

the second counter is used for counting the second comparison result and generating a second counting result indicating that 1 valley bottom is reduced when the counting result meets a preset condition;

the bidirectional counter is used for locking the current valley bottom number when the first counting result and the second counting result are not generated so as to obtain the target locking valley bottom number;

the valley bottom counter is used for counting the actual times that the drain voltage of the switching tube is reduced to the valley bottom voltage when the switching tube is in an off state, so as to obtain the actual locking valley bottom quantity; and

a data comparator for generating the first control signal when the number of target locking valleys is equal to the number of actual locking valleys.

8. The LED dimming control system of claim 1, wherein the first voltage-to-current conversion module comprises an operational amplifier, a resistor, and a current mirror, wherein:

the operational amplifier and the resistor are configured to convert the dimming reference voltage to an intermediate current;

the current mirror is used for obtaining the delay current based on the intermediate current.

9. The LED dimming control system of claim 1, wherein the dimming signal is an analog signal or a pulse width modulation signal.

10. An LED dimming control method is used for an LED dimming control system, the LED dimming control system comprises a switch tube, and the method comprises the following steps:

generating a first control signal for controlling the conduction of the switching tube based on a drain voltage of the switching tube, a sensing voltage representing an output current flowing through an LED load, and a dimming signal for controlling the brightness of the LED load;

converting a dimming reference voltage representative of the dimming signal into a delay current; and

and generating a second control signal for controlling the conduction of the switching tube based on the delay current and the first control signal, wherein the second control signal is a delay signal relative to the first control signal.

11. The LED dimming control method according to claim 10,