CN115087167B - LED dimming control chip - Google Patents

LED dimming control chip Download PDF

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Publication number
CN115087167B
CN115087167B CN202210844800.6A CN202210844800A CN115087167B CN 115087167 B CN115087167 B CN 115087167B CN 202210844800 A CN202210844800 A CN 202210844800A CN 115087167 B CN115087167 B CN 115087167B
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current
capacitor
switch
led
terminal
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CN115087167A (en
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束克留
万海军
韩兴成
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Suzhou Powerlink Microelectronics Inc
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Suzhou Powerlink Microelectronics Inc
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    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
    • H05B45/00—Circuit arrangements for operating light-emitting diodes [LED]
    • H05B45/30—Driver circuits
    • H05B45/32—Pulse-control circuits
    • H05B45/325—Pulse-width modulation [PWM]
    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
    • H05B45/00—Circuit arrangements for operating light-emitting diodes [LED]
    • H05B45/30—Driver circuits
    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
    • H05B45/00—Circuit arrangements for operating light-emitting diodes [LED]
    • H05B45/30—Driver circuits
    • H05B45/36—Circuits for reducing or suppressing harmonics, ripples or electromagnetic interferences [EMI]
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02B—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO BUILDINGS, e.g. HOUSING, HOUSE APPLIANCES OR RELATED END-USER APPLICATIONS
    • Y02B20/00—Energy efficient lighting technologies, e.g. halogen lamps or gas discharge lamps
    • Y02B20/40—Control techniques providing energy savings, e.g. smart controller or presence detection

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  • Electromagnetism (AREA)
  • Circuit Arrangement For Electric Light Sources In General (AREA)

Abstract

The invention discloses an LED dimming control chip, which comprises: LED drive circuit and dimming control circuit, dimming control circuit includes: a current integrator, a switched capacitor low pass filter, and a comparator. The current integrator is used for controlling the average driving current of the LED driving circuit; the switched capacitor low-pass filter is used for performing low-pass filtering on the integrated voltage on the integrating unit to obtain millivolt-level fluctuation amplitude and output voltage with stable fluctuation frequency; the comparator is used for comparing the output voltage with a reference voltage to obtain a control signal, and the LED driving circuit is controlled through the control signal to adjust the driving current. According to the LED dimming control chip provided by the embodiment of the invention, the PFM control signal frequency of the LED dimming control chip under low brightness can be more stable, and stroboscopic and photographing ripples of illumination of an LED lamp are eliminated; compared with the traditional on-chip RC low-pass filtering structure, the area of the chip is greatly saved.

Description

LED dimming control chip
Technical Field
The invention relates to the field of integrated circuits, in particular to an LED dimming control chip.
Background
Compared with about 15% of the traditional tungsten lamp and about 50% of the traditional fluorescent lamp, the conversion efficiency of the electric energy of the LED lamp to the light energy is as high as about 90%. Therefore, the LED lamp has the great advantages of low power consumption and less heat generation. In addition, the LED lamp has the advantage of being convenient for adjusting the brightness. The average current flowing through the LED lamp is controlled by using the control chip, namely, the brightness adjustment with large range and high precision is realized.
Generally, when the brightness ratio of dimming the LED lamp (i.e. the duty ratio d of the PWM dimming signal) is reduced to below about 10%, the operating frequency of the control chip in the PFM mode becomes lower and unstable, i.e. the light of the LED lamp flickers. Secondly, at such low brightness, water ripples may appear when the mobile phone takes a picture.
The information disclosed in this background section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.
Disclosure of Invention
The invention aims to provide an LED dimming control chip, which can enable the working frequency of the LED dimming control chip in a PFM mode to be stable on the premise of not increasing the cost, the area and the design complexity of the chip, and effectively solve the problems of stroboflash of an LED lamp under low brightness, water ripple during mobile phone photographing and the like.
To achieve the above object, an embodiment of the present invention provides an LED dimming control chip, including: the LED drive circuit is used for generating a drive current to drive an LED lamp, and the dimming control circuit is used for adjusting the drive current to adjust the brightness of the LED lamp, and the dimming control circuit comprises: a current integrator, a switched capacitor low pass filter, and a comparator.
The current integrator is used to control the average drive current of the LED drive circuit.
The current integrator comprises a current providing unit, an induction unit and an integration unit, wherein the current providing unit is used for providing a charging current which is controlled by a PWM dimming signal and is used for charging the integration unit, the induction unit is used for inducing a driving current to generate an induction current which is proportional to the driving current and is used for discharging the integration unit, and the integration unit is used for integrating the difference value of the asynchronous charging current and the induction current to obtain an integration voltage.
The switched capacitor low-pass filter is used for low-pass filtering the integrated voltage on the integrating unit to obtain millivolt-level fluctuation amplitude and output voltage with stable fluctuation frequency.
The comparator is used for comparing the output voltage with the reference voltage to obtain a PFM control signal with stable frequency, and the LED driving circuit is controlled through the PFM control signal to adjust the driving current.
In one or more embodiments of the present invention, the LED driving circuit includes a first switch, a diode, an inductor, and a first capacitor, a first end of the first switch is an input end, a second end of the first switch is connected to a first end of the inductor and a cathode of the diode, an anode of the diode is connected to ground, a second end of the inductor is connected to a first end of the first capacitor and connected to the LED lamp, a second end of the first capacitor is connected to ground, and closing and opening of the first switch are controlled by a PFM control signal.
In one or more embodiments of the present invention, the current supply unit includes a constant current source and a second switch connected, and the second switch is controlled to be turned on and off by the PWM dimming signal.
In one or more embodiments of the present invention, the current induction ratio of the induction unit is:
Figure 860363DEST_PATH_IMAGE001
wherein, in the step (A),
Figure 574241DEST_PATH_IMAGE002
in order to induce an electric current,
Figure 88399DEST_PATH_IMAGE003
is the drive current through the inductor.
In one or more embodiments of the invention, the average driving current on the inductor is:
Figure 14767DEST_PATH_IMAGE004
wherein, in the step (A),
Figure 858833DEST_PATH_IMAGE005
for the duty cycle of the PWM dimming signal,
Figure 478033DEST_PATH_IMAGE006
is the charging current.
In one or more embodiments of the present invention, the integration unit includes an integration capacitor, a first end of the integration capacitor is connected to the current providing unit and the sensing unit, a second end of the integration capacitor is connected to ground, the integration capacitor is charged by the charging current, and the integration capacitor is discharged by the sensing current.
In one or more embodiments of the present invention, the switched capacitor low pass filter includes a third switch, a fourth switch, a second capacitor, and a third capacitor, a first terminal of the third switch is connected to the integrating unit, a second terminal of the third switch is connected to a first terminal of the second capacitor, a second terminal of the second capacitor is connected to ground, a first terminal of the fourth switch is connected to a first terminal of the second capacitor, a second terminal of the fourth switch is connected to a first terminal of the third capacitor and an input terminal of the comparator, a second terminal of the third capacitor is connected to ground, and the third switch and the fourth switch are respectively controlled by two non-overlapping clock signals.
In one or more embodiments of the invention, the low pass transfer function of the output voltage to the integrated voltage is:
Figure 276225DEST_PATH_IMAGE007
；
wherein the content of the first and second substances,
Figure 209546DEST_PATH_IMAGE008
in order to output the voltage, the voltage is,
Figure 409583DEST_PATH_IMAGE009
in order to integrate the voltage, the voltage is,
Figure 934105DEST_PATH_IMAGE010
in order to be an integrating capacitance,
Figure 485172DEST_PATH_IMAGE011
is a second capacitance, and is a first capacitance,
Figure 645020DEST_PATH_IMAGE012
is a third capacitance, and is a third capacitance,
Figure 496302DEST_PATH_IMAGE013
，
Figure 457304DEST_PATH_IMAGE014
is a variable for the analysis in the frequency domain,
Figure 230088DEST_PATH_IMAGE015
，
Figure 239633DEST_PATH_IMAGE016
is a variable for a discrete time domain analysis,
Figure 936235DEST_PATH_IMAGE017
is a variable of the frequency of the signal,
Figure 802559DEST_PATH_IMAGE018
the two phases do not overlap the frequency of the clock signal.
In one or more embodiments of the invention, the third capacitance is much larger than the second capacitance, and the integrating capacitance is much larger than the second capacitance.
In one or more embodiments of the invention, the third capacitance is more than one order of magnitude larger than the second capacitance, and the integrating capacitance is more than one order of magnitude larger than the second capacitance.
Compared with the prior art, according to the LED dimming control chip provided by the embodiment of the invention, the PFM control signal frequency of the LED dimming control chip under low brightness (such as PWM dimming signal duty ratio d = 1%) can be more stable through the switched capacitor low-pass filter, and stroboscopic and photographing ripple waves of LED lamp illumination are eliminated; compared with the traditional on-chip RC low-pass filtering structure, the switched capacitor low-pass filter greatly saves the area of a chip; compared with the off-chip capacitor, the cost of the functional module is saved, and the area of the application module is reduced; compared with the traditional method that after the integration results of two analog signals are digitized, low-pass filtering is realized by using a digital low-pass filter, and the filtered analog signals are obtained through digital-to-analog conversion, the circuit structure is greatly simplified, and the area and the power consumption of a chip are saved.
Drawings
Fig. 1 is a schematic circuit diagram of an LED dimming control chip according to an embodiment of the present invention.
Fig. 2 is a circuit schematic of a switched capacitor low pass filter and an integrating capacitor according to an embodiment of the present invention.
FIG. 3 shows an exemplary PWM dimming signal and an exemplary sense current according to the present invention
Figure 328219DEST_PATH_IMAGE002
Schematic diagram of asynchronous relation between them.
Fig. 4 is a simulation result diagram of the transmission frequency characteristic of the switched capacitor low pass filter according to an embodiment of the present invention.
Fig. 5 is a graph of a simulation result of dimming control according to a conventional RC low pass filter.
Fig. 6 is a graph of a simulation result of dimming control of a switched capacitor low pass filter according to an embodiment of the present invention.
Detailed Description
Specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings, but it should be understood that the scope of the present invention is not limited to the specific embodiments.
Throughout the specification and claims, unless explicitly stated otherwise, the word "comprise", or variations such as "comprises" or "comprising", will be understood to imply the inclusion of a stated element or component but not the exclusion of any other element or component.
As shown in fig. 1, an LED dimming control chip includes: an LED driving circuit 10 and a dimming control circuit 20. The LED driving circuit 10 is used for generating a driving current
Figure 141454DEST_PATH_IMAGE003
To drive the LED lamp. The dimming control circuit 20 is used for adjusting the driving current
Figure 436169DEST_PATH_IMAGE003
To adjust the brightness of the LED lamp. The whole dimming control chip adopts an asynchronous Buck (Buck) direct current to direct current converter structure.
As shown in FIG. 1, the LED driver circuit 10 includes a first switch
Figure 738974DEST_PATH_IMAGE019
Diode, and method for manufacturing the same
Figure 424034DEST_PATH_IMAGE020
An inductor
Figure 103277DEST_PATH_IMAGE021
And a first capacitor
Figure 986919DEST_PATH_IMAGE022
。
Specifically, a first switch
Figure 663888DEST_PATH_IMAGE019
The first terminal of (1) is an input terminal and is used for inputting direct current voltage
Figure 632981DEST_PATH_IMAGE023
The direct current voltage
Figure 351801DEST_PATH_IMAGE023
Generally rectified from mains. First switch
Figure 355529DEST_PATH_IMAGE019
Second terminal and inductor
Figure 203399DEST_PATH_IMAGE021
First terminal and diode
Figure 659788DEST_PATH_IMAGE020
Are connected to the cathode of the diode
Figure 680834DEST_PATH_IMAGE020
Is connected to ground, an inductor
Figure 273489DEST_PATH_IMAGE021
Second terminal and first capacitor
Figure 292261DEST_PATH_IMAGE022
The first end of the first capacitor is connected with the LED lamp, and the first capacitor
Figure 235946DEST_PATH_IMAGE022
Is connected to ground.
When the first switch is turned on
Figure 60683DEST_PATH_IMAGE019
At closing, DC voltage
Figure 773424DEST_PATH_IMAGE023
Via inductance
Figure 697517DEST_PATH_IMAGE021
Generating a drive current
Figure 627034DEST_PATH_IMAGE003
A first capacitor for supplying power to the LED lamp
Figure 989882DEST_PATH_IMAGE022
For the drive current
Figure 25971DEST_PATH_IMAGE003
And (6) filtering. Detecting inductance
Figure 42338DEST_PATH_IMAGE021
Drive current of
Figure 226194DEST_PATH_IMAGE003
When the peak value is reached, the first switch is switched off
Figure 628619DEST_PATH_IMAGE019
Diode (D)
Figure 253635DEST_PATH_IMAGE020
Conducting, driving current
Figure 847428DEST_PATH_IMAGE003
Gradually decreasing to zero. First switch
Figure 190684DEST_PATH_IMAGE019
Is controlled by the dimming control circuit 20.
As shown in fig. 1, the dimming control circuit 20 includes: current integrator 21, switched capacitor low-pass filter 22, and comparator
Figure 895335DEST_PATH_IMAGE024
. The current integrator 21 includes a current supply unit 211, a sensing unit 212, and an integrating unit 213. The current integrator 21 is used to control the current through the inductor
Figure 702754DEST_PATH_IMAGE021
Average drive current of
Figure 201869DEST_PATH_IMAGE025
。
The current providing unit 211 is used for providing a charging current controlled by a PWM (pulse-width modulation) dimming signal and used for charging the integrating unit 213
Figure 32421DEST_PATH_IMAGE006
. The sensing unit 212 is used for controlling the driving current
Figure 540763DEST_PATH_IMAGE003
Inducing to generate and drive current
Figure 140372DEST_PATH_IMAGE003
Proportional and induced current for discharging of integration unit 213
Figure 810387DEST_PATH_IMAGE002
. Integration unit 213 is used to couple asynchronous charging currents
Figure 190553DEST_PATH_IMAGE006
And induced current
Figure 174690DEST_PATH_IMAGE002
Is integrated to obtain an integrated voltage
Figure 189657DEST_PATH_IMAGE009
。
Wherein the current providing unit 211 comprises a connected constant current source
Figure 30574DEST_PATH_IMAGE026
And a second switch
Figure 898036DEST_PATH_IMAGE027
. Second switch
Figure 685863DEST_PATH_IMAGE027
Is controlled by the PWM dimming signal. The integration unit 213 comprises an integration capacitor
Figure 56802DEST_PATH_IMAGE010
. Integrating capacitor
Figure 334199DEST_PATH_IMAGE010
Is connected to the current supply unit 211 and the sensing unit 212, integrating capacitor
Figure 361061DEST_PATH_IMAGE010
Is connected to ground.
In particular, the constant current source
Figure 749317DEST_PATH_IMAGE026
Is connected to a supply voltage, a constant current source
Figure 240341DEST_PATH_IMAGE026
Second terminal and second switch
Figure 423061DEST_PATH_IMAGE027
Is connected to a first terminal of a second switch
Figure 202798DEST_PATH_IMAGE027
Second terminal of (2), sensing unit 212 and integrating capacitor
Figure 630631DEST_PATH_IMAGE010
Is connected to a switched capacitor low pass filter 22, an integrating capacitor
Figure 976161DEST_PATH_IMAGE010
Is connected to ground.
In the present embodiment, it is preferred that,the inductive element 212 is not specifically configured and may be implemented in a variety of ways, such as by being mounted on an inductor
Figure 595362DEST_PATH_IMAGE021
The branch is connected with a small resistor in series or through an inductor
Figure 393553DEST_PATH_IMAGE021
A branch of a resistor and a capacitor connected in series with each other in parallel, or other inductible inductor
Figure 326874DEST_PATH_IMAGE021
Current, voltage. Induction of an inductance by the induction unit 212
Figure 526911DEST_PATH_IMAGE021
Current flowing through the inductor generates an induced current
Figure 317013DEST_PATH_IMAGE002
。
Charging current
Figure 805763DEST_PATH_IMAGE006
Via a second switch controlled by a PWM dimming signal
Figure 339513DEST_PATH_IMAGE027
To integral capacitance
Figure 394056DEST_PATH_IMAGE010
Charging and driving current
Figure 558321DEST_PATH_IMAGE003
Corresponding induced current
Figure 564061DEST_PATH_IMAGE002
Then the integrating capacitance continues to be made
Figure 901502DEST_PATH_IMAGE010
Discharging, and finally outputting the integrated voltage by the current integrator 21
Figure 76131DEST_PATH_IMAGE009
。
In this embodiment, the induced current
Figure 145718DEST_PATH_IMAGE002
And a current-through inductor
Figure 671377DEST_PATH_IMAGE021
Is proportional to the current of the sensing unit 212, the current sensing ratio of the sensing unit 212 is:
Figure 484613DEST_PATH_IMAGE001
wherein, in the process,
Figure 513749DEST_PATH_IMAGE002
in order to induce an electric current,
Figure 816554DEST_PATH_IMAGE003
is a current-flowing inductance
Figure 563930DEST_PATH_IMAGE021
Drive current, current induction ratio of
Figure 180856DEST_PATH_IMAGE028
Can be set to 1 to 1000, and in other embodiments, the current induction ratio
Figure 330078DEST_PATH_IMAGE028
Other values may be set.
In this embodiment, the inductor
Figure 7047DEST_PATH_IMAGE021
The average drive current above is:
Figure 477605DEST_PATH_IMAGE004
wherein, in the step (A),
Figure 694959DEST_PATH_IMAGE005
for the duty cycle of the PWM dimming signal,
Figure 901950DEST_PATH_IMAGE006
is the charging current. Normal charging current
Figure 280979DEST_PATH_IMAGE006
And current induction ratio
Figure 2947DEST_PATH_IMAGE028
Are all fixed values. Thus, the average driving current flowing through the LED lamp
Figure 758413DEST_PATH_IMAGE025
I.e. the brightness of the LED lamp, is dimmed only by the duty cycle of the PWM dimming signal
Figure 819910DEST_PATH_IMAGE005
Controlled and proportional thereto.
In this embodiment, a switched capacitor low pass filter 22 is used to filter the integrating capacitor
Figure 900999DEST_PATH_IMAGE010
Integrated voltage of
Figure 47946DEST_PATH_IMAGE009
Low-pass filtering to obtain millivolt-level fluctuation range and stable fluctuation frequency output voltage
Figure 341524DEST_PATH_IMAGE008
。
As shown in FIG. 2, the switched capacitor low pass filter 22 includes a third switch
Figure 319845DEST_PATH_IMAGE029
The fourth switch
Figure 804790DEST_PATH_IMAGE030
A second capacitor
Figure 439034DEST_PATH_IMAGE031
And a third capacitor
Figure 536303DEST_PATH_IMAGE032
。
In particular, the third switch
Figure 103551DEST_PATH_IMAGE029
And the integrating capacitor of the integrating unit 213
Figure 962660DEST_PATH_IMAGE010
Is connected to receive the integrated voltage
Figure 474413DEST_PATH_IMAGE009
Third switch
Figure 109793DEST_PATH_IMAGE029
Second terminal and second capacitor
Figure 389DEST_PATH_IMAGE031
Is connected to a first terminal of a second capacitor
Figure 328602DEST_PATH_IMAGE031
Is connected to ground. The fourth switch
Figure 235641DEST_PATH_IMAGE030
First terminal and second capacitor
Figure 143554DEST_PATH_IMAGE031
Is connected to the fourth switch
Figure 950973DEST_PATH_IMAGE030
Second terminal and third capacitor
Figure 450087DEST_PATH_IMAGE032
First terminal and comparator
Figure 280640DEST_PATH_IMAGE024
Is connected to output voltage
Figure 257823DEST_PATH_IMAGE008
Third capacitance
Figure 185328DEST_PATH_IMAGE032
Is connected to ground. Third switch
Figure 855344DEST_PATH_IMAGE029
And a fourth switch
Figure 173193DEST_PATH_IMAGE030
Respectively controlled by two non-overlapping clock signals, namely a CKb clock signal and a CK clock signal.
Integrating capacitor
Figure 219646DEST_PATH_IMAGE010
Integrated voltage of
Figure 939340DEST_PATH_IMAGE009
Third switch controlled by CKb clock signal
Figure 780257DEST_PATH_IMAGE029
Sampling to a very small second capacitance
Figure 146254DEST_PATH_IMAGE031
To the formed sampling voltage
Figure 730819DEST_PATH_IMAGE033
Sampling voltage
Figure 305020DEST_PATH_IMAGE033
Almost associated with the integral voltage
Figure 316839DEST_PATH_IMAGE009
And are equal. And a second capacitor
Figure 406017DEST_PATH_IMAGE031
Sampled voltage of
Figure 997536DEST_PATH_IMAGE033
And a fourth switch controlled by a non-overlapping CK clock signal
Figure 222981DEST_PATH_IMAGE030
Sampling to a relatively large third capacitance
Figure 671280DEST_PATH_IMAGE032
Form a low-pass filtered output voltage
Figure 247754DEST_PATH_IMAGE008
。
Sampling voltage
Figure 377384DEST_PATH_IMAGE033
And integrated voltage
Figure 722915DEST_PATH_IMAGE009
The relationship of (1) is:
Figure 843580DEST_PATH_IMAGE034
；
output voltage
Figure 845034DEST_PATH_IMAGE008
And the sampled voltage
Figure 575093DEST_PATH_IMAGE033
The relationship of (c) is:
Figure 775130DEST_PATH_IMAGE035
；
finally, the output voltage is obtained
Figure 565231DEST_PATH_IMAGE008
And integral voltage
Figure 788402DEST_PATH_IMAGE009
The low-pass transfer function of (d) is:
Figure 587731DEST_PATH_IMAGE007
；
wherein, the first and the second end of the pipe are connected with each other,
Figure 642275DEST_PATH_IMAGE010
in order to be an integrating capacitance, the capacitance of the capacitor,
Figure 540961DEST_PATH_IMAGE011
is a second capacitance that is a function of the first capacitance,
Figure 579324DEST_PATH_IMAGE012
is a third capacitance, and is a third capacitance,
Figure 854447DEST_PATH_IMAGE013
，
Figure 763498DEST_PATH_IMAGE014
is a variable for the analysis in the frequency domain,
Figure 659516DEST_PATH_IMAGE015
，
Figure 654017DEST_PATH_IMAGE016
is a variable for a discrete time domain analysis,
Figure 732831DEST_PATH_IMAGE017
as a function of the frequency,
Figure 27546DEST_PATH_IMAGE018
the two phases do not overlap the frequency of the clock signal.
Due to the third capacitance
Figure 64772DEST_PATH_IMAGE012
Much larger than the second capacitance
Figure 15411DEST_PATH_IMAGE011
Integral capacitance
Figure 694654DEST_PATH_IMAGE010
Much larger than the second capacitance
Figure 578296DEST_PATH_IMAGE011
. Specifically, the third capacitor
Figure 989686DEST_PATH_IMAGE012
Is larger than the second capacitance
Figure 958779DEST_PATH_IMAGE011
Integral capacitance greater by more than one order of magnitude
Figure 441713DEST_PATH_IMAGE010
Is larger than the second capacitance
Figure 383124DEST_PATH_IMAGE011
Greater by more than one order of magnitude, so that the output voltage is
Figure 529197DEST_PATH_IMAGE008
And integral voltage
Figure 251165DEST_PATH_IMAGE009
The low-pass transfer function of (c) can be further approximated as:
Figure 209894DEST_PATH_IMAGE036
。
as shown in FIGS. 1 and 2, the comparator
Figure 333708DEST_PATH_IMAGE024
Having a first input terminal, a second input terminal, an output terminal, a first input terminal of a comparator, and a third capacitor
Figure 149217DEST_PATH_IMAGE012
Are connected to a comparator
Figure 30586DEST_PATH_IMAGE024
Second input terminal for receiving a reference voltage
Figure 855322DEST_PATH_IMAGE037
. Comparator with a comparator circuit
Figure 568063DEST_PATH_IMAGE024
For the output voltage
Figure 757736DEST_PATH_IMAGE008
And a reference voltage
Figure 454297DEST_PATH_IMAGE037
Comparing to obtain a PFM (pulse-frequency modulation) control signal with stable frequency
Figure 551566DEST_PATH_IMAGE038
By PFM control signals
Figure 322076DEST_PATH_IMAGE038
Control the first switch
Figure 266939DEST_PATH_IMAGE019
To control the LED driving circuit 10 to adjust the driving current
Figure 919638DEST_PATH_IMAGE003
。
As shown in fig. 3, due to the charging current participating in the integration
Figure 23860DEST_PATH_IMAGE006
And induced current
Figure 976772DEST_PATH_IMAGE002
Is asynchronous and then necessarily leads to integrating capacitance
Figure 304985DEST_PATH_IMAGE010
Integrated voltage of
Figure 648242DEST_PATH_IMAGE009
Non-periodic fluctuations corresponding to the output voltage after the use of a conventional RC filter
Figure 352893DEST_PATH_IMAGE008
And comparator CMP outputs PFM control signals
Figure 894733DEST_PATH_IMAGE038
Non-periodic fluctuation is also generated, thereby causing problems such as stroboscopic of the LED lamp at low brightness and water ripple when taking a picture with a mobile phone.
Fig. 4 is a simulation result of the transmission frequency characteristic of the switched-capacitor low-pass filter 22. Wherein the corresponding simulation parameter is
Figure 393847DEST_PATH_IMAGE039
，
Figure 224400DEST_PATH_IMAGE040
，
Figure 732742DEST_PATH_IMAGE041
The switched capacitor low pass filter 22 has a bandwidth of
Figure 597929DEST_PATH_IMAGE042
。
Fig. 5 is a simulation result of a conventional dimming control using an RC low pass filter. The parameters of the RC low-pass filter in the simulation are
Figure 769410DEST_PATH_IMAGE043
，
Figure 415155DEST_PATH_IMAGE044
. As can be seen from the simulation results, because the bandwidth of the RC low-pass filter is too large, the PFM control signal output by the comparator CMP
Figure 461608DEST_PATH_IMAGE038
Is very unstable. That is, the operating frequency of the LED dimming control chip in the PFM mode is unstable.
Fig. 6 shows the simulation result of dimming control by applying the switched capacitor low pass filter 22. The bandwidth of the low pass filter 22 is reduced by a factor of 100, i.e. about 160Hz, compared to the bandwidth of a conventional RC low pass filter of about 16 kHz. Thereby making asynchronizationCharging current of
Figure 978040DEST_PATH_IMAGE006
And induced current
Figure 22220DEST_PATH_IMAGE002
Integrated and low-pass filtered output voltage
Figure 624102DEST_PATH_IMAGE008
The fluctuation amplitude of the wave (is only about 6 mV) is greatly reduced, and the fluctuation frequency is stable. And further, the working frequency of the LED dimming control chip in the PFM mode becomes stable, and the problems of stroboflash of the LED dimming lamp in low brightness, water ripple when a mobile phone takes a picture and the like are effectively solved.
In addition, it should be noted here that the average driving current is the same
Figure 411930DEST_PATH_IMAGE025
Lower, reduce the inductance
Figure 782868DEST_PATH_IMAGE021
The current peak in PFM mode may increase the frequency. Even if the frequency is stable, increasing the frequency in PFM mode helps to reduce the stroboflash and water ripple, but when the average driving current is the same
Figure 60266DEST_PATH_IMAGE025
When the frequency of the LED dimming control chip in the PFM mode is small, the improvement of the working frequency of the LED dimming control chip in the PFM mode is limited, and a necessary technical means is provided for improving the frequency stability of the LED dimming control chip in the PFM mode by reducing the low-pass filtering bandwidth.
The foregoing descriptions of specific exemplary embodiments of the present invention have been presented for purposes of illustration and description. It is not intended to limit the invention to the precise form disclosed, and obviously many modifications and variations are possible in light of the above teaching. The exemplary embodiments were chosen and described in order to explain certain principles of the invention and its practical application to enable one skilled in the art to make and use various exemplary embodiments of the invention and various alternatives and modifications as are suited to the particular use contemplated. It is intended that the scope of the invention be defined by the claims and their equivalents.

Claims (10)

1. An LED dimming control chip, comprising: the LED drive circuit is used for generating a drive current to drive an LED lamp, and the dimming control circuit is used for adjusting the drive current to adjust the brightness of the LED lamp, and the dimming control circuit comprises:
a current integrator for controlling an average driving current of the LED driving circuit;
the current integrator comprises a current providing unit, an induction unit and an integration unit, wherein the current providing unit is used for providing a charging current which is controlled by a PWM dimming signal and is used for charging the integration unit, the induction unit is used for inducing a driving current to generate an induction current which is proportional to the driving current and is used for discharging the integration unit, and the integration unit is used for integrating the difference value of the asynchronous charging current and the induction current to obtain an integration voltage;
the switch capacitor low-pass filter is used for carrying out low-pass filtering on the integrated voltage on the integrating unit to obtain millivolt-level fluctuation amplitude and output voltage with stable fluctuation frequency; and
and the comparator is used for comparing the output voltage with the reference voltage to obtain a PFM control signal with stable frequency, and the LED driving circuit is controlled by the PFM control signal to adjust the driving current.
2. The LED dimming control chip of claim 1, wherein said LED driving circuit comprises a first switch, a diode, an inductor, and a first capacitor, wherein a first terminal of said first switch is an input terminal, a second terminal of said first switch is connected to a first terminal of said inductor and a cathode of said diode, an anode of said diode is connected to ground, a second terminal of said inductor is connected to a first terminal of said first capacitor and is connected to said LED lamp, a second terminal of said first capacitor is connected to ground, and closing and opening of said first switch is controlled by a PFM control signal.
3. The LED dimming control chip of claim 2, wherein the current providing unit comprises a constant current source and a second switch connected, and the closing and opening of the second switch is controlled by a PWM dimming signal.
4. The LED dimming control chip of claim 3, wherein the current sense ratio of the sensing unit is:
Figure 339249DEST_PATH_IMAGE001
wherein, in the step (A),
Figure 727505DEST_PATH_IMAGE002
in order to induce an electric current,
Figure 218529DEST_PATH_IMAGE003
is the drive current through the inductor.
5. The LED dimming control chip of claim 4, wherein an average drive current across the inductor is:
Figure 401249DEST_PATH_IMAGE004
wherein, in the step (A),
Figure 915407DEST_PATH_IMAGE005
for the duty cycle of the PWM dimming signal,
Figure 841774DEST_PATH_IMAGE006
is the charging current.
6. The LED dimming control chip of claim 1, wherein the integration unit comprises an integration capacitor, a first end of the integration capacitor is connected to the current providing unit and the sensing unit, a second end of the integration capacitor is connected to ground, the integration capacitor is charged by the charging current, and the integration capacitor is discharged by the sensing current.
7. The LED dimming control chip of claim 6, wherein the switched capacitor low pass filter comprises a third switch, a fourth switch, a second capacitor and a third capacitor, a first terminal of the third switch is connected to the integrating unit, a second terminal of the third switch is connected to a first terminal of the second capacitor, a second terminal of the second capacitor is connected to ground, a first terminal of the fourth switch is connected to a first terminal of the second capacitor, a second terminal of the fourth switch is connected to a first terminal of the third capacitor and an input terminal of the comparator, a second terminal of the third capacitor is connected to ground, and the third switch and the fourth switch are controlled by two non-overlapping clock signals, respectively.
8. The LED dimming control chip of claim 7, wherein the low pass transfer function of the output voltage to the integrated voltage is:
Figure 452884DEST_PATH_IMAGE007
；
wherein the content of the first and second substances,
Figure 9767DEST_PATH_IMAGE008
in order to output the voltage, the voltage is,
Figure 309424DEST_PATH_IMAGE009
in order to integrate the voltage(s),
Figure 305062DEST_PATH_IMAGE010
in order to be an integrating capacitance,
Figure 505099DEST_PATH_IMAGE011
is a second capacitance, and is a first capacitance,
Figure 918369DEST_PATH_IMAGE012
is a third one of the capacitors of the first group,
Figure 203857DEST_PATH_IMAGE013
，
Figure 3186DEST_PATH_IMAGE014
is a variable for the analysis in the frequency domain,
Figure 57730DEST_PATH_IMAGE015
，
Figure 956416DEST_PATH_IMAGE016
is a variable that is analyzed in the discrete time domain,
Figure 994779DEST_PATH_IMAGE017
as a function of the frequency,
Figure 269902DEST_PATH_IMAGE018
the two phases do not overlap the frequency of the clock signal.
9. The LED dimming control chip of claim 8, wherein the third capacitance is substantially greater than the second capacitance, and wherein the integrating capacitance is substantially greater than the second capacitance.
10. The LED dimming control chip of claim 9, wherein the third capacitance is more than one order of magnitude larger than the second capacitance, and wherein the integrating capacitance is more than one order of magnitude larger than the second capacitance.
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Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN105556321A (en) * 2013-03-12 2016-05-04 谱瑞科技有限公司 Capacitance sensing circuits and methods

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US8174233B2 (en) * 2009-10-08 2012-05-08 Etymotic Research, Inc. Magnetically coupled battery charging system

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CN105556321A (en) * 2013-03-12 2016-05-04 谱瑞科技有限公司 Capacitance sensing circuits and methods

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任意阶开关电流低通滤波器的系统设计;龙英等;《微电子学》;20090220(第01期);全文 *

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