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CN114501726A - Multi-channel LED system, driving circuit and driving method - Google Patents

Multi-channel LED system, driving circuit and driving method Download PDF

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Publication number
CN114501726A
CN114501726A CN202111668829.5A CN202111668829A CN114501726A CN 114501726 A CN114501726 A CN 114501726A CN 202111668829 A CN202111668829 A CN 202111668829A CN 114501726 A CN114501726 A CN 114501726A
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China
Prior art keywords
signal
led
current
pulse
pulse width
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CN202111668829.5A
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Chinese (zh)
Inventor
杨袁钰
高尚
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Hangzhou Silergy Semiconductor Technology Ltd
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Shanghai Silijie Microelectronics Technology Co ltd
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Priority to CN202111668829.5A priority Critical patent/CN114501726A/en
Publication of CN114501726A publication Critical patent/CN114501726A/en
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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]
    • G—PHYSICS
    • G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
    • G09G—ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
    • G09G3/00—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes
    • G09G3/20—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters
    • G09G3/34—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters by control of light from an independent source
    • G09G3/3406—Control of illumination source
    • 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
    • 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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  • Engineering & Computer Science (AREA)
  • Physics & Mathematics (AREA)
  • Computer Hardware Design (AREA)
  • General Physics & Mathematics (AREA)
  • Theoretical Computer Science (AREA)
  • Circuit Arrangement For Electric Light Sources In General (AREA)

Abstract

A multi-channel LED system, a driving circuit and a driving method are disclosed. The pulse width and the amplitude of the LED current are adjusted to obtain a high dynamic range and improve the system efficiency, and the turn-off time of the multi-channel LED current pulse is set, so that the LED current can be uniformly distributed in a synchronous period to reduce the voltage ripple of the power supply voltage, and meanwhile, the multi-channel LED current is sequentially turned off to avoid the overvoltage of the power supply voltage.

Description

Multi-channel LED system, driving circuit and driving method
Technical Field
The invention relates to the technical field of power electronics, in particular to a multi-channel LED system, a driving circuit and a driving method.
Background
With the development of LEDs, LEDs have been increasingly used as the backlight of the display in recent years due to their characteristics of low power consumption, low heat generation, high brightness, long life, and the like. The LED backlight of the display is typically segmented, with each region being independently driven to control the brightness of that region. However, under the condition of a multi-channel LED, due to the influence of parasitic parameters in an actual circuit and the absence of completely identical devices, even if the voltage of each LED channel is the same as the LED current, the voltage of the LED driving side of a part of channels cannot be completely consistent, and when the multi-channel LED uses the same voltage source (or power converter) as a power supply voltage, the voltage of the LED driving side of the part of channels is higher than a target value, which results in large power consumption of the part of channels.
In addition, for multiple LED channels, the maximum value and the minimum value of the total current of the LEDs are different more under different brightness requirements, so that the voltage ripple and the peak power of the power supply voltage are larger.
Disclosure of Invention
In view of the above, the present invention provides a multi-channel LED system, a driving circuit and a driving method. The switching-off time of the multi-channel LED pulse is set, so that the LED current can be uniformly distributed in a synchronous period, the voltage ripple of the power supply voltage is reduced, the multi-channel LED current is sequentially switched off, and the overvoltage of the power supply voltage is avoided.
According to a first aspect of the present invention, a driving method of a multi-channel LED system is provided, comprising:
respectively generating an amplitude dimming signal and a pulse width dimming signal corresponding to the LED load of each channel according to the brightness requirement of each channel, wherein the amplitude dimming signal is used for adjusting the amplitude of the LED current, and the pulse width dimming signal is used for adjusting the pulse width of the LED current; and
and controlling the turn-off time of the LED current of each channel according to the synchronous signal and the corresponding time offset, so that the ending time of the pulse of each LED current is separated from the starting pulse of the synchronous signal by the corresponding time offset in one working cycle.
Specifically, the driving method further includes:
when the synchronous period of the synchronous signal comprises at least one pulse of the LED current, the ending time of the starting pulse of the LED current in each synchronous period is controlled to be away from the pulse of the synchronous signal in each synchronous period by the time offset, the next pulse of the LED current in each synchronous period is controlled to be away from the last pulse by the current period of the LED current, and the synchronous period is the work period.
Specifically, the driving method further includes:
and when the current period of the LED current comprises at least one pulse of the synchronous signal, controlling the end time of the pulse of the LED current in each current period to be away from the initial pulse of the synchronous signal in each current period by the time offset, wherein the current period is the work period.
Specifically, the time offset corresponding to the start pulse of the synchronization signal includes a time offset corresponding to the rising edge or the falling edge of the start pulse of the synchronization signal.
Specifically, the driving method further includes:
setting a corresponding time offset for each channel before the multi-channel LED system works normally; and
and time shifting the pulse width dimming signal according to the time shift and the synchronous signal to generate a first pulse width dimming signal, wherein the duty ratio of the first pulse width dimming signal is the same as that of the pulse width dimming signal, and the turn-off time of the first pulse width dimming signal is separated from the starting pulse of the synchronous signal by the corresponding time shift in each working period.
Specifically, the driving method further includes:
and generating a driving signal according to the first pulse width dimming signal and the amplitude dimming signal to control the working state of a first power tube connected with the LED load in series, so as to realize the amplitude and pulse width regulation of the LED current.
Specifically, the driving method further includes:
adjusting a driving voltage of the driving signal provided to the first power tube according to the amplitude dimming signal and a current sampling signal representing an amplitude of the LED current such that the current sampling signal is equal to the amplitude dimming signal;
generating a first pulse width dimming signal according to the synchronization signal, the time offset and the pulse width dimming signal, wherein the duty cycle of the first pulse width dimming signal is the same as that of the pulse width dimming signal, and the turn-off time of the first pulse width dimming signal is separated from the initial pulse of the synchronization signal by the corresponding time offset in each working period; and
and controlling the time for providing the driving voltage for the first power tube according to the first pulse width dimming signal.
Specifically, the driving method further includes:
and generating a first driving signal according to the first pulse width dimming signal to drive a first power tube connected with the LED load on the corresponding channel in series so as to adjust the pulse width of the LED current.
Specifically, the driving method further includes:
and adjusting the magnitude of a second driving signal according to the amplitude dimming signal and a current sampling signal representing the amplitude of the LED current so as to adjust the on-resistance of a second power tube connected with the first power tube in series on a corresponding channel, thereby adjusting the amplitude of the LED current, wherein the second driving signal is used for driving the second power tube.
According to a second aspect of the present invention, a driving circuit for a multi-channel LED system is presented, comprising:
the main control unit is configured to respectively generate an amplitude dimming signal and a pulse width dimming signal corresponding to the LED load of each channel according to the brightness requirement of each channel, and adjust the pulse width dimming signal according to a synchronous signal and a corresponding time offset so that the ending time of the pulse of the LED current of each channel is separated from the starting pulse of the synchronous signal by the corresponding time offset in one working cycle; and
a plurality of control circuits corresponding to a number of channels in the LED system, wherein each control circuit adjusts an amplitude of the LED current according to a corresponding amplitude dimming signal and adjusts a pulse width of the LED current according to a corresponding pulse width dimming signal.
In particular, when the synchronization period of the synchronization signal comprises at least one pulse of the LED current, the control circuit is configured to control an end time of a start pulse of the LED current in each synchronization period to be separated from a start pulse of the synchronization signal in each synchronization period by the time offset, a next pulse of the LED current to be separated from a previous pulse by a current period of the LED current, wherein the synchronization period is the duty period.
Specifically, when the current period of the LED current includes at least one pulse of the synchronization signal, the end time of the pulse of the LED current in each current period is controlled to be away from the start pulse of the synchronization signal in each current period by the time offset, wherein the current period is the duty period.
Specifically, the main control unit is configured to allocate a corresponding time offset to each channel before the multichannel LED system normally operates, and perform time offset on the pwm signal according to the time offset and the synchronization signal to generate a first pwm signal, where a duty cycle of the first pwm signal is the same as a duty cycle of the pwm signal, and a turn-off time of the first pwm signal is separated from a start pulse of the synchronization signal by the corresponding time offset in each operating period.
Specifically, the time offset corresponding to the start pulse of the synchronization signal includes a time offset corresponding to the rising edge or the falling edge of the start pulse of the synchronization signal.
Specifically, the control circuit is configured to generate a driving signal according to the first pulse width dimming signal to control an operating state of a first power tube connected in series with the LED load, so as to realize amplitude and pulse width adjustment of the LED current.
Specifically, each of the control circuits includes:
a feedback control circuit, a first input end receives the amplitude dimming signal, a second input end receives a current sampling signal representing the LED current, and an output end generates a driving voltage; and
a gate switch configured to be connected between the output terminal of the feedback control circuit and the control terminal of the first power tube, and controlled by the first pwm signal to deliver the driving voltage to the control terminal of the first power tube when the first pwm signal is active.
Specifically, the control circuit comprises a first control circuit configured to generate a first driving signal according to the first pulse width dimming signal to drive a first power tube connected with the LED load in series on a corresponding channel so as to adjust the pulse width of the LED current.
Specifically, the control circuit further includes a second control circuit configured to adjust a magnitude of a second driving signal according to the amplitude dimming signal and a current sampling signal representing an amplitude of the LED current to adjust an on-resistance of a second power tube connected in series with the first power tube on a corresponding channel, so as to adjust the amplitude of the LED current, wherein the second driving signal is used for driving the second power tube.
According to a third aspect of the invention, a multi-channel LED system is proposed, comprising:
a plurality of LED channels, wherein each LED channel comprises an LED load and at least one power tube connected in series; and
the drive circuit of any of the above.
Specifically, each LED channel further comprises a sampling resistor connected in series with the LED load to sample the magnitude of the LED current to obtain a current sampling signal.
In summary, according to the embodiments of the present invention, by setting the turn-off time of the multi-channel LED pulse, the LED current can be distributed relatively uniformly in one synchronization period to reduce the voltage ripple of the power supply voltage, and simultaneously, the multi-channel LED current is sequentially turned off to avoid the overvoltage of the power supply voltage.
Drawings
The above and other objects, features and advantages of the present invention will become more apparent from the following description of the embodiments of the present invention with reference to the accompanying drawings, in which:
FIG. 1 is a circuit diagram of a multi-channel LED system according to an embodiment of the present invention;
FIG. 2 is a detailed circuit diagram of a first driving circuit according to an embodiment of the present invention;
FIG. 3 is a detailed circuit diagram of a second driving circuit according to an embodiment of the present invention;
FIG. 4 is a first waveform illustrating operation of a multi-channel LED system according to an embodiment of the present invention;
FIG. 5 is a second waveform illustrating operation of a multi-channel LED system according to an embodiment of the present invention;
FIG. 6 is a third operating waveform of a multi-channel LED system according to an embodiment of the present invention;
FIG. 7 is a circuit diagram of a driver circuit incorporating adaptive tuning according to an embodiment of the present invention;
FIG. 8 is a fourth operating waveform of a multi-channel LED system according to an embodiment of the present invention; and
FIG. 9 is a fifth operating waveform of a multi-channel LED system according to an embodiment of the present invention.
Detailed Description
The present invention will be described below based on examples, but the present invention is not limited to only these examples. In the following detailed description of the present invention, certain specific details are set forth. It will be apparent to one skilled in the art that the present invention may be practiced without these specific details. Well-known methods, procedures, components and circuits have not been described in detail so as not to obscure the present invention.
Further, those of ordinary skill in the art will appreciate that the drawings provided herein are for illustrative purposes and are not necessarily drawn to scale.
Meanwhile, it should be understood that, in the following description, a "circuit" refers to a conductive loop constituted by at least one element or sub-circuit through electrical or electromagnetic connection. When an element or circuit is referred to as being "connected to" another element or element/circuit is referred to as being "connected between" two nodes, it may be directly coupled or connected to the other element or intervening elements may be present, and the connection between the elements may be physical, logical, or a combination thereof. In contrast, when an element is referred to as being "directly coupled" or "directly connected" to another element, it is intended that there are no intervening elements present.
Unless the context clearly requires otherwise, throughout the description and the claims, the words "comprise", "comprising", and the like are to be construed in an inclusive sense as opposed to an exclusive or exhaustive sense; that is, what is meant is "including, but not limited to".
In the description of the present invention, it is to be understood that the terms "first," "second," and the like are used for descriptive purposes only and are not to be construed as indicating or implying relative importance. In addition, in the description of the present invention, "a plurality" means two or more unless otherwise specified.
Fig. 1 is a circuit diagram of a multi-channel LED system according to an embodiment of the present invention. As shown in fig. 1, the LED system includes a plurality of LED channels and a driving circuit, wherein the plurality of LED channels use a voltage generated by the same voltage source (or power converter) as a supply voltage Vin. The drive circuit includes a plurality of control circuits (control circuit 1, control circuit 2, … … control circuit n) that control the plurality of LED channels, respectively, and a main control unit. Each LED channel comprises an LED load (LED1, LED2, … … LEDn) and a power tube connected in series between a supply voltage Vin and a reference ground, wherein the LED load is an LED string comprising at least one light emitting diode.
The main control unit is used for respectively generating an amplitude dimming signal Vrefi (i is 1, 2, … … n) and a pulse width dimming signal Vpwmi corresponding to each LED load according to different brightness requirements of the LED channel to be powered, and transmitting the amplitude dimming signal Vrefi and the pulse width dimming signal Vpwmi to corresponding control circuits, so that each control circuit can adjust the amplitude of the LED current according to the corresponding amplitude dimming signal Vrefi and adjust the pulse width of the LED current according to the corresponding pulse width dimming signal Vpwmi, so as to independently control the power tube on the corresponding LED channel, and thus, the LED load can meet the brightness requirements of the LED load. Wherein the amplitude dimming signal is representative of a desired LED current amplitude and the pulse width dimming signal is a PWM signal having a corresponding duty cycle. In this embodiment, to reduce the cost, only one power tube Qi is used in series with the LED load to control both the magnitude and the pulse width of the LED current. In addition, each LED channel further comprises a sampling resistor Ri connected in series between the power tube Qi and the reference ground to sample the current amplitude flowing through the LEDi to obtain a current sampling signal Ici. Therefore, each control circuit generates a driving signal Vgi according to the amplitude dimming signal Vrefi and the pulse width dimming signal Vpwmi to control the power tube Qi. In other embodiments, two power transistors (first and second power transistors) connected in series may be respectively used to connect in series with the LED load, in which case each control circuit generates a first driving signal according to the pulse width dimming signal Vpwmi to control the first power transistor so as to adjust the pulse width of the LED current, and generates a second driving signal according to the amplitude dimming signal Vrefi to control the second power transistor so as to adjust the amplitude of the LED current. In the following, a power tube is connected in series for explanation.
In this embodiment, the main control unit independently sets the amplitude dimming signal Vrefi and the pulse width dimming signal Vpwmi corresponding to each channel LED for each channel according to the brightness requirement of each channel LED and the user's requirement, and transmits them to the corresponding control circuit i. It should be understood that the amplitude dimming signal Vrefi and the pulse width dimming signal Vpwmi of each channel may be the same or different.
Further, the control circuit i adjusts the driving voltage of the driving signal Vgi according to the amplitude dimming signal Vrefi to adjust the LED current amplitude Ii so that the current amplitude Ii corresponds to the amplitude dimming signal Vrefi. In this embodiment, the gate-source voltage of the power tube Qi is adjusted by changing the driving voltage of the driving signal Vgi, and the on-state resistance of the power tube Qi is further changed, so as to achieve the purpose of adjusting the current amplitude Ii of the LED.
The control circuit i adjusts the duty cycle of the generated driving signal Vgi according to the pulse width dimming signal Vpwmi such that the duty cycle of the LED current is the same as the duty cycle of the pulse width dimming signal Vpwmi. It should be understood that, in each current period, the ratio of the width (i.e. pulse width) of the LED current pulse to the current period is the duty ratio of the LED current, and since the current period of the LED current is fixed in the present application, the pulse width of the current corresponds to the duty ratio, that is, the pulse width of the regulated LED current is the duty ratio of the regulated LED current. In the present embodiment, the time for providing the driving voltage to the power tube Qi is controlled according to the pulse width dimming signal Vpwmi to adjust the on-time (i.e., the duty ratio) of the power tube Qi. When the power tube is turned on, the LED current is generated, and when the power tube is turned off, the LED current is zero, so that the pulse width (duty ratio) of the LED current is also adjusted.
In summary, in the LED system according to the embodiment of the present invention, each LED channel only uses one power transistor, so that the pulse width and the amplitude of the LED current can be independently adjusted.
Fig. 2 shows a specific circuit diagram of a first driving circuit according to an embodiment of the present invention. The LED system is illustrated with 3 LED channels. As shown in fig. 2, each control circuit includes a feedback control circuit and a gate switch. The channel 1 is taken as an example for explanation. The control circuit 1 includes a feedback control circuit implemented with an amplifier a1 in the present embodiment, and a gate switch SW 1. The amplifier a1 has a first input terminal (i.e., non-inverting input terminal) receiving the amplitude dimming signal Vref1, a second input terminal (i.e., inverting input terminal) receiving a current sampling signal Ic1 representing the current of the LED1, and an output terminal generating a driving voltage to change the on-state resistance of the power transistor Q1 by changing the gate voltage of the power transistor Q1, so as to adjust the current amplitude I1 of the LED1, so that the current sampling signal Ic1 is equal to the amplitude dimming signal Vref 1. The gate switch SW1 is controlled by the pwm signal Vpwm1 to switch the power transistor Q1 on or off. The pulse width dimming signal Vpwm1 is a PWM signal, and the duty ratio is D1. When the pwm signal Vpwm1 is asserted, the gate switch SW1 is switched to 1, that is, the gate switch SW1 is turned on, so that the driving voltage output by the amplifier a1 is transmitted to the control terminal of the power transistor Q1, the driving signal Vg1 is asserted, the power transistor Q1 is turned on, and the gate voltage of the driving signal Vg1 is controlled by the driving voltage output by the amplifier a1 to adjust the on-resistance of the power transistor Q1, so as to adjust the current flowing through the power transistor Q1. When the pwm signal Vpwm1 is inactive, the gate switch SW1 switches to 0, so as to disconnect the amplifier a1 from the power transistor Q1, the gate voltage of the power transistor Q1 is pulled down to 0V, and the power transistor Q1 is turned off. In summary, the pwm signal Vpwm1 can control the time for the driving voltage to be transmitted to the power transistor Q1, so as to control the on-time of the power transistor Q1, i.e. the duty ratio D1, and thus the LED current only flows during the on-time of the power transistor Q1 and is zero during the off-time of the power transistor Q1.
In addition, in order to avoid a large difference between the maximum value and the minimum value of the total LED current, and thus a large voltage ripple and a large peak power of the power supply voltage, in this embodiment, in addition to controlling the LED current according to the amplitude dimming signal Vrefi and the pulse width dimming signal Vpwmi, the main control unit further adjusts the pulse width dimming signal according to the synchronization signal and the corresponding time offset, so as to control the turn-off time of the LED current of each channel, and thus the LED current is distributed more uniformly. Specifically, the main control unit adjusts the pulse width dimming signal according to the synchronization signal and the corresponding time offset so that the end time of the pulse of the LED current of each channel is separated from (the rising edge or the falling edge of) the start pulse of the synchronization signal by the corresponding time offset in one duty cycle. Wherein the end instant of the pulse of the LED current refers to the falling edge of the pulse. That is, the inactive timing of the driving signal Vg1, that is, the turn-off timing of the respective LED currents (that is, the timing of becoming zero) is controlled by the time offset.
Fig. 3 shows a specific circuit diagram of a second driving circuit according to an embodiment of the present invention. The LED system is illustrated with 3 LED channels. Taking the channel 1 as an example, different from the example shown in fig. 2, the main control unit receives the synchronization signal VSYNC and the time offsets T1, T2, and T3 of the respective channels, it should be understood that T1, T2, and T3 may be the same or different, and in this embodiment, the time offsets are set only once, that is, a corresponding time offset is set for each channel before the LED system normally operates. Thereafter, the PWM signal Vpwm1 (not shown in the figure) is shifted to output the first PWM signal PWM1, wherein the duty cycle of the first PWM signal PWM1 is the same as the duty cycle of the PWM signal Vpwm1, and the off time of the first PWM signal PWM1 is separated from the start pulse of the synchronization signal VSYNC by a time shift T1 in each duty cycle. The control circuit 1 generates a driving signal Vg1 according to the first pulse width dimming signal PWM1 and the amplitude dimming signal Vref1 to control the operating state of the power transistor Q1, so as to implement amplitude and pulse width adjustment of the LED current. Specifically, the control circuit 1 controls the time for providing the driving voltage to the power tube Q1 according to the first pulse width dimming signal PWM1, so that the duty ratio of the power tube Q1 is equal to the duty ratio of the first pulse width dimming signal PWM1, that is, equal to the duty ratio of the pulse width dimming signal Vpwm1, while the power tube Q1 is controlled to be turned off by the time offset T1 at the rising edge of the synchronization signal VSYNC, and the control circuit 1 adjusts the driving voltage provided to the power tube Q1 according to the amplitude dimming signal Vref1 and the current sampling signal Ic1, so that the current sampling signal Ic1 is equal to the amplitude dimming signal Vref 1. Of course, the embodiment of the present invention takes the rising edge of the synchronization signal VSYNC as an example, and in other embodiments, the time offset may be a distance from the falling edge of the synchronization signal VSYNC.
The operation of the driving circuit is further explained in conjunction with fig. 4. As shown in fig. 4, the synchronous period Ts and the current period of the synchronous signal VSYNC are the same as each other for explanation, and in this embodiment, the working period is the synchronous period Ts. Meanwhile, in one duty cycle, the time from the rising edge of the synchronization signal VSYNC to the falling edge of the LED current ILEDi is taken as an example of a time offset, that is, a tail alignment manner is adopted. At time T1, synchronization signal VSYNC is asserted, and by time offset T1, power transistor Q1 for channel 1 is turned off and LED current ILED1 is turned off. The duty cycle of the LED current ILED1 is equal to the duty cycle of the pulse width dimming signal Vpwm1, and the magnitude of the LED current ILED1 corresponds to the magnitude dimming signal Vref1, specifically the magnitude of the LED current ILED1 is proportional to the magnitude dimming signal Vref1, during the time that the power tube Q1 is conducting. Similarly, when the time offset T2 elapses from time T1, power transistor Q2 of channel 2 is turned off, and LED current ILED2 is turned off. The duty cycle of the LED current ILED2 is the same as the duty cycle of the pulse width dimming signal Vpwm2, and the magnitude of the LED current ILED2 corresponds to the magnitude dimming signal Vref2 during the conduction of the power tube Q2; after a time offset T3 from time T1, power transistor Q3 of channel 3 is turned off, and LED current ILED3 is turned off. The duty cycle of the LED current ILED3 is the same as the duty cycle of the pulse width dimming signal Vpwm3, and the magnitude of the LED current ILED3 corresponds to the magnitude dimming signal Vref3 during the time that the power tube Q3 is turned on. At time t2, the next duty cycle begins, the rising edge of the synchronization signal VSYNC comes, and each channel controls the LED current amplitude and pulse width of each channel again according to the given amplitude dimming signal and pulse width dimming signal, so as to realize independent control of each channel.
In summary, since the current of each channel is independently controlled, the control circuit can generate corresponding driving signals according to the amplitude dimming signal, the pulse width dimming signal and the time offset to control the amplitude, the pulse width and the turn-off time of the LED current. And due to the addition of the time offset, the LED currents of all the channels are staggered, so that the LED currents can be uniformly distributed in a working period, the voltage ripple of the power supply voltage is reduced, the multi-channel LED currents are sequentially closed, and the overvoltage of the power supply voltage is avoided.
In this embodiment, the time offset may be uniformly shifted according to the total number of channels performing the work, for example, a time offset T1 is preset for a first channel, and other channels performing the work are sequentially shifted by Δ T in an increasing or decreasing order. Fig. 4 shows the descending order, T1-T2 ═ Δ T, and T2-T3 ═ Δ T. In other embodiments, Δ T may not be the same. In another embodiment, assuming that M channels of the n channels are active, LED1 may be controlled to shift by 0/M × Ts, LED2 may shift by 1/M × Ts, … … and so on, and LEDm may shift by (M-1)/M × Ts, where Ts is the period of synchronization signal VSYNC. It should be understood that the setting of the time offset of each channel may be arbitrary, and the time offset of each channel may be the same or different, and is not limited herein.
In fig. 4, for example, the synchronization period of synchronization signal VSYNC is the same as the current period of the LED current, and in other embodiments, the duty cycle is the synchronization period when at least one pulse of the LED current is included in the synchronization period of synchronization signal VSYNC. In some embodiments, the synchronization period of synchronization signal VSYNC is k times the current period (k being a positive integer). In this case, the end instant (i.e., falling edge) of the start pulse of the LED current in each synchronization period is separated from the start pulse (i.e., rising edge or falling edge of the start pulse) of the synchronization signal in each synchronization period by a corresponding time offset, wherein the start pulse refers to the first pulse in the duty cycle. In addition, the next pulse of the LED current in each synchronization period is one current period apart from the previous pulse. Fig. 5 shows the operating waveform of the multi-channel LED system in this case, wherein 2 pulses of LED current are included in the synchronization period Ts.
During each duty cycle (sync period Ts), only the falling edge of the first pulse of LED current ILED1 in channel 1 is spaced from the rising edge of sync signal VSYNC by T1, the falling edge of the second pulse of ILED1 is spaced from the falling edge of the first pulse by a current period Tc, and the falling edge of the second pulse is spaced from sync signal VSYNC by T1+ Tc. Similarly, in each period Ts of synchronization signal VSYNC, only the falling edge of the first pulse of ILED2 in channel 2 is T2 away from the rising edge of synchronization signal VSYNC, and the falling edge of the second pulse of ILED2 is T2+ Tc away from synchronization signal VSYNC; the falling edge of the first pulse in channel 3, which is also ILED3, is spaced from the rising edge of synchronization signal VSYNC by T3, and the falling edge of the second pulse of ILED3 is spaced from synchronization signal VSYNC by T3+ Tc. Meanwhile, the amplitude and the pulse width of the LED current can be independently set in each LED current period Tc.
It is to be understood that the duty cycle is a current cycle when the current cycle of the LED current includes at least one pulse of the synchronization signal. In some embodiments, the current period of the LED current is m times the synchronization period of synchronization signal VSYNC, where m is a positive integer. In this case, the end time (i.e., falling edge) of the pulse of the LED current in each current period is separated from the start pulse (rising edge or falling edge of the first pulse) of synchronization signal VSYNC in each current period by a corresponding time offset. In summary, the duty cycle is the longer of the synchronization cycle and the current cycle. Fig. 6 shows the operating waveform of the multi-channel LED system in this case, wherein 3 pulses of the synchronization signal VSYNC are included in each current period Tc.
As shown in fig. 6, during each duty cycle (current period Tc), the falling edge of the pulse of LED current ILED1 in channel 1 is spaced from the rising edge of the first pulse (start pulse) of synchronization signal VSYNC during current period Tc by T1. Likewise, during each current period Tc, the falling edge of the pulse of ILED2 in channel 2 is spaced from the rising edge of the first pulse of synchronization signal VSYNC by T2; the falling edge of the pulse of ILED3 in channel 3 is spaced T3 from the rising edge of the first pulse of synchronization signal VSYNC. Meanwhile, the amplitude and the pulse width of the LED current can be independently set in each LED current period Tc.
The above-described manner of setting the time offset is not limited to the use in the LED channel of a single power transistor employed in the present invention, and is equally applicable to a system in which two power transistors are employed for each LED channel to perform current amplitude and pulse width control, respectively. When the LED load in each LED channel is respectively connected with the first power tube and the second power tube in series, the main control unit generates a first pulse width dimming signal and an amplitude dimming signal as above, each control circuit comprises a first control circuit and a second control circuit, and the first control circuit generates a first driving signal according to the first pulse width dimming signal to drive the first power tube on the corresponding channel so as to adjust the pulse width of the LED current; the second control circuit adjusts the magnitude of a second driving signal according to the amplitude dimming signal and a current sampling signal representing the amplitude of the LED current so as to adjust the on-resistance of a second power tube connected with the first power tube in series on a corresponding channel, and therefore the amplitude of the LED current is adjusted, wherein the second driving signal is used for driving the second power tube. The details of the above-described manner are not described in detail herein.
Furthermore, referring again to fig. 2, since the parasitic parameters on each channel are different, and there are no two devices that are identical, the voltage drops during conduction of the respective LED strings and power tubes may be different even if the current magnitude controlling each channel is the same. The LED current of each channel is controlled to be the same when the power supply voltage is 30V, the voltage drop of the LED1 is 29.6V and the voltage drop of the power tube Q1 is 0.3V during conduction; the voltage drop of the LED2 is 29V, and the voltage drop of the power tube Q2 is 0.9V; the voltage drop across the LED3 was 28.5V and across the power tube Q3 was 1.4V. The power tube with large voltage drop has large loss and is easy to generate heat, and the efficiency and the heating control of the whole LED system are not facilitated. Therefore, when the voltage drop of the power tubes of some channels is larger, the supply voltage Vin can be kept unchanged, the channels are subjected to self-adaptive adjustment, the LED current of the channels is increased, the voltage drop of the LED loads of the channels is increased, and the voltage drop of the corresponding power tubes is reduced; meanwhile, in order to keep the average current (or the luminous brightness) of each channel constant, the conduction time of the power tubes in the channels needs to be reduced so as to meet the requirements of brightness and loss at the same time.
It should be understood that in some other applications, the channels of the power tube with smaller voltage drop may also be adjusted to reduce the LED current of the channels and reduce the power supply voltage, so that the voltage drop of the power tube of each channel meets the requirement, and this method is not illustrated in this embodiment.
Fig. 7 shows a circuit diagram of a driving circuit incorporating adaptive adjustment according to an embodiment of the present invention. Compared with the method without adding the self-adaptive regulation, the main control unit also receives a feedback signal representing the voltage drop of the power tube of each channel, and in some embodiments, during the effective period of the LED current, the voltage of the second end of the LED load is sampled to serve as the feedback signal, and the first end of the LED load is connected with the supply voltage Vin. It should be understood that other signals that can be derived to characterize the voltage drop across the power tube can be adjusted as feedback signals, for example, the voltage across the LED load can also characterize the voltage drop across the power tube.
Firstly, the main control unit determines a main channel according to each feedback signal, wherein the voltage drop of a power tube connected with the LED load in series in the main channel during conduction is minimum, and secondly, amplitude dimming signals and pulse width dimming signals of other channels except the main channel are adjusted to increase the amplitude of LED current of the channels and reduce the pulse width of the LED current, so that the voltage drop of the power tubes of other channels is reduced. Specifically, the master control unit transmits an initial amplitude dimming signal and an initial pulse width dimming signal to the respective control circuits to adjust the LED currents of the respective channels. The main control unit further instructs the circuit generating the supply voltage Vin to adjust the supply voltage Vin so as to adjust the voltage drop of each power tube during the conduction period while meeting the current requirement of the LED, wherein the channel corresponding to the feedback signal which is first reduced to the first threshold (here, 0.3V) is the main channel. The supply voltage remains unchanged thereafter. It should be understood that the circuit for generating the supply voltage may be included inside the main control unit or may be independent from the main control unit, and is not limited herein.
In this embodiment, the power tube connected in series with the LED load is a first power tube connected in series between the LED load and a reference ground, and a voltage at the second end of the LED load is an on-voltage of the first power tube. In other embodiments, the power tube connected in series with the LED load includes a first power tube and a second power tube connected in series between the LED load and a reference ground, and the voltage at the second end of the LED load is the sum of conduction voltage drops of the first power tube and the second power tube. The description is given here by way of example only with one power tube in series with the LED load. Referring to fig. 2, the voltage drop of the power transistor Q1 in channel 1 during conduction is the smallest, so channel 1 is the main channel. Since the voltage drop of the power tube Q2 in the channel 2 and the voltage drop of the power tube Q3 in the channel 3 are large, adaptive adjustment is performed on the channels 2 and 3, and the adaptive adjustment process is specifically described below by taking the case where the supply voltage is kept unchanged as an example.
The adaptive adjustment of the channel 2 will be described as an example. The main control unit adjusts the amplitude dimming signal Vref2 according to the feedback signal Vd2, where the feedback signal Vd2 is greater than a second threshold (e.g., 0.4V), so that the amplitude dimming signal Vref2 is increased, and the control circuit 2 obtains the duty ratio D2 'of a new pulse width dimming signal Vpwm 2' according to the adjusted amplitude dimming signal Vref2 ', the amplitude dimming signal Vref2 before adjustment, and the duty ratio D2 of the pulse width dimming signal Vpwm2 before adjustment, wherein the product of the amplitude dimming signal Vref2 before adjustment and the duty ratio D2 of the pulse width dimming signal Vpwm2 is equal to the product of the adjusted amplitude dimming signal Vref 2' and the duty ratio D2 'of the pulse width dimming signal Vpwm 2'. Subsequently, the control circuit 2 adjusts the amplitude and duty ratio of the LED current according to the adjusted amplitude dimming signal Vref2 'and the pulse width dimming signal Vpwm 2'. The adjustment procedure for adjusting the amplitude and duty ratio of the LED current according to the amplitude dimming signal and the pulse width dimming signal is the same as the above description and will not be further described herein. In addition, since the amplitude dimming signal is proportional to the current amplitude, and the duty cycle of the pulse width dimming signal is the same as the duty cycle of the LED current, the product of the LED current amplitude I2 and the duty cycle D2 before and after the adjustment remains unchanged during the adjustment, i.e., the LED average current remains unchanged.
It is to be appreciated that when the feedback signal Vd2 is greater than the second threshold, the magnitude dimming signal Vref2 is increased; the magnitude dimming signal Vref2 is decreased when the feedback signal Vd2 is less than a second threshold, where the second threshold is greater than or equal to the first threshold, which is typically set slightly greater than the first threshold. In some embodiments, the amplitude dimming signal may be increased or decreased in steps of a preset step size. In addition, the main control unit may update the amplitude dimming signal and the pulse width dimming signal once in each current cycle according to the feedback signal, or update the amplitude dimming signal and the pulse width dimming signal once every other at least one current cycle, where the update cycle may be set as needed, and is not limited herein.
The following description will be given by taking the case of updating once per current cycle. When the power transistor Q2 of the current cycle is turned on, since the feedback signal Vd2 is greater than the second threshold, the amplitude dimming signal Vref2 of the previous current cycle is increased by a fixed step to obtain the amplitude dimming signal Vref2 'of the current cycle, and the duty ratio D2' of the new pulse width dimming signal Vpwm2 'is obtained according to the ratio of the product of the amplitude dimming signal Vref2 and the duty ratio D2 of the pulse width dimming signal Vpwm2 to the amplitude dimming signal Vref 2', so as to obtain the new pulse width dimming signal Vpwm2 ', and then the updated amplitude dimming signal Vref 2' and the updated pulse width dimming signal Vpwm2 'are transmitted to the control circuit 2, so that under the action of the amplifier a2, the current sampling signal Ic2 follows the amplitude dimming signal Vref 2' until they are equal, and the LED current amplitude I2 is increased. The control unit reduces the duty ratio of the power tube Q2 in the current period according to the adjusted pulse width dimming signal Vpwm 2'. When the power tube Q2 is turned on again in the next current period, the amplitude dimming signal Vref2 is increased by one step again, and a new pulse width dimming signal is obtained to continue to increase the current amplitude and decrease the duty cycle of the LED current pulse, and so on until the drain voltage of the power tube Q2 is detected to drop to the desired value. If the feedback signal Vd2 is detected to be smaller than the second threshold, the amplitude dimming signal Vref2 is decreased by one step, and a new pulse width dimming signal Vpwm2 ' is obtained according to the result of D2 ', Vref2 × D2/Vref2 ', so as to decrease the current amplitude and increase the current pulse width, so that the feedback signal Vd2 returns to the second threshold. Similarly, the adaptive adjustment of the channel 3 is also the same, and will not be described herein.
In addition, in some cases, it may happen that although the amplitude dimming signal is increased, the actual current amplitude cannot reach the value set by the increased amplitude dimming signal, and therefore, in some embodiments, the main control unit further obtains the current sampling signals (Ic1, Ic2, Ic3) representing the LED currents of the respective channels, and when determining whether the LED current amplitude reaches the desired value, that is, whether the current sampling signal is equal to the value of the amplitude dimming signal. And if the current sampling signal cannot reach the value of the amplitude dimming signal, reducing the amplitude dimming signal. It should be understood that in other embodiments, the voltage at the output of the amplifier a1 may be obtained to determine whether the LED current magnitude has reached a desired value.
After the adjustment, as can be seen from fig. 6, during the conduction period, the voltages at the second terminals of the LED2 and the LED3 are both 0.5V, the voltage drop of the power tube Q2 is reduced to 0.38V, the voltage drop of the power tube Q3 is reduced to 0.35V, which is not much different from the voltage drop of the power tube Q1, while the voltage drop of the LED load LED2 of the channel 2 is 29.5V, and the voltage drop of the LED load LED3 of the channel 3 is 29.5V, which is substantially the same as the voltage drop of the LED load LED1 of the channel 1. In addition, the voltage drop across the sampling resistor R2 is 0.12V, and the voltage drop across the sampling resistor R3 is 0.15V, which indicates that the LED current amplitudes of the channels 2 and 3 during conduction are slightly increased because R1, R2 and R3 are the same.
It will be understood by those skilled in the art that the above-mentioned manner of adjusting the current amplitude and the pulse width is only an example and not a limitation to the present invention, and other control manners for reducing the voltage drop of the power tube by adjusting the current amplitude and the current pulse width are within the scope of the present invention.
In summary, in the embodiments of the present invention, only one power tube connected in series in an LED channel is controlled, and meanwhile, the current amplitude and the duty ratio (current pulse width) are adjusted, and it is satisfied that the product of the current amplitude and the duty ratio is kept unchanged, that is, the voltage drop of the power tubes in each channel is balanced while the brightness requirement is satisfied, and excessive power consumption and heat generation of a part of the power tubes are avoided, thereby realizing the balance of the entire LED system.
In addition, the brightness of the LED and the current are not completely linear. In this case, if the relationship that the product of the amplitude of the LED current and the duty ratio is kept constant is still adopted, the emission luminance of the LED changes even if the average current is constant. The calculation may be performed based on a relational expression between the light emission luminance and the LED current, that is, the LED light emission luminance L ═ f (iled). And ensuring that the product of f (iled) and the duty ratio is kept unchanged, the brightness before and after adjustment is unchanged.
Fig. 8 shows a fourth waveform of operation of a multi-channel LED system according to an embodiment of the invention. As shown in fig. 7, the LED currents of channel 2 and channel 3 are adjusted, wherein the dotted line is the waveform before adjustment and the solid line is the waveform after adjustment. The LED current for channels 2 and 3 has an increased magnitude and a decreased pulse width, i.e., a decreased duty cycle, as compared to the current waveform prior to regulation. Taking channel 2 as an example, ILED2 'is the LED current before adjustment, ILED2 is the LED current after adjustment, and it can be seen that the amplitude of the LED current ILED2 after adjustment is greater than the amplitude of the LED current ILED 2' before adjustment. Moreover, Ton' is the on-time before adjustment, and Ton is the on-time after adjustment, and it can be seen that the on-time of the power tube is reduced after adjustment, and the pulse width of ILED2 is reduced, that is, the duty ratio of ILED2 is reduced. Furthermore, the hatched portion a1 in the figure indicates the area of the envelope of the current ILED 2' before the adaptive adjustment, and the hatched portion a2 indicates the area of the envelope of the current ILED2 after the adaptive adjustment, where a1 is equal to a2, that is, the product of the duty cycle and the current amplitude is kept constant before and after the adjustment, so that the average current of the channel 2 is constant.
Fig. 9 shows a fifth operating waveform of the multi-channel LED system according to the embodiment of the present invention. As shown in fig. 9, a time offset is introduced based on the adjustment of channel 2 and channel 3. Similarly, the dotted line represents the waveform before adjustment, and the solid line represents the waveform after adjustment. As with fig. 8, the LED current for channels 2 and 3 is increased in magnitude and decreased in pulse width as compared to the current waveform before regulation. In contrast, the falling edge of the pulse of LED current ILED1 is spaced from the rising edge of synchronization signal VSYNC by T1, the falling edge of the pulse of LED current ILED2 is spaced from the rising edge of synchronization signal VSYNC by T2, and the falling edge of the pulse of LED current ILED3 is spaced from the rising edge of synchronization signal VSYNC by T3. And since channels 2 and 3 are adaptively adjusted, taking channel 2 as an example, the falling edges of the pulses of adjusted LED current ILED2 and LED current ILED 2' before adjustment remain unchanged, and both maintain the time offset of T2 from the rising edge of synchronization signal VSYNC. Therefore, in the self-adaptive adjustment process, the LED currents of all the channels can be staggered mutually by controlling the turn-off time of the LED currents of all the channels, so that the LED currents can be distributed in a synchronous period uniformly to reduce the voltage ripple of the power supply voltage, and meanwhile, the multi-channel LED currents are turned off in sequence, so that the overvoltage of the power supply voltage is avoided. The other adjustment processes are the same as those in fig. 8 and will not be described here.
In summary, in the LED system provided in the embodiment of the present invention, each LED channel simultaneously adjusts the current amplitude and the current pulse width by controlling only one power tube, and the product of the current amplitude and the duty ratio is kept unchanged, that is, the voltage drop of the power tubes in each channel can be balanced while the brightness requirement is met, so as to achieve the balance of the entire LED system. In addition, the embodiment of the invention also adopts a tail alignment mode to set time offset for the LED current of each channel, so that the LED current of each channel works in a phase-staggered mode in one period, and the voltage ripple and the peak power of the power supply voltage are reduced; meanwhile, the turn-off time of the power tube in each channel is fixed, and the turn-on time is changed along with the duty ratio, so that the turn-off time of the power tube of each channel can be preset, the turn-off time of the LED current of each channel is staggered, the voltage overshoot of the power supply voltage caused by the simultaneous turn-off of the LED currents of a plurality of channels is avoided, and the damage to a power device is avoided.
The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention, and various modifications and changes may be made by those skilled in the art. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims (20)

1. A method of driving a multi-channel LED system, comprising:
respectively generating an amplitude dimming signal and a pulse width dimming signal corresponding to the LED load of each channel according to the brightness requirement of each channel, wherein the amplitude dimming signal is used for adjusting the amplitude of the LED current, and the pulse width dimming signal is used for adjusting the pulse width of the LED current; and
and controlling the turn-off time of the LED current of each channel according to the synchronous signal and the corresponding time offset, so that the ending time of the pulse of each LED current is separated from the starting pulse of the synchronous signal by the corresponding time offset in one working cycle.
2. The driving method according to claim 1, further comprising:
when the synchronous period of the synchronous signal comprises at least one pulse of the LED current, the ending time of the starting pulse of the LED current in each synchronous period is controlled to be away from the pulse of the synchronous signal in each synchronous period by the time offset, the next pulse of the LED current in each synchronous period is controlled to be away from the last pulse by the current period of the LED current, and the synchronous period is the work period.
3. The driving method according to claim 1, characterized by further comprising:
and when the current period of the LED current comprises at least one pulse of the synchronous signal, controlling the end time of the pulse of the LED current in each current period to be away from the initial pulse of the synchronous signal in each current period by the time offset, wherein the current period is the work period.
4. The driving method according to claim 1, wherein the time offset corresponding to a distance from a start pulse of the synchronization signal includes a time offset corresponding to a distance from a rising edge or a falling edge of the start pulse of the synchronization signal.
5. The driving method according to claim 1, further comprising:
setting a corresponding time offset for each channel before the multi-channel LED system works normally; and
and time shifting the pulse width dimming signal according to the time shift and the synchronous signal to generate a first pulse width dimming signal, wherein the duty ratio of the first pulse width dimming signal is the same as that of the pulse width dimming signal, and the turn-off time of the first pulse width dimming signal is separated from the starting pulse of the synchronous signal by the corresponding time shift in each working period.
6. The driving method according to claim 5, further comprising:
and generating a driving signal according to the first pulse width dimming signal and the amplitude dimming signal to control the working state of a first power tube connected with the LED load in series, so as to realize the amplitude and pulse width regulation of the LED current.
7. The driving method according to claim 6, further comprising:
adjusting a driving voltage of the driving signal provided to the first power tube according to the amplitude dimming signal and a current sampling signal representing an amplitude of the LED current such that the current sampling signal is equal to the amplitude dimming signal;
generating a first pulse width dimming signal according to the synchronization signal, the time offset and the pulse width dimming signal, wherein the duty cycle of the first pulse width dimming signal is the same as that of the pulse width dimming signal, and the first pulse width dimming signal is separated from the initial pulse of the synchronization signal by the corresponding time offset at the turn-off time of each duty cycle; and
and controlling the time for providing the driving voltage for the first power tube according to the first pulse width dimming signal.
8. The driving method according to claim 5, further comprising:
and generating a first driving signal according to the first pulse width dimming signal to drive a first power tube connected with the LED load on the corresponding channel in series so as to adjust the pulse width of the LED current.
9. The driving method according to claim 8, further comprising:
and adjusting the magnitude of a second driving signal according to the amplitude dimming signal and a current sampling signal representing the amplitude of the LED current to adjust the on-resistance of a second power tube connected with the first power tube in series on a corresponding channel, so as to adjust the amplitude of the LED current, wherein the second driving signal is used for driving the second power tube.
10. A driver circuit for a multi-channel LED system, comprising:
the main control unit is configured to respectively generate an amplitude dimming signal and a pulse width dimming signal corresponding to the LED load of each channel according to the brightness requirement of each channel, and adjust the pulse width dimming signal according to a synchronous signal and a corresponding time offset so that the ending time of the pulse of the LED current of each channel is separated from the starting pulse of the synchronous signal by the corresponding time offset in one working cycle; and
a plurality of control circuits corresponding to a number of channels in the LED system, wherein each control circuit adjusts an amplitude of the LED current according to a corresponding amplitude dimming signal and adjusts a pulse width of the LED current according to a corresponding pulse width dimming signal.
11. The driving circuit according to claim 10, wherein when the synchronization period of the synchronization signal comprises at least one pulse of the LED current, the control circuit is configured to control an end time of a start pulse of the LED current in each synchronization period to be separated from a start pulse of the synchronization signal in each synchronization period by the time offset, and a next pulse of the LED current is separated from a previous pulse by a current period of the LED current, wherein the synchronization period is the duty period.
12. The driving circuit according to claim 10, wherein when the current period of the LED current includes at least one pulse of the synchronization signal, the LED current is controlled to be separated from the start pulse of the synchronization signal in each current period by the time offset at the end time of the pulse in each current period, wherein the current period is the duty period.
13. The driving circuit according to claim 10, wherein the main control unit is configured to assign a corresponding time offset to each channel before the multichannel LED system normally operates, and time-shift the pwm signal according to the time offset and the synchronization signal to generate a first pwm signal, wherein a duty cycle of the first pwm signal is the same as a duty cycle of the pwm signal, and an off time of the first pwm signal is separated from a start pulse of the synchronization signal by the corresponding time offset in each operating period.
14. The driving circuit according to claim 10, wherein the corresponding time offset from the start pulse of the synchronization signal comprises a corresponding time offset from a rising edge or a falling edge of the start pulse of the synchronization signal.
15. The driving circuit as claimed in claim 13, wherein the control circuit is configured to generate a driving signal according to the first pwm signal to control an operation state of a first power tube connected in series with the LED load, so as to adjust a magnitude and a pulse width of the LED current.
16. The drive circuit according to claim 15, wherein each of the control circuits comprises:
a first input end of the feedback control circuit receives the amplitude dimming signal, a second input end of the feedback control circuit receives a current sampling signal representing the LED current, and an output end of the feedback control circuit generates a driving voltage; and
a gate switch configured to be connected between the output terminal of the feedback control circuit and the control terminal of the first power tube, and controlled by the first pwm signal to deliver the driving voltage to the control terminal of the first power tube when the first pwm signal is active.
17. The driving circuit as claimed in claim 10, wherein the control circuit comprises a first control circuit configured to generate a first driving signal to drive a first power tube connected in series with the LED load on a corresponding channel according to the first pulse width dimming signal to adjust the pulse width of the LED current.
18. The driving circuit as claimed in claim 17, wherein the control circuit further comprises a second control circuit configured to adjust a magnitude of a second driving signal according to the amplitude dimming signal and a current sampling signal representing the amplitude of the LED current to adjust an on-resistance of a second power transistor connected in series with the first power transistor on a corresponding channel, thereby adjusting the amplitude of the LED current, wherein the second driving signal is used for driving the second power transistor.
19. A multi-channel LED system, comprising:
a plurality of LED channels, wherein each LED channel comprises an LED load and at least one power tube connected in series; and
a driver circuit as claimed in claims 10 to 18.
20. The system of claim 19, wherein each LED channel further comprises a sampling resistor connected in series with the LED load to sample the magnitude of the LED current to obtain a current sample signal.
CN202111668829.5A 2021-12-31 2021-12-31 Multi-channel LED system, driving circuit and driving method Pending CN114501726A (en)

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