English:
[0001] This disclosure is generally directed to light emitting diode (LED) systems. More specifically, this disclosure relates to a compact and efficient driver for multiple LEDs.
[0002] Many systems use light emitting diodes (LEDs) to generate light. For example, LEDs are often used in display devices to generate red, green, and blue light. Each color could be generated using one or more strings of LEDs, where each string can include multiple LEDs coupled in series. Often times, LED strings are driven sequentially, where one string is turned on and off and then the next string is turned on and off (usually without overlap) .
[0003] Conventional devices operating in this manner can include a power converter that uses a fixed reference voltage to generate a fixed output voltage for the LED strings. Conventional devices can also include a linear regulator for each LED string. The linear regulator compares (i) a reference voltage for its LED string and (ii) a sense voltage generated by a sense resistor coupled in series with the LEDs in its string. The linear regulator typically controls a pass transistor coupled in series with the LEDs in its string.
[0004] This approach, however, is not particularly efficient. Linear regulators often require a voltage overhead so that the pass transistor operates in a gain region. Also, the voltage regulator generates a fixed output voltage regardless of the LED string being driven. These and other issues can cause large power losses. The worst case efficiency of a typical LED driver could be around 65%.
[0006] FIGURE 1 illustrates an example driving system for multiple light emitting diodes (LEDs) according to this disclosure;
[0007] FIGURE 2 illustrates an example binary-weighted transistor array in an LED driving system according to this disclosure ;
[0008] FIGURE 3 illustrates example waveforms associated with the driving system of FIGURE 1 according to this disclosure;
[0009] FIGURE 4 illustrates another example driving system for multiple LEDs according to this disclosure; and
[0010] FIGURE 5 illustrates an example method for driving multiple LEDs according to this disclosure.
[0011] FIGURES 1 through 5, discussed below, and the various embodiments used to describe the principles of the present invention in this patent document are by way of illustration only and should not be construed in any way to limit the scope of the invention. Those skilled in the art will understand that the principles of the invention may be implemented in any type of suitably arranged device or system.
[0012] FIGURE 1 illustrates an example driving system 100 for multiple light emitting diodes (LEDs) according to this disclosure. In this example, the driving system 100 includes or is used in conjunction with multiple LED strings 102a-102n. Each LED string 102a-102n here includes multiple LEDs 104. Each LED 104 represents any suitable semiconductor structure for generating light. The LEDs 104 could generate any suitable type of illumination, such as red, green, and blue light. In this example, each string 102a-102n includes multiple LEDs 104 that are coupled in series, and the strings 102a-102n are coupled in parallel. However, any other configuration involving the serial and/or parallel connection of multiple LEDs 104 to form a string could be used. Also, a string could include a single LED 104, and strings with one or multiple LEDs could be placed in any suitable arrangement.
[0013] The system 100 includes a power converter 108. The power converter 108 uses a supply voltage VS0PpLY and a variable reference voltage VRREFto generate a regulated direct current (DC) output voltage VLED. This causes currents ILEDI~ ILEDN to flow through the LED strings 102a-102n, driving the LED strings 102a- 102n. The power converter 108 includes any suitable structure for converting supply voltages in any form (including AC or DC voltages) to DC voltage. The power converter 108 can be capable of both sourcing and sinking current.
[0014] In this example, each LED string 102a-102n is associated with circuitry for controlling the current flowing through that LED string. For ease of explanation, this circuitry is described with respect to the LED string 102a. The same or similar circuitry could be used with each of the other LED strings 102b-102n.
[0016] The reference current IREF is provided to a matched transistor network 112. More specifically, the reference current IREFflows through a reference transistor 114 in the matched transistor network 112. The reference transistor 114 has an "on" resistance RREF, and the reference current IREFgenerates an internal reference voltage VIRi based on that resistance RREF.
[0017] The matched transistor network 112 also includes a binary-weighted transistor array 116. The transistor array 116 can provide a variable sense resistance RSNSI defined by the "on" resistance of one or more transistors in the array 116. The transistor array 116 could have the form shown in FIGURE 2, where multiple transistors 202a-202n are coupled in parallel. Each transistor 202a-202n is controlled by one bit of an L-bit control signal (Kn through Kn) . The transistors 202a-202n have "on" resistances that decrease in a binary fashion. The transistor 202a could have a resistance denoted xl, and the transistor 202b could have half the resistance denoted xl/2. The transistor 202m could have a resistance denoted xl/2L~2, and the transistor 202n could have a resistance denoted xl/2L_1. With L transistors 202a-202n, 2Ldifferent resistances can be created in the transistor array 116 (including an open circuit when all transistors are turned off) . The current ILEDI in the string 102a may approximately equal the reference resistance RREFdivided by the sense resistance RsNSi times the reference current IREF- As a result, increasing the sense resistance RSNsi can decrease the LED current ILEDI/ thereby reducing a brightness of the LED string 102a and vice versa. In some embodiments, the resistance of the transistor 202a matches the resistance of the reference transistor 114.
[0018] The transistor array 116 is also controlled by an enable signal LEDONi . The enable signal LEDONi indicates whether the LED string 102a is being driven or is currently turned off. If disabled, the enable signal LEDONi could cause all transistors 202a-202n in the transistor array 116 to open, creating an open circuit below the LED string 102a. If enabled, at least one of the transistors 202a-202n in the transistor array 116 can be closed, and the LED current ILEDIgenerates a sense voltage VSNSi across the sense resistance RSNSI- The enable signal LEDONi can also have a specified duty cycle in order to provide pulse width modulation (PWM) dimming control.
[0019] The matched transistor network 112 includes any suitable number of transistors for providing reference and sense resistances. The transistors 114, 202a-202n can represent any suitable transistor devices, such as n-channel metal oxide semiconductor (NMOS) transistors. Internal reference voltages VIR2-VIRNand sense voltages VSNs2-VSNsNcan be generated in the other LED strings 102b-102n in the same or similar manner using enable signals LEDON2-LEDONN.
[0020] The internal reference voltage VIRIand the sense voltage VSNSi are provided to a transconductance amplifier (Gm) 118, which amplifies a difference between the voltages and generates an output current. The output current is provided to a sample and hold circuit (S/H) 120, which samples its input current and outputs the sampled current. The sample and hold circuit 120 can capture a sample of its input current in response to a control signal SAMi. The sampled current that is output by the sample and hold circuit 120 is provided to a capacitor 122, which stores a reference voltage VR1. The transconductance amplifier 118 includes any suitable structure for generating a current based on a difference in input voltages, such as an amplifier with a high loop gain. The sample and hold circuit 120 includes any suitable structure for sampling a signal and outputting a sampled value. The capacitor 122 includes any suitable capacitive structure having any suitable capacitance. Note that while a capacitor 122 is shown here as storing a voltage, any other suitable voltage storage element could be used, such as an analog-to-digital converter coupled to a digital register .
[0021] As shown here, the driving system 100 can generate multiple reference voltages VRi-VRN, each of which denotes the error between the desired current through the LEDs in a string and the actual current through those LEDs. The reference voltages VR1-VRNare fed back to the power converter 108 as the variable reference voltage VRREF. A multiplexer 124 selects which of the reference voltages VR1-VRNis provided as the reference voltage VRREF. For example, the LED strings 102a-102n could be driven sequentially, such as by driving the string 102a with the enable signal LEDONi and then driving the string 102b with the enable signal LEDON2(without overlap between the driving of the strings 102a-102b) . The multiplexer 124 could output the reference voltage VRi-VRNthat is associated with the particular
[0022] The multiplexer 124 is controlled by a selector 126. The selector 126 uses the enable signals LEDONi-LEDONNto identify which reference voltage VRi-VRNshould be output by the multiplexer 124. The selector 126 then generates one or more control signals for the multiplexer 124, where those control signals cause the multiplexer 124 to output the appropriate reference voltage. The multiplexer 124 includes any suitable structure for receiving multiple input signals and selectively outputting at least one of the input signals. The selector 126 includes any suitable structure for generating at least one control signal for a multiplexer.
[0023] When the driving system 100 first starts or is otherwise initialized, an external controller can cause the driving system 100 to drive each LED string 102a-102n once sequentially. As each string is driven, its reference voltage VRI ~Vrnreaches a suitable value, which can be stored on the capacitor 122. After that, whenever the driving system 100 attempts to drive an LED string, the multiplexer 124 can output the voltage from that string's capacitor 122 as the reference voltage VRREF. This allows the power converter 108 to immediate change its output voltage VLEDin accordance with each LED string's reference voltage VRi-VRN.
[0024] In this manner, the driving system 100 can selectively provide different reference voltages to the power converter 108 as a reference voltage VRREF- The different reference voltages are associated with different LED strings 102a-102n. The use of different reference voltages may allow the LED currents ILEDI-ILEDN to have very fast slew rates (such as ten or several tens of microseconds) , allowing well-defined current pulses to be created. This also allows the power converter 108 to generate a voltage VLED that can vary depending on the forward voltage VFi-VFNof the LED string currently being driven. Further, dimming control can be supported through the LEDONi-LEDONNsignals and the transistor arrays 116 can be altered using the control signals Κχ-ΚΝ, allowing the LED currents ILEDI-ILEDNto be adjusted dynamically. All of this can be accomplished using a single power converter 108, which reduces the size and cost of the driving system 100. This can also help to reduce the voltage required to drive the LEDs 104 while still preserving current programmability, and the driving system 100 can be highly efficient (such as up to 93% efficient or even more) .
[0025] Note that this functionality could be used in a wide variety of devices or systems. For example, the driving system 100 could be used in projector systems, display devices, emergency signal lights, or other devices in which strings of LEDs are sequentially illuminated (such as to generate different colors) .
[0026] Although FIGURE 1 illustrates one example of a driving system 100 for multiple LEDs, various changes may be made to FIGURE 1. For example, the system 100 could drive any suitable number of LED strings, each of which could include any suitable number of LEDs. Also, while FIGURE 1 illustrates the use of specific circuitry to perform certain functions, other circuitry could be used to perform the same or similar functions. Although FIGURE 2 illustrates one example of a binary-weighted transistor array 116 in an LED driving system, various changes may be made to FIGURE 2. For instance, the transistor array 116 could include any number of transistors in any suitable configuration, and any suitable type(s) of transistors could be used.
[0027] FIGURE 3 illustrates example waveforms associated with the driving system 100 of FIGURE 1 according to this disclosure. In FIGURE 3, a waveform 302 denotes the output voltage VLEDfrom the power converter 108, and waveforms 304-308 denote LED currents ILEDI_ILED3 through three LED strings. The LED currents ILEDI~ILED3 may or may not be equal. As can be seen in FIGURE 3, the output voltage VLEDvaries over time as the multiplexer 124 outputs different reference voltages VRi-VRNas the reference voltage VRREF. Moreover, the LED currents ILEDI-ILED3 have clearly defined pulses with rapid slew rates. In particular embodiments, each LED current ILEDI_ILED3 could range from OA to about 2A with a slew rate of about l s .
[0029] Although FIGURE 3 illustrates examples of waveforms associated with the driving system 100 of FIGURE 1, various changes may be made to FIGURE 3. For example, the waveforms 302- 308 illustrate possible operations of the driving system 100. The driving system 100 could operate in any other appropriate manner .
[0030] FIGURE 4 illustrates another example driving system 400 for multiple LEDs according to this disclosure. As shown in FIGURE 4, the driving system 400 is similar in structure to the driving system 100 of FIGURE 1 and has many similar components 402a-426. In addition to driving the LED strings 402a-402n sequentially, at least one additional LED string 428 can be constantly driven or turned on, meaning it can be turned on while the driving system 400 is sequentially turning on and off the other LED strings 402a-402n. This could allow, for example, each LED string 428 to provide highlighting or backlighting while the other LED strings 402a-402n are driven sequentially.
[0031] In this example, each LED string 428 is associated with a reference current generator 430 and a matched transistor network 432 having a reference transistor 434 and a binary- weighted transistor array 436. The binary-weighted transistor array 436 can be enabled using an enable signal LEDON0. These components may be the same as or similar to analogous components associated with the other LED strings 402a-402n. A current regulator 438 receives a reference voltage generated across the reference transistor 434 and a sense voltage generated across the transistor array 436. The current regulator 438 can represent a difference amplifier that amplifies a difference between its input voltages and controls a pass transistor 440, which is coupled in series with the LED string 428. The current regulator 438 includes any suitable structure for regulating a current, such as a linear current regulator. The pass transistor 440 includes any suitable transistor device, such as an NMOS transistor .
[0032] In particular embodiments, one or more LED strings 428 can be concurrently turned on while the other LED strings 402a- 402n are being sequentially driven when one or more conditions are met. For example, an LED string 428 could be turned on if its forward voltage VF0, together with the overhead voltage of the pass transistor 440, is lower than the lowest forward voltage VFi-VFNof the LED strings 402a-402n.
[0033] Although FIGURE 4 illustrates another example of a driving system 400 for multiple LEDs, various changes may be made to FIGURE 4. For example, the system 400 could drive any suitable number of LEDs or LED strings. Also, while specific circuitry is shown in FIGURE 4, other circuitry could be used to perform the same or similar functions. In addition, while the figures described above illustrate different driving systems with different functions or features, various functions or features implemented in one system could be used in other systems described above, and additional functions or features could be added to each system.
[0034] FIGURE 5 illustrates an example method 500 for driving multiple LEDs according to this disclosure. For ease of explanation, the method 500 is described with respect to the driving system 100 of FIGURE 1. The method 500 could be used by any other device or system, such as the driving system 400.
[0035] As shown in FIGURE 5, a reference voltage for one or more LEDs is received at step 502. This could include, for example, the power converter 108 receiving the reference voltage VRREFfrom the multiplexer 124. The reference voltage VRREFcould be based on the voltage stored on one of the capacitors 122. The voltages on the capacitors 122 could be established during a prior initialization of the driving system 100. An output voltage for the one or more LEDs is generated at step 504. This could include, for example, the power converter 108 generating , the LED voltage VLEDbased on the received reference voltage VRREF-
[0036] A sense voltage associated with the one or more LEDs is generated at step 506. This could include, for example, closing at least one of the transistors 202a-202n in the transistor array 116 associated with the LEDs to establish a sense resistance RSNSX- The sense resistance RSNSx can be adjusted to control the amount of illumination by the LEDs . The LED current ILEDXgenerates a sense voltage VSNSxacross the sense resistance RSNSX- The reference voltage is adjusted using the sense voltage at step 508. This could include, for example, the transconductance amplifier 118 amplifying a difference between the sense voltage and an internal reference voltage ViRx, where the internal reference voltage VIRXis based on a reference current IREFflowing through the transistor 112. This allows, for example, the sense resistance RSNSXto be adjusted and the driving system 100 to adjust the reference voltage VRREFprovided to the power converter 108 dynamically.
[0037] If there are any other LEDs to drive at step 510, a different reference voltage is selected at step 512. This could include, for example, the multiplexer 124 outputting the reference voltage of the next LED string to be driven. Otherwise, the adjusted reference voltage can continue to be used. In either case, the method returns to step 502, and steps 502-508 can be repeated (for the same LEDs or different LEDs) . In this way, the method 500 can be used to drive multiple LEDs or strings of LEDs using different reference voltages. Among other things, this can help to reduce power losses in the driving system.
[0038] Although FIGURE 5 illustrates one example of a method 500 for driving multiple LEDs, various changes may be made to FIGURE 5. For example, while shown as a series of steps, various steps in FIGURE 5 may overlap, occur in parallel, occur in a different order, or occur any number of times. Also, other features could be supported, such as when one or more LEDs are constantly driven while other LEDs are driven sequentially.
[0039] It may be advantageous to set forth definitions of certain words and phrases that have been used within this patent document. The term "couple" and its derivatives refer to any direct or indirect communication between two or more components, whether or not those components are in physical contact with one another. The terms "include" and "comprise," as well as derivatives thereof, mean inclusion without limitation. The term "or" is inclusive, meaning and/or. The phrases "associated with" and "associated therewith, " as well as derivatives thereof, may mean to include, be included within, interconnect with, contain, be contained within, connect to or with, couple to or with, be communicable with, cooperate with, interleave, juxtapose, be proximate to, be bound to or with, have, have a property of, or the like.
[0040] While this disclosure has described certain embodiments and generally associated methods, alterations and permutations of these embodiments and methods will be apparent to those skilled in the art. Accordingly, the above description of example embodiments does not define or constrain this invention. Other changes, substitutions, and alterations are also possible without departing from the spirit and scope of this invention as defined by the following claims.

中文:
[0001]本发明大体针对发光二极管(LED)系统。更确切地说,本发明涉及用于多个LED的小型且高效的驱动器。
[0002]许多系统使用发光二极管(LED)来产生光。例如,经常在显示装置中使用LED来产生红光、绿光和蓝光。使用一个或一个以上LED串可产生每一种颜色,其中每一串可包括多个串联耦合的LED。通常情况下,LED串是被依序驱动的,其中打开并关闭一个串且接着打开并关闭下一个串(通常没有重叠)。
[0003]用这种方式操作的常规装置可包括功率转换器,所述功率转换器使用固定参考电压产生用于LED串的固定输出电压。常规装置还可包括用于每一个LED串的线性调节器。所述线性调节器比较(i)用于其LED串的参考电压与(ii)与其串中的LED串联耦合的感测电阻器所产生的感测电压。线性调节器一般控制与其串中的LED串联耦合的通路晶体管。
[0004]然而,此方法不是特别高效。线性调节器经常需要电压额外开销以使通路晶体管在增益区内操作。并且,电压调节器产生固定输出电压,而不管正在被驱动的LED串如何。这些及其它问题可引起大的功率损耗。在最坏的情况下,一般的LED驱动器的效率可约为65%。
[0006]图1说明根据本发明的用于多个发光二极管(LED)的实例驱动系统;
[0007]图2说明根据本发明的LED驱动系统中的实例二进制加权晶体管阵列;
[0008]图3说明根据本发明的与图1中的驱动系统相关联的实例波形;
[0009]图4说明根据本发明的用于多个LED的另一实例驱动系统;及
[0010]图5说明根据本发明的用于驱动多个LED的实例方法。
[0011]下文所论述的图1到5及用来描述本专利文献中本发明的原理的各种实施例仅通过说明且无论如何不应被解释为对本发明的范围的限制。所属领域的技术人员应了解,可在任何类型的经合适布置的装置或系统中实施本发明的原理。
[0012]图1说明根据本发明的用于多个发光二极管(LED)的实例驱动系统100。在此实例中,驱动系统100包括多个LED串102a到102n或与多个LED串102a到102n结合使用。此处每一LED串102a到102n包括多个LED 104。每一LED 104表示用于产生光的任何合适的半导体结构。LED 104可产生任何合适类型的照明,例如红光、绿光和蓝光。在此实例中,每一串102a到102n包括串联耦合的多个LED 104,且串102a到102n并联耦合。然而,可使用涉及多个LED 104的串联及/或并联以形成串的任何其它配置。并且,一串可包括单个LED 104,且可将具有一个或多个LED的串放置在任何合适的布置中。
[0013]系统100包括功率转换器108。功率转换器108使用供电电压VSUPPLY和可变参考电压VRREF来产生经调节直流(DC)输出电压VLED。这引起电流ILED1到ILEDN流经LED串102a到102n,从而驱动LED串102a到102n。功率转换器108包括用于将任何形式的供电电压(包括AC或DC电压)转换为DC电压的任何合适的结构。功率转换器108可既能够提供电流又能够吸收电流。
[0014]在此实例中,每一LED串102a到102n与用于控制流经所述LED串的电流的电路相关联。为便于解释,相对于LED串102a描述此电路。可将相同或类似的电路与其它LED串102b到102n中的每一者一起使用。
[0016]将参考电流IREF提供到匹配的晶体管网络112。更确切地说,参考电流IREF在匹配的晶体管网络112中流经参考晶体管114。参考晶体管114具有“开”电阻RREF,且参考电流IREF基于所述电阻RREF产生内部参考电压VIR1。
[0017]匹配的晶体管网络112还包括二进制加权晶体管阵列116。晶体管阵列116可提供由阵列116中的一个或一个以上晶体管的“开”电阻所定义的可变感测电阻RSNS1。晶体管阵列116可具有图2中所示的形式,其中多个晶体管202a到202n并联耦合。每一晶体管202a到202n由L位控制信号(Kn到Kn)中的一个位所控制。晶体管202a到202n具有以二进制方式减小的“开”电阻。晶体管202a可具有表示为x1的电阻,且晶体管202b可具有所述电阻的一半,其表示为x1/2。晶体管202m可具有表示为x1/2L-2的电阻,且晶体管202n可具有表示为x1/2L-1的电阻。利用L个晶体管202a到202n,可在晶体管阵列116(包括关闭所有晶体管时的开路)中创建2L个不同的电阻。串102a中的电流ILED1可约等于参考电阻RREF除以感测电阻RSNS1再乘以参考电流IREF。因此,增加感测电阻RSNS1可减小LED电流ILED1,因此减少LED串102a的亮度,且反之亦然。在一些实施例中,晶体管202a的电阻与参考晶体管114的电阻匹配。
[0018]晶体管阵列116还受启用信号LEDON1控制。启用信号LEDON1表明LED串102a是正在被驱动还是目前被关闭。如果被停用,那么启用信号LEDON1可引起晶体管阵列116中的所有晶体管202a到202n打开,从而在LED串102a下面创建开路。如果被启用,那么可关闭晶体管阵列116中的晶体管202a到202n中的至少一者,且LED电流ILED1在感测电阻RSNS1上产生感测电压VSNS1。启用信号LEDON1还可具有指定的工作循环以便提供脉宽调制(PWM)调光控制。
[0019]匹配的晶体管网络112包括用于提供参考电阻和感测电阻的任何合适数目的晶体管。晶体管114,202a到202n可表示任何合适的晶体管装置,例如n通道金属氧化物半导体(NMOS)晶体管。可在其它LED串102b到102n中以相同或类似的方式使用启用信号LEDON2到LEDONN产生内部参考电压VIR2-VIRN和感测电压VSNS2-VSNSN。
[0020]将内部参考电压VIR1和感测电压VSNS1提供到跨导放大器(Gm)118,跨导放大器(Gm)118放大电压之间的差并产生输出电流。将输出电流提供到取样及保持电路(S/H)120,取样及保持电路(S/H)120对其输入电流进行取样并输出经取样电流。取样及保持电路120可响应于控制信号SAM1俘获其输入电流的样本。将由取样及保持电路120所输出的经取样电流提供到电容器122,电容器122存储参考电压VR1。跨导放大器118包括用于基于输入电压中的差而产生电流的任何合适的结构,例如具有高环路增益的放大器。取样及保持电路120包括用于对信号进行取样并输出经取样值的任何合适的结构。电容器122包括具有任何合适的电容的任何合适的电容结构。注意,虽然电容器122在此处展示为存储电压,但是也可使用任何其它合适的电压存储元件,例如耦合到数字寄存器的模/数转换器。
[0021]如此处所示,驱动系统100可产生多个参考电压VR1到VRN,每一个参考电压表示经过串中的LED的所要电流与经过那些LED的实际电流之间的误差。将参考电压VR1到VRN反馈到功率转换器108作为可变参考电压VRREF。多路复用器124选择将参考电压VR1到VRN中的哪一者提供为参考电压VRREF。举例来说,可例如通过使用启用信号LEDON1驱动串102a并接着使用启用信号LEDON2驱动串102b(串102a到102b的驱动之间没有重叠)来依序驱动LED串102a到102n。多路复用器124可输出与正在被驱动的特定LED串相关联的参考电压VR1到VRN。这允许功率转换器108使用不同的参考电压来操作,视正在被驱动的LED串而定。
[0022]多路复用器124由选择器126控制。选择器126使用启用信号LEDON1到LEDONN来识别哪一参考电压VR1到VRN应该被多路复用器124输出。选择器126接着产生用于多路复用器124的一个或一个以上控制信号,其中那些控制信号引起多路复用器124输出合适的参考电压。多路复用器124包括用于接收多个输入信号并选择性地输出所述输入信号中的至少一者的任何合适的结构。选择器126包括用于产生用于多路复用器的至少一个控制信号的任何合适的结构。
[0023]当驱动系统100首次启动或以其它方式初始化时,外部控制器可引起驱动系统100依序驱动每一LED串102a到102n一次。当每一串都被驱动时,其参考电压VR1到VRN达到合适的值,其可被存储在电容器122上。此后,每当驱动系统100尝试驱动LED串时,多路复用器124可从所述串的电容器122输出电压作为参考电压VRREF。这允许功率转换器108根据每一LED串的参考电压VR1到VRN来直接改变其输出电压VLED。
[0024]用这种方式,驱动系统100可选择性地将不同的参考电压提供到功率转换器108作为参考电压VRREF。不同的参考电压与不同的LED串102a到102n相关联。使用不同的参考电压可允许LED电流ILED1到ILEDN具有非常快的转换速率(例如十或几十微秒),这允许创建定义明确的电流脉冲。这还允许功率转换器108产生电压VLED,其可随着目前正在被驱动的LED串的正向电压VF1到VFN而变化。此外,可通过LEDON1到LEDONN信号来支持调光控制且可使用控制信号K1到KN来改变晶体管阵列116,这允许LED电流ILED1到ILEDN被动态调整。所有这些均可使用单一功率转换器108来完成,其减少驱动系统100的大小并降低驱动系统100的成本。这还可有助于在仍保持电流可编程性的情况下减少驱动LED 104所需的电压,且驱动系统100可为极其高效的(例如高达93%的效率或更高)。
[0025]注意,此功能性可用于多种装置或系统中。举例来说,驱动系统100可用于投影系统、显示装置、紧急信号灯或其它装置(其中LED串被依序照明(例如产生不同的颜色))中。
[0026]虽然图1说明用于多个LED的驱动系统100的一个实例,但是也可对图1做出各种改变。举例来说,系统100可驱动任何合适数目的LED串,所述串中的每一者可包括任何合适数目的LED。并且,尽管图1说明使用具体的电路执行某些功能,但是也可使用其它的电路执行相同或类似的功能。虽然图2说明LED驱动系统中的二进制加权晶体管阵列116的一个实例,但是也可对图2做出各种改变。例如,晶体管阵列116可包括任何合适的配置中的任何数目的晶体管,且可使用任何合适类型的晶体管。
[0027]图3说明根据本发明的与图1的驱动系统100相关联的实例波形。在图3中,波形302表示来自功率转换器108的输出电压,且波形304到308表示流经三个LED串的LED电流ILED1到ILED3。LED电流ILED1到ILED3可能相等也可能不相等。如在图3中可见,当多路复用器124输出不同的参考电压VR1到VRN作为参考电压时VRREF时,输出电压VLED随着时间而变化。而且,LED电流ILED1到ILED3具有拥有较快转换速率的定义明确的脉冲。在特定实施例中,每一LED电流ILED1到ILED3可以约1μs的转换速率在0A到约2A的范围内变化。
[0029]虽然图3说明与图1的驱动系统100相关联的波形的实例,但是可对图3做出各种改变。举例来说,波形302到308说明驱动系统100的可能的操作。驱动系统100可以任何其它合适的方式操作。
[0030]图4说明根据本发明的用于多个LED的另一实例驱动系统400。如图4中所示,驱动系统400与图1的驱动系统100在结构上类似且具有许多类似的组件402a到426。除了依序驱动LED串402a到402n外,还可恒定地驱动或打开至少一个额外的LED串428,意味着在驱动系统400正在依序打开及关闭其它LED串402a到402n的同时,可打开LED串428。此可允许(例如)每一LED串428在其它LED串402a到402n被依序驱动的同时提供加亮显示或背光。
[0031]在此实例中,每一LED串428与参考电流产生器430以及具有参考晶体管434和二进制加权晶体管阵列436的匹配的晶体管网络432相关联。可使用启用信号LEDON0启用二进制加权晶体管阵列436。这些组件可同与其它LED串402a到402n相关联的相似组件相同或类似。电流调节器438接收在参考晶体管434上产生的参考电压及在晶体管阵列436上产生的感测电压。电流调节器438可表示差分放大器,所述差分放大器将其输入电压之间的差放大并控制通路晶体管440,所述通路晶体管与LED串428串联耦合。电流调节器438包括用于调节电流的任何合适的结构,例如线性电流调节器。通路晶体管440包括任何合适的晶体管装置,例如NMOS晶体管。
[0032]在特定实施例中,当一个或一个以上条件得到满足时,就可在其它LED串402a到402n正在被依序驱动的同时打开一个或一个以上LED串428。举例来说,如果LED串428的正向电压VF0连同通路晶体管440的额外开销电压小于LED串402a到402n的最低正向电压VF1到VFN,那么就可打开LED串428。
[0033]虽然图4说明用于多个LED的驱动系统400的另一实例,但是可对图4做出各种改变。例如,系统400可驱动任何合适数目的LED或LED串。并且,尽管图4中展示具体的电路,但是其它的电路也可用来执行相同或类似的功能。此外,尽管上文所描述的图式说明具有不同功能或特征的不同驱动系统,但是在一个系统中实施的各种功能或特征可用于上文所描述的其它系统中,且可将额外功能或特征添加到每一系统。
[0034]图5说明根据本发明的用于驱动多个LED的实例方法500。为便于解释,相对于图1的驱动系统100描述方法500。方法500可被任何其它装置或系统使用,例如驱动系统400。
[0035]如图5中所示,在步骤502处接收用于一个或一个以上LED的参考电压。举例来说,这可包括功率转换器108接收来自多路复用器124的参考电压VRREF。参考电压VRREF可基于存储在电容器122中的一者上的电压。在驱动系统100的优先初始化期间可确立电容器122上的电压。在步骤504处产生用于所述一个或一个以上LED的输出电压。举例来说,这可包括功率转换器108基于所接收的参考电压VRREF产生LED电压VLED。
[0036]在步骤506处产生与所述一个或一个以上LED相关联的感测电压。举例来说,这可包括关闭晶体管阵列116中与LED相关联的晶体管202a到202n中的至少一者以建立感测电阻RSNSx。感测电阻RSNSx可经调节以控制LED的照明量。LED电流ILEDx在感测电阻RSNSx上产生感测电压VSNSx。在步骤508处使用感测电压调节参考电压。举例来说,这可包括跨导放大器118放大感测电压与内部参考电压VIRx之间的差,其中内部参考电压VIRx基于流经晶体管112的参考电流IREF。举例来说,这允许调节感测电阻RSNSx且允许驱动系统100动态地调节提供到功率转换器108的参考电压VRREF。
[0037]在步骤510处如果存在待驱动的任何其它LED,则在步骤512处选择不同的参考电压。举例来说,这可包括多路复用器124输出待驱动的下一LED串的参考电压。否则,可继续使用经调节的参考电压。在任一情况下,所述方法返回到步骤502,且可重复步骤502到508(针对相同LED或者不同的LED)。以此方式,可使用方法500来利用不同的参考电压驱动多个LED或者LED串。这可(尤其)有助于减少驱动系统中的功率损失。
[0038]虽然图5说明用于驱动多个LED的方法500的一个实例,但是可对图5做出各种改变。举例来说,尽管展示为一连串的步骤,但是图5中的各个步骤可重叠,并行发生、以不同的次序发生或者发生任何数目的次数。并且,可支持其它特征,例如当恒定地驱动一个或一个以上LED时,同时依序驱动其它LED。
[0039]对在本专利文献中已经使用的某些词语和短语提出定义可为有益的。术语“耦合”及其派生词指两个或两个以上组件之间的任何直接或间接连通,而不论那些组件是否相互物理接触。术语“包括”和“包含”以及其派生词意味着不受限制的包含。术语“或”是包含的,意味着及/或。短语“与......相关联”及“与之相关联”以及其派生词可意味着包括、被包括在内、与......互连、含有、被包含在内、连接到或与......连接、耦合到或与......耦合、可与......连通、与......合作、交织、并置、邻近、绑定到或与......绑定、具有、具有......的性质或类似含义。
[0040]尽管本发明已经描述了某些实施例及通常相关联的方法,但是对于所属领域的技术人员来说,这些实施例及方法的变更及置换将是显而易见的。因此,上文对实例实施例的描述不界定或限制本发明。在不脱离所附权利要求书所界定的本发明的精神及范围的情况下,其它变化、代替及变更也是可能的。