CN111293886A - 具有输出电流校准的反激转换器 - Google Patents
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- H02M3/335—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal using semiconductor devices only
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- H02M3/33507—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal using semiconductor devices only with automatic control of the output voltage or current, e.g. flyback converters
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Abstract
本公开涉及具有输出电流校准的反激转换器。公开了一种输出电流校准以增加反激转换器的恒定电流模式的准确度和精度。
Description
技术领域
本申请涉及反激转换器，更具体地涉及具有输出电流校准的反激转换器。
背景技术
根据电池充电的状态，通过各种恒定电压或恒定电流模式对电池供电设备的电池进行充电。如名称所暗示的，充电电压在恒定电压模式期间保持恒定在某个固定水平，而充电电流可以变化。相反，充电电流在恒定电流模式期间保持恒定，而充电电压可以变化。就电池寿命而言，恒定电压和恒定电流模式的正确排序和控制至关重要。例如，智能电话的电池经常是集成且不可拆卸的。如果此类设备的电池损坏，则必须更换整个智能电话。因此，移动设备传统上包括控制电池的充电电压和充电电流的电池管理电路。
由于移动设备内的电池管理电路正在控制施加到电池的充电电压和充电电流，因此放宽了向移动设备供电的开关功率转换器的容差。图1中示出了示例性充电系统。诸如反激转换器100之类的开关功率转换器在恒定电压操作模式期间将输入电压转换为经调节的输出电压V_OUT。诸如智能电话105之类的电池供电设备包括电池管理电路110，其控制应用于电池的恒定电压或恒定电流充电，以使用来自反激转换器100的输出功率为系统115供电。例如，在恒定电压模式下，电池管理电路110将来自反激转换器100的恒定输出电压调节为电池的恒定充电电压。类似地，在恒定电流模式中，电池管理电路110将来自反激转换器100的恒定输出电流调节为电池的恒定充电电流。电池管理电路100的该调节为反激转换器100中的调节提供了一定程度的容差。
例如，对于恒定电压和恒定电流操作模式，如图2所示，反激转换器100的输出电压和输出电流容差可以是+/-5％。对于5V的期望恒定电压模式，5％容差意味着输出电压实际上可以在4.75V至5.25V的范围内。为了在恒定电压操作期间保持调节，反激转换器100中的初级侧控制器(未示出)需要一些感测输出电压的装置。在仅初级反馈配置中，可以通过辅助绕组(或通过初级绕组)来感测输出电压。同样如图2所示，在恒定电流操作模式期间，输出电流出现类似的容差范围。就像输出电压一样，初级侧控制器无法直接感测输出电流，但必须改为间接感测输出电流。为了间接地感测输出电流，初级侧控制器可以使用感测电阻器感测开关循环中通过功率开关的峰值电流。然后可以估计输出电流，因为输出电流与峰值电流成比例。具体而言，该比例性取决于包括变压器匝数比、开关周期、感测电阻器电阻和变压器复位时间在内的许多因素。
诸如图2所示，如果输出电流容差相当大，则输出电流的这种间接感测是足够的。但是已经开发出如下便携式设备，其中在本文中表示为直接充电系统之物中电池管理电路100要么不存在要么被旁路。在直接充电系统中，功率转换器自身直接为便携式设备的电池充电。但请注意，现代智能电话通常将电池不可拆卸地集成到电话中，所以如果电池有缺陷，则整个智能电话变得有缺陷。鉴于现代智能电话的高成本，这尤其成问题。因此至关重要的是：诸如反激转换器100之类的功率转换器以相当高的精度调节恒定电压和恒定电流模式，以便使移动设备的电池保持健康。因此，在直接充电系统中降低了这些操作模式的容差(例如，期望的恒定电流或恒定电压的+/-1％)。尽管降低了容差，但请注意，控制峰值电流和输出电流之间的比例性的组件参数(诸如感测电阻和变压器复位时间)存在可观的容差。因此，输出电流的初级侧调节在恒定电流操作期间实现必要的容差是有问题的。
因此，本领域中存在对在恒定电流操作期间具有对输出电流的改进初级侧调节的反激转换器的需要。
发明内容
用于直接充电应用的反激转换器设置有次级侧输出电流校准电路。该校准电路感测输出电流，使得可以响应于所感测的输出电流而调整对恒定电流操作模式中的功率开关循环的调节。但是，与功率开关循环频率相比，输出电流的该感测相对不频繁地进行，使得恒定电流操作的控制回路的稳定性不受输出电流校准的影响。
附图说明
图1是传统移动设备充电系统的示图，其中移动设备包括功率管理电路。
图2是示出在图1的系统中的功率转换器中恒定电压和恒定电流操作模式由于移动设备的功率管理电路的存在所增加的容差的曲线图。
图3A是根据本公开的一个方面的直接充电系统的示图，其中移动设备不包括功率管理电路并且其中反激转换器包括次级侧输出电流校准电路。
图3B是图3A中的反激转换器的框图。
图4是图3B的反激转换器的功率开关波形和峰值电压调整波形的曲线图。
图5是图3B的反激转换器的恒定电流校准的更详细的图示。
通过参考紧接着的具体实施方式，本公开的实施例及其优点得到最好的理解。应当领会到，相似的附图标记用于标识一个或多个附图中所示的相似元素。
具体实施方式
为了解决本领域中对在恒定电流操作期间改善对输出电流的初级侧调节的需要，引入了次级侧校准技术。该校准是相对较低的频率，因此不破坏或改变初级侧调节的回路稳定性。为了更好地领会该校准的优点，首先将讨论在反激转换器的恒定电流操作模式期间影响初级侧调节准确度的因素。在间断导通模式下工作的反激转换器的输出电流由下面的等式(1)给出：
其中I0是输出电流，Isec_pk是次级峰值电流，Tp是功率开关的开关循环周期，并且Trst是变压器复位时间。变压器复位时间由功率开关的循环关断与从其峰值(Isec_pk)下滑至零的次级电流的随后斜降之间的延迟来定义。次级峰值电流Isec_pk等于初级峰值电流Ipk乘以反激的变压器的匝数比Nps。由于感测电阻器Rsense用于通过在每个开关循环期间测量感测电阻器两端的峰值电压(Vipk)来测量初级峰值电流(Ipk)，因此可以如在下面的等式(2)所示重写等式(1)中的输出电流的关系：
对等式(2)的检查说明了保持对输出电流的精确调节时的困难。例如，Tp、Trst、Nps和Rsense的测量都受到制造公差、寄生效应、和由此产生的不确定性的影响。因此，在恒定电流操作模式期间输出电流的传统调节将不能满足直接充电系统的严格要求。从等式(2)可以看出，在恒定电流模式期间，常规上使用下面的等式(3)来设置峰值电压Vipk：
其中kCC是传统上为静态的比例常数。通过比较等式(2)和(3)，可以看出，通过根据等式(3)控制峰值电压Vipk使输出电流保持恒定，这适合于恒定电流操作模式。作为比例常数kCC的函数的输出电流由下面的等式(4)给出：
其中ηx是变压器转换率。开关周期Tp通常是恒定的(尽管它可能经受抖动)，所以变压器复位时间Trst控制对以峰值电压为基础的循环到循环的调整的大部分。在恒定输出电流的传统仅初级调节中，一个开关循环中的因子Tp和Trst被施加到后一开关循环以确定期望的峰值电压。然后将感测电阻器两端的电压与期望的峰值电压进行比较，以便通过一旦感测电阻器两端的电压达到期望的峰值电压就循环关断功率开关来确定开关导通时间。但是，就提供诸如直接充电系统所需要的期望程度的精度和容差而言，对输出电流的该传统初级侧调节是有问题的。
为了给恒定电流模式操作提供提高的调节精度和更严格的容差，提供了次级侧校准电路，其在已知的工作条件下直接测量输出电流。例如，次级侧校准电路可以使用次级侧感测电阻器。由于次级侧感测电阻器的电阻是已知的，因此如受欧姆定律支配，次级侧校准电路可通过检测次级侧感测电阻器两端的电压并除以次级侧感测电阻器的电阻来测量输出电流。应注意，在等式(3)的比例常数kCC和如受等式(4)支配的输出电流的期望值之间存在比例。因此，次级侧校准电路命令初级侧控制器基于期望的输出电流与所测量的输出电流之间的差异来调整其比例常数kCC。以这种方式，有利地提高了恒定电流模式调节精度。尽管使用了次级侧校准电路，但由于校准频率相对较低，因此初级侧调节回路不受影响。相比之下，功率开关的开关频率经常相对较高(例如，50KHz或更高)。由于校准相对不太频繁地执行，因此其对输出电流的初级侧调节没有实际影响。因此，没有由包含次级侧校准电路引起的稳定性问题。
图3A中示出了具有次级侧输出电流校准的示例性反激转换器300。次级侧输出电流校准所提供的精度使反激转换器300能够安全地直接对用于为移动设备301中的系统302供电的电池充电。在该直接充电配置中，移动设备301中没有控制对电池的充电的功率管理电路。替代地，反激转换器300必须调节电池的恒定电压和恒定电流充电模式。在图3B中更详细地示出了反激转换器300。初级侧控制器305控制功率开关晶体管S1的开关，以调节恒定电压或恒定电流操作模式下的操作。在恒定电压调节期间，控制器305通过对变压器T1的辅助绕组310上的反馈电压(VFB)进行采样来间接地对输出电压Vout进行采样。反馈电压在环路滤波器315中被滤波，并被与误差放大器(EA)处的参考电压(V_REF)进行比较以产生误差电压。根据误差电压和期望的输出电压，控制器305诸如通过脉冲宽度调制或脉冲频率调制来调整对功率开关晶体管S1的循环的调制，以在恒定电压操作期间将输出电压保持在期望的水平。但是，取决于正在移动设备中充电的电池(未示出)的充电状态，控制器305可能无法将输出电压调整到期望的水平。控制器305然后切换到如由CC模式控制器320表示的恒定电流操作模式，CC模式控制器320为了说明目的而被与控制器305分别示出，因为它通常将与控制器305集成。
在恒定电流操作模式中，控制器320监视在与功率开关晶体管S1串联的感测电阻器Rsense两端产生的峰值电压Vipk，该功率开关晶体管S1又与变压器T1的初级绕组串联。在每个功率开关循环的导通时间期间，经整流的输入电压V_IN使磁化电流流过功率开关晶体管S1并因此流过感测电阻器。一旦峰值电压Vipk达到期望的水平，控制器305就关断功率开关晶体管S1。峰值次级电流然后流过变压器T1的次级绕组，以产生流向负载(未示出)的输出电流I_OUT。输出电流对平滑电容器C2充电以产生输出电压。输出二极管D1对次级电流进行整流，但是应领会到可以使用如在同步整流技术中已知的同步整流开关来执行这种整流。
控制器320仅可以诸如通过使用上面的等式(3)间接地控制输出电流，因为控制器320通过变压器T1与反激转换器300的次级侧隔离。在等式(3)的传统使用中，比例常数kCC是常数。但是反激转换器300中的Vipk校准电路325直接测量输出电流，使得比例常数kCC可被调整以将输出电流保持在期望的水平。以这种方式，由诸如感测电阻器的寄生效应和组件容差引起的不准确性被减小，使得输出电流在恒定电流模式下可以根据直接充电应用所要求的严格容差(例如，+/-1％)被调节。Vipk校准电路325对输出电流的测量发生在变压器T1的次级侧。但是无法诸如通过导线或引线将该测量直接传送到变压器T1的初级侧，因为变压器T1的初级侧和次级侧的接地之间的隔离将被破坏。因此，Vipk校准电路325通过诸如光隔离器330之类的隔离通道来传送必要的校准信息。在替代实施例中，可使用其他类型的隔离通道，诸如电容器或变压器T1本身的使用。
鉴于关于所测量的输出电流的校准信息，控制器320相应地改变比例常数kCC。以这种方式，Vipk的水平被改变为与根据等式(3)的常规应用将提供的不同。图4中示出了功率开关循环和感测电阻器电压的一些示例波形。对于功率开关晶体管的每个导通时间，感测电阻器电压从地升高到Vipk，于是功率开关晶体管被循环关断。再次参考等式(3)，开关周期Tp基本上是恒定的，所以是变压器复位时间Trst控制着Vipk的常规循环到循环调整。但是比例常数kCC的校准使Vipk相应地提高或降低，从而使得输出电流被更加严格地调节。
在图5中示出了反激转换器300中的比例常数校准的其他细节。为了直接测量输出电流，将次级侧感测电阻器插入输出电压的接地路径返回。输出电流Iout在恒定电流操作期间被传递到负载(未示出)并且沿着接地路径返回以在次级侧感测电阻器两端产生与输出电流成比例的电压。次级侧输出校准电路325中的电流感测电路和模数转换器(ADC)500通过感测感测电阻器电压并且将其成比例地转换为表示输出电流的数字值来感测输出电流Iout。恒定电流模式检测和滤波电路501通过例如将输出电流与输出电流限制进行比较来检测负载是否正在恒定电流模式下被驱动。如果输出电压的调节驱动输出电流达到输出电流限制，则反激转换器300不再可以在恒定电压模式下工作，而是必须改为在恒定电流模式下工作，使得输出电流不超过输出电流限制。此外，恒定电流模式检测和滤波电路501对输出电流校准进行滤波，使得与功率开关循环频率相比，输出电流校准相对不频繁地完成。以这种方式，恒定电流操作模式的增益和相位裕度不受输出电流校准的影响。
在恒定电流操作模式期间，控制器320和305调节功率开关晶体管的循环以将输出电流保持在期望的水平，期望水平在本文中被指定为Iset。校准电路325包括加法器505，其形成所测量的输出电流与Iset之间的差异。然后在另一加法器510中从Iset中减去该差异，以形成校准后的期望输出电流(在本文中被指定为iset)。该经调整的期望输出电流映射到经调整的比例常数kCC(如由iset到kCC转换电路520定义的)，kCC然后通过诸如光隔离器330之类的隔离通信信道而被传送到反激转换器300的初级侧。如果输出电流校准指示所测量的输出电流大于期望的水平，则iset到kCC转换将kCC从其默认值降低，否则该默认值将用于实现期望水平的恒定电流操作。相反，如果输出电流校准指示所测量的输出电流小于期望的水平，则iset到kCC转换将kCC从其默认值增加，否则该默认值将用于实现期望水平的恒定电流操作。将会领会到，加法器505和510、转换电路520、以及恒定电流检测和滤波电路501可以在变压器的次级侧或初级侧被执行。
恒定电流模式控制器320使用如通过感测辅助绕组310上的反射电压而确定的变压器复位时间Trst，并且利用经调整的比例常数kCC使用等式(3)形成期望峰值电压的数字版本(Vipk_d)。数模转换器(DAC)将数字峰值电压转换为模拟峰值电压Vipk，使得其在比较器515中与初级侧感测电阻器电压进行比较。当感测电阻器电压达到峰值电压Vipk时，比较器输出信号转变为二进制一电平(例如，电源电压)以触发控制器305关断功率开关晶体管，以便终止其在当前功率开关循环中的接通时间。控制器305可以在脉冲宽度调制(PWM)或脉冲频率调制(PFM)操作模式下调节该功率开关循环。但请注意，由于对输出电流的感测进行了调整，因此作为结果的输出电流的调节现在受到严格得多的控制。
如本领域的那些技术人员到目前为止将认识到并且取决于手头的特定应用，在不脱离本公开的精神和范围的情况下，可以在本公开的设备的材料、装置、配置和使用方法中并对其进行许多修改、替换和变化。鉴于此，本公开的范围不应限于本文示出和描述的特定实施例的范围，因为它们仅仅当作其一些示例，而是应该与所附权利要求及其功能等同物的范围完全相称。
Claims (19)
1.一种用于反激转换器的电路，包括：
峰值电压确定电路，其被配置为响应于变压器复位时间和经调整的比例常数而确定功率开关晶体管的当前开关周期的期望峰值电压，其中，所述经调整的比例常数是响应于所述反激转换器的输出电流的确定而被调整的；
比较器，其被配置为将所述期望峰值电压与初级侧感测电阻器电压进行比较；以及
功率开关控制器，其被配置为响应于来自所述比较器的输出信号而关断功率开关晶体管，所述输出信号指示所述初级侧感测电阻器电压等于所述期望峰值电压。
2.如权利要求1所述的电路，其中，所述峰值电压确定电路还被配置为响应于所述功率开关晶体管的循环的开关周期而确定所述期望峰值电压。
3.如权利要求1所述的电路，其中，所述峰值电压确定电路和所述功率开关控制器都在微控制器内实现。
4.如权利要求1所述的电路，还包括：
电流感测电路，其被配置为感测次级侧感测电阻器电压；以及
模数转换器，其被配置为将所述次级侧感测电阻器电压转换为数字信号。
5.如权利要求4所述的电路，还包括：
第一加法器，其被配置为确定所述数字信号与所述输出电流的期望水平之间的差异。
6.如权利要求5所述的电路，还包括：
第二加法器，其被配置为确定所述输出电流的期望水平与来自所述第一加法器的差异之间的差异，以提供经调整的输出电流水平。
7.如权利要求6所述的电路，还包括：
转换电路，其被配置为将所述经调整的输出电流水平转换为所述经调整的比例常数。
8.如权利要求1所述的电路，还包括隔离通信信道，其中，所述峰值电压确定电路还被配置为从所述隔离通信信道接收所述经调整的比例常数。
9.如权利要求8所述的电路，其中，所述隔离通信信道包括光隔离器。
10.如权利要求8所述的电路，其中，所述隔离通信信道包括用于所述反激转换器的变压器。
11.如权利要求1所述的电路，其中，所述峰值电压确定电路还被配置为在所述反激转换器的恒定电流操作模式期间确定所述期望峰值电压。
12.一种用于在恒定电流操作模式期间校准反激转换器的方法，包括：
感测所述反激转换器的输出电流，以提供感测的输出电流；
响应于期望输出电流和所述感测的输出电流之间的差异而调整比例常数，以提供经调整的比例常数；以及
响应于所述经调整的比例常数，确定初级侧感测电阻器在功率开关晶体管的当前循环期间的峰值电压。
13.如权利要求12所述的方法，还包括：
响应于所述初级侧感测电阻器的电压等于所述峰值电压，在所述功率开关晶体管的当前循环期间关断所述功率开关晶体管。
14.如权利要求12所述的方法，其中，所述峰值电压的确定还响应于变压器复位时间。
15.如权利要求12所述的方法，其中，所述峰值电压的确定还响应于所述功率开关晶体管的循环周期。
16.如权利要求12所述的方法，其中，所述输出电流的感测包括感测次级侧感测电阻器的电压以提供感测的电压。
17.如权利要求16所述的方法，还包括将所述感测的电压数字化以提供经数字化的感测电压。
18.如权利要求17所述的方法，还包括确定所述期望输出电流和所述经数字化的感测电压之间的差异，以提供第一差异。
19.如权利要求18所述的方法，还包括确定所述期望输出电流和所述第一差异之间的差异以提供第二差异，并且其中，响应于期望输出电流和所述感测的输出电流之间的差异而调整所述比例常数包括响应于所述第二差异而调整所述比例常数。
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