TWI741596B

TWI741596B - Flyback converter, control circuit thereof, and associated control method

Info

Publication number: TWI741596B
Application number: TW109115626A
Authority: TW
Inventors: 林冠宇; 陳佑民; 林天麒; 陳廷瑋; 張湘忠; 于岳平
Original assignee: 加拿大商萬國半導體國際有限合夥公司
Priority date: 2020-05-11
Filing date: 2020-05-11
Publication date: 2021-10-01
Also published as: TW202143623A

Abstract

A flyback, including: a transformer, a sensing impedance, a switch and a control circuit. The transformer includes a primary side and a secondary side. The sensing impedance is coupled between the secondary side of the transformer and an output terminal of the flyback converter. The switch is coupled to the primary side of the transformer, wherein a current flowing through the primary side of the transformer is controlled by the switch. The control circuit is arranged to detect if the sensing impedance is bypassed, and further arranged to adjust an operating frequency of the switch when the sensing impedance is bypassed.

Description

返馳式轉換器、該返馳式轉換器的控制電路以及相關控制方法Flyback converter, control circuit of the flyback converter and related control method

本申請是有關於一種電子裝置，詳細來說，是有關於一種返馳式轉換器、該返馳式轉換器的控制電路以及相關控制方法。 This application relates to an electronic device, and in detail, it relates to a flyback converter, a control circuit of the flyback converter, and related control methods.

對於電源供應器而言，當電源供應器中的一個部件或元件(如電阻或電容)被斷路或旁路時，將導致流向輸出負載的電流增加，並可能會損壞電源或輸出負載，甚至引起火災。 For the power supply, when a component or element (such as a resistor or capacitor) in the power supply is disconnected or bypassed, it will cause the current flowing to the output load to increase, and may damage the power supply or output load, or even cause Fire.

因此，本申請的目的之一在於提供一種返馳式轉換器、該返馳式轉換器的控制電路以及相關控制方法來解決上述問題。 Therefore, one of the objectives of the present application is to provide a flyback converter, a control circuit of the flyback converter, and related control methods to solve the above-mentioned problems.

依據本申請的一實施例，揭露一種返馳式轉換器。該返馳式轉換器包括一變壓器、一感應阻抗、一開關以及一控制電路。該變壓器包括一一次側和一二次側。該感應阻抗耦接在該變壓器的該二次側和該返馳式轉換器的一輸出端之間。該開關耦接到該變壓器的該一次側，其中該開關控制流過該變壓器的該一次側的一電流。該控制電路用於檢測該感應阻抗是否被旁路，並且進一步用於當該感應阻抗被旁路時調整該開關的工作頻率。 According to an embodiment of the present application, a flyback converter is disclosed. The flyback converter includes a transformer, an inductive impedance, a switch and a control circuit. The transformer includes a primary side and a secondary side. The inductive impedance is coupled between the secondary side of the transformer and an output terminal of the flyback converter. The switch is coupled to the primary side of the transformer, wherein the switch controls a current flowing through the primary side of the transformer. The control circuit is used to detect whether the inductive impedance is bypassed, and is further used to adjust the operating frequency of the switch when the inductive impedance is bypassed.

依據本申請的一實施例，揭露一種返馳式轉換器的控制電路。該控制電路用於檢測橫跨一感應阻抗的一檢測電壓，其中該感應阻抗耦接在該返馳式轉換器的一變壓器和該返馳式轉換器的一輸出端之間，並且進一步用於至少根據該檢測電壓來調整該返馳式轉換器的一開關的一工作頻率。 According to an embodiment of the present application, a control circuit of a flyback converter is disclosed. The control circuit is used to detect a detection voltage across an inductive impedance, wherein the inductive impedance is coupled between a transformer of the flyback converter and an output terminal of the flyback converter, and is further used for A working frequency of a switch of the flyback converter is adjusted at least according to the detection voltage.

依據本申請的一實施例，揭露一種返馳式轉換器的控制方法，其中該返馳式轉換器包括一變壓器以及一開關。該控制方法包括：判斷一感應阻抗的兩端的一跨壓是否小於一參考電壓，其中該感應阻抗耦接在該變壓器和該返馳式轉換器的一輸出端之間；當該感應阻抗的兩端的該跨壓小於該參考電壓時，判斷該開關的一工作頻率是否大於一參考頻率；以及當該開關的該工作頻率大於該參考頻率時調整該工作頻率以限制該返馳式轉換器的一輸出電流。 According to an embodiment of the present application, a control method of a flyback converter is disclosed, wherein the flyback converter includes a transformer and a switch. The control method includes: determining whether a cross voltage across an inductive impedance is less than a reference voltage, wherein the inductive impedance is coupled between the transformer and an output terminal of the flyback converter; When the cross voltage at the terminal is less than the reference voltage, it is determined whether an operating frequency of the switch is greater than a reference frequency; and when the operating frequency of the switch is greater than the reference frequency, the operating frequency is adjusted to limit a flyback converter. Output current.

10:返馳式轉換器 10: Flyback converter

11:變壓器 11: Transformer

12:二極體 12: Diode

13:電容 13: Capacitance

14:開關 14: switch

15:開關控制電路 15: Switch control circuit

16:控制電路 16: control circuit

Vin:輸入電壓源 Vin: input voltage source

Vout1、Vout2:輸出端 Vout1, Vout2: output terminal

Rs:感應阻抗 Rs: Inductive impedance

Vs:檢測電壓 Vs: detection voltage

Vad:調整訊號 Vad: adjust the signal

Fad:調整頻率 Fad: adjust frequency

Vcot:時脈訊號 Vcot: Clock signal

Fcot、Fsc,ccm、Fsc,dcm:頻率 Fcot, Fsc, ccm, Fsc, dcm: frequency

Fsc:工作頻率 Fsc: working frequency

Vsc:開關控制訊號 Vsc: switch control signal

CTRL:控制訊號 CTRL: Control signal

Vfeed:反饋訊號 Vfeed: feedback signal

151:二次側控制電路 151: Secondary side control circuit

152:COT產生電路 152: COT generating circuit

153:隔離傳輸裝置 153: Isolated transmission device

154:一次側接收電路 154: Primary side receiving circuit

161:檢測電路 161: Detection Circuit

162:頻率控制電路 162: frequency control circuit

Fref:參考頻率 Fref: reference frequency

Vref:參考電壓 Vref: Reference voltage

41:電壓檢測電路 41: Voltage detection circuit

42:頻率檢測電路 42: Frequency detection circuit

43:邏輯電路 43: Logic Circuit

SI1:第一指示訊號 SI1: The first indicator signal

SI2:第二指示訊號 SI2: The second indicator signal

Fsc,max:最大工作頻率 Fsc,max: maximum operating frequency

601-603:步驟 601-603: steps

600:控制方法 600: control method

當結合附圖閱讀時，從以下詳細描述最佳理解本揭露之態樣。應注意，根據產業中之標準實踐，各種構件未按比例繪製。事實上，為了論述的清楚起見可任意增大或減小各種構件之尺寸。 When read in conjunction with the accompanying drawings, the aspect of the present disclosure is best understood from the following detailed description. It should be noted that according to standard practice in the industry, the various components are not drawn to scale. In fact, the size of various components can be increased or decreased arbitrarily for the sake of clarity of the discussion.

圖1是依據本申請一實施例之返馳式轉換器的示意圖。 Fig. 1 is a schematic diagram of a flyback converter according to an embodiment of the present application.

圖2是依據本申請一實施例之開關控制電路的示意圖。 FIG. 2 is a schematic diagram of a switch control circuit according to an embodiment of the present application.

圖3是依據本申請一實施例之控制電路的示意圖。 Fig. 3 is a schematic diagram of a control circuit according to an embodiment of the present application.

圖4是依據本申請一實施例之檢測電路的示意圖。 FIG. 4 is a schematic diagram of a detection circuit according to an embodiment of the present application.

圖5是依據本申請一實施例之工作頻率與負載的關係示意圖。 FIG. 5 is a schematic diagram of the relationship between the operating frequency and the load according to an embodiment of the present application.

圖6是依據本申請一實施例之返馳式轉換器的控制方法的流程圖。 FIG. 6 is a flowchart of a control method of a flyback converter according to an embodiment of the present application.

以下揭露提供用於實施本揭露之不同構件之許多不同實施例或實例。下文描述組件及配置之特定實例以簡化本揭露。當然，此等僅為實例且非意欲限制。舉例而言，在以下描述中之一第一構件形成於一第二構件上方或上可包含其中該第一構件及該第二構件經形成為直接接觸之實施例，且亦可包含其中額外構件可形成在該第一構件與該第二構件之間，使得該第一構件及該第二構件可不直接接觸之實施例。另外，本揭露可在各個實例中重複參考數字及/或字母。此重複出於簡化及清楚之目的且本身不指示所論述之各個實施例及/或組態之間的關係。 The following disclosure provides many different embodiments or examples of different components for implementing the disclosure. Specific examples of components and configurations are described below to simplify the disclosure. Of course, these are only examples and are not intended to be limiting. For example, in the following description, a first member formed on or on a second member may include an embodiment in which the first member and the second member are formed in direct contact, and may also include additional members therein An embodiment that can be formed between the first member and the second member so that the first member and the second member may not directly contact. In addition, the present disclosure may repeat reference numbers and/or letters in each example. This repetition is for the purpose of simplification and clarity and does not in itself indicate the relationship between the various embodiments and/or configurations discussed.

此外，為便於描述，諸如「下面」、「下方」、「下」、「上方」、「上」及類似者之空間相對術語可在本文中用於描述一個元件或構件與另一(些)元件或構件之關係，如圖中圖解說明。空間相對術語意欲涵蓋除在圖中描繪之定向以外之使用或操作中之裝置之不同定向。設備可以其他方式定向(旋轉90度或按其他定向)且因此可同樣解釋本文中使用之空間相對描述詞。 In addition, for ease of description, spatially relative terms such as "below", "below", "below", "above", "upper" and the like can be used herein to describe one element or component and another(s) The relationship between components or components is illustrated in the figure. Spatial relative terms are intended to cover different orientations of devices in use or operation other than those depicted in the figures. The device can be oriented in other ways (rotated by 90 degrees or in other orientations) and therefore the spatial relative descriptors used in this article can also be interpreted.

儘管陳述本揭露之寬泛範疇之數值範圍及參數係近似值，然儘可能精確地報告特定實例中陳述之數值。然而，任何數值固有地含有必然由於見於各自測試量測中之標準偏差所致之某些誤差。再者，如本文中使用，術語「大約」通常意謂在一給定值或範圍之10%、5%、1%或0.5%內。替代地，術語「大約」意謂在由此項技術之一般技術者考量時處於平均值之一可接受標準誤差內。除在操作/工作實例中以外，或除非以其他方式明確指定，否則諸如針對本文中揭露之材料之數量、時間之持續時間、溫度、操作條件、數量之比率及其類似者之全部數值範圍、數量、值及百分比應被理解為在全部例項中由術語「大約」修飾。相應地，除非相反地指示，否則本揭露及隨附發明申請專利範圍中陳述之數值參數係可根據需要變化之近似值。至少，應至少鑑於所報告有效數位之數目且藉由應用普通捨入技術解釋各數值參數。範圍可在本文中表達為從一個端點至另一端點或在兩個端點之間。本文中揭露之全部範圍包含端點，除非另有指定。 Although the numerical ranges and parameters stated in the broad scope of this disclosure are approximate values, the numerical values stated in the specific examples should be reported as accurately as possible. However, any value inherently contains certain errors inevitably due to the standard deviation seen in the respective test measurement. Furthermore, as used herein, the term "about" generally means within 10%, 5%, 1%, or 0.5% of a given value or range. Alternatively, the term "approximately" means within one acceptable standard error of the mean when considered by a general technician of the technology. Except in the operation/working example, or unless explicitly specified in other ways, such as the total numerical range of the quantity of materials disclosed in this article, the duration of time, temperature, operating conditions, the ratio of quantities and the like, Quantities, values and percentages should be understood as modified by the term "about" in all examples. Correspondingly, Unless indicated to the contrary, the numerical parameters stated in the scope of the present disclosure and the accompanying invention application are approximate values that can be changed as needed. At the very least, each numerical parameter should be explained at least in view of the number of significant digits reported and by applying ordinary rounding techniques. Ranges can be expressed herein as from one endpoint to the other or between two endpoints. All ranges disclosed herein include endpoints, unless otherwise specified.

對於電源供應器而言，當一部件或一元件(如電阻或電容)被意外地或故意地斷路或旁路時，將導致流向輸出負載的電流增加，這可能會損壞電源或輸出負載，甚至引發火災。一些專門檢測電源供應器的安全性的測試甚至會故意地將轉換器中的部件或元件(如電阻或電容)旁路，藉此來檢查輸出電流或輸出功率。本發明提供的返馳式轉換器及其控制電路和相關的控制方法採用一種負載電流抑制機制來解决上述問題。 For power supplies, when a component or a component (such as a resistor or capacitor) is accidentally or deliberately disconnected or bypassed, it will cause the current flowing to the output load to increase, which may damage the power supply or output load, or even Cause a fire. Some tests that specifically check the safety of the power supply even deliberately bypass components or components (such as resistors or capacitors) in the converter to check the output current or output power. The flyback converter and its control circuit and related control method provided by the present invention adopt a load current suppression mechanism to solve the above-mentioned problems.

圖1是依據本發明實施例的返馳式轉換器10的示意圖。返馳式轉換器10包括變壓器11、二極體12、電容13、開關14和開關控制電路15。二極體12的陽極耦接到變壓器11，二極體12的陰極耦接到輸出端Vout1。電容13耦接於返馳式轉換器10的輸出端Vout1和Vout2之間。開關14和輸入電壓源Vin耦接到變壓器11。 FIG. 1 is a schematic diagram of a flyback converter 10 according to an embodiment of the present invention. The flyback converter 10 includes a transformer 11, a diode 12, a capacitor 13, a switch 14 and a switch control circuit 15. The anode of the diode 12 is coupled to the transformer 11, and the cathode of the diode 12 is coupled to the output terminal Vout1. The capacitor 13 is coupled between the output terminals Vout1 and Vout2 of the flyback converter 10. The switch 14 and the input voltage source Vin are coupled to the transformer 11.

具體而言，變壓器11包括一次側和二次側。開關14耦接到變壓器的一次側以控制流過變壓器11的一次側的電流。當啟用開關14時，變壓器11的一次側接收來自輸入電壓源Vin的電能以進行充電。同時，二極體12被切斷，電容13向耦接在輸出端Vout1和Vout2之間的輸出負載(未示出)提供電力。當停用開關14時，變壓器11的二次側放電，電能從變壓器11的二次側傳輸到電容13。在本實施例中，變壓器11的一次側和二次側的匝數比為N，其中N是自然數。 Specifically, the transformer 11 includes a primary side and a secondary side. The switch 14 is coupled to the primary side of the transformer to control the current flowing through the primary side of the transformer 11. When the switch 14 is activated, the primary side of the transformer 11 receives electric energy from the input voltage source Vin for charging. At the same time, the diode 12 is cut off, and the capacitor 13 provides power to the output load (not shown) coupled between the output terminals Vout1 and Vout2. When the switch 14 is disabled, the secondary side of the transformer 11 is discharged, and electric energy is transferred from the secondary side of the transformer 11 to the capacitor 13. In this embodiment, the turns ratio of the primary side and the secondary side of the transformer 11 is N, where N is a natural number.

開關14的導通時間和斷開時間可以通過開關控制電路15根據反饋訊號Vfeed所產生的開關控制訊號Vsc來改變，其中開關控制訊號Vsc具有頻率Fsc，並且反饋訊號Vfeed指示包含輸出端Vout1的輸出功率、輸出電壓或輸出電流的資訊。需注意的是，開關控制訊號Vsc的頻率Fsc指示開關14的工作頻率。在以下段落中，為了方便起見，將開關14的工作頻率標記為Fsc。 The on time and off time of the switch 14 can be changed by the switch control circuit 15 according to the switch control signal Vsc generated by the feedback signal Vfeed, where the switch control signal Vsc has a frequency Fsc, and the feedback signal Vfeed indicates the output power including the output terminal Vout1 , Output voltage or output current information. It should be noted that the frequency Fsc of the switch control signal Vsc indicates the operating frequency of the switch 14. In the following paragraphs, for convenience, the operating frequency of the switch 14 is marked as Fsc.

參考圖5，圖5是開關14的工作頻率Fsc與輸出負載的對比示意圖。如圖5所示，當返馳式轉換器10以不連續導通模式(DCM)工作時，開關14的工作頻率Fsc與輸出負載正相關。換言之，當較重的輸出負載耦接到輸出端時，需要更高的工作頻率Fsc來驅動輸出負載。本技術領域具有通常知識者應能理解，開關14的工作頻率Fsc越高，產生的輸出電流就越大，並且可以驅動更大的輸出負載。在本實施例中，返馳式轉換器10可工作在DCM中的最小頻率標記為Fsc,dcm，並且返馳式轉換器10可工作在DCM中的最大頻率標記為Fsc,ccm。當達到頻率Fsc,ccm時，返馳式轉換器10進入連續導通模式(CCM)，並且在CCM中工作頻率Fsc將保持在固定頻率Fsc,ccm。 Referring to FIG. 5, FIG. 5 is a schematic diagram of comparison between the operating frequency Fsc of the switch 14 and the output load. As shown in FIG. 5, when the flyback converter 10 operates in a discontinuous conduction mode (DCM), the operating frequency Fsc of the switch 14 is positively correlated with the output load. In other words, when a heavier output load is coupled to the output terminal, a higher operating frequency Fsc is required to drive the output load. Those with ordinary knowledge in the art should understand that the higher the operating frequency Fsc of the switch 14 is, the larger the output current generated will be, and a larger output load can be driven. In this embodiment, the minimum frequency at which the flyback converter 10 can work in DCM is marked as Fsc, dcm, and the maximum frequency at which the flyback converter 10 can work in DCM is marked as Fsc, ccm. When the frequency Fsc, ccm is reached, the flyback converter 10 enters the continuous conduction mode (CCM), and the operating frequency Fsc will remain at the fixed frequency Fsc, ccm in the CCM.

在本申請中，開關控制電路15採用的是恆定導通時間(COT)結構來控制開關14。然而，此並非本發明的限制。在其它實施例中，開關控制電路15可以採用不同的電路結構來控制開關14。圖2是依據本申請一實施例之開關控制電路15的示意圖。在本實施例中，開關控制電路15包括但不限於二次側控制電路151、COT產生電路152、隔離傳輸裝置153和一次側接收電路154。 In this application, the switch control circuit 15 adopts a constant on-time (COT) structure to control the switch 14. However, this is not a limitation of the present invention. In other embodiments, the switch control circuit 15 may adopt a different circuit structure to control the switch 14. FIG. 2 is a schematic diagram of the switch control circuit 15 according to an embodiment of the present application. In this embodiment, the switch control circuit 15 includes but is not limited to a secondary side control circuit 151, a COT generating circuit 152, an isolated transmission device 153, and a primary side receiving circuit 154.

二次側控制電路151用於接收反饋訊號Vfeed，反饋訊號 Vfeed用於指示包含輸出端Vout1的輸出功率、輸出電壓或輸出電流的資訊。COT產生電路152用於根據反饋訊號Vfeed產生用於指示開關14的導通時間和斷開時間的時脈訊號Vcot。 The secondary side control circuit 151 is used to receive the feedback signal Vfeed, the feedback signal Vfeed is used to indicate the information including the output power, output voltage or output current of the output terminal Vout1. The COT generating circuit 152 is used for generating a clock signal Vcot for indicating the on time and off time of the switch 14 according to the feedback signal Vfeed.

隔離傳輸裝置153用於將時脈訊號Vcot從變壓器11的二次側傳輸到變壓器11的一次側。本技術領域具有通常知識者應當理解，經隔離傳輸裝置153傳輸後的時脈訊號Vcot，其訊號強度可能不同。然而，時脈訊號Vcot中包含的資訊將會被完全傳輸。舉例來說，開關14的導通時間和斷開時間的指示將會被完全轉移。在本實施例中，隔離傳輸裝置153包括但不限於變壓器、光耦合器或電容器。 The isolation transmission device 153 is used to transmit the clock signal Vcot from the secondary side of the transformer 11 to the primary side of the transformer 11. Those skilled in the art should understand that the signal strength of the clock signal Vcot transmitted by the isolated transmission device 153 may be different. However, the information contained in the clock signal Vcot will be completely transmitted. For example, the indication of the on-time and off-time of the switch 14 will be completely transferred. In this embodiment, the isolation transmission device 153 includes, but is not limited to, a transformer, an optocoupler, or a capacitor.

一次側接收電路154用於從隔離傳輸裝置153接收時脈訊號Vcot，並將其輸出為開關控制訊號Vsc，以實現對開關14的導通時間和斷開時間的控制。具體地，一次側接收電路154用於從隔離傳輸裝置153識別和解耦傳輸訊號中包括的資訊。例如，一次側接收電路154根據傳輸訊號的上升沿和下降沿來分別識別開關14的導通時間和斷開時間。 The primary-side receiving circuit 154 is used to receive the clock signal Vcot from the isolation transmission device 153 and output it as the switch control signal Vsc to control the on time and off time of the switch 14. Specifically, the primary side receiving circuit 154 is used to identify and decouple the information included in the transmission signal from the isolation transmission device 153. For example, the primary-side receiving circuit 154 respectively recognizes the on time and off time of the switch 14 according to the rising edge and the falling edge of the transmission signal.

本技術領域具有通常知識者應能輕易理解，時脈訊號Vcot和開關控制訊號Vsc之間的相位差可以忽略。在某些實施例中，時脈訊號Vcot和開關控制訊號Vsc可以被視為相同的訊號，並且時脈訊號Vcot的頻率Fcot與開關控制訊號Vsc的頻率Fsc相同。在某些實施例中，時脈訊號Vcot的頻率和相位與開關控制訊號Vsc的頻率和相位相同。 Those skilled in the art should easily understand that the phase difference between the clock signal Vcot and the switch control signal Vsc can be ignored. In some embodiments, the clock signal Vcot and the switch control signal Vsc can be regarded as the same signal, and the frequency Fcot of the clock signal Vcot is the same as the frequency Fsc of the switch control signal Vsc. In some embodiments, the frequency and phase of the clock signal Vcot are the same as the frequency and phase of the switch control signal Vsc.

再次參考圖1，返馳式轉換器10還包括感應阻抗Rs和控制電路16。感應阻抗Rs耦接在輸出端Vout2和變壓器11之間。然而，此並非本申請的限制。在其它實施例中，感應阻抗Rs可以設置在不同的位置。舉例來說，感應阻抗Rs可以耦接在二次側和二極體12之間。只要感應阻抗 Rs、變壓器11的二次側和二極體12串聯在輸出端Vout1和Vout2之間，皆應隸屬於本申請的範疇。 Referring again to FIG. 1, the flyback converter 10 also includes an inductive impedance Rs and a control circuit 16. The inductive impedance Rs is coupled between the output terminal Vout2 and the transformer 11. However, this is not a limitation of this application. In other embodiments, the inductive impedance Rs can be set at different positions. For example, the inductive impedance Rs can be coupled between the secondary side and the diode 12. As long as the inductive impedance Rs, the secondary side of the transformer 11, and the diode 12 are connected in series between the output terminals Vout1 and Vout2, and should all belong to the scope of this application.

當輸出負載耦接在輸出端Vout1和Vout2之間時，流經感應阻抗Rs的輸出電流在感應阻抗Rs上產生檢測電壓Vs。控制電路16用於檢測感應阻抗Rs是否有被旁路，並且進一步用於當感應阻抗Rs被旁路時調整開關14的工作頻率Fsc。在本實施例中，感應阻抗Rs可由電阻、電容或電感實現，此並非本申請的限制。關於控制電路16的細節將在後續段落中描述。 When the output load is coupled between the output terminals Vout1 and Vout2, the output current flowing through the inductive impedance Rs generates a detection voltage Vs on the inductive impedance Rs. The control circuit 16 is used to detect whether the inductive impedance Rs is bypassed, and is further used to adjust the operating frequency Fsc of the switch 14 when the inductive impedance Rs is bypassed. In this embodiment, the inductive impedance Rs can be realized by a resistor, a capacitor, or an inductance, which is not a limitation of the present application. The details of the control circuit 16 will be described in subsequent paragraphs.

圖3是依據本申請一實施例之控制電路16的示意圖。如圖3所示，控制電路16包括檢測電路161和頻率控制電路162。檢測電路161從感應阻抗Rs接收檢測電壓Vs，並從開關控制電路15接收時脈訊號Vcot。檢測電路161用於依據時脈訊號Vcot的頻率Fcot和檢測電壓Vs來產生控制訊號CTRL。需注意的是，在其他實施例中，控制電路16還包括放大器或低通濾波器，以用於將檢測電壓Vs放大預定增益倍數。在某些實施例中，檢測電壓Vs大約為幾毫伏特(mV)，而經放大後的檢測電壓Vs大約為數百毫伏特。 FIG. 3 is a schematic diagram of the control circuit 16 according to an embodiment of the present application. As shown in FIG. 3, the control circuit 16 includes a detection circuit 161 and a frequency control circuit 162. The detection circuit 161 receives the detection voltage Vs from the inductive impedance Rs, and receives the clock signal Vcot from the switch control circuit 15. The detection circuit 161 is used to generate the control signal CTRL according to the frequency Fcot of the clock signal Vcot and the detection voltage Vs. It should be noted that in other embodiments, the control circuit 16 further includes an amplifier or a low-pass filter for amplifying the detection voltage Vs by a predetermined gain multiple. In some embodiments, the detection voltage Vs is approximately several millivolts (mV), and the amplified detection voltage Vs is approximately several hundred millivolts.

參考圖4，圖4是依據本申請一實施例之檢測電路161的示意圖。檢測電路161包括電壓檢測電路41、頻率檢測電路42和邏輯電路43。電壓檢測電路41用於通過比較檢測電壓Vs與參考電壓Vref來產生第一指示訊號SI1。頻率檢測電路42用於通過比較頻率Fcot與參考頻率Fref來產生第二指示訊號SI2。邏輯電路43用於根據第一指示訊號SI1和第二指示訊號SI2產生控制訊號CTRL。 Referring to FIG. 4, FIG. 4 is a schematic diagram of a detection circuit 161 according to an embodiment of the present application. The detection circuit 161 includes a voltage detection circuit 41, a frequency detection circuit 42 and a logic circuit 43. The voltage detection circuit 41 is used to generate the first indication signal SI1 by comparing the detection voltage Vs with the reference voltage Vref. The frequency detection circuit 42 is used to generate the second indicator signal SI2 by comparing the frequency Fcot with the reference frequency Fref. The logic circuit 43 is used for generating the control signal CTRL according to the first instruction signal SI1 and the second instruction signal SI2.

在本實施例中，參考電壓Vref與檢測電壓Vs具有相同的數量級。舉例來說，若檢測電壓Vs為幾mV，則參考電壓Vref也為幾mV。舉例來說，如果檢測電壓Vs被放大器放大後具有數百mV，則參考電壓Vref也具有數百mV。在如此設置下，當第一指示訊號SI1指示檢測電壓Vs小於參考電壓Vref時，感應阻抗Rs可能已被旁路。 In this embodiment, the reference voltage Vref and the detection voltage Vs have the same number Magnitude. For example, if the detection voltage Vs is several mV, the reference voltage Vref is also several mV. For example, if the detection voltage Vs has hundreds of mV after being amplified by the amplifier, the reference voltage Vref also has hundreds of mV. With this setting, when the first indication signal SI1 indicates that the detection voltage Vs is less than the reference voltage Vref, the inductive impedance Rs may have been bypassed.

然而，如上所述，當返馳式轉換器10以低工作頻率工作時，例如以頻率Fsc,dcm工作時，變壓器11產生的輸出電流很小，因此，輸出電流產生的檢測電壓Vs可能仍小於參考電壓Vref。因此，頻率檢測電路42可提供另一種判斷機制。 However, as described above, when the flyback converter 10 operates at a low operating frequency, for example, when operating at the frequency Fsc, dcm, the output current generated by the transformer 11 is very small. Therefore, the detection voltage Vs generated by the output current may still be less than Reference voltage Vref. Therefore, the frequency detection circuit 42 can provide another judgment mechanism.

頻率檢測電路42將等同於開關14的當前工作頻率Fsc的頻率Fcot與作為上述低工作頻率的參考頻率Fref進行比較，以產生第二指示訊號SI2，其中參考頻率Fref可依據實際經驗設計得到。 The frequency detection circuit 42 compares the frequency Fcot equivalent to the current operating frequency Fsc of the switch 14 with the reference frequency Fref as the aforementioned low operating frequency to generate the second indicator signal SI2, where the reference frequency Fref can be designed based on actual experience.

如此一來，當第一指示訊號SI1指示檢測電壓Vs小於參考電壓Vref且第二指示訊號SI2指示頻率Fcot大於參考頻率Fref時，控制訊號CTRL指示感應阻抗Rs已被旁路。 In this way, when the first indicator signal SI1 indicates that the detection voltage Vs is less than the reference voltage Vref and the second indicator signal SI2 indicates that the frequency Fcot is greater than the reference frequency Fref, the control signal CTRL indicates that the inductive impedance Rs has been bypassed.

在某些實施例中，電壓檢測電路41包括一比較電路以比較檢測電壓Vs與參考電壓Vref。在某些實施例中，頻率檢測電路42包括比較電路以比較頻率Fcot與參考頻率Fref。在某些實施例中，邏輯電路43包括及閘，該及閘接收第一指示訊號SI1和第二指示訊號SI2以產生控制訊號CTRL。需注意的是，本申請並不限制電壓檢測電路41、頻率檢測電路42和邏輯電路43的實現方式。 In some embodiments, the voltage detection circuit 41 includes a comparison circuit to compare the detection voltage Vs with the reference voltage Vref. In some embodiments, the frequency detection circuit 42 includes a comparison circuit to compare the frequency Fcot with the reference frequency Fref. In some embodiments, the logic circuit 43 includes an AND gate which receives the first indicator signal SI1 and the second indicator signal SI2 to generate the control signal CTRL. It should be noted that this application does not limit the implementation of the voltage detection circuit 41, the frequency detection circuit 42 and the logic circuit 43.

此外，本申請也不限制參考電壓Vref和參考頻率Fref的實現方式。在某些實施例中，參考電壓Vref可通過電阻分壓而產生。在某些實施例中，參考電壓Vref由帶差參考電路(bandgap reference circuit)所產生。在某些實施例中，參考頻率Fref由鎖相迴路(PLL)電路產生。 In addition, this application does not limit the implementation of the reference voltage Vref and the reference frequency Fref. In some embodiments, the reference voltage Vref can be generated by resistor divider. In some embodiments, the reference voltage Vref is generated by a bandgap reference circuit (bandgap reference circuit). pregnancy. In some embodiments, the reference frequency Fref is generated by a phase locked loop (PLL) circuit.

再次參考圖3，頻率控制電路162用於當控制訊號CTRL指示感應阻抗Rs被旁路時，調整等同於開關14的當前工作頻率Fsc的頻率Fcot。具體地說，頻率控制電路162通過將時脈訊號Vcot的頻率Fcot降低至調整頻率Fad以調節時脈訊號Vcot，並藉此產生調整訊號Vad。當開關控制電路15接收到具有調整頻率Fad的調整訊號Vad時，開關控制電路15輸出調整訊號Vad作為開關控制訊號Vsc。據此，開關14的導通時間和斷開時間將由具有調整頻率Fad的調整訊號Vad控制。 3 again, the frequency control circuit 162 is used to adjust the frequency Fcot equal to the current operating frequency Fsc of the switch 14 when the control signal CTRL indicates that the inductive impedance Rs is bypassed. Specifically, the frequency control circuit 162 adjusts the clock signal Vcot by reducing the frequency Fcot of the clock signal Vcot to the adjustment frequency Fad, and thereby generates the adjustment signal Vad. When the switch control circuit 15 receives the adjustment signal Vad with the adjustment frequency Fad, the switch control circuit 15 outputs the adjustment signal Vad as the switch control signal Vsc. Accordingly, the on-time and off-time of the switch 14 will be controlled by the adjustment signal Vad with the adjustment frequency Fad.

由於調整頻率Fad小於當前工作頻率Fsc(或Fcot)，因此變壓器11的二次側產生的輸出電流將受到限制。據此，將可降低返馳式轉換器10損壞的風險。 Since the adjustment frequency Fad is less than the current operating frequency Fsc (or Fcot), the output current generated by the secondary side of the transformer 11 will be limited. Accordingly, the risk of damage to the flyback converter 10 can be reduced.

在某些實施例中，通過將開關14的最大工作頻率Fsc,max除以預定值M來獲得調整頻率Fad。換言之，Fad=Fsc,max/M，其中M是自然數。自然數M可經過挑選使得Fad<Fsc,ccm。需注意的是，頻率控制電路162的實現方式並非本申請的限制。在某些實施例中，頻率控制電路162包括除頻電路，該除頻電路用於將最大工作頻率Fsc,max除以預定值M以獲得調整頻率Fad。在某些實施例中，頻率控制電路162包括PLL電路。當控制訊號CTRL指示感應阻抗Rs被旁路時，該PLL電路可以產生具有調整頻率Fad的調整訊號Vad。 In some embodiments, the adjustment frequency Fad is obtained by dividing the maximum operating frequency Fsc,max of the switch 14 by a predetermined value M. In other words, Fad=Fsc,max/M, where M is a natural number. The natural number M can be selected such that Fad<Fsc,ccm. It should be noted that the implementation of the frequency control circuit 162 is not a limitation of the present application. In some embodiments, the frequency control circuit 162 includes a frequency divider circuit for dividing the maximum operating frequency Fsc,max by a predetermined value M to obtain the adjusted frequency Fad. In some embodiments, the frequency control circuit 162 includes a PLL circuit. When the control signal CTRL indicates that the inductive impedance Rs is bypassed, the PLL circuit can generate an adjustment signal Vad with an adjustment frequency Fad.

簡單歸納如下，在本申請所提出的返馳式轉換器中，當耦接到輸出端的電阻或電容被旁路時，通過降低工作頻率來限制輸出電流的大小。如此一來，可提升返馳式轉換器的安全性。 A brief summary is as follows. In the flyback converter proposed in this application, when the resistor or capacitor coupled to the output terminal is bypassed, the output current is limited by reducing the operating frequency. In this way, the safety of the flyback converter can be improved.

在某些安全性測試，例如，致力於測試電源供應器的安全性的IEC-60950或IEC-62368，都具有嚴苛的要求。舉例來說，測試包括了在最大負載下確認電源供應器狀態；增加電源供應器的負載直到達到超載邊緣；將限流電阻短路以模擬內部錯誤；以及將提供反饋至控制迴路的光耦合器旁路。以另一例子而言，測試包括了要求電源供應器的輸出電流不得超過8A或電源供應器的輸出功率不得超過100W。 In certain safety tests, for example, dedicated to testing the safety of power supplies IEC-60950 or IEC-62368, both have stringent requirements. For example, the test includes confirming the status of the power supply under the maximum load; increasing the load of the power supply until it reaches the edge of overload; short-circuiting the current-limiting resistor to simulate internal errors; and providing feedback to the optocoupler in the control loop road. For another example, the test includes requiring the output current of the power supply not to exceed 8A or the output power of the power supply not to exceed 100W.

然而，本申請所提出的返馳式轉換器在檢測到感應阻抗被旁路時，通過將工作頻率降低即可以滿足這些測試的要求。 However, when the flyback converter proposed in this application detects that the inductive impedance is bypassed, the operating frequency can be reduced to meet the requirements of these tests.

圖6是依據本申請一實施例之返馳式轉換器的控制方法600的流程圖。倘若大致上可以得到相同的結果，本申請並不限定完全依照圖6所示的步驟流程來執行。控制方法600大致歸納如下。 FIG. 6 is a flowchart of a control method 600 of a flyback converter according to an embodiment of the present application. Provided that substantially the same result can be obtained, this application does not limit the execution according to the step flow shown in FIG. 6 completely. The control method 600 is roughly summarized as follows.

步驟601：判斷一感應阻抗的兩端的一跨壓是否小於一參考電壓，若是，則進入步驟602；否則，進入步驟601。 Step 601: Determine whether a cross voltage across an inductive impedance is less than a reference voltage, if yes, go to step 602; otherwise, go to step 601.

步驟602：判斷一開關的一工作頻率是否大於一參考頻率，若是，則進入步驟603；否則，進入步驟601。 Step 602: Determine whether a working frequency of a switch is greater than a reference frequency, if yes, go to step 603; otherwise, go to step 601.

步驟603：調整該工作頻率以限制該返馳式轉換器的一輸出電流。 Step 603: Adjust the operating frequency to limit an output current of the flyback converter.

本技術領域具有通常知識者在閱讀完上述實施例後應能輕易理解控制方法600的詳細操作。詳細說明在此省略以省篇幅。 Those skilled in the art should be able to easily understand the detailed operation of the control method 600 after reading the above-mentioned embodiments. The detailed description is omitted here to save space.

在上述實施例中，較小的檢測電壓Vs在感應阻抗Rs被旁路時會傳送訊號至控制電路16以警示輸出負載阻抗降低且輸出電流將增加，藉此有效地避免返馳式轉換器的損壞以及預防發生火災。然而，此並非本申請的限制。在其它實施例中，可以在感應阻抗Rs被斷路時傳送訊號至控制電路16以警示將輸出負載及輸出電流的變化。 In the above embodiment, the smaller detection voltage Vs sends a signal to the control circuit 16 when the inductive impedance Rs is bypassed to warn that the output load impedance will decrease and the output current will increase, thereby effectively avoiding the flyback converter. Damage and prevention of fire. However, this is not a limitation of this application. In other embodiments, a signal can be sent to the control circuit 16 when the inductive impedance Rs is disconnected to warn the output load and the change of the output current.

前述內容概括數項實施例之特徵，使得熟習此項技術者可更佳地理解本揭露之態樣。熟習此項技術者應瞭解，其等可容易地使用本揭露作為用於設計或修改用於實行本文中介紹之實施例之相同目的及/或達成相同優點之其他製程及結構之一基礎。熟習此項技術者亦應瞭解，此等等效構造不背離本揭露之精神及範疇，且其等可在不背離本揭露之精神及範疇之情況下在本文中作出各種改變、置換及更改。 The foregoing content summarizes the features of several embodiments, so that those familiar with the art can better understand the aspect of the disclosure. Those familiar with the technology should understand that they can easily use the present disclosure as a basis for designing or modifying other processes and structures for implementing the same purpose and/or achieving the same advantages of the embodiments described herein. Those familiar with this technology should also understand that these equivalent structures do not depart from the spirit and scope of this disclosure, and they can make various changes, substitutions and alterations in this article without departing from the spirit and scope of this disclosure.

10:返馳式轉換器 10: Flyback converter

11:變壓器 11: Transformer

12:二極體 12: Diode

13:電容 13: Capacitance

14:開關 14: switch

15:開關控制電路 15: Switch control circuit

16:控制電路 16: control circuit

Fad:調整頻率 Fad: adjust frequency

Fcot:頻率 Fcot: frequency

Fsc:工作頻率 Fsc: working frequency

Rs:感應阻抗 Rs: Inductive impedance

Vad:調整訊號 Vad: adjust the signal

Vcot:時脈訊號 Vcot: Clock signal

Vin:輸入電壓源 Vin: input voltage source

Vout1,Vout2:輸出端 Vout1, Vout2: output terminal

Vs:檢測電壓 Vs: detection voltage

Vsc:開關控制訊號 Vsc: switch control signal

Claims

一種返馳式(flyback)轉換器，包括：一變壓器，包括一一次側及一二次側；一感應阻抗，耦接於該變壓器的該二次側及該返馳式轉換器的一輸出端之間；一開關，耦接至該變壓器的該一次側，其中該開關控制流經該變壓器的該一次側的一電流；一開關控制電路，耦接至該開關，其中該開關控制電路用於提供指示該開關的一工作頻率的一脈衝信號；以及一控制電路，耦接於該感應阻抗以及該開關控制電路之間，其中該控制電路用於判斷該感應阻抗是否被旁路，並另用於當該感應阻抗被旁路時通過參考來自該開關控制電路的該脈衝信號來調整該開關的一工作頻率。 A flyback converter includes: a transformer including a primary side and a secondary side; an inductive impedance coupled to the secondary side of the transformer and an output of the flyback converter A switch, coupled to the primary side of the transformer, wherein the switch controls a current flowing through the primary side of the transformer; a switch control circuit, coupled to the switch, wherein the switch control circuit is used To provide a pulse signal indicating an operating frequency of the switch; and a control circuit, coupled between the inductive impedance and the switch control circuit, wherein the control circuit is used to determine whether the inductive impedance is bypassed, and another It is used to adjust an operating frequency of the switch by referring to the pulse signal from the switch control circuit when the inductive impedance is bypassed.

如請求項1所述的返馳式轉換器，其中該控制電路另包括：一檢測電路，用於根據一檢測電壓和該工作頻率產生一控制訊號，其中該檢測電壓橫跨該感應阻抗的兩端；以及一頻率控制電路，用於當該控制信號指示該感應阻抗被旁路時調整該開關的該工作頻率。 The flyback converter according to claim 1, wherein the control circuit further comprises: a detection circuit for generating a control signal according to a detection voltage and the operating frequency, wherein the detection voltage is across two parts of the inductive impedance And a frequency control circuit for adjusting the operating frequency of the switch when the control signal indicates that the inductive impedance is bypassed.

一種返馳式(flyback)轉換器，包括：一變壓器，包括一一次側及一二次側；一感應阻抗，耦接於該變壓器的該二次側及該返馳式轉換器的一輸出端之間；一開關，耦接至該變壓器的該一次側，其中該開關控制流經該變壓器的該一次側的一電流；以及一控制電路，用於判斷該感應阻抗是否被旁路，並另用於當該感應阻抗被旁路時調整該開關的一工作頻率；其中該控制電路另包括：一檢測電路，用於根據一檢測電壓和該工作頻率產生一控制訊號，其中該檢測電壓橫跨該感應阻抗的兩端；以及一頻率控制電路，用於當該控制信號指示該感應阻抗被旁路時調整該開關的該工作頻率；其中該檢測電路包括：一電壓檢測電路，用於通過比較該檢測電壓與一參考電壓以產生一第一指示訊號；一頻率檢測電路，用於通過比較該工作頻率與一參考頻率以產生一第二指示訊號；以及一邏輯電路，用於根據該第一指示訊號與該第二指示訊號以產生該控制訊號；其中當該第一指示訊號指示該檢測電壓小於該參考電壓且該第二指示訊號指示該工作頻率大於該參考頻率時，該控制訊號指示該感應阻抗已被旁路。 A flyback converter includes: a transformer including a primary side and a secondary side; An inductive impedance is coupled between the secondary side of the transformer and an output terminal of the flyback converter; a switch is coupled to the primary side of the transformer, wherein the switch controls the flow through the transformer A current on the primary side; and a control circuit for judging whether the inductive impedance is bypassed, and for adjusting an operating frequency of the switch when the inductive impedance is bypassed; wherein the control circuit further includes: A detection circuit for generating a control signal based on a detection voltage and the operating frequency, wherein the detection voltage spans both ends of the inductive impedance; and a frequency control circuit for when the control signal indicates that the inductive impedance is bypassed The operating frequency of the switch is adjusted during the circuit; wherein the detection circuit includes: a voltage detection circuit for generating a first indication signal by comparing the detection voltage with a reference voltage; a frequency detection circuit for comparing the Operating frequency and a reference frequency to generate a second indicator signal; and a logic circuit for generating the control signal according to the first indicator signal and the second indicator signal; wherein when the first indicator signal indicates the detection voltage When the voltage is less than the reference voltage and the second indicator signal indicates that the operating frequency is greater than the reference frequency, the control signal indicates that the inductive impedance has been bypassed.

如請求項3所述的返馳式轉換器，其中該電壓檢測電路包括一比較電路，該比較電路用於比較該檢測電壓與該參考電壓以輸出該第一指示訊號。 The flyback converter according to claim 3, wherein the voltage detection circuit includes a comparison circuit The comparison circuit is used to compare the detection voltage with the reference voltage to output the first indication signal.

如請求項3所述的返馳式轉換器，其中該頻率檢測電路包括一比較電路，該比較電路用於比較該工作頻率與該參考頻率以輸出該第二指示訊號。 The flyback converter according to claim 3, wherein the frequency detection circuit includes a comparison circuit for comparing the operating frequency with the reference frequency to output the second indication signal.

如請求項3所述的返馳式轉換器，其中該邏輯電路包括一及閘，該及閘接收該第一指示訊號與該第二指示訊號，並輸出該控制訊號。 The flyback converter according to claim 3, wherein the logic circuit includes a and gate, and the gate receives the first instruction signal and the second instruction signal, and outputs the control signal.

如請求項3所述的返馳式轉換器，其中該頻率控制電路包括一除頻電路。 The flyback converter according to claim 3, wherein the frequency control circuit includes a frequency divider circuit.

一種返馳式轉換器的控制電路，其中該控制電路用於檢測橫跨一感應阻抗的一檢測電壓，該感應阻抗耦接於該返馳式轉換器的一變壓器以及該返馳式轉換器的一輸出端之間，且該控制電路另用於通過參考來自耦接於該開關以及該控制電路之間的一開關控制電路的一脈衝信號和該檢測電壓調整該返馳式轉換器的一開關的一工作頻率。 A control circuit of a flyback converter, wherein the control circuit is used to detect a detection voltage across an inductive impedance, the inductive impedance is coupled to a transformer of the flyback converter and the flyback converter Between an output terminal, and the control circuit is further used to adjust a switch of the flyback converter by referring to a pulse signal from a switch control circuit coupled between the switch and the control circuit and the detection voltage A working frequency.

如請求項8所述的控制電路，還包括：一檢測電路，用於依據該檢測電壓與該工作頻率產生一控制訊號；以及一頻率控制電路，用於當該控制訊號指示該感應阻抗被旁路時調整該工作頻率。 The control circuit according to claim 8, further comprising: a detection circuit for generating a control signal based on the detection voltage and the operating frequency; and a frequency control circuit for when the control signal indicates that the inductive impedance is bypassed Adjust the operating frequency when connecting.

一種返馳式轉換器的控制電路，其中該控制電路用於檢測橫跨一感應阻抗的一檢測電壓，該感應阻抗耦接於該返馳式轉換器的一變壓器以及該返馳式轉換器的一輸出端之間，且該控制電路另用於至少依據該檢測電壓調整該返馳式轉換器的一開關的一工作頻率；該控制電路包括：一檢測電路，用於依據該檢測電壓與該工作頻率產生一控制訊號；以及一頻率控制電路，用於當該控制訊號指示該感應阻抗被旁路時調整該工作頻率；其中該檢測電路包括：一電壓檢測電路，用於通過比較該檢測電壓與一參考電壓以產生一第一指示訊號；一頻率檢測電路，用於通過比較該工作頻率與一參考頻率以產生一第二指示訊號；以及一邏輯電路，用於根據該第一指示訊號與該第二指示訊號以產生該控制訊號；其中當該第一指示訊號指示該檢測電壓小於該參考電壓且該第二指示訊號指示該工作頻率大於該參考頻率時，該控制訊號指示該感應阻抗已被旁路。 A control circuit of a flyback converter, wherein the control circuit is used to detect a detection voltage across an inductive impedance, the inductive impedance is coupled to a transformer of the flyback converter and the flyback converter Between an output terminal, and the control circuit is further used to adjust an operating frequency of a switch of the flyback converter at least according to the detection voltage; the control circuit includes: a detection circuit for adjusting the detection voltage and the The operating frequency generates a control signal; and a frequency control circuit for adjusting the operating frequency when the control signal indicates that the inductive impedance is bypassed; wherein the detection circuit includes: a voltage detection circuit for comparing the detection voltage And a reference voltage to generate a first indicator signal; a frequency detection circuit for generating a second indicator signal by comparing the operating frequency with a reference frequency; and a logic circuit for generating a second indicator signal based on the first indicator signal and The second indicator signal to generate the control signal; wherein when the first indicator signal indicates that the detection voltage is less than the reference voltage and the second indicator signal indicates that the operating frequency is greater than the reference frequency, the control signal indicates that the inductive impedance has Bypassed.

如請求項10所述的控制電路，其中該電壓檢測電路包括一比較電路，該比較電路用於比較該檢測電壓與該參考電壓以輸出該第一指示訊號。 The control circuit according to claim 10, wherein the voltage detection circuit includes a comparison circuit for comparing the detection voltage with the reference voltage to output the first indication signal.

如請求項10所述的控制電路，其中該頻率檢測電路包括一比較電路，該比較電路用於比較該工作頻率與該參考頻率以輸出該第二指示訊號。 The control circuit according to claim 10, wherein the frequency detection circuit includes a comparison circuit for comparing the operating frequency with the reference frequency to output the second indication signal.

如請求項10所述的控制電路，其中該邏輯電路包括一及閘，該及閘接收該第一指示訊號與該第二指示訊號，並輸出該控制訊號。 The control circuit according to claim 10, wherein the logic circuit includes a and gate, and the gate receives the first instruction signal and the second instruction signal, and outputs the control signal.

如請求項11所述的控制電路，其中該頻率控制電路包括一除頻電路。 The control circuit according to claim 11, wherein the frequency control circuit includes a frequency divider circuit.

一種返馳式轉換器的控制方法，其中該返馳式轉換器包括一變壓器以及一開關，該控制方法包括：判斷一感應阻抗的兩端的一跨壓是否小於一參考電壓，其中該感應阻抗耦接於該變壓器與該返馳式轉換器的一輸出端；當該感應阻抗的兩端的該跨壓小於該參考電壓時判斷該開關的一工作頻率是否大於一參考頻率；以及當該開關的該工作頻率大於該參考頻率時調整該工作頻率以限制該返馳式轉換器的一輸出電流。 A control method of a flyback converter, wherein the flyback converter includes a transformer and a switch, the control method includes: determining whether a cross voltage across an inductive impedance is less than a reference voltage, wherein the inductive impedance coupler Connected to the transformer and an output terminal of the flyback converter; when the cross voltage across the inductive impedance is less than the reference voltage, it is determined whether an operating frequency of the switch is greater than a reference frequency; and when the switch is When the operating frequency is greater than the reference frequency, the operating frequency is adjusted to limit an output current of the flyback converter.