Flyback circuit

Abstract

The technical solution of the present application provides a flyback circuit, comprising: a primary-side control circuit for controlling voltage output and a secondary-side output circuit for outputting voltage, which share a transformer, wherein the primary-side control circuit comprises: a switch tube, a sampling resistor, and a control circuit, wherein the control circuit is configured to receive the sampled voltage and the voltage signal fed back by the secondary-side output circuit, and convert the voltage signal fed back by the secondary-side output circuit into a reference voltage, and then convert the reference voltage into a threshold voltage, and control the conduction or cutoff of the switch tube according to the threshold voltage; wherein the threshold voltage is converted according to the following relationship: V t =V FB / (k2‑k1×V FB ), where V t is the threshold voltage; V FB is the reference voltage; k1 is the first preset coefficient; k2 is the second preset coefficient. The flyback circuit of the technical solution of the present application can reduce conduction loss.

Description

Technical Field

[0001] The present application relates to the field of electrical engineering, and in particular to a flyback circuit. Background Art

[0002] Flyback circuits are widely used in electronic devices, such as chargers, due to their simple structure, ability to implement multiple power outputs, and isolation between AC and DC power. Typically, a low-voltage, high-current approach is used to increase charger power, but this method exponentially increases conduction losses.

[0003] Methods to reduce conduction loss usually include reducing current and reducing resistance. The way to reduce resistance is to start from the device itself, such as reducing the device's on-resistance (R ds ), but R ds It will not decrease indefinitely, and will also increase the die size, which will increase the cost. Therefore, we can also find a solution by reducing the current. Summary of the Invention

[0004] The technical problem to be solved by the present application is to provide a flyback circuit that can reduce conduction loss.

[0005] To solve the above technical problems, the present application provides a flyback circuit, comprising: a primary-side control circuit for controlling voltage output and a secondary-side output circuit for outputting voltage, which share a transformer, wherein the primary-side control circuit comprises: a switch tube, comprising an input end and an output end, wherein the input end is connected to the transformer; a sampling resistor, comprising a first end, wherein the first end of the sampling resistor is connected to the output end and generates a sampling voltage; a control circuit, configured to receive the sampling voltage and a voltage signal fed back by the secondary-side output circuit, and convert the voltage signal fed back by the secondary-side output circuit into a reference voltage, and then convert the reference voltage into a threshold voltage, and control the conduction or cutoff of the switch tube according to the threshold voltage; wherein the threshold voltage is converted according to the following relationship: V t =V FB / (k2-k1×V FB ), where V t is the threshold voltage; V FB is the reference voltage; k1 is the first preset coefficient; k2 is the second preset coefficient.

[0006] In the embodiment of the present application, the first preset coefficient is 0.6-1.2, the second preset coefficient is 5-6.5, and the reference voltage does not exceed 2.5V.

[0007] In the embodiment of the present application, k2 is 6, and V out，max The magnitude should not exceed 2.5V.

[0008] In an embodiment of the present application, the control circuit includes: a sampling monitoring end, connected to the first end of the sampling resistor, configured to receive the sampling voltage; a voltage control end, configured to receive the voltage signal fed back by the secondary output circuit; a signal conversion module, connected to the voltage control end, configured to convert the voltage signal fed back by the secondary output circuit into a reference voltage; a voltage conversion module, connected to the signal conversion module, configured to convert the reference voltage into a threshold voltage; a comparison module, connected to the voltage conversion module and the sampling monitoring end, configured to compare the threshold voltage and the sampling voltage and output a comparison result; and a control module, configured to receive the comparison result and control the on or off of the switch tube based on the comparison result.

[0009] In an embodiment of the present application, the signal conversion module includes: a reference voltage and a pull-up resistor, a first end of the pull-up resistor is connected to the reference voltage, and a second end of the pull-up resistor is connected to the voltage conversion module.

[0010] In an embodiment of the present application, the voltage conversion module is a digital circuit, and the digital circuit includes: a storage module, which is used to store a data group including a reference voltage and a threshold voltage, and the reference voltage and the threshold voltage in each data group are in a preset corresponding relationship; a reading module, which is connected to the storage module and the signal conversion module, and is used to receive the reference voltage and read the corresponding threshold voltage in the data group; an output module, which is connected to the reading module, and is used to output the threshold voltage read by the reading module.

[0011] In an embodiment of the present application, the voltage conversion module is an analog circuit, and the analog circuit includes: an amplifier, including a first positive terminal, a first negative terminal and a first output terminal, wherein the first output terminal is connected to the comparison module; a first resistor, the first end of the first resistor is connected to the voltage control terminal, and the second end of the first resistor is connected to the first positive terminal; a variable resistor, the first end of the variable resistor is connected to the first positive terminal, and the second end of the variable resistor is grounded; a second resistor, the first end of the second resistor is connected to the first negative terminal, and the second end of the second resistor is grounded; a third resistor, the first end of the third resistor is connected to the first end of the second resistor, and the second end of the third resistor is connected to the comparison module.

[0012] In an embodiment of the present application, the method for controlling the on or off of the switch tube based on the comparison result includes: when it is determined that the size of the sampling voltage does not exceed the size of the threshold voltage, the control module controls the switch tube to be cut off, and the secondary output circuit outputs the voltage; or when it is determined that the size of the sampling voltage exceeds the size of the threshold voltage, the control module controls the switch tube to be turned on, and the secondary output circuit stops outputting the voltage.

[0013] In an embodiment of the present application, the switch tube further includes a control end, the control circuit further includes a driving end, and one end of the driving end is connected to the control module, and the other end is connected to the control end.

[0014] In an embodiment of the present application, the primary-side control circuit further includes a capacitor, a first end of the capacitor is connected to the voltage control end, and a second end of the capacitor is grounded.

[0015] In an embodiment of the present application, the comparison module includes a comparator, which includes a second positive terminal, a second negative terminal and a second output terminal, wherein the second positive terminal is connected to the sampling and monitoring terminal, the second negative terminal is connected to the voltage conversion module, and the second output terminal is connected to the control module.

[0016] In the embodiment of the present application, the sampling resistor further includes a second end, and the second end of the sampling resistor is grounded.

[0017] In an embodiment of the present application, the primary side control circuit further includes an optocoupler, the anode of the optocoupler is connected to the secondary side output circuit, the collector of the optocoupler is connected to the voltage control terminal, and the anode and emitter of the optocoupler are both grounded.

[0018] In the embodiment of the present application, the switch tube is a MOS tube.

[0019] Compared with the prior art, the flyback circuit of the technical solution of the present application has the following beneficial effects:

[0020] By converting the voltage signal fed back by the secondary output circuit into a reference voltage, and then converting the reference voltage into a threshold voltage, the threshold voltage and the reference voltage have a nonlinear relationship, and the relationship satisfies V t =V FB / (k2-k1×V FB ), where V t is the threshold voltage; V FB is the reference voltage, k1 is the first preset coefficient; k2 is the second preset coefficient, so that the flyback circuit can reduce the current peak of the switch tube while keeping the energy transferred unchanged, thereby reducing the conduction loss and improving the thermal stability of the switch tube. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] The following figures describe in detail exemplary embodiments disclosed in this application. Identical reference numerals denote similar structures in several views of the drawings. Those skilled in the art will appreciate that these embodiments are non-limiting, exemplary embodiments, and that the drawings are for illustration and description purposes only and are not intended to limit the scope of this application. Other embodiments may also achieve the same inventive intent as described in this application. It should be understood that the drawings are not drawn to scale. Among them:

[0022] Figure 1 A schematic structural diagram of a flyback circuit according to an embodiment of the present application;

[0023] Figure 2 Graphs showing a linear relationship and a nonlinear relationship between the threshold voltage and the reference voltage in an embodiment of the present application;

[0024] Figure 3 This is a schematic diagram of the structure of the control circuit of an embodiment of the present application;

[0025] Figure 4 Schematic diagram of the circuit structure when the voltage conversion module of an embodiment of the present application is an analog circuit. DETAILED DESCRIPTION

[0026] As shown in this application and the claims, unless the context clearly indicates an exception, the words "a", "an", "a kind of" and / or "the" do not specifically refer to the singular and may also include the plural. Generally speaking, the terms "include" and "comprise" only indicate the inclusion of clearly identified steps and elements, and these steps and elements do not constitute an exclusive list. The method or device may also include other steps or elements. When used in this specification, the terms "include", "comprise" and / or "contain" mean the presence of the associated integers, steps, operations, elements and / or components, but do not exclude the presence of one or more other features, integers, steps, operations, elements, components and / or groups or the addition of other features, integers, steps, operations, elements, components and / or groups in the system / method. When describing the association of different components in this specification, it can be a direct relationship or an indirect relationship. For example, "A and B are connected" can mean that A and B are directly connected, or A and B are indirectly connected through other components.

[0027] These and other features disclosed herein, as well as the operation and function of the associated elements of the structure, and the economical assembly and manufacture of the components, can be significantly improved with consideration of the following description. Reference is made to the accompanying drawings, all of which form a part of this disclosure. However, it should be clearly understood that the drawings are for illustration and description purposes only and are not intended to limit the scope of this disclosure.

[0028] The following description provides specific application scenarios and requirements of the present application, with the purpose of enabling those skilled in the art to make and use the content of this application. Various local modifications to the disclosed embodiments will be apparent to those skilled in the art, and the general principles defined herein may be applied to other embodiments and applications without departing from the spirit and scope of this application. Therefore, this application is not limited to the embodiments shown, but is intended to be of the widest scope consistent with the claims.

[0029] refer to Figure 1 The present invention provides a flyback circuit, also known as a flyback switching power supply circuit, which can be used in a charger. The flyback circuit includes a primary control circuit 10 and a secondary output circuit 20, wherein the primary control circuit 10 is used to control the voltage output, and the secondary output circuit 20 is used to output the voltage under the control of the primary control circuit 10. The primary control circuit 10 and the secondary output circuit 20 share a transformer TR, which includes a primary transformer winding NP and a secondary transformer winding NS.

[0030] The primary control circuit includes a switch Q1, a sampling resistor Rs, and a control circuit 11. The switch Q1 includes an input terminal, an output terminal, and a control terminal, and the input terminal is connected to the primary winding NP of the transformer. In some embodiments, the switch Q1 can be a MOS transistor, such as an NMOS transistor. The input terminal can be the drain terminal of the NMOS transistor, the output terminal can be the source terminal of the NMOS transistor, and the control terminal can be the gate terminal of the NMOS transistor. By controlling the conduction or cutoff of the switch Q1, the output voltage is controlled.

[0031] The first end of the sampling resistor Rs is connected to the output end of the switch Q1. When the flyback circuit is operating, the first end of the sampling resistor Rs generates a sampling voltage, which is input to the control circuit 11 to implement the sampling and monitoring function of the flyback circuit. The second end of the sampling resistor Rs is grounded.

[0032] The control circuit 11 is configured to receive the sampled voltage and the voltage signal fed back by the secondary output circuit 20, convert the voltage signal fed back by the secondary output circuit 20 into a reference voltage, then convert the reference voltage into a threshold voltage, and control the on or off of the switch tube Q1 according to the threshold voltage.

[0033] The threshold voltage is converted by the following relationship: V t =V FB / (k2-k1×V FB ), where V t is the threshold voltage; V FBis the reference voltage; k1 is the first preset coefficient; k2 is the second preset coefficient. The relationship between the threshold voltage and the reference voltage in the embodiment of the present application is nonlinear, and as the reference voltage increases, the threshold voltage increases accordingly, and the magnitude of the increase in the threshold voltage also increases accordingly. When the load is fully loaded, the threshold voltage is equal to the reference voltage. The first preset coefficient and the second preset coefficient can be set according to specific circumstances. As an example, the first preset coefficient is 0.6 to 1.2, the second preset coefficient is 5 to 6.5, and the reference voltage does not exceed 2.5V.

[0034] Figure 2 are curves when the threshold voltage and the reference voltage are in a linear relationship and a nonlinear relationship, respectively. As an example, the threshold voltage V t With the reference voltage V FB The linear relationship is V t =V FB / 4, the threshold voltage V t With the reference voltage V FB The relationship when it is nonlinear is V t =V FB / (k2-k1×V FB ), the threshold voltage V t Reflects the maximum value of the sampling voltage when the flyback circuit is working. Figure 3 It can be seen that when the threshold voltage and the reference voltage have a nonlinear relationship, the maximum value of the sampling voltage can be reduced while the transferred energy remains unchanged, that is, the current peak of the switch tube Q1 is reduced, thereby reducing the conduction loss and improving the thermal stability of the switch tube Q1.

[0035] In some embodiments, the control circuit 11 includes a sampling monitoring terminal CS, a voltage control terminal FB, a signal conversion module, a voltage conversion module, a comparison module, and a control module. The sampling monitoring terminal CS is connected to the first end of the sampling resistor Rs for receiving the sampled voltage. The voltage control terminal FB is configured to receive the voltage signal fed back by the secondary output circuit 20. In some embodiments, the primary control circuit 10 also includes an optocoupler U, the anode of which is connected to the secondary output circuit 20, the collector of which is connected to the voltage control terminal FB, and the anode and emitter of which are both grounded. When the actual output voltage signal received by the anode of the optocoupler U changes, the conduction degree of the optocoupler U changes accordingly, thereby changing the voltage signal received by the voltage control terminal FB. In other embodiments, the optocoupler U can also be replaced by a transistor, the base of which is connected to the secondary output circuit 20, the collector of which is connected to the voltage control terminal FB, and the emitter of which is grounded. When the actual output voltage signal received by the base of the transistor changes, the conduction level of the transistor changes accordingly, thereby changing the voltage signal received by the voltage control terminal FB. Compared to the transistor, the optocoupler U also has the function of isolating the primary winding NP of the transformer from the secondary winding NS of the transformer, thereby improving circuit safety.

[0036] refer to Figure 3 The signal conversion module 110 is connected to the voltage control terminal FB and is configured to convert the voltage signal fed back by the secondary output circuit 20 into a reference voltage. In some embodiments, the signal conversion module 110 includes a reference voltage V reg and the pull-up resistor R d , the reference voltage V reg The size of the pull-up resistor R can be equal to the power supply voltage of the control circuit 11, or can be determined according to actual conditions. d The first end is connected to the reference voltage V reg , the pull-up resistor R d The second end is connected to the voltage conversion module.

[0037] refer to Figure 3 The voltage conversion module is connected to the signal conversion module 110 and is configured to convert the reference voltage into a threshold voltage. The voltage conversion module can be implemented in a digital circuit or an analog circuit.

[0038] refer to Figure 4 The voltage conversion module is an analog circuit. As an example, the analog circuit may include an amplifier 120, a first resistor R1, a second resistor R2, a third resistor R3 and a variable resistor R aThe amplifier 120 includes a first positive terminal, a first negative terminal, and a first output terminal, wherein the first output terminal is connected to the comparison module. The first terminal of the first resistor R1 is connected to the voltage control terminal FB, and the second terminal of the first resistor R1 is connected to the first positive terminal of the amplifier 120. The variable resistor R a The first end of the variable resistor R a The second end of the second resistor R2 is connected to the first negative terminal of the amplifier 120, and the second end of the second resistor R2 is grounded. The first end of the third resistor R3 is connected to the first end of the second resistor R2, and the second end of the third resistor R3 is connected to the comparison module.

[0039] In other embodiments, the voltage conversion module is a digital circuit. As an example, the digital circuit includes: a storage module, a reading module, and an output module. The storage module is used to store a data set including a reference voltage and a threshold voltage, and the reference voltage and the threshold voltage in each data set are in a preset corresponding relationship. The preset corresponding relationship refers to the numerical corresponding relationship between the reference voltage and the threshold voltage, and the corresponding relationship must satisfy V t =V FB / (k2-k1×V FB ). That is, a plurality of data sets are listed in advance using this relationship, and all of the data sets are stored in the storage module. The reading module is connected to the storage module and the signal conversion module 110, and is configured to receive the reference voltage and read the corresponding threshold voltage from the data set. The output module is connected to the reading module and is configured to output the threshold voltage read by the reading module.

[0040] refer to Figure 3The comparison module is connected to the voltage conversion module and the sampling and monitoring terminal CS, and is configured to compare the threshold voltage and the sampled voltage and output a comparison result. The control module is configured to receive the comparison result and control the on / off state of the switch tube Q1 based on the comparison result. Specifically, the method for controlling the on / off state of the switch tube Q1 based on the comparison result includes: when the sampled voltage does not exceed the threshold voltage, the control module controls the switch tube Q1 to be off, and the secondary output circuit 20 outputs a voltage; when the sampled voltage exceeds the threshold voltage, the control module controls the switch tube Q1 to be on, and the secondary output circuit 20 stops outputting a voltage. The comparison module may include a comparator, the comparator including a second positive terminal, a second negative terminal, and a second output terminal, wherein the second positive terminal is connected to the sampling and monitoring terminal CS, the second negative terminal is connected to the voltage conversion module, and the second output terminal is connected to the control module.

[0041] Combine Figure 1 and Figure 2 The control circuit 11 may further include a driving terminal DRV, which is connected to the control module and is also connected to the control terminal of the switch Q1. The control module controls the switching transistor Q1 through the driving terminal DRV. When the driving terminal DRV outputs a high level, the switch Q1 is turned on. When the driving terminal DRV outputs a low level, the switch Q1 is turned off.

[0042] During the operation of the flyback circuit:

[0043] If the driver terminal DRV outputs a high level, the switch Q1 is turned on, and primary current flows through the primary winding NP of the transformer. At this time, the voltage signal fed back by the secondary output circuit 20 and received by the voltage control terminal FB determines the peak value of the primary current. The primary current generates a sampling voltage at the first end of the sampling resistor Rs, and the sampling voltage is input to the sampling monitoring terminal CS, implementing the sampling monitoring and overcurrent protection functions of the flyback circuit. If the driver terminal DRV outputs a low level, the switch Q1 is turned off, and the primary current flowing through the primary winding NP of the transformer is transferred to the secondary winding NS of the transformer and output to the load through the secondary output circuit 20. When there is a deviation between the actual voltage output by the secondary output circuit 20 and the preset voltage, the secondary output circuit 20 outputs a corresponding error signal and feeds it back to the voltage control terminal FB to change the voltage falling on the voltage control terminal FB, thereby changing the peak value of the primary current and eliminating the deviation between the actual voltage of the secondary output circuit 20 and the preset voltage. Therefore, the flyback circuit implements the power output voltage regulation function.

[0044] In addition, the primary side control circuit 10 may further include a capacitor C, a first end of the capacitor C being connected to the voltage control terminal FB, and a second end of the capacitor C being grounded. The capacitor C may increase circuit stability and improve the anti-interference capability of the control circuit 11.

[0045] The embodiment of the present application adjusts the relationship between the threshold voltage and the reference voltage so that the threshold voltage and the reference voltage have a nonlinear relationship, thereby reducing the current peak of the switching tube while the flyback circuit transfers unchanged energy. On the one hand, it can reduce the conduction loss, and on the other hand, it can also improve the thermal stability of the switching tube.

[0046] In summary, after reading the contents of this application, those skilled in the art will understand that the foregoing contents are presented by way of example only and are not intended to be limiting. Although not expressly stated herein, those skilled in the art will understand that this application is intended to encompass various reasonable changes, improvements, and modifications to the embodiments. Such changes, improvements, and modifications are within the spirit and scope of the exemplary embodiments of this application.

Claims

1. A flyback circuit, characterized in that: include: A primary-side control circuit for controlling voltage output and a secondary-side output circuit for outputting voltage, both sharing a transformer, wherein the primary-side control circuit comprises: A switching tube, comprising an input end and an output end, wherein the input end is connected to the transformer; A sampling resistor, comprising a first end, wherein the first end of the sampling resistor is connected to the output end and generates a sampling voltage; The control circuit is configured to receive the sampled voltage and the voltage signal fed back by the secondary output circuit, convert the voltage signal fed back by the secondary output circuit into a reference voltage, and then convert the reference voltage into a threshold voltage. The threshold voltage is compared with the sampled voltage, and the switching tube is controlled to be turned on or off based on the comparison result. The threshold voltage is converted according to the following relationship: V t =V FB / (k2-k1×V FB ), where V t is the threshold voltage; V FB is the reference voltage; k1 is the first preset coefficient; k2 is the second preset coefficient.

2. The flyback circuit according to claim 1, wherein: The first preset coefficient is 0.6-1.2, the second preset coefficient is 5-6.5, and the reference voltage does not exceed 2.5V.

3. The flyback circuit according to claim 1, wherein: The control circuit comprises: a sampling monitoring terminal connected to the first terminal of the sampling resistor and configured to receive the sampled voltage; A voltage control terminal is configured to receive a voltage signal fed back by the secondary output circuit; a signal conversion module, connected to the voltage control terminal, and configured to convert the voltage signal fed back by the secondary output circuit into a reference voltage; a voltage conversion module, connected to the signal conversion module, and configured to convert the reference voltage into a threshold voltage; a comparison module, connected to the voltage conversion module and the sampling monitoring terminal, configured to compare the threshold voltage with the sampling voltage and output the comparison result; The control module is configured to receive the comparison result and control the switching on or off of the switch tube based on the comparison result.

4. The flyback circuit according to claim 3, wherein: The signal conversion module includes: a reference voltage and a pull-up resistor, a first end of the pull-up resistor is connected to the reference voltage, and a second end of the pull-up resistor is connected to the voltage conversion module.

5. The flyback circuit according to claim 3, wherein: The voltage conversion module is a digital circuit, and the digital circuit includes: A storage module, configured to store data groups including reference voltages and threshold voltages, wherein the reference voltages and threshold voltages in each data group are in a preset corresponding relationship; a reading module, connected to the storage module and the signal conversion module, configured to receive the reference voltage and read a corresponding threshold voltage in the data group; An output module is connected to the reading module and is used to output the threshold voltage read by the reading module.

6. The flyback circuit according to claim 3, wherein: The voltage conversion module is an analog circuit, and the analog circuit includes: an amplifier, comprising a first positive terminal, a first negative terminal and a first output terminal, wherein the first output terminal is connected to the comparison module; a first resistor, wherein a first end of the first resistor is connected to the voltage control end, and a second end of the first resistor is connected to the first positive terminal; a variable resistor, wherein a first end of the variable resistor is connected to the first positive terminal, and a second end of the variable resistor is grounded; a second resistor, wherein a first end of the second resistor is connected to the first negative terminal, and a second end of the second resistor is grounded; a third resistor, wherein a first end of the third resistor is connected to the first end of the second resistor, and a second end of the third resistor is connected to the comparison module.

7. The flyback circuit according to claim 3, wherein: The method for controlling the switching on or off of the switch tube based on the comparison result includes: When it is determined that the magnitude of the sampled voltage does not exceed the magnitude of the threshold voltage, the control module controls the switch tube to be turned off, and the secondary output circuit outputs the voltage; Alternatively, when it is determined that the magnitude of the sampled voltage exceeds the magnitude of the threshold voltage, the control module controls the switch tube to be turned on, and the secondary output circuit stops outputting voltage.

8. The flyback circuit according to claim 3, wherein: The switch tube further includes a control end, and the control circuit further includes a driving end, wherein one end of the driving end is connected to the control module, and the other end is connected to the control end.

9. The flyback circuit according to claim 3, wherein: The primary side control circuit further includes a capacitor, a first end of the capacitor is connected to the voltage control end, and a second end of the capacitor is grounded.

10. The flyback circuit according to claim 3, wherein: The comparison module includes a comparator, which includes a second positive terminal, a second negative terminal and a second output terminal, wherein the second positive terminal is connected to the sampling and monitoring terminal, the second negative terminal is connected to the voltage conversion module, and the second output terminal is connected to the control module.

11. The flyback circuit according to claim 1, wherein: The sampling resistor further includes a second end, and the second end of the sampling resistor is grounded.

12. The flyback circuit according to claim 3, wherein: The primary side control circuit further includes an optocoupler, an anode of the optocoupler is connected to the secondary side output circuit, a collector of the optocoupler is connected to the voltage control terminal, and both the anode and emitter of the optocoupler are grounded.

13. The flyback circuit according to claim 1, wherein: The switch tube is a MOS tube.

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