Active flyback circuit without auxiliary winding and switching power supply
By designing an active flyback circuit without auxiliary windings and utilizing a clamping circuit to recover peak current energy, the problems of numerous components and energy consumption are solved, achieving a high-efficiency and low-cost circuit design.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Utility models(China)
- Current Assignee / Owner
- ANKER INNOVATIONS TECH CO LTD
- Filing Date
- 2025-05-28
- Publication Date
- 2026-05-12
AI Technical Summary
The additional auxiliary winding in existing flyback circuits results in a large number of components and high circuit costs. Furthermore, the RCD circuit consumes energy, reduces overall efficiency, and generates heat.
An active flyback circuit without auxiliary windings is adopted, and the RCD circuit is replaced by a clamping circuit. The clamping circuit recovers the peak current energy when the switching circuit is open, and supplies power to the control circuit. The control circuit controls the conduction and disconnection of the clamping circuit and the switching circuit, thereby reducing energy waste.
It improves the efficiency of active flyback circuits, reduces the number of components and cost, and reduces heat generation.
Smart Images
Figure CN224233540U_ABST
Abstract
Description
Technical Field
[0001] This application relates to the field of switching power supply technology, and in particular to an active flyback circuit without auxiliary windings and a switching power supply. Background Technology
[0002] The flyback circuit is a common AC-DC converter circuit. Due to its simple structure and mature technology, it has been widely used in various low-power switching power supply designs and is the most common AC-DC conversion solution in power adapters for many low-power electronic devices.
[0003] In existing flyback circuits, the transformer typically requires three windings, one of which is an auxiliary winding primarily used to power the control circuitry of the flyback circuit. While this design meets basic power requirements, the additional auxiliary winding increases the number of components and raises the circuit cost.
[0004] Furthermore, existing flyback circuits use an RCD circuit composed of resistors, capacitors, and diodes to absorb the peak current generated by the transformer leakage inductance. However, the RCD circuit causes the energy flowing into it to be consumed by the resistors, which not only reduces the overall efficiency of the flyback circuit but also generates excess heat. Utility Model Content
[0005] This application mainly provides an active flyback circuit and switching power supply without auxiliary windings, which solves the problems of high component quantity, high circuit cost, low power density, and low overall efficiency of flyback circuits caused by additional auxiliary windings.
[0006] This application provides an active flyback circuit without auxiliary windings, comprising:
[0007] A rectifier and filter circuit is used to rectify and filter the input voltage.
[0008] A transformer includes a primary winding and a secondary winding, wherein the first end of the primary winding is connected to the output end of the rectifier and filter circuit;
[0009] The output circuit is connected to the secondary winding;
[0010] A clamping circuit is connected to the second end of the primary winding;
[0011] A switching circuit is connected to the second end of the primary winding;
[0012] A control circuit, wherein the first terminal of the control circuit is connected to the control terminal of the switching circuit, the second terminal of the control circuit is connected to the control terminal of the clamping circuit, and the power supply terminal of the control circuit is connected to the output terminal of the rectifier and filter circuit and the clamping circuit respectively.
[0013] The control circuit is used to control the clamping circuit to be turned on and the switching circuit to be turned off, the current between the first and second ends of the primary winding decreases, and the clamping circuit is used to supply power to the control circuit.
[0014] The clamping circuit includes a first switching transistor, a first capacitor, a first inductor, and a Zener diode. The first end of the first switching transistor is connected to the second end of the primary winding, and the second end of the first switching transistor is grounded through the first capacitor. The control terminal of the first switching transistor is connected to the second terminal of the control circuit. One end of the first inductor is connected to the second end of the first switching transistor, and the other end of the first inductor is connected to the power supply terminal of the control circuit and the negative terminal of the Zener diode. The positive terminal of the Zener diode is grounded.
[0015] The control circuit is used to control the first switching transistor to turn on. The first capacitor is connected to the second end of the primary winding through the first switching transistor. The first capacitor is charged. After the first capacitor is charged, it supplies power to the control circuit through the first inductor and the Zener diode.
[0016] The switching circuit includes a second switching transistor and a first resistor. The first end of the second switching transistor is connected to the second end of the primary winding, and the second end of the second switching transistor is grounded through the first resistor. The third end of the control circuit is connected between the second end of the second switching transistor and the first resistor.
[0017] The control circuit is used to control the second switch to turn off, the parasitic capacitance of the second switch to charge, and the parasitic capacitance of the second switch to supply power to the control circuit through the first inductor and the Zener diode.
[0018] The control circuit is used to control the second switch to be turned on and the first switch to be turned off, so that the transformer can operate normally.
[0019] The active flyback circuit further includes a second resistor and a third resistor, and the power supply terminal of the control circuit is connected to the output terminal of the rectifier and filter circuit through the second resistor and the third resistor.
[0020] The rectifier-filter circuit includes a first diode, a second diode, a third diode, a fourth diode, a second capacitor, a second inductor, and a third capacitor. The cathode of the first diode is connected to the anode of the second diode, the cathode of the second diode is connected to the cathode of the third diode, the anode of the third diode is connected to the cathode of the fourth diode, and the anode of the fourth diode is connected to the anode of the first diode. The connection point between the first and second diodes and the connection point between the third and fourth diodes receives the input voltage. One end of the second inductor is connected between the cathodes of the second and third diodes, and the other end of the second inductor is connected to one end of the second capacitor, one end of the primary winding, and one end of the second resistor. The other end of the second capacitor is connected between the anodes of the first and fourth diodes. One end of the third capacitor is connected to one end of the second inductor, and the other end of the third capacitor is connected to the other end of the second capacitor.
[0021] The output circuit includes a fifth diode, a fourth capacitor, and a fourth resistor. The positive terminal of the fifth diode is connected to the first end of the secondary winding, the negative terminal of the fifth diode is connected to one end of the fourth capacitor and one end of the fourth resistor, and the other end of the fourth resistor is connected to the second end of the fourth capacitor and the secondary winding.
[0022] This application also provides a switching power supply, including the active flyback circuit described above.
[0023] The beneficial effects of this application are as follows: The first terminal of the control circuit is connected to the control terminal of the switching circuit, and the second terminal of the control circuit is connected to the control terminal of the clamping circuit. The power supply terminal of the control circuit is connected to the output terminal of the rectifier-filter circuit and the clamping circuit, respectively. The control circuit controls the clamping circuit to conduct and controls the switching circuit to disconnect, causing the current between the first and second terminals of the primary winding to decrease. The clamping circuit then supplies power to the control circuit. A spike current is generated when the control switching circuit is disconnected, and the energy of this spike current is recovered through the clamping circuit to supply power to the control circuit, reducing energy waste and improving the efficiency of the active flyback circuit. Replacing the RCD circuit with the clamping circuit reduces energy consumption and heat generation. Using a transformer consisting of a primary winding and a secondary winding eliminates the need for additional auxiliary windings, reducing components and lowering costs. Attached Figure Description
[0024] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort. Wherein:
[0025] Figure 1 This is a schematic diagram of an embodiment of the active flyback circuit without auxiliary windings provided in this application;
[0026] Figure 2 This is a circuit diagram of an embodiment of the active flyback circuit without auxiliary windings provided in this application. Detailed Implementation
[0027] The embodiments of the technical solution of this application will now be described in detail with reference to the accompanying drawings. These embodiments are only used to more clearly illustrate the technical solution of this application and are therefore merely examples, and should not be used to limit the scope of protection of this application.
[0028] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains; the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the application; the terms “comprising” and “having”, and any variations thereof, in the specification, claims, and foregoing description of the drawings are intended to cover non-exclusive inclusion.
[0029] In the description of the embodiments of this application, technical terms such as "first" and "second" are used only to distinguish different objects and should not be construed as indicating or implying relative importance or implicitly indicating the number, specific order, or primary and secondary relationship of the indicated technical features.
[0030] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.
[0031] In the description of the embodiments in this application, the term "and / or" is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, and B existing alone. Additionally, the character " / " in this document generally indicates that the preceding and following related objects have an "or" relationship.
[0032] In the description of the embodiments of this application, the term "multiple" refers to two or more (including two), similarly, "multiple sets" refers to two or more (including two sets), and "multiple pieces" refers to two or more (including two pieces).
[0033] In the description of the embodiments of this application, unless otherwise expressly specified and limited, the technical terms such as "installation," "connection," "joining," and "fixing" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a connection between two components or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. For those skilled in the art, the specific meaning of the above terms in the embodiments of this application can be understood according to the specific circumstances.
[0034] In existing flyback circuits, the transformer typically requires three windings, one of which is an auxiliary winding primarily used to power the control circuitry of the flyback circuit. While this design meets basic power requirements, the additional auxiliary winding increases the number of components and raises the circuit cost.
[0035] Furthermore, existing flyback circuits use an RCD circuit composed of resistors, capacitors, and diodes to absorb the peak current generated by the transformer leakage inductance. However, the RCD circuit causes the energy flowing into it to be consumed by the resistors, which not only reduces the overall efficiency of the flyback circuit but also generates excess heat.
[0036] This application provides an active flyback circuit without auxiliary windings. Please refer to [link to relevant documentation]. Figure 1 As shown, Figure 1 This is a schematic diagram of an embodiment of the active flyback circuit without auxiliary windings provided in this application. The active flyback circuit 1 without auxiliary windings in this embodiment includes a rectifier filter circuit 10, a transformer 20, an output circuit 30, a clamping circuit 40, a switching circuit 50, and a control circuit 60.
[0037] The rectifier-filter circuit 10 is used to rectify and filter the input voltage. Specifically, the input terminal of the rectifier-filter circuit 10 receives the input voltage and outputs it after rectification and filtering. The input voltage can be alternating current (AC), including but not limited to 220V AC from the mains. The rectifier-filter circuit 10 rectifies the AC voltage into direct current (DC) and outputs it after filtering.
[0038] The transformer 20 includes a primary winding 21 and a secondary winding 22. The first end 211 of the primary winding 21 is connected to the output terminal of the rectifier and filter circuit 10. That is, after the rectifier and filter circuit 10 rectifies and filters the input voltage, it outputs the rectified and filtered input voltage to the first end 211 of the primary winding 21, so that the transformer 20 can receive the rectified and filtered input voltage.
[0039] The output circuit 30 is connected to the secondary winding 22. In some embodiments, the primary winding 21 of the transformer 20 receives the rectified and filtered input voltage and transmits it to the secondary winding 22, which outputs to the output circuit 30.
[0040] The primary winding 21 of transformer 20 is typically used to receive the input DC voltage and transfer the energy to the secondary winding 22 of transformer 20 through electromagnetic induction. The secondary winding 22 of transformer 20 is used to receive the energy transferred from the primary winding 21 and convert it into the required output voltage to supply the output circuit 30.
[0041] Clamping circuit 40 is connected to the second end 212 of primary winding 21 and is used to absorb the spike current generated by leakage inductance of transformer 20. Switching circuit 50 is connected to the second end 212 of primary winding 21 and is used to control the on / off state of primary winding 21 of transformer 20, so as to control primary winding 21 to transfer energy to secondary winding 22.
[0042] The first terminal GATE of the control circuit 60 is connected to the control terminal of the switch circuit 50, the second terminal GATE_1 of the control circuit 60 is connected to the control terminal of the clamping circuit 40, and the power supply terminal VDD of the control circuit 60 is connected to the output terminal of the rectifier filter circuit 10 and the clamping circuit 40 respectively.
[0043] The control circuit 60 includes, but is not limited to, a PWM control chip; wherein, the first terminal GATE of the control circuit 60 is the GATE terminal of the PWM control chip, the second terminal GATE_1 of the control circuit 60 is the GATE_1 terminal of the PWM control chip, and the power supply terminal VDD of the control circuit 60 is the VDD terminal of the PWM control chip.
[0044] In some embodiments, the second terminal GATE_1 of the control circuit 60 controls the on and off of the clamping circuit 40, the first terminal GATE of the control circuit 60 controls the on and off of the switching circuit 50, and the rectifier filter circuit 10 or the clamping circuit 40 supplies power to the control circuit 60.
[0045] Among them, the control circuit 60 is used to control the clamping circuit 40 to be turned on and the control switch circuit 50 to be turned off, the current between the first end 211 and the second end 212 of the primary winding 21 decreases, and the clamping circuit 40 is used to supply power to the control circuit 60.
[0046] In some embodiments, when the control circuit 60 controls the clamping circuit 40 to be turned on and the control switch circuit 50 is turned off, the primary winding 21 of the transformer 20 is disconnected due to the disconnection of the switch circuit 50. The current between the first end 211 and the second end 212 of the primary winding 21 drops rapidly, and the leakage inductance of the transformer 20 generates a spike current. At this time, the clamping circuit 40 absorbs the energy of the spike current so that the clamping circuit 40 supplies power to the control circuit 60.
[0047] In some embodiments, when the control circuit 60 controls the clamping circuit 40 to be disconnected and the control switch circuit 50 is turned on, the primary winding 21 of the transformer 20 is turned on, the first end 211 of the primary winding 21 receives the rectified and filtered input voltage, and the primary winding 21 transfers energy to the secondary winding 22; at this time, the clamping circuit 40 does not work, and the control circuit 60 is powered by the rectifier and filter circuit 10.
[0048] In this embodiment, the first terminal GATE of the control circuit 60 is connected to the control terminal of the switching circuit 50, and the second terminal GATE_1 of the control circuit 60 is connected to the control terminal of the clamping circuit 40. The power supply terminal VDD of the control circuit 60 is connected to the output terminal of the rectifier and filter circuit 10 and the clamping circuit 40, respectively. The control circuit 60 is used to control the clamping circuit 40 to conduct and control the switching circuit 50 to disconnect. The current between the first terminal 211 and the second terminal 212 of the primary winding 21 decreases, and the clamping circuit 40 is used to supply power to the control circuit 60. When the control switching circuit 50 is disconnected, a spike current is generated, and the energy of the spike current is recovered through the clamping circuit 40 to supply power to the control circuit 60, reducing energy waste and improving the efficiency of the active flyback circuit 1. By replacing the RCD circuit with the clamping circuit 40, energy consumption and heat generation are reduced. With the primary winding 21 and secondary winding 22 included in the transformer 20, no additional auxiliary winding is required, reducing components and lowering costs.
[0049] According to some embodiments of this application, see Figure 2 As shown, Figure 2 This is a circuit diagram of an embodiment of the active flyback circuit without auxiliary windings provided in this application. The clamping circuit 40 of this embodiment includes a first switching transistor Q1, a first capacitor C1, a first inductor L1, and a Zener diode ZD1.
[0050] In this circuit, the first terminal of the first switching transistor Q1 is connected to the second terminal 212 of the primary winding 21, the second terminal of the first switching transistor Q1 is grounded through the first capacitor C1, the control terminal of the first switching transistor Q1 is connected to the second terminal GATE_1 of the control circuit 60, one end of the first inductor L1 is connected to the second terminal of the first switching transistor Q1, and the other end of the first inductor L1 is connected to the power supply terminal VDD of the control circuit 60 and the negative terminal of the Zener diode ZD1, respectively. The positive terminal of the Zener diode ZD1 is grounded.
[0051] The first inductor L1 and the Zener diode ZD1 form a voltage regulator circuit.
[0052] According to some embodiments of this application, the control circuit 60 is used to control the first switch Q1 to be turned on, the first capacitor C1 is connected to the second terminal 212 of the primary winding 21 through the first switch Q1, the first capacitor C1 is charged, and after the first capacitor C1 is charged, it supplies power to the control circuit 60 through the first inductor L1 and the Zener diode ZD1.
[0053] In some embodiments, when the control circuit 60 controls the switch circuit 50 to be disconnected and controls the first switch transistor Q1 to be turned on, the primary winding 21 of the transformer 20 is disconnected, the current between the first end 211 and the second end 212 of the primary winding 21 drops rapidly, the leakage inductance generates a spike current, the first capacitor C1 absorbs the energy of the spike current through the first switch transistor Q1, the first capacitor C1 is charged, and after charging is completed, the first capacitor C1 supplies power to the control circuit 60 through the first inductor L1 and the Zener diode ZD1.
[0054] In traditional flyback circuits, the auxiliary winding power supply introduces additional energy loss. In this embodiment, after the first capacitor C1 is fully charged, it supplies power to the control circuit 60 through the first inductor L1 and the Zener diode ZD1, making full use of the energy in the main circuit and reducing energy waste.
[0055] According to some embodiments of this application, see Figure 2 As shown, the switching circuit 50 of this embodiment includes a second switching transistor Q2 and a first resistor R1. The first terminal of the second switching transistor Q2 is connected to the second terminal 212 of the primary winding 21, and the second terminal of the second switching transistor Q2 is grounded through the first resistor R1. The third terminal CS of the control circuit 60 is connected between the second terminal of the second switching transistor Q2 and the first resistor R1.
[0056] According to some embodiments of this application, the control circuit 60 is used to control the second switch Q2 to turn off, the parasitic capacitance Cq2 of the second switch Q2 is charged, and the parasitic capacitance Cq2 of the second switch Q2 supplies power to the control circuit 60 through the first inductor L1 and the Zener diode ZD1.
[0057] In some embodiments, when the control circuit 60 controls the second switch Q2 to turn off and controls the first switch Q1 to turn on, the first capacitor C1 absorbs the energy of the peak current through the first switch Q1 to charge; at the same time, the parasitic capacitance Cq2 of the second switch Q2 also absorbs part of the energy of the peak current and charges; when the peak current disappears, the parasitic capacitance Cq2 of the second switch Q2 discharges, transferring the stored energy to the first inductor L1 and the first capacitor C1, so as to supply power to the control circuit 60 through the first inductor L1 and the Zener diode ZD1; when the parasitic capacitance Cq2 of the second switch Q2 is discharged, that is, the voltage of the parasitic capacitance Cq2 of the second switch Q2 drops to zero, so that the voltage across the second switch Q2 is zero when the second switch Q2 is turned on again.
[0058] In this embodiment, by setting the parasitic capacitance Cq2 of the second switch Q2, zero-voltage turn-on of the second switch Q2 can be achieved, reducing switching losses.
[0059] According to some embodiments of this application, the control circuit 60 is used to control the second switch Q2 to turn on and control the first switch Q1 to turn off, so that the transformer 20 can work normally.
[0060] In some embodiments, when the control circuit 60 controls the second switch Q2 to be turned on and controls the first switch Q1 to be turned off, the first capacitor C1 does not work, and the transformer 20 works normally, that is, the primary winding 21 of the transformer 20 is turned on, and the primary winding 21 transfers energy to the secondary winding 22 for use by the output circuit 30; at this time, the control circuit 60 is powered by the rectifier and filter circuit 10.
[0061] According to some embodiments of this application, see Figure 2 As shown, the active flyback circuit 1 in this embodiment also includes a second resistor R2 and a third resistor R3. The power supply terminal VDD of the control circuit 60 is connected to the output terminal of the rectifier filter circuit 10 through the second resistor R2 and the third resistor R3.
[0062] Among them, the second resistor R2 and the third resistor R3 form the soft start circuit of the control circuit 60, which supplies power to the control circuit 60 before the transformer 20 starts working, so as to provide the start voltage for the control circuit 60.
[0063] This embodiment achieves a soft-start function by setting the second resistor R2 and the third resistor R3, enabling the control circuit 60 to start slowly and avoiding the impact of the surge current on the circuit during startup.
[0064] According to some embodiments of this application, see Figure 2As shown, the rectifier filter circuit 10 in this embodiment includes a first diode D1, a second diode D2, a third diode D3, a fourth diode D4, a second capacitor C2, a second inductor L2, and a third capacitor C3.
[0065] In this configuration, the cathode of the first diode D1 is connected to the anode of the second diode D2, the cathode of the second diode D2 is connected to the cathode of the third diode D3, the anode of the third diode D3 is connected to the cathode of the fourth diode D4, and the anode of the fourth diode D4 is connected to the anode of the first diode D1. The first diode D1, the second diode D2, the third diode D3, and the fourth diode D4 form a rectifier bridge.
[0066] The connection point of the first diode D1 and the second diode D2, and the connection point of the third diode D3 and the fourth diode D4, receive the input voltage. One end of the second inductor L2 is connected between the negative terminals of the second diode D2 and the third diode D3. The other end of the second inductor L2 is connected to one end of the second capacitor C2, the first terminal 211 of the primary winding 21, and one end of the second resistor R2. The other end of the second capacitor C2 is connected between the positive terminals of the first diode D1 and the fourth diode D4. One end of the third capacitor C3 is connected to one end of the second inductor L2, and the other end of the third capacitor C3 is connected to the other end of the second capacitor C2.
[0067] In this embodiment, the input voltage is first rectified by a rectifier bridge composed of a first diode D1, a second diode D2, a third diode D3, and a fourth diode D4, and then output as a stable DC voltage after passing through a filter circuit composed of a second capacitor C2, a second inductor L2, and a third capacitor C3.
[0068] According to some embodiments of this application, see Figure 2 As shown, the output circuit 30 of this embodiment includes a fifth diode D5, a fourth capacitor C4 and a fourth resistor R4. The positive terminal of the fifth diode D5 is connected to the first terminal 221 of the secondary winding 22, and the negative terminal of the fifth diode D5 is connected to one end of the fourth capacitor C4 and one end of the fourth resistor R4. The other end of the fourth resistor R4 is connected to the fourth capacitor C4 and the second terminal 222 of the secondary winding 22.
[0069] Among them, the fifth diode D5 serves as the rectifier tube of the secondary winding 22, which is used to rectify the electrical energy transmitted by the transformer 20 to form a DC voltage, which is then filtered by the fourth capacitor C4 and transmitted to the fourth resistor R4.
[0070] In some embodiments, one end of the fourth resistor R4 serves as the output terminal Vout, and the other end of the fourth resistor R4 is grounded. When the output voltage changes, feedback is sent to the fourth terminal (not shown) of the control circuit 60 through an optocoupler. At the same time, the third terminal CS of the control circuit 60 controls and adjusts the duty cycle of the primary winding 21 circuit by sampling the current of the primary winding 21 circuit to achieve output stability.
[0071] Among them, the third terminal CS of the control circuit 60 is the CS terminal of the PWM control chip, and the fourth terminal of the control circuit 60 is the FB terminal of the PWM control chip.
[0072] In some embodiments, the active flyback circuit 1 further includes a fifth capacitor C5, one end of which is connected to the power supply terminal VDD of the control circuit 60, and the other end of which is grounded.
[0073] In this embodiment, both the first switch Q1 and the second switch Q2 are N-type MOSFETs. The control terminals of the first switch Q1 and the second switch Q2 are the gates, the first terminals of the first switch Q1 and the second switch Q2 are the drains, and the second terminals of the first switch Q1 and the second switch Q2 are the sources. In other embodiments, the first switch Q1 and the second switch Q2 can be other types of switches, such as transistors.
[0074] Another embodiment of this application provides a switching power supply, including the active flyback circuit 1 of the above embodiment.
[0075] In summary, the first terminal GATE of the control circuit 60 is connected to the control terminal of the switching circuit 50, and the second terminal GATE_1 of the control circuit 60 is connected to the control terminal of the clamping circuit 40. The power supply terminal VDD of the control circuit 60 is connected to the output terminal of the rectifier-filter circuit 10 and the clamping circuit 40, respectively. The control circuit 60 is used to control the clamping circuit 40 to conduct and to control the switching circuit 50 to disconnect. The current between the first terminal 211 and the second terminal 212 of the primary winding 21 decreases, and the clamping circuit 40 is used to supply power to the control circuit 60. When the control switching circuit 50 is disconnected, a spike current is generated, and the energy of the spike current is recovered through the clamping circuit 40 to supply power to the control circuit 60, reducing energy waste and improving the efficiency of the active flyback circuit 1. Replacing the RCD circuit with the clamping circuit 40 reduces energy consumption and heat generation. Since the transformer 20 includes a primary winding 21 and a secondary winding 22, no additional auxiliary winding is needed, reducing components and lowering costs.
[0076] The above description is merely an embodiment of this application and does not limit the patent scope of this application. Any equivalent structural or procedural transformations made using the content of this application's specification and drawings, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of this application.
Claims
1. An active flyback circuit without auxiliary windings, characterized in that, include: A rectifier and filter circuit is used to rectify and filter the input voltage. A transformer includes a primary winding and a secondary winding, wherein the first end of the primary winding is connected to the output end of the rectifier and filter circuit; The output circuit is connected to the secondary winding; A clamping circuit is connected to the second end of the primary winding; A switching circuit is connected to the second end of the primary winding; A control circuit, wherein the first terminal of the control circuit is connected to the control terminal of the switching circuit, the second terminal of the control circuit is connected to the control terminal of the clamping circuit, and the power supply terminal of the control circuit is connected to the output terminal of the rectifier and filter circuit and the clamping circuit respectively. The control circuit is used to control the clamping circuit to be turned on and the switching circuit to be turned off, the current between the first and second ends of the primary winding decreases, and the clamping circuit is used to supply power to the control circuit.
2. The active flyback circuit according to claim 1, characterized in that, The clamping circuit includes a first switching transistor, a first capacitor, a first inductor, and a Zener diode. The first terminal of the first switching transistor is connected to the second terminal of the primary winding, and the second terminal of the first switching transistor is grounded through the first capacitor. The control terminal of the first switching transistor is connected to the second terminal of the control circuit. One end of the first inductor is connected to the second terminal of the first switching transistor, and the other end of the first inductor is connected to the power supply terminal of the control circuit and the negative terminal of the Zener diode. The positive terminal of the Zener diode is grounded.
3. The active flyback circuit according to claim 2, characterized in that, The control circuit is used to control the first switching transistor to turn on. The first capacitor is connected to the second end of the primary winding through the first switching transistor. The first capacitor is charged. After the first capacitor is charged, it supplies power to the control circuit through the first inductor and the Zener diode.
4. The active flyback circuit according to claim 2, characterized in that, The switching circuit includes a second switching transistor and a first resistor. The first end of the second switching transistor is connected to the second end of the primary winding, and the second end of the second switching transistor is grounded through the first resistor. The third end of the control circuit is connected between the second end of the second switching transistor and the first resistor.
5. The active flyback circuit according to claim 4, characterized in that, The control circuit is used to control the second switch to turn off, and the parasitic capacitance of the second switch to be charged. The parasitic capacitance of the second switch to supply power to the control circuit through the first inductor and the Zener diode.
6. The active flyback circuit according to claim 4, characterized in that, The control circuit is used to control the second switching transistor to turn on and the first switching transistor to turn off, so that the transformer can operate normally.
7. The active flyback circuit according to any one of claims 1-6, characterized in that, The active flyback circuit further includes a second resistor and a third resistor, and the power supply terminal of the control circuit is connected to the output terminal of the rectifier and filter circuit through the second resistor and the third resistor.
8. The active flyback circuit according to claim 7, characterized in that, The rectifier-filter circuit includes a first diode, a second diode, a third diode, a fourth diode, a second capacitor, a second inductor, and a third capacitor. The cathode of the first diode is connected to the anode of the second diode, the cathode of the second diode is connected to the cathode of the third diode, the anode of the third diode is connected to the cathode of the fourth diode, and the anode of the fourth diode is connected to the anode of the first diode. The connection point of the first and second diodes and the connection point of the third and fourth diodes receive the input voltage. One end of the second inductor is connected between the cathodes of the second and third diodes, and the other end of the second inductor is connected to one end of the second capacitor, one end of the primary winding, and one end of the second resistor. The other end of the second capacitor is connected between the anodes of the first and fourth diodes. One end of the third capacitor is connected to one end of the second inductor, and the other end of the third capacitor is connected to the other end of the second capacitor.
9. The active flyback circuit according to claim 7, characterized in that, The output circuit includes a fifth diode, a fourth capacitor, and a fourth resistor. The positive terminal of the fifth diode is connected to the first end of the secondary winding, the negative terminal of the fifth diode is connected to one end of the fourth capacitor and one end of the fourth resistor, and the other end of the fourth resistor is connected to the second end of the fourth capacitor and the secondary winding.
10. A switching power supply, characterized in that, Including the active flyback circuit as described in any one of claims 1-9.