Double-transistor flyback absorption circuit

Abstract

The invention belongs to the field of flyback power supplies, and particularly provides a double-transistor flyback absorption circuit which comprises a first flyback absorption module, a second flyback absorption module and an output transformer T1. The first flyback absorption module and the second flyback absorption module are electrically connected with the two ends of a primary side coil of the output transformer T1 respectively and are suitable for absorbing leakage inductance current of the output transformer T1 and enabling the leakage inductance current to flow back to the primary side coil of the output transformer T1. By arranging the first flyback absorption module and the second flyback absorption module, the leakage inductance current of the transformer T1 flows back to the bus voltage, energy is saved, and the utilization rate is improved. Meanwhile, each flyback absorption module is provided with an MOS tube, and the overall withstand voltage of the circuit is doubled compared with that of common single-tube flyback.

Description

Technical Field

[0001] The invention relates to the technical field of flyback power supplies, and in particular provides a double-tube flyback absorption circuit. Background Art

[0002] At present, switching power supplies are widely used in electronic systems because of their lightness, large input voltage range, and high efficiency. Most of the current household electronic devices are powered by switching power supplies, and switching power supplies have become an indispensable power supply method for the rapid development of today's electronic information industry. During the operation of the flyback switching power supply, due to the influence of parasitic parameters such as leakage inductance and distributed capacitance of the high-frequency transformer, the switching power supply will generate a very high peak voltage at the moment of switching. In order to suppress this peak voltage, an RCD absorption circuit is often added between the primary coils of the high-frequency transformer. The RCD absorption circuit is designed according to how much peak voltage should be absorbed under the highest input voltage and full load conditions. When the input voltage is low, the RCD circuit parameters are fixed, and the RCD circuit parameters at this time are not optimal relative to the working state at this time, resulting in low efficiency of the power supply at low voltage input.

[0003] In order to solve the above problems, the following methods are adopted in the related art: The first method is to add three transistors to control the leakage current after the MOS tube is turned off, so that it flows back to the power bus, thereby achieving the purpose of lossless absorption of the transformer leakage energy. The disadvantages are that the overall withstand voltage is low, more devices are used, the control is more complicated, and it is impossible to control the switching speed of the MOS tube and provide a release circuit for the GS capacitor.

[0004] The second method is to add the primary coil L1, diode D2, and capacitor C2 to filter the current on the primary side of the transformer, and then control the on and off of the energy release resistor R1 under the action of the voltage stabilizing diode ZD1 and the transistor Q2. In this way, only R2 can release energy when the input voltage is low, and R1 and R2 can release energy when the input voltage is high, so that the RCD circuit parameters can adapt to the optimal working state. This ensures that the loss can be reduced and the efficiency can be improved under the low input voltage state. The disadvantage is that there is only one MOS tube, the overall withstand voltage is small, and the transformer leakage inductance energy does not flow back to the power supply, resulting in energy waste and relatively low operating efficiency.

[0005] The third type uses dual MOS tube drive plus a middle absorption clamp circuit and an auxiliary voltage equalization circuit, so that the design can use a general MOS tube with a lower voltage resistance to realize a medium- and high-voltage flyback power supply, and the two MOS tubes have a good voltage equalization capability; compared with the original power frequency transformer step-down solution, it can reduce the weight and volume of the product, reduce the complexity of the system, thereby improving the product installation efficiency and greatly reducing the product cost. The disadvantage is that the transformer leakage inductance energy is not recycled, resulting in energy waste, the circuit is complex, more devices are used, and it is impossible to control the switching speed of the MOS tube and provide a release circuit for the GS capacitor.

[0006] The above problems need to be solved urgently. Summary of the invention

[0007] The purpose of the present invention is to provide a double-transistor flyback absorption circuit.

[0008] In order to solve the above technical problems, the present invention provides a dual-tube flyback absorption circuit, comprising: A first flyback absorption module, a second flyback absorption module and an output transformer T1; The first flyback absorption module and the second flyback absorption module are respectively connected to the DC bus VBUS and the DC bus GND; The first flyback absorption module and the second flyback absorption module are electrically connected to both ends of the primary coil of the output transformer T1 respectively, and are suitable for absorbing the leakage inductance current of the output transformer T1 and returning it to the primary coil of the output transformer T1.

[0009] Furthermore, the first flyback absorption module includes: A first MOS tube, a first absorption capacitor C1, a first consumption resistor R1 and a first diode D1; The drain of the first MOS tube is electrically connected to the DC bus VBUS; The source of the first MOS tube is electrically connected to one end of the primary coil of the output transformer T1; Two ends of the first absorption capacitor C1 and the first consumption resistor R1 connected in series are electrically connected to the drain and source of the first MOS tube respectively; The anode of the first diode D1 is electrically connected between the first absorption capacitor C1 and the first consumption resistor R1 , and the cathode of the first diode D1 is electrically connected between the source of the first MOS tube and the first consumption resistor R1 .

[0010] Furthermore, the second flyback absorption module includes: A second MOS tube, a second absorption capacitor C2, a second consumption resistor R2 and a second diode D2; The drain of the second MOS tube is electrically connected to one end of the primary coil of the output transformer T1; The source of the second MOS tube is electrically connected to the DC bus GND; Two ends of the second absorption capacitor C2 and the second consumption resistor R2 connected in series are electrically connected to the drain and source of the second MOS tube respectively; The anode of the second diode D2 is electrically connected between the second absorption capacitor C2 and the second consumption resistor R2, and the cathode of the second diode D2 is electrically connected between the source of the second MOS tube and the second consumption resistor R2.

[0011] Furthermore, the dual-transistor flyback absorption circuit also includes a driving transformer T2; The primary coil of the driving transformer T2 is electrically connected to an external driving source; Two ends of the secondary coil T21 of the driving transformer T2 are electrically connected to the gate of the first MOS transistor and the source of the first MOS transistor respectively; Two ends of the secondary coil T22 of the driving transformer T2 are electrically connected to the gate of the second MOS transistor and the source of the second MOS transistor respectively.

[0012] Furthermore, the first flyback absorption module also includes a resistor R3; The gate of the first MOS transistor is electrically connected to the secondary coil T21 of the driving transformer T2 through the resistor R3.

[0013] Furthermore, the first flyback absorption module also includes a resistor R4; One end of the resistor R4 is electrically connected between the resistor R3 and the gate of the first MOS transistor, and the other end of the resistor R4 is electrically connected to the source of the first MOS transistor.

[0014] Furthermore, the second flyback absorption module also includes a resistor R5; The gate of the second MOS transistor is electrically connected to the secondary coil T22 of the driving transformer T2 through the resistor R5.

[0015] Furthermore, the second flyback absorption module also includes a resistor R6; One end of the resistor R6 is electrically connected between the resistor R5 and the gate of the second MOS transistor, and the other end of the resistor R6 is electrically connected to the source of the second MOS transistor.

[0016] Furthermore, the dual-tube flyback absorption circuit further includes a third diode D3 and a fourth diode D4; The cathode of the third diode D3 is electrically connected to the drain of the first MOS tube; The anode of the third diode D3 is electrically connected to the drain of the second MOS tube; The cathode of the fourth diode D4 is electrically connected to the source of the first MOS tube; An anode of the fourth diode D4 is electrically connected to a source of the second MOS transistor.

[0017] Furthermore, the dual-tube flyback absorption circuit further includes a fifth diode D5; The fifth diode D5 is connected in series with one end of the output transformer T1.

[0018] The beneficial effect of the present invention is that the present invention provides a dual-tube flyback absorption circuit, including: a first flyback absorption module, a second flyback absorption module and an output transformer T1; the first flyback absorption module and the second flyback absorption module are respectively connected to the DC bus VBUS and the DC bus GND; the first flyback absorption module and the second flyback absorption module are respectively electrically connected to the two ends of the primary coil of the output transformer T1, and are suitable for absorbing the leakage inductance current of the output transformer T1 and returning it to the primary coil of the output transformer T1. By setting the first flyback absorption module and the second flyback absorption module, the leakage inductance current of the transformer T1 is returned to the bus voltage, which saves energy and improves the utilization rate. At the same time, each flyback absorption module is provided with a MOS tube, and the overall withstand voltage of the circuit is doubled compared with that of an ordinary single-tube flyback. Two resistors are directly connected to the gate of the MOS tube, which can adjust the switching speed of the MOS tube, the Miller platform oscillation waveform, and the discharge of the Miller capacitor. At the same time, a release loop can be provided for the GS capacitor in the MOS tube while removing the high-voltage static electricity of the external circuit. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] The present invention is further described below in conjunction with the accompanying drawings and embodiments.

[0020] Figure 1 It is a schematic diagram of the structure of a dual-transistor flyback absorption circuit provided in an embodiment of the present invention.

[0021] Figure 2 This is a current path diagram when the first MOS tube and the second MOS tube in the dual-tube flyback absorption circuit provided by an embodiment of the present invention are both turned on.

[0022] Figure 3 This is a current path diagram when the first MOS tube and the second MOS tube in the dual-tube flyback absorption circuit provided by an embodiment of the present invention are both turned off. DETAILED DESCRIPTION

[0023] The present invention will now be described in further detail with reference to the accompanying drawings. These drawings are simplified schematic diagrams, which only illustrate the basic structure of the present invention in a schematic manner, and therefore only show the components related to the present invention. Example

[0024] See also Figure 1 This embodiment provides a dual-tube flyback absorption circuit, including: a first flyback absorption module, a second flyback absorption module and an output transformer T1; the first flyback absorption module and the second flyback absorption module are respectively connected to the DC bus VBUS and the DC bus GND; the first flyback absorption module and the second flyback absorption module are respectively electrically connected to the two ends of the primary coil of the output transformer T1, and are suitable for absorbing the leakage inductance current of the output transformer T1 and returning it to the primary coil of the output transformer T1. By setting the first flyback absorption module and the second flyback absorption module, the leakage inductance current of the transformer T1 is returned to the bus voltage, which saves energy and improves the utilization rate.

[0025] Among them, the first flyback absorption module includes: a first MOS tube, a first absorption capacitor C1, a first consumption resistor R1 and a first diode D1; the drain of the first MOS tube is electrically connected to the DC bus VBUS; the source of the first MOS tube is electrically connected to one end of the primary coil of the output transformer T1; the two ends of the first absorption capacitor C1 and the first consumption resistor R1 are electrically connected in series to the drain and source of the first MOS tube respectively; the positive electrode of the first diode D1 is electrically connected between the first absorption capacitor C1 and the first consumption resistor R1, and the negative electrode of the first diode D1 is electrically connected between the source of the first MOS tube and the first consumption resistor R1.

[0026] The first absorption capacitor C1, the first consumption resistor R1 and the first diode D1 absorb and consume the high-frequency noise of the leakage inductance current, thereby reducing the loss of the transformer and improving the efficiency.

[0027] In this embodiment, the second flyback absorption module includes: a second MOS tube, a second absorption capacitor C2, a second consumption resistor R2 and a second diode D2; the drain of the second MOS tube is electrically connected to one end of the primary coil of the output transformer T1; the source of the second MOS tube is electrically connected to the DC bus GND; the two ends of the second absorption capacitor C2 and the second consumption resistor R2 are electrically connected in series to the drain and source of the second MOS tube respectively; the positive electrode of the second diode D2 is electrically connected between the second absorption capacitor C2 and the second consumption resistor R2, and the negative electrode of the second diode D2 is electrically connected between the source of the second MOS tube and the second consumption resistor R2.

[0028] The second absorption capacitor C2, the second consumption resistor R2 and the second diode D2 absorb and consume the high-frequency noise of the leakage inductance current, thereby reducing the loss of the transformer and improving the efficiency.

[0029] In order to drive the first MOS tube and the second MOS tube, in the present embodiment, the dual-tube flyback absorption circuit further includes a driving transformer T2; the primary coil of the driving transformer T2 is electrically connected to the external driving source; the two ends of the secondary coil T21 of the driving transformer T2 are electrically connected to the gate of the first MOS tube and the source of the first MOS tube respectively; the two ends of the secondary coil T22 of the driving transformer T2 are electrically connected to the gate of the second MOS tube and the source of the second MOS tube respectively.

[0030] When the driving transformer T2 is working, the first MOS tube and the second MOS tube can be driven to be turned off or turned on at the same time.

[0031] In this embodiment, the first flyback absorption module further includes a resistor R3; the gate of the first MOS tube is electrically connected to the secondary coil T21 of the driving transformer T2 through the resistor R3. By adjusting the resistance value of the resistor R3, the switching speed Miller platform oscillation waveform of the first MOS tube and the discharge of the Miller capacitor are adjusted.

[0032] It should be noted that the first flyback absorption module also includes a resistor R4; one end of the resistor R4 is electrically connected between the resistor R3 and the gate of the first MOS tube, and the other end is electrically connected to the source of the first MOS tube. By setting the resistor R4, a release loop is provided for the GS capacitor in the first MOS tube and high-voltage static electricity of the external circuit is removed at the same time.

[0033] In this embodiment, the second flyback absorption module further includes a resistor R5; the gate of the second MOS tube is electrically connected to the secondary coil T22 of the driving transformer T2 through the resistor R5. By adjusting the resistance value of the resistor R5, the switching speed Miller platform oscillation waveform of the second MOS tube and the discharge of the Miller capacitor are adjusted.

[0034] It should be noted that the second flyback absorption module also includes a resistor R6; one end of the resistor R6 is electrically connected between the resistor R5 and the gate of the second MOS tube, and the other end is electrically connected to the source of the second MOS tube. By setting the resistor R6, a release loop is provided for the GS capacitor in the second MOS tube and high-voltage static electricity of the external circuit is removed at the same time.

[0035] In this embodiment, the dual-tube flyback absorption circuit also includes a third diode D3 and a fourth diode D4; the cathode of the third diode D3 is electrically connected to the drain of the first MOS tube; the anode of the third diode D3 is electrically connected to the drain of the second MOS tube; the cathode of the fourth diode D4 is electrically connected to the source of the first MOS tube; and the anode of the fourth diode D4 is electrically connected to the source of the second MOS tube.

[0036] In this embodiment, the dual-transistor flyback absorption circuit further includes a fifth diode D5; the fifth diode D5 is connected in series with one end of the output transformer T1.

[0037] In this embodiment, the dual-transistor flyback absorption circuit further includes a capacitor C3 and a resistor R7; the capacitor C3 and the resistor R7 are connected in parallel to the two ends of the secondary side of the output transformer T1 to filter the output voltage of the output transformer T1.

[0038] The working process of the dual-tube flyback absorption circuit provided in this embodiment is as follows: When the first MOS tube G1 and the second MOS tube G2 are both turned on, the current of the double-tube flyback absorption circuit flows through the Figure 2 As shown. The current flows from the DC bus VBUS to the first MOS tube G1, then to the upper and lower ends of the primary coil of the output transformer T1, and then to the DC bus GND from the second MOS tube G2. From the relationship between the primary and secondary terminals of the output transformer T1, it can be seen that the upper end of the primary side of the output transformer T1 and the lower end of the secondary side of the output transformer T1 are positive electrodes, and the lower end of the primary side of the output transformer T1 and the upper end of the secondary side of the output transformer T1 are negative electrodes. At this time, the fifth diode D5 is cut off, and energy cannot be transferred from the primary side of the output transformer T1 to the secondary side. At this time, the energy is stored in the primary coil of the output transformer T1. At the same time, the first MOS tube G1, the first absorption capacitor C1, and the first consumption resistor R1 form a loop, and the energy of the first absorption capacitor C1 is consumed by the first consumption resistor R1; the second MOS tube G2, the second absorption capacitor C2, and the second consumption resistor R2 form a loop, and the energy of the second absorption capacitor C2 is consumed by the second consumption resistor R2.

[0039] When the first MOS tube G1 and the second MOS tube G2 are both turned off, the current direction of the inductor coil in the output transformer T1 cannot change suddenly, and it continues to flow from the upper end of the primary side of the output transformer T1 to the lower end. At this time, the voltage polarity of the secondary side of the output transformer T1 is reversed, with positive on the upper side and negative on the lower side. At this time, D5 is in the on state, and energy is transferred from the primary side to the secondary side. The current flow path at this time is as follows: Figure 3 As shown, the current flows from the DC bus VBUS through the first absorption capacitor C1 and the first diode D1 to the primary side of the output transformer T1, and then flows from the lower end of the output transformer T1 through the second absorption capacitor C2 and the second diode D2 to the DC bus GND. At this time, the leakage inductance current of the primary side of the output transformer T1 is absorbed by the capacitor C2, thereby resetting the magnetic core of the transformer.

[0040] In summary, the present invention provides a dual-tube flyback absorption circuit, including: a first flyback absorption module, a second flyback absorption module and an output transformer T1; the first flyback absorption module and the second flyback absorption module are respectively connected to the DC bus VBUS and the DC bus GND; the first flyback absorption module and the second flyback absorption module are respectively electrically connected to the two ends of the primary coil of the output transformer T1, and are suitable for absorbing the leakage inductance current of the output transformer T1 and returning it to the primary coil of the output transformer T1. By setting the first flyback absorption module and the second flyback absorption module, the leakage inductance current of the transformer T1 is returned to the bus voltage, which saves energy and improves the utilization rate. At the same time, each flyback absorption module is provided with a MOS tube, and the overall withstand voltage of the circuit is doubled compared with that of an ordinary single-tube flyback. Two resistors are directly connected to the gate of the MOS tube, which can adjust the switching speed of the MOS tube, the Miller platform oscillation waveform, and the discharge of the Miller capacitor. At the same time, a release loop can be provided for the GS capacitor in the MOS tube while removing the high-voltage static electricity of the external circuit.

[0041] All devices (parts without specific structure) selected in this application are universal standard parts or parts known to those skilled in the art, and their structures and principles can be known by those skilled in the art through technical manuals or conventional experimental methods. In addition, the software programs involved in this application are all prior art, and this application does not involve any improvement to the software programs.

[0042] In the description of the present invention, it should be noted that the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", etc., indicating the orientation or positional relationship, are based on the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as limiting the present invention. In addition, the terms "first", "second", and "third" are used for descriptive purposes only, and cannot be understood as indicating or implying relative importance.

[0043] In the several embodiments provided in the present application, it should be understood that the disclosed systems, devices and methods can be implemented in other ways. The device embodiments described above are merely schematic. For example, the division of the units is only a logical function division. There may be other division methods in actual implementation. For example, multiple units or components can be combined or integrated into another system, or some features can be ignored or not executed. Another point is that the mutual coupling or direct coupling or communication connection shown or discussed can be through some communication interfaces, and the indirect coupling or communication connection of devices or units can be electrical, mechanical or other forms.

[0044] The units described as separate components may or may not be physically separated, and the components shown as units may or may not be physical units, that is, they may be located in one place or distributed on multiple network units. Some or all of the units may be selected according to actual needs to achieve the purpose of the solution of this embodiment.

[0045] In addition, each functional unit in each embodiment of the present invention may be integrated into one processing unit, or each unit may exist physically separately, or two or more units may be integrated into one unit.

[0046] Based on the above ideal embodiments of the present invention, the relevant staff can make various changes and modifications without departing from the technical concept of the present invention through the above description. The technical scope of the present invention is not limited to the contents of the specification, and its technical scope must be determined according to the scope of the claims.

Claims

1. A dual-transistor flyback absorption circuit, characterized in that: include: A first flyback absorption module, a second flyback absorption module and an output transformer T1; The first flyback absorption module and the second flyback absorption module are respectively connected to the DC bus VBUS and the DC bus GND; The first flyback absorption module and the second flyback absorption module are electrically connected to both ends of the primary coil of the output transformer T1 respectively, and are suitable for absorbing the leakage inductance current of the output transformer T1 and returning it to the primary coil of the output transformer T1.

2. The double-transistor flyback absorption circuit according to claim 1, characterized in that: The first flyback absorption module comprises: A first MOS tube, a first absorption capacitor C1, a first consumption resistor R1 and a first diode D1; The drain of the first MOS tube is electrically connected to the DC bus VBUS; The source of the first MOS tube is electrically connected to one end of the primary coil of the output transformer T1; Two ends of the first absorption capacitor C1 and the first consumption resistor R1 connected in series are electrically connected to the drain and source of the first MOS tube respectively; The anode of the first diode D1 is electrically connected between the first absorption capacitor C1 and the first consumption resistor R1 , and the cathode of the first diode D1 is electrically connected between the source of the first MOS tube and the first consumption resistor R1 .

3. The double-transistor flyback absorption circuit as claimed in claim 2, characterized in that: The second flyback absorption module includes: A second MOS tube, a second absorption capacitor C2, a second consumption resistor R2 and a second diode D2; The drain of the second MOS tube is electrically connected to one end of the primary coil of the output transformer T1; The source of the second MOS tube is electrically connected to the DC bus GND; Two ends of the second absorption capacitor C2 and the second consumption resistor R2 connected in series are electrically connected to the drain and source of the second MOS tube respectively; The anode of the second diode D2 is electrically connected between the second absorption capacitor C2 and the second consumption resistor R2, and the cathode of the second diode D2 is electrically connected between the source of the second MOS tube and the second consumption resistor R2.

4. The double-transistor flyback absorption circuit as claimed in claim 3, characterized in that: The dual-tube flyback absorption circuit also includes a driving transformer T2; The primary coil of the driving transformer T2 is electrically connected to an external driving source; Two ends of the secondary coil T21 of the driving transformer T2 are electrically connected to the gate of the first MOS transistor and the source of the first MOS transistor respectively; Two ends of the secondary coil T22 of the driving transformer T2 are electrically connected to the gate of the second MOS transistor and the source of the second MOS transistor respectively.

5. The double-transistor flyback absorption circuit as claimed in claim 4, characterized in that: The first flyback absorption module also includes a resistor R3; The gate of the first MOS transistor is electrically connected to the secondary coil T21 of the driving transformer T2 through the resistor R3.

6. The double-transistor flyback absorption circuit as claimed in claim 5, characterized in that: The first flyback absorption module also includes a resistor R4; One end of the resistor R4 is electrically connected between the resistor R3 and the gate of the first MOS transistor, and the other end of the resistor R4 is electrically connected to the source of the first MOS transistor.

7. The double-transistor flyback absorption circuit as claimed in claim 4, characterized in that: The second flyback absorption module also includes a resistor R5; The gate of the second MOS transistor is electrically connected to the secondary coil T22 of the driving transformer T2 through the resistor R5.

8. The double-transistor flyback absorption circuit as claimed in claim 7, characterized in that: The second flyback absorption module also includes a resistor R6; One end of the resistor R6 is electrically connected between the resistor R5 and the gate of the second MOS transistor, and the other end of the resistor R6 is electrically connected to the source of the second MOS transistor.

9. The double-transistor flyback absorption circuit as claimed in claim 3, characterized in that: The double-tube flyback absorption circuit also includes a third diode D3 and a fourth diode D4; The cathode of the third diode D3 is electrically connected to the drain of the first MOS tube; The anode of the third diode D3 is electrically connected to the drain of the second MOS tube; The cathode of the fourth diode D4 is electrically connected to the source of the first MOS tube; An anode of the fourth diode D4 is electrically connected to a source of the second MOS transistor.

10. The double-transistor flyback absorption circuit according to claim 1, characterized in that: The dual-tube flyback absorption circuit also includes a fifth diode D5; The fifth diode D5 is connected in series with one end of the output transformer T1.

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