Circuit for realizing zero voltage turn-on of primary switch tube using synchronous rectification controller

Abstract

The utility model provides a circuit for realizing zero-voltage switching of a primary switch tube by using a synchronous rectification controller, comprising: a first capacitor and a first diode, wherein the first capacitor is electrically connected to a second resistor, wherein the second resistor is electrically connected to a first transistor, wherein the first transistor is electrically connected to a primary controller; and a transformer, wherein the transformer is electrically connected to the first transistor, and the right side of the transformer is electrically connected to a second transistor. The circuit for realizing zero-voltage switching of a primary switch tube by using a synchronous rectification controller provided by the utility model has a simple circuit structure, is stable and reliable, and only a few resistors and capacitors need to be added to the existing QR circuit with synchronous rectification to realize the ZVS function, and the ZVS control module 17 can be made into a fixed Vzvs voltage or an adaptive ZVS, and the Vzvs voltage is adjusted according to the output power, input voltage, and output voltage to realize the ZVS function under all working conditions, thereby reducing the switching loss.

Description

Technical Field

[0001] The utility model relates to the technical field of switch power supply conversion application, in particular to a circuit for realizing zero-voltage switching of a primary switch tube by utilizing a synchronous rectification controller. Background Art

[0002] In the application of portable PD power supply, small size, high power density, improving efficiency and reducing heat are the unanimous goals. Zero voltage turn-on technology can greatly reduce the turn-on loss of the switch tube and is recognized as the optimal control method to improve efficiency.

[0003] The QR flyback power supply turns on the primary switch tube when the switch tube Vds voltage resonates to the valley voltage. The valley voltage is Vin-N*Vo, where Vin is the input voltage, N is the transformer primary-secondary winding turns ratio, N=Np / Ns, Np is the transformer primary winding, Ns is the transformer secondary winding, and Vo is the output voltage. When the input voltage is high, such as with PFC in the front stage, and the output voltage is low, Vin will be much larger than N*Vo, resulting in large turn-on losses.

[0004] Therefore, it is necessary to provide a circuit that uses a synchronous rectifier controller to achieve zero voltage turn-on of the primary switch tube to solve the above technical problems. Utility Model Content

[0005] The utility model provides a circuit which utilizes a synchronous rectification controller to realize zero-voltage switching of a primary switch tube, thereby solving the problem of relatively large switching loss.

[0006] In order to solve the above technical problems, the utility model provides a circuit for realizing zero voltage switching of a primary switch tube by using a synchronous rectification controller, comprising:

[0007] a first capacitor and a first diode, the first capacitor is electrically connected to a second resistor, the second resistor is electrically connected to a first transistor, and the first transistor is electrically connected to a primary controller;

[0008] A transformer, the transformer is electrically connected to the first transistor, the right side of the transformer is electrically connected to a second transistor, the second transistor is electrically connected to a synchronous rectification controller, the synchronous rectification controller is electrically connected to a first bias resistor and a fourth capacitor, the fourth capacitor is electrically connected to a second bias resistor, and the second bias resistor is electrically connected to a ZVS control module.

[0009] Preferably, the first capacitor is also electrically connected to a first resistor, a second capacitor and a ground wire, and the first resistor and the second capacitor are both electrically connected to the first diode.

[0010] Preferably, the first resistor, the second capacitor and the first diode are all electrically connected to the transformer.

[0011] Preferably, the second resistor is electrically connected to the ground wire.

[0012] Preferably, the transformer is also electrically connected to a third resistor, and the third resistor is electrically connected to the synchronous rectification controller.

[0013] Preferably, the transformer is also electrically connected to a third capacitor, the third capacitor is electrically connected to the first bias resistor, and the ZVS control module is also electrically connected to the third capacitor and the first bias resistor.

[0014] Preferably, the primary controller turns on the primary switch tube, and the synchronous rectification controller is MP6908, SC3501 and MK91808.

[0015] Compared with the related art, the circuit provided by the utility model for realizing zero voltage switching of the primary switch tube by using the synchronous rectification controller has the following beneficial effects:

[0016] The utility model provides a circuit for realizing zero voltage turn-on of a primary switch tube by using a synchronous rectification controller. The circuit structure is simple, stable and reliable. In the existing QR circuit with synchronous rectification, only a few resistors and capacitors need to be added to realize the ZVS function. The ZVS control module 17 can be made into a fixed Vzvs voltage or an adaptive ZVS. The Vzvs voltage is adjusted according to the output power, input voltage and output voltage to realize the ZVS function under all working conditions, thereby reducing the turn-on loss. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 This is a traditional QR flyback circuit diagram with synchronous rectification function;

[0018] Figure 2 A schematic structural diagram of a preferred embodiment of a circuit for realizing zero-voltage switching of a primary switch tube by using a synchronous rectification controller provided by the utility model;

[0019] Figure 3 for Figure 2 The typical working timing waveform shown;

[0020] Figure 4 This is a workflow diagram of a ZVS control module for adaptive ZVS.

[0021] Numbers in the figure: 1. first capacitor, 2. first resistor, 3. second capacitor, 4. first diode, 5. primary controller, 6. second resistor, 7. ground wire, 8. first transistor, 9. third resistor, 10. transformer, 11. second transistor, 12. first bias resistor, 13. third capacitor, 14. synchronous rectification controller, 15. fourth capacitor, 16. second bias resistor, 17. ZVS control module. DETAILED DESCRIPTION

[0022] The utility model is further described below in conjunction with the accompanying drawings and implementation modes.

[0023] Please refer to Figure 2 , Figure 3 , Figure 4 ,in, Figure 2 A schematic structural diagram of a preferred embodiment of a circuit for realizing zero-voltage switching of a primary switch tube by using a synchronous rectification controller provided by the utility model; Figure 3 for Figure 2 The typical working timing waveform shown; Figure 4 The following is a flowchart of a ZVS control module for adaptive ZVS. A circuit for realizing zero voltage turn-on of a primary switch tube using a synchronous rectifier controller includes: a first capacitor 1 and a first diode 4, wherein the first capacitor 1 is electrically connected to a second resistor 6, wherein the second resistor 6 is electrically connected to a first transistor 8, and wherein the first transistor 8 is electrically connected to a primary controller 5;

[0024] Transformer 10, the transformer 10 is electrically connected to the first transistor 8, the right side of the transformer 10 is electrically connected to the second transistor 11, the second transistor 11 is electrically connected to the synchronous rectification controller 14, the synchronous rectification controller 14 is electrically connected to the first bias resistor 12 and the fourth capacitor 15, the fourth capacitor 15 is electrically connected to the second bias resistor 16, and the second bias resistor 16 is electrically connected to the ZVS control module 17.

[0025] The first capacitor 1 is also electrically connected to a first resistor 3 , a second capacitor 3 and a grounding wire 7 , and the first resistor 2 and the second capacitor 3 are both electrically connected to the first diode 4 .

[0026] The first resistor 2 , the second capacitor 3 , and the first diode 4 are all electrically connected to the transformer 10 .

[0027] The second resistor 6 is electrically connected to the ground line 7 .

[0028] The transformer 10 is also electrically connected to a third resistor 9 , and the third resistor 9 is electrically connected to the synchronous rectification controller 14 .

[0029] The transformer 10 is also electrically connected to a third capacitor 13 , and the third capacitor 13 is electrically connected to the first bias resistor 12 . The ZVS control module 17 is also electrically connected to the third capacitor 13 and the first bias resistor 12 .

[0030] The primary controller 5 turns on the primary switch tube, and the synchronous rectification controller 14 is MP6908, SC3501 and MK91808.

[0031] When ZVS needs to be implemented, the ZVS control module 17 sends out a Vzvs voltage, and the Vzvs voltage then biases the GND pin voltage of the synchronous rectifier controller, so that the synchronous rectifier controller 14 turns off the synchronous rectifier switch tube only when a certain reverse excitation current (different from the forward excitation current when the primary switch tube is turned on) appears in the synchronous rectifier switch tube. After the synchronous rectifier switch tube is turned off, the reverse excitation current is coupled to the primary side and continues to flow, so that the Vds voltage of the primary switch tube is reduced to close to zero volts or zero volts. At this time, the primary switch tube is turned on to implement ZVS turn-on control. When ZVS is not needed, the Vzvs voltage sent by the ZVS control module 17 is close to zero volts, and the circuit works in the normal QR fixed conduction mode.

[0032] The working principle of the circuit provided by the utility model for realizing zero voltage switching of the primary switch tube by using a synchronous rectification controller is as follows:

[0033] At time t1, the circuit operates in the traditional QR valley conduction mode, the Vzvs voltage of the ZVS control signal module 17 is a low level close to zero, the primary Vds oscillates to the valley voltage Vin-N*Vo, the primary controller 5 turns on the primary switch tube, and the secondary synchronous rectification controller is a universal synchronous rectification controller 14, including MP6908, SC3501, MK91808 and other universal models. When used normally, its GND Pin is connected to the Source pole of the SR MOS, and the SR MOS is turned on when the Vd_sr voltage is lower than Vd_on (usually around -100mV), and when the Vds_sr voltage rises to Vd_off (usually ≈0mV), that is, Vds_sr-V sr_gnd=Vds_off≈0mV, the SR MOS is turned off. Rd is the series resistor of Vd_sr. During the conduction period of SR MOS, the current flowing through it is very small, as low as a few uA level. The resistance value of Rd is usually within 1K ohm, so the voltage drop across the Rd resistor can be ignored during the conduction period of SR MOS.

[0034] At time t2, the circuit works in ZVS mode. The working principle of ZVS mode is as follows: the Vzvs voltage sent by the ZVS control module 17 is a higher level, which generates a bias voltage Vsr_gnd on the GND pin of the synchronous rectifier controller 14 through Rb1 and Rb2. Since Vsr_gnd≈Vzvs*Rb1 / (Rb1+Rb2), the SR controller will

[0035] When Vd_sr-Vsr_gnd=Vds_off≈0mV, turn off SR MOS, and there is a relationship:

[0036] Vd_sr=Ids*Rds_on≈Vzvs*Rb1 / (Rb1+Rb2)

[0037] Ids≈ Vzvs*Rb1 / (Rb1+Rb2) / Rds_on

[0038] At this time, Ids will be a positive current, flowing from the D pole of the SR MOS to the S pole. After the SR MOS is turned off, Ids will be coupled to the primary side through the transformer and become Ids / N, where N is the turns ratio of the primary and secondary windings of the transformer.

[0039] N=Np / Ns, the Ids / N current flows in from the same-name end and out from the opposite-name end, helping to resonate the Vds voltage across the D-pole equivalent capacitor Cp of the primary switch tube to near zero or zero volts. When Vds drops to zero volts, the primary switch tube is turned on, and the ZVS function is realized. The Ids current for achieving ZVS can be easily adjusted through the resistance values ​​of Rb1 and Rb2 and the Vzvs voltage, so that the ZVS function can be achieved under different input voltages and output voltages;

[0040] At time t3, the excitation current of transformer 10 passes through the zero point, and SR MOS continues to conduct, generating a positive excitation current for transformer 10, and assisting the primary switch tube to achieve ZVS;

[0041] At t4, Vd_sr-Vsr_gnd=Vds_off≈0mV, the SR controller turns off the SR MOS, and the Ids current is a forward current, Ids≈Vzvs*Rb1 / (Rb1+Rb2) / Rds_on;

[0042] At time t5, with the assistance of the reverse excitation current Ids / N, the primary switch tube Vds voltage resonates to zero volts, turning on the primary switch tube to achieve ZVS conduction.

[0043] Compared with the related art, the circuit provided by the utility model for realizing zero voltage switching of the primary switch tube by using the synchronous rectification controller has the following beneficial effects:

[0044] The circuit structure is simple, stable and reliable. In the existing QR circuit with synchronous rectification, only a few resistors and capacitors need to be added to realize the ZVS function. The ZVS control module 17 can be made into a fixed Vzvs voltage or an adaptive ZVS. The Vzvs voltage can be adjusted according to the output power, input voltage and output voltage to realize the ZVS function under all working conditions, thereby reducing the turn-on loss.

[0045] The above description is only an embodiment of the present invention, and does not limit the patent scope of the present invention. Any equivalent structure or equivalent process transformation made by using the contents of the specification and drawings of the present invention, or directly or indirectly applied in other related technical fields, are also included in the patent protection scope of the present invention.

Claims

1. A circuit for realizing zero voltage turn-on of a primary switch tube by using a synchronous rectification controller, characterized in that: include: a first capacitor and a first diode, the first capacitor is electrically connected to a second resistor, the second resistor is electrically connected to a first transistor, and the first transistor is electrically connected to a primary controller; A transformer, the transformer is electrically connected to the first transistor, the right side of the transformer is electrically connected to a second transistor, the second transistor is electrically connected to a synchronous rectification controller, the synchronous rectification controller is electrically connected to a first bias resistor and a fourth capacitor, the fourth capacitor is electrically connected to a second bias resistor, and the second bias resistor is electrically connected to a ZVS control module.

2. The circuit for realizing zero voltage switching of a primary switch tube by using a synchronous rectification controller according to claim 1, characterized in that: The first capacitor is also electrically connected to a first resistor, a second capacitor and a grounding wire, and the first resistor and the second capacitor are both electrically connected to the first diode.

3. The circuit for realizing zero voltage switching of a primary switch tube by using a synchronous rectification controller according to claim 2, characterized in that: The first resistor, the second capacitor and the first diode are all electrically connected to the transformer.

4. The circuit for realizing zero voltage switching of a primary switch tube by using a synchronous rectification controller according to claim 3, characterized in that: The second resistor is electrically connected to the ground line.

5. The circuit for realizing zero voltage switching of a primary switch tube by using a synchronous rectification controller according to claim 4, characterized in that: The transformer is also electrically connected to a third resistor, and the third resistor is electrically connected to the synchronous rectification controller.

6. The circuit for realizing zero voltage switching of a primary switch tube by using a synchronous rectification controller according to claim 5, characterized in that: The transformer is also electrically connected to a third capacitor, the third capacitor is electrically connected to the first bias resistor, and the ZVS control module is also electrically connected to the third capacitor and the first bias resistor.

7. The circuit for realizing zero voltage switching of a primary switch tube by using a synchronous rectification controller according to claim 1, characterized in that: The primary controller turns on the primary switch tube, and the synchronous rectification controller is MP6908, SC3501 and MK91808.

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