Fly-buck circuit and switching power supply

Abstract

The utility model discloses a fly-buck circuit and a switching power supply, the circuit comprises a fly-buck control IC, a main power supply loop, an auxiliary power supply loop and a coupling capacitor, the input end of the control IC is used for being connected with the input end of the switching power supply, the output end of the control IC is connected with the input end of the main power supply loop, and the main power supply loop and the auxiliary power supply loop are in coupling connection through the coupling capacitor. The coupling capacitor is connected between the main power supply loop and the auxiliary power supply loop, one end of the coupling capacitor is connected with the output end of the control IC, and the other end of the coupling capacitor is connected with the drain electrode of the main power tube; when the main power tube is switched on, the control IC supplies power to the floating drive of the drive circuit through the auxiliary power supply loop and supplies power to the control IC, except the drive circuit, of the switching power supply through the main power supply loop, and when the main power tube is switched off, the coupling capacitor couples the Vds voltage of the main power tube and provides energy for the main auxiliary circuit independently or together with the control IC. Therefore, the driving frequency of the built-in MOS tube is reduced or turned off by the control IC, the power consumption of the fly-buck circuit is reduced, and the efficiency of the switching power supply is improved.

Description

Technical Field

[0001] The utility model relates to the technical field of power supply, in particular to a fly-buck circuit and a switching power supply. Background Art

[0002] As switching power supplies continue to develop, the requirements for high efficiency and low power consumption of power modules are getting higher and higher. Therefore, it is particularly important to continuously optimize the efficiency and loss of each functional circuit inside the power module.

[0003] At present, the commonly used fly-buck circuit and switching power supply solutions are as follows Figure 1 As shown, during the entire operation period of the power module, the main and auxiliary paths of the fly-buck circuit provide energy to the outside through the fly-buck control IC, which results in large losses in the fly-buck circuit inside the power module and low overall efficiency of the power module. Utility Model Content

[0004] In view of the above background, the utility model provides a fly-buck circuit and a switching power supply. The fly-buck circuit fully works only during the startup process of the power module. After the output of the power module is established, due to the presence of the coupling capacitor CL, the Vds voltage of the main power tube TR2 can be coupled to provide energy for the fly-buck main and auxiliary circuits, thereby reducing the fly-buck control IC drive frequency or even shutting down the built-in MOS tube drive, thereby achieving the purpose of reducing the power consumption of the fly-buck circuit and improving the efficiency of the power module.

[0005] In order to achieve the above purpose, the utility model proposes the following technical solutions:

[0006] In a first aspect, a fly-buck circuit is provided, which is applied to a switching power supply, wherein the switching power supply comprises a forward active clamping circuit and a driving circuit, wherein the forward active clamping circuit comprises a transformer, a main power tube, a clamping tube, and a clamping capacitor, wherein the fly-buck circuit comprises: a fly-buck control IC, a main power supply circuit, an auxiliary power supply circuit, and a coupling capacitor, wherein an input end of the fly-buck control IC is used to be connected to an input end of the switching power supply, and an output end is connected to an input end of the main power supply circuit, wherein the main power supply circuit is coupled to the auxiliary power supply circuit via a coupling inductor, and the coupling capacitor is connected to the auxiliary power supply circuit via a coupling inductor. between the main power supply circuit and the auxiliary power supply circuit, and one end of the coupling capacitor is connected to the output end of the fly-buck control IC, and the other end of the coupling capacitor is connected to the drain of the main power tube; when the main power tube is turned on, the fly-buck control IC supplies power to the floating drive of the drive circuit through the auxiliary power supply circuit, and supplies power to the control IC of the switching power supply other than the drive circuit through the main power supply circuit; when the main power tube is turned off, the coupling capacitor couples the Vds voltage of the main power tube, and provides energy to the main power supply circuit and the auxiliary power supply circuit alone or together with the fly-buck control IC.

[0007] Preferably, the coupled inductor includes a first winding and a second winding, and the main power supply circuit includes a freewheeling tube D1, a capacitor C1 and the first winding of the coupled inductor; the cathode of the diode D1 is connected to one end of the first winding and serves as the input end of the main power supply circuit, and is connected to the output end of the fly-buck control IC and one end of the coupling capacitor; the anode of the diode D1 is connected to one end of the capacitor C1 and then grounded, and the other end of the capacitor C1 is connected to two ends of the first winding and serves as the output end of the main power supply circuit.

[0008] Preferably, the auxiliary power supply circuit includes a rectifier tube D2, a capacitor C2 and a second winding of the coupled inductor; after the 4 ends of the second winding are connected to the other end of the coupling capacitor and the other end of the capacitor C2, they are used to be connected to the drain of the main power tube, the source of the clamp tube and the 2 ends of the primary winding of the transformer and the SW end of the drive circuit; after the other end of the capacitor C2 is connected to the cathode of the rectifier tube C2, it serves as the output end of the auxiliary power supply circuit and is used to be connected to the BST end of the drive circuit; the cathode of the rectifier tube D2 is connected to the 3 ends of the second winding.

[0009] Preferably, when the main power tube is turned off, the fly-buck control IC reduces the switching frequency of the built-in MOS tube or turns off the MOS tube according to the load of the switching power supply through its internal feedback network, so that the coupling capacitor alone or together with the fly-buck control IC provides energy for the main power supply circuit and the auxiliary power supply circuit.

[0010] In a second aspect, a fly-buck circuit is provided, which is applied to a switching power supply, wherein the switching power supply includes a forward active clamping circuit and a driving circuit, wherein the forward active clamping circuit includes a transformer, a main power tube, a clamping tube, and a clamping capacitor, and the fly-buck circuit includes: a fly-buck control IC, a main power supply circuit, an auxiliary power supply circuit, and a coupling capacitor, wherein the main power supply circuit and the auxiliary power supply circuit are coupled through a coupling inductor; the main power supply circuit includes a freewheeling tube D1, a capacitor C1, and a first winding of the coupling inductor; the auxiliary power supply circuit includes a rectifier tube D2, a capacitor C2, and a second winding of the coupling inductor; the input end of the fly-buck control IC is used to be connected to the input end of the switching power supply; after the cathode of the diode D1 is connected to the 1 end of the first winding As the input end of the main power supply circuit, it is connected to the output end of the fly-buck control IC and one end of the coupling capacitor. The anode of the diode D1 is connected to one end of the capacitor C1 and then grounded; the other end of the capacitor C1 is connected to the two ends of the first winding and then serves as the output end of the main power supply circuit, which is used to be connected to the power supply end of the control IC of the switching power supply other than the drive circuit; the four ends of the second winding are connected to the other end of the coupling capacitor and the other end of the capacitor C2, and then are used to be connected to the drain of the main power tube, the source of the clamp tube and the two ends of the primary winding of the transformer, and the SW end of the drive circuit; the other end of the capacitor C2 is connected to the cathode of the rectifier tube C2, and then serves as the output end of the auxiliary power supply circuit, which is used to be connected to the BST end of the drive circuit; the cathode of the rectifier tube D2 is connected to the three ends of the second winding.

[0011] In a third aspect, a switching power supply is provided, comprising a forward active clamping circuit, a driving circuit and the fly-buck circuit as described above, wherein the forward active clamping circuit comprises a transformer, a main power tube, a clamping tube and a clamping capacitor.

[0012] Compared with the prior art, the utility model has the following beneficial effects:

[0013] The fly-buck circuit of the utility model fully works only during the startup process of the power module. After the output of the power module is established, due to the presence of the coupling capacitor CL, the Vds voltage of the main power tube TR2 can be coupled to provide energy for the fly-buck main and auxiliary circuits, thereby reducing the fly-buck control IC drive frequency or even shutting down the built-in MOS tube drive, thereby reducing the fly-buck circuit power consumption and improving the efficiency of the power module. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 It is a schematic diagram of a fly-buck circuit used in the prior art;

[0015] Figure 2The cathode voltage waveform of the freewheeling tube D1 of the fly-buck circuit used in the prior art;

[0016] Figure 3 This is a schematic diagram of the fly-buck circuit of the utility model;

[0017] Figure 4 The cathode voltage waveform of the freewheeling tube D1 of the fly-buck circuit described in the utility model;

[0018] Figure 5 Schematic diagram of an equivalent model of the voltage division of the Vds voltage SW of the main power tube TR2 through the coupling capacitor CL and the parasitic capacitor CD1 of the freewheeling tube D1. DETAILED DESCRIPTION

[0019] The following is a more clear and complete description of the technical solution of the present utility model in conjunction with the accompanying drawings in the present embodiment. It should be understood that the specific embodiments described herein are only used to explain the present utility model and are not used to limit the present utility model.

[0020] Any feature disclosed in this specification (including any abstract and drawings), unless otherwise stated, may be replaced by other equivalent or alternative features with similar purposes. That is, unless otherwise stated, each feature is only an example of a series of equivalent or similar features.

[0021] It should be noted that the terms "including" and "having" and any variations thereof described in the specification and claims of the present application are intended to cover non-exclusive inclusions. For example, the inclusion of a series of components or unit circuits is not necessarily limited to those components or unit circuits explicitly listed, but may include components or unit circuits that are not explicitly listed or inherent to these circuits.

[0022] Figure 3FIG. 1 is a schematic diagram of the fly-buck circuit of the present embodiment. In the present embodiment, a low-power fly-buck circuit is provided, which is applied to a switching power supply. The switching power supply includes a forward active clamping circuit 300 and a driving circuit 200. The forward active clamping circuit 300 includes a transformer, a main power tube, a clamping tube, and a clamping capacitor. The fly-buck circuit includes: a fly-buck control IC, a main power supply circuit, an auxiliary power supply circuit, and a coupling capacitor. The input end of the fly-buck control IC is used to be connected to the input end of the switching power supply, and the output end is connected to the input end of the main power supply circuit. The main power supply circuit and the auxiliary power supply circuit are coupled. The inductive coupling connection is combined, the coupling capacitor is connected between the main power supply circuit and the auxiliary power supply circuit, and one end of the coupling capacitor is connected to the output end of the fly-buck control IC, and the other end of the coupling capacitor is connected to the drain of the main power tube; when the main power tube is turned on, the fly-buck control IC supplies power to the floating drive of the drive circuit through the auxiliary power supply circuit, and supplies power to the control IC of the switching power supply other than the drive circuit through the main power supply circuit; when the main power tube is turned off, the coupling capacitor couples the Vds voltage of the main power tube, and provides energy to the main power supply circuit and the auxiliary power supply circuit alone or together with the fly-buck control IC.

[0023] Specifically, the coupled inductor includes a first winding and a second winding. As a specific implementation of the main power supply circuit, the main power supply circuit includes a freewheeling tube D1, a capacitor C1 and the first winding of the coupled inductor; the cathode of the diode D1 is connected to one end of the first winding and serves as the input end of the main power supply circuit, and is connected to the output end of the fly-buck control IC and one end of the coupling capacitor. The anode of the diode D1 is connected to one end of the capacitor C1 and then grounded. The other end of the capacitor C1 is connected to two ends of the first winding and serves as the output end of the main power supply circuit.

[0024] As a specific implementation of the auxiliary power supply circuit, the auxiliary power supply circuit includes a rectifier tube D2, a capacitor C2 and a second winding of the coupling inductor; after the 4 ends of the second winding are connected to the other end of the coupling capacitor and the other end of the capacitor C2, they are used to be connected to the drain of the main power tube, the source of the clamp tube and the 2 ends of the primary winding of the transformer and the SW end of the drive circuit; after the other end of the capacitor C2 is connected to the cathode of the rectifier tube C2, it serves as the output end of the auxiliary power supply circuit and is used to be connected to the BST end of the drive circuit; the cathode of the rectifier tube D2 is connected to the 3 ends of the second winding.

[0025] The output Vcc1 of the main power supply circuit is used to power other control ICs, and the output Vcc2 of the auxiliary power supply circuit is used to power the floating drive of the drive circuit 200. The two drives of the drive circuit 200 are respectively connected to the main power tube and the clamp tube of the active clamp circuit 300.

[0026] Specifically, the working principle of the fly-buck circuit is: when the built-in MOS tube of the fly-buck control IC switches, the cathode of the rectifier tube D2 generates a square wave voltage with a peak value of Vin, which excites and demagnetizes the coupled inductor, and provides energy to the output Vcc1 of the main power supply circuit and the output Vcc2 of the auxiliary power supply circuit during the excitation and demagnetization process.

[0027] When the main power tube is turned off, the coupling capacitor couples the Vds square wave voltage of the main power tube and divides the voltage through the parasitic capacitance of the freewheeling tube D1. When the built-in MOS tube switch of the fly-buck control IC is replaced, the cathode of the rectifier tube D2 generates a square wave voltage with a peak value of Vin, which provides energy for the main and auxiliary outputs, so that the fly-buck control IC reduces the driving frequency of the built-in MOS tube, or even completely turns off the built-in MOS tube drive.

[0028] Specifically, the control IC U1 includes: a first input terminal, a second input terminal, a third input terminal, a fourth input terminal and a fifth output terminal, and the coupling inductor L1 includes: a first input terminal, a fourth input terminal, a second output terminal and a third output terminal, wherein the first input terminal and the fourth input terminal are terminals of the same name; the first input terminal, the second input terminal, the third input terminal and the fourth input terminal of the control IC U1 are connected to the input voltage Vin, and the fifth output terminal of the control IC U1 is connected to the cathode of the freewheeling tube D1, the first input terminal of the coupling inductor L1 and one end of the coupling capacitor CL; the anode of the freewheeling tube D1 is grounded; the second output terminal of the coupling inductor L1 is connected to one end of the filter capacitor C1 as the main output Vcc1; the other end of the filter capacitor C1 is grounded; the other end of the coupling capacitor CL is connected to the fourth input terminal of the coupling inductor L1 and one end of the filter capacitor C2 as the SW terminal; the third output terminal of the coupling inductor L1 is connected to the anode of the rectifier tube D2; the cathode of the rectifier tube D2 is connected to the other end of the filter capacitor C2 as the output Vcc2 of the auxiliary power supply circuit.

[0029] Specifically, Figure 5 The equivalent model diagram of the voltage division of the Vds voltage SW of the main power tube TR2 through the coupling capacitor CL and the parasitic capacitor CD1 of the freewheeling tube, and the voltage division relationship satisfies:

[0030]

[0031] Among them, V D1 Represents the voltage of the cathode of diode D1, SW represents the Vds voltage of the main power tube TR2, CL Characterizes the capacitance of the coupling capacitor, C D1 Characterizes the capacitance of the parasitic capacitance CD1 of the diode D1.

[0032] Specifically, the control IC has a built-in MOS tube, and reduces the driving frequency or even turns off the built-in MOS tube driving according to the actual load situation.

[0033] Specifically, the driving circuit 200 is a driving IC U2, having four terminals: a BST terminal, a SW terminal, a HO terminal and a LO terminal; the BST terminal is connected to the cathode of the rectifier tube D2 and the other end of the filter capacitor C2 as an auxiliary power supply circuit output Vcc2, the SW terminal is connected to one end of the filter capacitor C2, the other end of the coupling capacitor CL and the D pole of the main power tube TR2; the HO terminal is connected to the G pole of the clamping tube TR1; and the LO terminal is connected to the G pole of the main power tube TR2.

[0034] Specifically, the forward active clamping circuit 300 includes a transformer T2A, a main power tube TR2, a clamping tube TR1, and a clamping capacitor C3. The transformer T2A includes a first input terminal, a sixth input terminal, a second output terminal, and a fifth output terminal, wherein the first input terminal and the sixth input terminal are terminals of the same name; one end of the clamping capacitor C3 is connected to the first input terminal of the transformer T2A and the input voltage Vin, and the other end of the clamping capacitor C3 is connected to the D pole of the clamping tube TR1; the S pole of the clamping tube TR1 is connected to the D pole of the main power tube TR2 and the second output terminal of the transformer T2A as the SW terminal; the S pole of the main power tube TR2 is grounded.

[0035] Specifically, Figure 4 As shown, the fly-buck circuit of this embodiment is fully operational only during the startup process of the power module. After the output of the power module is established, due to the presence of the coupling capacitor CL, the Vds voltage SW of the main power tube TR2 can be coupled to provide energy for the main and auxiliary circuits, thereby reducing the fly-buck control IC drive frequency or even turning off the built-in MOS tube drive, thereby reducing the power consumption of the fly-buck circuit and improving the efficiency of the power module.

[0036] The above are only preferred embodiments of the present invention, and those skilled in the art to which the present invention belongs may also make changes and modifications to the above specific embodiments. Therefore, the present invention is not limited to the specific control methods disclosed and described above, and some modifications and changes to the present invention should also fall within the scope of protection of the claims of the present invention. In addition, although some specific terms are used in this specification, these terms are only for the convenience of description and do not constitute any limitation to the present invention.

Claims

1. A fly-buck circuit, applied to a switching power supply, the switching power supply comprising a forward active clamping circuit and a driving circuit, the forward active clamping circuit comprising a transformer, a main power tube, a clamping tube, and a clamping capacitor, characterized in that: The fly-buck circuit includes: a fly-buck control IC, a main power supply circuit, an auxiliary power supply circuit and a coupling capacitor. The input end of the fly-buck control IC is used to connect to the input end of the switching power supply, and the output end is connected to the input end of the main power supply circuit. The main power supply circuit and the auxiliary power supply circuit are coupled through a coupling inductor. The coupling capacitor is connected between the main power supply circuit and the auxiliary power supply circuit, and one end of the coupling capacitor is connected to the output end of the fly-buck control IC, and the other end of the coupling capacitor is connected to the drain of the main power tube. When the main power tube is turned on, the fly-buck control IC supplies power to the floating drive of the drive circuit through the auxiliary power supply circuit, and supplies power to the control IC of the switching power supply other than the drive circuit through the main power supply circuit. When the main power tube is turned off, the coupling capacitor couples the Vds voltage of the main power tube, and provides energy to the main power supply circuit and the auxiliary power supply circuit alone or together with the fly-buck control IC.

2. The fly-buck circuit according to claim 1, characterized in that: The coupled inductor includes a first winding and a second winding, and the main power supply circuit includes a freewheeling tube D1, a capacitor C1 and the first winding of the coupled inductor; the cathode of the diode D1 is connected to one end of the first winding and serves as the input end of the main power supply circuit, and is connected to the output end of the fly-buck control IC and one end of the coupling capacitor; the anode of the diode D1 is connected to one end of the capacitor C1 and then grounded, and the other end of the capacitor C1 is connected to two ends of the first winding and serves as the output end of the main power supply circuit.

3. The fly-buck circuit according to claim 2, characterized in that: The auxiliary power supply circuit includes a rectifier tube D2, a capacitor C2 and a second winding of the coupling inductor; after the 4 ends of the second winding are connected to the other end of the coupling capacitor and the other end of the capacitor C2, they are used to be connected to the drain of the main power tube, the source of the clamp tube and the 2 ends of the primary winding of the transformer and the SW end of the drive circuit; after the other end of the capacitor C2 is connected to the cathode of the rectifier tube C2, it serves as the output end of the auxiliary power supply circuit and is used to be connected to the BST end of the drive circuit; the cathode of the rectifier tube D2 is connected to the 3 ends of the second winding.

4. The fly-buck circuit according to claim 1, characterized in that: When the main power tube is turned off, the fly-buck control IC reduces the switching frequency of the built-in MOS tube or turns off the MOS tube according to the load of the switching power supply through its internal feedback network, so that the coupling capacitor alone or together with the fly-buck control IC provides energy for the main power supply circuit and the auxiliary power supply circuit.

5. A fly-buck circuit, applied to a switching power supply, the switching power supply comprising a forward active clamping circuit and a driving circuit, the forward active clamping circuit comprising a transformer, a main power tube, a clamping tube, and a clamping capacitor, characterized in that: The fly-buck circuit includes: a fly-buck control IC, a main power supply circuit, an auxiliary power supply circuit and a coupling capacitor, wherein the main power supply circuit is coupled to the auxiliary power supply circuit through a coupling inductor; the main power supply circuit includes a freewheeling tube D1, a capacitor C1 and a first winding of the coupling inductor; the auxiliary power supply circuit includes a rectifier tube D2, a capacitor C2 and a second winding of the coupling inductor; the input end of the fly-buck control IC is used to be connected to the input end of the switching power supply; the cathode of the diode D1 is connected to one end of the first winding and serves as the input end of the main power supply circuit, and is connected to the output end of the fly-buck control IC and one end of the coupling capacitor. The anode of the diode D1 is connected to one end of the capacitor C1 and then grounded; the other end of the capacitor C1 is connected to the two ends of the first winding and serves as the output end of the main power supply circuit, which is used to be connected to the power supply end of the control IC of the switching power supply other than the driving circuit; the four ends of the second winding are connected to the other end of the coupling capacitor and the other end of the capacitor C2, and are used to be connected to the drain of the main power tube, the source of the clamp tube and the two ends of the primary winding of the transformer, and the SW end of the driving circuit; the other end of the capacitor C2 is connected to the cathode of the rectifier tube C2, and serves as the output end of the auxiliary power supply circuit, which is used to be connected to the BST end of the driving circuit; the cathode of the rectifier tube D2 is connected to the three ends of the second winding.

6. A switching power supply, characterized in that: It comprises a forward active clamping circuit, a driving circuit and a fly-buck circuit as claimed in any one of claims 1 to 5, wherein the forward active clamping circuit comprises a transformer, a main power tube, a clamping tube and a clamping capacitor.

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