Isolated step-up and step-down converter

Abstract

The utility model discloses an isolation boost buck converter, comprising a primary side circuit, a transformer and a secondary side circuit, the primary side circuit comprises a DC power supply, a first capacitor, a first switch tube, a second switch tube, a third switch tube, a first inductor, a second inductor and a freewheeling tube, and the direction of current passing through the freewheeling tube is from the second end of the freewheeling tube to the first end of the freewheeling tube. The anode of the DC power supply is connected with the first end of the first capacitor and the first end of the third switch tube, the second end of the third switch tube is connected with the first end of the first inductor, the first end of the second inductor and the first end of the follow current tube, and the second end of the first inductor is connected with the first end of the first switch tube and the first end of the primary winding. The second end of the second inductor is connected with the first end of the second switch tube and the second end of the primary winding. The cathode of the DC power supply is connected with the second end of the first capacitor, the second end of the follow current tube, the second end of the first switch tube and the second end of the second switch tube. The step-up and step-down circuit is completed through one stage, and the conversion efficiency is greatly improved.

Description

Technical Field

[0001] The utility model relates to the technical field of converters, and in particular to an isolated boost - buck converter. Background Art

[0002] An isolated boost - buck converter is a DC - DC converter, whose output voltage can be greater than the input voltage or less than the input voltage. However, the conversion efficiency of the current isolated boost - buck converter is difficult to improve, the cost is relatively high, and the circuit is complex with poor stability. Summary of the Utility Model

[0003] The purpose of the utility model is to solve the problem of improving the conversion efficiency of the isolated boost - buck converter, and provide an isolated boost - buck converter.

[0004] To achieve the above purpose, the utility model adopts the following technical solutions:

[0005] An isolated boost - buck converter includes a primary circuit, a transformer and a secondary circuit. The transformer includes a primary winding and a secondary winding. The primary circuit includes a DC power supply, a first capacitor, first to third switching tubes, first to second inductors and a free - wheeling diode. The direction of current passing through the free - wheeling diode is from the second end of the free - wheeling diode to the first end of the free - wheeling diode. The positive pole of the DC power supply is connected to the first end of the first capacitor and the first end of the third switching tube. The second end of the third switching tube is connected to the first end of the first inductor, the first end of the second inductor and the first end of the free - wheeling diode. The second end of the first inductor is connected to the first end of the first switching tube and the first end of the primary winding. The second end of the second inductor is connected to the first end of the second switching tube and the second end of the primary winding. The negative pole of the DC power supply is connected to the second end of the first capacitor, the second end of the free - wheeling diode, the second end of the first switching tube and the second end of the second switching tube.

[0006] In some embodiments, the first to third switching tubes are IGBT switching tubes. The collector of the first switching tube is connected to the second end of the first inductor and the first end of the primary winding. The emitter of the first switching tube is connected to the negative pole of the DC power supply, the second end of the first capacitor and the emitter of the second switching tube. The collector of the second switching tube is connected to the second end of the second inductor and the second end of the primary winding. The emitter of the second switching tube is connected to the negative pole of the DC power supply, the second end of the first capacitor and the emitter of the first switching tube. The collector of the third switching tube is connected to the positive pole of the DC power supply and the first end of the first capacitor. The emitter of the third switching tube is connected to the first end of the first inductor, the first end of the second inductor and the first end of the free - wheeling diode.

[0007] In some embodiments, the first to third switching transistors are all MOS transistors.

[0008] In some embodiments, the freewheeling diode is a diode, the negative electrode of the freewheeling diode is connected to the second end of the third switching transistor, the first end of the first inductor, and the first end of the second inductor; the positive electrode of the freewheeling diode is connected to the negative electrode of the DC power supply, the second end of the first capacitor, the second end of the first switching transistor, and the second end of the second switching transistor.

[0009] In some embodiments, the freewheeling diode is a MOS transistor.

[0010] In some embodiments, the freewheeling diode is an IGBT switching transistor, the collector of the freewheeling diode is connected to the second end of the third switching transistor, the first end of the first inductor, and the first end of the second inductor, and the emitter of the freewheeling diode is connected to the negative electrode of the DC power supply, the second end of the first capacitor, the second end of the first switching transistor, and the second end of the second switching transistor.

[0011] In some embodiments, the secondary circuit includes a rectifying circuit and a second capacitor. The secondary winding is connected to the input end of the rectifying circuit, and the second capacitor is connected in parallel to the output end of the rectifying circuit.

[0012] In some embodiments, the rectifying circuit is a full-bridge rectifying circuit.

[0013] The present utility model has the following beneficial effects: Through the reasonable arrangement of the first capacitor, the first to third switching transistors, the first to second inductors, and the freewheeling diode, the present application can make the third switching transistor conduct directly when the voltage is low, and only play a voltage-reducing role when the voltage is high. The first switching transistor and the second switching transistor play a voltage-boosting and current-changing role when the input voltage is low, and perform open-loop current-changing when the voltage is high, and transmit the energy to the transformer for isolation transformation. The step-up and step-down circuit of the present application is completed in one stage, greatly improving the conversion efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 is the circuit diagram of the isolated step-up and step-down converter in this embodiment;

[0015] Figure 2 is the circuit diagram of the isolated step-up and step-down converter in another embodiment;

[0016] Figure 3 is the working principle diagram of a certain time state of the isolated step-up and step-down converter when the input voltage is lower than the platform voltage in the embodiment of the present utility model;

[0017] Figure 4 is the working principle diagram of another time state of the isolated step-up and step-down converter when the input voltage is lower than the platform voltage in the embodiment of the present utility model;

[0018] Figure 5 It is the working schematic diagram of another time state of the isolated boost - buck converter when the input voltage is lower than the platform voltage in the embodiment of the present utility model;

[0019] Figure 6 It is the working schematic diagram of a certain time state of the isolated boost - buck converter when the input voltage is higher than the platform voltage in the embodiment of the present utility model;

[0020] Figure 7 It is the working schematic diagram of another time state of the isolated boost - buck converter when the input voltage is higher than the platform voltage in the embodiment of the present utility model;

[0021] Explanation of reference numerals:

[0022] T1 - transformer, C1 - first capacitor, C2 - second capacitor, Q1 - first switching transistor, Q2 - second switching transistor, Q3 - third switching transistor, Q4 - fourth switching transistor, L1 - first inductor, L2 - second inductor, D1 - first rectifying diode, D2 - second rectifying diode, D3 - third rectifying diode, D4 - fourth rectifying diode, free - wheeling diode - D5 Detailed implementation manners

[0023] The following makes a detailed description of the implementation manners of the present utility model. It should be emphasized that the following description is merely exemplary and not intended to limit the scope and application of the present utility model.

[0024] It should be noted that when an element is referred to as "fixed to" or "disposed on" another element, it can be directly on the other element or indirectly on the other element. When an element is referred to as "connected to" another element, it can be directly connected to the other element or indirectly connected to the other element. In addition, the connection can be for a fixing function or for a coupling or communicating function.

[0025] It should be understood that the orientation or positional relationship indicated by the terms "length", "width", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc. is based on the orientation or positional relationship shown in the drawings, and is only for the convenience of describing the embodiments of the present utility model 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 thus cannot be construed as a limitation of the present utility model.

[0026] In addition, the terms "first" and "second" are for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the quantity of the indicated technical features. Thus, features defined with "first" and "second" may explicitly or implicitly include one or more of such features. In the description of the embodiments of the present utility model, the meaning of "a plurality" is two or more, unless otherwise specifically defined.

[0027] Referring to Figure 1 - Figure 2 , the isolated boost-buck converter in this embodiment includes a primary circuit, a transformer T1, and a secondary circuit. The transformer includes a primary winding and a secondary winding. The primary circuit includes a DC power supply, a first capacitor C1, first to third switching tubes, first to second inductors, and a freewheeling tube. The direction of current through the freewheeling tube is from the second end to the first end of the freewheeling tube. The positive pole of the DC power supply is connected to the first end of the first capacitor C1 and the first end of the third switching tube Q3. The second end of the third switching tube Q3 is connected to the first end of the first inductor L1, the first end of the second inductor L2, and the first end of the freewheeling tube. The second end of the first inductor L1 is connected to the first end of the first switching tube Q1 and the first end of the primary winding. The second end of the second inductor L2 is connected to the first end of the second switching tube Q2 and the second end of the primary winding. The negative pole of the DC power supply is connected to the second end of the first capacitor C1, the second end of the freewheeling tube, the second end of the first switching tube Q1, and the second end of the second switching tube Q2.

[0028] In this embodiment, the first to third switching tubes are IGBT switching tubes. The collector of the first switching tube Q1 is connected to the second end of the first inductor L1 and the first end of the primary winding. The emitter of the first switching tube Q1 is connected to the negative pole of the DC power supply, the second end of the first capacitor C1, and the emitter of the second switching tube Q2. The collector of the second switching tube Q2 is connected to the second end of the second inductor L2 and the second end of the primary winding. The emitter of the second switching tube Q2 is connected to the negative pole of the DC power supply, the second end of the first capacitor C1, and the emitter of the first switching tube Q1. The collector of the third switching tube Q3 is connected to the positive pole of the DC power supply and the first end of the first capacitor C1. The emitter of the third switching tube Q3 is connected to the first end of the first inductor L1, the first end of the second inductor L2, and the first end of the freewheeling tube. In some other embodiments, the first to third switching tubes are all MOS tubes.

[0029] Referring to Figure 1 , in some embodiments, the freewheeling tube can be a freewheeling diode D5. The negative pole of the freewheeling tube (freewheeling diode D5) is connected to the second end of the third switching tube Q3, the first end of the first inductor L1, and the first end of the second inductor L2. The positive pole of the freewheeling tube (freewheeling diode D5) is connected to the negative pole of the DC power supply, the second end of the first capacitor C1, the second end of the first switching tube Q1, and the second end of the second switching tube Q2. In some other embodiments, the freewheeling tube can be a MOS tube; Referring toFigure 2 , in this embodiment, the freewheeling diode is an IGBT switch. The collector of the freewheeling diode (IGBT switch) is connected to the second end of the third switch Q3, the first end of the first inductor L1, and the first end of the second inductor L2. The emitter of the freewheeling diode (IGBT switch) is connected to the negative pole of the DC power supply, the second end of the first capacitor C1, the second end of the first switch Q1, and the second end of the second switch Q2.

[0030] In this embodiment, the secondary circuit includes a rectifier circuit and a second capacitor C2. The secondary winding is connected to the input end of the rectifier circuit, and the second capacitor C2 is connected in parallel at the output end of the rectifier circuit, where the rectifier circuit is a full-bridge rectifier circuit.

[0031] The circuit principle of this embodiment is as follows:

[0032] The input of this circuit passes through the BUCK buck switch (i.e., the third switch Q3) and the freewheeling diode D5 (or the fourth switch Q4 can be used for synchronous rectification), the main power inductors - the first inductor L1 and the second inductor L2, and the double BOOST switches - the first switch Q1 and the second switch Q2 are alternately turned on to achieve the conversion of electrical energy. It is transformed to the secondary side by the isolation transformer T1 and output after being rectified and filtered by the first rectifier diode D1, the second rectifier diode D2, the third rectifier diode D3, the fourth rectifier diode D4, and the second capacitor C2.

[0033] According to the turns ratio of the transformer T1 in this circuit, a suitable platform voltage can be set (the turns ratio of the transformer T1 can be designed according to requirements to make it work at a suitable platform voltage, for example, the platform voltage can be designed according to the voltage stress of the selected device). When the input voltage is low, lower than the platform voltage, the BUCK switch (i.e., the third switch Q3) conducts directly, and the current flows through the switch (at this time, there is only a very small conduction loss). The current is mainly controlled by the duty cycle of the double BOOST tubes - the first switch Q1 and the second switch Q2 (provided by the digital chip according to the algorithm). At this time, the digital chip outputs a suitable duty cycle to the first switch Q1 and the second switch Q2 according to the current magnitude to be controlled. The first switch Q1 and the second switch Q2 are alternately turned on to achieve current conversion, and the energy is output to the subsequent stage through electrical isolation by the transformer. When the input voltage is high, higher than the set platform voltage, at this time, the digital chip outputs the duty cycle to the BUCK circuit switch (the third switch Q3) according to the algorithm (which can vary from 0 to 100%), starting from 100% and decreasing, so that the current conduction time is reduced, and the freewheeling diode D5 conducts for freewheeling. At this time, the duty cycle output by the digital chip to the subsequent double BOOST switches is fixed at 50% (open-loop) and only functions as current conversion, and the energy is output to the subsequent stage through electrical isolation by the transformer (the first switch Q1 and the second switch Q2 are alternately turned on to change the current direction of the transformer to achieve current conversion).

[0034] Specifically, the isolated boost-buck converter in this embodiment mainly operates in the following modes:

[0035] Mode 1: Refer to Figure 3 - Figure 5 , when the input voltage is lower than the platform voltage, the BUCK switch (the third switch Q3) is directly connected: when the input voltage is lower than the platform voltage, at this time, the duty cycles of the first switch Q1 and the second switch Q2 are greater than 50% (the single-chip microcomputer outputs an appropriate duty cycle according to the level of the input voltage and controls the magnitude of the current. The lower the voltage, the larger the duty cycle, generally between 50% and 90%). Refer to Figure 3 , there is a common time for the two alternately conducting switches. If the switch is in the common time, the current passes through the third switch Q3, the first inductor L1, and the second inductor L2 for energy storage. The larger the duty cycle, the longer the common time (the single-chip microcomputer adjusts the duty cycle according to the level of the input voltage to achieve load current pulling). As the common time of the switch continues, the first inductor L1 or the second inductor L2 stores enough energy. At this time, refer to Figure 4 - Figure 5 , one of the first switch Q1 or the second switch Q2 is cut off first. The current passes through the transformer T1 to transfer the energy to the secondary side, and after being rectified by the first rectifier diode D1, the second rectifier diode D2, the third rectifier diode D3, and the fourth rectifier diode D4 respectively, it is filtered by the filter capacitor (the second capacitor C2) and output;

[0036] Mode 2: When the input voltage is higher than the platform voltage, the on-time of the BUCK switch (the third switch Q3) is controlled by the single-chip microcomputer: when the input voltage is higher than the platform voltage, the duty cycle of the BUCK switch (the third switch Q3) is controlled by the single-chip microcomputer (the single-chip microcomputer outputs an appropriate duty cycle according to the level of the input voltage and controls the magnitude of the current. The higher the voltage, the smaller the duty cycle, generally between 1% and 90%). The subsequent boost switches (the first switch Q1 and the second switch Q2) have a fixed 50% duty cycle and alternately turn on and off. In the first half cycle, the third switch Q3 conducts, and the current flows into the first inductor L1 and the second inductor L2 through the third switch Q3, and alternately turns on and off through the first switch Q1 or the second switch Q2, so that it becomes an alternating voltage and current, which is rectified by the transformer T1 and the diodes (the first rectifier diode D1, the second rectifier diode D2, the third rectifier diode D3, and the fourth rectifier diode D4) and then filtered by the filter capacitor (the second capacitor C2) and output. Refer to Figure 6 - Figure 7 , in the second half cycle, when the third switch Q3 is cut off, the fourth switch Q4 conducts for freewheeling (the third switch Q3 and the fourth switch Q4 are complementary to turn on and off). The energy stored in the first inductor L1 or the second inductor L2 is released and alternately turns on and off through the first switch Q1 or the second switch Q2, so that it becomes an alternating voltage and current, which is rectified by the transformer T1 and the diodes (the first rectifier diode D1, the second rectifier diode D2, the third rectifier diode D3, and the fourth rectifier diode D4) and then filtered by the filter capacitor (the second capacitor C2) and output.

[0037] The isolated boost - buck converter in this embodiment realizes isolated high - frequency and high - efficiency conversion within a wide voltage range. Compared with the existing buck - boost + open - loop push - pull, it has the following characteristics:

[0038] 1. Improved conversion efficiency: Before the input energy - storage inductor, there is a buck circuit. It is turned on or off according to the input voltage level. When the input voltage is low, the BUCK circuit conducts directly (without switching loss) and only plays a buck role when the voltage is high. After the energy - storage inductor, there is a dual - BOOST boost circuit, which has two functions: it plays a role in boosting and current conversion when the input voltage is low, and in open - loop current conversion when the voltage is high, delivering energy to the transformer for isolated conversion. This combination is completed in one stage, greatly improving the conversion efficiency.

[0039] 2. Cost reduction: Although the buck - boost strategy in this application seems to be completed in two stages, in fact, only one stage works at any given moment. This not only improves the conversion efficiency but also simplifies the circuit and reduces the number of components, making the control simple.

[0040] 3. Performance improvement: This application completes the conversion in one stage, without the process of rectification, filtering, and then conversion in the middle. The circuit is simple and the performance is stable, greatly improving the dynamic response and enhancing the compatibility in product applications.

[0041] This circuit adopts one - time conversion of boosting, bucking, and isolation, reducing the circuit complexity; when the input voltage is low, in the boost mode, the front - stage switch of the converter conducts directly, and only the rear - stage switch works, playing a role in boosting and isolated conversion, which is equivalent to only one stage working, reducing the switching loss and having a higher conversion efficiency than the currently commonly used two - stage independent conversion; when the input voltage is high, the front - stage switch works in the switching state to play a bucking role, and the rear - stage has a fixed duty cycle and only serves for isolated conversion. The two - stage combined work still has a high efficiency improvement without rectification and filtering in the middle.

[0042] The above content is a further detailed description of the present utility model in combination with specific / preferred embodiments, and it cannot be determined that the specific implementation of the present utility model is only limited to these descriptions. For those of ordinary skill in the art to which the present utility model pertains, without departing from the concept of the present utility model, several alternatives or modifications can be made to these described embodiments, and these alternative or modified forms should all be regarded as belonging to the protection scope of the present utility model. In the description of this specification, the description with reference to terms such as "an embodiment", "some embodiments", "preferred embodiments", "examples", "specific examples", or "some examples" means that the specific features, structures, materials, or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present utility model. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described can be combined in any one or more embodiments or examples in a suitable manner. Without contradiction, those skilled in the art can combine and combine the different embodiments or examples described in this specification and the features of different embodiments or examples. Although the embodiments of the present utility model and their advantages have been described in detail, it should be understood that various changes, substitutions, and alterations can be made herein without departing from the scope of protection of the patent application.

Claims

1. An isolated step-up / step-down converter, comprising a primary circuit, a transformer and a secondary circuit, wherein the transformer comprises a primary winding and a secondary winding, and wherein: The primary circuit includes a DC power supply, a first capacitor, first to third switching tubes, first to second inductors and a freewheeling tube. The direction of current passing through the freewheeling tube is from the second end of the freewheeling tube to the first end of the freewheeling tube. The positive electrode of the DC power supply is connected to the first end of the first capacitor and the first end of the third switching tube. The second end of the third switching tube is connected to the first end of the first inductor, the first end of the second inductor and the first end of the freewheeling tube. The second end of the first inductor is connected to the first end of the first switching tube and the first end of the primary winding. The second end of the second inductor is connected to the first end of the second switching tube and the second end of the primary winding. The negative electrode of the DC power supply is connected to the second end of the first capacitor, the second end of the freewheeling tube, the second end of the first switching tube and the second end of the second switching tube.

2. The isolated step-up / step-down converter according to claim 1, characterized in that: The first to third switch tubes are IGBT switch tubes, the collector of the first switch tube is connected to the second end of the first inductor and the first end of the primary winding, the emitter of the first switch tube is connected to the negative electrode of the DC power supply, the second end of the first capacitor, and the emitter of the second switch tube; the collector of the second switch tube is connected to the second end of the second inductor and the second end of the primary winding, the emitter of the second switch tube is connected to the negative electrode of the DC power supply, the second end of the first capacitor, and the emitter of the first switch tube; the collector of the third switch tube is connected to the positive electrode of the DC power supply and the first end of the first capacitor, and the emitter of the third switch tube is connected to the first end of the first inductor, the first end of the second inductor, and the first end of the freewheeling tube.

3. The isolated step-up / step-down converter according to claim 1, wherein: The first to third switch tubes are all MOS tubes.

4. The isolated step-up / step-down converter according to claim 1, wherein: The freewheeling tube is a diode, and the cathode of the freewheeling tube is connected to the second end of the third switch tube, the first end of the first inductor, and the first end of the second inductor; the anode of the freewheeling tube is connected to the negative electrode of the DC power supply, the second end of the first capacitor, the second end of the first switch tube, and the second end of the second switch tube.

5. The isolated step-up / step-down converter according to claim 1, wherein: The freewheeling tube is an IGBT switch tube, the collector of the freewheeling tube is connected to the second end of the third switch tube, the first end of the first inductor and the first end of the second inductor, and the emitter of the freewheeling tube is connected to the negative electrode of the DC power supply, the second end of the first capacitor, the second end of the first switch tube and the second end of the second switch tube.

6. The isolated step-up / step-down converter according to claim 1, wherein: The freewheeling tube is a MOS tube.

7. The isolated step-up / step-down converter according to claim 1, wherein: The secondary circuit includes a rectifier circuit and a second capacitor. The secondary winding is connected to the input end of the rectifier circuit, and the output end of the rectifier circuit is connected in parallel with the second capacitor.

8. The isolated step-up / step-down converter according to claim 7, characterized in that: The rectifier circuit is a full-bridge rectifier circuit.

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