Push-pull conversion topology and switching power supply

Abstract

The invention provides a push-pull conversion topology and a switching power supply, and the push-pull conversion topology comprises a transformer which comprises a first primary winding, a second primary winding and a secondary winding; the primary side circuit comprises a first switching tube, a second switching tube and a resonant inductor, and the resonant inductor comprises a first winding and a second winding; the secondary circuit comprises an output rectifying circuit and a resonant capacitor, and the resonant capacitor is connected between the first input end of the output rectifying circuit and one end of the secondary winding or between the second input end of the output rectifying circuit and the other end of the secondary winding; wherein one end of the first primary winding, the other end of the second primary winding and one end of the secondary winding are dotted terminals; one end of the first winding and the other end of the second winding are dotted terminals; and the resonant inductor and the resonant capacitor form a resonant network for realizing soft switching of the first switching tube and the second switching tube. The driving circuit has the advantages of realization of soft switching of the primary side switching tube, simple driving circuit, low cost and the like.

Description

Technical Field

[0001] The invention relates to the field of DC-DC converter topology, and in particular to a push-pull conversion topology and a switching power supply. Background Art

[0002] With the development of power electronics technology, switching power supplies are widely used in various fields of social production. The rapid development of technology in various fields has also led to higher requirements for the performance of switching power supplies, such as high efficiency, low cost, small size, high power density and high reliability.

[0003] In recent years, in low voltage and high current input applications, traditional push-pull converters, such as Figure 1 As shown in the figure, it is widely used because of its high transformer core utilization, small output ripple voltage and simple driving circuit. It can maintain a large power output even when the input voltage is very low. However, the primary switch tube of the traditional push-pull converter has the problem of hard switching and is not suitable for occasions with high efficiency requirements.

[0004] In order to improve the efficiency of the traditional push-pull converter, the patented "LLC resonant push-pull forward converter topology" proposes a converter that can realize soft switching of the primary switch tube, such as Figure 2 However, the source of the primary switch tube S2 of this LLC resonant push-pull forward conversion topology is not connected to the negative end of the input power supply, and a bootstrap drive circuit is required. In addition, the secondary rectifier circuit is a bridge rectifier circuit, which has two more diodes than the voltage doubler rectifier circuit, and is not suitable for occasions with simple drive circuits and low cost requirements. Summary of the invention

[0005] In view of this, the technical problem to be solved by the present invention is to provide a push-pull conversion topology and a switching power supply, which can at least solve the deficiencies of the prior art to a certain extent.

[0006] As a first aspect of the present invention, a technical solution of an embodiment of a push-pull conversion topology is provided as follows:

[0007] A push-pull conversion topology, comprising:

[0008] A transformer, comprising a first primary winding, a second primary winding and a secondary winding;

[0009] A primary circuit, comprising a first switch tube, a second switch tube and a resonant inductor, wherein the resonant inductor comprises a first winding and a second winding, one end of the first winding and one end of the second winding are simultaneously connected to the positive input end of the push-pull conversion topology, the other end of the first winding is connected to one end of the first primary winding, the other end of the second winding is connected to one end of the second primary winding, the first switch tube is connected between the other end of the first primary winding and the negative input end of the push-pull conversion topology, and the second switch tube is connected between the other end of the second primary winding and the negative input end of the push-pull conversion topology;

[0010] A secondary circuit, comprising an output rectifier circuit and a resonant capacitor, wherein a first input terminal of the output rectifier circuit is connected to one end of the secondary winding, a second input terminal is connected to the other end of the secondary winding, a positive output terminal of the output rectifier circuit is connected to the positive output terminal of the push-pull conversion topology, and a negative output terminal is connected to the negative output terminal of the push-pull conversion topology, and the resonant capacitor is connected between the first input terminal of the output rectifier circuit and one end of the secondary winding or between the second input terminal of the output rectifier circuit and the other end of the secondary winding;

[0011] Among them: one end of the first primary winding, the other end of the second primary winding and one end of the secondary winding are the same-named ends; one end of the first winding and the other end of the second winding are the same-named ends; the resonant inductor and the resonant capacitor form a resonant network, which is used to realize soft switching of the first switch tube and the second switch tube.

[0012] As an equivalent replacement for the technical solution of the above embodiment, the first winding is an inductor in which the first primary winding and the secondary winding are not coupled, the second winding is an inductor in which the second primary winding and the secondary winding are not coupled, and one end of the first primary winding and one end of the second primary winding are simultaneously connected to the positive input end of the push-pull conversion topology.

[0013] Preferably, the first switch tube and / or the second switch tube is a MOS tube.

[0014] Preferably, the output rectifier circuit is a voltage doubler rectifier circuit or a bridge rectifier circuit.

[0015] Furthermore, the first switch tube and the second switch tube are controlled by complementary driving pulses.

[0016] Furthermore, the frequency of the driving pulses of the first switch tube and the second switch tube is greater than or equal to the resonant frequency of the resonant network.

[0017] Preferably, a PFM control mode, a PWM control mode, or a PFM and PWM mixed control mode is adopted for control.

[0018] As a first aspect of the present invention, a technical solution of an embodiment of a switching power supply is provided as follows: a switching power supply, wherein: the circuit topology adopted is the push-pull conversion topology described in any one of the first aspects above.

[0019] Based on the traditional push-pull converter, the present invention eliminates the peak voltage of the rectifier tube in the secondary output rectifier circuit through a resonant network composed of a primary resonant inductor and a secondary resonant capacitor, and realizes the soft switching of the primary switch tube. Compared with the prior art, the present invention has the following beneficial effects:

[0020] (1) It can improve the EMC characteristics of the push-pull conversion topology, reduce the loss of the primary side switch tube and the secondary side rectifier tube, and thus improve the efficiency of the push-pull conversion topology DC to DC power conversion;

[0021] (2) The resonant network composed of the resonant inductor and the resonant capacitor allows the current flowing through the secondary rectifier to reach zero, which can realize the zero-current shutdown of the secondary rectifier, thereby eliminating the shutdown spike on the secondary rectifier. Therefore, the RC or CDD absorption loop for the reverse recovery spike of the diode (the body diode when it is a synchronous rectifier) ​​as the secondary rectifier in the traditional push-pull conversion topology circuit can be removed, and the filter inductor behind the rectifier circuit can also be removed;

[0022] (3) The circuit topology is simple, the cost is low, and the switch tubes are driven by a common ground, so there is no need for floating ground drive. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Attached Figure 1 This is a diagram of the topology of a traditional push-pull converter;

[0024] Attached Figure 2 This is a LLC resonant push-pull forward converter topology diagram provided by the prior art;

[0025] Attached Figure 3 It is the first push-pull conversion topology provided by the first embodiment of the structure diagram of the present invention;

[0026] Attached Figure 4 is a second push-pull conversion topology diagram provided by the first embodiment of the present invention;

[0027] Attached Figure 5 is a third push-pull conversion topology diagram provided by the first embodiment of the present invention;

[0028] Attached Figure 6 is a fourth push-pull conversion topology diagram provided by the first embodiment of the present invention;

[0029] Attached Figure 7 yes Figure 3 and Figure 5 The topological equivalent diagram of ;

[0030] Attached Figure 8 The present invention Figure 3 and Figure 5 Topological modal timing diagram. DETAILED DESCRIPTION

[0031] It should be noted that, in the absence of conflict, the embodiments and features in the embodiments of the present application can be combined with each other. The present application will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0032] In order to enable those skilled in the art to better understand the solution of the present application, the technical solution in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of the present application.

[0033] It should be noted that the terms "first", "second", etc. in the specification and claims of the present application and the above-mentioned drawings are used to distinguish similar objects, and are not necessarily used to describe a specific order or sequential order. It should be understood that the data used in this way can be interchanged where appropriate, so that the embodiments of the present application are described here. In addition, the terms "including" and "having" and any of their variations are intended to cover non-exclusive inclusions, for example, the process, method, system, product or equipment comprising a series of steps or units is not necessarily limited to those steps or units clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products or equipment.

[0034] It should be understood that, in the specification, claims and drawings, when a step is described as being connected to another step, the step may be directly connected to the other step, or be connected to the other step through a third step; when an element / unit is described as being "connected" to another element / unit, the element / unit may be "directly connected" to the other element / unit, or be "connected" to the other element / unit through a third element / unit.

[0035] In addition, the drawings of the present disclosure are only schematic diagrams of the present disclosure and are not necessarily drawn to scale. The same symbols in the drawings represent the same or similar parts, and thus repeated descriptions thereof will be omitted. Some of the block diagrams shown in the drawings are functional entities and do not necessarily correspond to physically or logically independent entities. These functional entities can be implemented using software, or implemented in one or more hardware modules or integrated circuits, or implemented in different networks and / or processor devices and / or microcontrollers.

[0036] First embodiment

[0037] This embodiment provides a push-pull conversion topology. Figure 2 and Figure 3 Two structural diagrams are provided, which include: a transformer, including a first primary winding Np1, a second primary winding Np2 and a secondary winding Ns; a primary circuit, including a first switch tube S1, a second switch tube S2 and a resonant inductor Lr, wherein the resonant inductor Lr includes a first winding S1 and a second winding P1, one end of the first winding S1 and one end of the second winding P1 are simultaneously connected to the positive input end of the push-pull conversion topology, the other end of the first winding S1 is connected to one end of the first primary winding Np1, the other end of the second winding P1 is connected to one end of the second primary winding Np2, the first switch tube S1 is connected between the other end of the first primary winding Np1 and the negative input end of the push-pull conversion topology, and the second switch tube S2 is connected between the other end of the second primary winding Np2 and the negative input end of the push-pull conversion topology. The secondary circuit includes an output rectifier circuit and a resonant capacitor Cr, wherein the first input terminal of the output rectifier circuit is connected to one end of the secondary winding Ns, the second input terminal is connected to the other end of the secondary winding Ns, the positive output terminal of the output rectifier circuit is connected to the positive output terminal of the push-pull conversion topology, and the negative output terminal is connected to the negative output terminal of the push-pull conversion topology, and the resonant capacitor Cr is connected between the second input terminal of the output rectifier circuit and the other end of the secondary winding; wherein: one end of the first primary winding Np1, the other end of the second primary winding Np2 and one end of the secondary winding Ns are the same-named ends; one end of the first winding S1 and the other end of the second winding S2 are the same-named ends; the resonant inductor Lr and the resonant capacitor Cr form a resonant network, which is used to realize the soft switching of the first switch tube S1 and the second switch tube S2.

[0038] It should be noted that: Figure 3 and Figure 4 The first primary winding Np1, the second primary winding Np2 and the secondary winding Ns of the transformer and the first winding S1 end and the second winding S2 of the resonant inductor Lr do not have a same-name terminal relationship with each other; as an equivalent replacement, the resonant capacitor Cr can also be connected between the first input terminal of the output rectifier circuit and one end of the secondary winding.

[0039] In addition, the soft switching of the first switch tube S1 and the second switch tube S2 means that the first switch tube S1 and the second switch tube S2 can be turned on with zero voltage and turned off with approximately zero current. Since the resonant current of the resonant network composed of the resonant inductor and the resonant capacitor can take away the electricity at both ends of the switch tube, the drain-source voltage of the switch tube is 0 before the switch tube is turned on. Therefore, there is still a certain current when the first switch tube S1 and the second switch tube S2 are turned off, but the turn-off current is very small, so it is called approximately zero current shutdown.

[0040] Above Figure 3 and Figure 4The push-pull conversion topology is based on the traditional push-pull converter. The resonant network composed of the primary resonant inductor and the secondary resonant capacitor is used to eliminate the peak voltage of the secondary rectifier tube, thereby realizing the soft switching of the primary switch tube. Compared with the existing technology: (1) It can improve the EMC characteristics of the push-pull conversion topology, reduce the loss of the primary switch tube and the secondary rectifier tube, and thus improve the efficiency of the push-pull conversion topology DC to DC power conversion; (2) The resonant network composed of the resonant inductor and the resonant capacitor allows the current flowing through the secondary rectifier tube to reach zero, which can realize the zero current shutdown of the secondary rectifier tube, thereby eliminating the shutdown spike on the secondary rectifier tube. Therefore, the RC or CDD absorption loop for the reverse recovery spike of the diode (the body diode when it is a synchronous rectifier tube) as the secondary rectifier tube in the traditional push-pull conversion topology circuit can be removed, and the filter inductor behind the rectifier circuit can also be removed; (3) The circuit topology is simple and low in cost, and the switch tube driver has a common ground, so there is no need for floating ground driver.

[0041] As Figure 3 and Figure 4 An equivalent replacement of the technical solution, wherein the first winding S1 is an inductor in which the first primary winding Np1 and the secondary winding Ns are not coupled, the second winding S2 is an inductor in which the second primary winding Np2 and the secondary winding Ns are not coupled, one end of the first primary winding Np1 and one end of the second primary winding Np2 are simultaneously connected to the positive input end of the push-pull conversion topology. For a specific structural diagram, please refer to Figure 5 and Figure 6 ,and Figure 3 and Figure 4 The difference is that the resonant inductor Lr in the primary circuit is replaced by the leakage inductance of the transformer. Figure 5 and Figure 6 The resonant inductor Lr is removed, and one end of the first primary winding Np1 and one end of the second primary winding Np2 are directly and simultaneously connected to the positive input end of the push-pull conversion topology. When designing the transformer, a suitable leakage inductance is formed, which can also form a resonant network with the resonant capacitor Cr to realize soft switching of the first switch tube S1 and the second switch tube S2.

[0042] Preferably, the first switch tube and / or the second switch tube is a MOS tube, wherein Figures 3 to 6 The first switch tube and the second switch tube in the embodiment are both MOS tubes.

[0043] Preferably, the output rectifier circuit is a voltage doubler rectifier circuit or a bridge rectifier circuit.

[0044] Please go back Figure 3 and Figure 5, wherein the output rectifier circuit is a voltage doubler rectifier circuit, including a diode D1 and a diode D2, the diode D1 and the diode D2 are connected in series in the same direction, the connection point between the anode of the diode D2 and the cathode of the diode D1 is the first input terminal of the output rectifier circuit, the cathode of the diode D2 is the positive output terminal of the output rectifier circuit, the anode of the diode D1 is the second input terminal of the output rectifier circuit and the negative output terminal of the output rectifier circuit, the voltage doubler rectifier circuit is two diodes connected in series, compared with Figure 2 Compared with the existing topology, the number of components in the circuit can be significantly reduced. At the same time, since the two switches on the primary side share a common ground, there is no need for floating ground drive. Figure 2 The drive control is simpler for the existing topology.

[0045] Please go back Figure 4 and Figure 6 , wherein the output rectifier circuit is a bridge rectifier circuit, including a diode D1, a diode D2, a diode D3 and a diode D4, wherein the diode D1 and the diode D2 are connected in series in the same direction, and the diode D3 and the diode D4 are connected in series in the same direction, the connection point of the anode of the diode D2 and the cathode of the diode D1 is the first input terminal of the output rectifier circuit, the connection point of the anode of the diode D4 and the cathode of the diode D3 is the second input terminal of the output rectifier circuit, the cathode of the diode D2 and the cathode of the diode D4 are connected together as the positive output terminal of the output rectifier circuit, and the anode of the diode D1 and the anode of the diode D3 are connected together as the negative output terminal of the output rectifier circuit. Although the number of components increases when the bridge rectifier circuit is adopted, the output rectifier circuit as a bridge rectifier circuit also has application value. Specifically, the advantage of the output rectifier circuit as a voltage doubler circuit is that a higher output voltage can be achieved, and the output rectifier circuit as a bridge rectifier can make the output current smaller. Therefore, the application scenarios applicable to the two are different, and technicians in this field can make a selection according to needs. In addition, technicians in this field can also select other suitable output rectifier circuits according to actual conditions. The specific selection is not limited by the present invention.

[0046] Furthermore, the first switch tube S1 and the second switch tube S2 are controlled by complementary driving pulses, that is, when the first switch tube S1 is turned on, the second switch tube S2 is turned off; when the first switch tube S1 is turned off, the second switch tube S2 is turned on. In order to prevent the first switch tube S1 and the second switch tube S2 from being turned on together and burning, a dead time needs to be set when the first switch tube S1 and the second switch tube S2 are alternately turned on. The duty ratios of the first switch tube S1 and the second switch tube S2 are both 50% after ignoring the dead time.

[0047] Furthermore, the frequency of the driving pulses of the first switch tube S1 and the second switch tube S2 is greater than or equal to the resonant frequency of the resonant network, so as to achieve soft switching.

[0048] Preferably, the control strategy for the push-pull converter to adjust the output voltage includes but is not limited to the following methods:

[0049] (1) adopting the PFM control method, the specific implementation method can be to detect the output voltage of the push-pull conversion topology, and adjust the frequency of the driving pulses of the first switch tube S1 and the second switch tube S2 according to the detection result, so as to adjust the output voltage of the push-pull conversion topology;

[0050] (2) Using PWM control, the specific implementation method can be to detect the output voltage of the push-pull conversion topology, and adjust the duty cycle of the driving pulses of the first switch tube S1 and the second switch tube S2 according to the detection result, so as to adjust the output voltage of the push-pull conversion topology;

[0051] (3) A hybrid control method of PFM and PWM is adopted. The specific implementation method is to detect the output voltage of the push-pull conversion topology, and adjust the frequency and duty cycle of the driving pulses of the first switch tube S1 and the second switch tube S2 according to the detection result, thereby adjusting the output voltage of the push-pull conversion topology.

[0052] The following Figure 3 The working process of the push-pull conversion topology of this embodiment in a working cycle is analyzed by taking the topological structure as an example, so as to better understand the working principle of this embodiment. Figure 7 yes Figure 3 The topological equivalent diagram of Figure 8 The present invention Figure 3 The topological modal timing diagram is shown in Figure 1, where g1 is the driving pulse of the first switch tube S1; g2 is the driving pulse of the second switch tube S2; Vds1 is the drain-source voltage of the first switch tube S1; Vds2 is the drain-source voltage of the second switch tube S2; Ir is the current in the resonant capacitor Cr; VD1 is the voltage across the diode D1; ID1 is the current in the diode D1; VD2 is the voltage across the diode D2; ID2 is the current in the diode D2:

[0053] (1) Before time t1, the drain-source voltage of the first switch tube S1 is already zero.

[0054] (2) At time t1, the first switch tube S1 is turned on, and the first switch tube S1 is turned on with zero voltage, and the current flowing through the first primary winding Np1 increases linearly; the resonant capacitor Cr resonates with the resonant inductor Lr, the voltage across the resonant capacitor Cr drops, and the transformer primary transmits energy to the secondary side. In this mode, the drain-source voltage of the first switch tube S1 is zero; the drain-source voltage of the second switch tube S2 is clamped at 2Uin. The diode D2 is turned on, and the diode D1 is in the off state.

[0055] (3) At time t2, the first switch tube S1 is turned off, and the second switch tube S2 is also turned off. The drain-source voltage of the first switch tube S1 rises rapidly from zero and is clamped to 2Uin. The drain-source voltage of the second switch tube S2 drops rapidly from 2Uin to zero. The diode D2 is turned off with zero current and there is no reverse recovery spike.

[0056] (4) At time t3, the second switch tube S2 is turned on, and the second switch tube S2 is turned on with zero voltage, and the current flowing through the second primary winding Np2 increases linearly; the resonant capacitor Cr resonates with the resonant inductor Lr, the voltage across the resonant capacitor Cr rises, and the primary side transfers energy to the resonant capacitor Cr. In this mode, the drain-source voltage of the second switch tube S2 is zero; the drain-source voltage of the first switch tube S1 is clamped at 2Uin. The secondary diode D1 is turned on, and the diode D2 is in the off state.

[0057] (5) At time t4, the second switch tube S2 is turned off. At this time, the first switch tube S1 is also turned off. The drain-source voltage of the second switch tube S2 rises rapidly from zero and is clamped to 2Uin. The drain-source voltage of the first switch tube S1 drops rapidly from 2Uin to zero. The diode D1 is turned off with zero current and there is no reverse recovery spike.

[0058] Second embodiment

[0059] This embodiment provides a switching power supply, wherein: the circuit topology adopted is the push-pull conversion topology described in any one of the first embodiments. Since the circuit topology adopted in this embodiment is the push-pull conversion topology described in any one of the first embodiments, it has the advantages of realizing soft switching of the primary switch tube, simple driving circuit, low cost, etc., and is particularly suitable for low-voltage and high-current input occasions.

[0060] The above are only preferred embodiments of the present invention, and it should be noted that the above preferred embodiments should not be regarded as limiting the present invention. For those skilled in the art, several equivalent substitutions, improvements and modifications can be made without departing from the spirit and scope of the present invention, and these equivalent substitutions, improvements and modifications should also be regarded as the protection scope of the present invention. The embodiments will not be repeated here, and the protection scope of the present invention shall be based on the scope defined by the claims.

Claims

1. A push-pull conversion topology, characterized in that: include: A transformer, comprising a first primary winding, a second primary winding and a secondary winding; A primary circuit, comprising a first switch tube, a second switch tube and a resonant inductor, wherein the resonant inductor comprises a first winding and a second winding, one end of the first winding and one end of the second winding are simultaneously connected to the positive input end of the push-pull conversion topology, the other end of the first winding is connected to one end of the first primary winding, the other end of the second winding is connected to one end of the second primary winding, the first switch tube is connected between the other end of the first primary winding and the negative input end of the push-pull conversion topology, and the second switch tube is connected between the other end of the second primary winding and the negative input end of the push-pull conversion topology; A secondary circuit, comprising an output rectifier circuit and a resonant capacitor, wherein a first input terminal of the output rectifier circuit is connected to one end of the secondary winding, a second input terminal is connected to the other end of the secondary winding, a positive output terminal of the output rectifier circuit is connected to the positive output terminal of the push-pull conversion topology, and a negative output terminal is connected to the negative output terminal of the push-pull conversion topology, and the resonant capacitor is connected between the first input terminal of the output rectifier circuit and one end of the secondary winding or between the second input terminal of the output rectifier circuit and the other end of the secondary winding; Among them: one end of the first primary winding, the other end of the second primary winding and one end of the secondary winding are the same-named ends; one end of the first winding and the other end of the second winding are the same-named ends; the resonant inductor and the resonant capacitor form a resonant network, which is used to realize soft switching of the first switch tube and the second switch tube.

2. The push-pull conversion topology according to claim 1, characterized in that: The first winding is an inductor that is uncoupled between the first primary winding and the secondary winding, the second winding is an inductor that is uncoupled between the second primary winding and the secondary winding, and one end of the first primary winding and one end of the second primary winding are simultaneously connected to the positive input end of the push-pull conversion topology.

3. The push-pull conversion topology according to claim 1 or 2, characterized in that: The first switch tube and / or the second switch tube is a MOS tube.

4. The push-pull conversion topology according to claim 1 or 2, characterized in that: The output rectifier circuit is a voltage doubler rectifier circuit or a bridge rectifier circuit.

5. The push-pull conversion topology according to claim 1 or 2, characterized in that: The first switch tube and the second switch tube are controlled by complementary driving pulses.

6. The push-pull conversion topology according to claim 1 or 2, characterized in that: The frequencies of the driving pulses of the first switch tube and the second switch tube are greater than or equal to the resonant frequency of the resonant network.

7. The push-pull conversion topology according to any one of claims 1 or 2, characterized in that: The control is performed by adopting a PFM control method, a PWM control method, or a mixed control method of PFM and PWM.

8. A switching power supply, characterized in that: The circuit topology adopted is the push-pull conversion topology described in any one of claims 1 to 7.

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