CN115224945A

CN115224945A - Control method, device, medium, processor and switching power supply of switching power supply

Info

Publication number: CN115224945A
Application number: CN202210724541.3A
Authority: CN
Inventors: 龙宪良; 尹增鹤; 刘峥嵘
Original assignee: Mornsun Guangzhou Science and Technology Ltd
Current assignee: Mornsun Guangzhou Science and Technology Ltd
Priority date: 2022-06-23
Filing date: 2022-06-23
Publication date: 2022-10-21

Abstract

The invention discloses a control method, a device, a medium, a processor and a switching power supply, wherein the switching power supply comprises a primary side circuit, a transformer and a secondary side circuit, and the primary side circuit comprises the following components: the power supply device comprises first to third switching tubes, a first diode, a power supply capacitor, a clamping capacitor, a primary winding of a transformer and a control device; the positive input end of the switching power supply, the primary winding, the second switching tube, the first diode, the power supply capacitor and the input ground end of the switching power supply are sequentially connected to form a first loop; the positive input end of the switching power supply, the primary winding, the second switching tube, the first switching tube and the input ground end of the switching power supply are sequentially connected to form a second loop; one end of the clamping capacitor, the primary winding, the third switching tube and the other end of the clamping capacitor are sequentially connected to form a third loop, and the control device controls the first switching tube, the second switching tube, the third switching tube and the third switching tube to be switched on and switched off, so that the demagnetization energy and the reverse demagnetization energy of the primary winding are not transmitted to the secondary side circuit when the switching power supply is in light and no load, and the output voltage is prevented from floating high.

Description

Control method, device, medium, processor and switching power supply of switching power supply

Technical Field

The invention relates to the field of switching power supplies, in particular to a control method, a control device, a control medium, a control processor and a switching power supply of a switching power supply.

Background

In the switching power supply, a supply voltage signal is required to be provided for driving components (such as a driver, a clock signal generator, and the like) inside the switching power supply to work. In an alternating current-direct current (AC-DC) switching power supply, a low dropout linear regulator, an integrated clamp circuit, a third winding, and the like are often used to generate a supply voltage signal. Although the structure of generating the power supply voltage signal by adopting the low-dropout linear regulator and the integrated clamping circuit is simple, the loss is large, and the efficiency of the switching power supply is reduced. Although the control mode of generating the supply voltage signal VCC through the third winding is simple, the third winding will result in an increase in cost and low integration of the AC-DC switching power supply. In order to solve the difficulty, extensive researchers invented the following patents:

a patent No. CN106602883B discloses a power MOS transistor switching power supply integrated power supply circuit without auxiliary winding, and fig. 1a is a schematic diagram of the power MOS transistor switching power supply integrated power supply circuit without auxiliary winding provided in this patent, where a capacitor CVCC is a power supply capacitor.

A patent No. CN107612107a discloses a supply voltage generating circuit and an integrated circuit thereof, fig. 1b is a schematic diagram of the supply voltage generating circuit and the integrated circuit thereof provided in the patent, wherein the capacitor 14 is a supply capacitor.

The above patent and other prior no-winding power supply patents mainly charge the power supply capacitor through the main winding, and the switch tube on the charging loop is saturated and conducted, so that the power supply capacitor is charged while the main winding is excited in the forward direction, and the advantage of low loss of the charging circuit is achieved.

Disclosure of Invention

The inventor of the application finds that the scheme really achieves the effects of high conversion efficiency and saving the third winding when the load is larger, but the power consumption of the primary side chip needs to be reduced or the loss of the secondary side needs to be increased when the load is light and no-load, so that the energy conservation law can be met.

In view of the above-identified deficiencies of the prior art, the present invention provides a method, an apparatus, a medium, a processor, and a switching power supply, which are used to control the switching power supply, so that when the switching power supply adopts a power supply scheme without an auxiliary winding, there is no need to reduce the power consumption of the primary chip or increase the loss of the secondary chip under a light-no-load condition.

As a first aspect of the present invention, there is provided an embodiment of a control method of a switching power supply, as follows:

a control method of a switching power supply including a primary side circuit, a transformer, and a secondary side circuit, the primary side circuit comprising: the transformer comprises a first switching tube, a second switching tube, a third switching tube, a first diode, a power supply capacitor, a clamping capacitor, a primary winding of the transformer and a control device; the positive input end of the switching power supply, the primary winding of the transformer, the second switching tube, the anode of the first diode, the cathode of the first diode, the power supply capacitor and the input ground end of the switching power supply are sequentially connected to form a first loop; the positive input end of the switching power supply, the primary winding of the transformer, the second switching tube, the first switching tube and the input ground end of the switching power supply are sequentially connected to form a second loop; one end of the clamping capacitor, the primary winding of the transformer, the third switching tube and the other end of the clamping capacitor are sequentially connected to form a third loop, and the control device controls the first switching tube, the second switching tube and the third switching tube to be switched on and off; the control method comprises the following steps:

acquiring a first signal representing the current output power of the switching power supply;

acquiring a second signal representing the current voltage value at two ends of the power supply capacitor;

comparing the first signal with a first set value to generate a third signal;

comparing the second signal with a second set value to generate a fourth signal;

and controlling the first switching tube, the second switching tube and the third switching tube to be switched on and off according to the third signal and the fourth signal, so that the switching power supply works in different working processes, wherein when the first signal is smaller than the first set value and the second signal is smaller than the second set value, the demagnetization energy and the reverse demagnetization energy of the primary winding of the transformer are not transmitted to the secondary side circuit in the working process of the switching power supply.

Further, when the demagnetization energy and the reverse demagnetization energy of the primary winding of the transformer are not transferred to the secondary side circuit in the working process of the switching power supply, the demagnetization energy is transferred to the clamping capacitor firstly, then the transformer is excited reversely by the clamping capacitor, and finally the reverse demagnetization energy is transferred to the input end of the switching power supply.

Further, when the first signal is smaller than the first set value and the second signal is smaller than the second set value, the working process of the switching power supply comprises:

turning off the first switching tube, turning on the second switching tube, turning off the third switching tube, and charging the power supply capacitor while positively exciting the primary winding of the transformer through the first loop;

turning off the second switching tube, starting demagnetization of the primary winding of the transformer, conducting the diode of the third switching tube firstly, then conducting the third switching tube, transferring the demagnetization energy of the primary winding of the transformer to the clamping capacitor through the third loop, and gradually reducing the current in the primary winding of the transformer to zero;

the third switching tube is continuously conducted for a first time, the clamping capacitor reversely excites the primary winding of the transformer, the current in the primary winding of the transformer is reversely increased from zero, and partial energy of the clamping capacitor is transferred to the primary winding of the transformer through the third loop;

and step four, the third switching tube is turned off, the primary winding of the transformer starts to demagnetize reversely, the body diode of the first switching tube and the body diode of the second switching tube are conducted, and the reverse demagnetization energy of the primary winding of the transformer is transferred to the input end of the switching power supply through the second loop.

Further, in the third stage, when part of the energy of the clamping capacitor is transferred to the primary winding of the transformer, the voltage at two ends of the clamping capacitor is controlled to be smaller than the product of the turn ratio of the transformer and the output voltage of the switching power supply.

Further, in the third stage, the voltage across the clamping capacitor is controlled to be smaller than the product of the turn ratio of the transformer and the output voltage of the switching power supply by controlling the first time length.

As a second aspect of the present invention, there is provided an embodiment of a control device for a switching power supply, comprising:

a control apparatus of a switching power supply including a primary side circuit, a transformer, and a secondary side circuit, the primary side circuit comprising: the transformer comprises a first switching tube, a second switching tube, a third switching tube, a first diode, a power supply capacitor, a clamping capacitor, a primary winding of the transformer and a control device; the positive input end of the switching power supply, the primary winding of the transformer, the second switching tube, the anode of the first diode, the cathode of the first diode, the power supply capacitor and the input ground end of the switching power supply are sequentially connected to form a first loop; the positive input end of the switching power supply, the primary winding of the transformer, the second switching tube, the first switching tube and the input ground end of the switching power supply are sequentially connected to form a second loop; one end of the clamping capacitor, the primary winding of the transformer, the third switching tube and the other end of the clamping capacitor are sequentially connected to form a third loop, and the control device controls the first switching tube, the second switching tube and the third switching tube to be switched on and off; the control device includes:

the first acquisition unit is used for acquiring a first signal representing the current output power of the switching power supply;

the second obtaining unit is used for obtaining a second signal representing the magnitude of the current voltage value at two ends of the power supply capacitor;

the first comparison unit is used for comparing the first signal with a first set value to generate a third signal;

the second comparison unit is used for comparing the second signal with a second set value to generate a fourth signal;

and the processing unit is used for controlling the conduction and the disconnection of the first switching tube, the second switching tube and the third switching tube according to the third signal and the fourth signal, so that the switching power supply works in different working processes, wherein when the first signal is smaller than the first set value and the second signal is smaller than the second set value, the demagnetization energy and the reverse demagnetization energy of the primary winding of the transformer are not transmitted to the secondary side circuit in the working process of the switching power supply.

As a third aspect of the present invention, there is provided an embodiment of a computer-readable storage medium as follows:

a computer-readable storage medium, characterized in that the computer-readable storage medium includes a stored program, wherein the program executes any one of the above-described control methods of a switching power supply.

As a fourth aspect of the present invention, an embodiment of a processor is provided as follows:

a processor, characterized in that the processor is configured to run a program, wherein the program is configured to execute any one of the above control methods of the switching power supply when running.

As a fifth aspect of the present invention, there is provided an embodiment of a switching power supply as follows:

a switching power supply, comprising:

a primary side circuit, a transformer, and a secondary side circuit, the primary side circuit comprising: the transformer comprises a first switching tube, a second switching tube, a third switching tube, a first diode, a power supply capacitor, a clamping capacitor, a primary winding of the transformer and a control device; the positive input end of the switching power supply, the primary winding of the transformer, the second switching tube, the anode of the first diode, the cathode of the first diode, the power supply capacitor and the input ground end of the switching power supply are sequentially connected to form a first loop; the positive input end of the switching power supply, the primary winding of the transformer, the second switching tube, the first switching tube and the input ground end of the switching power supply are sequentially connected to form a second loop; one end of the clamping capacitor, the primary winding of the transformer, the third switching tube and the other end of the clamping capacitor are sequentially connected to form a third loop, and the control device controls the first switching tube, the second switching tube and the third switching tube to be switched on and off;

and the control device.

The embodiment of the invention at least comprises the following beneficial effects: when the first signal is smaller than the first set value and the second signal is smaller than the second set value, the demagnetization energy and the reverse demagnetization energy of the primary winding of the transformer are not transmitted to the secondary side circuit in the working process of the switching power supply, namely the energy of the transformer is not transmitted to the secondary side when the switching power supply is in light no-load and the power supply capacitor is in undervoltage, so that the problems of high output voltage drift and low no-load power consumption caused by high power consumption of the primary side control device of the switching power supply in the conventional winding-free power supply scheme are solved, and the design difficulty of the control device can be greatly reduced for some complicated control devices when the switching power supply allows the use of the control device with higher power consumption.

Additional features and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.

Drawings

FIG. 1a is a schematic diagram of an integrated power supply circuit of a conventional power MOS transistor switching power supply without an auxiliary winding;

FIG. 1b is a schematic diagram of a conventional supply voltage generating circuit and an integrated circuit thereof;

FIG. 2 is a schematic diagram of an embodiment of a switching power supply circuit to which the present invention is applicable;

FIG. 3 is a flow chart of an embodiment of a control method provided by the present invention for the switching power supply shown in FIG. 2;

fig. 4 is a schematic diagram of an embodiment of a control device provided for the switching power supply shown in fig. 2 according to the present invention;

fig. 5 is a waveform diagram illustrating operation of an embodiment of the switching power supply of the present invention.

Detailed Description

It should be noted that the embodiments and features of the embodiments in the present application may be combined with each other without conflict. The present application will be described in detail below with reference to the embodiments with reference to the attached drawings.

In order to make the technical solutions of the present application better understood by those skilled in the art, the technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application, and it is obvious that the described embodiments are only some embodiments of the present application, and not all embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present application.

It should be noted that the terms "first," "second," and the like in the description and claims of this application and in the drawings described above are used for distinguishing between similar elements and not necessarily for describing a particular sequential or chronological order. It should be understood that the data so used may be interchanged under appropriate circumstances such that embodiments of the application described herein may be used. Moreover, the terms "comprises," "comprising," and "having," and any variations thereof, are intended to cover a non-exclusive inclusion, such that a process, method, system, article, or apparatus that comprises a list of steps or elements is not necessarily limited to those steps or elements expressly listed, but may include other steps or elements not expressly listed or inherent to such process, method, article, or apparatus.

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

Furthermore, the drawings of the present disclosure are merely schematic representations, not necessarily drawn to scale. The same reference numerals in the drawings denote the same or similar parts, and thus, a repetitive description thereof will be omitted. Some of the block diagrams shown in the figures are functional entities and do not necessarily correspond to physically or logically separate entities. These functional entities may be implemented in software, or in one or more hardware modules or integrated circuits, or in different networks and/or processor devices and/or micro-control devices.

Fig. 2 is a schematic diagram of an embodiment of a switching power supply circuit to which the present invention is applied, including a primary side circuit, a transformer T1, and a secondary side circuit.

Wherein the primary side circuit includes: the power supply circuit comprises a first switching tube Q1, a second switching tube Q2, a third switching tube Q3, a first diode D1, a power supply capacitor Cv, a clamping capacitor C1, a transformer primary winding Np and a control device U1; a positive input end Vin of a switching power supply, a primary winding Np of a transformer, a second switching tube Q2, an anode of a first diode D1, a cathode of the first diode D1, a power supply capacitor Cv and an input ground end GND of the switching power supply are sequentially connected to form a first loop; the positive input end Vin of the switching power supply, a primary winding Np of a transformer, a second switching tube Q2, a first switching tube Q1 and a ground input end GND of the switching power supply are sequentially connected to form a second loop; one end of the clamping capacitor C1, the primary winding Np of the transformer, the third switching tube Q3 and the other end of the clamping capacitor C1 are sequentially connected to form a third loop, and the control device U1 controls the first switching tube Q1, the second switching tube Q2 and the third switching tube Q3 to be switched on and off.

The primary side circuit further includes an input filter capacitor Cin, the input filter capacitor Cin serving as a switching power supply can be implemented by an external capacitor in the art, a person skilled in the art can select how to set the input filter capacitor Cin according to an actual situation, and the switching power supply in the embodiment of the present invention is not limited to setting the capacitor.

Wherein the secondary side circuit E1 includes: the rectifier diode Do, the output filter capacitor Co, and the secondary side circuit may be a conventional flyback circuit, or a circuit with other topology structures, the rectifier scheme may adopt the diode rectifier scheme in fig. 2, or may also adopt a synchronous switching tube to perform synchronous rectification to improve the efficiency of the switching power supply, and a person skilled in the art may design a specific secondary side circuit according to the actual application scenario needs, and the switching power supply of the embodiment of the present invention is not limited thereto.

The control device U1 outputs a control signal SW1 through the first control signal output end to control the on and off of the first switching tube Q1, outputs a control signal SW2 through the second control signal output end to control the on and off of the second switching tube Q2, and outputs a control signal SW3 through the third control signal output end to control the on and off of the third switching tube Q3, different control methods can make the working process of the switching power supply different, and the analysis is as follows:

(1) The transformer excitation stage is divided into the following two conditions:

under the first condition, the power supply capacitor Cv supplies power to components inside the switching power supply, so that energy stored by the power supply capacitor Cv is consumed, and when the voltage at two ends of the power supply capacitor Cv is detected to be smaller than a first undervoltage value V _L1 When the transformer is used, the control device U1 controls the first switching tube Q1 to be switched off, the second switching tube Q2 to be switched on and the third switching tube Q3 to be switched off, the first loop is switched on, and the first loop carries out forward excitation through the primary winding Np of the transformer and simultaneously charges the power supply capacitor Cv.

When the power supply capacitor Cv is charged, the power P in the single period of the power supply capacitor Cv _Cv Is expressed as：

Wherein, C _Cv To the capacitance of the supply capacitor Cv, V _Cv1 The voltage at the end of charging the power supply capacitor Cv; v _Cv0 The voltage at the beginning of charging the supply capacitor Cv; f. of _sw Is the switching frequency of the switching power supply.

Single-cycle power P converted from excitation energy generated by transformer T1 when charging supply capacitor Cv _L1 The expression of (a) is:

wherein L is _p Is the inductance of the primary winding Np of the transformer, I _L1 The current flowing through the primary winding Np when the charging of the power supply capacitor Cv is finished; I.C. A _L0 The current flowing through the primary winding Np starts to charge the power supply capacitor Cv; f. of _sw Is the switching frequency of the switching power supply.

In case two, the voltage across the supply capacitor Cv is greater than or equal to the second undervoltage value V _L2 When the transformer T1 is in a normal state, the control device U1 controls the first switching tube Q1 to be conducted, the second switching tube Q2 to be conducted and the third switching tube Q3 to be turned off, the second loop is conducted, and forward excitation is conducted on the second loop only through the primary winding Np of the transformer T1.

Wherein the first under-voltage value V _L1 And a second undervoltage value V _L2 Has a voltage value therebetween, and V _L1 ＜V _L2 The purpose of setting the return difference is to ensure that the first condition and the second condition are not switched repeatedly.

(2) Demagnetization phase of transformer

The control device U1 controls the second switching tube Q2 to be switched off, after the second switching tube Q2 is switched off, the transformer T1 starts to be demagnetized, and after the clamping capacitor C1 stores a small part of energy, other excitation energy is transmitted to the secondary side to supply power to the load.

In the conventional control method, no matter which condition the transformer works in the excitation stage, the transformer transmits excitation energy generated by the first loop or excitation energy generated by the second loop to the secondary side to be provided to the load end.

When the load of the switching power supply is larger, the output power Po of the switching power supply is large, the excitation energy generated by the second loop is adjusted through closed-loop control, so that the output voltage can be stabilized at the rated voltage value under different load conditions, and when the load of the switching power supply is larger, P is larger _L1 Will be much less than Po and thus will not cause the switching power supply to work abnormally.

However, when the load is very small (i.e. when the load is in light load or no load, abbreviated as light no load), the output power Po is very small (usually within 20 mW), and the transformer excitation stage is the above condition one, P _L1 The output voltage must be equal to or less than Po to avoid the output voltage rising abnormality, and the following formula can be derived:

the switch power supply works in DCM mode during no load, I _L1 And =0A. In this case, the control unit U1 is required to achieve extremely low losses to meet the requirements. When the power consumption of the control device U1 is larger, P _L1 Will be much larger than Po, P _L1 Can be transmitted to the secondary side, resulting in excessive output energy and abnormal output voltage.

The prior art has two solutions to the above problem, one is to add dummy load, but light no-load power consumption is increased; the other is to reduce the power consumption of the control device U1, which makes the chip design difficult.

Therefore, in the current power supply scheme of the switch power supply without the auxiliary winding, linear power taking is directly carried out from the drain electrode of the input filter capacitor Cin or the second switch tube Q2 during light and no load, and although the problem of high output voltage fluctuation caused by light and no load is solved in the schemes, the power consumption of the linear power taking is equal to the power consumption current of the input voltage multiplied by the control device U1, so that the power consumption of the linear power taking is very large, the light and no load loss is large, and the defect is obvious.

It should be noted that, when the load is extremely small, if the transformer excitation stage is the first condition, although a person skilled in the art notices the problem that the output voltage of the switching power supply is abnormally high, it is difficult to think a more complete solution, and finally, the problem is solved by adopting a linear power-taking mode, and the power consumption of the chip is extremely good as much as possible.

First embodiment

Referring to fig. 3, a flowchart of an embodiment of a control method provided by the present invention for the switching power supply shown in fig. 2 includes the following steps:

s101, acquiring a first signal representing the current output power of the switching power supply;

s102, acquiring a second signal representing the current voltage value at two ends of the power supply capacitor;

s103, comparing the first signal with a first set value to generate a third signal;

the step is set to judge the on-load condition of the switching power supply, so as to identify whether the switching power supply is in a light no-load state, wherein a person skilled in the art may set the first setting value according to an actual condition, for example, a first signal value corresponding to 10% of a rated output power of the switching power supply may be used as the first setting value, and how to design a person skilled in the art may analyze and calculate according to the actual condition, the key point is to ensure that the output voltage does not drift high, which is not limited in this embodiment.

S104, comparing the second signal with a second set value to generate a fourth signal;

the step is set to judge whether the power supply capacitor Cv is in an undervoltage state, so that it can be ensured that the power supply capacitor Cv serves as an auxiliary power supply device to provide energy for normal operation of an active device inside the switching power supply, wherein a second set value may be set by a person skilled in the art according to an actual situation, for example, 11V may be set as the second set value, and how to design a person skilled in the art may analyze and calculate according to the actual situation, the key point is to ensure that the control device U1 does not trigger undervoltage protection, and the embodiment does not limit the undervoltage protection.

And S104, controlling the conduction and the disconnection of the first switching tube, the second switching tube and the third switching tube according to the third signal and the fourth signal, so that the switching power supply works in different working processes, wherein when the first signal is smaller than a first set value and the second signal is smaller than a second set value, the demagnetization energy and the reverse demagnetization energy of the primary winding of the transformer in the working process of the switching power supply are not transmitted to the secondary winding.

The on/off of the first switch tube, the second switch tube and the third switch tube is controlled according to the third signal and the fourth signal, the on/off of the first switch tube, the second switch tube and the third switch tube may be controlled by directly using the third signal and the fourth signal, or the on/off of the first switch tube, the second switch tube and the third switch tube may be controlled by using the preprocessed signal after preprocessing (such as amplification, attenuation, isolation, and the like) the third signal and the fourth signal.

In this step, when the first signal is smaller than the first set value and the second signal is smaller than the second set value, it means that the switching power supply is in a light no-load state and the power supply capacitor Cv is in an under-voltage state, and at this time, the energy of the secondary side is sufficient and the power supply capacitor Cv needs to supplement energy.

The sequence of the steps S101 and S102 is not sequential, and is performed simultaneously and in real time, after the two steps obtain corresponding signals, the steps S103 and S104 are respectively used for comparing, the sequence of the steps S103 and S104 is also not sequential, and is performed simultaneously and in real time, the comparison result obtained in the steps S103 and S104 is used as the basis for the step S105 to execute, and the on and off of the first switching tube Q1, the second switching tube Q2 and the third switching tube Q3 are controlled, so that the switching power supply works in different working processes.

In the control method of the embodiment, when the first signal is smaller than the first set value and the second signal is smaller than the second set value, the demagnetization energy and the reverse demagnetization energy of the primary winding of the transformer are not transmitted to the secondary side circuit in the working process of the switching power supply, namely, the energy of the transformer is not transmitted to the secondary side when the switching power supply is in light no-load and the power supply capacitor is in undervoltage, so that the problems of high output voltage drift and low no-load power consumption caused by high power consumption of the primary control device of the switching power supply in the existing winding-free power supply scheme are solved, and when the switching power supply allows the use of a control device with high power consumption, the design difficulty of the control device can be greatly reduced for some complicated control devices, and in addition, the auxiliary winding-free power supply scheme can reduce the cost of the switching power supply and improve the integration level of the switching power supply.

Further, when the demagnetization energy and the reverse demagnetization energy of the primary winding of the transformer are not transferred to the secondary side circuit in the working process of the switching power supply, the demagnetization energy is transferred to the clamping capacitor C1 firstly, then the transformer is subjected to reverse excitation through the clamping capacitor C1, and finally the reverse demagnetization energy is transferred to the input end Vin of the switching power supply.

The reverse demagnetizing energy is transferred to the input terminal Vin of the switching power supply and then stored in the input filter capacitor Cin as shown in fig. 2, and finally the energy is not transferred to the secondary side circuit, so that the output voltage is stabilized at the rated value.

Further, when the first signal is smaller than the first set value and the second signal is smaller than the second set value, the working process of the switching power supply includes:

in the first stage, the first switching tube Q1 is turned off, the second switching tube Q2 is conducted, the third switching tube Q3 is turned off, and the power supply capacitor Cv is charged while the primary winding Np of the transformer is positively excited through the first loop;

turning off the second switching tube Q2, starting demagnetization of the primary winding Np of the transformer, firstly conducting a body diode of the third switching tube Q3, then conducting the third switching tube Q3, transferring the demagnetization energy of the primary winding Np of the transformer to the clamping capacitor Cv through a third loop, and gradually reducing the current in the primary winding Np of the transformer to zero;

step three, continuously conducting a third switching tube Q3 for a first time, reversely exciting the primary winding Np of the transformer by the clamping capacitor, reversely increasing the current in the primary winding Np of the transformer from zero, and transferring partial energy of the clamping capacitor Cv to the primary winding Np of the transformer through a third loop;

the first time length is mainly to control the voltage at two ends of the clamping capacitor C1 to be always smaller than the product of the turn ratio of the transformer and the output voltage of the switching power supply, so as to ensure that the demagnetizing energy is not transmitted to the secondary side.

And step four, the third switching tube Q3 is turned off, the primary winding Np of the transformer starts to be demagnetized reversely, the body diode of the first switching tube Q1 and the body diode of the second switching tube Q2 are conducted, and the reverse demagnetization energy of the primary winding Np of the transformer is transferred to the input end Vin of the switching power supply through the second loop.

Further, in the third stage, when part of the energy of the clamping capacitor C1 is transferred to the primary winding of the transformer, the voltage V across the clamping capacitor C1 is controlled _C1 Is smaller than the product of the turn ratio of the transformer (number of primary winding turns Np/number of secondary winding turns Ns) and the output voltage Vo of the switching power supply, i.e. V _C1 ＜(Np/Ns)·Vo。

The purpose of controlling VC1 < (Np/Ns) · Vo is that when a rectifying switch tube of a secondary side circuit adopts diode rectification (a diode Do in figure 2 is a rectifying switch tube), in the third stage, the voltage at two ends of a primary winding of a transformer is the voltage VC1 at two ends of a clamping capacitor, the voltage induced by the voltage at a secondary winding Ns of the transformer is VNs = (VC 1/Np) · Ns, so VNs < Vo, therefore, the diode in the secondary side circuit can be guaranteed to bear reverse bias voltage and cut, and energy cannot be transmitted to the secondary side circuit.

Further, in a third stage, the voltage across the clamping capacitor is controlled to be smaller than the product of the turn ratio of the transformer and the output voltage of the switching power supply by controlling the first time length.

Second embodiment

Referring to fig. 4, a schematic diagram of an embodiment of a control device provided in the switching power supply of fig. 2 according to the present invention includes:

the first obtaining unit 101 is configured to obtain a first signal representing a current output power of the switching power supply;

for example, the first signal representing the current output power of the switching power supply may be obtained through the feedback signal, the output current signal, and the input current signal, and how to obtain the current output power of the switching power supply is not limited in this embodiment.

The second obtaining unit 102 is configured to obtain a second signal representing a current voltage value at two ends of the power supply capacitor;

in an actual application process, for example, the second signal representing the magnitude of the current voltage value at the two ends of the power supply capacitor may be obtained through the amplifying circuit, and how to obtain the present embodiment is not limited to this.

A first comparing unit 103 for comparing the first signal with a first set value to generate a third signal;

in an actual application process, for example, the first comparing unit may be designed by the comparator and necessary auxiliary devices, and how to design the embodiment is not limited to this.

A second comparing unit 104, configured to compare the second signal with a second set value, and generate a fourth signal;

in an actual application process, for example, the second comparing unit may be designed by the comparator and necessary auxiliary devices, and how to design the embodiment is not limited to this.

And the processing unit 105 is configured to control the first switching tube, the second switching tube, and the third switching tube to be turned on and off according to the third signal and the fourth signal, so that the switching power supply operates in different operating processes, where when the first signal is smaller than a first set value and the second signal is smaller than a second set value, both demagnetization energy and reverse demagnetization energy of the primary winding of the transformer are not transmitted to the secondary side circuit during the operating process of the switching power supply.

In an actual application process, for example, a special controller, a single chip Microcomputer (MCU), or a Digital Signal Processor (DSP) may be designed to control the on and off of the first switching tube, the second switching tube, and the third switching tube according to the third signal and the fourth signal, and how to implement this embodiment is not limited to this.

When the first signal is smaller than the first set value and the second signal is smaller than the second set value, the demagnetization energy and the reverse demagnetization energy of the primary winding of the transformer are not transmitted to the secondary side circuit in the working process of the switching power supply, namely, the energy of the transformer is not transmitted to the secondary side when the switching power supply is in light no-load and the power supply capacitor is in undervoltage, so that the problems of high power consumption of the primary side control device of the switching power supply and low output voltage and no-load power consumption caused by the conventional winding-free power supply scheme are solved, and when the switching power supply allows the use of a control device with high power consumption, the design difficulty of the control device can be greatly reduced for some complicated control devices, and in addition, the cost of the switching power supply can be reduced and the integration level of the switching power supply can be improved by the auxiliary winding-free power supply scheme.

Further, when the demagnetization energy and the reverse demagnetization energy of the primary winding of the transformer are not transferred to the secondary side circuit in the working process of the switching power supply, the demagnetization energy is transferred to the clamping capacitor C1 first, then the transformer is reversely excited by the clamping capacitor C1, and finally the reverse demagnetization energy is transferred to the input terminal Vin of the switching power supply.

Further, the processing unit 105 enables, when the first signal is smaller than the first set value and the second signal is smaller than the second set value, the operation process of the switching power supply to include:

Further, the control device further comprises a first control unit for controlling the voltage V across the clamping capacitor C1 in stage three when part of the energy of the clamping capacitor C1 is transferred to the primary winding of the transformer _C1 Less than the product of the transformer turn ratio and the output voltage Vo of the switching power supply.

Further, the control device further comprises a second control unit, which is used for controlling the voltage at two ends of the clamping capacitor to be smaller than the product of the turn ratio of the transformer and the output voltage of the switching power supply by controlling the first time length.

In the present embodiment, it should be understood that the disclosed technology can be implemented in other ways. The above-described embodiments of the apparatus are merely illustrative, and for example, the above-described division of the units may be a logical division, and in actual implementation, there may be another division, for example, multiple units or components may be combined or may be integrated into another system, or some features may be omitted, or not executed. In addition, the shown or discussed mutual coupling or direct coupling or communication connection may be an indirect coupling or communication connection through some interfaces, units or modules, and may be in an electrical or other form.

The units described as separate parts in this embodiment may or may not be physically separate, and parts displayed as units may or may not be physical units, may be located in one place, or may be distributed over a plurality of units. Some or all of the units can be selected according to actual needs to achieve the purpose of the solution of the embodiment.

In addition, in this embodiment, each functional unit in each embodiment may be integrated into one processing unit, or each unit may exist alone physically, or two or more units are integrated into one unit. The integrated unit may be implemented in the form of hardware, or may also be implemented in the form of a software functional unit.

The integrated unit in this embodiment may be stored in a computer-readable storage medium if it is implemented in the form of a software functional unit and sold or used as a separate product. Based on such understanding, the technical solution of the present invention may be embodied in the form of a software product, which is stored in a storage medium and includes instructions for causing a computer device (which may be a personal computer, a server, or a network device) to execute all or part of the steps of the above methods according to the embodiments of the present invention. And the aforementioned storage medium includes: a U-disk, a Read-Only Memory (ROM), a Random Access Memory (RAM), a removable hard disk, a magnetic or optical disk, and other various media capable of storing program codes.

Third embodiment

A third embodiment of the present invention provides a computer-readable storage medium including a stored program that performs the method of any one of the embodiments of the first embodiment.

Fourth embodiment

A fourth embodiment of the present invention provides a processor, configured to execute a program, where the program executes the method described in any of the embodiments in the first embodiment.

Fifth embodiment

A fifth embodiment of the present invention provides a switching power supply, referring to fig. 2, including:

primary side circuit, transformer T1 and secondary side circuit E1, the primary side circuit includes: the power supply circuit comprises a first switching tube Q1, a second switching tube Q2, a third switching tube Q3, a first diode D1, a power supply capacitor Cv, a clamping capacitor C1, a transformer primary winding Np and a control device U1; a positive input end Vin of a switching power supply, a primary winding Np of a transformer, a second switching tube Q2, an anode of a first diode D1, a cathode of the first diode D1, a power supply capacitor Cv and an input ground end GND of the switching power supply are sequentially connected to form a first loop; the positive input end Vin of the switching power supply, a primary winding Np of a transformer, a second switching tube Q2, a first switching tube Q1 and a ground input end GND of the switching power supply are sequentially connected to form a second loop; one end of a clamping capacitor C1, a primary winding Np of the transformer, a third switching tube Q3 and the other end of the clamping capacitor C1 are sequentially connected to form a third loop, and a control device U1 controls the conduction and the disconnection of the first switching tube Q1, the second switching tube Q2 and the third switching tube Q3;

and a control device U1.

The control device U1 is the control device according to any one of the embodiments in the second embodiment.

Fig. 5 is a waveform diagram of the operation of the switching power supply provided in this embodiment, where the meanings of the waveform identifiers are as follows:

vo: outputting a voltage waveform;

V _Ns : voltage waveforms at two ends of the secondary winding Ns of the transformer;

vin: inputting a voltage waveform of the capacitor Cin;

V _C1 : clamp capacitance C1 voltage waveform;

vcc: the supply capacitor Cv voltage waveform;

IL: the current waveform of a primary winding Np of the transformer;

SW3: the driving waveform of the third switching tube Q3 is switched on at a high level and switched off at a low level;

SW2: the driving waveform of the second switch tube Q2 is switched on at a high level and switched off at a low level;

SW1: the driving waveform of the first switching tube Q1 is switched on at a high level and switched off at a low level.

With reference to the circuit shown in fig. 2, the operation of the switching power supply during light no-load (i.e. when the first signal is smaller than the first set value) is analyzed as follows:

state 1: when the supply capacitor Cv is reduced to the undervoltage V _L When the voltage across the primary winding Np of the transformer is Vin-V, the first switch tube Q1 is turned off, the second switch tube Q2 is turned on, the third switch tube Q3 is turned off, the first loop consisting of the positive input end Vin of the switch power supply, the primary winding Np of the transformer, the second switch tube Q2, the first diode D1, the power supply capacitor Cv and the input ground end GND of the switch power supply is turned on, and the voltage across the primary winding Np of the transformer is Vin-V _Cv (neglecting the conduction voltage drop of the switch tube), the primary winding Np of the transformer starts to be excited in the forward direction, the power supply capacitor Cv is charged at the same time, the current IL flowing through the primary winding Np of the transformer and the power supply capacitor Cv is gradually increased, the primary winding Np of the transformer is excited, and the voltage at two ends of the power supply capacitor Cv is also gradually increased.

State 2: when the voltage of the power supply capacitor Cv rises to the clamping voltage V _H Then, the first switching tube Q1 is switched on, the second switching tube Q2 is switched off, the third switching tube Q3 is kept switched off, the charging of the power supply capacitor Cv is stopped, the demagnetization is started after the excitation of the primary winding Np of the transformer is finished, and the voltage on the clamping capacitor C1 is controlled

(in order to prevent energy from being transmitted to the secondary side), the energy stored in the primary winding Np of the transformer is only used for charging the clamping capacitor C1, the diode of the third switching tube body is firstly conducted, the third switching tube Q3 is turned on after a dead time, the energy stored in the primary winding Np of the transformer is transferred to the clamping capacitor C1, and the voltage V of the clamping capacitor is reduced along with the reduction of the current IL _C1 Increasing; wherein: v _L1 ＜V _H ＜V _L2 The control unit U1 passes the clamping voltage V _H To control the charging duration of the supply capacitor Cv.

State 3: when the current IL is reduced to 0A, the voltage V of the clamping capacitor _C1 To the maximum voltage value, the transformerThe energy of the primary winding Np is transferred entirely to the clamping capacitor C1. In the whole process of the energy transfer, the voltage V on the clamping capacitor C1 is ensured by controlling the conducting time of the third switching tube Q3 _C1 Is always less than

The secondary-side diode Do is thus not sufficiently conductive, so that energy is not transferred to the secondary side.

And 4: because the third switching tube Q3 is kept conducted, the voltage of the clamping capacitor C1 is added to the transformer T1, the primary winding Np of the transformer starts to be excited reversely, the current IL is increased reversely, and the voltage V of the clamping capacitor _C1 And gradually reducing, and turning off the third switching tube Q3 after the set on-time of the third switching tube Q3 is reached. Part of the energy stored on the clamp capacitor C1 is transferred again to the primary winding Np of the transformer.

And a state 5: when the third switching tube Q3 is turned off, since the first switching tube Q1 is turned on and the body diode of the second switching tube Q2 is turned on by the reverse current IL, the energy stored in the primary winding Np of the transformer charges the input capacitor Cin, so that the energy stored in the primary winding Np of the transformer is finally transferred to the input terminal Vin of the switching power supply, i.e., the input filter capacitor Cin in fig. 2.

As can be seen from the above working process analysis, in the switching power supply of this embodiment, when the first signal is smaller than the first set value and the second signal is smaller than the second set value, the demagnetization energy and the reverse demagnetization energy of the primary winding of the transformer are not transferred to the secondary side circuit in the working process of the switching power supply, that is, the transformer energy is not transferred to the secondary side when the switching power supply is in light no-load and the supply capacitor is under-voltage, so as to solve the problems of high power consumption of the primary side control device of the switching power supply, which leads to high output voltage and low no-load power consumption in the existing winding-free power supply scheme.

The foregoing is merely a preferred embodiment of the present invention, and it should be noted that the above-described preferred embodiment should not be construed as limiting the present invention. For those skilled in the art, several equivalent power sources, modifications and decorations can be made without departing from the spirit and scope of the present invention, and these equivalent power sources, modifications and decorations should be regarded as the protection scope of the present invention, and no description is given here, and the protection scope of the present invention should be subject to the scope defined by the claims.

Claims

1. A control method of a switching power supply including a primary side circuit, a transformer, and a secondary side circuit, the primary side circuit comprising: the transformer comprises a first switching tube, a second switching tube, a third switching tube, a first diode, a power supply capacitor, a clamping capacitor, a primary winding of the transformer and a control device; the positive input end of the switching power supply, the primary winding of the transformer, the second switching tube, the anode of the first diode, the cathode of the first diode, the power supply capacitor and the input ground end of the switching power supply are sequentially connected to form a first circuit; the positive input end of the switching power supply, the primary winding of the transformer, the second switching tube, the first switching tube and the input ground end of the switching power supply are sequentially connected to form a second loop; one end of the clamping capacitor, the primary winding of the transformer, the third switching tube and the other end of the clamping capacitor are sequentially connected to form a third loop, and the control device controls the first switching tube, the second switching tube and the third switching tube to be switched on and off; the control method is characterized by comprising the following steps:

comparing the first signal with a first set value to generate a third signal;

2. The control method of the switching power supply according to claim 1, characterized in that: when the demagnetization energy and the reverse demagnetization energy of the primary winding of the transformer are not transmitted to the secondary side circuit in the working process of the switching power supply, the demagnetization energy is firstly transferred to the clamping capacitor, then the transformer is reversely excited by the clamping capacitor, and finally the reverse demagnetization energy is transferred to the input end of the switching power supply.

3. The control method of the switching power supply according to claim 1 or 2, characterized in that:

when the first signal is smaller than the first set value and the second signal is smaller than the second set value, the working process of the switching power supply comprises the following steps:

4. The control method of the switching power supply according to claim 3, characterized in that: and in the third stage, when part of energy of the clamping capacitor is transferred to the primary winding of the transformer, controlling the voltage at two ends of the clamping capacitor to be smaller than the product of the turn ratio of the transformer and the output voltage of the switching power supply.

5. The control method of the switching power supply according to claim 4, characterized in that: and in the third stage, the voltage at two ends of the clamping capacitor is controlled to be smaller than the product of the turn ratio of the transformer and the output voltage of the switching power supply by controlling the first time length.

6. A control apparatus of a switching power supply including a primary side circuit, a transformer, and a secondary side circuit, the primary side circuit comprising: the transformer comprises a first switching tube, a second switching tube, a third switching tube, a first diode, a power supply capacitor, a clamping capacitor, a primary winding of the transformer and a control device; the positive input end of the switching power supply, the primary winding of the transformer, the second switching tube, the anode of the first diode, the cathode of the first diode, the power supply capacitor and the input ground end of the switching power supply are sequentially connected to form a first loop; the positive input end of the switching power supply, the primary winding of the transformer, the second switching tube, the first switching tube and the input ground end of the switching power supply are sequentially connected to form a second loop; one end of the clamping capacitor, the primary winding of the transformer, the third switching tube and the other end of the clamping capacitor are sequentially connected to form a third loop, and the control device controls the first switching tube, the second switching tube and the third switching tube to be switched on and off; characterized in that the control device comprises:

the second acquisition unit is used for acquiring a second signal representing the current voltage value of the two ends of the power supply capacitor;

and the processing unit is used for controlling the conduction and the disconnection of the first switching tube, the second switching tube and the third switching tube according to the third signal and the fourth signal so that the switching power supply works in different working processes, wherein when the first signal is smaller than the first set value and the second signal is smaller than the second set value, the demagnetization energy and the reverse demagnetization energy of the primary winding of the transformer in the working process of the switching power supply are not transmitted to the secondary side circuit.

7. A computer-readable storage medium, comprising a stored program, wherein the program performs the method of any one of claims 1 to 5.

8. A processor, characterized in that the processor is configured to run a program, wherein the program when running performs the method of any of claims 1 to 5.

9. A switching power supply, comprising:

and a control device as claimed in claim 6.