CN116979814B

CN116979814B - Flyback switching power supply

Info

Publication number: CN116979814B
Application number: CN202311226750.6A
Authority: CN
Inventors: 朱理贤; 杨晓东
Original assignee: Kunshan Shuotong Electronics Co ltd
Current assignee: Kunshan Shuotong Electronics Co ltd
Priority date: 2023-09-22
Filing date: 2023-09-22
Publication date: 2023-12-15
Anticipated expiration: 2043-09-22
Also published as: CN116979814A

Abstract

The invention discloses a flyback switching power supply, which comprises: a primary circuit including a primary coil and a power switch; the secondary circuit comprises a secondary coil, an output circuit, a leakage inductance absorption circuit and a leakage inductance charging circuit; the output loop and the leakage inductance absorption loop are electrically connected with the secondary coil; the leakage inductance charging loop is respectively and electrically connected with the leakage inductance absorbing loop and the output loop; the output loop is used for outputting an electric signal when the power switch is turned on and charging when the power switch is turned off; the leakage inductance absorption loop is used for absorbing leakage inductance energy of the primary coil when the power switch is turned off; the leakage inductance charging loop is used for providing the leakage inductance energy absorbed by the leakage inductance absorbing loop to the output loop when the power switch is turned on. The invention can reduce peak voltage of the power switch, protect the power switch from being damaged easily and improve reliability of the flyback switching power supply; and when the power switch is turned on, leakage inductance energy can be provided for the output loop, so that the energy conversion efficiency of the flyback switching power supply is improved.

Description

Flyback switching power supply

Technical Field

The invention relates to the technical field of switching power supplies, in particular to a flyback switching power supply.

Background

With the continuous popularization and diversification of electronic devices, the requirements on power supplies are also increasing, and flyback switching power supplies are widely applied due to being suitable for wide-range input or output.

However, when the common flyback switching power supply is turned off, leakage inductance energy is directly lost, so that the energy conversion efficiency is low, the voltage stress of a switching tube is large, the switching tube is easy to fail, and the reliability of the flyback switching power supply is poor.

Disclosure of Invention

The invention provides a flyback switching power supply which is used for absorbing leakage inductance energy and reducing voltage stress of a switching tube.

According to an aspect of the present invention, there is provided a flyback switching power supply comprising: a primary line and a secondary line;

the primary circuit comprises a primary coil and a power switch connected in series with the primary coil; the secondary circuit comprises a secondary coil, an output circuit, a leakage inductance absorption circuit and a leakage inductance charging circuit;

the output loop is electrically connected with the secondary coil; the leakage inductance absorption loop is also electrically connected with the secondary coil; the leakage inductance charging loop is respectively and electrically connected with the leakage inductance absorption loop and the output loop;

the output loop is used for outputting an electric signal when the power switch is turned on and charging when the power switch is turned off; the leakage inductance absorption loop is used for absorbing leakage inductance energy of the primary coil when the power switch is turned off; the leakage inductance charging loop is used for providing the leakage inductance energy absorbed by the leakage inductance absorbing loop to the output loop when the power switch is turned on.

Optionally, the output loop comprises a rectifier diode and an output capacitor;

the first polar plate of the output capacitor is electrically connected with the homonymous end of the secondary coil; the second polar plate of the output capacitor is electrically connected with the synonym end of the secondary coil;

the anode of the rectifying diode is electrically connected with the homonymous end of the secondary coil, and the cathode of the rectifying diode is electrically connected with the first polar plate of the output capacitor; or, the cathode of the rectifying diode is electrically connected with the synonym end of the secondary coil, and the anode of the rectifying diode is electrically connected with the second plate of the output capacitor.

Optionally, the leakage inductance absorption loop comprises an auxiliary capacitor;

the first polar plate of the auxiliary capacitor is electrically connected with the homonymous end of the secondary coil; the second polar plate of the auxiliary capacitor is electrically connected with the synonym end of the secondary coil;

the auxiliary capacitor is used for charging when the power switch is turned off and discharging when the power switch is turned on.

Optionally, the leakage inductance absorption loop further comprises a first diode;

the anode of the first diode is electrically connected with the homonymous end of the secondary coil, and the cathode of the first diode is electrically connected with the first polar plate of the auxiliary capacitor; or, the cathode of the first diode is electrically connected with the synonym end of the secondary coil, and the anode of the first diode is electrically connected with the second plate of the auxiliary capacitor.

Optionally, the leakage inductance absorption loop further comprises a second diode;

the cathode of the second diode is electrically connected with the first polar plate of the auxiliary capacitor, and the anode of the second diode is electrically connected with the second polar plate of the auxiliary capacitor.

Optionally, the leakage inductance charging loop comprises a third diode and an auxiliary coil;

the anode of the third diode is electrically connected with the first polar plate of the auxiliary capacitor, the cathode of the third diode is electrically connected with the homonymous end of the auxiliary coil, and the heteronymous end of the auxiliary coil is electrically connected with the first polar plate of the output capacitor; or, the cathode of the third diode is electrically connected with the second plate of the auxiliary capacitor, the anode of the third diode is electrically connected with the synonym end of the auxiliary coil, and the synonym end of the auxiliary coil is electrically connected with the second plate of the output capacitor.

Optionally, the leakage inductance charging circuit further comprises a first inductor;

the first inductor is connected in series between the auxiliary capacitor and the third diode.

Optionally, the primary circuit further includes a first filter capacitor;

the first filter capacitor is connected in parallel with the primary coil and the power switch.

Optionally, the primary circuit further includes a second filter capacitor;

the first polar plate of the second filter capacitor is electrically connected with the first end of the power switch; and a second polar plate of the second filter capacitor is electrically connected with a second end of the power switch.

Optionally, the primary line further comprises a spike absorption loop;

the peak absorption loop comprises an absorption resistor, an absorption capacitor and an absorption diode; the anode of the absorption diode is electrically connected with the homonymous end of the primary coil; and the cathode of the absorption diode is electrically connected with the synonym end of the primary coil through the absorption resistor and the absorption capacitor respectively.

According to the technical scheme, the leakage inductance absorption loop and the leakage inductance charging loop are arranged on the secondary coil, so that when the power switch is turned off, the leakage inductance energy of the primary coil can be absorbed, the peak voltage of the power switch is reduced, the power switch is protected from being damaged easily, and the reliability of the flyback switching power supply is improved; when the power switch is turned on, leakage inductance energy absorbed by the leakage inductance absorption loop is provided for the output loop, so that the leakage inductance energy is provided for a load, and the energy conversion efficiency of the flyback switching power supply is improved.

It should be understood that the description in this section is not intended to identify key or critical features of the embodiments of the invention or to delineate the scope of the invention. Other features of the present invention will become apparent from the description that follows.

Drawings

In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for the description of the embodiments will be briefly described below, and it is apparent that the drawings in the following description are only some embodiments of the present invention, and other drawings may be obtained according to these drawings without inventive effort for a person skilled in the art.

Fig. 1 is a schematic structural diagram of a flyback switching power supply according to an embodiment of the present invention;

FIG. 2 is a voltage waveform diagram of two ends of a power switch according to an embodiment of the present invention;

fig. 3 is a schematic structural diagram of another flyback switching power supply according to an embodiment of the present invention;

FIG. 4 is a graph showing a voltage waveform across a power switch according to an embodiment of the present invention;

fig. 5 is a schematic structural diagram of another flyback switching power supply according to an embodiment of the present invention;

fig. 6 is a schematic structural diagram of another flyback switching power supply according to an embodiment of the present invention;

fig. 7 is a schematic structural diagram of another flyback switching power supply according to an embodiment of the present invention;

fig. 8 is a current waveform diagram of an excitation inductor according to an embodiment of the present invention;

FIG. 9 is a current waveform diagram of leakage inductance according to an embodiment of the present invention;

fig. 10 is a voltage waveform diagram of two ends of an auxiliary capacitor according to an embodiment of the present invention;

FIG. 11 is a schematic diagram of a flyback switching power supply according to an embodiment of the present invention;

fig. 12 is a schematic structural diagram of another flyback switching power supply according to an embodiment of the present invention;

fig. 13 is a schematic structural diagram of another flyback switching power supply according to an embodiment of the present invention.

Detailed Description

In order that those skilled in the art will better understand the present invention, a technical solution in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in which it is apparent that the described embodiments are only some embodiments of the present invention, not all embodiments. All other embodiments, which can be made by those skilled in the art based on the embodiments of the present invention without making any inventive effort, shall fall within the scope of the present invention.

It should be noted that the terms "first," "second," and the like in the description and the claims of the present invention and the above figures are used for distinguishing between similar objects and not necessarily for describing a particular sequential or chronological order. It is to be understood that the data so used may be interchanged where appropriate such that the embodiments of the invention described herein may be implemented in sequences other than those illustrated or otherwise described herein. Furthermore, 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.

Fig. 1 is a schematic structural diagram of a flyback switching power supply according to an embodiment of the present invention. Referring to fig. 1, a flyback switching power supply includes a primary line 10 and a secondary line 20; the primary line 10 includes a primary coil T1A and a power switch Q1 connected in series with the primary coil T1A; the secondary line 20 includes a secondary coil T1B, an output loop 210, a leakage inductance absorbing loop 220, and a leakage inductance charging loop 230; the output loop 210 is electrically connected with the secondary coil T1B; the leakage inductance absorbing circuit 220 is also electrically connected with the secondary coil T1B; the leakage inductance charging circuit 230 is electrically connected to the leakage inductance absorbing circuit 220 and the output circuit 210, respectively. The output circuit 210 is configured to output an electrical signal when the power switch Q1 is turned on, and to charge when the power switch Q1 is turned off; the leakage inductance absorbing circuit 220 is used for absorbing leakage inductance energy of the primary coil T1A when the power switch Q1 is turned off; the leakage inductance charging circuit 230 is configured to provide the leakage inductance energy absorbed by the leakage inductance absorbing circuit 220 to the output circuit 210 when the power switch Q1 is turned on.

In an embodiment, the synonym end of the primary coil T1A is electrically connected with the INPUT positive end INPUT +, the synonym end of the primary coil T1A is electrically connected with the INPUT negative end INPUT-through the power switch Q1, the synonym end of the secondary coil T1B is electrically connected with the output positive end OUT +, and the synonym end of the secondary coil T1B is electrically connected with the output negative end OUT-. The power switch Q1 includes, but is not limited to, a MOS transistor, and in one embodiment, the power switch Q1 is an N-type MOS transistor, a source thereof is electrically connected to the INPUT negative terminal INPUT-and a drain thereof is electrically connected to a same-name terminal of the primary coil T1A. The leakage inductance is the leakage inductance of the transformer T1, that is, the inductance of the leakage inductance generated by the magnetic force lines generated by the primary winding T1A of the transformer T1 cannot all pass through the secondary winding T1B. The transformer T1 further includes an excitation inductance, that is, a basis for transmitting energy of the transformer T1 from the primary coil T1A to the secondary coil T1B, and the excitation inductance generates magnetic flux to be transmitted to the secondary coil T1B through the magnetic core, thereby generating an induced voltage at the secondary coil T1B.

Specifically, when the power switch Q1 is turned on, the voltages of the same-name ends of the primary coil T1A and the secondary coil T1B are low, the secondary coil T1B cannot provide the electric signal to the output loop 210, and the output loop 210 can output the electric signal stored by the power switch Q1 before being turned on to the output positive end out+ and/or the output negative end OUT-; meanwhile, the secondary coil T1B cannot charge the leakage inductance absorbing circuit 220, and the leakage inductance charging circuit 230 may provide the leakage inductance energy absorbed by the leakage inductance absorbing circuit 220 before the power switch Q1 is turned on to the output circuit 210. When the power switch Q1 is turned off, the voltages of the same-name ends of the primary coil T1A and the secondary coil T1B are higher, the leakage inductance charging circuit 230 does not work, the secondary coil T1B can charge the leakage inductance absorbing circuit 220 and the output circuit 210, wherein the secondary coil T1B charges the leakage inductance absorbing circuit 220 first in an initial stage of turning off the power switch Q1, and the leakage inductance absorbing circuit 220 can absorb the leakage inductance energy of the primary coil T1A.

Fig. 2 is a voltage waveform diagram of two ends of a power switch according to an embodiment of the present invention, and referring to fig. 2, an N-type MOS transistor is taken as an example of the power switch Q1. In the first phase t1, the power switch Q1 is always turned on, and the source-drain voltage of the power switch Q1 is always zero. In the second phase T2, the power switch Q1 is turned off, a current still exists in the primary winding T1A, the source-drain voltage of the power switch Q1 increases, and meanwhile, the parasitic capacitance of the power switch Q1 charges until the source-drain voltage increases to a voltage between the INPUT positive terminal input+ and the INPUT negative terminal INPUT-, and the second phase T2 ends. The voltage between the INPUT positive side input+ and the INPUT negative side INPUT-may be 405V, for example, and since the current in the primary winding T1A does not suddenly change, the signal may oscillate, such as a spike between 400V and 500V in the second phase T2. The second stage T2 is at the initial stage of turning off the power switch Q1, and the leakage inductance absorbing circuit 220 absorbs the leakage inductance of the primary winding T1A at this stage.

In the third stage T3, since the current in the primary coil T1A does not suddenly decrease to zero, the source-drain voltage of the power switch Q1 continues to increase, and since the leakage inductance absorbing circuit 220 can absorb the leakage inductance of the primary coil T1A, a larger peak voltage is avoided, the source-drain voltage of the power switch Q1 does not increase any more when the source-drain voltage increases to about 600V, and after the leakage inductance energy of the primary coil T1A is absorbed by the leakage inductance absorbing circuit 220, the energy of the exciting inductance in the primary coil T1A can charge the output circuit 210 through the transformer T1 until the energy of the exciting inductance is consumed.

In the fourth stage t4, the energy of the exciting inductance is consumed, the parasitic capacitance of the power switch Q1 is discharged, the source-drain voltage of the power switch Q1 is reduced until the source-drain voltage of the power switch Q1 is reduced to zero, and the first stage t1 in the next cycle is entered. In the first phase t1 of the next cycle, the power switch Q1 is turned on, and the leakage inductance energy absorbed by the leakage inductance absorbing circuit 220 in the previous cycle may charge the output circuit 210 through the leakage inductance charging circuit 230.

According to the flyback switching power supply provided by the embodiment of the invention, the leakage inductance absorption loop and the leakage inductance charging loop are arranged on the secondary coil, so that the leakage inductance energy of the primary coil can be absorbed when the power switch is turned off, the peak voltage of the power switch is reduced, the power switch is protected from being damaged easily, and the reliability of the flyback switching power supply is improved; when the power switch is turned on, leakage inductance energy absorbed by the leakage inductance absorption loop is provided for the output loop, so that the leakage inductance energy is provided for a load, and the energy conversion efficiency of the flyback switching power supply is improved.

Optionally, fig. 3 is a schematic structural diagram of another flyback switching power supply according to an embodiment of the present invention, and referring to fig. 3, the primary circuit 10 further includes a first filter capacitor C1; the first filter capacitor C1 is connected in parallel with the primary coil T1A and the power switch Q1.

Taking the power switch Q1 as an N-type MOS transistor as an example. The first polar plate of the first filter capacitor C1 is electrically connected with the synonym end of the primary coil T1A; the second polar plate of the first filter capacitor C1 is electrically connected with the source electrode of the power switch Q1.

The first filter capacitor C1 has the functions of energy storage and filtering, and after the electric signals INPUT into the positive end INPUT+ and the negative end INPUT-pass through the first filter capacitor C1, the primary coil T1A is charged through the power switch Q1, and the first filter capacitor C1, the primary coil T1A and the power switch Q1 can form a resonant circuit. When the power switch Q1 is turned off, the first filter capacitor C1 may charge the parasitic capacitor of the power switch Q1 through the primary coil T1A, for example, in the second stage T2 in fig. 2 and 4. When the energy of the exciting inductance in the primary coil T1A is consumed, the energy stored in the parasitic capacitance of the power switch Q1 may charge the first filter capacitor C1 through the primary coil T1A, reducing the source-drain voltage of the power switch Q1, during which there may be a small amount of oscillation of the source-drain voltage of the power switch Q1, for example, in the second stage T4 in fig. 4.

Optionally, with continued reference to fig. 3, the primary line 10 further includes a second filter capacitor C2; the first polar plate of the second filter capacitor C2 is electrically connected with the first end of the power switch Q1; the second polar plate of the second filter capacitor C2 is electrically connected to the second end of the power switch Q1.

Taking the power switch Q1 as an N-type MOS transistor as an example. The first polar plate of the second filter capacitor C2 is electrically connected with the drain electrode of the power switch Q1; the second polar plate of the second filter capacitor C2 is electrically connected with the source electrode of the power switch Q1. The second filter capacitor C2 can be charged when the power switch Q1 is turned off, so as to raise the voltage of the first polar plate of the second filter capacitor C2, and the voltage at two ends of the second filter capacitor C2 is the source-drain voltage of the power switch Q1. By arranging the second filter capacitor C2, the storage capacity of charges can be increased, a certain filter effect is achieved, partial voltage spikes can be offset, the capacity deficiency of parasitic capacitance of the power switch Q1 is avoided, the source-drain voltage of the power switch Q1 rises too fast, and higher voltage spikes are generated.

Optionally, the output loop 210 includes a rectifying diode D1 and an output capacitor C4. Fig. 5 is a schematic structural diagram of another flyback switching power supply according to an embodiment of the present invention, and referring to fig. 5, a first pole plate of an output capacitor C4 is electrically connected to a homonymous terminal of a secondary coil T1B; the second polar plate of the output capacitor C4 is electrically connected with the synonym end of the secondary coil T1B. In an alternative embodiment, the anode of the rectifying diode D1 is electrically connected to the same name terminal of the secondary winding T1B, and the cathode of the rectifying diode D1 is electrically connected to the first plate of the output capacitor C4. In another alternative embodiment, fig. 6 is a schematic structural diagram of another flyback switching power supply according to an embodiment of the present invention, referring to fig. 6, a cathode of a rectifying diode D1 is electrically connected to a synonym terminal of a secondary winding T1B, and an anode of the rectifying diode D1 is electrically connected to a second plate of an output capacitor C4.

Illustratively, a first plate of the output capacitor C4 is electrically connected to the output positive terminal OUT+, a second plate of the output capacitor C4 is electrically connected to the output negative terminal OUT-, and a voltage across the output capacitor C4 is a voltage between the output positive terminal OUT+ and the output negative terminal OUT-. When the power switch Q1 is turned on, voltages of the same-name ends of the primary coil T1A and the secondary coil T1B are low, voltages of different-name ends of the primary coil T1A and the secondary coil T1B are high, the rectifying diode D1 is turned off, and an electric signal stored in the output capacitor C4 can be provided for an output positive end OUT+ and/or an output negative end OUT-. When the power switch Q1 is turned off, voltages at the same-name ends of the primary coil T1A and the secondary coil T1B are both higher, voltages at the different-name ends of the primary coil T1A and the secondary coil T1B are both lower, the rectifier diode D1 is turned on, and the output capacitor C4 is charged.

The voltage of the first plate of the output capacitor C4 is the voltage of the output positive terminal out+, and in the initial stage of turning off the power switch Q1, the voltages of the homonymous terminals of the primary coil T1A and the secondary coil T1B just start to increase, the voltages of the heteronymous terminals of the primary coil T1A and the secondary coil T1B just start to decrease, and the rectifier diode D1 is not turned on, so that leakage inductance energy in the primary coil T1A can be absorbed by the leakage inductance absorbing circuit 220, for example, in the second stage T2 of fig. 2 and 4. The rectifier diode D1 is turned on, and the charging of the output capacitor C4 mainly occurs in the middle and later stages of the turn-off of the power switch Q1, for example, in the third stage T3 of fig. 2 and 4, at this time, the voltage at the same-name end of the primary coil T1A is clamped by the voltage at the two ends of the output capacitor C4 through the transformer T1, the voltage at the same-name end of the primary coil T1A is equal to the voltage at the two ends of the output capacitor C4 multiplied by the turns ratio of the transformer T1, for example, the voltage at the same-name end of the primary coil T1A is clamped at about 600V, that is, the voltage at the two ends of the power switch Q1 is stabilized at about 600V in the third stage T3.

Optionally, fig. 7 is a schematic structural diagram of another flyback switching power supply according to an embodiment of the present invention, and referring to fig. 7, a leakage inductance absorbing circuit 220 includes an auxiliary capacitor C3; the first polar plate of the auxiliary capacitor C3 is electrically connected with the homonymous end of the secondary coil T1B; the second polar plate of the auxiliary capacitor C3 is electrically connected with the synonym end of the secondary coil T1B; the auxiliary capacitor C3 is used for charging when the power switch Q1 is turned off and discharging when the power switch Q1 is turned on.

For convenience of explanation, the primary circuit 10 in fig. 7 is equivalent to the excitation inductance Lm and the leakage inductance Lr of the primary coil T1A.

Fig. 8 is a current waveform diagram of an excitation inductance according to an embodiment of the present invention, fig. 9 is a current waveform diagram of a leakage inductance according to an embodiment of the present invention, fig. 10 is a voltage waveform diagram of both ends of an auxiliary capacitor according to an embodiment of the present invention, and the first stage t1, the second stage t2, the third stage t3, and the fourth stage t4 in fig. 8 to 10 are the same as those in fig. 2 and 4. Referring to fig. 8 to 10, in the first stage t1, after the power switch Q1 is turned on, the INPUT positive terminal input+ and the INPUT negative terminal INPUT continuously store energy for the excitation inductance Lm and the leakage inductance Lr, and the currents of the excitation inductance Lm and the leakage inductance Lr are gradually increased; when the power switch Q1 is turned on, the auxiliary capacitor C3 is continuously discharged to the output capacitor C4 through the leakage inductance charging circuit 230, and the voltage of the auxiliary capacitor C3 is reduced to zero and maintained at zero voltage.

In the second stage T2, the power switch Q1 is turned off, the current of the excitation inductance Lm is not suddenly changed, the current is gradually reduced, the excitation inductance Lm generates an induced voltage in the secondary coil T1B through the transformer T1, the voltage of the same-name end of the secondary coil T1B is larger, the auxiliary capacitor C3 is charged, the voltage of the auxiliary capacitor C3 is rapidly increased, at this time, the voltage of the excitation inductance Lm is clamped in a smaller range by the auxiliary capacitor C3, the voltage of both ends of the excitation inductance Lm is smaller, meanwhile, the drain voltage of the power switch Q1 is larger, the reverse voltage of both ends of the leakage inductance Lr (that is, the voltage of the lower end of the leakage inductance is higher than the voltage of the upper end in fig. 7) is larger, the current of the leakage inductance Lr is rapidly reduced to zero, and the current oscillates to a negative value. In this stage, the voltage of the excitation inductance Lm is clamped in a small range, so that the voltage of the power switch Q1 can quickly release the energy of the leakage inductance Lr without being excessively large, a large voltage spike is avoided, and in this stage, the energy charged in the auxiliary capacitor C3 is mainly the energy from the leakage inductance Lr, and thus the current of the excitation inductance Lm is slowly reduced.

In the third stage T3, most of the energy of the leakage inductance Lr is absorbed, and still a small part of the energy oscillates in a small range, after the voltage of the auxiliary capacitor C3 rises to the voltage of the output capacitor C4, the energy of the excitation inductance Lm charges the output capacitor C4 through the transformer T1, the output capacitor C4 supplies power to the load, and the current of the excitation inductance Lm gradually decreases until zero. At this stage, the voltage of the auxiliary capacitor C3 is equal to the voltage of the output capacitor C4. The voltage across the output capacitor C4 is a voltage between the output positive terminal out+ and the output negative terminal OUT-, and is generally a stable voltage.

In the fourth stage t4, after the energy release of the excitation inductance Lm is completed, the parasitic capacitance of the power switch Q1 and the second filter capacitance C2 are discharged, the current of the excitation inductance Lm and the current of the leakage inductance Lr are reduced to a negative value and then restored to zero, the source-drain voltage of the power switch Q1 is reduced to zero, the power switch Q1 is about to be turned on, and the first stage t1 in the next cycle is entered. At this stage, the current of the excitation inductance Lm and the current of the leakage inductance Lr decrease after decreasing to a negative value, and the voltage at the same terminal of the secondary coil T1B slightly decreases, and the auxiliary capacitor C3 is slightly discharged, and the voltage of the auxiliary capacitor C3 also slightly decreases.

Optionally, with continued reference to fig. 7, the leakage inductance absorption loop 220 further includes a first diode D2. In an alternative embodiment, the anode of the first diode D2 is electrically connected to the same-name terminal of the secondary winding T1B, and the cathode of the first diode D2 is electrically connected to the first plate of the auxiliary capacitor C3. In another alternative embodiment, fig. 11 is a schematic structural diagram of another flyback switching power supply according to the embodiment of the present invention, referring to fig. 11, a cathode of a first diode D2 is electrically connected to a synonym terminal of a secondary winding T1B, and an anode of the first diode D2 is electrically connected to a second plate of an auxiliary capacitor C3.

The first diode D2 can prevent the auxiliary capacitor C3 from charging the secondary coil T1B when the auxiliary capacitor C3 discharges, and only charges the output capacitor C4 through the leakage inductance charging circuit 230, thereby improving energy conversion efficiency; the state of the secondary coil T1B is prevented from being influenced by the electric leakage of the auxiliary capacitor C3, and the reliability of the flyback switching power supply is improved.

Optionally, the leakage inductance absorption loop 220 further includes a second diode D4; the cathode of the second diode D4 is electrically connected to the first plate of the auxiliary capacitor C3, and the anode of the second diode D4 is electrically connected to the second plate of the auxiliary capacitor C3. In this way, the second diode D4 can be turned on when the auxiliary capacitor C3 is discharged and the voltage across the auxiliary capacitor C3 is reduced to zero, thereby maintaining and stabilizing the voltage across the auxiliary capacitor C3.

Optionally, fig. 12 is a schematic structural diagram of another flyback switching power supply according to an embodiment of the present invention, fig. 13 is a schematic structural diagram of another flyback switching power supply according to an embodiment of the present invention, and referring to fig. 12 and fig. 13, a leakage inductance charging circuit 230 includes a third diode D3 and an auxiliary coil T1C; the anode of the third diode D3 is electrically connected with the first polar plate of the auxiliary capacitor C3, the cathode of the third diode D3 is electrically connected with the homonymous end of the auxiliary coil T1C, and the homonymous end of the auxiliary coil T1C is electrically connected with the first polar plate of the output capacitor C4; or, the cathode of the third diode D3 is electrically connected to the second electrode plate of the auxiliary capacitor C3, the anode of the third diode D3 is electrically connected to the synonym end of the auxiliary coil T1C, and the synonym end of the auxiliary coil T1C is electrically connected to the second electrode plate of the output capacitor C4.

The auxiliary coil T1C is also a coil winding in the transformer T1 formed by the primary coil T1A and the secondary coil T1B.

Illustratively, when the power switch Q1 is turned on, the voltage at the same-name terminal of the auxiliary coil T1C is low, and the current in the auxiliary coil T1C tends to flow from the different-name terminal of the auxiliary coil T1C to the same-name terminal, but the third diode D3 is turned off, so that the energy in the output loop 210 is not transferred to the leakage inductance absorbing loop 220. When the power switch Q1 is turned off, the voltage at the same-name end of the auxiliary coil T1C is higher, the current in the auxiliary coil flows from the same-name end to the different-name end of the auxiliary coil T1C, the third diode D3 is turned on, and the leakage inductance charging circuit 230 transmits the energy in the leakage inductance absorbing circuit 220 to the output circuit 210. The third diode D3 and the auxiliary coil T1C function as a bias such that the leakage inductance charging circuit 230 is turned on only when the power switch Q1 is turned off.

Optionally, with continued reference to fig. 12 and 13, the leakage inductance charging circuit 230 further includes a first inductance L1; the first inductor L1 is connected in series between the auxiliary capacitor C3 and the third diode D3. The first inductor L1 can limit the discharge speed of the auxiliary capacitor C3, and prevent the voltage of the auxiliary capacitor C3 from dropping to a negative value.

Optionally, with continued reference to fig. 12 and 13, the primary line 10 further includes a spike absorbing loop 110; the peak absorption loop comprises an absorption resistor R1, an absorption capacitor C5 and an absorption diode D5; the anode of the absorption diode D5 is electrically connected with the homonymous terminal of the primary coil T1A; the cathode of the absorption diode D5 is electrically connected to the opposite end of the primary coil T1A through the absorption resistor R1 and the absorption capacitor C5, respectively. The voltage clamping is performed by the snubber diode D5 and the snubber capacitor C5 of the peak snubber circuit 110, so that the peak voltage of the power switch Q1 can be reduced, and the snubber resistor R1 can be used to discharge the absorbed energy, so that the peak voltage can be further reduced, and the reliability of the flyback switching power supply can be improved.

Note that the above is only a preferred embodiment of the present invention and the technical principle applied. It will be understood by those skilled in the art that the present invention is not limited to the particular embodiments described herein, but is capable of various obvious changes, rearrangements and substitutions as will now become apparent to those skilled in the art without departing from the scope of the invention. Therefore, while the invention has been described in connection with the above embodiments, the invention is not limited to the embodiments, but may be embodied in many other equivalent forms without departing from the spirit or scope of the invention, which is set forth in the following claims.

Claims

1. A flyback switching power supply, comprising: a primary line and a secondary line;

the output loop is used for outputting an electric signal when the power switch is turned on and charging when the power switch is turned off; the leakage inductance absorption loop is used for absorbing leakage inductance energy of the primary coil when the power switch is turned off; the leakage inductance charging loop is used for providing the leakage inductance energy absorbed by the leakage inductance absorbing loop to the output loop when the power switch is turned on;

the leakage inductance absorption loop comprises an auxiliary capacitor; the first polar plate of the auxiliary capacitor is electrically connected with the homonymous end of the secondary coil; the second polar plate of the auxiliary capacitor is electrically connected with the synonym end of the secondary coil; the auxiliary capacitor is used for charging when the power switch is turned off and discharging when the power switch is turned on;

the leakage inductance charging loop comprises a third diode and an auxiliary coil; the anode of the third diode is electrically connected with the first polar plate of the auxiliary capacitor, the cathode of the third diode is electrically connected with the homonymous end of the auxiliary coil, and the heteronymous end of the auxiliary coil is electrically connected with the output loop; or, the cathode of the third diode is electrically connected with the second plate of the auxiliary capacitor, the anode of the third diode is electrically connected with the synonym end of the auxiliary coil, and the synonym end of the auxiliary coil is electrically connected with the output loop.

2. The flyback switching power supply of claim 1 wherein the output loop comprises a rectifier diode and an output capacitor;

3. The flyback switching power supply of claim 1 wherein the leakage inductance absorption loop further comprises a first diode;

4. The flyback switching power supply of claim 1 wherein the leakage inductance absorption loop further comprises a second diode;

5. The flyback switching power supply of claim 1 wherein the leakage inductance charging circuit further comprises a first inductance;

6. The flyback switching power supply of claim 1 wherein the primary line further comprises a first filter capacitor;

7. The flyback switching power supply of claim 1 wherein the primary line further comprises a second filter capacitor;

8. The flyback switching power supply of claim 1 wherein the primary line further comprises a spike absorption loop;