WO2018161748A1

WO2018161748A1 - Flyback switching power supply

Info

Publication number: WO2018161748A1
Application number: PCT/CN2018/074968
Authority: WO
Inventors: 王保均
Original assignee: 广州金升阳科技有限公司
Priority date: 2017-03-10
Filing date: 2018-02-01
Publication date: 2018-09-13
Also published as: CN106655791B; CN106655791A

Abstract

A flyback switching power supply, which is based on a common three-winding absorption flyback converter: connecting a common-polarity end of a first primary winding (N_P1) in a transformer (B) to a power supply, and connecting a common-polarity end of a second primary winding (N_P2) to ground, ensuring that the first primary winding (N_P1) and the second primary winding (N_P2) are dual-wire windings; adding a capacitor (C1), an end of the capacitor (C1) being connected to an opposite-polarity end of the first primary winding (N_P1), while another end is connected to an opposite-polarity end of the second primary winding (N_P2), thus achieving: when a field effect transistor (Q1) is saturated and turned on, both the first primary winding (N_P1) and the second primary winding (N_P2) are excited; when the field effect transistor (Q1) is turned off, a secondary winding (N_S) outputs energy, and energy from leakage inductance is non-destructively absorbed by the second primary winding (N_P2) by means of a diode (D1); the present invention is suitable for operation at low voltages, and improves the utilization rate and current density of primary windings, and thus power density is high, allowing for a large leakage inductance between primary and secondary sides, while conversion efficiency is high.

Description

Flyback switching power supply

Technical field

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

Background technique

At present, the switching power supply is widely used. For applications where the input power is below 75W and the power factor (PF, power factor) is not required, the fly-back switching power supply has a fascinating advantage: the circuit The topology is simple and the input voltage range is wide. Since the number of components is small, the reliability of the circuit is relatively high, so the application is wide. For convenience, many documents are also known as flyback switching power supplies, flyback power supplies, and flyback converters. In Japan and Taiwan, they are also called flyback converters, flyback switching power supplies, and flyback power supplies. A common topology for an AC/DC converter is shown in Figure 1. The prototype is from the "Switching Power Supply Converter Topology and Design" by Dr. Zhang Xingzhu, ISBN 978-7-5083-9015-4. This book is referred to herein simply as: Reference 1. The rectifier bridge 101, the filter circuit 200, and the basic flyback topology unit circuit 300 are also referred to as the main power stage. The practical circuit is also provided with a varistor, an NTC thermistor, and an EMI (Electromagnetic Interference) in front of the rectifier bridge. ) Protect the circuit to ensure that the electromagnetic compatibility of the flyback power supply meets the requirements for use. The flyback switching power supply requires that the leakage inductance between the primary and secondary windings is as small as possible, so that the conversion efficiency is high, and the withstand voltage of the primary side main power switch tube is also lowered, and the RCD network is used as the demagnetization and absorption counter. The converter, the loss of the RCD network is also reduced. Note: RCD absorption refers to the absorption circuit composed of resistors, capacitors and diodes. The literature in China is the same as the international one. Generally, the letter R is used to give the resistance number and represents the resistance. The letter C is used to number the capacitor and represent the capacitor. The letter D is used to give the diode. Numbered and represents the diode, the resistor and capacitor are connected in parallel, and then connected in series with the diode to form an RCD network.

The rectifier bridge 101 is generally composed of four rectifier diodes. When there is no

rectifier bridge

101, 200, 300 can constitute a DC/DC switching power supply or converter. Because it is DC power supply, there is no power factor requirement, and the power can be 75W. the above. In fact, the use of a flyback topology in a low-voltage DC/DC switching power supply is not mainstream. This is because at low voltage, the input current of the flyback switching power supply is discontinuous and the ripple is large, which requires more power supply equipment. High; the output current is not continuous, the ripple is large, and the capacity of the subsequent filter capacitor is high; especially when the input voltage is low, since the excitation current becomes larger, the primary winding has to be wound with multiple strands; The inductance of the side winding is also low. It is often found that the calculated number of turns cannot be tiled to the left to the right of the slot of the full frame. Especially when the working voltage is high, the sandwich series winding method can be used. Next, it is forced to adopt the sandwich parallel winding method. Since the two primary windings are not in the same layer, there is a leakage inductance between the two primary windings, and the leakage inductance will cause loss, thereby making the switching power supply less efficient. The problem caused by the leakage inductance between two parallel primary windings:

1) During excitation, due to the leakage inductance, the induced voltage difference has a voltage difference in the leakage inductance, causing a loss that cannot be ignored. This makes it easier to understand: if two turns of the primary winding are different, the equivalent is This short circuit between turns is simply a short circuit of the DC internal resistance of the two parallel primary windings. Relatively speaking, the loss is not as large as the true turn-to-turn short circuit.

2) When demagnetizing, that is, the rectifier diode of the secondary side is turned on, and the output filter capacitor is reciprocally charged. At this time, the primary side induces a reflected voltage, and the two parallel primary windings induce an unequal voltage due to the winding. The internal resistance is low, and the current induced by the unequal voltage is not small, causing loss and large electromagnetic interference.

3) If the third winding is used for demagnetization, who is the third winding and the two parallel primary windings? Only two third windings can be used, which are respectively wound with two parallel primary windings, and then connected in parallel to form a "third winding". The process is complicated, and the third winding connected in parallel by two windings also induces unequal unequal The voltage, which causes losses and large electromagnetic interference.

In fact, for the common third winding demagnetization, the advantage is non-destructive demagnetization, the efficiency is higher, but the choice of the wire diameter of the third winding is also a problem: the selection is relatively thin, and the winding of the primary winding is more troublesome, easy to put The thin wire is broken; if the same wire diameter is selected as the primary winding, the cost is high. The third winding demagnetization flyback converter is also referred to as a "three-winding absorption flyback converter".

Two parallel primary windings are used for low-voltage DC/DC switching power supplies. Low-voltage DC/DC switching power supplies generally refer to input voltages below 48V. Some low-voltage DC/DC switching power supplies can operate up to 160V DC, such as railway power supplies.

Summary of the invention

In view of this, the present invention solves the shortcomings of the existing low-voltage flyback switching power supply, and provides a flyback switching power supply. The primary winding can be used without the need of two separate parallel connections, that is, the primary secondary winding can be allowed. The leakage inductance between the two is large, and the third winding is not used for demagnetization, and the conversion efficiency is not lowered, and the loss during excitation and demagnetization is reduced.

The object of the present invention is achieved by a flyback switching power supply including a transformer, an N-channel FET, a second capacitor, a first diode, a second diode, and a transformer including a first primary side The winding, the second primary winding and the secondary winding, the secondary winding opposite end is connected to the second diode anode, the second diode cathode is connected to one end of the second capacitor, and forms an output positive, and the secondary winding has the same name end Connected to the other end of the second capacitor and formed an output negative; the positive terminal of the input DC power supply is simultaneously connected with the same name end of the first primary winding, the cathode of the first diode, the first primary winding different name end and the N channel field The drain of the effect transistor is connected; the anode of the first diode is connected to the opposite end of the second primary winding, the source of the N-channel FET is connected to the same end of the second primary winding, and the connection point is simultaneously connected to the input DC power supply. a negative terminal; a gate connection control signal of the N-channel field effect transistor; wherein the first primary winding and the second primary winding are two-wire winding, and further comprising a first capacitor, one end of the first capacitor and the first The primary winding is connected to the different name, the first electric The other end of the capacitor is connected to the opposite end of the second primary winding.

The present invention also provides an equivalent solution of the foregoing solution 1. The second embodiment of the present invention can also be implemented. A flyback switching power supply includes a transformer, an N-channel FET, a second capacitor, and a first diode. a tube, a second diode, the transformer comprises a first primary winding, a second primary winding and a secondary winding, the secondary winding opposite end is connected to the second diode anode, the second diode cathode and the second One end of the capacitor is connected and forms an output positive, the same-side end of the secondary winding is connected to the other end of the second capacitor, and the output is negative; the positive terminal of the input DC power supply is different from the drain of the N-channel FET and the second primary winding. The terminals are connected, the source of the N-channel FET is connected to the same name end of the first primary winding; the second-side winding has the same name end connected to the cathode of the first diode, and the first primary winding has a different name and the first end The anode of the diode is connected, the connection point is simultaneously connected to the negative terminal of the input DC power supply; the gate of the N-channel FET is connected with the control signal; and the first primary winding and the second primary winding are double-wired and wound Also includes the first capacitor A first end of the first capacitor and is connected to the dotted end of the primary winding, a first capacitor connected to the other end of the primary winding of the second dot end.

The invention also provides a technical scheme using a P-channel field effect tube. On the basis of the above scheme 1, the polarity of the power source, the diode and the same name end are reversed (the output rectification part does not need to be reversed), then the scheme 3: an inverse is obtained. The excitation switching power supply comprises a transformer, a P-channel FET, a second capacitor, a first diode, a second diode, and the transformer comprises a first primary winding, a second primary winding and a secondary winding, The second side of the secondary winding is connected to the anode of the second diode, the cathode of the second diode is connected to one end of the second capacitor, and the output is positive, and the end of the secondary winding is connected with the other end of the second capacitor, and the output is negative. The negative terminal of the input DC power source is simultaneously connected to the opposite end of the first primary winding and the anode of the first diode, and the first primary winding has the same name end connected to the drain of the P channel FET; the first diode The cathode is connected to the same end of the second primary winding, the source of the P-channel FET is connected to the second end of the second primary winding, and the connection point is simultaneously connected to the positive terminal of the input DC power supply; the gate connection of the P-channel FET control signal; The first primary winding and the second primary winding are two-wire winding, and further comprise a first capacitor, one end of the first capacitor is connected to the same end of the first primary winding, and the other end of the first capacitor is The two primary windings are connected to the same name end.

The invention also provides the equivalent scheme of the foregoing scheme 3, and the technical scheme of adopting the P-channel field effect transistor for the scheme 2, on the basis of the foregoing scheme 2, the polarity of the power source, the diode and the same name end are reversed (the output rectification part does not need to be reversed) According to the fourth aspect of the present invention, a flyback switching power supply includes a transformer, a P-channel FET, a second capacitor, a first diode, and a second diode. The transformer comprises a first primary winding, a second primary winding and a secondary winding, the secondary winding opposite end is connected to the second diode anode, and the second diode cathode is connected to one end of the second capacitor and forms an output positive The secondary winding has the same name end connected to the other end of the second capacitor, and forms an output negative; the negative terminal of the input DC power supply is simultaneously connected with the drain of the P channel field effect transistor and the same end of the second primary winding, and the P channel field effect transistor The source is connected to the first name of the first primary winding; the second end of the second winding is connected to the anode of the first diode, and the first end of the first winding is connected to the cathode of the first diode, and is connected Point simultaneously Connected to the positive terminal of the input DC power supply; the gate of the P-channel FET is connected to the control signal; the first primary winding and the second primary winding are wound in a double line, and further includes a first capacitor and a first capacitor One end of the first capacitor is connected to the opposite end of the first primary winding, and the other end of the first capacitor is connected to the opposite end of the second primary winding.

As an improvement of the above four schemes, the first primary winding and the second primary winding have the same wire diameter.

Preferably, the second primary winding participates in the excitation by the first capacitance.

Preferably, the physical path of the excitation current of the first primary winding and the second primary winding is reversed in the PCB layout.

The working principle will be explained in detail in conjunction with the embodiments. The beneficial effects of the invention are as follows: the leakage inductance between the primary and secondary windings is allowed to be large, and the primary side is still wound by two wires, the conversion efficiency is high, and the EMI performance is very good.

DRAWINGS

1 is a schematic diagram of a conventional flyback switching power supply for alternating current to direct current;

2 is a schematic diagram of a first embodiment of a flyback switching power supply scheme according to the present invention;

2-1 is a schematic diagram of charging the capacitor C1 at the time of power-on in the first embodiment;

2-2 is a schematic diagram showing voltage polarities of charging of capacitor C1 after power-on in the first embodiment;

2-3 is a schematic diagram of generating two

excitation currents

41, 42 when Q1 is saturated in the first embodiment;

2-4 is a schematic diagram of the Q1 cutoff in the first embodiment, generating a freewheeling current 43 and a demagnetizing current 44;

3 is a schematic diagram of a second embodiment of a flyback switching power supply scheme according to the present invention;

4 is a schematic diagram of a third embodiment of a flyback switching power supply scheme according to the present invention;

FIG. 5 is a schematic diagram of a fourth embodiment of a flyback switching power supply scheme according to the present invention.

detailed description

First embodiment

2 is a schematic diagram of a flyback switching power supply according to a first embodiment of the present invention, including a transformer B, an N-channel FET Q1, a second capacitor C2, a first diode D1, and a second diode Tube D2, transformer B includes a first primary winding N _P1 , a second primary winding N _P2 and a secondary winding N _S , the secondary winding N _S different end is connected to the second diode D2 anode, the second diode the cathode end of diode D2 is connected to a second capacitor C2, and outputs the positive form, as in FIG Vout + terminal of the secondary winding N _S dotted terminal connected to the other terminal of the second capacitor C2, and the formation of negative output as Vout in FIG. - end; DC input voltage U _DC (hereinafter, also referred to as a direct current power source U _DC, power source U _DC, or U _DC) while the positive terminal +, and the cathode terminal of the first primary winding N _P1 of the same name of the first diode D1 Connected, the first primary winding N _{P1 is} connected to the drain D of the N-channel field effect transistor Q1; the anode of the first diode D1 is connected to the second primary winding N _P2 , N-channel field effect The source S of the tube Q1 is connected to the same end of the second primary winding N _P2 , and the connection point is simultaneously connected to the negative terminal of the input DC power supply U _DC - the gate G of the N-channel FET Q1 Connecting the control signal; the first primary winding N _P1 and the second primary winding N _P2 are wound in a double line, and further includes a first capacitor C1, one end of the first capacitor C1 and the first primary winding N _P1 The different ends are connected, and the other end of the first capacitor C1 is connected to the different end of the second primary winding N _P2 .

End of the same name: one end of the winding in the figure marked with a black dot;

Heterogeneous end: one end of the winding in the figure where there is no black mark;

Control signal: including various pulse waves such as PWM pulse width modulation signal and PFM pulse frequency modulation;

Transformer B: the first primary winding N _P1 and the second primary winding N _{P2 are} in the figure, the cores are connected by a broken line, indicating that they are wound around a transformer and share the same core, not a separate transformer, just for The graphics are clear and the connection relationship is simple, and the drawing method in the figure is used.

In FIG. 2, the source of the N-channel FET Q1 is connected to the same end of the second primary winding N _P2 , and the connection point is simultaneously connected to the negative terminal of the input DC power supply U _DC - that is, the source of the FET Q1 is connected to the input DC. The negative terminal of the power supply U _DC - this does not exist directly in the actual application, because in the field of switching power supply, the analysis of the working principle of the basic topology will omit unnecessary factors. In practical applications, the source of the FET is connected to a current sense resistor or a current transformer to detect the average current or peak current to implement various control strategies. The current sense resistor or current transformer is connected to the source. Equivalent to the source, which is well known in the art, this application follows the industry default rules. If a current transformer is used, the current transformer can appear anywhere in the excitation circuit, such as the drain of a FET, such as the same or different end of the first primary winding, and the current transformer has a conventional primary side. It is also a Hall sensor that is a "wire" and a magnetic core transformer whose secondary side is a multi-turn coil.

Working principle: Referring to Figure 2, when the first capacitor C1 (for the convenience of analysis, according to the textbook standard, hereinafter referred to as capacitor C1 or C1, the other devices are the same) does not exist, the circuit is a third winding demagnetization flyback The switching power supply, the second primary winding N _P2 becomes the "third winding" dedicated to demagnetization, but the invention is that after the capacitor C1 is added, the working principle of the circuit is completely different from the prior art;

When the circuit of Figure 2 is powered on, D1 does not work due to reverse bias. Q1 does not work because it does not receive the control signal. It is equivalent to an open circuit. Then, the power supply U _DC charges C1 through the first primary winding N _P1 . Returning to the negative terminal of the power supply U _DC through the second primary winding N _P2 , as shown in Figure 2-1, the direction of the charging current to C1 is indicated by two arrows in the figure. It can be seen that the first primary winding N _P1 The charging current is: flowing from the same name end to the different name end; the charging current of the second primary winding N _P2 is: flowing from the different name end to the same name end; N _P1 and N _P2 are two lines and winding, the two currents are equal in magnitude The generated magnetic flux is reversed and completely canceled. That is, at the time of power-on, the power supply U _DC charges C1 through the two windings of the transformer B. These two windings cancel out due to mutual inductance, and do not work, and C1 is equivalent to passing N _P1 and The DC internal resistance of N _P2 is connected in parallel with the power supply U _DC , and C1 still functions as power supply filtering and decoupling;

As time goes by, the terminal voltage of C1 is equal to the voltage of U _DC , and the left is right and the right is negative, as shown in Figure 2-2.

When Q1 receives the control signal normally, taking one cycle as an example, when the gate of Q1 is high, Q1 is saturated and its internal resistance is equal to the on-state internal resistance R _ds(ON) . For the convenience of analysis, this is the case. It is regarded as straight through, which is a wire. As shown in Figure 2-3, D1 is in a reverse bias state and does not participate in the work; at this time, two excitation currents are generated, as shown by 41 and 42 in Figure 2-3;

The current 41 is: the positive end of the power supply U _DC passes through the same name end of the first primary winding N _P1 , the different name of N _P1 is output, the drain of Q1 enters, the source of Q1 is out, and returns to the negative end of the power supply U _DC ;

The current 42 is: the left positive end of the capacitor C1 enters through the drain of Q1, the source of Q1 is out, and then enters through the same name of the second primary winding N _P2 , the different name of N _P2 is terminated, and the capacitor C1 is right negative. end;

For convenience, the negative terminal of the power supply U _DC is assumed to be grounded here, called ground. Because the left positive end of C1 is connected to the negative terminal of the power supply U _DC through saturation, that is, the ground is negative, then the voltage at the right negative end of C1 is about -U. _DC , in this excitation process, if the terminal voltage of C1 is insufficient due to insufficient capacity, that is, the voltage at the right negative end of C1 tends to rise, and its absolute value is smaller than U _DC , then in the process of excitation, Q1 When the saturation conduction is excited to the first primary winding N _P1 , a positive voltage is induced at the same end, and a negative voltage is induced at the opposite end. The magnitude is equal to the voltage applied across N _P1 , equal to U _DC , at this time, due to N _P1 and N _P2 is double wound and wound, N _P2 is also induced at both ends: the same name end induces a positive voltage, the different name end induces a negative voltage, the size is equal to U _DC , this voltage will directly charge C1, this is a positive The process is such that the terminal voltage of C1 does not drop anyly due to insufficient capacity; as mentioned above: the power supply U _DC charges C1 through the two windings of the transformer B. These two windings cancel out due to the mutual inductance, which does not work, and C1 is equivalent. DC internal resistance through N _P1 and N _P2 In parallel with the power supply U _DC , the power supply U _DC directly supplies power to C1 through a very low DC internal resistance, and its terminal voltage remains stable;

It can be seen that the excitation currents of 41 and 42 are in parallel. Since the inductances of N _P1 and N _P2 are the same, the excitation voltages are the same, and they are equal to U _DC , 41 and 42 are completely equal. During the excitation process, the secondary winding N _{S is} pressed. than the same induced voltage, the induced voltage is: n dot end induced voltage, induced-phase terminal of a negative voltage equal to U _DC magnitude multiplied by the turns ratio n, i.e., N _S induced positive voltage on the negative, this voltage In series with the terminal voltage of C2, added to both ends of D2, D2 is reverse biased and not turned on, then the secondary side is equivalent to no load, no output;

During the excitation process, the currents of 41 and 42 increase linearly upward; the current direction flows from the same name end to the different name end in the inductance;

In order to ensure that the electromagnetic compatibility meets the requirements of use, it is tricky when wiring. Observe 41 and 42 in Figure 2-3, 41 is the clockwise current direction, and 42 is the counterclockwise direction. If it is on the board, it is also guaranteed. When the two currents are clockwise and the other is counterclockwise, the magnetic flux generated during the excitation can be cancelled at a distance, so that the EMI performance of the flyback switching power supply of the present invention will be very good. .

The gate of Q1 changes from high level to low level, Q1 also turns from saturation conduction to off. Since the current in the inductor cannot be abrupt, even though Q1 is off at this time, the currents of 41 and 42 still flow from the same name end. At the opposite end, since the current loop of the primary side has been cut, the energy in the core flows from the same name to the opposite end on the secondary side. Referring to Figure 2-4, the secondary winding N _S appears to flow from the same name end to the different name end. As shown in Figure 2-4, the initial magnitude of the current = (the sum of 41 and 42 at the instant of Q1 turn-off) / 匝 ratio n, which causes D2 to conduct a forward conduction, and through the D2 of the forward conduction, Capacitor C2 is charged and Vout establishes voltage or continuously outputs energy. This process is also the process of demagnetization.

The output of the flyback switching power supply is named after the primary winding is disconnected from the power supply. The output voltage depends on the loop control circuit and the flyback transformer (as shown in Figure 1, Figure 2, Series B). The primary side has nothing to do with the turns ratio of the secondary side; in the energy transfer process, the transformer B is not a function of transforming the voltage, but is an isolated version of the Buck-Boost converter through the function of the core freewheeling; therefore, the transformer B is usually Called a flyback transformer;

Since the primary winding and the secondary winding are not normally wound in a double line, there must be a leakage inductance. The energy stored on the primary winding's magnetizing inductance is transmitted to the secondary winding N _S and the output terminal through the transformer B after the Q1 is turned off, but the energy on the leakage inductance is not transmitted, causing overvoltage at both ends of the Q1 tube and damaging the Q1 tube. . The circuit for demagnetizing the leakage inductance of the present invention is composed of D1 and a second primary winding N _P2 , and the working principle is:

N _P1 of the first primary winding and a second primary winding of bifilar N _P2, leakage inductance between the two windings is zero, after Q1 is turned off and the moment, the leakage inductance energy is not transferred to the secondary edge of electrical energy, a second primary winding leakage inductance N _P2 in which the direction of current in the same direction when energized, to flow from the dotted end dot end, i.e., in FIG. 2-4, by the upward flow, the opening of D1, and This electrical energy is absorbed by the DC power source U _{DC to} form a leakage inductance demagnetizing current as indicated by 44;

The leakage energy of the first primary winding N _P1 is coupled to the second primary winding N _P2 without leakage inductance, and demagnetization is realized by D1, and the leakage inductance demagnetization current shown by 44 is also formed;

Obviously, the output voltage Vout is divided by the turns ratio n, which is the "reflected voltage" formed on the primary side when the secondary winding N _S is turned on at D2. For good demagnetization, the reflected voltage cannot be greater than the value of the DC power source U _DC . This circuit works well. Since the currents of 41 and 42 are the same, the wire diameters of the first primary winding and the second primary winding are the same, so that the winding is convenient, the wire diameters described herein are the same, and they are all of the same size Litz wire, the color can be Different, that is, multi-strand stranding, for the convenience of identification, the same specification wire including the Litz wire can have different colors. As the operating frequency increases, the high frequency current tends to flow on the surface of the enameled wire. In this case, the Litz wire can solve this problem. Of course, two different colors of enameled wire are used to make the Litz wire first, and the first primary winding and the second primary winding are separated by color, or the wire diameter and the number of strands of the two windings are different. , both achieve the purpose of the invention.

It can be seen that compared with the conventional three-winding absorption flyback converter, the invention has many differences, mainly: the "third winding" of the conventional three-winding absorption flyback converter does not participate in the excitation, and only participates in demagnetization; In the invention, there is no third winding, and both primary windings participate in the excitation, and in the demagnetization, the second primary winding N _P2 participates in the demagnetization of the leakage inductance, thereby achieving the lossless absorption of the leakage energy. Because the lossless absorption of the leakage inductance energy is realized, the leakage inductance of the primary and secondary sides is allowed to be large, and the conversion efficiency of the converter is not affected, so that high efficiency is achieved, and in the present invention, the demagnetization winding is the second. primary winding N _P2, it is also involved in the excitation to improve the current density of the primary winding, increases the power density converters. The source of the DC power source U _DC can be obtained by rectifying the AC power and filtering it by electrolytic capacitor filtering or valley filling circuit.

Therefore, compared with the prior art, the present invention has the following beneficial effects: the leakage inductance between the primary and secondary windings is allowed to be large, the primary side is still wound by two wires, and the conversion efficiency is high; and the current density of the primary winding is improved. , to improve the power density of the converter; and suitable for lower operating voltage applications.

Second embodiment

The present invention further provides an equivalent solution of the above first embodiment. Corresponding to the second solution, referring to FIG. 3, a flyback switching power supply includes a transformer B, an N-channel FET Q1, and a second capacitor C2. The pole tube D1, the second diode D2, and the transformer B include a first primary winding N _P1 , a second primary winding N _P2 and a secondary winding N _S , and a secondary winding N _S different name end and a second diode D2 anode connection, the cathode of the second diode D2 is connected with one end of the second capacitor C2, and forms an output positive, which is the + end of Vout in the figure, and the opposite end of the secondary winding N _S is connected with the other end of the second capacitor C2, and is formed. The output is negative, which is the end of Vout in the figure; the positive terminal of the input DC power supply U _DC is simultaneously connected to the drain of the N-channel FET Q1 and the second-side winding N _P2 , and the N-channel FET Q1 The source is connected to the first end of the first primary winding N _P1 ; the second primary winding N _P2 is connected to the cathode of the first diode D1 at the same end, and the first primary winding N _{P1 is} different from the first and second poles the anode of diode D1 is connected to the connection point while connected to the negative terminal of the DC power source input U _DC; a gate connected to a control signal N-channel MOSFET Q1 Wherein: a first primary winding N _P1 and the second primary winding N _P2 is bifilar, further comprising a first capacitor C1, a first capacitor C1 is connected to one end of the primary winding with a first terminal of the same name N _P1, The other end of the first capacitor C1 is connected to the same end of the second primary winding N _P2 .

In fact, the second embodiment is a modification of the first embodiment: on the basis of FIG. 2 of the first embodiment, the series devices of the two excitation circuits are interchanged, that is, N _P1 and Q1 are interchanged, and at the same time D1 and N _P2 exchange position, C1 is still connected between the connection points of two series devices, and the circuit of Fig. 3 of the second embodiment is obtained. Since the source voltage of Q1 is fluctuating, this circuit is floating. The driver should be costly and should not be used.

A brief description of its working principle:

Referring to Figure 3, when the circuit is powered on, D1 does not work due to reverse bias. Q1 does not work because it does not receive the control signal. It is equivalent to an open circuit. Then the power supply U _DC charges C1 through N _P2 , and the current passes through N _P1 at the same time. Returning to the negative terminal of the power supply U _DC , also at the time of power-on, the power supply U _DC charges C1 through the two windings of the transformer B. These two windings cancel out due to the mutual inductance, and do not work, and C1 is equivalent to passing N _P2 and N. The DC internal resistance of _P1 is connected in parallel with the power supply U _DC , and C1 still functions as power supply filtering and decoupling;

Over time, the terminal voltage of C1 is equal to the voltage of U _DC , right and left negative;

When Q1 is saturated, its internal resistance is equal to the on-state internal resistance R _ds(ON) , which is regarded as a wire as before, and two excitation currents are generated at this time;

The first way is: the positive end of the power supply U _DC enters through the drain of Q1, the source of Q1 is out, and then enters through the same name of the first primary winding N _P1 , and the different name of N _P1 is output, returning to the power supply U _DC Negative end

The second way is: the right positive end of the capacitor C1 passes through the same name of the second primary winding N _P2 , the different name of N _P2 is output, the drain of Q1 enters, the source of Q1 is out, and the left negative end of capacitor C1 is returned. ;

For convenience, the negative terminal of the power supply U _DC is assumed to be grounded here, called ground. Since the left negative end of C1 is connected to the positive terminal of the power supply U _DC through the saturated conduction Q1, then the voltage at the right positive end of C1 is about 2U _DC to ground. In this excitation process, if the terminal voltage of C1 is insufficient due to insufficient capacity, that is, the voltage at the right positive end of C1 decreases, and the absolute value of C1 is less than U _DC , then in the process of excitation, Q1 saturates to conduct the first When the primary winding N _{P1 is} excited, a positive voltage is induced at the same name, and a negative voltage is induced at the opposite end. The magnitude is equal to the voltage applied across N _P1 , equal to U _DC . At this time, since N _P1 and N _P2 are double wound and Around, N _P2 ends are also induced: the same name end induces a positive voltage, the different name end induces a negative voltage, the size is U _DC , this voltage will directly charge C1, this is a positive process, making the end of C1 The voltage will not drop any due to insufficient capacity; as mentioned above: the power supply U _DC charges C1 through the two windings of the transformer B. These two windings cancel out due to mutual inductance and do not work. C1 is equivalent to passing N _P1 and N. The DC internal resistance of _P2 is connected in parallel with the power supply U _DC , and the power supply U _DC The electric energy is directly supplied to C1 through a very low DC internal resistance, and the terminal voltage thereof is maintained stable;

It can be seen that the first and second excitation currents are in parallel relationship. Since the inductances of N _P1 and N _P2 are the same and the excitation voltages are the same, they are equal to U _DC , and the two paths are completely equal. During the excitation process, the secondary winding N _S The induced voltage is also generated according to the 匝 ratio, the positive voltage is induced by the same name end, and the negative voltage is induced by the different name. The size is equal to U _DC multiplied by the 匝 ratio n, that is, N _S induces a positive and negative voltage, this voltage and C2 The terminal voltage is connected in series, and is applied to both ends of D2, and D2 is reverse biased and not turned on. At this time, the secondary side is equivalent to no load, and no output;

During the excitation process, the first and second excitation currents increase linearly upward; the current direction flows from the same name end to the different name end in the inductance;

When Q1 is cut off, the current in the inductor cannot be abruptly changed. The energy in the core flows from the same name to the opposite end on the secondary side, and the secondary winding N _S appears to flow from the same name to the opposite end. The current passes through the D2 of the forward conduction. Capacitor C2 is charged and Vout establishes a voltage or continuously outputs energy. This process is also the process of demagnetization.

A second circuit example, the leakage inductance is demagnetized by D1 and the second primary winding N _P2 composition, works as follows:

At the instant of Q1 turn-off and after, the energy on the leakage inductance is not transmitted to the secondary side, and the electric energy of the leakage inductance in the second primary winding N _{P2 is} in the same direction as the direction of the excitation, flowing from the same name end to the opposite end. Flowing from bottom to top, opening D1, and this electric energy is absorbed by the DC power source U _{DC to} form a leakage inductance demagnetization current loop;

Similarly, the leakage energy of the first primary winding N _P1 is coupled to the second primary winding N _P2 without leakage inductance, and demagnetization is realized by D1, and a leakage inductance demagnetization current loop is also formed;

The second embodiment is a modification of the first embodiment, and the working principle is equivalent, and the object of the invention is also achieved. As a technical solution using an N-channel FET, it can also be realized by a P-channel field effect transistor. The P-channel FET has a low cost at a low operating voltage, and at this time, the basis of the first embodiment described above. In the above, the polarity of the power supply, the diode, and the end of the same name are reversed, and the output rectification portion is not reversed, so the third embodiment is obtained, as described below.

Third embodiment

Referring to FIG. 4, which is also the foregoing scheme 3, a flyback switching power supply includes a transformer B, a P-channel FET Q1, a second capacitor C2, a first diode D1, and a second diode D2. The transformer B includes a first primary winding N _P1 , a second primary winding N _P2 and a secondary winding N _S , the secondary winding N _S different end is connected to the second diode D2 anode, and the second diode D2 is cathode Connected to one end of the second capacitor C2, and form an output positive, which is the + end of Vout in the figure, the second end of the secondary winding N _S is connected with the other end of the second capacitor C2, and forms an output negative, which is the end of Vout in the figure; Input the negative terminal of the DC power supply U _DC - simultaneously connected to the first primary winding N _P1 different name end, the anode of the first diode D1, the first primary winding N _{P1 the} same name end and the P channel FET Q1 leakage The pole of the first diode D1 is connected to the same end of the second primary winding N _P2 , the source of the P channel FET Q1 is connected to the second primary winding N _P2 , and the connection point is connected to the input DC at the same time. the positive terminal of the power of + U _DC; connected to the gate control signal P-channel MOSFET Q1; N _P1 of the first primary winding and the second primary winding N _P2 Bifilar, further comprising a first capacitor C1 is connected, at one end of the first capacitor C1 and the first primary winding N _P1 dotted terminal connected to the other end of the first capacitor C1 and the second primary winding N _P2 dot end.

2 and FIG. 4, it can be found that the third embodiment reverses the polarity of the same name terminal of the power source U _DC , the diode D1, the first primary winding N _P1 and the second primary winding N _P2 of the first embodiment. , N tube is replaced by P tube. It should be noted that the positive terminal of the input power source U _DC in FIG. 4 is ground, and belongs to the switching power supply of the negative power supply. The P-channel FET itself is also driven by a negative level, which is just right.

Therefore, the working principle is the same as that of the first embodiment, and details are not described herein again, and the object of the invention is also achieved.

Fourth embodiment

The present invention also provides an equivalent of the above third embodiment. Referring to FIG. 5, a flyback switching power supply includes a transformer B, a P-channel FET Q1, a second capacitor C2, and a first diode D1. The second diode D2, the transformer B includes a first primary winding N _P1 , a second primary winding N _P2 and a secondary winding N _S , and the secondary winding N _S different end is connected to the second diode D2 anode, The cathode of the second diode D2 is connected to one end of the second capacitor C2, and forms an output positive, which is the + end of Vout in the figure, and the secondary winding N _S is connected with the other end of the second capacitor C2, and forms an output negative. In the figure, the end of Vout is input; the negative terminal of the input DC power supply is simultaneously connected with the drain of the P-channel FET Q1 and the second-side winding N _P2 , and the source and the first source of the P-channel FET Q1 The side winding N _P1 is connected to the opposite end; the second primary winding N _{P2 is} connected to the anode of the first diode D1, and the first primary winding N _P1 is connected to the cathode of the first diode D1 at the same end. connected to the connection point while the positive terminal of the DC power input +; connected to the gate control signal P-channel MOSFET Q1; a first primary winding N _P1 The second primary winding is bifilar N _P2, further comprising a first capacitor C1, one end of the first capacitor C1 is connected to the first primary winding N _P1 dotted end, the other end of the first capacitor C1 and the second primary The side windings N _P2 are connected at different ends.

The fourth embodiment of FIG. 5 is a modification of the third embodiment: on the basis of FIG. 4 of the third embodiment, the series devices of the two excitation circuits are interchanged, that is, the positions of N _P1 and Q1 are interchanged, and D1 and N _{P2 are} interchanged, and C1 is still connected between the two series primary windings N _P1 and N _P2 , and the circuit of FIG. 5 of the fourth embodiment is obtained. Since the source voltage of Q1 is fluctuating, This circuit is floating drive and should be costly and should not be used.

3 and FIG. 5, it can be seen that the fourth embodiment is the pole of the same name of the power source U _DC , the diode D1, the first primary winding N _P1 and the second primary winding N _P2 of the second embodiment of FIG. 3 . In turn, the N tube is replaced by a P tube. It should be noted that the positive terminal of the input power source U _DC in FIG. 5 is ground, and also belongs to the switching power supply of the negative power supply. The P-channel FET itself is also driven by a negative level, which is just right.

Therefore, the working principle is the same as that of the second embodiment, and details are not described herein again, and the object of the invention is also achieved.

The above is only a preferred embodiment of the present invention, and it should be noted that the above preferred embodiments are not to be construed as limiting the invention. It will be apparent to those skilled in the art that several modifications and refinements can be made without departing from the spirit and scope of the present invention, such as adding a control loop to achieve regulation of the output, as is apparent from the prior art. If the switch tube Q1 or the like with other symbols is used, the output of the secondary side is added to the multi-output, and the filtering is performed by using the π-type filter. These improvements and refinements should also be regarded as the protection scope of the present invention, and the present invention is not described herein again. The scope of protection should be based on the scope defined by the claims.

Claims

A flyback switching power supply includes a transformer, an N-channel FET, a second capacitor, a first diode, a second diode, and the transformer includes a first primary winding, a second primary winding, and a secondary The side winding, the opposite side of the secondary winding is connected to the anode of the second diode, the cathode of the second diode is connected to one end of the second capacitor, and the output is positive, and the end of the secondary winding is connected to the other end of the second capacitor, and Forming an output negative; the positive terminal of the input DC power source is simultaneously connected to the cathode of the first name of the first primary winding, and the cathode of the first diode is connected to the drain of the N-channel field effect transistor; The anode of the diode is connected to the opposite end of the second primary winding, the source of the N-channel FET is connected to the same end of the second primary winding, and the connection point is simultaneously connected to the negative terminal of the input DC power supply; the N-channel FET is The gate connection control signal is characterized in that: the first primary winding and the second primary winding are double-wired and wound, and further includes a first capacitor, and one end of the first capacitor is connected to the first-side winding different-name end, The other end of a capacitor is different from the second primary winding The names are connected.
A flyback switching power supply includes a transformer, an N-channel FET, a second capacitor, a first diode, a second diode, and the transformer includes a first primary winding, a second primary winding, and a secondary The side winding, the opposite side of the secondary winding is connected to the anode of the second diode, the cathode of the second diode is connected to one end of the second capacitor, and the output is positive, and the end of the secondary winding is connected to the other end of the second capacitor, and Forming an output negative; the positive terminal of the input DC power supply is simultaneously connected to the drain of the N-channel FET and the opposite end of the second primary winding, and the source of the N-channel FET is connected to the same-name end of the first primary winding; The second-side winding has the same name end connected to the cathode of the first diode, and the first primary winding different-name end is connected to the anode of the first diode, and the connection point is simultaneously connected to the negative terminal of the input DC power supply; the N-channel field effect transistor The gate connection control signal is characterized in that: the first primary winding and the second primary winding are two wires and wound, and further includes a first capacitor, and one end of the first capacitor is connected to the same end of the first primary winding, The other end of a capacitor and the second primary winding Connected to the same name.
A flyback switching power supply includes a transformer, a P-channel FET, a second capacitor, a first diode, a second diode, and the transformer includes a first primary winding, a second primary winding, and a secondary The side winding, the opposite side of the secondary winding is connected to the anode of the second diode, the cathode of the second diode is connected to one end of the second capacitor, and the output is positive, and the end of the secondary winding is connected to the other end of the second capacitor, and Forming an output negative; the negative terminal of the input DC power supply is simultaneously connected to the opposite end of the first primary winding and the anode of the first diode, and the first primary winding is connected to the drain of the P-channel FET; The cathode of the diode is connected to the same end of the second primary winding, the source of the P-channel FET is connected to the opposite end of the second primary winding, and the connection point is simultaneously connected to the positive end of the input DC power supply; the P-channel FET is The gate connection control signal is characterized in that: the first primary winding and the second primary winding are two-wire and wound, and further includes a first capacitor, and one end of the first capacitor is connected to the same end of the first primary winding, first The other end of the capacitor is the same as the second primary winding The names are connected.
A flyback switching power supply includes a transformer, a P-channel FET, a second capacitor, a first diode, a second diode, and the transformer includes a first primary winding, a second primary winding, and a secondary The side winding, the opposite side of the secondary winding is connected to the anode of the second diode, the cathode of the second diode is connected to one end of the second capacitor, and the output is positive, and the end of the secondary winding is connected to the other end of the second capacitor, and Forming an output negative; the negative terminal of the input DC power supply is simultaneously connected to the drain of the P-channel FET and the same end of the second primary winding, and the source of the P-channel FET is connected to the different end of the first primary winding; The opposite end of the two primary windings is connected to the anode of the first diode, and the first primary winding has the same name end connected to the cathode of the first diode, and the connection point is simultaneously connected to the positive end of the input DC power supply; the P channel field effect transistor The gate connection control signal is characterized in that: the first primary winding and the second primary winding are wound in a double line, and further includes a first capacitor, and one end of the first capacitor is connected to the opposite end of the first primary winding, The other end of the first capacitor and the second primary winding The synonyms are connected.
The flyback switching power supply according to any one of claims 1 to 4, characterized in that the first primary winding and the second primary winding have the same wire diameter.
The flyback switching power supply according to any one of claims 1 to 4, characterized in that the second primary winding participates in the excitation by the first capacitance.
The flyback switching power supply according to any one of claims 1 to 4, characterized in that the physical path of the exciting current of the first primary winding and the second primary winding is opposite in direction when the PCB is wired.