WO2019001179A1 - Flyback switch power supply - Google Patents

Abstract

A flyback switch power supply, which, on the basis of an LCL flyback converter, keeps a common-polarity end of a first primary winding (NP1) of a transformer (B) connected to the positive end of a power supply, and a common-polarity end of a second primary winding (NP2) connected to the negative end of the power supply; the first primary winding and the second primary winding are double-wire parallel windings, and one end of a first capacitor (C1) is connected to an opposite-polarity end of the first primary winding, while another end is connected to an opposite-polarity end of the second primary winding; the opposite-polarity end of the first primary winding is connected to the power source by means of a first field-effect transistor (Q1), and the opposite-polarity end of the second primary winding is connected to the power supply by means of a clamping network (400) in which a second field-effect transistor (Q2) is connected in series to a third capacitor (C3). When the first field-effect transistor saturatedly conducts, the first primary winding and the second primary winding are both excited, and when the first field-effect transistor is closed, a secondary winding (NS) of the transformer outputs energy, while energy from leakage inductance achieves active clamping by means of passing through the clamping network from the second primary winding. After an appropriate control strategy is selected, zero-voltage switching (ZVS), lossless absorption, and a duty cycle greater than 0.5 may be achieved, while having high power density and high conversion efficiency.

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. . 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. Under normal circumstances, 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 V is also reduced, for using the RCD network as a go Magnetic and absorbing flyback converters also reduce losses in the RCD network. 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 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 more than 75W. . In fact, the use of flyback topology in low-voltage DC/DC switching power supplies is not the mainstream. This is because the input current of the flyback power supply is discontinuous and the ripple is large at low voltage, which requires higher requirements for the power supply equipment of the former stage. The output current is also 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; Two parallel primary windings are used for low-voltage DC/DC. 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.

The inductance of the primary winding is also low. It is often found that the calculated number of turns cannot be tiled from 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. Under the voltage, the sandwich parallel winding method is forced. 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 efficiency of the switching power supply variable. Low, loss caused by leakage inductance between two parallel primary windings: this will exist during excitation and demagnetization; if the third winding is used for demagnetization, it is not good to choose the third winding and two parallel Whoever wraps in the primary winding can only use two third windings, 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 two windings are connected in parallel. The presence of three windings also induces unequal voltages, causing 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".

The two applications in China are: 201710142832.0, 201710142797.2, the two names are "a flyback switching power supply", respectively, showing the technical solutions of Figure 2, Figure 3, to solve the above problems, namely: primary winding It is possible to eliminate the use of two separate parallel connections, that is, to allow a large leakage inductance between the primary and secondary windings, and to demagnetize without using the third winding, while the conversion efficiency is not lowered, and the loss during excitation and demagnetization is reduced. However, in this two schemes, the demagnetization mode of Figure 2 requires strict leakage inductance. Otherwise, the energy of the excitation may be directly returned from the DC power source U _DC by D1, instead of appearing in the secondary winding N _S , resulting in There is no current in the secondary side D2, so that the output voltage is low or no output; and the reflected voltage generated when D2 is turned on cannot be greater than the DC power supply U _DC , and if the duty ratio cannot be greater than 0.5, the power density cannot be further improved. For Figure 3, the demagnetization circuit itself is a more classic topology, the duty cycle can be greater than 0.5, but the leakage inductance energy is not recycled.

For convenience, the inventors have defined the topology used in the flyback switching power supply with the Chinese application numbers 201710142832.0 and 201710142797.2, respectively, and will include the forward topology using the inventive concept, and the basic topology excluding the demagnetization mode is defined. For the LCL converter, it consists of two primary-side magnetizing inductances and a capacitor connected in series with them. Such as LCL flyback converter, also refers to LCL flyback switching power supply.

Summary of the invention

In view of the above, the present invention solves the above-mentioned shortcomings of the existing low-voltage LCL flyback switching power supply, and provides a flyback switching power supply, which requires loose leakage between the primary and secondary windings and achieves demagnetization. The energy recovery of the circuit further realizes zero voltage switching of the main power switch tube, further reducing losses and improving conversion efficiency.

The object of the present invention is achieved by a flyback switching power supply including a transformer, a first N-channel FET, a first capacitor, a second capacitor, a first diode, a clamp network, and a transformer including a first primary winding, a second primary winding and a secondary winding, the clamping network comprises at least an anode and a cathode, and the secondary winding is connected to the first diode anode, the first diode cathode and the second capacitor One end is connected, and the output is positive, the second side of the secondary winding is connected with the other end of the second capacitor, and the output is negative; the positive end of the input DC power supply is simultaneously connected with the cathode of the same name of the first primary winding and the cathode of the clamp network, a primary winding different name end is connected to the drain of the first N-channel FET; the anode of the clamp network is connected to the second end of the second primary winding, and the source of the first N-channel FET is connected to the second original The side winding has the same name end, and the connection point is connected to the negative end of the input DC power supply at the same time; the gate of the first N-channel FET is connected with the driving control signal; the first primary winding and the second primary winding are double-wired and wound, first One end of the capacitor and the first The side windings are connected at different ends, and the other end of the first capacitor is connected to the different end of the second primary winding, wherein the clamp network includes at least a third capacitor and a second N-channel FET, a third capacitor and a The two N-channel FETs are connected in series, and the series connection is one of the following two ways:

(1) One end of the third capacitor is the cathode of the clamp network, the other end of the third capacitor is connected to the drain of the second N-channel FET, and the source of the second N-channel FET is the anode of the clamp network, a gate connection clamp control signal of the two N-channel FET;

(2) one end of the third capacitor is the anode of the clamp network, the other end of the third capacitor is connected to the source of the second N-channel FET, and the drain of the second N-channel FET is the cathode of the clamp network, The gate of the two N-channel FET is connected to the clamp control signal.

As an alternative to the first solution: the first N-channel FET can be replaced by a P-channel FET, and the body diode inside the P-channel FET is in the same polarity as the body diode inside the first N-channel FET. 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, a first N-channel FET, a first capacitor and a second capacitor. a first diode, a clamp network, the transformer includes a first primary winding, a second primary winding, and a secondary winding, the clamping network includes at least an anode and a cathode, and the secondary winding has a different name and a first diode The anode of the tube is connected, the first diode cathode is connected to one end of the second capacitor, and the output is positive, the second end of the secondary winding is connected with the other end of the second capacitor, and the output is negative; the positive end of the input DC power supply is simultaneously The drain of the N-channel field effect transistor and the second primary winding are connected at different ends, and the source of the first N-channel field effect transistor is connected to the same name end of the first primary winding; the second primary winding has the same name end and the clamp network The cathode of the first primary winding is connected to the anode of the clamp network, and the connection point is simultaneously connected to the negative terminal of the input DC power supply; the gate of the first N-channel FET is connected to drive the control signal; the first primary side Winding and The second primary winding is wound in two lines, 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 connected to the same end of the second primary winding, and the characteristic is that the clamp network is at least The third capacitor and the second N-channel FET are connected, and the third capacitor and the second N-channel FET are connected in series, and the series connection is one of the following two ways:

(1) One end of the third capacitor is the cathode of the clamp network, the other end of the third capacitor is connected to the drain of the second N-channel FET, and the source of the second N-channel FET is the anode of the clamp network, a gate connection clamp control signal of the two N-channel FET;

(2) one end of the third capacitor is the anode of the clamp network, the other end of the third capacitor is connected to the source of the second N-channel FET, and the drain of the second N-channel FET is the cathode of the clamp network, The gate of the two N-channel FET is connected to the clamp control signal.

As an alternative to the second solution: the first N-channel FET can be replaced by a P-channel FET, and the body diode inside the P-channel FET has the same polarity as the body diode inside the first N-channel FET.

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

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: allowing the leakage inductance between the primary and secondary windings to be large, and the energy of the leakage inductance is recycled by the clamp network, and the duty ratio can be greater than that by those skilled in the art by selecting an appropriate control strategy. 0.5, the power density is high, and the conversion efficiency is not reduced, and the zero voltage switch of the switch tube can be realized, thereby further improving the conversion efficiency.

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 disclosed technical solution of Chinese Application No. 201710142832.0;

Figure 3 is a schematic diagram of the disclosed technical solution of Chinese Application No. 201710142797.2;

4-1 is a schematic diagram of a first embodiment of the present invention, and the clamp network adopts (1) mode;

4-2 is a second schematic diagram of the first embodiment of the present invention, and the clamp network adopts (2) mode;

4-3 is a schematic diagram showing the generation of two excitation currents 41, 42 when Q1 is saturated in the first embodiment;

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

5-1 is a schematic diagram of a second embodiment of the present invention, and the clamp network adopts (1) mode;

FIG. 5-2 is a second schematic diagram of the second embodiment of the present invention, and the clamp network adopts the (2) mode.

Detailed ways

First embodiment

4-1 and 4-2 illustrate a schematic diagram of a flyback switching power supply according to a first embodiment of the present invention, including a transformer B, a first N-channel FET Q1, a first capacitor C1, and a second capacitor. C2, a first diode D2, a clamp network 400, and a transformer B includes a first primary winding N _P1 , a second primary winding N _P2 and a secondary winding N _S , and the clamp network 400 includes at least an anode and a cathode, and a pair The edge of the side winding N _{S is} connected to the anode of the first diode D2, and the cathode of the first 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 The same name end is connected to the other end of the second capacitor C2, and forms an output negative, which is the end of Vout in the figure; the positive end of the input DC power source U _DC (hereinafter also referred to as DC power source U _DC , power source U _DC , or U _DC ) + Also connected to the cathode of the first primary winding N _P1 dotted terminal clamp network 400 connected to the first primary winding N _P1-phase terminal and the drain d N-channel MOSFET Q1; an anode clamp network 400 N _P2 and a second primary winding connected to the dotted end side, N-channel field effect transistor Q1 is connected to the source s of the dot end of the second primary winding N _P2, while the connection point An input connected to the negative terminal of the DC power source U _DC -; g N-channel gate of transistor Q1 is connected to a drive control signal; characterized in that: a first primary winding N _P1 and the second primary winding is bifilar N _P2 The first capacitor C1 has one end connected to the first primary winding N _P1 , and the other end of the first capacitor C1 is connected to the second primary winding N _P2 , the clamp network 400 includes at least a third capacitor C3 and a second N-channel FET Q2, and the third capacitor C3 and the second N-channel FET Q2 are connected in series, and the series connection is one of the following two ways:

(1) One end of the third capacitor C3 is the cathode of the clamp network 400, the other end of the third capacitor C3 is connected to the drain d of the second N-channel FET Q2, and the source s of the second N-channel FET Q2 For the anode of the clamp network 400, the gate g of the second N-channel FET Q2 is connected to the clamp control signal, as shown in FIG. 4-1;

(2) One end of the third capacitor C3 is the anode of the clamp network 400, the other end of the third capacitor C3 is connected to the source s of the second N-channel FET Q2, and the drain d of the second N-channel FET Q2 For the cathode of the clamp network 400, the gate g of the second N-channel FET Q2 is connected to the clamp control signal, as shown in Figure 4-2.

It can be seen that the anode and cathode of the clamp network 400 and the body diode of the second N-channel FET Q2 therein are corresponding. In Figure 4-1, the anode of the body diode of Q2 is the anode of 400. The cathode of the body diode of Q2 is the cathode of 400 after passing C3. In Figure 4-2, the cathode of the body diode of Q2 is the cathode of 400, and the anode of the body diode of Q2 is the anode of 400 after passing C3. When Q2 is replaced by For a P-channel FET, ensure that the body diode inside the P-channel FET is in the same direction as the body diode in Figure 4-1 or Figure 4-2.

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;

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

Clamp control signal: includes various square waves such as PWM pulse width modulation signal and PFM pulse frequency modulation, but appears differently from the drive control signal;

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 Figure 4-1 and Figure 4-2, 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 FET The source of Q1 is connected to the negative terminal of the input DC power supply U _DC - which does not exist directly in practical applications. This is 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 FIG. 4-1 and FIG. 4-2, when the clamp network 400 is replaced by a diode having the same direction as the body diode, it is the prior art circuit of FIG. 2, but the clamp circuit is added to the present invention. After 400, the working principle of the circuit is completely different from the prior art;

Figure 4-1, Figure 4-2 When the circuit is powered up, the second N-channel FET Q2 (for the convenience of analysis, according to the standard of the textbook, hereinafter referred to as the effect transistor Q2 or Q2, the other devices are the same) does not work, Q1 Since the drive control signal is not received and does not work, which is equivalent to an open circuit, the power supply U _DC is charged to C1 through the first primary winding N _P1 , and the current is simultaneously returned to the negative terminal of the power supply U _DC through the second primary winding N _P2 . The charging current of the first primary winding N _P1 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 double lines and Winding, the two currents are equal in magnitude, and the generated magnetic flux is opposite, 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 the mutual inductance, and do not work. C1 is equivalent to the DC internal resistance of N _P1 and N _P2 in parallel with the power supply U _DC . C1 still functions as power supply filtering and decoupling; as time passes, the terminal voltage of C1 is equal to the voltage of U _DC , left positive And right negative.

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 a straight-through, which is a wire. As shown in Figure 4-3, Q2 is in the off state and does not participate in the work. In the figure, 400 is drawn as an open state; at this time, two excitation currents are generated, 41 in Figure 4-3. And 42;

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. The induced voltage is the same. The induced voltage is: a positive voltage is induced at the same name, and a negative voltage is induced at the opposite end. The magnitude is equal to U _DC multiplied by the turns ratio n, that is, N _S induces a positive and negative 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;

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 4-4, the secondary winding N _S appears to flow from the same end to the different end. As shown in Figure 4-4, 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 pass the forward-directed D2 to 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 transformer B is not the function of the voltage conversion, but is the isolated version of the Buck-Boost converter. Therefore, transformer B is often referred to as 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 a clamp network 400 composed of Q2 and C3 and a second primary winding N _P2 , and the working principle is:

The first primary winding N _P1 and the second primary winding N _P2 are double-wired and wound, and the leakage inductance between the two windings is zero. At the instant of Q1 turn-off and after, the energy on the leakage inductance is not transmitted to the secondary 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 end to the opposite end, that is, in FIG. 4-4, flowing from bottom to top, opening the body of Q2 a diode, a current flowing from the source s of Q2 to the drain d, and this electrical energy is charged to C3 to form a leakage inductance demagnetization 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 is demagnetized by the body diode of Q2, and the leakage inductance demagnetization current shown by 44 is also formed. ;

In Figure 4-4, the portion of Q2 that is not active is painted in light color, and the active body diode is shown in dark color.

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. Since there is C3 blocking, the reflected voltage is greater than the value of the DC power source U _DC , the circuit It can also work normally. When D2 is freewheeling, C2 is equivalent to a voltage source, which is "excited" to the secondary winding N _S and the primary side forms a "reflected voltage". At this time, the primary winding is equivalent to a voltage source having a voltage equal to the reflected voltage and The leakage inductance is connected in series, and the current in D2 drops to zero, and D2 turns off, and the primary winding is restored to the series connection of the magnetizing inductance and the leakage inductance.

Then, during the D2 open freewheeling, there will be a variety of working modes, that is, after C3 absorbs the leakage inductance energy, there are many working modes of the circuit, and the working principle is as follows:

(1) If Q2 is not conducting, after the body diode charges C3, D2 is also turned off. At this time, Q2 is turned on, then the voltage on C3 is connected in series with U _DC , and the energy is output to the secondary side through the forward excitation mode. The ratio is not ideal, the energy loss is large, and the partial leakage energy of the primary side is realized.

(2) If Q2 and the body diode are synchronously turned on or lag-on, during the period of D2 conduction, the primary side is connected in series with the leakage inductance. At this time, the leakage inductance and C3 resonate, and the main power tube Q1 is realized by using this resonance. The zero voltage switch (Zero Voltage Switch is abbreviated as ZVS), also known as soft switching technology, realizes the recycling of primary leakage energy. This mode is extremely complicated and has dozens of working modes.

(3) If Q2 is not conducting, after the body diode charges C3, the next cycle is followed by charging. In a certain cycle after multiple cycles, Q2 and the body diode are turned on or lag-on, during D2 conduction, the original The voltage source and the leakage inductance are connected in series. At this time, the leakage inductance and C3 resonate. The ZVS mode of the main power tube Q1 is realized by using this resonance, and the recycling of the primary side leakage inductance energy is realized, which is also extremely complicated, and there are dozens of kinds of work. mode.

(4) If C3 and the primary inductor resonate after D2 is turned off, the terminal voltage of C3 will be close to or equal to twice the U _DC voltage at a certain time, and it is up and down, due to the terminal voltage of C1. It is always left positive and right negative, and equal to U _DC . At this moment, the left terminal voltage of C1 is zero volt, that is, the terminal voltage of Q1 is also zero volt. If Q1 is saturated at this moment, then zero of Q1 is realized. The voltage is turned on, and this mode must be the current interrupt mode, and the time when Q1 is turned on is extremely easy to detect.

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.

In order to ensure that the electromagnetic compatibility meets the requirements of use, it is tricky when wiring. Observe the currents 41 and 42 in Figure 4-3 and 4-4, 41 is the clockwise current direction, 42 is the counterclockwise direction, if it is on the cloth board When it is ensured that the two currents are clockwise and the other is counterclockwise, that is, the physical path of the excitation current of the first primary winding and the second primary winding in the PCB wiring is opposite, then the magnetic force generated during the excitation Passing, looking farther away, can be offset, so that the EMI performance of the flyback switching power supply of the present invention will be very good.

It can be seen that compared with the existing LCL converter, the invention has many differences, mainly: allowing the leakage inductance between the primary and secondary windings to be large, and the leakage inductance energy is recycled by the clamp network, thus achieving high efficiency. . It also increases the current density of the primary winding, increases the power density of the converter, and is suitable for applications with lower operating voltages.

Second embodiment

The present invention further provides an equivalent solution of the above first embodiment. Corresponding to the second solution, referring to FIG. 5-1 and FIG. 5-2, a flyback switching power supply includes a transformer B, a first N-channel FET Q1, a first capacitor C1, a second capacitor C2, a first diode D2, a clamp network 400, and a transformer B including a first primary winding N _P1 , a second primary winding N _{P2 ,} and a secondary winding N _S , a clamp network The 400 includes at least an anode and a cathode, and the secondary winding N _{S is} connected to the anode of the first diode D2, and the cathode of the first diode D2 is connected to one end of the second capacitor C2, and forms an output positive, which is Vout in the figure. + terminal, the secondary winding N _{S has the} same name end connected to the other end of the second capacitor C2, and forms an output negative, which is the end of Vout in the figure; the positive terminal of the input DC power supply U _DC + simultaneously with the N-channel FET Q1 The drain and the second primary winding N _P2 are connected to each other. The source of the N-channel FET Q1 is connected to the same end of the first primary winding N _P1 ; the second primary winding N _{P2 is the} same name and the clamp network 400 is connected to the cathode, the anode connected to a first primary winding N _P1 dotted end of the clamp network 400, while the connection point of the DC input connector Source U _DC negative terminal; a connection control signal gate N-channel MOSFET Q1; N _Pl a first primary winding and a second primary winding _P2 is N bifilar, further comprising a first capacitor C1, a first One end of the capacitor C1 is connected to the same end of the first primary winding N _P1 , and the other end of the first capacitor C1 is connected to the same end of the second primary winding N _P2 . The clamping network 400 includes at least a third capacitor C3 and a second N-channel. The MOSFET Q2, the third capacitor C3 and the second N-channel FET Q2 are connected in series, and the series connection is one of the following two ways:

(1) One end of the third capacitor C3 is the cathode of the clamp network 400, the other end of the third capacitor C3 is connected to the drain d of the second N-channel FET Q2, and the source s of the second N-channel FET Q2 For the anode of the clamp network 400, the gate g of the second N-channel FET Q2 is connected to the clamp control signal, as shown in FIG. 5-1;

(2) One end of the third capacitor C3 is the anode of the clamp network 400, the other end of the third capacitor C3 is connected to the source s of the second N-channel FET Q2, and the drain d of the second N-channel FET Q2 For the cathode of the clamp network 400, the gate g of the second N-channel FET Q2 is connected to the clamp control signal as shown in Figure 5-2.

In fact, the second embodiment is a modification of the first embodiment: on the basis of FIG. 4-1 of the first embodiment, the series devices of the two excitation circuits are interchanged, that is, the positions of N _P1 and Q1 are interchanged. At the same time, the clamp network 400 and N _{P2 are} interchanged, and C1 is still connected between the connection points of the two series devices, and the circuit of FIG. 5-1 of the second embodiment is obtained. Since the source voltage of Q1 is fluctuating, Therefore, this circuit is floating drive, but obtains the direct drive of the second N-channel FET Q2 for clamping. On the basis of Figure 5-1, C3 and Q2 in the clamp network 400 are interchanged. Position, you can get the circuit of Figure 5-2.

A brief description of its working principle:

Referring to Figure 5-1 and Figure 5-2, when the circuit is powered on, Q2 does not work, and Q1 does not work. It is equivalent to an open circuit. Then the power supply UDC charges C1 through NP2, and the current returns to the negative of the power supply UDC through NP1. At the same time, also at power-on, the power supply UDC charges C1 through the two windings of the transformer B. These two windings cancel out due to the mutual inductance, and the C1 is equivalent to the DC internal resistance of the NP2 and NP1 in parallel with the power supply UDC. C1 still plays the role of power supply filtering and decoupling;

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

When Q1 is saturated and turned on, its internal resistance is equal to the on-state internal resistance Rds(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 UDC enters through the drain of Q1, the source of Q1 is out, and then enters the same name of the first primary winding NP1, and the different name of NP1 is output, and returns to the negative end of the power supply UDC;

The second way is: the right positive end of the capacitor C1 passes through the same name of the second primary winding NP2, the opposite end of NP2 is output, the drain of Q1 enters, the source of Q1 comes out, and returns to the left negative end of the capacitor C1;

It can be seen that the first and second excitation currents are in parallel relationship. Since the NP1 and NP2 have the same inductance and the same excitation voltage, they are equal to UDC, and the two paths are completely equal. In the excitation process, the secondary winding NS is the same as the 匝 ratio. The induced voltage is generated, the positive voltage is induced by the same name, and the negative voltage is induced by the different name. The size is equal to UDC multiplied by the turns ratio n, that is, NS induces a positive and negative voltage. This voltage is connected in series with the terminal voltage of C2. At both ends of D2, D2 is reversed and not turned on. At this time, the secondary side is equivalent to no load, and there is 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 NS 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 voltage or continuously outputs energy. This process is also the process of demagnetization.

In the second embodiment, the circuit for demagnetizing the leakage inductance is composed of the clamp network 400 and the second primary winding NP2, and the working principle is:

At the instant of Q1 turn-off and after, the energy on the leakage inductance is not transmitted to the secondary side, and the electrical energy of the leakage inductance in the second primary winding NP2 is in the same direction as the direction of the excitation, flowing from the same name to the opposite end. Flowing downwards and upwards, the Q2 body diode in the clamp network 400 is turned on to charge C3, and this electric energy is absorbed by C3 to form a leakage inductance demagnetization current loop;

Similarly, the leakage energy of the first primary winding NP1 is coupled to the second primary winding NP2 without leakage inductance, and is demagnetized by the clamp network 400 to form a leakage inductance demagnetization current loop;

There are also a variety of working modes, that is, after C3 absorbs the energy of the leakage inductance, there are many working modes of the circuit, and will not be described here.

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. Similarly, Q2 can be replaced with a P-channel FET. It is necessary to ensure that the body diode inside the P-channel FET is in the same direction as the body diode in Figure 5-1 or Figure 5-2.

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 with other symbols is used, the secondary output is added to multiple outputs, and the filter uses π-type filtering. For the purpose of improving efficiency, the parallel connection between the drain and the source of the FET is the same as the body diode. Low dropout, fast recovery diodes, such improvements are well known in the art and should be considered equivalent to body diodes; these improvements and finishes should also be considered as protection scope of the present invention, and the description of the present invention will not be repeated here. The scope of protection shall be determined by the scope defined by the claims.

Claims (6)

A flyback switching power supply includes a transformer, a first N-channel FET, a first capacitor, a second capacitor, a first diode, a clamp network, and the transformer includes a first primary winding and a second original The side winding and the secondary winding, the clamping network includes at least an anode and a cathode, and the secondary winding opposite end is connected to the first diode anode, and the first diode cathode is connected to one end of the second capacitor, and forms an output positive and a vice The same name end of the side winding is connected with the other end of the second capacitor, and the output is negative; the positive end of the input DC power supply is simultaneously connected with the same name end of the first primary winding, the cathode of the clamp network, and the first primary winding different name end and the first The drain of an N-channel FET is connected; the anode of the clamp network is connected to the opposite end of the second primary winding, and the source of the first N-channel FET is connected to the same end of the second primary winding, and the connection point is simultaneously connected Inputting a negative terminal of the DC power supply; a gate of the first N-channel FET is connected to drive a control signal; the first primary winding and the second primary winding are wound in a double line, and one end of the first capacitor and the first primary winding Same name end connected, first capacitor The other end is connected to the second-side winding different-name end, wherein the clamp network includes at least a third capacitor and a second N-channel FET, and the third capacitor and the second N-channel FET are connected in series, in series In one of two ways: (1) One end of the third capacitor is the cathode of the clamp network, the other end of the third capacitor is connected to the drain of the second N-channel FET, and the source of the second N-channel FET is the anode of the clamp network, a gate connection clamp control signal of the two N-channel FET; (2) one end of the third capacitor is the anode of the clamp network, the other end of the third capacitor is connected to the source of the second N-channel FET, and the drain of the second N-channel FET is the cathode of the clamp network, The gate of the two N-channel FET is connected to the clamp control signal. The flyback switching power supply of claim 1 wherein the first N-channel FET is replaced by a P-channel FET, the body diode inside the P-channel FET and the first N-channel FET The internal body diodes have the same polarity. A flyback switching power supply includes a transformer, a first N-channel FET, a first capacitor, a second capacitor, a first diode, a clamp network, and the transformer includes a first primary winding and a second original The side winding and the secondary winding, the clamping network includes at least an anode and a cathode, and the secondary winding opposite end is connected to the first diode anode, and the first diode cathode is connected to one end of the second capacitor, and forms an output positive and a vice The same name end of the side winding is connected with the other end of the second capacitor, and the output is negative; the positive end of the input DC power supply is simultaneously connected with the drain of the first N-channel FET and the different end of the second primary winding, the first N-channel The source of the MOSFET is connected to the same name end of the first primary winding; the same end of the second primary winding is connected to the cathode of the clamp network, and the opposite end of the first primary winding is connected to the anode of the clamp network, and the connection point is simultaneously Connecting the negative terminal of the input DC power supply; the gate of the first N-channel FET is connected to the driving control signal; the first primary winding and the second primary winding are wound in a double line, and one end of the first capacitor and the first primary side The winding is connected to the same name, the first electricity The other end of the capacitor is connected to the same end of the second primary winding, wherein the clamp network comprises at least a third capacitor and a second N-channel FET, and the third capacitor and the second N-channel FET are connected in series, in series In one of two ways: (1) One end of the third capacitor is the cathode of the clamp network, the other end of the third capacitor is connected to the drain of the second N-channel FET, and the source of the second N-channel FET is the anode of the clamp network, a gate connection clamp control signal of the two N-channel FET; (2) one end of the third capacitor is the anode of the clamp network, the other end of the third capacitor is connected to the source of the second N-channel FET, and the drain of the second N-channel FET is the cathode of the clamp network, The gate of the two N-channel FET is connected to the clamp control signal. The flyback switching power supply according to claim 3, wherein the first N-channel FET is replaced with a P-channel FET, the body diode inside the P-channel FET and the first N-channel FET The internal body diodes have the same polarity. 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 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.

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