WO2019001305A1

WO2019001305A1 - Forward switch mode power supply

Info

Publication number: WO2019001305A1
Application number: PCT/CN2018/091787
Authority: WO
Inventors: 王保均; 王志燊
Original assignee: 广州金升阳科技有限公司
Priority date: 2017-06-30
Filing date: 2018-06-19
Publication date: 2019-01-03
Also published as: CN107786094A; CN107786094B

Abstract

A forward switch power supply, in which, on the basis of an LCL forward converter, an NP1 common-polarity end in a transformer B is connected to a power supply, and an NP2 common-polarity end is grounded; NP1 and NP2 are double-wire parallel windings, and an end of a capacitor C1 is connected to an NP1 opposite-polarity end, while the other end is connected to an NP2 opposite-polarity end, and the NP2 opposite-polarity end is connected to the power supply by means of C3, thus achieving: when Q1 saturatedly conducts, both NP1 and NP2 are excited, and a secondary side NS outputs energy; when Q1 is turned off, L1 freewheels and outputs energy, D1 being synchronously turned off, and energy that is generated by excitation resonating and being demagnetized by NP2 by means of C3; a primary side is inductive, C3 is resonant with primary-side inductance, and when the end voltage at C3 is twice the power supply voltage, Q1 is turned on when the end voltage thereof is zero. The forward switch power supply achieves a duty cycle that may be greater than 0.5, demagnetized energy recovery, and improved efficiency.

Description

Forward switching power supply

Technical field

The present invention relates to the field of switching power supplies, and more particularly to forward switching power supplies that use resonant demagnetization.

Background technique

At present, the switching power supply is widely used, and the industry is often called a converter. The basic forward converter in the forward switching power supply is an ideal isolated version of the Buck converter. The common topology has a single-ended forward converter and a symmetric drive. Half-bridge converter, full-bridge converter, push-pull converter, symmetric push-pull forward converter, etc. Need to mention is a symmetric push-pull forward converter, as shown in Figure 1-1, the picture is taken from Dr. Zhang Xingzhu's book, ISBN 978-7-5083-9015-4 "Switching Power Supply Converter Topology And Figure 5-14 on page 91 of the design, which is referred to herein as: Reference 1.

Symmetrical push-pull forward converters are referred to in the patent literature as straight-in converters, which were first seen in the 1999 Institute of Electrical and Electronics Engineers (IEEE) Proceedings (0-7803-5160-6/99), page 279 "A Novel High-input-voltage, High Efficiency and Fast Transient Voltage Regulator Module" by Xunwei Zhou, Bo Yang, Luca Amoroso, Fred C. Lee and Pit-leong Wong;

And in the IEEE Proceedings of 2002 (0-7803-7404-5/02), page 843, "Single Magnetic Push-Pull Forward Converter featuring Built-in Input Filter and Coupled-Inductor Current Doubler for 48V VRM", author Peng Xu, Mao Ye (Ye Mao) and Fred C. Lee, the paper also mentioned "PUSH-PULL FORWARD CONVERTER";

And on page 6 of the 2004 Master's thesis published by Dai Weili of Nanjing University of Aeronautics and Astronautics, "Push-Pull Forward Circuit", its output is called "Push-Pull Forward Circuit". Full-wave rectification with freewheeling inductor L.

Various forward converters have their preferred uses due to their different circuit topologies:

Single-ended forward converter: good loop response, suitable for powering dynamic loads such as motors. Japan's COSEL industrial power supply is still implemented with PFC + three-winding demagnetization single-ended forward converter, for this reason, but the power is generally around 150W;

Half-bridge converter: suitable for applications with high working voltage, such as power supply for desktop computers; high power;

Full-bridge converter: suitable for high-voltage and high-power applications, common in power sections above 1Kw;

Push-pull converter: mostly used for low voltage, power less than 300W;

Symmetric push-pull forward converter: low voltage and high power, but did not see the practical product launch market;

As mentioned above, the single-ended forward converter is suitable for powering dynamic loads due to good loop response. Therefore, the circuit still has a large amount of use, especially in the case of low voltage operation, the circuit topology of the three winding demagnetization is as follows. Figure 1-2 shows Nc, Figure 1-2 from Figure 3-8 (a) on page 33 of Reference 1, the output of which is a common single-ended forward topology output rectifier circuit, diode VD1 is the switch tube ( Or the power tube) the rectifier tube that is synchronously turned on when the V saturation is turned on, the diode VD2 is the freewheeling tube when the switching tube V is turned off, and the current in the inductor L continues to supply the output filter capacitor C and the load R through the VD2. The third winding demagnetization forward converter is also referred to as a "three-winding absorption forward converter".

In Section 3.3 of Reference 1, the resonant demagnetization forward converter is highlighted, and the circuit topology of the three circuit structures is given. Figure 3-15 of the original book is incorporated in the present application and is incorporated herein by reference. In order to avoid misunderstanding, in Figure 1-3, the black line is used to add a strikethrough to the "Figure 3-15" of the original book.

In the Chinese application number 201710141802.8 named "A Forward Switching Power Supply", the technical scheme of Figure 1-4 is shown, which solves some problems in Figure 1-2. The third winding realizes the excitation and realizes at the same time. For the convenience of loss, the inventors have defined the topology used by the forward switching power supply, including the flyback topology, and the basic topology excluding the demagnetization mode is defined as: LCL converter, derived from the two The primary side is a magnetizing inductance and a capacitor in series with them. Such as LCL forward converter, also refers to LCL forward switching power supply.

The technical solution in Figure 1-4 also introduces some new problems, such as the duty ratio cannot be greater than 0.5, resulting in low power density, unable to achieve the zero voltage switch of the switch Q1 in Figure 1-4 (abbreviated as ZVS).

Summary of the invention

In view of this, the present invention solves the shortcomings of the existing LCL forward switching power supply, and provides a new circuit topology of a forward switching power supply using resonant demagnetization, the duty ratio can be greater than 0.5, the power density is high, and the switch is realized. The zero voltage of the tube is turned on to further improve the conversion efficiency.

The object of the present invention is achieved by a forward switching power supply including a transformer, a first N-channel FET, a first capacitor, a second capacitor, a first diode, and a transformer including a first primary winding, The second primary winding and the secondary winding, the secondary winding forms a secondary output rectifier circuit and is connected in one of two ways:

(1) comprising a second capacitor and a first diode, wherein the secondary winding has the same name end 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 secondary winding different The name end is connected to the other end of the second capacitor, and forms an output negative;

(2) further comprising a second diode and a first inductor, wherein the secondary winding is connected to the first diode anode at the same end, and the first diode cathode is simultaneously connected to the cathode of the second diode and the first inductor Connecting, the other end of the first inductor is connected to one end of the second capacitor, and forms an output positive, and the opposite end of the secondary winding is simultaneously connected with the anode of the second diode and the other end of the second capacitor, and forms an output negative;

The positive end of the input DC power supply is connected to the same end of the first primary winding, the first primary winding is connected to the drain of the N-channel FET; the source of the N-channel FET is connected to the second primary winding. The connection point is simultaneously connected to the negative end of the input DC power supply; the gate of the N-channel FET is connected to the drive control signal; the first primary winding and the second primary winding are wound in two lines, one end of the first capacitor and the first A primary winding is connected to the different name end, and the other end of the first capacitor is connected to the second end of the second primary winding, and is characterized in that: a third capacitor is further included, and one end of the third capacitor is connected to the positive end of the input DC power supply, The other end of the three capacitors is connected to the different 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 forward switching power supply includes a transformer, a first N-channel field effect transistor, a first capacitor, and a second capacitor. A diode comprising a first primary winding, a second primary winding and a secondary winding, the secondary winding forming a secondary output rectifier circuit and connected in one of two ways:

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-end end of the first primary winding; the first primary winding The opposite end is connected to the negative terminal of the input DC power supply U _DC - the gate of the N-channel FET is connected to the drive control signal; the first primary winding and the second primary winding are wound in two lines, one end of the first capacitor is The first primary winding is connected to the same name end, and the other end of the first capacitor is connected to the same end of the second primary winding, and is characterized in that: the third capacitor is further included, and one end of the third capacitor is connected to the negative end of the input DC power supply, and the third The other end of the capacitor is connected to the same end of the second primary winding.

As an improvement of the above two schemes, the zero-voltage turn-on of the N-channel FET is realized by the resonance of the second primary winding and the third capacitor.

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 invention has the beneficial effects that the duty ratio can be greater than 0.5, and at the same time, the energy recovery of the demagnetization circuit is realized, and further, the zero voltage turn-on of the main power switch tube is realized, further reducing the loss and improving the conversion efficiency, especially at light load. When the conversion efficiency is improved.

DRAWINGS

Figure 1-1 is a schematic diagram of a topology of a PPFC converter in a conventional forward switching power supply;

Figure 1-2 is a schematic diagram of the topology of a conventional three-winding demagnetized single-ended forward converter;

Figure 1-3 is a schematic diagram of three structures of a conventional resonant demagnetization forward converter;

Figure 1-4 is a schematic diagram of a technical solution shown in the prior application No. 201710141802.8;

2-1 is a schematic diagram of a first embodiment of the present invention, and the secondary side output rectifier circuit adopts (1) mode;

2-2 is a second schematic diagram of the first embodiment of the present invention, and the secondary side output rectifier circuit adopts (2) mode;

2-3 is a schematic diagram of charging a capacitor C1 at the time of power-on according to the first embodiment of the present invention;

2-4 are schematic diagrams showing the generation of two

excitation currents

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

2-5 are schematic diagrams showing the Q1 cutoff, the freewheeling current 43b, and the demagnetization current 44 in the first embodiment of the present invention;

3-1 is a schematic diagram of a second embodiment of the present invention, where the secondary side output rectifier circuit adopts (1) mode;

3-2 is a second schematic diagram of the second embodiment of the present invention, and the secondary side output rectifier circuit adopts the (2) mode.

Detailed ways

First embodiment

2-1 and 2-2 are schematic diagrams showing an active clamp forward switching power supply according to a first embodiment of the present invention, including a transformer B, a first N-channel FET Q1, and a first capacitor C1. a second capacitor C2, a first diode D1, 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 secondary winding N _S forms a secondary output rectifier circuit, and Connect in one of two ways:

(1) comprising a second capacitor C2 and a first diode D1, wherein the secondary winding N _S is connected to the anode of the first diode D1 at the same end, and the cathode of the first diode D1 is connected to one end of the second capacitor C2 and formed The output is positive, which is the + end of Vout in the figure, the opposite side 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; see Figure 2-1;

(2) further comprising a second diode D2, a first inductor L1, the secondary winding N _{S having the} same name end connected to the anode of the first diode D1, and the cathode of the first diode D1 simultaneously with the second diode D2 The cathode and the first inductor L1 are connected at one end, and the other end of the first inductor L1 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 simultaneously and secondly The anode of the diode D2 and the other end of the second capacitor C2 are connected, and form an output negative, which is the end of Vout in the figure; see FIG. 2-2;

The secondary output rectifier circuit is a circuit including the secondary winding N _S . Obviously, the above (1) mode has no output freewheeling inductance, and is suitable for operating in an open loop mode, that is, the output voltage is proportional to the input voltage; and the above (2) The method is suitable for working in the closed loop mode because of the output freewheeling inductance, that is, the output voltage is controlled by the duty ratio, and the output is easy to achieve high precision voltage regulation;

The positive terminal of the input DC power source U _DC is connected to the same name end of the first primary winding N _P1 , and the first primary winding N _P1 is connected to the drain of the N-channel FET Q1; the N-channel FET Q1 The source s 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 is connected to the driving control signal; the first primary winding N _P1 And the second primary winding N _P2 is wound in two lines, one end of the first capacitor C1 is connected to the different end of the first primary winding N _P1 , and the other end of the first capacitor C1 is different from the second primary winding N _P2 The terminal is connected to the third capacitor C3. One end of the third capacitor C3 is connected to the positive terminal of the input DC power supply, and the other end of the third capacitor C3 is connected to 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;

Driving 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 Figure 2-1 and Figure 2-2, 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 being directly connected 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: See Figure 2-1 and Figure 2-2. When C3 (for the convenience of analysis, according to the standard of textbook, capacitor C3 is hereinafter referred to as C3, other devices are the same), when replaced with a diode, it is the figure 1-4. Prior art circuit, but after the invention adds C3, the working principle of the circuit is completely different from the prior art;

Since Figure 2-1 and Figure 2-2 are only the secondary side output rectifier circuit, here is an example of Figure 2-2. Figure 2-3 shows the operation of the circuit at power-on. Q1 does not receive the drive control signal. If it is not working, it is equivalent to an open circuit, then 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 end of the power supply U _DC through the second primary winding N _P2 , 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. The magnetic fluxes of the two windings cancel out due to mutual inductance, and do not work, and C1 is equivalent to The DC internal resistance of N _P1 and N _P2 is connected in parallel with the power supply U _DC . 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 negative is negative. At the same time, the terminal voltage of the capacitor C3 is up-down and negative, equal to the voltage of U _DC .

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. Seen as straight through, is a wire, then the excitation current generated by N _{p1 is} shown as 41 in 2-4; if the circuit is a better model circuit, the excitation current 42 should not exist, because N _P2 The induced voltage is equal to the terminal voltage of C1, but since the actual circuit is not an ideal model, the exciting current 42 is real. As shown in Figure 2-4, two excitation currents are generated at this time, as shown by 41 and 42 in Figure 2-4.

It can be seen that the excitation currents of 41 and 42 are in parallel relationship. During the excitation process, the secondary winding N _S also generates an induced voltage according to the turns ratio. The induced voltage is: a positive voltage is induced at the same name, and a negative voltage is induced at the opposite end. The size is equal to U _DC multiplied by the 匝 ratio n, that is, N _S induces a voltage that is positive and negative. This voltage causes D2 to conduct a forward conduction, and through the forward-conducting D2, charges the capacitor C2 through the inductor L1, and the charging current is as As shown at 43a, Vout establishes a voltage or continuously outputs energy. During the Q1 conduction excitation process, the secondary side has an energy output, which is characteristic of the forward converter. If the circuit of Figure 2-1 is used, the output voltage is equal to U _DC multiplied by the turns ratio n, independent of the duty cycle, and can be used as a bus supply.

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

In order to ensure that the electromagnetic compatibility meets the requirements for use, it is tricky when wiring. Observe 41 and 42 in Figure 2-4, 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 offset at a distance, so that the EMI performance of the forward switching power supply of the present invention will be very good. .

When 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 abruptly changed, even though Q1 is turned off, the secondary side mapping current disappears simultaneously, but 41 And the 42 magnetizing current still flows from the same name to the opposite end. Although this current is very small, 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, see Figure 2-5. The secondary winding N _S attempts to flow from the same name end to the different name end. This current can turn on D2, but cannot be generated due to D1 reverse bias, and the current of 43a in Figure 2-4 flows through L1, and the inductor L1 The current in the current cannot be abrupt, and the current seeking path of 43a continues to flow, forming a freewheeling current as shown by 43b, starting from the right end of the inductor L1, to the positive end of C2, to the negative end of C2, and then to the anode of D3, and then Go to the cathode of D3 and return to the left end of inductor L1.

The basic forward converter in a forward switching power supply is an ideal isolated version of the Buck converter, which is also commonly referred to as a forward transformer;

The circuit for demagnetizing the circuit of the present invention is composed of 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 wound in two lines, and the leakage inductance between the two windings is zero. The energy of the exciting current is not transmitted to the secondary side at the instant of Q1 turn-off and after. The electric energy of the excitation current 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 Figure 2-5, flowing from bottom to top, this electric energy is directed to C3 Discharge, forming a demagnetization current of the excitation current indicated by 44; the terminal voltage of C3 is decreased;

The electric energy of the exciting current in the first primary winding N _P1 is coupled to the second primary winding N _P2 without leakage inductance, and also forms a demagnetizing current of the exciting current indicated by 44;

At the instant of Q1 turn-off and after, C3 resonates with the magnetizing inductance of the transformer, and after the demagnetization process ends, it enters the process of reverse excitation. This process D1 is turned off. The winding N _{P2 is} subjected to a voltage with the same name being negative and a different name end being positive, and the reverse excitation is started, and the exciting current is charged by C3. During this process, the voltage of N _P2 gradually decreases, and in the opposite direction, it becomes positive at the same name end and negative at the opposite end, and the terminal voltage of Q1 gradually decreases. When the voltage of C3 becomes twice the voltage of U _DC , the terminal voltage of Q1 is zero. Due to the clamping action of the Q1 body diode, the voltage of C3 becomes twice the voltage of U _DC , and the terminal voltage of Q1 is zero. Before the excitation current is reversed, if the driving voltage of Q1 is high and Q1 is saturated, ZVS is realized.

In order to achieve a longer resonance time, the capacity of C3 is relatively large. Because C3 is large and the terminal voltage can be increased, the voltage of the terminal voltage and the voltage of the DC power supply U _DC are in series. Using the volt-second balance law, the duty ratio can be greater than 0.5, and all can work normally.

In order to further improve the efficiency, a diode with the same low-voltage drop and fast recovery in the same direction as the Q1 body diode is connected in parallel between the drain and the source of the field effect transistor Q1. This improvement is a well-known technique and should be regarded as equivalent to a body diode. The invention is no longer protected by the embodiments;

Since the excitation currents of 41 and 42 are relatively close, 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 all include the same size Litz wire. The colors can be different, that is, stranded strands are twisted. For convenience of identification, the same size of the wire including the Litz wire can be different in color. 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.

The present invention is a forward switching power supply. On the basis of the LCL forward converter, the N _{P1 of the} transformer B is terminated with the same name, the N _{P2 is} grounded at the same name, N _P1 and N _P2 are double-wired, and one end of the capacitor C1 It is connected to the N _P1 different name end, the other end is connected to the N _P2 different name end, and the N _P2 same name end is connected to the power supply through C3. Thus, when Q1 is saturated, both N _P1 and N _P2 are excited, and the secondary side N _S Output energy, when Q1 is turned off, L1 freewheeling output energy, D1 synchronously turns off, the energy generated by excitation is resonated by N _P2 via C3, the primary side is inductive, C3 is resonant with the primary inductance, and the voltage at C3 is When the power supply voltage is twice, Q1 is turned on when the terminal voltage is zero; the duty ratio can be greater than 0.5, the demagnetization energy is recovered, and the efficiency is improved.

It can be seen that compared with the existing forward LCL converter, the present invention has many differences, mainly: the duty ratio can be greater than 0.5, realizing zero voltage turn-on of the main power switch tube, and simultaneously realizing energy recovery of the demagnetization circuit, further Reduce the loss and improve the conversion efficiency.

Second embodiment

The present invention further provides an equivalent solution of the above first embodiment. Corresponding to the second scheme, referring to FIG. 3-1 and FIG. 3-2, an active clamp forward switching power supply includes a transformer B, a first N-channel field effect. The tube Q1, the first capacitor C1, the second capacitor C2, the first diode D1, 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 Form a secondary output rectifier circuit and connect in one of two ways:

(1) comprising a second capacitor C2 and a first diode D1, wherein the secondary winding N _S is connected to the anode of the first diode D1 at the same end, and the cathode of the first diode D1 is connected to one end of the second capacitor C2 and formed The output is positive, which is the + end of Vout in the figure, the opposite side 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; see Figure 3-1;

(2) further comprising a second diode D2, a first inductor L1, the secondary winding N _{S having the} same name end connected to the anode of the first diode D1, and the cathode of the first diode D1 simultaneously with the second diode D2 The cathode and the first inductor L1 are connected at one end, and the other end of the first inductor L1 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 simultaneously and secondly The anode of the diode D2 and the other end of the second capacitor C2 are connected, and form an output negative, which is the end of Vout in the figure; see FIG. 3-2;

The secondary output rectifier circuit is a circuit including the secondary winding N _S . Obviously, the above (1) mode has no output freewheeling inductance, and is suitable for operating in an open loop mode, that is, the output voltage is proportional to the input voltage; and the above (2) The method has an output freewheeling inductor L1, and is suitable for working in a closed loop mode, that is, the output voltage is controlled by the duty ratio, and the output is easy to achieve high precision voltage regulation;

The positive terminal of the input DC power source U _DC is simultaneously connected to the drain d of the N-channel FET Q1 and the second-side winding N _P2 , and the source s of the N-channel FET Q1 and the first primary winding N _P1 is connected to the same name end; the first primary winding N _P1 is connected to the negative terminal of the input DC power supply U _DC - the gate g of the N-channel FET Q1 is connected to the driving control signal; the first primary winding N _P1 and The second primary winding N _P2 is wound in two lines. One end of the first 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 third capacitor C3 is further connected, and one end of the third capacitor C3 is connected to the negative terminal of the input DC power supply, and the other end of the third capacitor C3 is connected to the same end of the second primary winding N _P2 .

In fact, the second embodiment is an equivalent variant of the first embodiment: on the basis of Fig. 2-1 or Fig. 2-2 of the first embodiment, the series devices in the excitation circuit are interchanged, i.e., N _P1 and Q1 Interchanging the position, while C3 and N _{P2 are} interchanged, and C1 is still connected between the connection points of the two series devices, and the corresponding circuit of Figure 3-1 or Figure 3-2 of the second embodiment is obtained, due to Q1 The source voltage is variable, so this circuit is floating drive and the cost of the drive is higher.

A brief description of its working principle:

Referring to Figure 3-1 and Figure 3-2, when the circuit is powered on, Q1 does not work because it does not receive the control signal, which is equivalent to an open circuit. Then the power supply U _DC charges C1 through N _P2 , and the current returns through N _P1 at the same time. 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. The magnetic flux of the two windings cancels out due to the mutual inductance, and does not work, and C1 is equivalent to passing N _P2 and The DC internal resistance of N _P1 is connected in parallel with the power supply U _DC . 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 , right and left negative; meanwhile, capacitor C3 The terminal voltage is positive and negative, equal to the voltage of U _DC .

When Q1 is saturated and turned on, its internal resistance is equal to the on-state internal resistance R _ds(ON) , which is regarded as a wire as before, and two exciting 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. If the circuit is a more ideal model circuit, the second excitation current should not exist. This is because the induced voltage of N _P2 is equal to the terminal voltage of C1, but since the actual circuit is not an ideal model, the second excitation current actually exists. .

The first and second excitation currents are in parallel. 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 . The two paths are completely equal. During the excitation process, the secondary windings N _{S are} pressed. The analogy produces the induced voltage. The same name induces a positive voltage. The opposite end induces a negative voltage. The magnitude is equal to U _DC multiplied by the turns ratio n. That is, N _S induces a positive and negative voltage. This voltage causes D1 to guide. Pass, and through the forward conduction D1, through the inductor L1 to charge the capacitor C2, Vout establish voltage or continuously output energy.

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 excitation inductance of the transformer;

In the second embodiment, the circuit for demagnetizing the circuit of the present invention is composed of C3 and the second primary winding N _P2 , and the operation principle is the same as that of the first embodiment.

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 same name of the power source, the diode, and the transformer is reversed, and the output rectification portion is not reversed. Then, the third embodiment is obtained, which is not described here, and is regarded as a non-creative labor by those skilled in the art using known techniques. It is equivalent to the first and second aspects of the present invention.

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, which is apparent from the prior art. Yixian sees, such as the switch tube Q1 with other symbols, the secondary output is added to multiple outputs, and the filter uses π-type filtering; these improvements are known techniques and should be considered equivalent to body diodes; these improvements and retouching are also The scope of the present invention should be construed as the scope of the present invention, and the scope of the present invention should be defined by the scope of the claims.

Claims

A forward switching power supply includes a transformer, a first N-channel FET, a first capacitor, a second capacitor, a first diode, and the transformer includes a first primary winding, a second primary winding, and a secondary winding The secondary winding forms a secondary output rectifier circuit, that is, the secondary output rectifier circuit includes a secondary winding, a second capacitor and a first diode, and the connection relationship is that the secondary winding of the secondary winding is connected to the first diode anode The first diode cathode is connected to one end of the second capacitor, and forms an output positive, the opposite end of the secondary winding is connected with the other end of the second capacitor, and forms an output negative; the positive terminal of the input DC power supply is simultaneously with the first primary side The winding is connected to the same name end, the first primary winding is connected to the drain of the N-channel FET; the source of the N-channel FET is connected to the same end of the second primary winding, and the connection point is connected to the negative of the input DC power supply at the same time. The gate of the 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 is connected to the different end of the first primary winding, first The other end of the capacitor The two primary windings are connected at different ends, and are characterized by:

The third capacitor is further connected, one end of the third capacitor is connected to the positive end of the input DC power source, and the other end of the third capacitor is connected to the different end of the second primary winding.
The forward switching power supply according to claim 1, wherein the secondary output rectifier circuit further comprises a second diode and a first inductor, and the secondary winding has the same name and is connected to the first diode anode, the first two The cathode of the pole tube is simultaneously connected to the cathode of the second diode and one end of the first inductor, and the other end of the first inductor is connected to one end of the second capacitor, and the output is positive, and the opposite end of the secondary winding is simultaneously connected with the second pole The anode of the tube and the other end of the second capacitor are connected and form an output negative.
The forward switching power supply according to claim 1 or 2, wherein the zero-voltage turn-on of the N-channel FET is realized by the resonance of the second primary winding and the third capacitor.
The forward switching power supply according to any one of claims 1 to 3, characterized in that the first primary winding and the second primary winding have the same wire diameter.
The forward switching power supply according to any one of claims 1 to 3, 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.
A forward switching power supply includes a transformer, a first N-channel FET, a first capacitor, a second capacitor, a first diode, and the transformer includes a first primary winding, a second primary winding, and a secondary winding The secondary winding forms a secondary output rectifier circuit, that is, the secondary output rectifier circuit includes a secondary winding, a second capacitor and a first diode, and the connection relationship is that the secondary winding of the secondary winding is connected to the first diode anode The first diode cathode is connected to one end of the second capacitor, and forms an output positive, the opposite end of the secondary winding is connected with the other end of the second capacitor, and the output is negative; the positive terminal of the input DC power source and the N-channel field effect simultaneously The drain of the tube and the second primary winding are connected to each other, and the source of the N-channel field effect transistor is connected to the same end of the first primary winding; the first primary winding is connected to the negative terminal of the input DC power supply; The gate of the channel FET is connected to the driving control signal; the first primary winding and the second primary winding are 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 Same as the second primary winding End is connected, wherein:

The third capacitor is further connected, one end of the third capacitor is connected to the negative end of the input DC power source, and the other end of the third capacitor is connected to the same end of the second primary winding.
The forward switching power supply according to claim 6, wherein the secondary output rectifier circuit further comprises a second diode and a first inductor, and the secondary winding has the same name and is connected to the first diode anode, the first two The cathode of the pole tube is simultaneously connected to the cathode of the second diode and one end of the first inductor, and the other end of the first inductor is connected to one end of the second capacitor, and the output is positive, and the opposite end of the secondary winding is simultaneously connected with the second pole The anode of the tube and the other end of the second capacitor are connected and form an output negative.
The forward switching power supply according to claim 6 or 7, wherein the zero-voltage turn-on of the N-channel FET is realized by the resonance of the second primary winding and the third capacitor.
A forward switching power supply according to any one of claims 6 to 8, wherein the first primary winding and the second primary winding have the same wire diameter.
The forward switching power supply according to any one of claims 6 to 8, 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.