CN113014110A - Forward converter and system of secondary-side parallel LCD circuit - Google Patents

Forward converter and system of secondary-side parallel LCD circuit Download PDF

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Publication number
CN113014110A
CN113014110A CN202110283152.7A CN202110283152A CN113014110A CN 113014110 A CN113014110 A CN 113014110A CN 202110283152 A CN202110283152 A CN 202110283152A CN 113014110 A CN113014110 A CN 113014110A
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diode
forward converter
inductor
capacitor
circuit
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CN113014110B (en
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刘树林
王成
刘旭
鲜大帅
李洁
李雪婷
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Xian University of Science and Technology
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Xian University of Science and Technology
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    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M3/00—Conversion of dc power input into dc power output
    • H02M3/22—Conversion of dc power input into dc power output with intermediate conversion into ac
    • H02M3/24—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters
    • H02M3/28—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac
    • H02M3/325—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal
    • H02M3/335—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal using semiconductor devices only
    • H02M3/33507—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal using semiconductor devices only with automatic control of the output voltage or current, e.g. flyback converters
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M1/00—Details of apparatus for conversion
    • H02M1/14—Arrangements for reducing ripples from dc input or output
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M3/00—Conversion of dc power input into dc power output
    • H02M3/22—Conversion of dc power input into dc power output with intermediate conversion into ac
    • H02M3/24—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters
    • H02M3/28—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac
    • H02M3/325—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal
    • H02M3/335—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal using semiconductor devices only
    • H02M3/33507—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal using semiconductor devices only with automatic control of the output voltage or current, e.g. flyback converters
    • H02M3/33523—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal using semiconductor devices only with automatic control of the output voltage or current, e.g. flyback converters with galvanic isolation between input and output of both the power stage and the feedback loop
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02B—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO BUILDINGS, e.g. HOUSING, HOUSE APPLIANCES OR RELATED END-USER APPLICATIONS
    • Y02B70/00—Technologies for an efficient end-user side electric power management and consumption
    • Y02B70/10—Technologies improving the efficiency by using switched-mode power supplies [SMPS], i.e. efficient power electronics conversion e.g. power factor correction or reduction of losses in power supplies or efficient standby modes

Abstract

The invention relates to the field of switching power supplies, in particular to a forward converter and a system of a secondary side parallel LCD circuit. The forward converter comprises a forward converter main circuit and an energy transfer and transmission circuit, wherein the forward converter main circuit comprises a high-frequency transformer, a switching tube, a first diode, a second diode, a first inductor and a first capacitor, and the energy transfer and transmission circuit comprises a third diode, a second capacitor and a second inductor. The invention has the following advantages: the input and output are electrically isolated, the multi-path output is easy to realize, the power consumption of the whole circuit is low, and the practicability is strong; the magnetic reset circuit has the characteristics of high stability, high reliability and the like, and is simple in structure, low in power loss, high in energy transmission efficiency and convenient to apply and popularize; the excitation energy can be transferred to the load side, the utilization rate of the transformer excitation energy is effectively improved, and the efficiency of the converter is integrally improved; and the current increase and decrease of the two inductors at the output end are opposite, so that the output current ripple of the converter can be reduced.

Description

Forward converter and system of secondary-side parallel LCD circuit
Technical Field
The invention relates to the field of switching power supplies, in particular to a forward converter and a system of a secondary side parallel LCD circuit.
Background
In a plurality of isolated switching power supply conversion topologies, compared with a flyback converter, the efficiency of a forward converter is higher, and the output power is not limited by the energy storage capacity of a transformer; compared with a half-bridge converter and a full-bridge converter, the forward converter has the advantages that the possibility of direct connection of a switch bridge arm is avoided, the reliability is high, the circuit structure is relatively simple, and the cost is low.
However, since the high-frequency transformer core of the single-tube forward converter can be magnetized only in one direction, it cannot perform magnetic reset by itself, which may cause magnetic saturation. Once magnetic saturation occurs, the current flowing through the switching tube will surge and even damage the switching tube. Therefore, measures must be taken to reset the transformer core so that the converter operates reliably. The reset mode can be divided into a primary side reset mode and a secondary side reset mode according to the position of the reset circuit in the converter.
The common primary side reset mode mainly comprises the following steps: auxiliary winding reset, primary RCD or LCD reset circuit reset, active clamp reset, resonant reset, etc. The auxiliary winding reset can transfer excitation energy to an input power supply, but can complicate the design of the transformer; although the traditional RCD clamping reset mode circuit is simpler, the main problem is that loss is generated on a resistor R, so that the overall efficiency of the system is difficult to improve; the LCD can realize the duty ratio more than 0.5 and the lossless reset, but causes the current stress on the switch tube to be overhigh; the active clamp reset circuit can realize the bidirectional magnetization of the transformer, reduce the volume of the transformer, but need to additionally increase an auxiliary switching tube; the resonance reset mode has the simplest structure and the least devices, but the voltage stress on the switch tube is overhigh. In summary, the primary reset mode consumes or transfers the excitation energy to the input power supply, and the utilization rate of the excitation energy is low.
The secondary side reset mode is that a reset circuit is arranged on the secondary side of the transformer, and the excitation energy can be transmitted to a load end during the turn-off period of the switching tube, so that the high-efficiency utilization of the excitation energy is realized. However, the conventional secondary side reset mode either limits the working mode of the forward inductor or other electrical performance indexes, so that the forward inductor cannot realize high-power output; or the complexity of the circuit is higher, so that the design difficulty and the manufacturing cost of the converter are increased; or more switching tubes are adopted, so that the complexity of a control circuit is increased; or more diodes are needed to be passed when energy transfer is realized, and the loss is increased.
Therefore, the research on a high-performance magnetic reset method becomes a problem of intensive research by those skilled in the art.
Disclosure of Invention
The technical problem to be solved by the present invention is to provide a forward converter and a system of a secondary-side parallel LCD circuit, aiming at the above-mentioned defects in the prior art, so as to solve the problems of low utilization rate of excitation energy, complex circuit composition, large power loss and low efficiency of the existing magnetic reset circuit.
The technical scheme adopted by the invention for solving the technical problems is as follows: the forward converter of the secondary side parallel LCD circuit comprises a forward converter main circuit and an energy transfer and transmission circuit, wherein the forward converter main circuit comprises a high-frequency transformer, a switching tube, a first diode, a second diode, a first inductor and a first capacitor; the primary-side dotted terminal of the high-frequency transformer is a positive voltage input terminal of a main circuit of the forward converter, the primary-side dotted terminal of the high-frequency transformer is connected with a drain electrode of a switching tube, the secondary-side dotted terminal of the high-frequency transformer is respectively connected with a cathode of a second diode and one end of a first inductor, and the secondary-side dotted terminal of the high-frequency transformer is respectively connected with a cathode of a first diode and an anode of a third diode; the source electrode of the switching tube is a negative voltage input end of the main circuit of the forward converter, and the grid electrode of the switching tube is a control signal input end; the other end of the first inductor is connected with one end of the first capacitor and one end of the second inductor respectively and serves as a positive voltage output end of the forward converter main circuit; the anode of the first diode is respectively connected with the anode of the second diode, the other end of the first capacitor and one end of the second capacitor and is a cathode voltage output end of the forward converter main circuit, and the cathode voltage output end is grounded; and the other end of the second capacitor is respectively connected with the cathode of the third diode and the other end of the second inductor.
Wherein, the preferred scheme is: the first diode and the second diode are both fast recovery diodes.
Wherein, the preferred scheme is: the switch tube is a full-control power semiconductor device.
Wherein, the preferred scheme is: the switch tube is an NMOS switch tube.
Preferably, the selecting step of the second capacitor includes: step S110, selecting the capacitance value C of the second capacitor2(ii) a Step S120, calculating the withstand voltage value V of the second capacitorC2,max(ii) a Step S130, selecting the capacity value as C2And the withstand voltage value is larger than VC2,maxAs the second capacitance.
Preferably, the selecting step of the second inductor includes: step S210, determining the inductance value L of the second inductor2The value range of (a); step S220, determining the maximum current I flowing through the second inductorL2,max(ii) a Step S230, according to the sensitivity value L2Value range of (1) and maximum current IL2,maxAnd selecting the inductor meeting the condition as a second inductor.
Preferably, the selecting step of the third diode includes: step S310, calculating the maximum current I flowing through the third diodeD3,max(ii) a Step S320, according to the maximum current ID3,maxAnd selecting the diode meeting the condition as a third diode.
The technical scheme adopted by the invention for solving the technical problems is as follows: the forward conversion system comprises the forward converter, a power supply connected with a positive voltage input end and a negative voltage input end of the forward converter, a controller connected with a control signal input end of the forward converter, and a load connected with a positive voltage output end and a negative voltage output end of the forward converter.
Compared with the prior art, the invention has the advantages that:
1. the invention can combine the advantages of the forward converter circuit and the flyback converter circuit, the input and output are electrically isolated, the multi-path output is easy to realize, the power consumption of the whole circuit is low, and the practicability is strong;
2. compared with the auxiliary winding reset, the design difficulty of related parameters of the transformer is reduced;
3. the magnetic reset circuit has the characteristics of high stability, high reliability and the like, and is simple in structure, low in power loss, high in energy transmission efficiency and convenient to apply and popularize;
4. the excitation energy can be transferred to the load side, the utilization rate of the transformer excitation energy is effectively improved, and the efficiency of the converter is integrally improved;
5. compared with the traditional forward converter, the current increase and decrease of the forward inductor and the auxiliary inductor are opposite during the switching-on and switching-off of the switching tube, so that the output current ripple can be reduced;
6. compared with most of the conventional secondary side magnetic reset forward converters, the forward inductor can work in a continuous conduction mode, and can be applied to occasions with higher power compared with the conventional forward converter;
7. the inductor of the energy transfer and transmission circuit is connected with the one-way conductive diode in series, so that the energy of the output end can be prevented from flowing backwards, the loss is reduced, and the efficiency is further improved;
8. the working stability, reliability and safety are higher, and the energy utilization rate can be effectively improved by the energy transmission and transfer circuit; the method can be widely applied to a plurality of fields such as industrial control, computer power supply, aerospace power supply system, medical communication power supply and the like, and has higher popularization and application values.
Drawings
The invention will be further described with reference to the accompanying drawings and examples, in which:
FIG. 1 is a circuit schematic of a forward converter of the present invention;
FIG. 2 is a schematic circuit diagram of the forward conversion system of the present invention;
FIG. 3 is a schematic flow chart of a second capacitor according to the present invention;
FIG. 4 is a schematic flow chart of a second inductor selection according to the present invention;
FIG. 5 is a flow chart illustrating the selection of a third diode according to the present invention.
Detailed Description
The preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings.
As shown in fig. 1, the present invention provides a preferred embodiment of a forward converter with a self-reset circuit using LCD for the secondary side.
A forward converter of a secondary side parallel LCD circuit comprises a forward converter main circuit 110 and an energy transfer and transmission circuit 120, wherein the forward converter main circuit 110 comprises a high-frequency transformer T, a switching tube S, a first diode D1, a second diode D2, a first inductor L1 and a first capacitor C1, and the energy transfer and transmission circuit 120 comprises a third diode D3, a second capacitor C2 and a second inductor L2; the primary-side dotted terminal of the high-frequency transformer T is a positive voltage input terminal of the forward converter main circuit 110, the primary-side dotted terminal thereof is connected to the drain of the switching tube S, the secondary-side dotted terminal thereof is respectively connected to the cathode of the second diode D2 and one end of the first inductor L1, and the secondary-side dotted terminal thereof is respectively connected to the cathode of the first diode D1 and the anode of the third diode D3; the source of the switching tube S is the negative voltage input end of the main circuit 110 of the forward converter, and the gate thereof is the control signal input end; the other end of the first inductor L1 is connected to one end of the first capacitor C1 and one end of the second inductor L2 respectively and is a positive voltage output end of the forward converter main circuit 110; the anode of the first diode D1 is connected to the anode of the second diode D2, the other end of the first capacitor C1 and one end of the second capacitor C2 respectively and is the negative voltage output end of the forward converter main circuit 110, and the negative voltage output end is grounded; the other end of the second capacitor C2 is connected to the cathode of the third diode D3 and the other end of the second inductor L2, respectively.
The high-frequency transformer T includes a primary winding w1 and a secondary winding w 2.
Specifically, and with reference to fig. 2, a forward converter system is provided that includes the forward converter, a power supply 200 connected to the positive voltage input and the negative voltage input of the forward converter, a controller 300 connected to the control signal input of the forward converter, and a load 400 connected to the positive voltage output and the negative voltage output of the forward converter.
In this embodiment, the first diode D1 and the second diode D2 are both fast recovery diodes, and the fast recovery diode (FRD for short) is a semiconductor diode with good switching characteristics and short reverse recovery time, and is mainly applied to electronic circuits such as a switching power supply, a PWM pulse width modulator, and a frequency converter, and the fast recovery diode has short reverse recovery time, low forward voltage drop, and high reverse breakdown voltage (withstand voltage), and reduces the reverse recovery loss of the high frequency converter T by shortening the reverse recovery time of the first diode D1 and the second diode D2. In particular, the second diode D2 is used to freewheel the first inductor L1.
In this embodiment, the switch transistor S is a fully-controlled power semiconductor device, which is also called a self-turn-off device, and refers to a power electronic device that can be controlled to be turned on and turned off by a control signal. Preferably, the switch tube S is an NMOS switch tube.
In the present embodiment, the first inductor L1 and the first capacitor C1 are used for filtering and providing a stable voltage for the load 400.
In this embodiment, regarding the operation principle of the forward converter, first, it is assumed that the first inductor L1, the second inductor L2, and the excitation inductor of the primary winding w1 of the high-frequency transformer T operate in CCM; the CCM is in a continuous conduction mode, and the current of the component never goes to zero in a switching period, or the component never resets, which means that the flux of the component never goes back to zero in the switching period, and when the power tube is closed, the current still flows through the coil. And for the second capacitor C2, the voltage is assumed to be positive-going and negative-going; for the secondary winding w2, the current is assumed to be forward current from bottom to top and reverse current from top to bottom.
The switching tube S comprises four phases during the off period:
assuming that the voltage of the second capacitor C2 has dropped to 0 before the turn-off time of the switching tube S, the current of the first inductor L1 and the secondary winding w2 rises to a maximum value. The first diode D1 is turned on, and the second diode D2 and the third diode D3 are turned off.
In the first stage, the switching tube S is in a transition from on to off, the parasitic capacitor Cc of the switching tube S is charged by the exciting current and the reflected current of the secondary winding w2, the primary current and the secondary current of the high-frequency transformer T are reduced until the forward current of the secondary winding w2 is reduced to 0, and the voltage of the switching tube S is increased to ViThe current of the first inductor L1 rises to a maximum value, and this phase ends. At this stage, the first diode D1 remains on, the second inductor L2 freewheels, and the second diode D2 is turned off.
In the second phase, after the forward current of the secondary winding w2 is reduced to zero, the first diode D1 and the second diode D2 naturally commutate, and the first inductor L1 and the second inductor L2 freewheel. The third diode D3 is turned on, the secondary current of the high frequency transformer T charges the second capacitor C2 through the third diode D3 and the second diode D2, and the voltage across the second capacitor C2 increases from zero. When the voltage of the second capacitor C2 increases to VoAt this time, the current of the second inductor L2 drops to a minimum value, and this stage ends. At this stage, the voltage borne by the two ends of the switch tube S is Vi+nVC2(N is the turn ratio of the primary side to the secondary side of the high-frequency transformer T N1: N2).
In the third phase, the secondary current of the high frequency transformer T continues to charge the second capacitor C2 through the third diode D3 and the second diode D2, and also charges the second inductor L2, and the voltage of the second capacitor C2 rises first and then falls until the voltage of the second capacitor C2 falls to be equal to VoAnd this stage ends. In the process, the first inductor L1 freewheels, and the voltage borne by the two ends of the switching tube S is still Vi+nVC2And at this stage, the voltage across the switching tube S will peak following the voltage across the second capacitor C2 reaching a maximum value.
In the fourth phase, when the voltage of the second capacitor C2 is equal to VoMeanwhile, the second capacitor C2 and the second inductor L2 supply power to the load 400 together, and the voltage of the second capacitor C2 continues to drop. In this process, the first inductor L1 freewheels; the voltage born by the two ends of the switch tube S is still Vi+nVC2This phase ends until the next switching cycle. The reverse current of the secondary winding w2 also drops to a minimum value at this time.
During the conduction period of the switching tube S, a phase is included:
after the switch tube S is conducted, the voltage V is inputiThe voltage applied to the primary winding w1 of the high frequency transformer T, which is coupled to the secondary winding w2, is positive, negative, and the first diode D1 is turned on, so that the forward energy is transferred to the load 400 through the first inductor L1 and the first diode D1, the current of the first inductor L1 rises linearly, and the second inductor L2 freewheels through the first diode D1 and the third diode D3. This process ends until the switch is turned off.
As shown in fig. 3 to 5, the present invention provides selected preferred embodiments of the second capacitor C2, the second inductor L2 and the third diode D3.
The selecting step of the second capacitor C2 comprises:
step S110, selecting the capacitance value C of the second capacitor C22；
Step S120, calculating the withstand voltage value V of the second capacitor C2C2,max；
Step S130, selecting the capacity value as C2And the withstand voltage value is larger than VC2,maxAs a second capacitance C2.
Specifically, in step S110, the capacitance value C of the second capacitor C2 for excitation energy storage is selected according to the formula (a1)2；
Figure BDA0002979365940000081
In step S120, the withstand voltage value V of the second capacitor C2 is calculated according to the formula (A2)C2,max；
Figure BDA0002979365940000082
Wherein, VoIs the output voltage, L, of the main circuit 110 of the forward converterw2The inductance of the secondary winding w2 of the high-frequency transformer T is shown, and f is the operating frequency of the forward converter main circuit 110.
And, referring to fig. 4, the selecting step of the second inductor L2 includes:
step S210, determining the inductance value L of the second inductor L22The value range of (a);
step S220, determining the maximum current I flowing through the second inductor L2L2,max；
Step S230, according to the sensitivity value L2Value range of (1) and maximum current IL2,maxThe inductance satisfying the condition is selected as the second inductance L2.
Specifically, in step S210, the inductance value L of the second inductance L2 is determined according to the formula (a3)2The value range of (a);
Figure BDA0002979365940000091
wherein L ismThe value is the excitation inductance value of the high-frequency transformer T, and n is the winding turn ratio of the high-frequency transformer T; in step S220, the current of the second inductor L2 is determined according to the formula (a4),
Figure BDA0002979365940000092
and, referring to fig. 5, the selecting step of the third diode D3 includes:
step S310, calculating the maximum current I flowing through the third diode D3D3,max；
Step S320, according to the maximum current ID3,maxThe diode satisfying the condition is selected as the third diode D3.
Specifically, the maximum current I flowing through the third diode D3 is calculated according to the formula (a5)D3,max；
Figure BDA0002979365940000093
Wherein, ViThe converter input voltage.
In addition, in the present embodiment, the voltage across the second capacitor C2 is already reduced to 0 before the switching tube S is turned on, and the third diode D3 does not need to bear the reverse voltage any more, so that the voltage stress of the third diode D3 is reduced.
The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the scope of the present invention, but rather as embodying the invention in a wide variety of equivalent variations and modifications within the scope of the appended claims.

Claims (8)

1. A forward converter of a secondary side parallel LCD circuit is characterized in that: the forward converter comprises a forward converter main circuit and an energy transfer and transmission circuit, wherein the forward converter main circuit comprises a high-frequency transformer, a switching tube, a first diode, a second diode, a first inductor and a first capacitor, and the energy transfer and transmission circuit comprises a third diode, a second capacitor and a second inductor; wherein the content of the first and second substances,
the primary dotted terminal of the high-frequency transformer is a positive voltage input terminal of a main circuit of the forward converter, the primary dotted terminal of the high-frequency transformer is connected with a drain electrode of a switching tube, the secondary dotted terminal of the high-frequency transformer is respectively connected with a cathode of a second diode and one end of a first inductor, and the secondary dotted terminal of the high-frequency transformer is respectively connected with a cathode of a first diode and an anode of a third diode;
the source electrode of the switching tube is a negative voltage input end of the main circuit of the forward converter, and the grid electrode of the switching tube is a control signal input end;
the other end of the first inductor is connected with one end of the first capacitor and one end of the second inductor respectively and serves as a positive voltage output end of the forward converter main circuit; the anode of the first diode is respectively connected with the anode of the second diode, the other end of the first capacitor and one end of the second capacitor and is a cathode voltage output end of the forward converter main circuit, and the cathode voltage output end is grounded; and the other end of the second capacitor is respectively connected with the cathode of the third diode and the other end of the second inductor.
2. A forward converter as claimed in claim 1 wherein: the first diode and the second diode are both fast recovery diodes.
3. A forward converter as claimed in claim 1 wherein: the switch tube is a full-control power semiconductor device.
4. A forward converter as claimed in claim 1 or 3, wherein: the switch tube is an NMOS switch tube.
5. A forward converter as claimed in claim 1 wherein said second capacitance is selected by:
step S110, selecting the capacitance value C of the second capacitor2；
Step S120, calculating the withstand voltage value V of the second capacitorC2,max；
Step S130, selecting the capacity value as C2And the withstand voltage value is larger than VC2,maxAs the second capacitance.
6. A forward converter as claimed in claim 1 wherein said second inductor is selected by the step of:
step S210, determining the inductance value L of the second inductor2The value range of (a);
step S220, determining the maximum current I flowing through the second inductorL2,max；
Step S230, according to the sensitivity value L2Value range of (1) and maximum current IL2,maxAnd selecting the inductor meeting the condition as a second inductor.
7. A forward converter as claimed in claim 1 wherein said third diode is selected by the step of:
step S310, calculating the flow through the third stepMaximum current I of the diodeD3,max；
Step S320, according to the maximum current ID3,maxAnd selecting the diode meeting the condition as a third diode.
8. A forward transform system, characterized by: the forward converter system comprises a forward converter according to any one of claims 1 to 7, a power supply connected to the positive voltage input and the negative voltage input of the forward converter, a controller connected to the control signal input of the forward converter, and a load connected to the positive voltage output and the negative voltage output of the forward converter.
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