CN111682777B - A Secondary Parallel LCD Forward Converter Can Avoid Reverse Charging of Energy Storage Capacitor - Google Patents

Abstract

The invention discloses a secondary side parallel LCD forward converter capable of avoiding reverse charging of an energy storage capacitor, which comprises a forward converter main circuit and an energy transfer and transmission circuit, wherein the forward converter main circuit comprises a high-frequency transformer T, a switching tube S, a diode D1, a diode D2, an inductor L1 and a capacitor C1, and the energy transfer and transmission circuit comprises a diode D3, a capacitor C2, an inductor L2 and a diode D4. The circuit of the invention has simple structure and high reliability, the diode D4 ensures that C2 can not be charged reversely, the reactive loss of the converter is reduced, the problem of reverse recovery of the D4 can be eliminated, the loss of the diode is reduced, the excitation energy is transferred to the load side, the forward energy can be transmitted, the energy transmission efficiency is improved, and the invention is suitable for high-power transmission.

Description

A Secondary Parallel LCD Forward Converter Can Avoid Reverse Charging of Energy Storage Capacitor

technical field

The invention belongs to the technical field of switching power supplies, and in particular relates to a secondary parallel LCD forward converter capable of avoiding reverse charging of an energy storage capacitor.

Background technique

In many isolated switching power supply conversion topologies, compared with the flyback converter, the power of the forward converter is not limited by the ability of the transformer to store energy; compared with the half-bridge and full-bridge converters, the forward converter As far as it is concerned, it uses fewer components, simpler circuits, lower cost, and higher reliability. Therefore, due to its relatively simple structure, low cost, input and output isolation, and high operational reliability, the forward converter circuit is more suitable for applications in small and medium power conversion applications, and has received high attention from the industry.

But for the single-transistor forward converter, because it works in the forward excitation state, its high-frequency transformer core is unidirectionally magnetized, and it has no magnetic reset function, so it is very likely to cause problems such as core saturation. The result of magnetic saturation will lead to a sharp increase in the current flowing through the switch tube, and even damage the switch tube, which limits the promotion of the forward converter to a large extent, so a special magnetic reset circuit or energy transfer circuit must be added to prevent the magnetic core from being damaged. saturation.

The main working mechanism of the magnetic reset circuit is to transfer the excitation energy during the switch off time of each cycle, which can be consumed on other devices or returned to the input power supply or transmitted to the load terminal. There are many types of magnetic reset circuits used in existing forward converters, which can be roughly divided into three types:

The first is to connect the reset winding at the input end to return the energy to the input power supply;

The second is to connect RCD, LCD and other reset circuits on the primary side of the transformer, so that the energy is consumed or returned to the input terminal;

The third is to take reset measures on the secondary side, which can transfer energy to the output.

However, the traditional RCD clamping circuit is relatively simple, and its disadvantage is that the excitation energy is consumed in the clamping resistance, which makes it difficult to improve the overall efficiency of the system; active clamping technology can be used to achieve magnetic reset, which is an excellent performance method, but it increases the complexity, design difficulty and cost of the converter circuit; while the magnetic reset winding reset method is mature and reliable, and the excitation energy can be returned to the input power supply, but the magnetic reset winding increases the complexity of the transformer structure, and Increase the voltage stress of the power switch tube.

The existing secondary side reset either needs to increase the reset winding or make the circuit complex, but increases the difficulty and cost of the design and manufacture of the transformer or circuit; or needs to set more diodes to achieve energy transfer, but will increase the circuit loss; or will It affects the working mode or other electrical performance indicators of the forward inductor, which is not conducive to high-power transmission.

Therefore, in order to further popularize and apply the forward converter, solve its magnetic reset problem, improve its overall performance, and address the shortcomings of other reset methods, researching new magnetic reset methods is a topic that needs to be continuously discussed.

Contents of the invention

The technical problem to be solved by the present invention is to provide a secondary parallel LCD forward converter that can avoid reverse charging of the energy storage capacitor in view of the above-mentioned deficiencies in the prior art, so as to solve the problem of low excitation energy utilization rate of the existing magnetic reset circuit The circuit composition is complex, the loss is large, and the efficiency is low.

In order to solve the above-mentioned technical problems, the technical solution adopted in the present invention is: provide a kind of secondary parallel LCD forward converter that can avoid the reverse charge of energy storage capacitor, it is characterized in that: comprise forward converter main circuit (1), And an energy transfer and transmission circuit (2) connected to the main circuit of the forward converter (1); wherein, the main circuit of the forward converter (1) includes a high-frequency transformer T, a switch tube S, a diode D1, and a diode D2 , inductance L1 and capacitor C1, the same-named end of the primary side of the high-frequency transformer T is the positive voltage input terminal IN+ of the main circuit of the forward converter (1) and is connected with the positive output terminal of the external power supply, and the high-frequency transformer T The opposite end of the primary side is connected to the drain of the switch tube S, the source of the switch tube S is the negative voltage input terminal IN- of the main circuit of the forward converter (1) and is connected to the negative output terminal of the external power supply, so The gate of the switching tube S is connected to the output terminal of the external controller, the same-named terminal of the secondary side of the high-frequency transformer T is connected to the anode of the diode D1, and the cathode of the diode D1 is connected to the cathode of the diode D2 and one end of the inductor L1 The other end of the inductance L1 is connected to one end of the capacitor C1 and is the positive voltage output end OUT+ of the main circuit (1) of the forward converter, and the opposite end of the secondary side of the high-frequency transformer T is connected to the anode of the diode D2 It is connected to the other end of the capacitor C1 and is the negative voltage output terminal OUT- of the main circuit of the forward converter (1), and the negative voltage output terminal OUT- of the main circuit of the forward converter (1) is grounded; the energy transfer The transmission circuit (2) includes a diode D3 and a capacitor C2, the anode of the diode D3 is connected to the anode of the diode D2, the cathode of the diode D3 is connected to the second end of the capacitor C2, and the first end of the capacitor C2 is connected to the second end of the capacitor C2. The anode of the diode D1 is connected; the energy transfer and transmission circuit (2) includes a diode D3, a capacitor C2, an inductor L2 and a diode D4, the anode of the diode D3 is connected to the anode of the diode D2, and the cathode of the diode D3 is connected to the capacitor The second end of C2 is connected, the first end of the capacitor C2 is connected to the anode of the diode D1, one end of the inductor L2 is connected to the cathode of the diode D3, and the other end is connected to the positive pole of the forward converter main circuit (1). The voltage output terminal OUT+ is connected, the anode of the diode D4 is connected to the first end of the capacitor C2 of the energy transfer and transmission circuit (2), and the second end of the cathode capacitor C2 is connected.

Wherein, a preferred solution is: the diodes D1 and D2 are fast recovery diodes.

Among them, a preferred solution is: the switch tube S is a full-control power semiconductor device.

Among them, the preferred solution is: the capacitor C2 is selected according to the first selection step; wherein, the steps of the first selection step include:

Step 101, selecting the capacitance C ₂ of the excitation energy storage capacitor C2;

Step 102, and calculate the withstand voltage V _C2,Ton of the capacitor C2;

Step 103: Select a capacitor with a capacitance value of _C2 and a withstand voltage greater than V _C2,Ton as the capacitor C2.

Wherein, the preferred solution is: the inductance L2 is selected according to the second selection step; wherein, the steps of the second selection step include:

Step 201, obtaining the average value of the current variation flowing through the inductor L2 during the entire period, and obtaining the average current of the inductor L1;

Step 202, determine the value range of the inductance value L2 of the inductance L2 _;

Step 203, combining steps 201 and 202, determine the maximum current I _L2,max flowing through the inductor L2.

Wherein, the preferred solution is: the diode D3 and the diode D4 are selected according to the third selection step; wherein, the steps of the third selection step include:

Step 301, calculating the maximum current I _D3,max flowing through the diode D3;

Step 302, calculating the maximum withstand voltage V _D3,max of the diode D3;

Step 303, select the diode D3 according to the maximum current I _D3,max flowing through the diode D3 and the withstand voltage V _{D3,max of} the diode D3;

Step 304, calculating the maximum current I _D4,max flowing through the diode D4;

Step 305, calculating the maximum withstand voltage V _D4,max of the diode D4;

Step 306, select the diode D4 according to the maximum current I _D4,max flowing through the diode D4 and the withstand voltage V _{D4,max of} the diode D4.

Compared with the prior art, the present invention has the following advantages:

1. The present invention realizes the transfer of excitation energy to the load side through the secondary parallel LCD forward converter that can avoid reverse charging of the energy storage capacitor, and improves the overall efficiency of the converter.

2. The secondary side parallel LCD forward converter designed and realized by the present invention has high working stability and reliability, simple circuit, no complicated control scheme, and has wide popularization value.

3. The secondary LCD magnetic reset forward converter circuit designed in the present invention reduces the design difficulty of the transformer compared with the auxiliary winding reset.

4. The capacitance of the energy transfer and transmission circuit of the present invention is connected in parallel with a unidirectional conduction diode, which can prevent reverse charging of C2, reduce reactive power, and further improve efficiency.

5. The reverse recovery problem of the diode D4 can be eliminated, and the loss of the diode can be reduced.

6. Inductor L2 can work in CCM, suitable for high power transmission.

7. The energy transfer and transmission circuit of the present invention can also transmit forward energy, can disperse power transmission, further improves reliability, and is more suitable for high-power applications.

8. After using the present invention in the switching power supply, the working safety and reliability of the switching power supply are higher, and the energy transfer and transmission circuit can improve the energy utilization rate, and can be widely used in computers, medical communications, industrial control, aerospace equipment, etc. field, so the present invention has higher application value;

In summary, the circuit structure of the present invention is simple, easy to implement and low in cost, simple in working mode, high in working stability and reliability, long in service life, low in power consumption, high in transformer utilization, high in energy transmission efficiency, and capable of improving switching The working safety and reliability of the power supply are strong in practicability and high in popularization and application value.

The technical solutions of the present invention will be described in further detail below with reference to the accompanying drawings and embodiments.

Description of drawings

FIG. 1 is a schematic circuit diagram of a secondary parallel LCD forward converter capable of avoiding reverse charging of an energy storage capacitor according to the present invention.

Explanation of reference signs:

1—Forward converter main circuit; 2—Energy transfer and transmission circuit.

detailed description

As shown in Figure 1, the secondary side parallel LCD forward converter that can avoid the reverse charge of the energy storage capacitor of the present invention includes the main circuit 1 of the forward converter, and the energy transfer and connection with the main circuit 1 of the forward converter. Transmission circuit 2; wherein, the main circuit 1 of the forward converter includes a high-frequency transformer T, a switch tube S, a diode D1, a diode D2, an inductor L1 and a capacitor C1, and the terminal with the same name on the primary side of the high-frequency transformer T is positive The positive voltage input terminal IN+ of the main circuit 1 of the exciter converter is connected to the positive output terminal of the external power supply, the opposite terminal of the primary side of the high-frequency transformer T is connected to the drain of the switch tube S, and the source of the switch tube S The negative voltage input terminal IN- of the main circuit 1 of the forward converter is connected to the negative output terminal of the external power supply, the gate of the switching tube S is connected to the output terminal of the external controller, and the secondary side of the high-frequency transformer T The end with the same name of the diode D1 is connected to the anode of the diode D1, the cathode of the diode D1 is connected to the cathode of the diode D2 and one end of the inductor L1, and the other end of the inductor L1 is connected to one end of the capacitor C1 and is the main circuit 1 of the forward converter The anode voltage output terminal OUT+ of the high-frequency transformer T secondary side is connected to the anode of the diode D2 and the other end of the capacitor C1 and is the negative voltage output terminal OUT- of the main circuit 1 of the forward converter. The negative voltage output terminal OUT- of the forward converter main circuit 1 is grounded; the energy transfer and transmission circuit 2 includes a diode D3 and a capacitor C2, the anode of the diode D3 is connected to the anode of the diode D2, and the cathode of the diode D3 It is connected to the second end of the capacitor C2, and the first end of the capacitor C2 is connected to the anode of the diode D1; the energy transfer and transmission circuit 2 includes a diode D3, a capacitor C2, an inductor L2 and a diode D4, and the diode D3 The anode is connected to the anode of the diode D2, the cathode of the diode D3 is connected to the second end of the capacitor C2, the first end of the capacitor C2 is connected to the anode of the diode D1, and one end of the inductor L2 is connected to the cathode of the diode D3 , the other end of which is connected to the positive voltage output terminal OUT+ of the main circuit of the forward converter 1, the anode of the diode D4 is connected to the first end of the capacitor C2 of the energy transfer and transmission circuit 2, and the second end of the cathode capacitor C2 connect.

During specific implementation, the load RL is connected between the positive voltage output terminal OUT+ and the negative voltage output terminal OUT- of the forward converter main circuit 1 . In the main circuit 1 of the forward converter, both the inductor L1 and the capacitor C1 are used for filtering.

In this embodiment, the diode D1 is a rectifier diode, and the diode D2 is a fast recovery diode. Diode D2 is used for freewheeling.

In this embodiment, the switch tube S is an NMOS switch tube.

The working principle of this embodiment is:

Before analyzing the working principle of this embodiment, it is assumed that the forward inductor L1 works in DCM, and the auxiliary inductor L2 and transformer secondary inductor Lw2 work in CCM. The working principle of this embodiment is analyzed below by dividing the switching tube into the off period and the on period. In order to facilitate the introduction of the principle, it is agreed that for C2, it is assumed that its voltage is negative on the left and positive on the right as a positive voltage, and positive on the left and negative on the right is a reverse voltage.

First, the working principle during the conduction period of the switch tube S:

Assuming that before the switch is turned on, the forward voltage of C2 reaches the maximum value, the current of Lw2 and L2 drops to the minimum value, and the current of the inductor L1 remains zero. D3 is turned on, and D1, D2, and D4 are turned off.

The first stage: D4 is turned off, and C2 releases positive energy storage

After the switch tube is turned on, the input voltage Vi is applied to both ends of the primary winding of the transformer, and the voltage coupled to the secondary winding w2 is positive and negative, D1 is turned on, and the forward energy is transmitted to the load through two branches. D1 and L1 are transmitted to the load, and the current of L1 rises linearly. Second, after transferring energy to the load through C2, D4, and L2, the forward energy storage of C2 is released from the maximum value, and the current curve of L2 rises until the forward voltage of C2 drops to zero, and this stage ends. In this stage, D2, D3, and D4 are still cut off.

The second stage: D4 is turned on, and energy is transferred to the load through D4 and L2

After the forward voltage of C2 drops to zero, D4 is naturally turned on, C2 is short-circuited, and energy is transmitted to the load through D4 and L2. At this time, the current of L2 keeps increasing linearly. At the same time, D1 remains on, and the current of L1 continues to rise linearly until the next switch off cycle arrives, and the currents of L1 and L2 both reach the maximum value, and this process ends. At this stage, D4 is turned on with zero voltage.

Second, the working principle when the switch tube S is turned off:

The first stage: L1 and L2 continue to provide energy to the load at the same time

After the switch tube S is turned off, D3 is turned on, and the secondary winding stores positive energy for C2 through D3, and the voltage at both ends of C2 increases positively from zero. At the same time, the inductor L2 freewheels through D3, and the current of the inductor L2 decreases linearly. During this process, D2 is turned on, L1 provides energy to the load through continuous flow through D2, and the current of inductor L1 decreases linearly until the current of L1 drops to zero, and this phase ends.

The second stage: only L2 freewheeling provides energy to the load

After the current of inductor L1 drops to zero, D2 is cut off, D3 remains on, C2 continues to store excitation energy, the forward voltage of C2 gradually increases, and the current coupled to the secondary winding decreases slowly. At the same time, inductor L2 continues to freewheel through D3. Until the next switch conduction period arrives, the L2 current and the current coupled to the secondary winding both drop to the minimum value, and the C2 voltage reaches the maximum value, and this phase ends.

In this embodiment, the capacitor C2 is selected according to the first selection step; wherein, the steps in the first selection step include:

选取励磁储能电容C2的容值C₂；Step 101, according to the formula

Select the capacitance C ₂ of the excitation energy storage capacitor C2;

Step 102, calculate the withstand voltage V _C2,Ton of the capacitor C2 according to the formula (A1);

Among them, d is the duty cycle of the switch tube S, n is the turns ratio of the primary winding of the high frequency transformer T to the secondary winding, L _m is the excitation inductance of the primary winding of the high frequency transformer T, and f is the forward conversion The operating frequency of the main circuit 1 of the device, λ is generally taken as 0.8≤λ≤1, the maximum excitation current of the excitation inductance L _m in one cycle is I _Lm,max , and the minimum excitation current is I _Lm,min , the specific formula is:

Among them, V _i is the input voltage of the main circuit 1 of the forward converter;

Step 103: Select a capacitor with a capacitance value of _C2 and a withstand voltage greater than V _C2,Ton as the capacitor C2.

In this embodiment, the inductance L2 is selected according to the second selection step; wherein, the steps of the second selection step include:

Step 201, determine the value range of the inductance value L2 of the inductance L2 according to _formula (A8) and formula (A9);

Among them, V _o is the output voltage of the main circuit 1 of the forward converter;

Step 202, determine the maximum current I _L2,max flowing through the inductor L2 according to the formula (A10);

Among them, the time for the voltage across the capacitor C2 to drop to zero is

Before the voltage across the capacitor C2 drops to zero in the inductor L2, the current expression of the inductor L2 is

In the whole cycle, the average value of the current variation flowing through the inductor L2 is

The average current of inductor L1 is

In this embodiment, the diode D3 and the diode D4 are selected according to the third selection step; wherein, the steps of the second selection step include:

Step 301, calculate the maximum current I _D3,max flowing through the diode D3 according to the formula (A15)

Among them, I _L1,max is the maximum current flowing through the primary winding of the high-frequency transformer T, and I _L2 is the current flowing through the inductor L2;

Step 302, calculate the maximum withstand voltage V _D3,max of the diode D3 according to the formula (A16)

Step 303, select the diode D3 according to the maximum current I _D3,max flowing through the diode D3 and the withstand voltage V _{D3,max of} the diode D3.

Step 304, calculate the maximum current I _D4,max flowing through the diode D4 according to the formula (A17);

Step 305, calculate the maximum withstand voltage value V _D4,max of the diode D4 according to the formula (A18);

Step 303, select the diode D4 according to the maximum current I _D4,max flowing through the diode D4 and the withstand voltage V _{D4,max of} the diode D4.

Of course, the above description is only to illustrate the feasibility of the technical solution of the present invention, and the principle of one of the working modes and its corresponding formula are listed, but it is not the only and limited description, and is only used as a reference.

It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit them. Those skilled in the art can modify the technical solutions described in the above embodiments, or modify some of the technical solutions. Features are equivalently replaced; and all these modifications and replacements should belong to the protection scope of the appended claims of the present invention.

Claims (6)

1. A secondary parallel LCD forward converter that can avoid reverse charging of the energy storage capacitor is characterized in that: it comprises a forward converter main circuit (1), and is connected with the forward converter main circuit (1). Energy transfer and transmission circuit (2); wherein, the main circuit (1) of the forward converter includes a high-frequency transformer T, a switch tube S, a diode D1, a diode D2, an inductor L1 and a capacitor C1, and the high-frequency transformer T The terminal with the same name on the primary side is the positive voltage input terminal IN+ of the main circuit of the forward converter (1) and is connected to the positive output terminal of the external power supply, and the terminal with the same name on the primary side of the high-frequency transformer T is connected to the drain of the switch tube S connected, the source of the switching tube S is the negative voltage input terminal IN- of the main circuit of the forward converter (1) and is connected to the negative output terminal of the external power supply, the gate of the switching tube S is connected to the output of the external controller The terminal of the same name on the secondary side of the high-frequency transformer T is connected to the anode of the diode D1, the cathode of the diode D1 is connected to the cathode of the diode D2 and one end of the inductor L1, and the other end of the inductor L1 is connected to the capacitor C1 One end is connected and is the positive voltage output terminal OUT+ of the main circuit (1) of the forward converter, and the opposite end of the secondary side of the high-frequency transformer T is connected to the anode of the diode D2 and the other end of the capacitor C1 and is a forward converter The negative voltage output terminal OUT- of the main circuit (1), the negative voltage output terminal OUT- of the forward converter main circuit (1) is grounded; the energy transfer and transmission circuit (2) includes a diode D3, a capacitor C2, Inductor L2 and diode D4, the anode of the diode D3 is connected to the anode of the diode D2, the cathode of the diode D3 is connected to the second end of the capacitor C2, and the first end of the capacitor C2 is connected to the anode of the diode D1, so One end of the inductance L2 is connected to the cathode of the diode D3, the other end is connected to the positive voltage output terminal OUT+ of the main circuit of the forward converter (1), and the anode of the diode D4 is connected to the capacitance of the energy transfer and transmission circuit (2) The first terminal of C2 is connected, and its cathode is connected with the second terminal of capacitor C2. 2 . The secondary parallel LCD forward converter capable of avoiding reverse charging of the energy storage capacitor according to claim 1 , wherein the diodes D1 and D2 are fast recovery diodes. 3 . 3. The secondary parallel LCD forward converter capable of avoiding reverse charging of the energy storage capacitor according to claim 1, characterized in that: said switch tube S is a fully-controlled power semiconductor device. 4. The secondary parallel LCD forward converter capable of avoiding reverse charging of the energy storage capacitor according to claim 1, wherein: the capacitor C2 is selected according to the first selection step; wherein, the first selection step The steps include: Step 101, selecting the capacitance C ₂ of the excitation energy storage capacitor C2; Step 102, and calculate the withstand voltage V _C2,Ton of the capacitor C2; Step 103: Select a capacitor with a capacitance value of _C2 and a withstand voltage greater than V _C2,Ton as the capacitor C2. 5. The secondary parallel LCD forward converter capable of avoiding reverse charging of the energy storage capacitor according to claim 4, characterized in that: the inductance L2 is selected according to the second selection step; wherein, the second selection step The steps include: Step 201, obtaining the average value of the current variation flowing through the inductor L2 during the entire period, and obtaining the average current of the inductor L1; Step 202, determine the value range of the inductance value L2 of the inductance L2 _; Step 203, combining steps 201 and 202, determine the maximum current I _L2,max flowing through the inductor L2. 6. The secondary parallel LCD forward converter capable of avoiding reverse charging of the energy storage capacitor according to claim 4 or 5, characterized in that: the diode D3 and the diode D4 are selected according to the third selection step; wherein, the The steps of the third selection step include: Step 301, calculating the maximum current I _D3,max flowing through the diode D3; Step 302, calculating the maximum withstand voltage V _D3,max of the diode D3; Step 303, select the diode D3 according to the maximum current I _D3,max flowing through the diode D3 and the withstand voltage V _{D3,max of} the diode D3; Step 304, calculating the maximum current I _D4,max flowing through the diode D4; Step 305, calculating the maximum withstand voltage V _D4,max of the diode D4; Step 306, select the diode D4 according to the maximum current I _D4,max flowing through the diode D4 and the withstand voltage V _{D4,max of} the diode D4.

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