CN114337299A

CN114337299A - Control system of secondary rectifier tube

Info

Publication number: CN114337299A
Application number: CN202111584193.6A
Authority: CN
Inventors: 颜耀; 王亚洲; 王廷营; 刘文煜; 李伟鹏; 仲羿诚; 王永生; 孟杰; 唐海瑞; 陆杨军; 杨涛
Original assignee: Lianyungang Jierui Electronics Co Ltd
Current assignee: Shanghai Jieruizhao New Information Technology Co ltd
Priority date: 2021-12-22
Filing date: 2021-12-22
Publication date: 2022-04-12
Anticipated expiration: 2041-12-22
Also published as: CN114337299B

Abstract

The invention discloses a control system of a secondary rectifier tube. The control system obtains a turn-off signal of the first switching tube according to detection of secondary side voltage of a transformer in the converter, the turn-off signal is used as a turn-on signal of the secondary side rectifying tube, the turn-off signal of the secondary side rectifying tube is obtained by judging completion of magnetic reset of the transformer, slope compensation is added to provide a certain advanced turn-off amount for the secondary side rectifying tube, and stability of the system is guaranteed. The control system is simple to realize, does not need isolation transmission of signals, and can effectively improve the power density of the converter.

Description

Control system of secondary rectifier tube

Technical Field

The invention belongs to the technical field of converters, and particularly relates to a control system of a secondary rectifier tube in a double-clamp zero-voltage switching converter.

Background

The double-clamping zero-voltage switching converter is an isolated DC/DC circuit topology and comprises first to fourth switching tubes Q₁～Q₄Secondary rectifier Q₅And a power transformer T, one end of the primary side of which is connected to the first switch tube Q₁And a second switching tube Q₂The other end is connected with a third switching tube Q₃And a fourth switching tube Q₄One end of the secondary side of the transformer is connected with the output voltage v_oOne end of the positive end of the rectifying tube is connected with the secondary side rectifying tube Q₅。

For the case of small output current, the secondary rectifier Q₅The diodes are adopted for rectification, so that the control complexity of the converter can be effectively reduced; however, when the output current is large, the conduction loss of the diode is large, so that the efficiency of the converter is low; in order to reduce the conduction loss of the diode, a switching tube with smaller conduction resistance can be used for replacing the diode, so that the efficiency of the converter can be improved.

Secondary side rectifier tube Q₅Control signal S of₅The current can be generated by a primary side control circuit of the converter and is transmitted to a secondary side through isolation; the secondary side can also be independently generated by detecting the voltage or current of the secondary side. Secondary side rectifier tube Q₅Control signal S of₅And a third switching tube Q₃Control signal S of₃The same, therefore, the third switch tube Q can be used₃Control signal S of₃And transmitting to a secondary side through isolation to obtain. However, in order to realize the isolated transmission of signals, an isolation transformer or the like is required for transmission, and the volume of the isolation transformer is increased sharply with the increase of the primary and secondary side insulation withstand voltages, which significantly reduces the power density of the converter. In addition, a secondary rectifier Q₅The control signal can be generated by a secondary synchronous rectification controller, specifically by sampling a secondary rectifier Q₅Of the drain-source voltage v_dsIt is sent to a synchronous rectification controller to generate a secondary rectifier Q₅Control signal S₅. However, in practical application, the secondary rectifier Q₅The parasitic inductor of the package causes the drain-source voltage to include the inductive voltage component introduced by the parasitic inductor of the package during the conduction period, which causes the secondary rectifier Q₅The secondary current is turned off in advance when the secondary current does not drop to zero, and then the secondary current will flow from the secondary rectifier tube Q₅The current flows through the body diode(s) of the converter(s), so that the conduction loss of the converter(s) is increased and the efficiency is reduced.

Disclosure of Invention

The present invention is directed to solve the above problems of the prior art, and an object of the present invention is to provide a control system for a secondary rectifier, which utilizes the feature of volt-second balance of a power transformer in a cycle to generate a secondary rectifier Q at the secondary side of a converter₅Control signal S of₅Without need of isolated transmission of active clamping tube Q₃Control signal S of₃The power density of the converter can be effectively improved.

The technical solution for realizing the purpose of the invention is as follows: a control system of a secondary rectifier tube is used for the secondary rectifier tube of a double-clamping zero-voltage switch converter, the double-clamping zero-voltage switch converter comprises a first switch tube, a second switch tube, a fourth switch tube, the secondary rectifier tube and a power transformer T, one end of the primary side of the power transformer is connected between the first switch tube and the second switch tube, the other end of the primary side of the power transformer is connected between the third switch tube and the fourth switch tube, one end of the secondary side of the transformer is connected with an output voltage v_oOne end of the positive end is connected with the secondary rectifier tube, and the system comprises S₁Reproduction circuit, integral sampling circuit, volt-second balance detection circuit and S₅A generating circuit; wherein the output voltage v of the converter_oAnd the drain voltage v of the secondary rectifier_dFor this purpose, the input ends of the control system are all connected into S₁Reproducing circuit, while v_dAn integral sampling circuit is also connected; integral sampling signal v generated by integral sampling circuit_senAnd S₁Control signal S generated by reproduction circuit₁₁The voltage-second balance detection circuit is connected to generate S₅Off signal S_{5_off}Further, S₅Off signal S_{5_off}And S₁Control signal S generated by reproduction circuit₁₁Access S₅Generating circuit, finally S₅The generating circuit generates a control signal S of the secondary rectifier₅。

Further, said S₁The reproduction circuit is used for reproducing a control signal S of the primary side first switching tube on the secondary side₁And the reproduced signal is denoted as S₁₁。

Further, said S₁The reproduction circuit comprises two signal input terminals, each of which is an output voltage v_oAnd the drain voltage v of the secondary rectifier_dThe signal output end is a control signal S of a primary side first switching tube₁Is reproduced signal S₁₁，v_oAnd v_dScaled to k by a scaling circuit_i·v_oAnd k_i·v_dThen connected to the negative end and the positive end of the first comparator respectively, the negative end of the first comparator passes through the resistor R_bias1Is connected to a DC voltage source V_bias1Wherein k is_iIs a scaling factor.

Further, the integral sampling circuit is connected with the secondary side of the transformer in parallel.

Further, the integral sampling circuit is connected with the secondary side rectifying tube in parallel.

Furthermore, the integration sampling circuit comprises a first resistor, a second resistor and a first capacitor, wherein the first resistor is connected with the first capacitor in series, and the second resistor is connected with the first capacitor in parallel.

Furthermore, the volt-second balance detection circuit comprises a first monostable trigger, a sampling switch tube, a sampling holding capacitor, a pull-up resistor and a second comparator, wherein the second monostable trigger comprises two signal input ends which are respectively the output v of the integrating circuit_senAnd S₁Output signal S of a reproduction circuit₁₁And also a signal output, i.e. S₅A shutdown signal; s₁Output signal of reproduction circuitNumber S₁₁Is connected to the input end of the first monostable trigger, and the first monostable trigger takes out S₁₁And output to the grid of the sampling switch tube; output v of integral sampling circuit_senThe negative input end of the second comparator is connected with the drain electrode of the sampling switch tube; the source electrode of the sampling switch tube is connected with one end of the sampling holding capacitor, the other end of the sampling holding capacitor is connected to the reference ground, and the common end of the source electrode of the sampling switch tube and the sampling holding capacitor is connected with the non-inverting input end of the second comparator; one end of the pull-up resistor is connected to the non-inverting input end of the second comparator, and the other end is connected to a bias voltage source V_bias2。

Further, said S₅The generating circuit comprises a second monostable flip-flop and an RS flip-flop which have two signal input ends respectively being the output signal S of the volt-second balance detecting circuit_{5_off}And S₁Output signal S of a reproduction circuit₁₁，S₁₁The falling edge of the second monostable trigger is taken out and then is connected to a set end, namely an S end, of the RS trigger, and the second monostable trigger is used for switching on a secondary rectifier tube; s_{5_off}The signal is connected to the reset end (namely the R end) of the RS trigger and is used for turning off the secondary rectifier tube.

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

1) the control signal of the secondary rectifier tube can be directly generated by the secondary side, so that the control signal of the primary active clamping tube Q3 is prevented from being transmitted to the secondary side and introduced into circuits such as an isolation transformer and the like, the space is saved, and the power density of the converter can be effectively improved.

2) The traditional synchronous rectification controller can lead to the problem that the secondary rectifier tube is turned off in advance due to the packaging parasitic inductance of the secondary rectifier tube, so that the conduction loss of a converter is increased, and the efficiency is reduced. The invention has no problem of early turn-off of the secondary rectifier tube, obtains the turn-off signal of the first switch tube according to the detection of the secondary voltage of the transformer in the converter, and uses the turn-off signal as the turn-on signal of the secondary rectifier tube, obtains the turn-off signal of the secondary rectifier tube by judging the completion of the magnetic reset of the transformer, and adds slope compensation to provide a certain early turn-off quantity for the secondary rectifier tube so as to ensure the stability of the system.

The present invention is described in further detail below with reference to the attached drawing figures.

Drawings

Fig. 1 is a block diagram of a primary and secondary side control structure of a dual-clamp zero-voltage switching converter in an embodiment.

Fig. 2 is an internal block diagram of the synchronous rectification controller in one embodiment.

FIG. 3 is a diagram illustrating S in the synchronous rectification controller according to an embodiment₁The circuit diagram is reproduced.

FIG. 4 is a diagram illustrating S in the synchronous rectification controller according to an embodiment₁A typical waveform diagram of the reproduction circuit.

FIG. 5 is a diagram of an integrating and sampling circuit in a synchronous rectification controller according to an embodiment, in which (a) the integrating and sampling circuit is connected in parallel with a secondary side of a transformer, and (b) the integrating and sampling circuit is connected with a secondary side rectifier Q₅And (4) connecting in parallel.

Fig. 6 is a circuit diagram of volt-second balance detection in the synchronous rectification controller according to one embodiment.

FIG. 7 is a diagram illustrating S in the synchronous rectification controller according to an embodiment₅A signal generating circuit diagram.

Fig. 8 is a block diagram of a specific implementation of the synchronous rectification controller in one embodiment.

FIG. 9 is a waveform diagram of a control simulation in one embodiment.

Detailed Description

In order to make the objects, technical solutions and advantages of the present application more apparent, the present application is described in further detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the present application and are not intended to limit the present application.

It should be noted that, if directional indications (such as up, down, left, right, front, and back … …) are involved in the embodiment of the present invention, the directional indications are only used to explain the relative positional relationship between the components, the movement situation, and the like in a specific posture (as shown in the drawing), and if the specific posture is changed, the directional indications are changed accordingly.

In addition, if there is a description of "first", "second", etc. in an embodiment of the present invention, the description of "first", "second", etc. is for descriptive purposes only and is not to be construed as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one such feature. In addition, technical solutions between various embodiments may be combined with each other, but must be realized by a person skilled in the art, and when the technical solutions are contradictory or cannot be realized, such a combination should not be considered to exist, and is not within the protection scope of the present invention.

Fig. 1 shows a block diagram of a main controller and a synchronous rectification controller in a dual-clamp zero-voltage switching converter according to an embodiment of the present invention. The master controller has four signal input terminals, which are respectively the input voltage V of the converter_inA first switch tube Q₁And a second switching tube Q₂To ground voltage v_AA third switching tube Q₃And a fourth switching tube Q₄To ground voltage v_BVoltage v of clamp capacitor_c(ii) a The main controller also has four signal output ends, which are respectively a first switch tube Q₁A second switch tube Q₂And a third switching tube Q₃And a fourth switching tube Q₄Control signal S of₁、S₂、S₃、S₄(ii) a The synchronous rectification controller has two signal input terminals for outputting a voltage v_oSecondary rectifier Q₅Voltage v of the drain electrode_d. The synchronous rectification controller has a signal output terminal as a secondary side rectification tube Q₅Control signal S of₅。

FIG. 2 is a block diagram of the synchronous rectification controller according to the embodiment of the present invention, which specifically includes S₁Reproduction circuit, integral sampling circuit, volt-second balance detection circuit and S₅A circuit is generated. Wherein the output voltage v_oSecondary rectifier Q₅Voltage v of the drain electrode_dThe input terminals controlled for this purpose are all connected to S₁Reproduction circuit, further v_dAlso incorporate integrationA sampling circuit. Integral sampling signal v generated by integral sampling circuit_senAnd S₁Control signal S generated by reproduction circuit₁₁S generated by the voltage-second balance detection circuit₅Off signal S_{5_off}Further, S₅Off signal S_{5_off}And S₁Control signal S generated by reproduction circuit₁₁Access S₅Generating circuit, finally S₅Secondary side rectifier Q generated by generating circuit₅Control signal S of₅。

S₁The reproduction circuit is used for reproducing a control signal S of the primary side first switching tube on the secondary side₁The reproduced signal is named S₁₁. FIG. 3 shows S proposed in the embodiment of the present invention₁A reproduction circuit comprising two signal inputs, each for an output voltage v_oSecondary rectifier Q₅Voltage v of the drain electrode_dThe signal output end is a control signal S of a primary side first switching tube₁Is reproduced signal S₁₁。

v_oAnd v_dScaled to k by a scaling circuit_i·v_oAnd k_i·v_dWherein k is_iIs connected to the negative end and the positive end of the comparator 1 respectively for scaling factor, and the negative end of the comparator 1 is connected with the resistor R_bias1To a direct voltage source V_bias1。S₁A typical waveform for a recurrent circuit is shown in fig. 4 when the dual-clamp zero-voltage switching converter operates at: 1) an energy storage stage: first switch tube Q₁And a fourth switching tube Q₄During conduction, the secondary rectifier Q₅Voltage v of the drain electrode_dIs equal to the output voltage v_oAnd an input voltage V_inThe sum of the voltages reduced to the secondary side is greater than the output voltage, and the comparator 1 outputs a high level; 2) and (3) energy transfer stage: second switch tube Q₂And a third switching tube Q₃During conduction, the secondary rectifier Q₅Voltage v of the drain electrode_dApproximately zero, below the output voltage v_oThe comparator 1 outputs a low level; 3) a resonance stage: secondary side rectifier tube Q₅Voltage v of the drain electrode_dGradually rising but always having an amplitude lower than the output voltagev_oThe comparator 1 outputs a low level; 4) a follow current stage: secondary side rectifier tube Q₅Voltage v of the drain electrode_dIs equal to the output voltage v_oHowever, since a negative end of the comparator 1 is superimposed with a certain bias voltage, the comparator 1 outputs a low level. In summary, the output S of the comparator 1₁₁In the first switching tube Q only₁The on period being set to high, i.e. S₁₁Reproduces the primary side first switch tube Q₁Control signal S of₁。

To obtain a secondary rectifier Q₅Control signal S of₅The time of its rising and falling edges needs to be acquired.

1) Obtaining S₅Rising edge: with the first switch tube Q₁And a fourth switching tube Q₄Turn-off, secondary side rectifier Q₅Voltage v of the drain electrode_dGradually decrease when v_d<v_oWhen S is present₁Output signal S of a reproduction circuit₁₁Set low if the output voltage v of the converter_oLower, can be regarded as a secondary rectifier Q₅Approximately effecting soft switching, at which time S₁₁The falling edge of the rectifier can be used as a secondary rectifier tube Q₅Control signal S of₅The rising edge of (d); if the output voltage v of the converter is_oHigher, can be for S₁₁After a certain time delay, the falling edge is taken out to be used as a secondary rectifier tube Q₅Control signal S of₅The rising edge of (c).

2) Obtaining S₅Falling edge: the power transformers in a dual-clamp zero-voltage switching converter are volt-second balanced in each switching cycle. The double-clamping zero-voltage switching converter has four working stages, the resonant stage is short in time, the influence on the volt-second of the power transformer is small, and the volt-second of the power transformer is kept unchanged in the follow current stage, so that the power transformer can be approximately considered to realize the volt-second balance in the input energy storage stage and the primary and secondary side energy transfer stages. In other words, the magnetic reset completion time of the power transformer is S₅The moment of turn-off.

In order to determine whether the magnetic reset of the power transformer is completed, firstly, volt-second information of the power transformer needs to be acquired, and therefore, the embodiment of the inventionAn integral sampling circuit is introduced to integrate the secondary side voltage of the transformer. FIG. 5 shows a specific implementation of the integrating and sampling circuit of this embodiment, which is composed of a resistor R₁,R₂And a capacitor C₁Is formed of a resistor R₁And a capacitor C₁Series connected, resistance R₂And a capacitor C₁In parallel, and there are:

R₁·C₁＞＞T_s

the integrating and sampling circuit can be directly connected in parallel with the secondary side of the transformer, as shown in fig. 5(a), or can be connected with a secondary side rectifier tube Q₅In parallel, as shown in FIG. 5(b), it is recommended to adopt the mode shown in FIG. 5 (b). At this time, by adjusting R₁And R₂The ratio of (C) can be adjusted₁D.c. voltage V on_dc，V_dcThe expression of (a) is:

to avoid the capacitor C₁The voltage on the capacitor is too high, and the signal processing of a subsequent circuit is influenced.

After the volt-second information of the power transformer is obtained, it needs to further determine when the magnetic reset of the power transformer is completed, for this reason, a volt-second balance detection circuit is introduced in this embodiment, as shown in fig. 6, and the volt-second balance detection circuit is composed of a monostable trigger, a sampling switch tube, and a sampling hold capacitor C_SHPull-up resistor R_bias2D.C. voltage source V_bias2And a comparator 2. It comprises two signal input terminals, each of which is the output v of an integrating circuit_senAnd S₁Output signal S of a reproduction circuit₁₁. In addition, it also comprises a signal output terminal, namely S₅The signal is turned off. S₁Output signal S of a reproduction circuit₁₁Is connected to the input of the monostable flip-flop which takes out S₁₁And output to the grid of the sampling switch tube;output v of the integrating circuit_senThe drain electrode of the sampling switch tube is connected with the inverting input end of the comparator 2; source electrode of sampling switch tube and sampling holding capacitor C_SHIs connected to one terminal of a sample-and-hold capacitor C_SHIs connected to reference ground, and the connection point between the two is connected to the non-inverting input end of the comparator 2; resistance R_bias2One end of the output voltage is connected to the non-inverting input end of the comparator 2, and the other end is connected to a bias voltage source V_bias2。

At the beginning of the switching cycle, i.e. the first switching tube Q₁Pair of turn-on times v_senSample and hold, sample and hold capacitor C_SHHas a voltage value of v_SH. With the first switch tube Q₁And a fourth switching tube Q₄On, the power transformer starts to magnetize, v_senGradually increase, v_sen>v_SH(ii) a When the first switch tube Q₁And a fourth switching tube Q₄After being turned off, the second switch tube Q₂And a third switching tube Q₃Secondary rectifier Q₅Start to conduct, power transformer start to demagnetize, v_senAnd gradually decreases. When v is_senIs reduced to v_SHThen the magnetic reset of the power transformer is completed, the output of the comparator 2 is set high, and S is generated₅Turn-off signal S_{5_off}. Notably, due to the sample-and-hold capacitance C_SHHas certain leakage current, load impedance is not infinite, and voltage v of the sampling holding capacitor_SHWill exhibit natural droop characteristics which will cause the secondary rectifier Q₅The turn-off is delayed. And Q₅The delayed turn-off will cause the secondary energy to sink back to the primary side, and to solve the above problem, this embodiment proposes to add a pull-up resistor R_bias2Is connected to a DC voltage source V_bias2By means of a flow through R_bias2While slowly charging the sample-and-hold capacitor, so that the voltage v of the sample-and-hold capacitor_SHExhibits a rising characteristic such that the secondary rectifier Q₅The energy of the secondary side can be effectively prevented from flowing back to the primary side by switching off in advance, and the stability of the system is improved.

S₅The generating circuit consists of a monostable trigger and an RS trigger, and is provided with two signal input ends which are respectively an output signal S of the volt-second balance detection circuit_{5_off}And S₁Output signal S of a reproduction circuit₁₁。S₁₁The falling edge of the monostable trigger is taken out and then connected to a positioning end (S end) of an RS trigger for turning on a secondary rectifier tube Q₅；S_{5_off}The signal is connected to the reset end (R end) of the RS trigger and used for turning off the secondary rectifier tube Q₅. The circuit structure is shown in fig. 7.

In order to more clearly express the connection relationship between the functional modules, fig. 8 shows a specific implementation circuit of a secondary rectifier control signal of a dual-clamp zero-voltage switching converter according to an embodiment of the present invention.

To further illustrate the effectiveness of the control system, fig. 9 shows a simulation waveform, which can be obtained from the figure that the control method of the secondary rectifier proposed in this embodiment can be implemented in the first switching transistor Q₁And a fourth switching tube Q₄Quickly turning on secondary rectifier Q after turn-off₅(ii) a While at the secondary side current i_sWhen the voltage is approximately 0, the secondary rectifier Q is turned off₅That is, the control method of the secondary rectifier tube provided in this embodiment can accurately generate the secondary rectifier tube Q₅Can solve the problem of signal primary and secondary transmission existing in the prior art, and a secondary rectifier tube Q₅The problem of early shutdown.

In summary, the control system of the secondary rectifier provided by the invention has the following advantages: the control signal of the secondary rectifier tube can be directly generated by the secondary side, so that the condition that the primary third switch tube Q is connected with the secondary side is avoided₃The control signal is transmitted to the secondary side, and circuits such as an isolation transformer and the like are introduced, so that the space is saved, and the power density of the converter can be effectively improved. The traditional synchronous rectification controller can lead to the problem that the secondary rectifier tube is turned off in advance due to the packaging parasitic inductance of the secondary rectifier tube, so that the conduction loss of a converter is increased, and the efficiency is reduced. The control method provided by the embodiment does not have the problem of early turn-off of the secondary rectifier tube.

The technical solutions of the present invention are not limited to the above embodiments, and modifications and equivalent substitutions made according to the technical solutions of the present invention should be included in the scope of the present invention.

Claims

1. A control system for a secondary rectifier of a dual-clamp zero-voltage switching converter including first to fourth switching tubes (Q)₁～Q₄) And a secondary rectifier (Q)₅) And a power transformer T, one end of the primary side of which is connected to the first switching tube (Q)₁) And a second switching tube (Q)₂) The other end is connected with a third switching tube (Q)₃) And a fourth switching tube (Q)₄) One end of the secondary side of the transformer is connected with the output voltage v_oOne end of the positive end of the secondary rectifier tube (Q) is connected with the secondary rectifier tube₅) Characterized in that the system comprises S₁Reproduction circuit, integral sampling circuit, volt-second balance detection circuit and S₅A generating circuit; wherein the output voltage v of the converter_oAnd a secondary rectifier (Q)₅) Voltage v of the drain electrode_dFor this purpose, the input ends of the control system are all connected into S₁Reproducing circuit, while v_dAn integral sampling circuit is also connected; integral sampling signal v generated by integral sampling circuit_senAnd S₁Control signal S generated by reproduction circuit₁₁The voltage-second balance detection circuit is connected to generate S₅Off signal S_{5_off}Further, S₅Off signal S_{5_off}And S₁Control signal S generated by reproduction circuit₁₁Access S₅Generating circuit, finally S₅Generating circuit generating secondary side rectifier (Q)₅) Control signal S of₅。

2. The control system of a secondary rectifier of claim 1, wherein S is₁The reproduction circuit is used for reproducing the first switch tube (Q) on the primary side on the secondary side₁) Control signal S of₁And the reproduced signal is denoted as S₁₁。

3. The control system of a secondary rectifier as claimed in claim 1 or 2, wherein S is₁The reproduction circuit comprises two signal input terminals, each of which is an output voltage v_oAnd a secondary rectifier (Q)₅) Voltage v of the drain electrode_dThe signal output end is a control signal S of a primary side first switching tube₁Is reproduced signal S₁₁，v_oAnd v_dScaled to k by a scaling circuit_i·v_oAnd k_i·v_dThen connected to the negative end and the positive end of the first comparator respectively, the negative end of the first comparator passes through the resistor R_bias1Is connected to a DC voltage source V_bias1Wherein k is_iIs a scaling factor.

4. The control system of a secondary rectifier of claim 1, wherein the integrating and sampling circuit is connected in parallel with the secondary of the transformer.

5. A control system for a secondary rectifier as claimed in claim 1, characterized in that the integrating and sampling circuit is connected to the secondary rectifier (Q)₅) And (4) connecting in parallel.

6. A control system for a secondary rectifier as claimed in claim 4 or 5, characterized in that the integrating and sampling circuit comprises a first resistor (R)₁) A second resistor (R)₂) A first capacitor (C)₁) Wherein the first resistance (R)₁) And a first capacitance (C)₁) In series, a second resistance (R)₂) And a first capacitance (C)₁) And (4) connecting in parallel.

7. Control system for a secondary rectifier tube according to claim 6, characterized in that said first resistance (R)₁) A second resistor (R)₂) A first capacitor (C)₁) The following relationships exist:

R₁·C₁＞＞T_s

in the formula, T_sIs the switching period of the converter, f_sIs T_sThe reciprocal of (c).

8. A control system for a secondary rectifier according to claim 7, characterized in that the first resistance (Rc) is adjusted₁) A second resistor (R)₂) The first capacitance (C) can be adjusted₁) D.c. voltage V on_dc，V_dcThe expression is as follows:

9. the control system of a secondary rectifier of claim 3, wherein the volt-second balance detection circuit comprises a first monostable flip-flop, a sampling switch tube, a sampling hold capacitor (C)_SH) Pull-up resistor (R)_bias2) And a second comparator including two signal inputs, each being the output v of the integrating circuit_senAnd S₁Output signal S of a reproduction circuit₁₁And also a signal output, i.e. S₅A shutdown signal; s₁Output signal S of a reproduction circuit₁₁Is connected to the input end of the first monostable trigger, and the first monostable trigger takes out S₁₁And output to the grid of the sampling switch tube; output v of integral sampling circuit_senThe negative input end of the second comparator is connected with the drain electrode of the sampling switch tube; source electrode and sample hold capacitor (C) of sampling switch tube_SH) Is connected to one terminal of a sample-and-hold capacitor (C)_SH) Is connected to a reference ground, the source of the sampling switch tube and the sampling hold capacitor (C)_SH) The common end of the first comparator is connected with the non-inverting input end of the second comparator; pull-up resistor (R)_bias2) One end of the first comparator is connected to the non-inverting input end of the second comparator, and the other end of the first comparator is connected to a bias voltage source V_bias2。

10. The control system of a secondary rectifier of claim 9, wherein S is₅The generating circuit comprises a second monostable flip-flop and an RS flip-flop which have two signal input ends respectively being the output signal S of the volt-second balance detecting circuit_{5_off}And S₁Output signal S of a reproduction circuit₁₁，S₁₁The falling edge of the second monostable trigger is taken out and then connected to the set end (S end) of the RS trigger for turning on a secondary rectifier (Q)₅)；S_{5_off}The signal is connected to the reset end (R end) of the RS trigger and used for turning off the secondary rectifier tube (Q)₅)。