A control method and control device for a half-bridge resonant flyback circuit

Abstract

The present application discloses a control method and a control device for a half-bridge resonant flyback circuit. The half-bridge resonant flyback circuit includes a main pipe, a freewheeling pipe, an excitation inductor, a leakage inductor and a resonant capacitor; the control method includes the following steps: when the main pipe is turned on, the excitation current change rate and the first voltage of the excitation inductor are obtained; wherein the first voltage is the voltage of the excitation inductor when the main pipe is turned on; the first excitation current is obtained; the first excitation current is the current flowing through the excitation inductor at the moment when the main pipe is turned off; the equivalent inductance is determined according to the excitation current change rate and the first voltage; when the freewheeling pipe is turned on, the second voltage is obtained; the second voltage is the voltage of the excitation inductor when the freewheeling pipe is turned on; the conduction time of the freewheeling pipe is determined at least according to the equivalent inductance, the second voltage and the first excitation current. The control method is simple, reliable and highly adaptive.

Description

Technical Field

[0001] The present application relates to the field of power electronics technology, and in particular to a control method and a control device for a half-bridge resonant flyback circuit. Background Art

[0002] With the development of consumer electronics applications, people's requirements for device charging are constantly increasing, and USB charging standards are constantly being updated. The latest USB PD3.1 adds an extended power range (EPR), and the maximum power is extended from 100W to 240W. PD3.1 provides a more flexible charging solution for devices that support higher power, such as gaming laptops, monitors, printers, and even electric vehicles.

[0003] The circuit topology used by mainstream portable charging devices is mainly based on flyback converters. Its topology is simple, low-cost, can achieve electrical isolation between the primary and secondary sides, and provide good electrical and safety performance. However, the transformer of the flyback converter is large and the power efficiency is low, which makes it difficult to meet people's requirements for high-efficiency and miniaturized charging devices. The LLC resonant converter can achieve ZVS (Zero Voltage Switch) and has higher power density and efficiency, but in scenarios with a wide output voltage range such as PD, the efficiency cannot always be kept optimal; the efficiency will decrease when the output voltage changes; and, compared with the flyback converter, the cost is higher.

[0004] Therefore, the half-bridge resonant flyback circuit shown in FIG1 has been favored in recent years because of its advantages of simple structure, low cost, ability to achieve ZVS and adaptability to a wide output voltage range. The control method of the half-bridge resonant flyback circuit mainly includes: adopting a complementary control strategy for the main switch tube Q1 and the synchronous tube Q2, or adopting a non-complementary control strategy for the main switch tube Q1 and the synchronous tube Q2. Among them, Q1 can adopt peak current control. Since the complementary control strategy of the main switch tube Q1 and the synchronous tube Q2 will lead to excessive negative current in the system, large system loop energy, and reduced overall efficiency, it is rarely used. For the non-complementary control strategy, for the control of the synchronous tube Q2, the user needs to configure a curve of output voltage and conduction time. This method undoubtedly increases the complexity of system use, has a low degree of adaptability, and is easily affected by the main circuit parameters. In addition, in order to ensure that the system always achieves ZVS, an adaptive adjustment strategy for the synchronous tube Q2 is introduced; its adjustment control strategy is adaptive adjustment according to the time when the ZCD signal (zero-crossing signal) appears. However, the time when the ZCD signal appears is not completely related to whether the main switch tube Q1 achieves ZVS. Therefore, it is necessary to repeatedly try and adjust the expected time for the ZCD signal to appear, which further increases the difficulty of use. Summary of the invention

[0005] In order to address the deficiencies of the prior art, the purpose of the present application is to provide a control method and a control device for a half-bridge resonant flyback circuit, which have the advantages of being simple and reliable, highly adaptable and less affected by main circuit parameters.

[0006] To achieve the above objectives, this application adopts the following technical solutions:

[0007] A control method for a half-bridge resonant flyback circuit, the half-bridge resonant flyback circuit comprising a main tube, a freewheeling tube, an excitation inductor, a leakage inductor and a resonant capacitor; the control method comprises the following steps:

[0008] When the main pipe is turned on, the excitation current change rate and the first voltage of the excitation inductor are obtained; wherein the first voltage is the voltage of the excitation inductor when the main pipe is turned on;

[0009] Obtaining a first excitation current; the first excitation current is the current flowing through the excitation inductor when the main tube is turned off;

[0010] determining an equivalent inductance according to the excitation current change rate and the first voltage;

[0011] When the freewheeling tube is turned on, a second voltage is obtained; the second voltage is the voltage of the excitation inductor when the freewheeling tube is turned on;

[0012] The conduction time of the freewheeling diode is determined at least according to the equivalent inductance, the second voltage and the first excitation current.

[0013] The control method obtains the equivalent inductance according to the excitation current change rate when the main tube is turned on and the first voltage on the excitation inductance, and then determines the turn-on time of the freewheeling tube according to the second voltage on the excitation inductance when the freewheeling tube is turned on, the equivalent inductance and the first excitation current when the main tube is turned off; thereby realizing the control of the half-bridge resonant flyback circuit. The control method performs circuit control according to the equivalent inductance calculated in real time, rather than simply using the known excitation inductance for control, so that the control is less affected by the main circuit parameters or the device processing technology; the control method is simple, reliable and highly adaptive.

[0014] A control device for a half-bridge resonant flyback circuit, the half-bridge resonant flyback circuit comprising a main tube, a freewheeling tube, an excitation inductor, a leakage inductor and a resonant capacitor; the control device comprises:

[0015] A voltage sampling unit, used to sample a first voltage and a second voltage; the first voltage is the voltage of the excitation inductor when the main tube is turned on; the second voltage is the voltage of the excitation inductor when the freewheeling tube is turned on;

[0016] A slope acquisition unit, used to acquire change parameter information related to the rate of change of the excitation current of the excitation inductor when the main tube is turned on;

[0017] an equivalent inductance calculation unit, configured to determine an equivalent inductance according to the change parameter information and the first voltage;

[0018] The freewheeling tube conduction time calculation unit is used to determine the conduction time of the freewheeling tube at least according to the equivalent inductance, the second voltage and the first excitation current; the first excitation current is the current flowing through the excitation inductance when the main tube is turned off.

[0019] The control device is used to implement the above control method, and also has the advantages of simple and reliable control, high degree of adaptability and little influence by main circuit parameters or device processing technology. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 It is a principle schematic diagram of a half-bridge resonant flyback circuit;

[0021] Figure 2 A flow chart of a control method for a half-bridge resonant flyback circuit provided in the present application;

[0022] Figure 3 A schematic diagram of the principle of a half-bridge resonant flyback circuit provided by the present application, and showing the position of the signal required to be used in the control method provided by an embodiment of the present application;

[0023] Figure 4 for Figure 3 The main waveforms of the circuit shown;

[0024] Figure 5 is a graph showing the relationship between the absolute value of the expected excitation inductor current and the input voltage of the half-bridge resonant flyback circuit in one embodiment;

[0025] Figure 6 A principle block diagram of a control device for a half-bridge resonant flyback circuit provided in one embodiment of the present application;

[0026] Figure 7 A principle block diagram of a control device for a half-bridge resonant flyback circuit provided in another embodiment of the present application;

[0027] Figure 8 A schematic diagram of the principle of a conduction time increment calculation unit of a control device provided by another embodiment of the present application;

[0028] Fig. 9 A schematic diagram of the principle of a half-bridge resonant flyback circuit provided in an embodiment of the present application. DETAILED DESCRIPTION

[0029] In order to enable those skilled in the art to better understand the solution of the present application, the technical solution in the specific implementation manner of the present application will be clearly and completely described below in conjunction with the drawings in the implementation manner of the present application.

[0030] Figure 1 A half-bridge resonant flyback circuit is shown, including a main tube Q1, a freewheeling tube Q2, an excitation inductor L m , leakage inductance L r and resonant capacitor C r ; The magnetizing inductance and leakage inductance can be obtained by setting the transformer T, which may not exist in the actual circuit. r , L m and C r Together they form the resonant cavity of the half-bridge resonant flyback circuit; and the resonant capacitor C r It can also transfer energy to the secondary side, which helps to reduce the size of the system transformer. The main tube Q1 and the freewheeling tube Q2 are mutually exclusive. When the main tube Q1 is turned on, the excitation inductance L m Excitation, the circuit is driven from the input voltage V in Absorbs energy and stores it in the excitation inductor L m and resonant capacitor C r When the freewheeling tube Q2 is turned on, the excitation inductance L m The excitation is demagnetized and the circuit starts to transfer energy to the secondary side.

[0031] In order to improve the shortcomings of the existing control method of the half-bridge resonant flyback circuit mentioned in the background technology. The embodiment of the present application provides a control method of the half-bridge resonant flyback circuit. The control method is simple and reliable, has a high degree of adaptability, can give full play to the advantages of the topology, and achieve higher efficiency. For the convenience of description, the control method of the present application is combined with Figure 1 The circuit diagram is shown in Figure 1. Figure 2 As shown, the control method includes the following steps:

[0032] Step S1: Obtain the excitation current change rate and the first voltage when the main pipe is turned on; specifically, when the main pipe Q1 is turned on, obtain the current flowing through the excitation inductance L m The excitation current change rate k and the first voltage V1; wherein the first voltage V1 is the excitation inductance L when the main pipe Q1 is turned on m The voltage of the resistor Q1 is 0.04V; where k = di1 / dt1, di1 is the change of the excitation current in a certain period of time during the conduction of the resistor Q1, and dt1 is the length of the period of time;

[0033] Step S2: Obtain the first excitation current i Lm1 Specifically, the first excitation current is the main Q1 off moment, flowing through the excitation inductor L m The current;

[0034] Step S3: determining the equivalent inductance according to the excitation current change rate k and the first voltage V1; the inductor works according to Faraday's law of electromagnetic induction, and therefore, the equivalent inductance can be determined according to the excitation current change rate and the first voltage.

[0035] In actual use, due to the influence of factors such as the working environment and the manufacturing process, it is difficult to ensure the consistency of the excitation inductance, and its inductance value will fluctuate or deviate. The present application calculates the equivalent inductance in real time, which is equivalent to determining the equivalent excitation inductance in real time, and uses it for subsequent control, making the control more accurate and more adaptable. Therefore, the equivalent inductance not only includes the inductance value of the excitation inductance, but also includes the inductance deviation caused by each link, so it can reduce the impact of the main circuit or other circuit parameters or process deviations on the control.

[0036] Step S4: obtaining a second voltage when the freewheeling tube is turned on; specifically, when the freewheeling tube Q2 is turned on, obtaining a second voltage V2; the second voltage is when the freewheeling tube Q2 is turned on, the excitation inductance L m Voltage;

[0037] Step S5: Determine the conduction time of the freewheeling tube; the excitation and demagnetization processes of the inductor follow Faraday's law of electromagnetic induction. Therefore, the conduction time of the freewheeling tube can be determined based on the equivalent inductance, the second voltage and the first excitation current; because in the freewheeling stage, the excitation inductor is demagnetized, and its current drops from the current at the time when Q1 is turned off to the expected excitation inductance current, which is the expected excitation inductance current at the time when the freewheeling tube Q2 is turned off. The current value can be 0; it can also be a negative value I neg , so as to achieve ZVS (zero voltage switching) of Q1. The current change of the excitation inductor in the freewheeling stage is the difference between the first excitation current and the desired excitation inductor current.

[0038] This embodiment determines the conduction time of the freewheeling tube by calculating the equivalent inductance of the circuit, which effectively reduces the influence of circuit parameters on the control, is conducive to improving the accuracy of the control, and the control method is simple and reliable.

[0039] Further, such as Figure 3 As shown, an auxiliary winding is set to sample the first voltage and the second voltage. That is, the half-bridge resonant flyback circuit includes a transformer, which includes not only a primary winding and a secondary winding, but also an auxiliary winding; the corresponding number of winding turns is respectively recorded as N p 、N s and N aux The transformer includes an excitation inductance and a leakage inductance, and the excitation inductance and the leakage inductance are obtained by designing the transformer. The first voltage and the second voltage are obtained by sampling the voltage of the auxiliary winding.

[0040] Specifically, in one embodiment, the first voltage is obtained by the following steps:

[0041] When the main pipe Q1 is turned on, the voltage of the auxiliary winding is sampled to obtain the first auxiliary winding voltage V aux1 ;

[0042] The first voltage V1 is calculated by the following formula:

[0043] V1=V aux1 *(N p / N aux );

[0044] Among them, N p is the number of turns of the primary winding of the transformer, N aux is the number of turns of the auxiliary winding of the transformer.

[0045] The second voltage is obtained by the following steps:

[0046] When the main tube Q1 is turned off, that is, when the freewheeling tube Q2 is turned on, the voltage of the auxiliary winding is sampled to obtain the second auxiliary winding voltage V aux2 ;

[0047] The second voltage is calculated by the following formula:

[0048] V2=V aux2 *(N p / N aux ); where N p is the number of turns of the primary winding of the transformer, N aux is the number of turns of the auxiliary winding of the transformer.

[0049] In this embodiment, the equivalent inductance is calculated by the following formula:

[0050] L eq =V aux1 *(dt1 / di1), where dt1 / di1 is the inverse of the excitation current change rate, that is, 1 / k; V aux1 It is the sampling voltage of the auxiliary winding when the main circuit is turned on.

[0051] The conduction time of the freewheeling tube is T on_Q2 Calculated by the following formula:

[0052] T on_Q2 =L eq * (di2 / V aux2 ), di2 is the first excitation current i Lm1 and the expected magnetizing inductor current i neg difference.

[0053] The working principle of this embodiment is as follows:

[0054] The formula for the induced voltage of the excitation inductance is shown in formula (1.1):

[0055] (1.1)

[0056] During the conduction phase of Q1,

[0057] (1.2)

[0058] Where L m is the magnetizing inductance value, due to the leakage inductance L r is relatively small, so the influence of leakage inductance can be ignored when the half-bridge resonant flyback circuit is excited; V1 is L m When excited, the voltage across its two ends; di1 and dt1 are the current change and time change during the conduction phase of Q1 respectively.

[0059] Further, according to the physical relationship of the transformer, the first voltage V1 and the first auxiliary winding voltage V aux1 The relationship between them, formula (1.2) can be further transformed into

[0060] (1.3)

[0061] Transform formula (1.3) to obtain

[0062] (1.4)

[0063] Due to L m 、N aux 、N p Under ideal conditions, it can be regarded as constant and the combination of the three is equivalent to the inductance L eq ; Further, during the conduction phase of Q2, ignoring the effect of the dead zone, in order to make the inductor L m The current in the magnetizing inductor drops to the expected magnetizing inductor current. Taking the expected magnetizing inductor current as 0 as an example, it is necessary to satisfy

[0064] (1.5)

[0065] V2 is L m The voltage across the inductor during demagnetization; di2 and dt2 are the current change and time change during the conduction phase of Q2, respectively.

[0066] Furthermore, according to the physical relationship of the transformer, the relationship between the second voltage and the second auxiliary winding voltage, the formula can be further converted into

[0067] (1.6)

[0068] The equivalent inductance L calculated in formula (1.4) eq As the excitation inductance value L m , we can further get

[0069] (1.7)

[0070] Where di2 is the first excitation current i Lm1 and the expected magnetizing inductor current i neg The expected excitation inductance current i neg Can be set to 0, at which time di2 is equal to the first excitation current i Lm1 is equal to the current corresponding to the closing moment of Q1, then the conduction time T of the freewheeling tube Q2 can be obtained. on_Q2 as follows:

[0071] (1.8)

[0072] The above method realizes the on-time control of the freewheeling tube Q2, while the control of the main tube Q1 can be realized by peak current control; after Q1 is turned on, if the excitation inductance current increases to the peak command value of the peak current control, Q1 is controlled to be turned off. In one embodiment, the first excitation current is the peak command value of the peak current control; the excitation current change rate is determined by the duration of the excitation current increasing from 0 to the preset excitation current and the preset excitation current during the conduction period of the main tube Q1; the preset excitation current is less than or equal to the peak command value. In other words, during the conduction period of the main tube, a certain time period is intercepted to calculate the excitation current change rate, and the equivalent inductance is calculated based on this, and then the on-time of the freewheeling tube Q2 is calculated to control the half-bridge resonant flyback circuit.

[0073] Of course, the main tube Q1 can also be realized by constant on-time control, that is, a time parameter is generated according to the circuit input and output signal, and the time parameter is the on-time of Q1; at this time, the rate of change of the excitation current is determined by the rate of change of the excitation current within a preset time during the on-time of the main tube; the preset time is less than or equal to the on-time of the main tube. In other words, during the on-time of the main tube, a certain time period is intercepted to calculate the rate of change of the excitation current, and the equivalent inductance is calculated based on this, and then the on-time of the freewheeling tube Q2 is calculated to achieve control of the half-bridge resonant flyback circuit. In this embodiment, it is necessary to increase current sampling in order to obtain real-time excitation current and obtain the first excitation current.

[0074] Under this control method, Figure 3 The core waveform of the circuit is as follows Figure 4 As shown, Q1 and Q2 are turned on in sequence. Q1 and G Q2 is the driving signal, V aux is the auxiliary winding voltage, I Lm is the magnetizing inductor current, I Lr is the leakage inductance resonant current. According to the driving signals of Q1 and Q2, Q1 is turned on and delayed by tsam1 Get the first auxiliary winding voltage V aux1 ; and after Q2 turns on and delays t sam2 Get the second auxiliary winding voltage V aux2 The sampling and acquisition of information here can be realized in a digital way, that is, converted into a digital quantity through an ADC, or in an analog way, the level signal is locked on a capacitor.

[0075] The control method of "calculating the equivalent inductance first and then calculating the conduction time of Q2" can ensure that the system can be controlled relatively simply under various input voltage and load conditions, without being affected by the main circuit parameter offset or processing technology, so that the system always maintains a high efficiency.

[0076] Furthermore, in order to ensure that the system achieves ZVS under various input voltage and load conditions and is not affected by the deviation of the main circuit parameters, so that the system always maintains a high efficiency, thereby further leveraging the topological advantages of the half-bridge resonant flyback circuit and achieving higher efficiency, it is necessary to turn on Q2 for a sufficient time so that the excitation inductor has sufficient negative current I neg , which helps Q1 tube achieve ZVS; that is, the aforementioned expected excitation inductor current is set to negative current I neg In another embodiment, the desired target negative current can be set directly according to the characteristics of the tube junction capacitance, and then the Q2 conduction time increment ΔT can be calculated. on_Q2 According to the input bus voltage information, the required negative current size I is adaptively adjusted neg , as the input voltage V in The higher the negative current required, the higher the Figure 5 As shown. Where V in is the DC voltage input to the half-bridge resonant flyback circuit, |I neg | is the target negative current value. That is to say, in order to ensure the ZVS of Q1, the expected excitation inductor current is set to be positively correlated with the input voltage of the half-bridge resonant flyback circuit.

[0077] In another embodiment, the on-time increment △T of Q2 can be derived according to the above formula (1.8): on_Q2 ,as follows

[0078] (1.9)

[0079] like Figure 8 As shown, the on-time increment of Q2 is △T on_Q2 Superimposed on the standard on-time T of Q2 on_Q2 Get the actual conduction time T of the freewheeling tube Q2 on_Q2_Fin, which can effectively ensure the realization of ZVS of the main controller Q1; at this time, the standard on-time is calculated using formula (1.8), and di2 used to calculate the standard on-time of Q2 is the first excitation current i Lm1 .

[0080] Based on the above control method, the embodiment of the present application also provides a control device for a half-bridge resonant flyback circuit, such as Figure 3 As shown, the half-bridge resonant flyback circuit includes the main tube Q1, the freewheeling tube Q2, and the excitation inductor L m , leakage inductance L r and resonant capacitor C r .like Figure 6 As shown, the control device includes:

[0081] The voltage sampling unit 11 is used to sample a first voltage V1 and a second voltage V2; the first voltage V1 is the excitation inductance L when the main pipe Q1 is turned on. m The second voltage V2 is the voltage of the excitation inductance L when the freewheeling tube Q2 is turned on. m Voltage;

[0082] The slope acquisition unit 12 is used to obtain the excitation inductance L when the main pipe Q1 is turned on. m The related parameter information may be the excitation current change rate k; the related parameter information may be the excitation current change amount and the corresponding time change amount, or the time change amount and the corresponding excitation current change amount;

[0083] An equivalent inductance calculation unit 13, used to determine the equivalent inductance according to the above-mentioned change parameter information and the first voltage;

[0084] The freewheeling tube conduction time calculation unit 13 is used to determine the conduction time of the freewheeling tube Q2 at least according to the equivalent inductance, the second voltage and the first excitation current; the first excitation current i Lm1 is the moment when Q1 is turned off, and the current flowing through the excitation inductor L m In one embodiment, if the expected excitation inductance current is not 0, the influence of the expected excitation inductance current should also be considered, that is, the conduction time of the freewheeling tube is determined according to the equivalent inductance, the second voltage, the first excitation current and the expected excitation inductance current. The specific principle is shown in the above control method, which will not be repeated here.

[0085] Furthermore, the half-bridge resonant flyback circuit includes a transformer, the transformer includes an excitation inductance and a leakage inductance, and the inductance values ​​corresponding to the excitation inductance and the leakage inductance are obtained by designing the transformer. The voltage sampling unit includes an auxiliary winding, the auxiliary winding is a winding of the transformer, and the first voltage and the second voltage are obtained by sampling the voltage of the auxiliary winding, the number of turns of the primary winding, and the number of turns of the auxiliary winding. Figure 7 As shown, the voltage sampling unit is an auxiliary winding voltage sampling unit 111 .

[0086] Further, such as Figure 7 As shown, the slope acquisition unit 12 includes a first comparator 121, a second comparator 122 and a timer 123;

[0087] The first comparator 121 is used to sample the excitation current signal V cs and zero current signal V cs_zero Perform comparison, generate a zero-crossing signal, and output it to the timer 123;

[0088] The second comparator 122 is used to sample the excitation current signal V cs and preset excitation current signal V cs_slope Compare, generate a comparison signal, and output it to the timer 123; wherein the preset excitation current signal V cs_slope Less than the peak command value. Among them, the excitation current sampling signal V cs It can be obtained by sampling the excitation current, refer to Fig. 9 , can be obtained by sampling circuit R cs The excitation current is sampled to obtain the excitation current sampling signal V cs , the excitation current is the excitation current sampling signal and the sampling resistor R cs Similarly, the preset excitation current signal is the voltage signal corresponding to the preset excitation current.

[0089] The timer 123 is used to count the time from receiving the zero-crossing signal to receiving the comparison signal to obtain the timing duration; the change parameter information related to the excitation current change rate k includes the timing duration T on_slope ;

[0090] The equivalent inductance calculation unit is composed of the timing duration T on_slope , preset excitation current signal V cs_slope and the auxiliary winding sampling voltage V aux1 The calculation is obtained by the following formula:

[0091] L eq =V aux1 *(T on_slope / V cs_slope );

[0092] Among them, V aux1 is the sampling voltage of the auxiliary winding when the main winding is turned on, that is, the first auxiliary winding voltage; the preset excitation current signal V cs_slope Corresponding to the preset excitation current, refer to Fig. 9 , is the preset excitation current and sampling resistor R cs The product of .

[0093] refer to Figure 7 , combined with Figure 3 Schematic diagram of the circuit principle, the first auxiliary winding voltage V aux1 and the second auxiliary winding voltage V aux2 According to the drive G of Q1 tube Q1 and Q2 tube driver G Q2 Sampling is obtained. V cs_slope Used to calculate the excitation current change di1 in the equivalent inductance formula. This value can be directly equal to the peak command value V of the peak current control of Q1 tube cs_ref , can also be equal to other preset excitation current signal V cs_slope , satisfying V cs_slope ≤ V cs_ref The timer is used to calculate the current from 0A to V during the conduction period of Q1 tube. cs_slope / R cs Time spent at the location T on_slope , V cs_zero is the threshold point corresponding to the excitation current of 0A, V cs For R cs The voltage across the resistor. When Q1 is turned on and the current is greater than 0A, counter 123 starts counting. When the excitation current (corresponding to V cs / R cs ) is greater than V cs_slope / R cs After that, stop counting and finally get the time change dt1 in the above formula. Then, combine the above formula (1.8) to deduce and calculate the conduction time of Q2. The di2 in the formula is V cs_ref / R cs , which is the current starting point corresponding to the moment when Q2 is turned on, and is also the excitation current value corresponding to the moment when Q1 is turned off.

[0094] Furthermore, the standard on-time of Q2 can be calculated first, and then the on-time increment △T of Q2 can be calculated according to the preset resonant current. on_Q2 And superimposed on the standard Q2 standard on-time T on_Q2 Get the actual conduction time T of the freewheeling tube Q2 on_Q2_Fin , to ensure the ZVS of Q1 tube. Figure 8 As shown, it also includes a conduction time increment calculation unit 15, which is used to calculate the conduction time increment △T of Q2 according to formula (1.9). on_Q2 The standard on-time is calculated by formula (1.8), which is used to calculate the standard on-time T of Q2. on_Q2 di2 is the first excitation current i Lm1 .

[0095] The control device can be an integrated circuit or can be constructed by discrete devices. When it is an integrated circuit, the integrated circuit U1 is suitable for controlling a half-bridge resonant flyback circuit. Fig. 9 As shown, the integrated circuit U1 is a control chip that integrates the above control strategy. Q1 and G Q2 The conduction time is to achieve the output voltage V out The control can ensure the reliable and stable operation of the system, and help improve the system efficiency and give full play to its topological advantages. In this embodiment, Q1 adopts the peak current control method, according to the output feedback information of the system (such as the common optocoupler / TL431 feedback voltage V comp ), adjust the current flowing through resistor R when Q1 is turned on cs Of course, Q1 can also be controlled by using a constant on-time.

[0096] The functions of each pin of the control chip U1 are:

[0097] ZCD: Get the auxiliary winding voltage V aux , thereby obtaining the auxiliary winding voltage zero-crossing signal and the first auxiliary winding voltage V aux1 and the second auxiliary winding voltage V aux2 .

[0098] FB: Get the external compensation voltage signal, such as the feedback voltage V of the optocoupler / TL431 comp , thereby controlling the system operating mode and the command value of peak current control.

[0099] CS: The current sampling signal of the receiving circuit, which can be the current flowing through the excitation inductor for peak current control and protection; for example, the receiving current sampling resistor R cs The voltage across the two ends, V cs_bus .

[0100] HV: Receives the input voltage V of the half-bridge resonant flyback circuit in The sampling signal of the excitation inductor current i can be obtained. neg In addition, high voltage startup of the circuit can also be achieved.

[0101] GH, GL: Output the driving signal G of the main tube Q1 and the freewheeling tube Q2 in the half-bridge resonant flyback circuit respectively Q1 and G Q2 .

[0102] The control chip U1 receives the signals required to implement the control method of the present application through the above-mentioned pins, and controls the main tube and the freewheeling tube of the half-bridge resonant flyback circuit accordingly. The control process is simple and highly adaptable, and the parameters of the main circuit - the half-bridge resonant flyback circuit itself have little effect on the control.

[0103] In the description of this application, the terms "first", "second", etc. are used for descriptive purposes only and cannot be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Therefore, the features defined as "first" and "second" may explicitly or implicitly include at least one of the features. The meaning of "multiple" is two or more, unless otherwise clearly and specifically defined. Electrical connection includes direct electrical connection and indirect electrical connection, so as to realize the corresponding circuit principle as the protection core, and the connection method is the expression method of the circuit principle.

[0104] The technical features of the above embodiments may be combined arbitrarily. To make the description concise, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0105] It should be understood that those skilled in the art can make improvements or changes based on the above description, and all these improvements and changes should fall within the scope of protection of the claims attached to this application.

Claims

1. A control method for a half-bridge resonant flyback circuit, wherein the half-bridge resonant flyback circuit comprises a main tube, a freewheeling tube, an excitation inductor, a leakage inductor and a resonant capacitor; characterized in that: The control method comprises the following steps: When the main pipe is turned on, the excitation current change rate and the first voltage of the excitation inductor are obtained; wherein the first voltage is the voltage of the excitation inductor when the main pipe is turned on; Obtaining a first excitation current; the first excitation current is the current flowing through the excitation inductor when the main tube is turned off; determining an equivalent inductance according to the excitation current change rate and the first voltage; When the freewheeling tube is turned on, a second voltage is obtained; the second voltage is the voltage of the excitation inductor when the freewheeling tube is turned on; The conduction time of the freewheeling diode is determined at least according to the equivalent inductance, the second voltage and the first excitation current.

2. The control method according to claim 1, characterized in that: The half-bridge resonant flyback circuit includes a transformer, the transformer includes the excitation inductance and the leakage inductance, and the first voltage and the second voltage are obtained by sampling the voltage of the auxiliary winding.

3. The control method according to claim 2, characterized in that: The first voltage is obtained by the following steps: When the main pipe is turned on, sampling is performed to obtain the voltage of the first auxiliary winding; The first voltage is calculated by the following formula: V1=V aux1 *(N p / N aux ); Among them, V aux1 is the first auxiliary winding voltage; N p is the number of turns of the primary winding of the transformer, N aux is the number of turns of the transformer auxiliary winding; The second voltage is obtained by the following steps: When the main pipe is turned off, sampling is performed to obtain the voltage of the second auxiliary winding; The second voltage is calculated by the following formula: <h2 style=";text-align:left;direction:ltr">V2=V<h2 style=";text-align:left;direction:ltr"> aux2 <h2 style=";text-align:left;direction:ltr"> *(N<h2 style=";text-align:left;direction:ltr"> p <h2 style=";text-align:left;direction:ltr"> / N<h2 style=";text-align:left;direction:ltr"> aux <h2 style=";text-align:left;direction:ltr"> ); Among them, V aux2 is the second auxiliary winding voltage; N p is the number of turns of the primary winding of the transformer, N aux is the number of turns of the transformer auxiliary winding.

4. The control method according to claim 3, characterized in that: The equivalent inductance is calculated by the following formula: L eq =V aux1 *(dt1 / di1); Among them, L eq is the equivalent inductance; dt1 / di1 is the inverse of the excitation current change rate; V aux1 is the first auxiliary winding voltage.

5. The control method according to claim 4, characterized in that: The conduction time of the freewheeling tube is calculated by the following formula: T on_Q2 =L eq *(di2 / V aux2 ); Among them, T on_Q2 is the conduction time of the freewheeling tube; di2 is the difference between the first excitation current and the expected excitation inductance current; the expected excitation inductance current is the expected excitation inductance current at the moment when the freewheeling tube is turned off.

6. The control method according to claim 5, characterized in that: The expected excitation inductor current is positively correlated with the input voltage of the half-bridge resonant flyback circuit; Alternatively, the expected excitation inductance current is 0.

7. The control method according to any one of claims 1 to 6, characterized in that: The on-time control of the main pipe is realized by peak current control; the first excitation current is the peak command value of the peak current control; the excitation current change rate is determined by the duration of the excitation current increasing from 0 to the preset excitation current during the on-time of the main pipe and the preset excitation current; The preset excitation current is less than or equal to the peak command value; Alternatively, the on-time control of the main pipe is realized by constant on-time control; the excitation current change rate is determined by the excitation current change rate within a preset time during the on-time period of the main pipe; The preset time is less than or equal to the conduction time of the main pipe.

8. A control device for a half-bridge resonant flyback circuit, the half-bridge resonant flyback circuit comprising a main tube, a freewheeling tube, an excitation inductor, a leakage inductor and a resonant capacitor; characterized in that: The control device comprises: A voltage sampling unit, used to sample a first voltage and a second voltage; the first voltage is the voltage of the excitation inductor when the main tube is turned on; the second voltage is the voltage of the excitation inductor when the freewheeling tube is turned on; A slope acquisition unit, used to acquire change parameter information related to the rate of change of the excitation current of the excitation inductor when the main tube is turned on; an equivalent inductance calculation unit, configured to determine an equivalent inductance according to the change parameter information and the first voltage; The freewheeling tube conduction time calculation unit is used to determine the conduction time of the freewheeling tube according to at least the equivalent inductance, the second voltage and the first excitation current; the first excitation current is the current flowing through the excitation inductance when the main tube is turned off.

9. The control device according to claim 8, characterized in that: The half-bridge resonant flyback circuit includes a transformer, the transformer includes the excitation inductance and the leakage inductance, the voltage sampling unit includes an auxiliary winding, and the first voltage and the second voltage are obtained through the sampling voltage of the auxiliary winding, the number of turns of the primary winding of the transformer, and the number of turns of the auxiliary winding of the transformer.

10. The control device according to claim 9, characterized in that: The slope acquisition unit includes a first comparator, a second comparator and a timer; The first comparator is used to compare the excitation current sampling signal with the zero current signal, generate a zero-crossing signal, and output the zero-crossing signal to the timer; The second comparator is used to compare the excitation current sampling signal with a preset excitation current signal, generate a comparison signal, and output it to the timer; The timer is used to measure the time from receiving the zero-crossing signal to receiving the comparison signal to obtain the timing duration; The change parameter information includes the timing duration; The equivalent inductance calculation unit calculates the equivalent inductance by the timing duration, the preset excitation current signal and the auxiliary winding sampling voltage through the following formula: L eq =V aux1 *(T on_slope / V cs_slope ); Among them, V aux1 is the sampling voltage of the auxiliary winding when the main pipe is turned on; T on_slope is the timing duration; V cs_slope is the preset excitation current signal.

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