Asymmetric half-bridge circuit control method, control chip, power supply circuit and charger

Abstract

The present invention discloses a control method, a control chip, a power supply circuit and a charger for an asymmetric half-bridge circuit. The control method comprises: obtaining first detection data of the asymmetric half-bridge circuit; if the first detection data meets a preset light load condition, controlling the first switch tube to turn off, obtaining the current output voltage and the current turn-off current of the first switch tube; obtaining the current on-time of the second switch tube according to the current output voltage and the current turn-off current of the first switch tube, wherein the current on-time is in direct proportion to the current turn-off current and in inverse proportion to the current output voltage. In the control method, the current on-time of the second switch tube is in inverse proportion to the current output voltage, which can overcome the change in the demagnetization time of the excitation inductance caused by the change in the output voltage of the asymmetric half-bridge circuit, and can make the negative current of the transformer after demagnetization within a preset range.

Description

Technical Field

[0001] The present invention relates to the technical field of asymmetric half-bridge circuits, and in particular to a control method, a control chip, a power supply circuit and a charger for an asymmetric half-bridge circuit. Background Art

[0002] With the continuous development of fast charging technology, the charging power of fast charging power supplies is also constantly improving. The existing high-power fast charging power supplies can expand the maximum output voltage to 48V, the output current to 5A, and the power to 240W. This type of power supply usually uses an asymmetric half-bridge topology to improve circuit efficiency and has good EMC characteristics.

[0003] When controlling an asymmetric half-bridge circuit, different operating modes can be used for different load conditions. For example, under light load conditions, the asymmetric half-bridge circuit usually uses a discontinuous conduction (DCM) mode to improve the operating efficiency of the current circuit.

[0004] At present, when controlling an asymmetric half-bridge circuit in DCM mode, a linear difference method is usually used to calculate the conduction time of the lower tube of the asymmetric half-bridge circuit. However, since the actual positive current of the upper tube at light load is less than the positive current of the upper tube at full load, and the output voltage is variable when the asymmetric half-bridge circuit is used in the design of a fast charging power supply, the demagnetization time of the transformer excitation inductance will also change with the change of the output voltage. The conduction time of the lower tube calculated by the linear difference method is obtained according to the linear difference of the demagnetization curve at full load, which will result in too long demagnetization time and too large negative current. Summary of the invention

[0005] The embodiments of the present invention provide a control method, a control chip, an asymmetric half-bridge circuit, a power supply circuit and a charger for an asymmetric half-bridge circuit to solve the problem in the prior art that the negative current of the asymmetric half-bridge circuit is too large under light load conditions and the working efficiency is poor.

[0006] An embodiment of the present invention provides a control method for an asymmetric half-bridge circuit, wherein the asymmetric half-bridge circuit includes a transformer, a first switch tube, a second switch tube, a resonant inductor, and a resonant capacitor; the first end of the first switch tube is used to connect a rectifier bridge and a PFC circuit, the second end of the first switch tube is used to connect a control chip, and the third end of the first switch tube is connected to the first end of the second switch tube; the second end of the second switch tube is used to connect the control chip, and the third end of the second switch tube is grounded; the resonant inductor, the resonant capacitor, and the primary winding of the transformer are connected in series between the third end of the first switch tube and the third end of the second switch tube, and the control method includes:

[0007] Acquire first detection data of an asymmetric half-bridge circuit;

[0008] If the first detection data meets the preset light load condition, the first switch tube is controlled to be turned off, and the current output voltage and the current turn-off current of the first switch tube are obtained;

[0009] Acquire a current on-time of the second switch tube according to the current output voltage and the current off-current of the first switch tube, wherein the current on-time is in direct proportion to the current off-current and in inverse proportion to the current output voltage;

[0010] During the current on-time, the second switch tube is controlled to be on, so that when the second switch tube is turned off, the current off-current of the second switch tube is within a preset range.

[0011] Preferably, the first detection data includes a current output current;

[0012] The preset light load condition is that the current output current is less than a preset current.

[0013] Preferably, acquiring the current on-time of the second switch tube according to the current output voltage and the current off-current of the first switch tube includes:

[0014] Obtaining the rated off current of the first switch tube and the rated on time of the second switch tube under the rated maximum power;

[0015] The current on-time of the second switch tube is acquired according to the rated off-current of the first switch tube, the rated on-time of the second switch tube, the current output voltage and the current off-current of the first switch tube.

[0016] Preferably, obtaining the rated turn-off current of the first switch tube at the rated maximum power includes:

[0017] Based on the output current at rated maximum power and the transformer ratio of the asymmetric half-bridge circuit, a target shutdown current at rated maximum power is obtained, where the target shutdown current is the sum of the rated shutdown current of the second switch tube and the rated shutdown current of the first switch tube;

[0018] Based on the rated turn-off current and the target turn-off current of the second switch tube, the rated turn-off current of the first switch tube at the rated maximum power is obtained.

[0019] Preferably, obtaining the rated on-time of the second switch tube under the rated maximum power includes:

[0020] Based on the output voltage at the rated maximum power and the transformer ratio of the asymmetric half-bridge circuit, the resonant capacitor voltage stored in the resonant capacitor when the first switch tube is turned off and the body diode of the second switch tube is freewheeling is obtained;

[0021] Based on the rated off current of the first switch tube and the preset rated off current of the second switch tube, obtaining the current change amount under the rated maximum power;

[0022] Based on the transformer inductance of the asymmetric half-bridge circuit, the current change at the rated maximum power and the resonant capacitor voltage, the rated conduction time of the second switch tube at the rated maximum power is obtained.

[0023] Preferably, acquiring the current on-time of the second switch tube according to the rated off-current of the first switch tube, the rated on-time of the second switch tube, the current output voltage and the current off-current of the first switch tube includes:

[0024] Substitute the rated off current of the first switch tube, the rated on time of the second switch tube, the current output voltage and the current off current of the first switch tube into the formula , obtain the current on-time of the second switch tube, where K is the correction coefficient, toff_nom is the rated on-time of the second switch tube, Vnom is the output voltage of the asymmetric half-bridge circuit at the maximum power gear, I_Mag_pos_DCM is the current off-current of the first switch tube, Vout_DCM is the current output voltage, and I_Mag_pos_nom is the rated off-current of the first switch tube.

[0025] Preferably, when the current turn-off current of the first switch tube is within a first preset range, the correction coefficient K takes a first correction value;

[0026] When the current turn-off current of the first switch tube is within the second preset range, the correction coefficient K takes a second correction value.

[0027] An embodiment of the present invention also provides a control chip, including a memory, a processor, and a computer program stored in the memory and executable on the processor. The control chip is applied in an asymmetric half-bridge circuit, and when the processor executes the computer program, a control method for the asymmetric half-bridge circuit according to any one of the above items is implemented.

[0028] The embodiment of the present invention further provides a power supply circuit, including a rectifier bridge and a PFC circuit, an electrolytic capacitor, an asymmetric half-bridge circuit, a secondary rectifier filter circuit, a protocol control module and the above-mentioned control chip;

[0029] The input end of the rectifier bridge and the PFC circuit is used to connect to the mains circuit, and the output end of the rectifier bridge and the PFC circuit is connected to the electrolytic capacitor;

[0030] The input end of the asymmetric half-bridge circuit is connected to the electrolytic capacitor, and the output end of the asymmetric half-bridge circuit is connected to the input end of the secondary rectifier filter circuit;

[0031] The output end of the secondary rectifier and filter circuit is used to connect to an external load to supply power to the external load;

[0032] The control chip is connected to the first switch tube and the second switch tube in the asymmetric half-bridge circuit, and is used to control the second switch tube to be turned on within the current on time when the first detection data of the asymmetric half-bridge circuit meets the preset light load condition, so that the current off current of the second switch tube is within a preset range;

[0033] The protocol control module is connected to the output end of the secondary rectifier and filter circuit, the asymmetric half-bridge circuit and the control chip, and is used to output a voltage adjustment signal to the control chip according to the power supply demand of the external load, so that the control chip controls and adjusts the power supply voltage output by the asymmetric half-bridge circuit according to the voltage adjustment signal.

[0034] An embodiment of the present invention further provides a charger, comprising the above-mentioned power supply circuit.

[0035] In the control method, control chip, power supply circuit and charger of the asymmetric half-bridge circuit provided by the embodiments of the present invention, the current on-time of the second switch tube is inversely proportional to the current output voltage and directly proportional to the current off-current of the first switch tube. This can overcome the change in demagnetization time of the excitation inductance caused by the change in the output voltage of the asymmetric half-bridge circuit, and can make the negative current of the transformer after demagnetization within a preset range, thereby meeting the requirements of the first switch tube when the asymmetric half-bridge circuit is in DCM mode. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings required for use in the description of the embodiments of the present invention will be briefly introduced below. Obviously, the accompanying drawings in the following description are only some embodiments of the present invention. For ordinary technicians in this field, other accompanying drawings can be obtained based on these accompanying drawings without paying creative labor.

[0037] Figure 1 is a circuit diagram of an asymmetric half-bridge circuit in one embodiment of the present invention;

[0038] Figure 2 is a working waveform diagram of an asymmetric half-bridge circuit in one embodiment of the present invention;

[0039] Figure 3 is another working waveform diagram of the asymmetric half-bridge circuit in one embodiment of the present invention;

[0040] Figure 4 is a flow chart of a control method of an asymmetric half-bridge circuit in one embodiment of the present invention;

[0041] Figure 5 is another flow chart of a control method for an asymmetric half-bridge circuit in one embodiment of the present invention;

[0042] Figure 6 is another flow chart of a control method for an asymmetric half-bridge circuit in one embodiment of the present invention;

[0043] Figure 7 is another flow chart of a control method for an asymmetric half-bridge circuit in one embodiment of the present invention. DETAILED DESCRIPTION

[0044] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0045] It should be understood that the present invention can be implemented in different forms and should not be construed as being limited to the embodiments set forth herein. On the contrary, providing these embodiments will make the disclosure thorough and complete and fully convey the scope of the present invention to those skilled in the art. In the accompanying drawings, the sizes and relative sizes of layers and regions may be exaggerated for clarity. The same reference numerals throughout represent the same elements.

[0046] It should be understood that when an element or layer is referred to as being "on, adjacent to, connected to or coupled to other elements or layers, it may be directly on, adjacent to, connected to or coupled to other elements or layers, or there may be intervening elements or layers. In contrast, when an element is referred to as being "directly on, directly adjacent to, directly connected to or directly coupled to other elements or layers, there may be no intervening elements or layers. It should be understood that, although the terms first, second, third, etc. may be used to describe various elements, components, regions, layers and / or parts, these elements, components, regions, layers and / or parts should not be limited by these terms. These terms are only used to distinguish one element, component, region, layer or part from another element, component, region, layer or part. Therefore, without departing from the teachings of the present invention, the first element, component, region, layer or part discussed below may be represented as a second element, component, region, layer or part.

[0047] Spatially relative terms such as "under," "beneath," "below," "under," "above," "above," and the like may be used herein for ease of description to describe the relationship of an element or feature shown in the figures to other elements or features. It should be understood that the spatially relative terms are intended to include different orientations of the device in use and operation in addition to the orientations shown in the figures. For example, if the device in the accompanying drawings is flipped, then the elements or features described as "under other elements" or "under" or "under" will be oriented as "above" the other elements or features. Thus, the exemplary terms "under" and "under" may include both upper and lower orientations. The device may be otherwise oriented (rotated 90 degrees or other orientations) and the spatial descriptors used herein are interpreted accordingly.

[0048] The purpose of the terms used herein is only to describe specific embodiments and is not intended to be limiting of the present invention. When used herein, the singular forms "one", "an" and "said / the" are also intended to include plural forms, unless the context clearly indicates otherwise. It should also be understood that the terms "consisting of" and / or "comprising", when used in this specification, determine the presence of the features, integers, steps, operations, elements and / or parts, but do not exclude the presence or addition of one or more other features, integers, steps, operations, elements, parts and / or groups. When used herein, the term "and / or" includes any and all combinations of the relevant listed items.

[0049] In order to fully understand the present invention, detailed structures and steps will be presented in the following description to illustrate the technical solutions proposed by the present invention. The preferred embodiments of the present invention are described in detail below, but in addition to these detailed descriptions, the present invention may also have other implementations.

[0050] The embodiment of the present invention provides a control method for an asymmetric half-bridge circuit. Figure 1 As shown, the asymmetric half-bridge circuit includes a transformer T1, a first switch tube Q1, a second switch tube Q2, a resonant inductor L1 and a resonant capacitor C1; the first end of the first switch tube Q1 is used to connect the rectifier bridge and the PFC circuit, the second end of the first switch tube Q1 is used to connect the control chip, and the third end of the first switch tube Q1 is connected to the first end of the second switch tube Q2; the second end of the second switch tube Q2 is used to connect the control chip, and the third end of the second switch tube Q2 is grounded; the resonant inductor L1, the resonant capacitor C1 and the primary winding of the transformer T1 are connected in series between the third end of the first switch tube Q1 and the third end of the second switch tube Q2.

[0051] like Figure 1The asymmetric half-bridge circuit shown can adopt different working modes under different load conditions. For example, under heavy load conditions, the critical conduction mode (CRM mode) is usually adopted, and under light load conditions, the discontinuous conduction mode (DCM mode) is usually adopted. The light load condition refers to the situation where the load rate of the asymmetric half-bridge circuit is low, the output current is small, and the output power is low. The heavy load condition refers to the situation where the load rate of the asymmetric half-bridge circuit is high, the output current is large, and the output power is high.

[0052] When the asymmetric half-bridge circuit works in CRM mode, the working waveform is as follows: Figure 2 As shown:

[0053] (1) t0~t2 stage. Before t0, the body diode of the first switch tube Q1 is gradually turned on, and the turn-off current of the second switch tube Q2, that is, the negative current I_Mag_neg, causes the voltage at the VHB point to gradually rise from 0V to Vbus, providing conditions for the first switch tube Q1 to achieve zero voltage switching (ZVS). At t0, the control chip outputs a high level to the gate of the first switch tube Q1, causing the current to transfer from the body diode of the first switch tube Q1 to the channel, where IMAGneg is the negative current peak.

[0054] During the time period t1 to t2, the resonant cavity current flows through the resonant inductor L1, the excitation inductor LM of the primary side of the transformer T1, and the resonant capacitor C2 in sequence. The current is recorded as I_Mag_pos. The current rises linearly and stores energy in the resonant cavity. Among them, IMAGpos is the positive working current peak of the first switch tube Q1.

[0055] (2) t2~t5 stage. At t2, the control chip outputs a low level to the gate of the first switch tube Q1, I_Mag_pos continues to flow through the body diode of Q2, and the voltage at the VHB point drops from Vbus to 0, providing conditions for the second switch tube Q2 to achieve ZVS. At t3, the control chip outputs a high level to the gate of the second switch tube Q2, and the current is transferred from the body diode of the second switch tube Q2 to the channel. During the t3~t5 period, the energy stored in the resonant cavity is released to the secondary side. At this time, the output freewheeling diode D1 connected to the secondary side of the transformer T1 is turned on. During this period, the voltage across the excitation inductor LM is clamped at NVout, where N represents the ratio of the number of turns of the primary side of the transformer T1 to the number of turns of the secondary side, and Vout represents the output voltage. Therefore, the excitation current decreases linearly according to the slope of NVout / LM; at the same time, the resonant capacitor C1 and the resonant inductor L1 resonate, and the resonant current changes according to the law of the sine wave. When the resonant current is equal to the excitation current, the output freewheeling diode is turned off, corresponding to the t5 moment.

[0056] When the asymmetric half-bridge circuit works in DCM mode, the operating waveform is as follows: Figure 3 As shown:

[0057] (1) Process 1 to 5: consistent with the t1 to t5 stage in the CRM condition.

[0058] (2) Process 6: The turn-off current of the second switch tube Q2, that is, the negative current I_Mag_neg_DCM1, causes the voltage at the VHB point to rise to the Vbus voltage, causing the first switch tube Q1 to be soft-turned on.

[0059] (3) Process 7: VHB is maintained at Vbus, and i(LM) transitions from I_Mag_neg_DCM1 to 0A.

[0060] (4) Processes 8-10: VHB free oscillation process, in which the voltage at point VHB oscillates to 0 V in process 9.

[0061] (5) Process 11: The second switch tube Q2 is turned on, causing i(LM) to construct a negative current I_Mag_neg_DCM2.

[0062] (6) Process 12: The negative current I_Mag_neg_DCM2 of the second switch tube Q2 during free oscillation enables the first switch tube Q1 to achieve ZVS.

[0063] In DCM mode, if the negative current I_Mag_neg_DCM1 is too large, the voltage at the VHB point in process 6 will rise too fast, affecting the EMC performance, and will also cause the maintenance time of process 7 to be too long. In process 8, the VHB voltage drops to zero, which may cause false triggering of synchronous rectification. Therefore, it is necessary to ensure that the negative current I_Mag_neg_DCM1 is within the preset reasonable range. Since the negative current I_Mag_neg_DCM1 is related to the lower tube conduction time of processes 3 to 5, that is, t3 to t5, it is necessary to control the lower tube conduction time of t3 to t5 to keep the negative current I_Mag_neg_DCM1 within the preset range.

[0064] The method is applied to the above-mentioned asymmetric half-bridge circuit as an example for explanation. Figure 4 As shown, the control method of the asymmetric half-bridge circuit includes:

[0065] S401: Acquire first detection data of an asymmetric half-bridge circuit;

[0066] S402: If the first detection data meets the preset light load condition, the first switch tube is controlled to be turned off, and the current output voltage and the current off current of the first switch tube are obtained;

[0067] S403: acquiring a current on-time of the second switch tube according to the current output voltage and the current off-current of the first switch tube, wherein the current on-time is directly proportional to the current off-current and inversely proportional to the current output voltage;

[0068] S404: During the current on-time, control the second switch tube to be turned on, so that when the second switch tube is turned off, the current off current of the second switch tube is within a preset range.

[0069] Among them, the first detection data is detected in real time by the control chip, and is used to determine whether the asymmetric half-bridge circuit is currently in a light load condition. For example, the first detection data can be the current output current Iout_DCM. If the current output current Iout_DCM is less than the preset current, the control chip determines that the current asymmetric half-bridge circuit is in a light load condition.

[0070] As an example, in step S401, the control chip performs real-time detection on the first detection data, such as the current output current Iout_DCM, and determines whether the asymmetric half-bridge circuit is currently in a light load condition based on the first detection data, so as to control the asymmetric half-bridge circuit to operate in DCM mode when the asymmetric half-bridge circuit is in a light load condition.

[0071] The current turn-off current I_Mag_pos_DCM of the first switch tube Q1 is a light load of the asymmetric half-bridge circuit, and after entering the DCM mode, Figure 3 In the process stage 2 shown, the positive operating current peak of the first switch tube Q1.

[0072] As an example, in step S402, if the control chip detects that the current asymmetric half-bridge circuit is in a light load condition, the asymmetric half-bridge circuit is controlled to enter the DCM mode, and the first switch tube Q1 and the second switch tube Q2 are controlled to operate according to the DCM mode. After the first switch tube Q1 is turned off, the control chip obtains the current output voltage Vout_DCM of the asymmetric half-bridge circuit and the current shutdown current I_Mag_pos_DCM of the first switch tube Q1.

[0073] The current on-time toff_DCM of the second switch tube Q2 is the on-time of the second switch tube Q2 after the asymmetric half-bridge circuit is lightly loaded and enters the DCM mode, such as Figure 3 As shown in process 3-5.

[0074] As an example, in step S403, the control chip obtains the current on-time toff_DCM of the second switch tube Q2 according to the current output voltage Vout_DCM and the current off-current I_Mag_pos_DCM of the first switch tube Q1. The current on-time toff_DCM of the second switch tube Q2 is inversely proportional to the current output voltage Vout_DCM and is proportional to the current off-current I_Mag_pos_DCM of the first switch tube Q1, so that the current on-time toff_DCM of the second switch tube Q2 decreases as the output voltage increases according to an inversely proportional function to adapt to the change in demagnetization time caused by the change in output voltage, and avoid the problems of too long demagnetization time and too large negative current.

[0075] Specifically, the above conclusion can be drawn according to the following derivation process:

[0076] According to the voltage regulation principle of the asymmetric half-bridge circuit, the resonant capacitor voltage Vcr ≈ the transformer excitation inductance voltage VLM, and the transformer excitation inductance voltage , N is the transformer T1 ratio, Vout is the output voltage, and the resonant capacitor voltage , where LM is the inductance of transformer T1, IMAGpos is the positive operating current peak of the first switch tube Q1, IMAGneg is the negative current peak, and tLS_on is the turn-on time of the second switch tube Q2. Therefore, when the asymmetric half-bridge circuit is at the maximum power level, the resonant capacitor voltage Satisfy the formula:

[0077] , (Formula 1), where Vnom is the output voltage at the maximum power level;

[0078] When the asymmetric half-bridge circuit is in light load condition and enters DCM mode, the resonant capacitor voltage Satisfy the formula

[0079] , (Equation 2), where Vout_DCM is the current output voltage of the asymmetric half-bridge circuit in DCM mode;

[0080] According to the fact that the inductance LM of the asymmetric half-bridge circuit is equal in the maximum power gear and DCM mode, the combined equation 1 and equation 2 yields:

[0081] , (Formula 3);

[0082] Therefore, according to the voltage regulation principle of the asymmetric half-bridge circuit, it can be deduced that the second on-time toff_DCM is inversely proportional to the current output voltage Vout_DCM, and is directly proportional to the second off-current I_Mag_pos_DCM. Therefore, when the current on-time toff_DCM of the second switch tube Q2 is set, the current on-time toff_DCM of the second switch tube Q2 decreases according to an inversely proportional function as the current output voltage Vout_DCM increases. This is more in line with the voltage regulation principle of the asymmetric half-bridge circuit, adapts to the change in demagnetization time caused by the change in output voltage, and can avoid the problems of too long demagnetization time and too large negative current.

[0083] The current turn-off current I_Mag_neg_DCM of the second switch tube Q2 is the negative current peak value when the asymmetric half-bridge circuit is in the DCM mode. Figure 3 As shown in the process 5 stage, when the current asymmetric half-bridge circuit is in the DCM mode, the first switch tube Q1 can achieve zero voltage turn-on (ZVS).

[0084] As an example, in step S404, the control chip controls the second switch tube Q2 to turn on based on the current on time toff_DCM of the second switch tube Q2, so that the current off current I_Mag_neg_DCM of the second switch tube Q2, that is, the negative current is within a preset range, so that when the asymmetric half-bridge circuit is in the DCM mode, the first switch tube Q1 can successfully achieve ZVS.

[0085] In this example, the control chip obtains the current on-time toff_DCM of the second switch tube Q2 according to the current output voltage Vout_DCM and the current off-current I_Mag_pos_DCM of the first switch tube Q1. The current on-time toff_DCM of the second switch tube Q2 is inversely proportional to the current output voltage Vout_DCM, and is directly proportional to the current off-current I_Mag_pos_DCM of the first switch tube Q1. It can overcome the change in demagnetization time of the excitation inductance caused by the change in the output voltage of the asymmetric half-bridge circuit, and can make the negative current of the transformer T1 after demagnetization within a preset range, thereby meeting the ZVS requirement of the first switch tube Q1 when the asymmetric half-bridge circuit is in DCM mode.

[0086] In one embodiment, the first detection data includes a current output current Iout_DCM; and the preset light load condition is that the current output current Iout_DCM is less than a preset current.

[0087] As an example, the first detection data includes the current output current Iout_DCM of the asymmetric half-bridge circuit detected by the control chip. When the current output current Iout_DCM is less than the preset current, the control chip determines that the asymmetric half-bridge circuit is currently in a light-load condition and controls the asymmetric half-bridge circuit to operate in DCM mode. The preset current is a pre-set current used to determine whether the current asymmetric half-bridge circuit is in a light-load condition. The preset current can be 20% of the full-load current of the circuit or other values. For example, when the full-load current is 5A, the preset current is 1A. When the current output current Iout_DCM is less than 1A, it indicates that the asymmetric half-bridge circuit is in a light-load condition, and the control chip controls the asymmetric half-bridge circuit to operate in DCM mode.

[0088] In one embodiment, if Figure 5 As shown, in step S403, according to the current output voltage and the current off current of the first switch tube, the current on time of the second switch tube is obtained, including:

[0089] S501: Obtaining a rated off current of the first switch tube and a rated on time of the second switch tube at a rated maximum power;

[0090] S502: Obtain a current on-time of the second switch tube according to a rated off-current of the first switch tube, a rated on-time of the second switch tube, a current output voltage, and a current off-current of the first switch tube.

[0091] The rated off current I_Mag_pos_nom of the first switch tube Q1 is the positive operating current peak value of the first switch tube Q1 at the rated maximum power. The rated on time toff_nom of the second switch tube Q2 is the on time of the second switch tube Q2 at the rated maximum power.

[0092] As an example, in step S501, the control chip obtains the rated turn-off current I_Mag_pos_nom of the first switch tube Q1 and the rated turn-on time toff_nom of the second switch tube Q2 when the asymmetric half-bridge circuit is at the rated maximum power based on the original circuit parameters of the asymmetric half-bridge circuit, such as the transformation ratio N of the transformer T1, and the maximum output voltage and maximum output current of the asymmetric half-bridge circuit under rated operating conditions.

[0093] As an example, in step S502, the control chip obtains the current on-time toff_DCM of the second switch tube Q2 according to the current output voltage Vout_DCM, the current off-current I_Mag_pos_DCM of the first switch tube Q1, the rated on-time toff_nom of the second switch tube Q2, and the rated off-current I_Mag_pos_nom of the first switch tube Q1. The current on-time toff_DCM of the second switch tube Q2 is inversely proportional to the current output voltage Vout_DCM and is proportional to the current off-current I_Mag_pos_DCM of the first switch tube Q1.

[0094] Specifically, according to the voltage regulation principle of the asymmetric half-bridge circuit, we can get:

[0095] , (Formula 3);

[0096] During the operation of the asymmetric half-bridge circuit, the average current input to the asymmetric half-bridge circuit IMAGpos is the positive operating current peak value of the first switch tube Q1, IMAGneg is the negative current peak value, and the input power , output power , according to the energy conservation between input and output , and the relationship between input voltage and output voltage: , we can get ;

[0097] Therefore, according to the formula , we can use the formula 3 It is expressed by Iout_DCM and I_Mag_pos_DCM, and finally the formula 3 is Approximately I_Mag_pos_DCM, replace the Approximately I_Mag_pos_nom.

[0098] In order to eliminate the error caused by the approximation, the approximated formula 3 can be multiplied by the correction coefficient K to obtain:

[0099] ;

[0100] Simplify to get , (Formula 4);

[0101] Substituting the current output voltage Vout_DCM, the current turn-off current I_Mag_pos_DCM of the first switch tube Q1, the rated turn-on time toff_nom of the second switch tube Q2 and the rated turn-off current I_Mag_pos_nom of the first switch tube Q1 into Formula 4, the current turn-on time toff_DCM of the second switch tube Q2 can be calculated.

[0102] In this example, the control chip obtains the current on-time toff_DCM of the second switch tube Q2 according to the current output voltage Vout_DCM, the current off-current I_Mag_pos_DCM of the first switch tube Q1, the rated on-time toff_nom of the second switch tube Q2 and the rated off-current I_Mag_pos_nom of the first switch tube Q1, and the current on-time toff_DCM of the second switch tube Q2 is inversely proportional to the current output voltage Vout_DCM, and is directly proportional to the current off-current I_Mag_pos_DCM of the first switch tube Q1, which can overcome the change in demagnetization time of the excitation inductance caused by the change in the output voltage of the asymmetric half-bridge circuit, and can make the negative current of the transformer T1 after demagnetization within a preset range, thereby meeting the ZVS requirement of the first switch tube Q1 when the asymmetric half-bridge circuit is in DCM mode.

[0103] In one embodiment, if Figure 6 As shown, in step S501, obtaining the rated off current of the first switch tube under the rated maximum power includes:

[0104] S601: obtaining a target turn-off current at rated maximum power based on the output current at rated maximum power and the transformation ratio of the transformer of the asymmetric half-bridge circuit, where the target turn-off current is the sum of the rated turn-off current of the second switch tube and the rated turn-off current of the first switch tube;

[0105] S602: Based on the rated turn-off current and the target turn-off current of the second switch tube, obtain the rated turn-off current of the first switch tube at the rated maximum power.

[0106] As an example, in step S601, during the AHB operation, the average current input to the AHB is IMAGpos is the positive operating current peak value of the first switch tube Q1, IMAGneg is the negative current peak value, then the input power , output power , according to the energy conservation between input and output , and the relationship between input voltage and output voltage: , we can get ,therefore, , where Iout_nom is the output current at rated maximum power. The control chip is based on the output current Iout_nom at rated maximum power and the transformation ratio N of the transformer T1 of the asymmetric half-bridge circuit, according to the formula , the sum of the rated turn-off current I_Mag_neg_nom of the second switch tube Q2 and the rated turn-off current I_Mag_pos_nom of the first switch tube Q1 , that is, the target turn-off current, can be calculated.

[0107] Among them, the rated turn-off current I_Mag_neg_nom of the second switch tube Q2 is pre-set, and can enable the asymmetric half-bridge circuit to achieve ZVS current of the first switch tube Q1 when it is at the rated maximum power. It is determined by the current ZVS requirement of the first switch tube Q1, and requires that the product of the inductance LM of the transformer T1 and the preset rated turn-off current I_Mag_neg_nom of the second switch tube Q2 is greater than the product of twice the electrolytic capacitor voltage Vbus and the parasitic capacitance of the first switch tube Q1.

[0108] As an example, in step S602, under rated maximum power, the rated turn-off current I_Mag_pos_nom of the first switch tube Q1 under rated maximum power can be obtained according to the preset rated turn-off current I_Mag_neg_nom of the second switch tube Q2, the calculated sum of the rated turn-off current I_Mag_neg_nom of the second switch tube Q2 and the rated turn-off current I_Mag_pos_nom of the first switch tube Q1.

[0109] In one embodiment, if Figure 7 As shown, in step S501, obtaining the rated on-time of the second switch tube under the rated maximum power includes:

[0110] S701: based on the output voltage at the rated maximum power and the transformer ratio of the asymmetric half-bridge circuit, obtaining the resonant capacitor voltage stored in the resonant capacitor when the first switch tube is turned off and the body diode of the second switch tube is freewheeling;

[0111] S702: Obtain a current change at a rated maximum power based on a rated turn-off current of the first switch tube and a preset rated turn-off current of the second switch tube;

[0112] S703: Based on the transformer inductance of the asymmetric half-bridge circuit, the current change at the rated maximum power, and the resonant capacitor voltage, obtain the rated conduction time of the second switch tube at the rated maximum power.

[0113] As an example, in step S701, according to the voltage regulation principle of the asymmetric half-bridge circuit, the resonant capacitor voltage Vcr≈the transformer excitation inductance voltage VLM, and the transformer excitation inductance voltage , N is the transformation ratio of transformer T1, and Vout is the output voltage. When AHB is at the rated maximum power, after the first switch tube Q1 is turned off, the resonant capacitor voltage stored in the resonant capacitor Cr is , where Vnom is the rated maximum output voltage.

[0114] As an example, in step S702, the control chip obtains the rated turn-off current I_Mag_pos_nom of the first switch tube Q1 and the preset rated turn-off current I_Mag_neg_nom of the second switch tube Q2. Then, during the turn-on time of the first switch tube Q1, the current change on the transformer excitation inductance LM is the difference between the rated turn-off current I_Mag_pos_nom of the first switch tube Q1 and the preset rated turn-off current I_Mag_neg_nom of the second switch tube Q2, that is, .

[0115] As an example, in step S703, due to the resonant capacitor voltage IMAGpos is the positive operating current peak value of the first switch tube Q1, and IMAGneg is the negative current peak value. Therefore, the first conduction time of the second switch tube Q2 at the rated maximum power is The control chip is based on the inductance LM of the transformer T1 of the asymmetric half-bridge circuit and the current change at the rated maximum power. and the resonant capacitor voltage , according to the formula The rated on-time toff_nom of the second switch tube Q2 under the rated maximum power can be calculated.

[0116] In one embodiment, step S502, obtaining the current on-time of the second switch tube according to the rated off-current of the first switch tube, the rated on-time of the second switch tube, the current output voltage and the current off-current of the first switch tube, includes:

[0117] Substitute the rated off current I_Mag_pos_nom of the first switch tube Q1, the rated on time toff_nom of the second switch tube Q2, the current output voltage Vout_DCM and the current off current I_Mag_pos_DCM of the first switch tube Q1 into the formula , obtain the second on-time toff_DCM of the current second switch tube Q2, where K is the correction coefficient.

[0118] As an example, according to the voltage regulation principle of the asymmetric half-bridge circuit, the resonant capacitor voltage Vcr ≈ the transformer excitation inductance voltage VLM, and the transformer excitation inductance voltage , N is the transformer T1 ratio, Vout is the output voltage, and the resonant capacitor voltage , where LM is the inductance of transformer T1, IMAGpos is the positive operating current peak of the first switch tube Q1, IMAGneg is the negative current peak, and tLS_on is the turn-on time of the second switch tube Q2. Therefore, when the asymmetric half-bridge circuit is at the maximum power level, the resonant capacitor voltage Satisfy the formula

[0119] , (Formula 1), where Vnom is the output voltage at the maximum power level;

[0120] When the asymmetric half-bridge circuit is in light load condition and enters DCM mode, the resonant capacitor voltage Satisfy the formula:

[0121] , (Equation 2), where Vout_DCM is the current output voltage of the asymmetric half-bridge circuit in DCM mode;

[0122] According to the fact that the inductance LM of the asymmetric half-bridge circuit is equal in the maximum power gear and DCM mode, the combined equation 1 and equation 2 yields:

[0123] , (Formula 3);

[0124] It can be concluded that toff_DCM is inversely proportional to the current output voltage Vout_DCM, and is directly proportional to the second shutdown current I_Mag_pos_DCM;

[0125] During the operation of the asymmetric half-bridge circuit, the average current input to the asymmetric half-bridge circuit IMAGpos is the positive operating current peak value of the first switch tube Q1, IMAGneg is the negative current peak value, and the input power , output power , according to the energy conservation between input and output , and the relationship between input voltage and output voltage: , we can get ;

[0126] Therefore, according to the formula , we can use the formula 3 It is expressed by Iout_DCM and I_Mag_pos_DCM, and finally the formula 3 is Approximately I_Mag_pos_DCM, replace the Approximately I_Mag_pos_nom.

[0127] In order to eliminate the error caused by the approximation, the approximated formula 3 can be multiplied by the correction coefficient K, where the value of the correction coefficient K can be 1.1-1.7, and the result is:

[0128] ;

[0129] Simplify to get , (Formula 4);

[0130] The control chip substitutes the current output voltage Vout_DCM, the current off current I_Mag_pos_DCM of the first switch tube Q1, the rated on time toff_nom of the second switch tube Q2 and the rated off current I_Mag_pos_nom of the first switch tube Q1 into Formula 4 to calculate the second on time toff_DCM.

[0131] In one embodiment, when the current turn-off current I_Mag_pos_DCM of the first switch tube Q1 is within the first preset range, the correction coefficient K takes the first correction value; when the current turn-off current I_Mag_pos_DCM of the first switch tube Q1 is within the second preset range, the correction coefficient K takes the second correction value.

[0132] Among them, the first preset range and the second preset range are the ratio of the current turn-off current I_Mag_pos_DCM of the first switch tube Q1 to the rated turn-off current I_Mag_pos_nom when the asymmetric half-bridge circuit is in DCM mode. For example, when the current turn-off current I_Mag_pos_DCM is within the first preset range, the current turn-off current I_Mag_pos_DCM is 50%-70% of the rated turn-off current I_Mag_pos_nom; when the current turn-off current I_Mag_pos_DCM is within the second preset range, the current turn-off current I_Mag_pos_DCM is 30%-50% of the rated turn-off current I_Mag_pos_nom.

[0133] As an example, in the actual application of the asymmetric half-bridge circuit, the value of the correction coefficient K is related to the ratio of the current off current I_Mag_pos_DCM of the first switch tube Q1 to the rated off current I_Mag_pos_nom. Approximately I_Mag_pos_DCM, replace the Approximately I_Mag_pos_nom. If the proportion of the current shutdown current I_Mag_pos_DCM to the rated shutdown current I_Mag_pos_nom is low, for example, when the current shutdown current I_Mag_pos_DCM is 30% of the rated shutdown current I_Mag_pos_nom, a large error will be generated. If K takes a smaller value, such as 1.1, it will be difficult to form an obvious correction effect. Therefore, when the current turn-off current I_Mag_pos_DCM of the first switch tube Q1 is within the first preset range, for example, when the current turn-off current I_Mag_pos_DCM is 50%-70% of the rated turn-off current I_Mag_pos_nom, the correction coefficient K takes a first correction value, for example, 1.1. At this time, the proportion of the current turn-off current I_Mag_pos_DCM to the rated turn-off current I_Mag_pos_nom is relatively high, and K can achieve the correction purpose by taking a smaller correction value; when the current turn-off current I_Mag_pos_DCM of the first switch tube Q1 is within the second preset range, for example, when the current turn-off current I_Mag_pos_DCM is 30%-50% of the rated turn-off current I_Mag_pos_nom, the correction coefficient K takes a second correction value, for example, 1.7. At this time, the proportion of the current turn-off current I_Mag_pos_DCM to the rated turn-off current I_Mag_pos_nom is relatively low, and K can achieve the correction purpose by taking a larger correction value.

[0134] The embodiment of the present invention further provides a control chip, including a memory, a processor, and a computer program stored in the memory and executable on the processor. The control chip can be used as a control chip U1 in an asymmetric half-bridge circuit. When the processor in the control chip executes the computer program, the control method of the asymmetric half-bridge circuit in the above embodiment is implemented. For example, Figure 4 S401-S404 shown are not described here again to avoid repetition.

[0135] The embodiment of the present invention further provides a power supply circuit, including a rectifier bridge and a PFC circuit, an electrolytic capacitor C2, an asymmetric half-bridge circuit, a secondary rectifier and filter circuit, a protocol control module, and a control chip in the above embodiment; the input end of the rectifier bridge and the PFC circuit is used to connect to the mains circuit, and the output end of the rectifier bridge and the PFC circuit is connected to the electrolytic capacitor C2; the input end of the asymmetric half-bridge circuit is connected to the electrolytic capacitor C2, and the output end of the asymmetric half-bridge circuit is connected to the input end of the secondary rectifier and filter circuit; the output end of the secondary rectifier and filter circuit is used to connect to an external load to supply power to the external load; the control chip is connected to the first rectifier and filter circuit in the asymmetric half-bridge circuit. A switch tube Q1 is connected to a second switch tube Q2, and is used to control the second switch tube Q2 to be turned on within the current on-time toff_DCM when the first detection data of the asymmetric half-bridge circuit meets the preset light load condition, so that the current off-current I_Mag_neg_DCM of the second switch tube Q2 is within a preset range; the protocol control module is connected to the output end of the secondary rectifier and filter circuit, the asymmetric half-bridge circuit and the control chip, and is used to output a voltage adjustment signal to the control chip according to the power supply demand of the external load, so that the control chip controls and adjusts the size of the power supply voltage output by the asymmetric half-bridge circuit according to the voltage adjustment signal.

[0136] As an example, the power supply circuit includes a rectifier bridge and a PFC circuit, an electrolytic capacitor C2, an asymmetric half-bridge circuit, a secondary rectifier and filter circuit, a protocol control module, and a control chip in the above example; the input end of the rectifier bridge and the PFC circuit is used to connect to the mains circuit, and the output end of the rectifier bridge and the PFC circuit is connected to the electrolytic capacitor C2; the input end of the asymmetric half-bridge circuit is connected to the electrolytic capacitor C2 for receiving the input voltage Vin, and the output end of the asymmetric half-bridge circuit is connected to the input end of the secondary rectifier and filter circuit; the output end of the secondary rectifier and filter circuit is used to connect to the external The secondary rectifier filter circuit is used to passively adjust the output current Iout according to the charging demand of the external load and the resistance value at the connected external load interface; the control chip is connected to the first switch tube Q1 and the second switch tube Q2 in the asymmetric half-bridge circuit, and is used to control the second switch tube Q2 to be turned on within the current on time toff_DCM when the first detection data of the asymmetric half-bridge circuit meets the preset light load condition, so that the current off current I_Mag_neg_DCM of the second switch tube Q2 is within the preset range. The protocol control module is connected to the output end of the secondary rectifier filter circuit, the asymmetric half-bridge circuit and the control chip, and is used to output a voltage adjustment signal to the control chip according to the power supply demand of the external load, so that the control chip controls the asymmetric half-bridge circuit to adjust the output power supply voltage Vout according to the voltage adjustment signal.

[0137] In this example, the control chip in the power supply circuit can obtain the current on-time toff_DCM of the second switch tube Q2 according to the current output voltage Vout_DCM, the current off-current I_Mag_pos_DCM of the first switch tube Q1, the rated on-time toff_nom of the second switch tube Q2 and the rated off-current I_Mag_pos_nom of the first switch tube Q1, and the current on-time toff_DCM of the second switch tube Q2 is inversely proportional to the current output voltage Vout, and is directly proportional to the current off-current I_Mag_pos_DCM of the first switch tube Q1, which can overcome the change in demagnetization time of the excitation inductance caused by the change in the output voltage of the asymmetric half-bridge circuit, and can make the negative current of the transformer T1 after demagnetization within a preset range, thereby meeting the ZVS requirement of the first switch tube Q1 when the asymmetric half-bridge circuit is in DCM mode.

[0138] An embodiment of the present invention further provides a charger, comprising the power supply circuit in the above embodiment.

[0139] As an example, the charger includes the power supply circuit in the above example. In this example, the control chip in the power supply circuit can obtain the current on-time toff_DCM of the second switch tube Q2 according to the current output voltage Vout_DCM, the current off-current I_Mag_pos_DCM of the first switch tube Q1, the rated on-time toff_nom of the second switch tube Q2, and the rated off-current I_Mag_pos_nom of the first switch tube Q1, and the current on-time toff_DCM of the second switch tube Q2 is inversely proportional to the current output voltage Vout, and is directly proportional to the current off-current I_Mag_pos_DCM of the current first switch tube Q1, which can overcome the change in the demagnetization time of the excitation inductance caused by the change in the output voltage of the asymmetric half-bridge circuit, and can make the negative current of the transformer T1 after demagnetization within a preset range, so as to meet the ZVS requirement of the first switch tube Q1 when the asymmetric half-bridge circuit is in the DCM mode.

[0140] The embodiments described above are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that the technical solutions described in the aforementioned embodiments may still be modified, or some of the technical features may be replaced by equivalents. Such modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention, and should all be included in the protection scope of the present invention.

Claims

1. A control method for an asymmetric half-bridge circuit, the asymmetric half-bridge circuit comprising a transformer, a first switch tube, a second switch tube, a resonant inductor and a resonant capacitor; the first end of the first switch tube is used to connect a rectifier bridge and a PFC circuit, the second end of the first switch tube is used to connect a control chip, and the third end of the first switch tube is connected to the first end of the second switch tube; the second end of the second switch tube is used to connect the control chip, and the third end of the second switch tube is grounded; the resonant inductor, the resonant capacitor and the primary winding of the transformer are connected in series between the third end of the first switch tube and the third end of the second switch tube, characterized in that The control method comprises: Acquire first detection data of an asymmetric half-bridge circuit; If the first detection data meets the preset light load condition, the first switch tube is controlled to be turned off, and the current output voltage and the current turn-off current of the first switch tube are obtained; Acquire a current on-time of the second switch tube according to the current output voltage and the current off-current of the first switch tube, wherein the current on-time is in direct proportion to the current off-current and in inverse proportion to the current output voltage; During the current on-time, the second switch tube is controlled to be on, so that when the second switch tube is turned off, the current off-current of the second switch tube is within a preset range.

2. The control method of the asymmetric half-bridge circuit according to claim 1, characterized in that: The first detection data includes a current output current; The preset light load condition is that the current output current is less than a preset current.

3. The control method of the asymmetric half-bridge circuit according to claim 1, characterized in that: The acquiring the current on-time of the second switch tube according to the current output voltage and the current off-current of the first switch tube comprises: Obtaining the rated off current of the first switch tube and the rated on time of the second switch tube under the rated maximum power; The current on-time of the second switch tube is acquired according to the rated off-current of the first switch tube, the rated on-time of the second switch tube, the current output voltage and the current off-current of the first switch tube.

4. The control method of the asymmetric half-bridge circuit according to claim 3, characterized in that: Obtain the rated turn-off current of the first switch tube at the rated maximum power, including: Based on the output current at rated maximum power and the transformer ratio of the asymmetric half-bridge circuit, a target shutdown current at rated maximum power is obtained, where the target shutdown current is the sum of the rated shutdown current of the second switch tube and the rated shutdown current of the first switch tube; Based on the rated turn-off current and the target turn-off current of the second switch tube, the rated turn-off current of the first switch tube at the rated maximum power is obtained.

5. The control method of the asymmetric half-bridge circuit according to claim 3, characterized in that: The step of obtaining the rated on-time of the second switch tube under the rated maximum power includes: Based on the output voltage at the rated maximum power and the transformer ratio of the asymmetric half-bridge circuit, the resonant capacitor voltage stored in the resonant capacitor when the first switch tube is turned off and the body diode of the second switch tube is freewheeling is obtained; Based on the rated off current of the first switch tube and the preset rated off current of the second switch tube, obtaining the current change amount under the rated maximum power; Based on the transformer inductance of the asymmetric half-bridge circuit, the current change at the rated maximum power and the resonant capacitor voltage, the rated conduction time of the second switch tube at the rated maximum power is obtained.

6. The control method of the asymmetric half-bridge circuit according to claim 3, characterized in that: The obtaining the current on-time of the second switch tube according to the rated off-current of the first switch tube, the rated on-time of the second switch tube, the current output voltage and the current off-current of the first switch tube includes: Substitute the rated off current of the first switch tube, the rated on time of the second switch tube, the current output voltage and the current off current of the first switch tube into the formula , obtain the current on-time of the second switch tube, where K is the correction coefficient, toff_nom is the rated on-time of the second switch tube, Vnom is the output voltage of the asymmetric half-bridge circuit at the maximum power gear, I_Mag_pos_DCM is the current off-current of the first switch tube, Vout_DCM is the current output voltage, and I_Mag_pos_nom is the rated off-current of the first switch tube.

7. The control method of the asymmetric half-bridge circuit according to claim 6, characterized in that: When the current turn-off current of the first switch tube is within the first preset range, the correction coefficient K takes a first correction value; When the current turn-off current of the first switch tube is within the second preset range, the correction coefficient K takes a second correction value.

8. A control chip, comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, characterized in that: The control chip is applied in an asymmetric half-bridge circuit, and the processor implements the control method of the asymmetric half-bridge circuit according to any one of claims 1 to 7 when executing the computer program.

9. A power supply circuit, characterized in that: It includes a rectifier bridge and a PFC circuit, an electrolytic capacitor, an asymmetric half-bridge circuit, a secondary rectifier filter circuit, a protocol control module and the control chip according to claim 8; The input end of the rectifier bridge and the PFC circuit is used to connect to the mains circuit, and the output end of the rectifier bridge and the PFC circuit is connected to the electrolytic capacitor; The input end of the asymmetric half-bridge circuit is connected to the electrolytic capacitor, and the output end of the asymmetric half-bridge circuit is connected to the input end of the secondary rectifier filter circuit; The output end of the secondary rectifier and filter circuit is used to connect to an external load to supply power to the external load; The control chip is connected to the first switch tube and the second switch tube in the asymmetric half-bridge circuit, and is used to control the second switch tube to be turned on within the current on time when the first detection data of the asymmetric half-bridge circuit meets the preset light load condition, so that the current off current of the second switch tube is within a preset range; The protocol control module is connected to the output end of the secondary rectifier and filter circuit, the asymmetric half-bridge circuit and the control chip, and is used to output a voltage adjustment signal to the control chip according to the power supply demand of the external load, so that the control chip controls and adjusts the power supply voltage output by the asymmetric half-bridge circuit according to the voltage adjustment signal.

10. A charger, characterized in that: Includes the power supply circuit as claimed in claim 9.

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