CN117856602A - Start control method and start control circuit of switching converter - Google Patents
Start control method and start control circuit of switching converter Download PDFInfo
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- CN117856602A CN117856602A CN202410012345.2A CN202410012345A CN117856602A CN 117856602 A CN117856602 A CN 117856602A CN 202410012345 A CN202410012345 A CN 202410012345A CN 117856602 A CN117856602 A CN 117856602A
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Classifications
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
- H02M1/00—Details of apparatus for conversion
- H02M1/36—Means for starting or stopping converters
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
- H02M1/00—Details of apparatus for conversion
- H02M1/0003—Details of control, feedback or regulation circuits
- H02M1/0038—Circuits or arrangements for suppressing, e.g. by masking incorrect turn-on or turn-off signals, e.g. due to current spikes in current mode control
-
- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
- H02M1/00—Details of apparatus for conversion
- H02M1/08—Circuits specially adapted for the generation of control voltages for semiconductor devices incorporated in static converters
-
- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
- H02M1/00—Details of apparatus for conversion
- H02M1/08—Circuits specially adapted for the generation of control voltages for semiconductor devices incorporated in static converters
- H02M1/083—Circuits specially adapted for the generation of control voltages for semiconductor devices incorporated in static converters for the ignition at the zero crossing of the voltage or the current
-
- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
- H02M1/00—Details of apparatus for conversion
- H02M1/08—Circuits specially adapted for the generation of control voltages for semiconductor devices incorporated in static converters
- H02M1/088—Circuits specially adapted for the generation of control voltages for semiconductor devices incorporated in static converters for the simultaneous control of series or parallel connected semiconductor devices
-
- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
- H02M1/00—Details of apparatus for conversion
- H02M1/32—Means for protecting converters other than automatic disconnection
-
- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
- H02M3/00—Conversion of dc power input into dc power output
- H02M3/01—Resonant DC/DC converters
-
- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
- H02M3/00—Conversion of dc power input into dc power output
- H02M3/22—Conversion of dc power input into dc power output with intermediate conversion into ac
- H02M3/24—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters
- H02M3/28—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02B—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO BUILDINGS, e.g. HOUSING, HOUSE APPLIANCES OR RELATED END-USER APPLICATIONS
- Y02B70/00—Technologies for an efficient end-user side electric power management and consumption
- Y02B70/10—Technologies improving the efficiency by using switched-mode power supplies [SMPS], i.e. efficient power electronics conversion e.g. power factor correction or reduction of losses in power supplies or efficient standby modes
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- Engineering & Computer Science (AREA)
- Power Engineering (AREA)
- Dc-Dc Converters (AREA)
Abstract
The application relates to the field of switching converters, and discloses a starting control method of a switching converter, which comprises the following steps: the control switch converter sequentially passes through the following three working phases in the starting process: a low frequency start-up phase, a first frequency up phase and a second frequency up phase. According to the method and the device, on the one hand, the starting speed of the switching converter and the starting capacity of the switching converter can be effectively improved. On the other hand, the full-course zero-voltage switch and the zero-current switch of the main power tube and the secondary rectifying tube in the starting process can be realized, and the problems of large primary side voltage and current stress and large secondary side voltage stress existing in the conventional converter during power-on starting are solved.
Description
Technical Field
The present disclosure relates to the field of switching converters, and in particular, to a method and circuit for controlling the start of a switching converter.
Background
When the switching converter works, the rear stage is always provided with a larger output capacitance or capacitive load, the former is used for filtering output current, the latter is used for increasing the load carrying capacity of a switching power supply system, the structure can easily cause overshoot of output voltage in the building process or damage of a switching tube due to overlarge current in the starting process, and the common solution is to gradually increase the duty ratio of a driving signal of the switching tube in the starting process, so that the building of the output voltage slowly rises from low voltage to rated output voltage for a longer time, and soft starting is realized.
For an asymmetric half-bridge flyback converter (AHBF) system, when a conventional high-frequency soft start scheme is adopted, when the output voltage is not established yet, the demagnetizing current is slow in dropping speed, so that a main power tube cannot realize zero-voltage switching (ZVS), a secondary rectifying diode cannot realize zero-current switching (ZCS), a reverse recovery process exists, a larger dv/dt (voltage change rate) is generated at the moment that the main power tube is turned on, resonance is generated on parasitic inductance and parasitic capacitance Coss of an auxiliary power tube by the current, so that the midpoint voltage of a bridge arm is increased, lower tube voltage stress in the main switching tube is increased, and the lower tube voltage stress is coupled to a secondary side through a transformer, so that the stress peak of the secondary side rectifying tube is increased.
To sum up, under the conventional soft start scheme, the asymmetric half-bridge flyback converter system is easy to generate current spikes, and has the problems of large primary side voltage and current stress and large secondary side voltage stress, and the root causes are whether the soft start level can be switched smoothly, whether the secondary side rectifying tube can realize Zero Current Switching (ZCS) when the main power tube is switched on, and whether the main power tube can realize ZVS.
To improve the start-up stress problem described above, the prior art has proposed to employ a "variable gate drive" scheme to reduce the conduction speed of the main power transistor, thereby reducing dv/dt (voltage rate of change) and di/dt (current rate of change) when it is on. However, when different types of MOS tubes or MOS tubes are at different temperatures, the starting voltages are different, and the control is complex.
Therefore, it is necessary to provide a starting control mode to realize ZCS and ZVS in the starting process, improve the starting stress problem, and improve the starting speed and the starting capability of the switching converter.
Disclosure of Invention
In view of this, the technical problems to be solved in the present application are: the starting control method and the starting control circuit for the switching converter are provided, so that the problems that the current spike is easy to occur, the primary side voltage and current stress is large, and the secondary side voltage stress is large when the existing asymmetric half-bridge flyback converter system is electrified and started are solved, and meanwhile, the starting capacity and the starting speed of the asymmetric half-bridge flyback converter are improved.
In order to solve the technical problems, the technical scheme adopted by the application is as follows:
the starting control method of the switching converter is an asymmetric half-bridge flyback converter, and the switching converter comprises a main switching tube, an auxiliary switching tube, a resonant inductor, a resonant capacitor and a transformer, and the starting control method comprises the following steps: the control switch converter sequentially passes through the following three working phases when being started: a low frequency start-up phase, a first frequency boost phase and a second frequency boost phase; in the low-frequency starting stage, the driving signal of the main switching tube and the driving signal of the auxiliary switching tube are not complementary, the auxiliary switching tube is conducted in a time period from a set time when the main switching tube is disconnected in the current working period to a time when the main switching tube is conducted in the next working period, and the set time is when the demagnetizing current of the transformer excitation inductance of the switching converter reaches zero; in the first frequency raising stage, the driving signal of the main switching tube is not complementary with the driving signal of the auxiliary switching tube, and the auxiliary switching tube is conducted at a set moment after the main switching tube is disconnected in the current working period; in the second frequency raising stage, the driving signals of the main switching tube and the auxiliary switching tube are not complementary, and the auxiliary switching tube is conducted in the time period from the disconnection of the main switching tube to the set time of the current working period. The switching frequency of the switching converter in the low-frequency starting stage is smaller than that in the first frequency raising stage, and the switching frequency of the switching converter in the first frequency raising stage is smaller than that in the second frequency raising stage.
Preferably, in the low-frequency starting stage, the conduction time of the auxiliary switching tube is a first time T Q2_1 ：
In the second up-conversion stage, the conduction time of the auxiliary switching tube is the second time T Q2_2 ：
Wherein Lr is the inductance of the resonant inductor and Cr is the capacity of the resonant capacitor, M is the ratio of the conduction time of the auxiliary switching tube to the resonance period of the resonant capacitor and the resonant inductor, and the value of M is 1/2 in the low-frequency starting stage; in the second up-conversion stage, M takes a value of 3/4.
Preferably, in the first up-conversion stage, the conduction time of the auxiliary switching tube is equal to the first time T Q2_1 The same applies.
Preferably, in the second frequency raising stage, the turn-off time of the auxiliary switching tube is a third time T after the set time d Is used for the time of day (c),
wherein I is N Is the negative current value of the excitation inductance of the transformer, lm is the inductance of the excitation inductance of the transformer, N is the turn ratio of the transformer, V nom And outputting voltage for the steady state after the starting process of the switching converter is completed.
Preferably, in the second up-conversion phase, the time difference between the off-time of the main switching tube and the on-time of the auxiliary switching tube decreases with increasing output voltage of the switching converter.
Preferably, in the second up-conversion stage, when the output voltage of the switching converter rises to 100% V nom When the dead time is ignored, the conduction time of the auxiliary switching tube is the turn-off time of the main switching tube, and the conduction time of the auxiliary switching tube is the time when the demagnetizing current is 100% Ipmax; when the output voltage of the switching converter rises to 50% V nom The conduction time of the auxiliary switching tube is that the demagnetizing current is reduced to 50 percent ipTime of max, where V nom For the steady-state output voltage of the switching converter after the start-up process is completed, ipmax is the maximum value of the exciting current of the exciting inductance of the transformer.
Preferably, the switching converter operates in a low frequency start-up phase and the switching converter is controlled to enter a first boost phase from the low frequency start-up phase when the demagnetization current is detected to be zero;
when the switching converter works in the first frequency-raising stage and the output voltage of the switching converter is detected to reach a set value, the switching converter is controlled to enter a second frequency-raising stage from the first frequency-raising stage, wherein the set value is a% V nom A% is 10% -40%, V nom And outputting voltage for the steady state after the starting process of the switching converter is completed.
The application also provides a controlling means of switching converter, and switching converter is asymmetric half-bridge flyback converter, and switching converter includes main switch tube, auxiliary switch tube, resonant inductance, resonance electric capacity and transformer, and controlling means is used for controlling switching converter and passes through following three working phase in proper order in the start-up process: a low frequency start-up phase, a first frequency up-conversion phase and a second frequency up-conversion phase, wherein,
when the switching converter works in a low-frequency starting stage, the driving signal of the main switching tube and the driving signal of the auxiliary switching tube are not complementary, the auxiliary switching tube is conducted in a time period from a set time after the main switching tube is disconnected in the current working period to a time before the main switching tube is conducted in the next working period, and the set time is the time when the demagnetizing current of the transformer excitation inductance of the switching converter reaches zero;
when the switching converter works in the first frequency raising stage, the driving signal of the main switching tube is not complementary with the driving signal of the auxiliary switching tube, and the auxiliary switching tube is conducted at a set moment after the main switching tube is disconnected in the current working period;
when the switching converter works in the second frequency raising stage, driving signals of the main switching tube and the auxiliary switching tube are not complementary, and the auxiliary switching tube is conducted in a time period from the disconnection of the main switching tube to the set time in the current working period.
The application further provides a start control method of a switching converter, for controlling a start process of the switching converter, where the switching converter is an asymmetric half-bridge flyback converter, and the switching converter includes a main switching tube, an auxiliary switching tube, a resonant inductor, a resonant capacitor and a transformer, and the start control method includes: the control switch converter sequentially passes through the following two working phases when being started: a low frequency start-up phase and an up-conversion phase, wherein,
in the low-frequency starting stage, the driving signal of the main switching tube and the driving signal of the auxiliary switching tube are non-complementary, and the auxiliary switching tube is conducted in a time period from a set time after the main switching tube is disconnected in the current working period to a time before the main switching tube is conducted in the next working period, wherein the set time is when the magnetizing inductance demagnetizing current of the switching converter reaches zero;
in the frequency raising stage, the driving signal of the main switching tube and the driving signal of the auxiliary switching tube are not complementary, and the auxiliary switching tube is conducted in the time period from the disconnection of the main switching tube to the set time in the current working period.
Compared with the prior art, the application has the following beneficial effects:
(1) The on time of the auxiliary switching tube is controlled respectively in different stages, so that zero voltage on (ZVS) of a main switching tube and zero current off (ZCS) of a secondary switching tube of the switching converter in the starting process are realized, and the problems that the current spike is easy to occur, the primary side voltage and current stress is large and the secondary side voltage stress is large when the existing asymmetric half-bridge flyback converter is electrified and started are solved;
(2) In the second frequency raising stage, the time difference between the turn-off time of the main switching tube and the turn-on time of the auxiliary switching tube is reduced along with the rise of the output voltage of the switching converter, so that the starting capability and speed of the switching converter are effectively improved.
Drawings
FIG. 1 is a schematic diagram of a switching converter of the present application;
FIG. 2 is a timing diagram of a low frequency start-up phase of the switching converter of the present application at start-up;
FIG. 3 is a timing diagram illustrating a low frequency start-up phase to a first up-conversion phase when the switching converter of the present application is started;
fig. 4 is a timing diagram of a first up-conversion stage to a second up-conversion stage on the start of the switching converter of the present application.
Detailed Description
In order to make the objects, technical solutions and advantages of the present application more apparent, the present application is further described in detail below with reference to the accompanying drawings and examples. It should be understood that the specific embodiments described herein are for purposes of illustration only and are not intended to limit the present application.
It should be noted that the terms "first," "second," and the like in the description and claims of the present application and the above figures are used for distinguishing between similar objects and not necessarily for describing a particular sequential or chronological order. It is to be understood that the data so used may be interchanged where appropriate in order to describe embodiments of the present application herein. Furthermore, the terms "comprises," "comprising," and "having," and any variations thereof, are intended to cover a non-exclusive inclusion, such that a process, method, system, article, or apparatus that comprises a list of steps or elements is not necessarily limited to those steps or elements expressly listed but may include other steps or elements not expressly listed or inherent to such process, method, article, or apparatus.
In addition, embodiments and features of embodiments in this application may be combined with each other without conflict.
It should be understood that in the specification, claims and drawings, when a step is described as being continued to another step, the step may be continued directly to the other step or through a third step to the other step; when an element/unit is described as being "connected" to another element/unit, the element/unit may be "directly connected" to the other element/unit or "connected" to the other element/unit through a third element/unit.
Moreover, the drawings of the present disclosure are schematic representations of the present disclosure and are not necessarily drawn to scale. The same reference numerals in the drawings denote the same or similar parts, and thus a repetitive description thereof will be omitted. Some of the block diagrams shown in the figures are functional entities and do not necessarily correspond to physically or logically separate entities. The functional entities may be implemented in software or in one or more hardware modules or integrated circuits or in different networks and/or processor devices and/or micro-control devices.
First embodiment
Referring to fig. 1, the present embodiment provides a switching converter, which is an asymmetric half-bridge flyback converter (hereinafter referred to as a switching converter), and includes a main switching tube Q1 located in an upper bridge arm, an auxiliary switching tube Q2 located in a lower bridge arm, a resonant inductor Lr, a resonant capacitor Cr, a transformer Tr (including an auxiliary winding Na), an excitation current sampling circuit, an output voltage sampling circuit, a start control circuit, and a driving circuit.
The exciting current sampling circuit is used for sampling exciting current of the exciting inductance Lm of the transformer; the output voltage sampling circuit is used for sampling the output voltage Vo (i.e., the voltage between the output positive terminal vo+ and the output negative terminal Vo-of the switching converter).
The starting control circuit is used for controlling the starting process of the switching converter, so that the switching converter sequentially passes through a low-frequency starting stage, a first frequency-raising stage and a second frequency-raising stage in the starting process. The switching frequency of the switching converter in the low-frequency starting stage is smaller than that in the first frequency-raising stage, and the switching frequency of the switching converter in the first frequency-raising stage is smaller than that in the second frequency-raising stage.
Referring to fig. 2 to 4, wherein in fig. 2 to 4, Q1 represents a driving signal of the main switching tube Q1, and Q2 represents a driving signal of the auxiliary switching tube Q2; ilr represents the current of the resonant inductor Lr (indicated by solid line); ilm represents the current of the transformer excitation inductance Lm, wherein the dotted line represents the demagnetizing current, and the solid line portion overlapping the current Ilr of the resonance inductance Lr represents the excitation current; ld represents the output diode D3 current.
In the low-frequency starting stage, the driving signal of the main switching tube Q1 and the driving signal of the auxiliary switching tube Q2 are not complementary, and the auxiliary switching tube Q2 is turned on in a period from a set time after the main switching tube Q1 is turned off in the current working period to a time before the main switching tube Q1 is turned on in the next working period, wherein the set time is a time when the demagnetizing current of the transformer excitation inductance Lm of the switching converter reaches zero Ilm (shown by a dotted line in fig. 3), that is, the auxiliary switching tube Q2 is turned on after the demagnetizing current Ilm of the transformer excitation inductance Lm reaches zero.
In the first frequency raising stage, the driving signal of the main switching tube Q1 and the driving signal of the auxiliary switching tube Q2 are not complementary, and the auxiliary switching tube Q2 is turned on at a set time after the main switching tube Q1 is turned off in the current working period, that is, the auxiliary switching tube Q2 is turned on at a time when the demagnetizing current Ilm of the transformer excitation inductance Lm reaches zero.
In the second frequency raising stage, the driving signals of the main switching tube Q1 and the auxiliary switching tube Q2 are not complementary, and the auxiliary switching tube Q2 is turned on in a period from the turn-off of the main switching tube Q1 to the set time in the current working period, that is, the auxiliary switching tube Q2 is turned on before the demagnetizing current Ilm of the transformer excitation inductance Lm reaches zero.
The embodiment of the application also provides a start control method of the switching converter, which is used for controlling the driving time sequences of the main switching tube Q1 and the auxiliary switching tube Q2 in the start process of the switching converter. The following describes the start control method provided in the embodiment of the present application in conjunction with the start control circuit.
The starting control method of the switching converter provided by the application comprises the following steps: the control switch converter sequentially passes through the following three working phases in the starting process: a low frequency start-up phase, a first frequency up phase and a second frequency up phase.
Referring to fig. 3, during the low frequency start-up phase (i.e., at the beginning of the start-up), the switching converter is operated at a lower frequency fmin, ensuring that the demagnetization current Ilm of each cycle of the switching converter can reach zero, i.e., the period t2-t3 exists, and the demagnetization time t1-t2 is longer due to the low output voltage at the beginning of the start-up, so that the frequency fmin is generally smaller, and the specific magnitude is related to different system parameters. At time t3, the auxiliary switching tube Q2 is turned on, that is, the auxiliary switching tube Q2 is turned on after the demagnetizing current Ilm of the transformer excitation inductance Lm reaches zero, in the time period t3-t4,the auxiliary switch tube Q2 is kept on, the resonance capacitor Cr resonates with the resonance inductor Lr, and the conduction time (first time) of the auxiliary switch tube Q2 is designed to beThe secondary rectifying diode D3 is guaranteed to realize Zero Current Switching (ZCS), and meanwhile, the auxiliary switching tube Q2 is conducted to reversely excite the transformer excitation inductance Lm to generate negative current, so that the primary main switching tube Q1 can realize ZVS.
When the switching converter operates for some time in the low-frequency starting stage, the output voltage Vo is raised, and when the zero crossing detection module can detect the zero crossing time of the demagnetizing current ILm, the switching converter switches into the first frequency raising stage, in the first frequency raising stage, the conduction time of the auxiliary switching tube Q2 is advanced, that is, the switching tube Q2 is turned on at the time (t 2 time) of the zero crossing point of the demagnetizing current ILm, and in the first frequency raising stage, the conduction time (second time) of the auxiliary switching tube Q2 isThe secondary rectifying diode D3 is guaranteed to realize Zero Current Switching (ZCS), meanwhile, as the output voltage Vo rises, the negative current is further increased, the ZVS effect is deepened, and the primary main switching tube Q1 is better capable of realizing ZVS. When the switching converter works in the first frequency-raising stage, as the output voltage Vo is raised, the demagnetization time period t2-t3 is gradually reduced, the switching frequency is gradually raised, and automatic frequency raising of zero-crossing detection is realized, so that the starting speed is further increased.
Specifically, if the switching converter works in the first frequency-raising stage, if the zero-crossing detection module detects that a problem occurs, and the zero-crossing moment detection of the demagnetizing current ILm is lost, and when the frequency suddenly decreases, the switching converter works at the frequency fmin set in the low-frequency starting stage, so as to ensure that the converter works normally. Referring to fig. 4, after the switching converter operates for some time in the first up-conversion stage, the output voltage Vo is further increased, if the output voltage Vo detected by the output voltage sampling circuit reaches the steady-state output voltage V nom I.e. the output voltage vo=a% V nom When the switch becomesThe exchanger cuts into the second up-conversion stage, wherein a% ranges from 10% to 40%, preferably a% is 20%. In the second frequency raising stage, the conduction time of the auxiliary switching tube Q2 is advanced again, the auxiliary switching tube Q2 is turned on at time t2 (i.e. turned on before the set time), i.e. before the zero crossing point of the demagnetizing current ILm (time t 3), the specific turn-on time is determined by the output voltage Vo, and when the output voltage Vo rises to a% V nom When the demagnetizing current ILm decreases to a% Ipmax, the auxiliary switching transistor Q2 is turned on, and Ipmax is the maximum exciting current value of the transformer exciting inductance Lm allowed at the time of starting. For example, when the output voltage Vo of the switching converter rises to 100% V nom When the dead time is ignored, the on time of the auxiliary switching tube Q2 is the off time of the main switching tube Q1, and the on time of the auxiliary switching tube Q2 is the time when the demagnetizing current ILm is 100% Ipmax; when the output voltage Vo of the switching converter rises to 50% v nom The conduction time of the auxiliary switching transistor Q2 is the time when the demagnetization current drops to 50% ipmax, and so on.
In the second up-conversion stage, when the demagnetizing current ILm crosses zero, i.e. at time T3, the third time T is delayed d After that, the auxiliary switching tube Q2 is turned off by setting a third time T d The magnitude of the current ensures the proper negative current, T, required by different systems when starting d The method comprises the following steps:
wherein I is N Negative current of excitation inductance Lm of transformer, inductance Lm of excitation inductance of transformer, turn ratio of N and V nom Is a steady state output voltage.
Further, according to the negative current conditions required by different systems, different T's are set d In the second frequency raising stage, the conducting time T of the auxiliary switch tube Q2 Q2_2 The method comprises the following steps:
namely:Δi is the excitation current variation, Δi=ipmax+i N ；
In general, in circuit design, in order to ensure that the secondary rectifying diode D3 can realize zero current turn-off in a steady state, the conduction time of the auxiliary switching tube Q2 in the steady state is designed to be 3/4 of a resonance period, namely:
wherein Lr is the resonant inductance and Cr is the resonant capacitance, and M is the ratio of the conduction time of the auxiliary switch tube Q2 to the resonant period of the resonant capacitance Cr and the resonant inductance Lr.
Therefore, in the second up-conversion stage, the on-time T of the auxiliary switching tube Q2 Q2_2 Also 3/4 of the resonance period, namely:m takes on a value of 3/4.
Therefore, in the second frequency raising stage, the conduction energy of the auxiliary switching tube Q2 ensures that the secondary rectifying diode D3 can realize zero current turn-off and the primary main switching tube Q1 can realize zero voltage turn-on (ZVS), thereby effectively reducing the problems of large current and voltage stress of the converter in the starting process. Meanwhile, the on time of the auxiliary switching tube Q2 is gradually advanced along with the rising of the output voltage Vo, namely, the time difference between the off time of the switching tube and the on time of the auxiliary switching tube is reduced along with the rising of the output voltage of the switching converter, so that the starting capability and the starting speed of the converter are effectively improved.
In particular, in the startup control method of the present application, if the first frequency-up stage is omitted, the startup effect can also be achieved. The specific implementation steps are as follows: at the beginning of the same start-up, the switching converter operates in the manner described above for the low-frequency start-up phase, when the output voltage Vo rises to the set value a% V nom The switching converter then switches into a second up-conversion phase (up-conversion phase), wherein a% is in the range of 10% -40%, preferably 20%. Later onThe working mode is the same as the working mode of the second frequency raising stage.
The foregoing is merely a preferred embodiment of the present application, and it should be noted that the above-mentioned preferred embodiment should not be construed as limiting the present application, and that several modifications and alterations can be made by those skilled in the art without departing from the spirit and scope of the present application, which should also be construed as the protection scope of the present application, which is defined by the claims without further description of the examples.
Claims (10)
1. The starting control method of the switching converter, the switching converter is an asymmetric half-bridge flyback converter, the switching converter comprises a main switching tube, an auxiliary switching tube, a resonant inductor, a resonant capacitor and a transformer, and the starting control method is characterized by comprising the following steps: the switching converter is controlled to sequentially pass through the following three working phases in the starting process: a low frequency start-up phase, a first frequency boost phase and a second frequency boost phase; wherein,
in a low-frequency starting stage, the driving signal of the main switching tube and the driving signal of the auxiliary switching tube are not complementary, and the auxiliary switching tube is conducted in a period from a set time after the main switching tube is disconnected in a current working period to a time before the main switching tube is conducted in a next working period, wherein the set time is when the demagnetizing current of a transformer excitation inductor of the switching converter reaches zero;
in a first frequency raising stage, the driving signal of the main switching tube is not complementary with the driving signal of the auxiliary switching tube, and the auxiliary switching tube is conducted at the set moment after the main switching tube is disconnected in the current working period;
in the second frequency raising stage, the driving signals of the main switching tube and the auxiliary switching tube are not complementary, and the auxiliary switching tube is conducted in a time period from the disconnection of the main switching tube to the set time in the current working period.
2. The start-up control method according to claim 1, characterized in thatCharacterized in that in the low-frequency starting stage, the conduction time of the auxiliary switching tube is the first time T Q2_1 ：
In the second up-conversion stage, the conduction time of the auxiliary switching tube is a second time T Q2_2 ：
Wherein Lr is the inductance of the resonant inductor and Cr is the capacity of the resonant capacitor, M is the ratio of the on time of the auxiliary switching tube to the resonant period of the resonant capacitor and the resonant inductor, and in the low-frequency starting stage, the value of M is 1/2; in the second frequency raising stage, the value of M is 3/4.
3. The method according to claim 2, wherein in a first up-conversion stage, the on-time of the auxiliary switching tube is equal to the first time T Q2_1 The same applies.
4. The start-up control method according to claim 1, wherein the second frequency-raising stage is a third time T after the set time is the turn-off time of the auxiliary switching tube d Is used for the time of day (c),
wherein I is N Lm is the inductance of the excitation inductance of the transformer, N is the turn ratio of the transformer, and V nom And outputting a voltage for the switch converter in a steady state after the start-up process is completed.
5. The startup control method according to claim 1, wherein in a second up-conversion stage, a time difference between an off-time of the main switching tube and an on-time of the auxiliary switching tube decreases as an output voltage of the switching converter increases.
6. The start-up control method according to claim 1, wherein in the second up-conversion stage, when the output voltage of the switching converter rises to 100% v nom When the dead time is ignored, the conduction time of the auxiliary switching tube is the turn-off time of the main switching tube, and the conduction time of the auxiliary switching tube is the time when the demagnetizing current is 100% Ipmax; when the output voltage of the switching converter rises to 50% V nom The conduction time of the auxiliary switching tube is the time when the demagnetizing current drops to 50% Ipmax, wherein V nom And for the steady-state output voltage of the switching converter after the starting process is completed, the IPmax is the maximum value of exciting current of the exciting inductance of the transformer in the starting process.
7. The start-up control method according to claim 1, wherein,
the switching converter works in a low-frequency starting stage, and the switching converter is controlled to enter a first frequency raising stage from the low-frequency starting stage when the demagnetizing current of the excitation inductance of the transformer is detected to reach zero;
when the switching converter works in a second frequency-raising stage and the output voltage of the switching converter is detected to reach a set value, the switching converter is controlled to enter the second frequency-raising stage from the first frequency-raising stage, wherein the set value is a%V nom A% is 10% -40%, V nom And outputting a voltage for the switch converter in a steady state after the start-up process is completed.
8. The start-up control method of claim 1, wherein the switching frequency of the switching converter during the low frequency start-up phase is less than the switching frequency during the first boost phase, and wherein the switching frequency of the switching converter during the first boost phase is less than the switching frequency during the second boost phase.
9. The starting control circuit of the switching converter is an asymmetric half-bridge flyback converter, and comprises a main switching tube, an auxiliary switching tube, a resonant inductor, a resonant capacitor and a transformer, and is characterized in that the starting control circuit is used for controlling the switching converter to sequentially pass through the following three working phases in the starting process: a low frequency start-up phase, a first frequency up-conversion phase and a second frequency up-conversion phase, wherein,
when the switching converter works in a low-frequency starting stage, the driving signal of the main switching tube and the driving signal of the auxiliary switching tube are not complementary, the auxiliary switching tube is conducted in a time period from a set time after the main switching tube is disconnected in a current working period to the time before the main switching tube is conducted in a next working period, and the set time is the time when the demagnetizing current of the transformer excitation inductance of the switching converter reaches zero;
when the switching converter works in a first frequency-raising stage, the driving signal of the main switching tube is not complementary with the driving signal of the auxiliary switching tube, and the auxiliary switching tube is conducted at the set moment after the main switching tube is disconnected in the current working period;
when the switching converter works in the second frequency-raising stage, the driving signals of the main switching tube and the auxiliary switching tube are not complementary, and the auxiliary switching tube is conducted in a time period from the disconnection of the main switching tube to the set time in the current working period.
10. The starting control method of the switching converter is used for controlling the starting process of the switching converter, the switching converter is an asymmetric half-bridge flyback converter, and the switching converter comprises a main switching tube, an auxiliary switching tube, a resonant inductor, a resonant capacitor and a transformer, and is characterized by comprising the following steps: the switching converter is controlled to sequentially pass through the following two working phases when being started: a low frequency start-up phase and an up-conversion phase, wherein,
in a low-frequency starting stage, the driving signal of the main switching tube and the driving signal of the auxiliary switching tube are not complementary, and the auxiliary switching tube is conducted in a period from a set time after the main switching tube is disconnected in a current working period to a time before the main switching tube is conducted in a next working period, wherein the set time is when the magnetizing inductance demagnetizing current of the switching converter reaches zero;
in the frequency raising stage, the driving signal of the main switching tube is not complementary with the driving signal of the auxiliary switching tube, and the auxiliary switching tube is conducted in a time period from the disconnection of the main switching tube to the set time in the current working period.
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| CN118282217A (en) * | 2024-05-31 | 2024-07-02 | 杰华特微电子股份有限公司 | Asymmetric half-bridge flyback converter, control circuit and control method thereof |
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| CN118282217A (en) * | 2024-05-31 | 2024-07-02 | 杰华特微电子股份有限公司 | Asymmetric half-bridge flyback converter, control circuit and control method thereof |
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