CN112564489A - Mode control method of switch converter and switch converter - Google Patents
Mode control method of switch converter and switch converter Download PDFInfo
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- CN112564489A CN112564489A CN202011210399.8A CN202011210399A CN112564489A CN 112564489 A CN112564489 A CN 112564489A CN 202011210399 A CN202011210399 A CN 202011210399A CN 112564489 A CN112564489 A CN 112564489A
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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
- 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
- H02M3/325—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 using devices of a triode or a transistor type requiring continuous application of a control signal
- H02M3/335—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 using devices of a triode or a transistor type requiring continuous application of a control signal using semiconductor devices only
- H02M3/3353—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 using devices of a triode or a transistor type requiring continuous application of a control signal using semiconductor devices only having at least two simultaneously operating switches on the input side, e.g. "double forward" or "double (switched) flyback" converter
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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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Abstract
The invention relates to the field of switch converter design and discloses a mode control method of an asymmetric half-bridge flyback converter. According to the invention, the operation mode control of the asymmetric half-bridge flyback converter is carried out by collecting the input voltage and the load information, so that the problems that the efficiency is better in a wide input voltage range and the no-load loss is larger in the existing mode control scheme only adopting the load current are effectively solved, and the efficiency of the asymmetric half-bridge flyback converter is better in a full-voltage and full-load range.
Description
Technical Field
The present invention relates to the field of switching converter design, and in particular, to a mode control method for a switching converter and a switching converter.
Background
The switching converter is also called a switching power supply, is a power supply device for realizing electric energy conversion and transmission by controlling the on and off of a semiconductor switching device, has the advantages of high efficiency, small volume, light weight and the like compared with the traditional power supply, and is widely applied to the fields of consumer electronics, new energy, industrial control, aerospace and the like. In recent years, with the enhancement of environmental protection and energy saving consciousness in the global range and the development of power electronic technology, the energy efficiency index of a switching converter product is gradually improved, and in some application occasions, besides the requirement of high efficiency of a rated working point, the switching converter in a wide input voltage range and a full load range is also required to work efficiently.
The topology of the asymmetric half-bridge flyback converter has the characteristic of soft switching, and the characteristic is that the prior switching converter has high efficiencyOne of the research hotspots of the application. Fig. 1 is a circuit diagram of a switching converter formed by an existing asymmetric half-bridge flyback converter, which includes an asymmetric half-bridge flyback converter 110 and a controller 120, where the asymmetric half-bridge flyback converter 110 includes an input capacitor Cin, a main switch Q1, an auxiliary switch Q2, a resonant capacitor Cr, a transformer 112, a rectifier switch D, an output filter capacitor Co, and an isolation feedback circuit 113, and the controller 120 receives output voltage information through the isolation feedback circuit 113 and adjusts the output to a desired level by controlling the main switch Q1 and the auxiliary switch Q2. Fig. 2 is a schematic diagram illustrating mode switching of the conventional asymmetric half-bridge flyback switching converter shown in fig. 1, in which the controller 120 controls the main switch Q1 and the auxiliary switch Q2 to switch when the output load is greater than the set current value I0And 3, enabling the switching converter to work in an asymmetric half-bridge flyback Mode (AHBF Mode), and enabling the output load to be smaller than a current set value I0At time 3, the switching converter is operated in a burst mode (burst mode).
The asymmetric half-bridge flyback converter shown in fig. 1 generally has higher conversion efficiency when being fully loaded and heavily loaded, but the negative peak value of the exciting inductor current increases with the reduction of the load, exceeds the requirement of the converter main switch for realizing zero voltage switching, generates ineffective loss, and thus causes the converter to have lower light-load efficiency.
In order to solve the problem of low light load efficiency of the asymmetric half-bridge flyback converter, a chinese patent "switching power supply device" with application number 201911352361.1 proposes to adopt the asymmetric half-bridge flyback converter and a controller as shown in fig. 3, to perform Mode switching according to load current by adding a unidirectional clamp network connected in parallel with a primary side of a transformer and adopting a Mode switching curve as shown in fig. 4, and to control the converter to operate in an asymmetric half-bridge flyback Mode (AHBF Mode) when the load current is greater than or equal to a first set value Io 1; when the load current is smaller than a first set value Io1 and larger than or equal to a second set value Io2, controlling the converter to work in a clamping asymmetric half-bridge flyback Mode (CAHBF Mode), and reducing the switching frequency along with the reduction of the load; when the load current is smaller than a second set value Io2, the converter is controlled to work in a Burst Mode (CAHBF Mode). The mode switching method can ensure optimal efficiency under heavy load, can realize effective control on the negative peak value of the exciting inductance current under light load, and greatly improves the light load efficiency of the converter, so that the asymmetrical half-bridge flyback converter can keep better efficiency under both light load and heavy load.
The chinese patent "switching variable power supply device" with application number 201911352361.1 effectively solves the problem of low light load efficiency of the asymmetric half-bridge flyback converter, but the proposed mode switching method still has the following two problems:
1. only considering the influence of the load current on the working mode of the converter, when the converter is applied to the occasion of fixed input voltage, the system efficiency in the range from light load to heavy load under the fixed input voltage is better, but when the input voltage of the converter is in a range, especially the application occasion of wide input voltage, for the same load, when the input voltage is increased, if the switching frequency is still kept unchanged, the turn-off loss of the switching tube and the loss of the transformer are correspondingly increased, so that the system efficiency is reduced when the input voltage is increased. Therefore, the method of switching the modes only by the load current has a problem that the system efficiency in a wide input voltage range cannot be considered at the same time.
A60W asymmetrical half-bridge flyback converter sample model is designed and manufactured according to the input and output specifications listed in Table 1. Through efficiency optimization tests of a prototype, the switching frequency, the load current and the input voltage are in a curve relation shown in fig. 5 when the prototype works in an optimal efficiency state under different loads and different input voltages, and therefore the problem that the system efficiency in a wide input voltage range cannot be considered simultaneously only by carrying out mode switching through the load current is further verified.
TABLE 1
| Input voltage range | 85VAC-264VAC (bus voltage range is about 120VDC-370VDC) |
| Output specification | Vo＝12V、Io＝5A、Po＝60W |
| |
30 kHz-300 kHz (full load 300kHz) |
2. When the load is lower than the second set value, especially when the converter is in idle operation, if the converter still operates in the asymmetric half-bridge flyback mode with a lower fixed switching frequency, the problem of large idle loss exists.
Disclosure of Invention
In view of this, the present invention provides a mode switching method for a switching converter, which can effectively solve the problem that the existing mode switching method cannot give consideration to both the problem of high efficiency in a wide input voltage range and the problem of high no-load loss.
The invention conception of the application is as follows: the input voltage is introduced, the mode switching is determined by the input voltage and the load together, and in addition, when the load is light enough, the system works in a Burst mode.
In order to solve the technical problem, the present invention provides a mode control method for a switching converter, which is used for controlling an operation mode of an asymmetric half-bridge flyback converter, wherein the asymmetric half-bridge flyback converter comprises a main switching tube, an auxiliary switching tube, a transformer and a unidirectional clamp circuit, and the method comprises the following steps:
controlling the working mode of the asymmetric half-bridge flyback converter according to the input voltage and the load information;
under a certain input voltage, when the load is greater than or equal to a first load set value, the controller controls the asymmetric half-bridge flyback converter to work in an asymmetric half-bridge flyback mode with fixed switching frequency;
when the load is smaller than the first load set value and larger than or equal to the second load set value, the controller controls the asymmetric half-bridge flyback converter to work in a clamping asymmetric half-bridge flyback mode, and the switching frequency of the asymmetric half-bridge flyback converter linearly decreases along with the reduction of the load;
when the load is smaller than a second load current set value, the controller controls the asymmetric half-bridge flyback converter to work in an intermittent wave-sending mode;
the first load set value is larger than the second load set value, and the higher the input voltage is, the larger the first load set value is.
In one embodiment, the input voltage is a positive bus voltage of the asymmetric half-bridge flyback converter or a drain voltage of the main switch or a drain voltage of the auxiliary switch during conduction of the main switch; the load information is the load current of the asymmetric half-bridge flyback converter or an output voltage isolation feedback signal capable of reflecting the magnitude of the load current.
In one embodiment, the second load settings for different input voltages are the same.
In one embodiment, when the load is less than or equal to the second load setting value, the controller controls the asymmetric half-bridge flyback converters to operate in the intermittent wave-generating mode at different input voltages.
In one embodiment, the lowest switching frequency of the switching frequencies is above the human hearing range.
The present invention also provides a switching converter, the switching power supply including:
an asymmetric half-bridge flyback converter, an input end of which is configured to be connected with an input voltage and an output end of which is configured to be connected with a load;
an input voltage sampling module configured to collect an input voltage;
a load sampling module configured to collect load information;
the controller is configured to confirm a first load set value according to the input voltage, wherein the larger the input voltage is, the larger the corresponding first load set value is, and is configured to control the working mode of the symmetrical half-bridge flyback converter according to the load information;
under a certain input voltage, when the load is greater than or equal to a first load set value, the controller controls the asymmetric half-bridge flyback converter to work in an asymmetric half-bridge flyback mode with fixed switching frequency;
when the load is smaller than a first load set value and larger than or equal to a second load set value, the controller asymmetric half-bridge flyback converter works in a clamping asymmetric half-bridge flyback mode, and the switching frequency of the asymmetric half-bridge flyback converter linearly decreases along with the reduction of the load, wherein the first load set value is larger than the second load set value;
and when the load is smaller than the second load current set value, the controller controls the asymmetric half-bridge flyback converter to work in an intermittent wave-sending mode.
The present invention further provides a mode control method of a switching converter, which includes:
a load detection step, which is to detect the load size of the asymmetric half-bridge flyback converter;
an input voltage detection step, which is used for detecting the input voltage of the asymmetric half-bridge flyback converter;
a load set value determining step of determining a first load set value according to the detected magnitude of the input voltage, wherein the larger the input voltage is, the larger the first load set value is;
a working mode control step, under a certain input voltage, controlling the working mode of the asymmetric half-bridge flyback converter to be any one of an asymmetric half-bridge flyback mode with fixed switching frequency, a clamping asymmetric half-bridge flyback mode or an intermittent wave generation mode according to the load size;
when the load is greater than or equal to a first load set value, controlling the asymmetric half-bridge flyback converter to work in an asymmetric half-bridge flyback mode with fixed switching frequency;
when the load is smaller than a first load set value and larger than or equal to a second load set value, controlling the asymmetric half-bridge flyback converter to work in a clamping asymmetric half-bridge flyback mode, and linearly reducing the switching frequency of the asymmetric half-bridge flyback converter along with the reduction of the load, wherein the first load set value is larger than the second load set value;
and when the load is smaller than the second load current set value, controlling the asymmetric half-bridge flyback converter to work in an intermittent wave-sending mode.
In one embodiment, in the load detection step, the load magnitude is detected by detecting the load current of the asymmetric half-bridge flyback converter or an output voltage isolation feedback signal capable of reflecting the load current magnitude.
In one embodiment, in the load set value adjusting step, the input voltage is segmented according to the detected magnitude of the input voltage, and the input voltages in the same segment of voltage range correspond to the same first load set value.
Interpretation of terms:
asymmetric half-bridge flyback mode: in a switching cycle period, the main switch and the auxiliary switch are complementarily turned on, and the controller controls the one-way clamping network to be always in an off state, which is abbreviated as AHBF Mode in english.
Clamped asymmetric half-bridge flyback mode: in one switching cycle, the main switch, the auxiliary switch and the unidirectional clamping network are alternately switched on or off, and specifically, each cycle comprises five stages: an excitation stage, an auxiliary switch zero voltage switching-on stage, a demagnetization stage, a current clamping stage and a main switch zero voltage switching-on stage; in the excitation stage and the auxiliary switch zero voltage switching-on stage, the one-way clamping network is switched off; in the demagnetization stage, the auxiliary switch is switched on, the one-way clamping network can be switched on or off, and no current flows through the one-way clamping network; at the end of the stage, when the exciting inductance current reaches a set value, the auxiliary switch is turned off, the one-way clamping network is in a conducting state, and the clamping current flows through the one-way clamping network; in the current clamping stage, the one-way clamping network is switched on, the clamping current flows through the one-way clamping network, the one-way clamping network keeps the clamping current basically unchanged, and the one-way clamping network is switched off at the end moment of the current clamping stage; at the stage of the main switch zero voltage switching-on, the unidirectional clamping network is switched off, the clamping current in the unidirectional clamping network is released, the voltage of the main switch is reduced to zero or close to zero, the main switch is controlled to be switched on at the moment, and the main switch zero voltage switching-on, which is called CAHBF Mode for short in English, is realized.
Burst mode: also known as intermittent Mode, the converter operates continuously in CAHBF Mode for several switching periods, and then stops for several switching periods, so that in such a cycle, during the power switch stop period, the output energy is provided by the output capacitor.
The working principle of the invention is analyzed by combining with the specific embodiment, which is not described herein, and the beneficial effects of the invention are as follows:
1. the system efficiency of the asymmetric half-bridge flyback converter is better in the full-voltage and full-load range;
2. the asymmetric half-bridge flyback converter has lower loss when the converter is in idle load.
Drawings
Fig. 1 is a circuit block diagram of a prior asymmetric half-bridge flyback switching converter;
fig. 2 is a schematic diagram of mode switching of a conventional asymmetric half-bridge flyback switching converter;
fig. 3 is a circuit diagram of a switching converter of chinese patent 201911352361.1;
FIG. 4 is a schematic diagram illustrating mode switching of the switching converter of Chinese patent 201911352361.1;
fig. 5 is a mode switching curve when the efficiency of the 60W asymmetric half-bridge flyback converter is optimal;
fig. 6 is a circuit block diagram of an asymmetric half-bridge flyback converter according to the present invention;
fig. 7 is a schematic diagram of mode switching of an asymmetric half-bridge flyback converter according to the present invention;
fig. 8 is a schematic diagram of an equivalent circuit of the asymmetric half-bridge flyback converter of the present invention;
fig. 9 is a diagram of typical operating waveforms of an asymmetric half-bridge flyback converter operating in a CAHBF mode;
fig. 10 is a graph of the measured efficiency of a 240W asymmetric half-bridge flyback converter using the mode switching method of the present invention.
Detailed Description
In order to make the present invention more clearly understood, the following description will be made more clearly and completely in conjunction with the accompanying drawings and the specific embodiments.
Referring to fig. 6, a switching converter includes: an asymmetric half-bridge flyback converter and a controller.
The asymmetric half-bridge flyback converter (hereinafter referred to as a converter) comprises an input capacitor Cin, a main switch tube S1, an auxiliary switch tube S2, a resonant capacitor Cr, a unidirectional clamping network, a transformer, a rectifier switch D, an output filter capacitor Co, an output voltage isolation sampling module and an input voltage sampling module.
The output voltage isolation sampling module is a load sampling module and is provided with two input ends and an output end, and the two input ends are respectively connected with an output filter capacitor C of the asymmetric half-bridge flyback converter0The positive pole and the negative pole of the voltage divider are connected, one output end of the voltage divider is connected with an input end FB of the controller and used for collecting output voltage isolation feedback signals, outputting the output voltage isolation feedback signals to the controller, controlling the output voltage to be stable and reflecting load information at the same time so as to be used for switching subsequent modes.
The input voltage sampling module is provided with an input end and an output end, and the input end V1The positive bus is electrically connected and used for detecting input voltage; output end V2And controller input terminal VdcAnd the electric coupling is used for sampling the input voltage of the converter and conditioning the input voltage into a value which can be identified by the controller for subsequent mode switching.
The controller is provided with an input end VdcInput terminal FB and output terminal GS1And an output terminal GS2And an output terminal GS3。
Input terminal VdcAnd the output end V of the input voltage sampling module2Electrically connected; the input end FB is electrically connected with the output voltage isolation feedback signal; output terminal GS1Is electrically connected with the grid electrode of the main switching tube S1, and the output end GS1The driving circuit is used for outputting a driving signal Vgs1 to the main switch tube S1 to control the main switch tube S1 to be switched on or switched off; output terminal GS2Electrically connected with the grid electrode of the auxiliary switch tube S2, and an output end GS2The auxiliary switch tube S2 is used for outputting a driving signal Vgs2 to control the auxiliary switch tube S2 to be switched on or switched off; output terminal GS3The grid electrode of the switching tube S3 of the unidirectional clamping network is electrically connectedIs connected to and output end GS3And the switching tube S3 is used for outputting a driving signal Vgs3 to the unidirectional clamping network to control the switching tube S3 to be switched on or switched off. In the present embodiment, the drive signal Vgs1, the drive signal Vgs2, and the drive signal Vgs3 are PWM signals, respectively.
The controller is mainly used for outputting voltage stabilization and switching modes, and on one hand, the controller carries out output voltage closed-loop control according to an output voltage isolation feedback signal output by the output voltage isolation sampling module; on the other hand, the controller controls the working mode of the converter according to the mode switching curve shown in fig. 7 according to the input voltage signal output by the input voltage sampling module and the output voltage isolation feedback signal (load information) output by the output voltage isolation sampling module; the controller outputs gate driving signals Vgs1, Vgs2 and Vgs3 for controlling a main switch tube S1, an auxiliary switch tube S2 and a switch tube S3 of the unidirectional clamping network so as to realize output voltage stabilization and mode control.
The mode control process is that under a certain voltage and when the load is heavy, the controller controls the converter to work in an AHBF mode; when the load is lightened, the controller controls the converter to work in a CAHBF mode, and the switching frequency is reduced along with the reduction of the load; when the load is further relieved, the controller controls the converter to work in a Burst mode. When the input voltage rises, the controller correspondingly reduces the switching frequency for the same load point so as to offset the efficiency loss caused by the rising of the input voltage.
The mode control method of the switching converter according to the present invention will be specifically described below with reference to fig. 6 and 7.
The mode control method of the switching converter of the present invention is characterized in that: the mode control curve is determined by the input voltage and the load information. The control method specifically comprises the following steps:
and a load detection step, wherein the load size of the asymmetric half-bridge flyback converter is detected. In the embodiment, the load size is detected by collecting an output voltage isolation feedback signal capable of reflecting the load current size.
And an input voltage detection step, namely detecting the size of the input voltage of the asymmetric half-bridge flyback converter.
A load set value determining step of determining a first load set value according to the detected magnitude of the input voltage, wherein the higher the input voltage is, the larger the first load set value of the mode switching curve of the input voltage is (V)load3>Vload2>Vload1) (ii) a The mode switching curves corresponding to different input voltages have the same second load set value, and the second load set value is smaller than the first load set value. In other implementations, the input voltage may be segmented, and the input voltages in the same segment voltage range correspond to the same first load setting value.
And a working mode control step, wherein under a certain input voltage, the working mode of the converter is controlled to be any one of an asymmetric half-bridge flyback mode with fixed switching frequency, a clamping asymmetric half-bridge flyback mode or an intermittent wave generation mode according to the load size.
Specifically, the method comprises the following steps: different input voltages correspond to different mode control curves (V)in1<Vin2<Vin3) (ii) a Under a certain input voltage, when the load is greater than or equal to a first load set value (such as V)in1V corresponding to timeload1、Vin2V corresponding to timeload2、Vin3V corresponding to timeload3) The controller operates the converter at a maximum switching frequency fmaxAHBF mode of (1); when the output load is less than the first load set value and greater than or equal to the second load set value (V)load0) When the controller makes the converter work in CAHBF mode, the switching frequency decreases linearly with the load reduction, and the lowest switching frequency fminAbove the human auditory range (normally, the human ear cannot hear sounds above the 20KHZ frequency); when the load is smaller than the second load set value, the controller enables the converter to work in a Burst mode.
Preferably, when the load is less than or equal to the second load set value, the different input voltage down-converters are all operated in Burst mode.
Referring to fig. 8 and 9, exemplary waveforms for operating the converter in the CAHBF mode include five phases per cycle: the excitation stage, the auxiliary switch zero voltage switching-on stage, the demagnetization stage, the current clamping stage and the main switch zero voltage switching-on stage. The working principle of each cycle is as follows:
and (3) excitation stage: from the time t0 to the time t1, the main switching tube S1 is controlled to be switched on, the input voltage Vin charges the resonant capacitor Cr, the resonant inductor Lr and the excitation inductor Lm, the excitation inductor current ILm and the resonant inductor current ILr rise linearly, namely the input voltage Vin excites the transformer, in the stage, the driving signals Vgs2 and Vgs3 are low level, and the auxiliary switching tube S2 and the unidirectional clamping network Sow are switched off;
and (3) auxiliary switch zero voltage switching-on stage: from the time t1 to the time t2, the main switching tube S1 is controlled to be turned off, the capacitor C1, the capacitor C2, the resonant inductor Lr and the excitation inductor Lm form series resonance, the resonant inductor current ILr charges the capacitor C1 and discharges the capacitor C2, so that the voltage VC1 at two ends of the capacitor C1 rises, the voltage VC2 at two ends of the capacitor C2 falls, the capacitor C2 finishes discharging, the VC2 falls to zero, the diode D2 is naturally turned on, the resonant inductor current ILr flows through the diode D2, the auxiliary switching tube S2 is controlled to be turned on at the time t2, and the auxiliary switching tube S2 achieves zero-voltage turning-on. At this stage, the driving signal Vgs3 is still at a low level, and the unidirectional clamp network Sow is turned off;
and (3) demagnetizing: from the time t2 to the time t3, the auxiliary switching tube S2 is controlled to be connected, the main switching tube S1 is continuously switched off, the rectifier switch D is connected, the current I2 of the rectifier switch D is increased, the voltage at two ends of the excitation inductor Lm is clamped, the voltage is negative at the top and positive at the bottom, the excitation inductor current ILm is linearly reduced, the transformer is demagnetized, and the auxiliary switching tube S2 is controlled to be switched off when the excitation inductor current reaches a set value at the time t 3. At this stage, the driving signal Vgs3 is at a high level, the unidirectional clamp network Sow is turned on, the turn-on time of the unidirectional clamp network Sow may be any time between t2 and t3 (i.e., the unidirectional clamp network Sow between t2 and t3 may be turned on or off), and since the unidirectional clamp network Sow only allows current to flow from the anode to the cathode, no current flows through the unidirectional clamp network Sow in this process;
a current clamping stage: from the time t3 to the time t4, at the time t3, the auxiliary switching tube S2 is turned off, the unidirectional clamping network Sow continues to be turned on, the capacitor C1, the capacitor C2, the resonant capacitor Cr and the resonant inductor Lr form series resonance, the resonant inductor current ILr is negative and rapidly and positively increases, the capacitor C1 is discharged and the capacitor C2 is charged, so that the voltage VC1 at the two ends of the capacitor C1 decreases and the voltage VC2 at the two ends of the capacitor C2 increases until the VC2 increases and becomes the same as the voltage VCr, the anode voltage of the unidirectional clamping network Sow is zero, the exciting inductor current ILm and the resonant inductor current ILr are equal, the rectifier switch D is turned off, the exciting inductor current ILm (or clamping current) naturally flows to the cathode through the anode of the unidirectional clamping network Sow, the unidirectional clamping network Sow keeps the clamping current basically unchanged, and at the time t4, the driving signal Vgs3 becomes low level, and the unidirectional clamping network Sow;
a main switch zero voltage switching-on stage: starting from time t4 to time t5, turning off the unidirectional clamp network Sow at time t4, keeping the main switch tube S1 and the auxiliary switch tube S2 in an off state, releasing clamp current held by the unidirectional clamp network Sow, continuously discharging the capacitor C1, continuously charging the capacitor C2, continuously decreasing the voltage VC1 at two ends of the capacitor C1, continuously increasing the voltage VC2 at two ends of the capacitor C2 until the voltage at two ends of the capacitor C1 drops to zero, starting to flow through the diode D1 by clamp current, turning on the driving signal Vgs1 to a high level at time t5, turning on the main switch tube S1, and turning on the main switch tube S1 at a zero voltage.
When converter work in AHBF mode, in a switching cycle period, the clamp switch tube is in the off-state all the time, and main switch tube and auxiliary switch tube complementary work, every cycle period contains four stages: an excitation stage, an auxiliary switch zero voltage switching-on stage, a demagnetization stage and a main switch zero voltage switching-on stage.
The working principle of the excitation stage and the auxiliary switch zero voltage switching-on stage is the same as that of the CAHBF mode, and the description is omitted here. The working principle of the demagnetization stage and the main switch zero voltage switching-on stage of the AHBF mode is as follows:
and (3) demagnetizing: keeping the auxiliary switch tube S2 on, turning off the main switch tube S1, turning on the rectifier switch D, increasing the current I2 of the rectifier switch D, clamping the voltage at two ends of the excitation inductor Lm, linearly reducing the excitation inductor current ILm, demagnetizing the transformer, and controlling the auxiliary switch tube S2 to turn off when the excitation inductor current reaches a set value. At this stage, the driving signal Vgs3 is low, and the unidirectional clamp network Sow is turned off.
A main switch zero voltage switching-on stage: the main switch tube S1 and the auxiliary switch tube S2 are kept in an off state, the capacitor C1, the capacitor C2, the resonant capacitor Cr and the resonant inductor Lr form series resonance, the resonant inductor current ILr is negative, and rapidly and positively increases, the capacitor C1 is discharged, the capacitor C2 is charged, the voltage VC1 at the two ends of the capacitor C1 is reduced, the voltage VC2 at the two ends of the capacitor C2 is increased, and when the voltage VC2 is increased and is the same as the voltage VCr, the excitation inductor current ILm and the resonance inductor current ILr are equal, the rectifier switch D is turned off, the excitation inductor current ILm and the resonance inductor current ILr are released, and the capacitor C1 continues to be discharged and the capacitor C2 continues to be charged, the voltage VC1 at the two ends of the capacitor C1 continues to fall, the voltage VC2 at the two ends of the capacitor C2 continues to rise until the voltage at the two ends of the capacitor C1 falls to zero, the resonant inductor current ILr starts to flow through the diode D1, at this time, the main switch tube S1 is controlled to be conducted, and the main switch tube S1 realizes zero-voltage switching-on.
A 240W converter prototype using the mode switching method of the present invention was designed and manufactured according to the input/output specifications listed in table 2.
TABLE 2
| Input voltage range | 170VAC-264VAC (bus voltage range is about 240VDC-370VDC) |
| Output specification | Vo＝12V、Io＝20A、Po＝240W |
| Switching frequency range | 30 kHz-300 kHz (full load 300kHz) |
Fig. 10 shows that the measured efficiencies of the 240W converter in the full voltage and full load ranges are both above 90% when the model adopts the mode switching method of the scheme of the invention, and the system efficiency is better.
It should be noted that the mode switching method of the converter according to the embodiment of the present invention is implemented by changing the position of the resonant cavity of the converter, the connection manner of the unidirectional clamping network and the transformer, the input voltage detection manner, the load detection manner, and the like, and still falls within the protection scope of the present invention.
The resonant cavity position of the converter, the connection mode of the unidirectional clamping network and the transformer can be combined in various ways, and a great number of embodiments are provided in the Chinese patent with the application number of 201911352361.1 and the Chinese patent application with the application number of 201910513578.X, which belong to the scope of the converter disclosed by the invention.
The input voltage detection module can also be connected with the bus and the switch tube of the converter in various ways, including but not limited to the following two ways:
(1) the input end of the input voltage detection module is electrically connected with the drain electrode of the main switching tube S1, and the input voltage is reflected by sampling the voltage of the drain electrode of the main switching tube S1;
(2) the input end of the input voltage detection module is electrically connected with the source electrode of the main switch tube S1 and the drain electrode of the auxiliary switch tube S2, and the voltage at the point after the main switch tube S1 is conducted is sampled to reflect the input voltage.
Different implementations of the load information in the mode switching are possible, including but not limited to the following two ways:
(1) and a sampling resistor is added at the output end of the converter, the voltage of the load current on the resistor is used for directly reflecting the magnitude of the load current, and the voltage value is used as load information.
(2) And calculating the load current according to the circuit working condition and the circuit parameter, and taking the calculated load current as load information.
The above is only a preferred embodiment of the present invention, and it should be noted that the above preferred embodiment should not be considered as limiting the present invention, and it will be apparent to those skilled in the art that several modifications and decorations can be made without departing from the spirit and scope of the present invention, and these modifications and decorations should also be considered as the protection scope of the present invention, which is not described herein by way of example, and the protection scope of the present invention should be subject to the scope defined by the claims.
Claims (11)
1. A mode control method of a switching converter is used for controlling the working mode of an asymmetric half-bridge flyback converter, and the asymmetric half-bridge flyback converter is provided with a main switching tube, an auxiliary switching tube, a transformer and a one-way clamping circuit, and is characterized by comprising the following steps:
controlling the working mode of the asymmetric half-bridge flyback converter according to the input voltage and the load information;
under a certain input voltage, when the load is greater than or equal to a first load set value, the controller controls the asymmetric half-bridge flyback converter to work in an asymmetric half-bridge flyback mode with fixed switching frequency;
when the load is smaller than a first load set value and larger than or equal to a second load set value, the controller controls the asymmetric half-bridge flyback converter to work in a clamping asymmetric half-bridge flyback mode, and the switching frequency of the asymmetric half-bridge flyback converter linearly decreases along with the reduction of the load;
when the load is smaller than the second load current set value, the controller controls the asymmetric half-bridge flyback converter to work in an intermittent wave-generating mode;
wherein the first load setting value is greater than the second load setting value, and the higher the input voltage, the greater the first load setting value.
2. The mode control method of a switching converter according to claim 1, characterized in that: the input voltage is a positive bus voltage of the asymmetric half-bridge flyback converter or a drain voltage of the main switch or a drain voltage of the auxiliary switch during the conduction period of the main switch; the load information is the load current of the asymmetric half-bridge flyback converter or an output voltage isolation feedback signal capable of reflecting the magnitude of the load current.
3. The mode control method of a switching converter according to claim 1, characterized in that: the second load set values corresponding to different input voltages are the same.
4. Mode control method of a switching converter according to claims 3 and 4, characterized in that: and segmenting the input voltage, wherein the input voltage in the same segment of voltage range corresponds to the same first load set value.
5. The mode control method of a switching converter according to claim 1, characterized in that: when the load is smaller than or equal to the second load set value and under different input voltages, the controller controls the asymmetric half-bridge flyback converters to work in the intermittent wave-sending mode.
6. The mode control method of a switching converter according to claim 1, characterized in that: the lowest switching frequency of the switching frequencies is above the human hearing range.
7. A switching converter, characterized in that the switching power supply comprises:
an asymmetric half-bridge flyback converter, an input end of which is configured to be connected with an input voltage and an output end of which is configured to be connected with a load;
an input voltage sampling module configured to collect the input voltage;
a load sampling module configured to collect load information;
the controller is configured to confirm a first load set value according to the input voltage, wherein the larger the input voltage is, the larger the corresponding first load set value is, and is configured to control the working mode of the symmetrical half-bridge flyback converter according to the load information;
under a certain input voltage, when the load is greater than or equal to the first load set value, the controller controls the asymmetric half-bridge flyback converter to work in an asymmetric half-bridge flyback mode with a fixed switching frequency;
when the load is smaller than a first load set value and larger than or equal to a second load set value, the controller controls the asymmetric half-bridge flyback converter to work in a clamping asymmetric half-bridge flyback mode, and the switching frequency of the asymmetric half-bridge flyback converter is linearly reduced along with the reduction of the load, wherein the first load set value is larger than the second load set value;
when the load is smaller than the second load current set value, the controller controls the asymmetric half-bridge flyback converter to work in an intermittent wave-sending mode.
8. A method of mode control for a switching converter, comprising:
a load detection step, which is to detect the load size of the asymmetric half-bridge flyback converter;
an input voltage detection step, detecting the input voltage of the asymmetric half-bridge flyback converter;
a load set value determining step of determining a first load set value according to the detected magnitude of the input voltage, wherein the first load set value is larger as the input voltage is larger;
a working mode control step, under a certain input voltage, controlling the working mode of the asymmetric half-bridge flyback converter to be any one of an asymmetric half-bridge flyback mode with fixed switching frequency, a clamping asymmetric half-bridge flyback mode or an intermittent wave generation mode according to the load size;
when the load is greater than or equal to a first load set value, controlling the asymmetric half-bridge flyback converter to work in an asymmetric half-bridge flyback mode with fixed switching frequency;
when the load is smaller than a first load set value and larger than or equal to a second load set value, controlling the asymmetric half-bridge flyback converter to work in a clamping asymmetric half-bridge flyback mode, wherein the switching frequency of the asymmetric half-bridge flyback converter is linearly reduced along with the reduction of the load, and the first load set value is larger than the second load set value;
and when the load is smaller than the second load current set value, controlling the asymmetric half-bridge flyback converter to work in an intermittent wave-generating mode.
9. The mode control method of the switching converter according to claim 9, characterized in that: in the load detection step, the load size is detected by detecting the load current of the asymmetric half-bridge flyback converter or an output voltage isolation feedback signal capable of reflecting the load current size.
10. The mode control method of the switching converter according to claim 9, characterized in that: the second load set values corresponding to different input voltages are the same.
11. The mode control method of the switching converter according to claim 9, characterized in that: in the load set value adjusting step, the input voltage is segmented according to the detected magnitude of the input voltage, and the input voltages in the same voltage range correspond to the same first load set value.
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