CN113131748B - Control method and control device of flyback converter - Google Patents
Control method and control device of flyback converter Download PDFInfo
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- CN113131748B CN113131748B CN202110282874.0A CN202110282874A CN113131748B CN 113131748 B CN113131748 B CN 113131748B CN 202110282874 A CN202110282874 A CN 202110282874A CN 113131748 B CN113131748 B CN 113131748B
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- flyback converter
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- rectifying unit
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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
- H02M3/33569—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 several active switching elements
- H02M3/33576—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 several active switching elements having at least one active switching element at the secondary side of an isolation transformer
- H02M3/33592—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 several active switching elements having at least one active switching element at the secondary side of an isolation transformer having a synchronous rectifier circuit or a synchronous freewheeling circuit at the secondary side of an isolation transformer
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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
- H02M1/08—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
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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
Abstract
The invention provides a control method and a control device of a flyback converter, which judge whether the flyback converter works in a first working mode or a second working mode by detecting an input voltage signal or detecting the input voltage signal and output power. According to the invention, through mode switching, according to different input voltages or different input voltages and output loads, cost and efficiency under high-frequency application occasions can be taken into consideration, and compared with the traditional flyback mode, the scheme reduces the number of active clamp tubes on the primary side, thereby reducing the cost; meanwhile, quasi-resonance control can be realized under low input voltage, and ZVS is realized under high input voltage and different output power, so that switching loss is reduced, and efficiency is improved.
Description
Technical Field
The present invention relates to the field of switching converters, and in particular, to a method and an apparatus for controlling a flyback converter.
Background
The flyback converter is widely applied to a low-power switching power supply, and along with the development requirements of high frequency and small volume, the switching loss of the flyback converter is remarkably increased, especially under a specific high-voltage condition.
The quasi-resonance flyback converter (QRFflyback) can realize the wave trough conduction of the primary side main power switch unit and reduce the switching loss, has lower circuit cost and simple control method, and is a popular topological structure in the application occasions of the current low-power switch power supply. However, in high frequency applications, although the quasi-resonant flyback converter can achieve the trough conduction, the switching loss is larger and larger at high voltage input, which seriously affects the efficiency of the converter.
In order to further improve the operating frequency and achieve zero voltage conduction (abbreviated as ZVS in english) in the full voltage range, the skilled person proposes an active clamp flyback converter, the circuit schematic diagram of which is shown in fig. 1(a), fig. 1(b) is a working timing diagram of the active clamp flyback converter, and the ZVS of the primary side main power switch unit is achieved by turning on a clamp switching tube for a period of time by giving a G _ SA driving signal before the primary side main power switch unit is turned on, but the converter has one more clamp switching tube in a primary side clamping circuit, which increases the cost, and the control signal needs to be driven in a floating manner, the control is more complicated, and the clamp switching tube also has switching loss, so the advantages of the solution in the low-power application occasions are not obvious.
When the output power of the converter is small or the converter works in a high-frequency light-load mode, although the active clamp can realize ZVS of the primary-side main power switch unit, a certain negative current needs to be generated on the primary side, and the negative current increases along with the increase of the input voltage. This increases the effective value of the primary current, increases the copper and hysteresis losses of the transformer, and has no advantages in synchronous rectification under such operating conditions, even limits the up-conversion of the converter.
If the active clamp flyback converter controlled by the secondary side is adopted, as shown in fig. 2(a), the converter works in a continuous mode, and needs a secondary side rectification switch unit to be turned off for a period of time after demagnetization is finished so as to generate negative current to realize ZVS of a primary side main power switch unit, and the working timing diagram of the converter is shown in fig. 2 (b); or the secondary side rectifying switch unit is required to be switched on twice (two pulses) to realize ZVS of the primary side main power switch unit, and the operation timing diagram of the secondary side rectifying switch unit is shown in fig. 2 (c).
The control method of the control scheme is complex, and the ZVS of the primary side main power switch unit is realized by controlling the secondary side switch rectifying unit to be switched on twice (outputting double pulses), so that the MOS tube loss is increased; and when light load is output or small power is output, copper loss and iron loss of the transformer are additionally increased, so that the system efficiency is influenced.
The advantages of the above-mentioned prior art solutions in low power applications are therefore not obvious. Therefore, a more economical solution is needed to meet low power, wide input voltage range applications.
Disclosure of Invention
Therefore, the present invention aims to provide a control method and a control device for a flyback converter, which mainly solve the problem of loss of the conventional flyback converter under high-frequency and high-voltage working conditions, and are suitable for small-power occasions with small output current and can save cost.
In order to solve the technical problem, the technical scheme of the control method of the flyback converter provided by the invention is as follows:
a control method of a flyback converter is applicable to the flyback converter and comprises a primary side main power switch unit, a secondary side switch rectifying unit and a transformer; the flyback converter is characterized in that the flyback converter is controlled to work in one of the following modes according to the input voltage of the flyback converter, or the drain-source voltage of the secondary side switch rectifying unit, or the input voltage and the output power of the flyback converter, or the drain-source voltage and the output power of the secondary side switch rectifying unit:
a first operating mode: the secondary side switch rectifying unit is switched on once in a period of time after the demagnetization of the transformer is finished, negative excitation current of the secondary side is generated in the switching-on time, and the primary side main power switch unit is switched on after a period of dead time, so that zero voltage switching-on of the primary side main power switch unit is realized;
a second working mode: the secondary side switch rectifying unit is turned on once during transformer demagnetization to realize synchronous rectification of the secondary side switch rectifying unit.
Further, comparing the input voltage of the flyback converter or the drain-source voltage of the secondary side switch rectifying unit with a first threshold value; when the input voltage of the flyback converter or the drain-source voltage of a secondary side switch rectifying unit is larger than or equal to a first threshold value, controlling the flyback converter to work in a first working mode; and when the input voltage of the flyback converter or the drain-source voltage of the secondary side switch rectifying unit is smaller than a first threshold value, controlling the flyback converter to work in a second working mode.
Further, comparing the input voltage of the flyback converter or the drain-source voltage of the secondary side switch rectifying unit with a first threshold value, and comparing the output power of the flyback converter with a second threshold value; when the input voltage of the flyback converter or the drain-source voltage of a secondary side switch rectifying unit is larger than or equal to a first threshold and the output power is larger than or equal to a second threshold, controlling the flyback converter to work in a first working mode; and when the input voltage of the flyback converter or the drain-source voltage of the secondary side switch rectifying unit is smaller than a first threshold or the output power is smaller than a second threshold, controlling the flyback converter to work in a second working mode.
Further, when the flyback converter operates in the first operating mode, the amplitude of the secondary side negative excitation current is proportional to the amplitude of the input voltage of the flyback converter, that is, the width of the driving pulse of the secondary side switch rectifying unit is proportional to the amplitude of the input voltage of the flyback converter.
Further, the operation mode of the flyback converter is a discontinuous mode.
Correspondingly, the technical scheme of the control device of the flyback converter provided by the invention is as follows:
a control device of a flyback converter is applicable to the flyback converter and comprises a primary side main power switch unit, a secondary side switch rectifying unit and a transformer; the method is characterized in that: the control device controls the flyback converter to work in one of the following modes according to the input voltage of the flyback converter, or the drain-source voltage of the secondary side switch rectifying unit, or the input voltage and the output power of the flyback converter, or the drain-source voltage and the output power of the secondary side switch rectifying unit:
a first operating mode: the secondary side switch rectifying unit is switched on once in a period of time after the demagnetization of the transformer is finished, negative excitation current of the secondary side is generated in the switching-on time, and the primary side main power switch unit is switched on after a period of dead time, so that zero voltage switching-on of the primary side main power switch unit is realized;
a second working mode: the secondary side switching rectifying unit is switched on once during demagnetization of the transformer so as to realize synchronous rectification of the secondary side switching rectifying unit.
Further, comparing the input voltage of the flyback converter or the drain-source voltage of the secondary side switch rectifying unit with a first threshold value; when the input voltage of the flyback converter or the drain-source voltage of a secondary side switch rectifying unit is larger than or equal to a first threshold value, controlling the flyback converter to work in a first working mode; and when the input voltage of the flyback converter or the drain-source voltage of the secondary side switch rectifying unit is smaller than a first threshold value, controlling the flyback converter to work in a second working mode.
Further, comparing the input voltage of the flyback converter or the drain-source voltage of the secondary side switch rectifying unit with a first threshold value, and comparing the output power of the flyback converter with a second threshold value; when the input voltage of the flyback converter or the drain-source voltage of a secondary side switch rectifying unit is larger than or equal to a first threshold value and the output power is larger than or equal to a second threshold value, controlling the flyback converter to work in a first working mode; and when the input voltage of the flyback converter or the drain-source voltage of the secondary side switch rectifying unit is smaller than a first threshold or the output power is smaller than a second threshold, controlling the flyback converter to work in a second working mode.
Further, when the flyback converter operates in the first operating mode, the amplitude of the secondary side negative excitation current is directly proportional to the amplitude of the input voltage of the flyback converter, that is, the width of the driving pulse of the secondary side switch rectifying unit is directly proportional to the amplitude of the input voltage of the flyback converter.
Further, the operation mode of the flyback converter is an intermittent mode.
Compared with the prior art, the invention has the following beneficial effects:
(1) through mode switching, cost and efficiency under high-frequency application occasions can be considered, and compared with a traditional flyback mode, the scheme reduces active clamp tubes on the primary side, so that cost is reduced;
(2) quasi-resonance control can be realized under low input voltage, and ZVS is realized under high input voltage and different output power, so that switching loss is reduced, and efficiency is improved;
(3) the control mode is switched only according to the sampling input voltage or the input voltage and the output power, the control is simple, and the mode switching in a low-power application occasion can be realized;
(4) the secondary side controller and the primary side controller can independently exist and control, and the application is flexible and changeable.
Drawings
Fig. 1(a) is a schematic diagram of a prior art active clamp flyback circuit controlled on the primary side;
fig. 1(b) is a timing diagram of active clamp flyback operation controlled on the primary side in the prior art;
fig. 2(a) is a schematic diagram of a prior art active clamp flyback circuit controlled on the secondary side;
FIG. 2(b) is a timing diagram of the operation of a single pulse controlled on the secondary side according to the prior art;
FIG. 2(c) is a timing diagram of two pulse operations controlled on the secondary side according to the prior art;
fig. 3 is a schematic circuit diagram of a flyback converter according to a first embodiment of the present invention;
fig. 4 is a flowchart of a switching method of the flyback converter according to the first embodiment of the present invention;
fig. 5 is a waveform diagram illustrating a switching method of the flyback converter according to the first embodiment of the present invention;
fig. 6 is a schematic circuit diagram of a flyback converter according to a second embodiment of the present invention;
fig. 7 is a flowchart of a switching method of a flyback converter according to a second embodiment of the present invention;
fig. 8 is a schematic circuit diagram of a flyback converter according to a third embodiment of the present invention;
fig. 9 is a flowchart of a first switching method of a flyback converter according to a third embodiment of the present invention;
fig. 10 is a flowchart of a second switching method of a flyback converter according to a third embodiment of the present invention.
Detailed Description
Exemplary embodiments that embody features and advantages of the present disclosure will be described in detail in the following description in conjunction with the accompanying drawings. It is to be understood that the disclosure is capable of various modifications in various embodiments without departing from the scope of the disclosure, and that the description and drawings are to be taken as illustrative of the modifications in nature, and not as limiting the disclosure.
The signal codes and the like according to the present invention are many and will be described in detail as follows:
vin: an input voltage of the flyback converter;
vout: an output voltage of the flyback converter;
vin _ s: inputting a voltage detection signal;
vth _ vin 1: a first threshold value;
vth _ vo 1: second threshold value
Vds _ SP: a primary side main power switch unit drain-source voltage;
vds _ SR: the voltage at two ends of the secondary side switch rectifying unit;
FB: outputting a power detection signal;
SW primary side main power switch unit control signal;
g _ S2: isolating a front secondary side switch rectifying unit control signal;
g _ SR: isolating a rear secondary side switch rectifying unit control signal;
co: an output capacitor;
Δ t 1: a first dead time;
Δ t 2: a second dead time;
iset: setting a threshold value for the secondary side negative excitation current;
i _ p: primary side excitation current;
i _ np: a primary side negative excitation current;
i _ s: a secondary side excitation current;
i _ ns: a secondary side negative excitation current;
n: the primary side and secondary side turn ratio of the transformer;
204: a clamp circuit;
210: inputting a voltage;
220: a transformer;
230: a secondary side switch rectifying unit;
240: a primary side controller;
241: an isolation circuit;
242: a secondary-side controller;
250: primary side main power switch unit.
First embodiment
Fig. 3 is a schematic circuit diagram of a flyback converter according to a first embodiment of the present invention, where the flyback converter of fig. 3 includes a primary-side main power switch unit 250, a secondary-side switch rectifying unit 230, a transformer T1, a clamp circuit 204, a feedback circuit 243, an output capacitor Co, and a control device according to the present invention; the control means includes a primary side controller 240, an isolation circuit 241, a secondary side controller 242, and a feedback circuit 243; the primary controller 240 detects an input voltage to generate an input voltage detection signal Vin _ S, the feedback circuit 243 detects an output power to generate an output power detection signal FB, and outputs the output power detection signal FB to the primary controller 240, the primary controller 240 generates a control signal SW according to the input voltage detection signal Vin _ S and the output power detection signal FB to control the primary main power switch unit 250 to be turned on and off, and the primary controller 240 determines an operation mode of the flyback converter according to the input voltage detection signal Vin _ S to generate another control signal G _ S2, and generates a control signal G _ SR to the secondary controller 242 to control the secondary switch rectifying unit 230 to be turned on and off through the isolation circuit 241.
Fig. 4 is a flowchart of a switching method of a flyback converter according to a first embodiment of the present invention, which is directed to a control method and a control device of an economical flyback converter suitable for a low power application. In order to overcome the higher loss caused by hard switching of the primary side main power switch unit 250 when the input voltage is higher, in the present embodiment, when the input voltage detection signal Vin _ S is greater than or equal to the first threshold Vth _ Vin1, the flyback converter is selected to operate in the first operating mode, the primary side controller 240 generates the control signal G _ S1 to control the primary side main power switch unit 250 to be turned on and off, and the primary side controller generates the control signal G _ S2 to the secondary side controller 242 through the isolation circuit 241 to generate the control signal G _ SR to control the secondary side switch rectifying unit 240 to be turned on once before the primary side main power switch unit 250 is turned on, so as to implement ZVS of the primary side main power switch unit 250. As shown in fig. 3, the direction indicated by the magnetizing inductance Lm in the figure is the forward magnetizing direction. In the first operation mode, because the switching loss is also generated during the turn-off process of the secondary side switching rectifying unit 230, the switching losses of the primary side main power switching unit 250 and the secondary side switching rectifying unit 230 are taken into consideration comprehensively, when the input voltage detection signal Vin _ S is smaller than the first threshold value Vth _ Vin1, the flyback converter is selected to operate in the second operation mode, the primary side controller 240 generates the control signal G _ S2, and the control signal G _ SR is generated to the secondary side controller 242 through the isolation circuit 241 to control the secondary side switching rectifying unit 230 to implement synchronous rectification when the transformer T1 is demagnetized.
In the switching process, the primary side and the secondary side are simple in structure and control and easy to operate and realize, and the problem that the hard switching loss of the primary side main power switch unit is large under high input voltage can be solved.
Each cycle of the first operating mode of the flyback converter in this embodiment is shown in the left half of fig. 5, and is divided into four stages, which are analyzed as follows:
in the first phase (t0-t1), the primary side control signal SW output by the primary side controller 240 is at a high level, the primary side main power switch unit 250 is controlled to be turned on, and the primary side excitation current I _ p is generated to flow in the forward direction in the primary winding; after the first phase is finished, the primary side control signal SW is at a low level, the primary side main power switch unit 250 is turned off, and after a first dead time Δ t1(t1-t2), the flyback converter enters a second phase;
in the second stage (t2-t3), the primary side control signal SW and the secondary side switch rectifying unit control signal G _ SR are both at a low level, the primary side main power switch unit 250 and the secondary side switch rectifying switch unit 230 are both turned off, at this time, the flyback converter performs demagnetization freewheeling through a parasitic diode or a parallel diode of the secondary side switch rectifying unit 230, the secondary side excitation current I _ s decreases, when the secondary side excitation current I _ s decreases to 0, the second stage ends, and the flyback converter enters the third stage;
in the third stage (t3-t4), the primary side inductor resonates with the drain-source parasitic capacitor of the primary side main power switch unit 250, the secondary side inductor resonates with the drain-source parasitic capacitor of the secondary side switch rectifying unit 230 at the same time, the drain-source voltage Vds _ SP of the primary side main power switch unit 250 resonates to a peak, and at this time, when the voltage Vds _ SR at the two ends of the secondary side switch rectifying unit 230 resonates to a trough, the secondary side switch rectifying unit 230 is turned on, and the flyback converter enters the fourth stage;
in the fourth stage (t4-t5), a voltage is output to the secondary winding for reverse excitation, the secondary side excitation current is reversed to be a secondary side negative excitation current I _ ns, the secondary side negative excitation current I _ ns is detected, the secondary side negative excitation current I _ ns is compared with a secondary side negative excitation current setting threshold Iset, when the amplitude of the secondary side negative excitation current I _ ns is greater than the secondary side negative excitation current setting threshold Iset, the secondary side switch rectifying unit 230 is controlled to be turned off, and meanwhile, the primary side main power switch unit 250 is turned on after a set second dead time Δ t2(t5-t6) to realize zero-voltage switching.
At this point, the flyback converter ends a duty cycle and begins to enter the next duty cycle.
Each period of the second operation mode of the flyback converter in this embodiment is shown in the right half of fig. 5, and is a quasi-resonant (QR) operation mode known to those skilled in the art, or a low-frequency operation mode burst of a skip period, so that analysis is not performed.
As a specific analysis that the primary side main power switch unit 250 respectively realizes zero voltage switching in two operating modes, the following is:
when the flyback converter operates in the first operation mode, in the third stage, that is, after the demagnetization of the transformer T1 is completed, the excitation inductor resonates with the drain-source parasitic capacitor Cds of the primary-side main power switch unit 250. When the drain-source voltage Vds _ SP of the primary side main power switch unit 250 resonates to a peak, and at this time, the voltage Vds _ SR at the two ends of the secondary side switch rectifying unit 230 resonates to a trough, at this time, the primary side controller 240 controls the secondary side switch rectifying unit 230 to be turned on once through the isolation circuit 241, and during the turn-on period of the secondary side switch rectifying unit 230, the secondary side excitation current I _ s generated by the transformer is reversed to the secondary side negative excitation current I _ ns. The secondary-side switching rectifying unit 230 is turned off when the secondary-side negative-direction exciting current I _ ns reaches the secondary-side negative-direction exciting current setting threshold Iset. Since the secondary side switch rectifying unit 230 is turned off, the primary side generates a primary side negative excitation current I _ np, and the primary side negative excitation current I _ np participates in resonance of the excitation inductor and the drain-source junction capacitance Cds of the primary side main power switch unit 250, so as to realize zero-voltage turn-on of the primary side main power switch unit 250.
When the flyback converter operates in the second operating mode, after the primary side main power switching unit 250 is turned off for a period of time, the secondary side controller 242 controls the secondary side switching rectification unit 230 to be turned on, so as to implement synchronous rectification in the demagnetization stage of the transformer T1, and when the negative excitation current I _ ns of the secondary side falls to 0, the secondary side switching rectification unit 230 is turned off; after the demagnetization of the transformer T1 is completed, the exciting inductance resonates with the drain-source parasitic capacitance Cds of the primary side main power switching unit 250. When the drain-source voltage Vds _ SP of the primary side main power switch unit 250 resonates to the nth wave trough, and the drain-source voltage Vds _ SR of the secondary side switch rectifying unit resonates to the nth wave crest, the primary side controller 240 controls quasi-resonant turn-on of the primary side main power switch unit 250.
Preferably, the secondary side switching rectification unit 230 includes a transistor, or a transistor and a diode connected in parallel. In the second phase (t2-t3), the transistor included in the secondary side switching rectification unit 230 or the diode connected in parallel therewith can act as a transformer demagnetization freewheeling loop.
Preferably, the transistors included in the secondary side switching rectification unit 230 are enhancement type n-channel MOS transistors.
Preferably, when the flyback converter operates in the first operation mode for the fourth time period, the magnitude I _ ns of the negative-going excitation current on the secondary side is proportional to the magnitude of the input voltage Vin. That is, the secondary side switching rectifying unit 230 drives the pulse width in proportion to the magnitude of the input voltage Vin. The reason is that as the input voltage rises, the larger the driving pulse width is, the realization of ZVS of the primary side main power switch unit can be guaranteed, and at the moment, the ZVS of the primary side main power switch unit can be realized as long as the system works in the first working mode.
Preferably, when the flyback converter operates in the second operation mode, the second operation mode may be a quasi-resonant (QR) operation mode or a low-frequency operation mode burst of a skip cycle, which are commonly used in the art and will not be described in detail herein. It should be noted that the second operation mode refers to the operation state of the secondary-side switching rectifying unit 230, and the quasi-resonant (QR) operation mode or the low-frequency operation mode burst of the skip cycle describes the operation state of the primary-side main power switching unit 250, which are independently distinguished from each other, and the two operation modes do not conflict with each other.
Preferably, the input voltage detection signal Vin _ s may be obtained by directly dividing the voltage by a sampling resistor and a sampling resistor; or indirectly by detecting the drain-source voltage Vds _ SP and the output voltage of the primary side main power switch unit in the demagnetization stage of the transformer, and the related calculation formula is Vin _ s-Vds-N Vout.
Preferably, the operation mode of the flyback converter is a discontinuous mode. The reason is that the inverter can be operated at a set frequency by operating in the discontinuous mode, and the switching loss is reduced.
Preferably, the flyback converter is a passive-clamp flyback converter or an active-clamp flyback converter. The reason is that the production cost can be reduced by adopting a passive clamping mode, and the leakage inductance energy can be recovered by adopting an active clamping mode, so that the voltage spike of the primary side main power switch unit during working is reduced.
Second embodiment
Fig. 6 is a schematic circuit diagram of a flyback converter according to a second embodiment of the present invention, and fig. 6 is different from the first embodiment in that the embodiment determines the operation mode of the flyback converter through two signals, i.e., the input voltage detection signal Vin _ s and the output power detection signal FB.
Fig. 7 is a flowchart of a handover method according to a second embodiment of the present invention: when the input voltage detection signal Vin _ s is greater than or equal to the first threshold value Vth _ Vin1 and the output power detection signal FB is greater than or equal to the second threshold value Vth _ vo1, the flyback converter operates in the first operation mode; conversely, when the input voltage detection signal Vin _ s is smaller than the first threshold Vth _ Vin1 or the output power detection signal FB is smaller than the second threshold Vth _ vo1, the flyback converter operates in the second operation mode.
The waveform diagrams of the second and first operating modes and the second operating mode are the same as the first embodiment, and each cycle in the first operating mode is also divided into four stages, which are the same as the first embodiment and are not repeated herein.
Third embodiment
As shown in fig. 8, a schematic circuit diagram of a third embodiment of the present invention is different from the second embodiment in that the primary controller and the secondary controller operate independently, and the secondary side does not need to obtain a control signal from the primary controller, so that an isolation circuit 241 is not required, and the operating mode of the flyback converter does not need to be determined by detecting the input voltage.
The switching flow chart of the present embodiment is shown in fig. 9 or fig. 10.
By detecting the drain-source voltage Vds _ SR of the secondary side switch rectifying unit, when the Vds _ SR is greater than or equal to a first threshold Vth _ vin1, the flyback converter works in a first working mode. When Vds _ SR is less than the first threshold Vth-vin1, the flyback converter operates in the second operation mode, as shown in fig. 9.
Or when Vds _ SR is greater than or equal to the first threshold Vth _ vin1 and FB is greater than or equal to the second threshold Vth _ vo1, the flyback converter operates in the first operation mode. When Vds _ SR is less than the first threshold Vth-vin1 or FB is less than the second threshold Vth _ vo1, the flyback converter operates in the second operation mode, as shown in fig. 10.
In light of the above teachings, the present invention may be embodied in many other forms of modification, substitution, or alteration without departing from the spirit of the invention as set forth above, which fall within the scope of the claims.
Claims (6)
1. A control method of a flyback converter is applicable to the flyback converter and comprises a primary side main power switch unit, a secondary side switch rectifying unit and a transformer; the method is characterized in that: comparing the input voltage of the flyback converter or the drain-source voltage of a secondary side switch rectifying unit with a first threshold value; when the input voltage of the flyback converter or the drain-source voltage of a secondary side switch rectifying unit is larger than or equal to a first threshold value, controlling the flyback converter to work in a first working mode; when the input voltage of the flyback converter or the drain-source voltage of the secondary side switch rectifying unit is smaller than a first threshold value, controlling the flyback converter to work in a second working mode; or comparing the input voltage of the flyback converter or the drain-source voltage of the secondary side switch rectifying unit with a first threshold value, and comparing the output power of the flyback converter with a second threshold value; when the input voltage of the flyback converter or the drain-source voltage of a secondary side switch rectifying unit is larger than or equal to a first threshold and the output power is larger than or equal to a second threshold, controlling the flyback converter to work in a first working mode; when the input voltage of the flyback converter or the drain-source voltage of the secondary side switch rectifying unit is smaller than a first threshold or the output power is smaller than a second threshold, controlling the flyback converter to work in a second working mode;
wherein, the first working mode is as follows: the secondary side switch rectifying unit is switched on once in a period of time after the demagnetization of the transformer is finished, negative excitation current of the secondary side is generated in the switching-on time, and the primary side main power switch unit is switched on after a period of dead time so as to realize zero-voltage switching-on of the primary side main power switch unit;
wherein, the second working mode is: the secondary side switch rectifying unit is turned on once during transformer demagnetization to realize synchronous rectification of the secondary side switch rectifying unit.
2. The control method according to claim 1, characterized in that: when the flyback converter works in the first working mode, the amplitude of the secondary side negative excitation current is in direct proportion to the amplitude of the input voltage of the flyback converter, namely the width of the driving pulse of the secondary side switch rectifying unit is in direct proportion to the amplitude of the input voltage of the flyback converter.
3. The control method according to any one of claims 1 to 2, characterized in that: the operation mode of the flyback converter is an intermittent mode.
4. A control device of a flyback converter is applicable to the flyback converter and comprises a primary side main power switch unit, a secondary side switch rectifying unit and a transformer; the method is characterized in that: comparing the input voltage of the flyback converter or the drain-source voltage of a secondary side switch rectifying unit with a first threshold value; when the input voltage of the flyback converter or the drain-source voltage of a secondary side switch rectifying unit is larger than or equal to a first threshold value, controlling the flyback converter to work in a first working mode; when the input voltage of the flyback converter or the drain-source voltage of the secondary side switch rectifying unit is smaller than a first threshold value, controlling the flyback converter to work in a second working mode; or comparing the input voltage of the flyback converter or the drain-source voltage of the secondary side switch rectifying unit with a first threshold value, and comparing the output power of the flyback converter with a second threshold value; when the input voltage of the flyback converter or the drain-source voltage of a secondary side switch rectifying unit is larger than or equal to a first threshold value and the output power is larger than or equal to a second threshold value, controlling the flyback converter to work in a first working mode; when the input voltage of the flyback converter or the drain-source voltage of a secondary side switch rectifying unit is smaller than a first threshold value or the output power is smaller than a second threshold value, controlling the flyback converter to work in a second working mode;
wherein, the first working mode is: the secondary side switch rectifying unit is switched on once in a period of time after the demagnetization of the transformer is finished, negative excitation current of the secondary side is generated in the switching-on time, and the primary side main power switch unit is switched on after a period of dead time so as to realize zero-voltage switching-on of the primary side main power switch unit;
wherein, the second mode of operation is: the secondary side switch rectifying unit is turned on once during transformer demagnetization to realize synchronous rectification of the secondary side switch rectifying unit.
5. The control device according to claim 4, characterized in that: when the flyback converter works in the first working mode, the amplitude of the secondary side negative excitation current is in direct proportion to the amplitude of the input voltage of the flyback converter, namely the width of the driving pulse of the secondary side switch rectifying unit is in direct proportion to the amplitude of the input voltage of the flyback converter.
6. The control device according to any one of claims 4 to 5, characterized in that: the working mode of the flyback converter is a discontinuous mode.
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| CN113489328B (en) * | 2018-11-08 | 2024-02-27 | 立锜科技股份有限公司 | Zero-voltage switching control circuit, flyback power supply circuit and control method thereof |
| CN111628632B (en) * | 2019-02-28 | 2022-03-01 | 立锜科技股份有限公司 | Flyback power supply circuit and zero voltage switching control circuit and control method thereof |
| US11201554B2 (en) * | 2019-02-28 | 2021-12-14 | Richtek Technology Corporation | Flyback power converter and ZVS control circuit and control method thereof |
| CN212677084U (en) * | 2020-04-10 | 2021-03-09 | 杭州士兰微电子股份有限公司 | Flyback converter and control circuit thereof |
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