CN113708634A - Control method and control device of flyback converter - Google Patents
Control method and control device of flyback converter Download PDFInfo
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- CN113708634A CN113708634A CN202110725240.8A CN202110725240A CN113708634A CN 113708634 A CN113708634 A CN 113708634A CN 202110725240 A CN202110725240 A CN 202110725240A CN 113708634 A CN113708634 A CN 113708634A
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- flyback converter
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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
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- Power Engineering (AREA)
- Dc-Dc Converters (AREA)
Abstract
The invention discloses a control method and a control device of a flyback converter, which carry out switching control of a first working mode and a second working mode through input voltage detection or input voltage detection and output power detection, realize quasi-resonant turn-on of a primary side main power switch tube and synchronous rectification of a secondary side switch rectifying unit under low input voltage, and realize zero voltage turn-on of the primary side main power switch tube and synchronous rectification of the secondary side switch rectifying unit under high input voltage or a certain load above high input voltage. The invention has simple control and low circuit cost, and can give consideration to low cost and high efficiency in high-frequency application occasions.
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 a primary side main power switch tube 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 switching (abbreviated as ZVS in english) in the full voltage range, the skilled person proposes an active clamp flyback converter controlled on the primary side, 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 controlled on the primary side, and the ZVS of the primary side main power switching tube is achieved by providing a G _ SA driving signal to switch on the clamp switching tube for a period of time before the primary side main power switching tube is switched on. However, the converter has an additional clamp switching tube in the primary side clamping circuit, which increases the cost and is more complicated to control, and the clamp switching tube of the clamp circuit also has switching loss, so that the advantages of the solutions in low-power application occasions are not obvious.
When the output power of the converter is low or the converter works in a high-frequency light-load mode, although the primary side controlled active clamping flyback converter can realize ZVS of a primary side main power switch tube, a negative primary side inductive current is required to be generated on the primary side, and the current is increased along with the increase of input voltage, so that the effective value of the primary side inductive current is increased, and the copper loss and the hysteresis loss of a transformer are increased.
If a secondary side controlled active clamping flyback converter as shown in fig. 2(a) appears, and the working timing diagram of the converter is shown in fig. 2(b), the converter works in a continuous mode, and needs a secondary side synchronous rectifier to be turned off after the demagnetization of the transformer is finished for a certain time (i.e. a time period t2-t3 in fig. 2 (b)), the transformer is reversely excited in the time period to generate a negative secondary side inductive current I _ s, after the secondary side synchronous rectifier is turned off, the reverse excitation of the transformer is finished and the reverse demagnetization is started, because a negative secondary side inductive current I _ s is generated after the reverse excitation before the transformer is finished, the ZVS of a primary side main power switching tube can be realized through the negative secondary side inductive current I _ s, but the control method of the converter is complex, and frequency conversion control is needed to realize wide input voltage range, ZVS of a primary side main power switching tube in a load range increases copper loss and iron loss of the transformer on the contrary in a low output power or high-frequency light-load mode.
The advantages of the above-mentioned prior art solutions in low power applications are therefore not obvious. Therefore, a more economical solution is needed for 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.
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 tube, a secondary side switch rectifying unit and a transformer, and is characterized in that the flyback converter is controlled to work in one of the following modes according to input voltage or input voltage and output power of the flyback converter:
a first operating mode: the secondary side switch rectifying unit is switched on once after the primary side main power switch tube is switched off and before the primary side main power switch tube is switched on, wherein the secondary side switch rectifying unit is switched on for the first time after the primary side main power switch tube is switched off so as to realize synchronous rectification of the secondary side switch rectifying unit during the demagnetization period of the transformer; switching on for the second time before the primary side main power switching tube is switched on so as to realize zero voltage switching on of the primary side main power switching tube;
a second working mode: the secondary side switch rectifying unit is switched on once only after the primary side main power switch tube is switched off so as to realize the synchronous rectification of the secondary side switch rectifying unit.
Further, when the flyback converter works in a first working mode, the secondary side switch rectifying unit is firstly switched on when the transformer is demagnetized, the transformer is demagnetized in a synchronous rectification mode until the transformer is firstly switched off when the demagnetization is finished, after the demagnetization of the transformer is finished, an excitation inductor and a leakage inductor are connected in series, then the parasitic capacitance of a drain-source electrode of the primary side main power switch tube generates resonance, when the drain-source voltage of the primary side main power switch tube resonates to an mth wave peak, namely the drain-source voltage of the secondary side switch rectifying unit resonates to the mth wave peak, the secondary side switch rectifying unit is controlled to be switched on for the second time to generate a negative secondary side inductor current, the secondary side switch rectifying unit is switched off for the second time after the current reaches a set value, and the primary side main power switch tube is switched on after a period of dead time, so as to realize the zero-voltage switching-on of the primary side main power switch tube, wherein m is a positive integer.
Further, when the flyback converter works in a second working mode, the switching rectification unit on the secondary side is controlled to be switched on during the demagnetization of the transformer, after the demagnetization of the transformer is finished, the excitation inductor and the leakage inductor are connected in series, and then the parasitic capacitance of the drain-source electrode of the main power switching tube on the primary side resonates, when the voltage of the drain-source electrode of the main power switching tube on the primary side resonates to the nth wave trough, namely the voltage of the drain-source electrode of the switching rectification unit on the secondary side resonates to the nth wave crest, the quasi-resonant switching of the main power switching tube on the primary side is controlled to be switched on, wherein n is a positive integer.
Further, comparing an input voltage detection signal of the flyback converter with a first threshold value; when the input voltage detection signal is greater than or equal to a first threshold value, controlling the flyback converter to work in a first working mode; and when the input voltage detection signal is smaller than the first threshold value, controlling the flyback converter to work in a second working mode.
Further, comparing an input voltage detection signal of the flyback converter with a first threshold value, and comparing the output power of the flyback converter with a second threshold value; when the input voltage detection signal is greater than or equal to a first threshold value and the output power detection signal is greater than or equal to a second threshold value, controlling the flyback converter to work in a first working mode; and when the input voltage detection signal is smaller than the first threshold or the output power detection signal is smaller than the second threshold, controlling the flyback converter to work in a second working mode.
Further, an input voltage detection signal is obtained by directly dividing voltage through a sampling resistor, or indirectly obtained by detecting the drain-source voltage of a primary side main power switch tube and the detection output voltage at the demagnetization stage of the transformer, or indirectly obtained by detecting the drain-source voltage of a secondary side switch rectification unit and the detection output voltage at the excitation stage of the transformer; the output power detection signal is obtained by detecting the output voltage.
Further, when the flyback converter operates in the first operating mode, the amplitude of the negative secondary side inductor current is directly proportional to the amplitude of the input voltage of the flyback converter, that is, the width of the second on 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 flyback converter operates in a current chopping 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 tube, a secondary side switch rectifying unit and a transformer, and is characterized in that the control device controls the flyback converter to work in one of the following modes according to input voltage or the input voltage and output power of the flyback converter:
a first operating mode: the secondary side switch rectifying unit is switched on once after the primary side main power switch tube is switched off and before the primary side main power switch tube is switched on, wherein the secondary side switch rectifying unit is switched on for the first time after the primary side main power switch tube is switched off so as to realize synchronous rectification of the secondary side switch rectifying unit during the demagnetization period of the transformer; switching on for the second time before the primary side main power switching tube is switched on so as to realize zero voltage switching on of the primary side main power switching tube;
a second working mode: the secondary side switch rectifying unit is switched on once only after the primary side main power switch tube is switched off so as to realize the synchronous rectification of the secondary side switch rectifying unit.
Further, when the flyback converter works in a first working mode, the secondary side switch rectifying unit is firstly switched on when the transformer is demagnetized, the transformer is demagnetized in a synchronous rectification mode until the transformer is firstly switched off when the demagnetization is finished, after the demagnetization of the transformer is finished, an excitation inductor and a leakage inductor are connected in series, then the parasitic capacitance of a drain-source electrode of the primary side main power switch tube generates resonance, when the drain-source voltage of the primary side main power switch tube resonates to an mth wave peak, namely the drain-source voltage of the secondary side switch rectifying unit resonates to the mth wave peak, the secondary side switch rectifying unit is controlled to be switched on for the second time to generate a negative secondary side inductor current, the secondary side switch rectifying unit is switched off for the second time after the current reaches a set value, and the primary side main power switch tube is switched on after a period of dead time, so as to realize the zero-voltage switching-on of the primary side main power switch tube, wherein m is a positive integer.
Further, when the flyback converter works in a second working mode, the switching rectification unit on the secondary side is controlled to be switched on during the demagnetization of the transformer, after the demagnetization of the transformer is finished, the exciting inductor and the leakage inductor are connected in series, and then the parasitic capacitance of the drain-source electrode of the main power switching tube on the primary side resonates, when the voltage of the drain-source electrode of the main power switching tube on the primary side resonates to the nth wave trough, namely the voltage of the drain-source electrode of the switching rectification unit on the secondary side resonates to the nth wave crest, the quasi-resonant switching of the main power switching tube on the primary side is controlled to be switched on, wherein n is a positive integer.
Further, comparing an input voltage detection signal of the flyback converter with a first threshold value; when the input voltage detection signal is greater than or equal to a first threshold value, controlling the flyback converter to work in a first working mode; and when the input voltage detection signal is smaller than the first threshold value, controlling the flyback converter to work in a second working mode.
Further, comparing an input voltage detection signal of the flyback converter with a first threshold value, and comparing the output power of the flyback converter with a second threshold value; when the input voltage detection signal is greater than or equal to a first threshold value and the output power is greater than or equal to a second threshold value, controlling the flyback converter to work in a first working mode; and when the input voltage detection signal is smaller than the first threshold or the output power detection signal is smaller than the second threshold, controlling the flyback converter to work in a second working mode.
Further, an input voltage detection signal is obtained by directly dividing voltage through a sampling resistor, or indirectly obtained by detecting the drain-source voltage of a primary side main power switch tube and the detection output voltage at the demagnetization stage of the transformer, or indirectly obtained by detecting the drain-source voltage of a secondary side switch rectification unit and the detection output voltage at the excitation stage of the transformer; the output power detection signal is obtained by detecting the output voltage.
Further, when the flyback converter operates in the first operating mode, the amplitude of the negative secondary side inductor current is directly proportional to the amplitude of the input voltage of the flyback converter, that is, the width of the second on 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 flyback converter operates in a current chopping mode.
Compared with the prior art, the invention has the following beneficial effects:
(1) after the active clamp flyback converter is applied to the active clamp flyback converter controlled by the secondary side, compared with the existing active clamp flyback converter controlled by the secondary side, the control method is simpler, the working mode switching is carried out only by detecting the input voltage or the input voltage and the output power, the control is simple, and the mode switching under the low-power application occasion can be realized;
(2) the invention can also be applied to the flyback converter without adopting the active clamping technology, and compared with the active clamping flyback converter adopting primary side control in the prior art, the invention can reduce one clamping switch tube, but can also realize a primary side main power switch tube ZVS, and has low cost and high efficiency under the high-frequency application occasion;
(3) the invention can realize quasi-resonance control and synchronous rectification of the secondary side switch rectifying unit at low input voltage, and can realize synchronous rectification of the primary side main power switch tube ZVS and the secondary side switch rectifying unit at high input voltage or high input voltage and output power, thereby reducing loss;
(4) as a specific implementation mode of the control device, the first-time switching-on driving pulse of the secondary side switch rectifying unit can be generated after the primary side synchronous signal SR of the primary side controller enables the secondary side controller to detect the pulse or directly generated by the primary side synchronous signal SR through the secondary side controller, the control is flexible, the first-time switching-on and switching-off of the secondary side switch rectifying unit can be reliably realized, and the common use with a primary side main power switch tube is avoided.
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 ZVS waveform diagram for active clamped flyback implementation 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 waveform diagram of a prior art single pulse implementation of ZVS controlled on the secondary side;
fig. 3(a) is a schematic circuit diagram of a flyback converter according to a first embodiment of the present invention;
fig. 3(b) is a waveform diagram illustrating two operation modes of the flyback converter according to the first embodiment of the present invention;
fig. 3(c) is a switching flow chart of the flyback converter according to the first embodiment of the present invention;
fig. 4(a) is a schematic circuit diagram of a flyback converter according to a second embodiment of the present invention;
fig. 4(b) is a switching flow chart of the flyback converter according to the second embodiment of the present invention.
Detailed Description
The invention of the application is characterized in that switching control of a first working mode and a second working mode is carried out through input voltage detection or input voltage detection and output power detection, quasi-resonance turning-on of a primary side main power switch tube and synchronous rectification of a secondary side switch rectifying unit are achieved under low input voltage, and zero voltage turning-on of the primary side main power switch tube and synchronous rectification of the secondary side switch rectifying unit are achieved under high input voltage or high input voltage and above a certain load. The invention has simple control and low circuit cost, and can give consideration to low cost and high efficiency in high-frequency application occasions.
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.
It is further noted that where the same terms are used throughout this application, they are intended to represent different expressions which have the same meaning, for example:
(1) the power supply comprises a main power tube, a main power switch tube, a primary side switch unit, a primary side main power tube, a primary side power switch tube, a primary side main power switch tube, a primary side power switch and the like;
(2) the synchronous rectifier comprises a synchronous rectifier tube, a secondary side switch tube, a secondary side transistor, a secondary side switch rectifying unit, a secondary side switch unit, a secondary side rectifier tube, a secondary side rectifying unit, a secondary side rectifier switch tube, a secondary side synchronous rectifier tube, a secondary side synchronous rectifying unit and the like.
Furthermore, the drawings of the present disclosure are merely schematic representations, 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. These 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 microcontroller devices.
The signal codes and the like according to the present invention are many and will be described in detail as follows:
vin: inputting a voltage;
vout: outputting the voltage;
GND 1: a flyback converter is connected to the original side ground;
GND 2: a flyback converter secondary side ground;
vin _ s: inputting a voltage detection signal;
vth _ vin 1: a first threshold value;
vth _ vo 1: a second threshold value;
vds _ SR _ th 3: a third threshold value;
vds _ SR _ th 4: a fourth threshold value;
FB: outputting a power detection signal;
SW: a control signal of a primary side main power switch tube;
g _ SR: a control signal of the secondary side switch rectifying unit;
SR: a primary side synchronization signal;
vds _ SP: a drain-source voltage of a primary side main power switch tube;
vds _ SR: a secondary side switch rectifying unit drain-source voltage;
td 1: a first dead time of the control signal SW and the control signal G _ SR;
td 2: a second dead time of the control signal SW and the control signal G _ SR;
i _ p: primary side inductance current;
i _ s: secondary side inductive current;
is _ 1: setting a threshold value for the secondary side inductance current, wherein the flowing direction is negative;
m1: a primary side main power switch tube;
t1: a transformer;
lm: an excitation inductor;
and Lk: leakage inductance;
n: the primary side and secondary side turn ratio of the transformer;
210: inputting a power supply;
230: a secondary side switch rectifying unit;
240: a primary side controller;
241: an isolation circuit;
242: a secondary-side controller;
243: a feedback circuit.
First embodiment
Fig. 3(a) 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(a) includes a primary side main power switch M1, a secondary side switch rectifying unit 230, a transformer T1, a clamping 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 side controller 240 generates a control signal SW to control the primary side main power switch M1 to be turned on and off according to an input voltage detection signal Vin _ s obtained from an input voltage, and determines a working mode according to the input voltage detection signal Vin _ s to generate another primary side synchronous signal SR, and outputs a control signal G _ SR to the secondary side controller 242 through the isolation circuit 241 to control the secondary side switch rectifying unit 230 to be turned on and off.
Fig. 3(b) is a schematic diagram of waveforms of two operation modes of the flyback converter according to the first embodiment of the present invention, and fig. 3(c) is a switching flow chart of the flyback converter according to the first embodiment of the present invention, which is to satisfy the requirements of the economical flyback converter control method and the economical flyback converter control device in the low-power application situation. In order to overcome the high loss generated by the hard switching of the primary side main power switch tube when the input voltage is high, in the embodiment, when the input voltage detection signal Vin _ s is greater than the first threshold Vth _ Vin1, the flyback converter is selected to operate in the first operating mode, and when the input voltage detection signal Vin _ s is less than the first threshold Vth _ Vin1, the flyback converter is selected to operate in the second operating mode.
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 of large hard switching loss of the primary side main power switching tube under high input voltage can be solved. The following is a detailed description with reference to fig. 3(b) and 3 (c).
Each cycle of the first operation mode of the flyback converter of the present embodiment is as shown in the left half of fig. 3(b), and is divided into four stages, which are analyzed in detail as follows.
In the first stage (t0-t 1): the primary side controller 240 provides a control signal SW to switch on the primary side main power switch tube M1 to work, and the primary side inductive current I _ p flows in the primary winding in the forward direction; after the first phase is finished, the primary side control signal SW turns off the primary side main power switch tube M1, and after a dead time Td1(t1-t2) is passed, the flyback converter enters a second phase;
in the second stage (t2-t 3): the primary side main power switch tube M1 is turned off, the primary side inductor current I _ p quickly charges the drain-source capacitance Cds of the primary side main power switch tube M1 to raise the drain-source voltage, when the voltage rises to Vin + N × Vout, the secondary side switch rectifying unit 230 is turned on, the transformer T1 starts demagnetization, the secondary side controller 242 receives the primary side synchronous signal SR, the primary side controller 242 controls the first turn-on and turn-off of the transistor in the secondary side switch rectifying unit 230, the second time period is finished, and then the flyback converter enters the third stage; specifically, the primary side synchronization signal SR enables the secondary side controller 242 through the isolation circuit 241, the secondary side controller 242 starts to detect a drain-source voltage Vds _ SR of the transistor of the secondary side switch rectifying unit 230, when the drain-source voltage Vds _ SR drops to a third threshold Vds _ SR _ th3, the secondary side switch rectifying unit 230 is controlled to be turned on for the first time after the primary side main power switch tube M1 is turned off for a period of time, the secondary side inductive current I _ s drops, when the secondary side inductive current I _ s drops to 0, the drain-source voltage Vds _ SR reaches a fourth threshold Vds _ SR _ 4 (close to 0V), and the secondary side switch rectifying unit 230 is turned off for the first time;
in the third stage (t3-t 4): after the demagnetization of the transformer T1 is finished, the magnetizing inductor Lm and the leakage inductor Lk are connected in series, and then the drain-source parasitic capacitor Cds of the primary side main power switch tube M1 resonates, when the drain-source voltage Vds _ SP of the primary side main power switch tube M1 reaches a set certain resonant peak, and at this time, when the voltage Vds _ SR at the two ends of the secondary side switch rectifying unit 230 reaches a set certain resonant valley, the secondary side switch rectifying unit 230 is turned on for the second time, and the fourth stage is entered;
in the fourth stage (t4-t 5): the output voltage Is reversely excited to a transformer T1, the secondary side inductance current I _ s Is reversely increased, the secondary side inductance current I _ s Is detected and compared with a secondary side inductance current set threshold value Is _1, when the amplitude of the secondary side inductance current I _ s reaches the secondary side inductance current threshold value Is _1, the secondary side switch rectifying unit 230 Is controlled to be turned off for the second time, the transformer T1 starts to be demagnetized, during the demagnetization period, the primary side inductance current I _ p Is reduced from the negative direction, the primary side inductance current I _ p participates in the resonance of series connection of an excitation inductance Lm and a leakage inductance Lk followed by a primary side main power switch tube M1 junction capacitor Cds, and the primary side main power switch tube M1 Is turned on after a set dead time Td2(T5-T6) to realize zero-voltage turn-on.
Each period of the second operation mode of the flyback converter of this embodiment is shown in the right half of fig. 3(b), which is a double-pulse operation mode well known to those skilled in the art, so that, without performing analysis, it should be mentioned that, when the flyback converter operates in the second operation mode, the secondary side switch rectifying unit 230 is controlled to be on during the transformer demagnetization, and after the transformer demagnetization is finished, the excitation inductance and the leakage inductance are connected in series and then resonated by the drain-source parasitic capacitance Cds of the primary side main power switch tube M1, when the drain-source voltage of the primary side main power switch tube M1 resonates to the nth wave trough, the drain-source voltage of the secondary side transistor resonates to the nth wave crest, the primary side main power switch tube M1 is controlled to be turned on in a quasi-resonant mode, and n is a positive integer, so that the switching losses of the primary side main power switching tube and the secondary side transistor can be reduced, and the efficiency of the flyback converter can be improved. 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 and the diode connected in parallel therewith can be used as a demagnetizing free-wheeling loop of the transformer T1.
Preferably, the secondary side transistor is an enhancement type n-channel MOS tube.
Preferably, when the flyback converter operates in the fourth stage of the first operation mode, the magnitude of the negative secondary side inductor current is proportional to the magnitude of the input voltage. That is, the transistor drive pulse width in the secondary side switch rectifier unit 230 is proportional to the input voltage magnitude to achieve zero voltage turn-on of the primary side main power switch M1 over a high input voltage range.
Preferably, the input voltage detection signal Vin _ s may be obtained by directly dividing the voltage by a sampling resistor, or indirectly obtained by detecting the drain-source voltage Vds _ SP of the primary side main power switch tube in the demagnetization stage of the transformer and detecting the output voltage, and the calculation formula is as follows: vin _ s is Vds _ SP-N Vout, or indirectly obtained by detecting the drain-source voltage Vds _ SR of the secondary side transistor in the transformer excitation stage and detecting the output voltage; the output power detection signal is obtained by detecting the output voltage, and the calculation formula is as follows: vin _ s ═ N (Vds _ SR-Vout).
Preferably, the flyback converter operates in the current interruption mode, and the purpose is to facilitate detecting when the secondary side switch rectifying unit 230 resonates to the trough after demagnetization is finished when the flyback converter operates in the first operation mode, and control the secondary side switch rectifying unit 230 to be turned on for the second time.
Second embodiment
Fig. 4(a) is a schematic circuit diagram of a flyback converter according to a second embodiment of the present invention, and the difference between fig. 4(a) and the first embodiment is that an output power detection signal FB is obtained by a feedback circuit 243 to detect an input voltage and an output power to switch an operation mode of the flyback converter. The present embodiment increases the detection output power, and aims to further control the switching condition between the first operating mode and the second operating mode under different situations of high input voltage, so as to optimize the performance under different loads under high input voltage.
Fig. 4(b) is a schematic diagram of a switching waveform of the flyback converter according to the second embodiment of the present invention, when the input voltage detection signal Vin _ s is greater than or equal to the first threshold Vth _ Vin1 and the output power detection signal FB is greater than or equal to the second threshold Vth _ vo1, the flyback converter operates in the first operating 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 first working mode and the second working mode in this embodiment are the same as the first embodiment, and each cycle in the first working mode is also divided into four stages, which are the same as the first embodiment, and therefore, the description thereof is omitted.
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 (16)
1. A control method of a flyback converter is applicable to the flyback converter and comprises a primary side main power switch tube, a secondary side switch rectifying unit and a transformer, and is characterized in that the flyback converter is controlled to work in one of the following modes according to input voltage or input voltage and output power of the flyback converter:
a first operating mode: the secondary side switch rectifying unit is switched on once after the primary side main power switch tube is switched off and before the primary side main power switch tube is switched on, wherein the secondary side switch rectifying unit is switched on for the first time after the primary side main power switch tube is switched off so as to realize synchronous rectification of the secondary side switch rectifying unit during the demagnetization period of the transformer; switching on for the second time before the primary side main power switching tube is switched on so as to realize zero voltage switching on of the primary side main power switching tube;
a second working mode: the secondary side switch rectifying unit is switched on once only after the primary side main power switch tube is switched off so as to realize the 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 a first working mode, the secondary side switch rectifying unit is switched on for the first time when the transformer is demagnetized, the transformer is demagnetized in a synchronous rectification mode until the transformer is switched off for the first time when demagnetization is finished, after the demagnetization of the transformer is finished, the excitation inductor and the leakage inductor are connected in series, then the parasitic capacitance of the drain-source electrode of the primary side main power switch tube resonates, when the voltage of the drain-source electrode of the primary side main power switch tube resonates to the mth wave peak, namely, when the drain-source voltage of the secondary side switch rectifying unit resonates to the mth wave trough, the secondary side switch rectifying unit is controlled to be switched on for the second time to generate negative secondary side inductive current, and after the current reaches a set value, the secondary side switch rectifying unit is turned off for the second time, and the primary side main power switch tube is turned on after a period of dead time, so that zero voltage turning-on of the primary side main power switch tube is realized, wherein m is a positive integer.
3. The control method according to claim 1, characterized in that: when the flyback converter works in a second working mode, the switching rectification unit on the secondary side is controlled to be switched on during the demagnetization of the transformer, after the demagnetization of the transformer is finished, the excitation inductor and the leakage inductor are connected in series, then the parasitic capacitance of the drain-source electrode of the main power switching tube on the primary side resonates, when the voltage of the drain-source electrode of the main power switching tube on the primary side resonates to the nth wave trough, namely the voltage of the drain-source electrode of the switching rectification unit on the secondary side resonates to the nth wave crest, the quasi-resonant switching of the main power switching tube on the primary side is controlled to be switched on, wherein n is a positive integer.
4. The control method according to claim 1, characterized in that: comparing an input voltage detection signal of the flyback converter with a first threshold value; when the input voltage detection signal is greater than or equal to a first threshold value, controlling the flyback converter to work in a first working mode; and when the input voltage detection signal is smaller than the first threshold value, controlling the flyback converter to work in a second working mode.
5. The control method according to claim 1, characterized in that: comparing an input voltage detection signal of the flyback converter with a first threshold value, and comparing the output power of the flyback converter with a second threshold value; when the input voltage detection signal is greater than or equal to a first threshold value and the output power detection signal is greater than or equal to a second threshold value, controlling the flyback converter to work in a first working mode; and when the input voltage detection signal is smaller than the first threshold or the output power detection signal is smaller than the second threshold, controlling the flyback converter to work in a second working mode.
6. The control method according to claim 4 or 5, characterized in that: the input voltage detection signal is obtained by directly dividing the voltage through a sampling resistor, or indirectly obtained by detecting the drain-source voltage and the detection output voltage of a primary side main power switch tube in the demagnetization stage of the transformer, or indirectly obtained by detecting the drain-source voltage and the detection output voltage of a secondary side switch rectifying unit in the excitation stage of the transformer; the output power detection signal is obtained by detecting the output voltage.
7. The control method according to claim 1, characterized in that: when the flyback converter works in the first working mode, the amplitude of the negative secondary side inductor current is in direct proportion to the amplitude of the input voltage of the flyback converter, namely the width of the second-time conduction driving pulse of the secondary side switch rectifying unit is in direct proportion to the amplitude of the input voltage of the flyback converter.
8. The control method according to claim 1, characterized in that: the flyback converter operates in a current chopping mode.
9. A control device of a flyback converter is applicable to the flyback converter and comprises a primary side main power switch tube, a secondary side switch rectifying unit and a transformer, and is characterized in that the control device controls the flyback converter to work in one of the following modes according to input voltage or the input voltage and output power of the flyback converter:
a first operating mode: the secondary side switch rectifying unit is switched on once after the primary side main power switch tube is switched off and before the primary side main power switch tube is switched on, wherein the secondary side switch rectifying unit is switched on for the first time after the primary side main power switch tube is switched off so as to realize synchronous rectification of the secondary side switch rectifying unit during the demagnetization period of the transformer; switching on for the second time before the primary side main power switching tube is switched on so as to realize zero voltage switching on of the primary side main power switching tube;
a second working mode: the secondary side switch rectifying unit is switched on once only after the primary side main power switch tube is switched off so as to realize the synchronous rectification of the secondary side switch rectifying unit.
10. The control device according to claim 8, characterized in that: when the flyback converter works in a first working mode, the secondary side switch rectifying unit is switched on for the first time when the transformer is demagnetized, the transformer is demagnetized in a synchronous rectification mode until the transformer is switched off for the first time when demagnetization is finished, after the demagnetization of the transformer is finished, the excitation inductor and the leakage inductor are connected in series, then the parasitic capacitance of the drain-source electrode of the primary side main power switch tube resonates, when the voltage of the drain-source electrode of the primary side main power switch tube resonates to the mth wave peak, namely, when the drain-source voltage of the secondary side switch rectifying unit resonates to the mth wave trough, the secondary side switch rectifying unit is controlled to be switched on for the second time to generate negative secondary side inductive current, and after the current reaches a set value, the secondary side switch rectifying unit is turned off for the second time, and the primary side main power switch tube is turned on after a period of dead time, so that zero voltage turning-on of the primary side main power switch tube is realized, wherein m is a positive integer.
11. The control device according to claim 8, characterized in that: when the flyback converter works in a second working mode, the switching rectification unit on the secondary side is controlled to be switched on during the demagnetization of the transformer, after the demagnetization of the transformer is finished, the exciting inductor and the leakage inductor are connected in series, then the parasitic capacitance of the drain-source electrode of the main power switching tube on the primary side resonates, when the voltage of the drain-source electrode of the main power switching tube on the primary side resonates to the nth wave trough, namely the voltage of the drain-source electrode of the switching rectification unit on the secondary side resonates to the nth wave crest, the quasi-resonant switching on of the main power switching tube on the primary side is controlled, wherein n is a positive integer.
12. The control device according to claim 8, characterized in that: comparing an input voltage detection signal of the flyback converter with a first threshold value; when the input voltage detection signal is greater than or equal to a first threshold value, controlling the flyback converter to work in a first working mode; and when the input voltage detection signal is smaller than the first threshold value, controlling the flyback converter to work in a second working mode.
13. The control device according to claim 8, characterized in that: comparing an input voltage detection signal of the flyback converter with a first threshold value, and comparing the output power of the flyback converter with a second threshold value; when the input voltage detection signal is greater than or equal to a first threshold value and the output power is greater than or equal to a second threshold value, controlling the flyback converter to work in a first working mode; and when the input voltage detection signal is smaller than the first threshold or the output power detection signal is smaller than the second threshold, controlling the flyback converter to work in a second working mode.
14. The control method according to claim 12 or 13, characterized in that: the input voltage detection signal is obtained by directly dividing the voltage through a sampling resistor, or indirectly obtained by detecting the drain-source voltage and the detection output voltage of a primary side main power switch tube in the demagnetization stage of the transformer, or indirectly obtained by detecting the drain-source voltage and the detection output voltage of a secondary side switch rectifying unit in the excitation stage of the transformer; the output power detection signal is obtained by detecting the output voltage.
15. The control device according to claim 8, characterized in that: when the flyback converter works in the first working mode, the amplitude of the negative secondary side inductor current is in direct proportion to the amplitude of the input voltage of the flyback converter, namely the width of the second-time conduction driving pulse of the secondary side switch rectifying unit is in direct proportion to the amplitude of the input voltage of the flyback converter.
16. The control device according to claim 8, characterized in that: the flyback converter operates in a current chopping mode.
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| CN2021102816531 | 2021-03-16 | ||
| CN202110281653 | 2021-03-16 |
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Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN116111806A (en) * | 2023-04-12 | 2023-05-12 | 珠海智融科技股份有限公司 | Output current determining method and system based on flyback topological structure secondary side parameters |
| CN117214636A (en) * | 2023-10-23 | 2023-12-12 | 北京理工大学唐山研究院 | Flyback coil turn-to-turn insulation detection device and control method |
Citations (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN108155799A (en) * | 2016-12-06 | 2018-06-12 | 台达电子企业管理（上海）有限公司 | For the control method and control device of flyback converter circuit |
| 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 |
-
2021
- 2021-06-29 CN CN202110725240.8A patent/CN113708634A/en not_active Withdrawn
Patent Citations (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN108155799A (en) * | 2016-12-06 | 2018-06-12 | 台达电子企业管理（上海）有限公司 | For the control method and control device of flyback converter circuit |
| 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 |
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN116111806A (en) * | 2023-04-12 | 2023-05-12 | 珠海智融科技股份有限公司 | Output current determining method and system based on flyback topological structure secondary side parameters |
| CN117214636A (en) * | 2023-10-23 | 2023-12-12 | 北京理工大学唐山研究院 | Flyback coil turn-to-turn insulation detection device and control method |
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