CN113708635A - Switching method and control device of flyback converter - Google Patents

Switching method and control device of flyback converter Download PDF

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Publication number
CN113708635A
CN113708635A CN202110725253.5A CN202110725253A CN113708635A CN 113708635 A CN113708635 A CN 113708635A CN 202110725253 A CN202110725253 A CN 202110725253A CN 113708635 A CN113708635 A CN 113708635A
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China
Prior art keywords
secondary side
primary side
switch unit
flyback converter
power switch
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Withdrawn
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CN202110725253.5A
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Chinese (zh)
Inventor
尹增鹤
王海洲
李樟红
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Mornsun Guangzhou Science and Technology Ltd
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Mornsun Guangzhou Science and Technology Ltd
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Publication of CN113708635A publication Critical patent/CN113708635A/en
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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
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M1/00—Details of apparatus for conversion
    • H02M1/08—Circuits specially adapted for the generation of control voltages for semiconductor devices incorporated in static converters
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M1/00—Details of apparatus for conversion
    • H02M1/08—Circuits specially adapted for the generation of control voltages for semiconductor devices incorporated in static converters
    • H02M1/083—Circuits specially adapted for the generation of control voltages for semiconductor devices incorporated in static converters for the ignition at the zero crossing of the voltage or the current
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • 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
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02B—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO BUILDINGS, e.g. HOUSING, HOUSE APPLIANCES OR RELATED END-USER APPLICATIONS
    • Y02B70/00—Technologies for an efficient end-user side electric power management and consumption
    • Y02B70/10—Technologies improving the efficiency by using switched-mode power supplies [SMPS], i.e. efficient power electronics conversion e.g. power factor correction or reduction of losses in power supplies or efficient standby modes

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  • Engineering & Computer Science (AREA)
  • Power Engineering (AREA)
  • Dc-Dc Converters (AREA)

Abstract

The invention discloses a control method and a control device of a flyback converter, which are suitable for the flyback converter and comprise a primary side power switch tube, a secondary side switch unit, a transformer and an output capacitor, wherein when the input voltage is greater than or equal to a first threshold value, or when the input voltage is not less than the first threshold value and the output power is not less than a second threshold value, the flyback converter is controlled to work in a first working mode, the secondary side switch unit is switched on once before the primary side power switch tube is switched on, and the secondary side switch unit is switched on only after the demagnetization of the transformer is finished, negative exciting current is generated in the switching-on time, and the zero-voltage switching-on of the primary side power switch tube is realized; and under other conditions, the flyback converter is controlled to work in a second working mode, the secondary side switch unit is always kept in an off state, and the primary side power switch tube maintains normal output of the flyback converter. The invention effectively reduces the loss, meets the requirements of low-power application occasions, and has simple switching control and easy operation.

Description

Switching method and control device of flyback converter
Technical Field
The invention relates to the field of flyback converters, in particular to the switching of working modes of a flyback converter.
Technical Field
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.
Although the quasi-resonant Flyback converter (QR Flyback) can realize zero voltage conduction (ZVS) of the primary side main power tube under the condition of low input voltage. However, when the input voltage Vin > nVout, the conduction of the trough of the main power tube can only be realized, wherein n represents the turn ratio of the primary side and the secondary side of the transformer, and Vout is the output voltage. The switching losses at high frequencies of this type of converter remain a major factor limiting its application.
In order to further increase the operating frequency and achieve ZVS of the power tube over the full voltage range, active clamp flyback converters have been proposed by those skilled in the art. As shown in fig. 1, the active-clamp flyback converter can inject partial energy when the primary side main power tube parasitic capacitor Cds resonates with the primary side inductor Lm by using the leakage inductance energy stored in the clamp capacitor CR; alternatively, as shown in fig. 2, the secondary side synchronous rectifier is still conducted for a period of time after the demagnetization is finished, so that part of energy is transferred to the primary side to participate in resonance. Both methods can enable the voltage between the drain and the source of the primary side main power tube to resonate to zero, thereby realizing ZVS of the main power tube. The converters using the two methods have certain advantages in medium and high power application occasions, but the converter using the former method adds a clamping switch tube in a primary side clamping circuit, so that compared with the traditional flyback converter, the cost is increased, the control is more complex, and the clamping switch tube also has switching loss; the converter using the latter method also increases the complexity of the secondary side synchronous rectification control, and synchronous rectification especially under light-load frequency conversion conditions has no advantage. The advantages of the above solution in low power applications are therefore 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 flyback converter can realize ZVS of the primary side main power tube, 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, increasing the hysteresis and copper losses of the inductor. In addition, the synchronous rectification under such working conditions has no advantages, and even has a certain limitation on the frequency boost of the converter, for example, as shown in fig. 2, a source clamping scheme in an intermittent mode needs the secondary side synchronous rectification tube to be turned on twice (two pulses) to realize ZVS of the primary side main power tube; or an active clamp flyback converter working in a continuous mode is adopted, but the secondary side synchronous rectifier is required to be turned off for a long time after demagnetization is finished.
Disclosure of Invention
Therefore, the present invention aims to provide a switching 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 light-load conditions, and are suitable for small-power occasions with small output current, and can save cost.
In terms of method, a flyback converter suitable for use includes a primary side power switching tube, a secondary side switching unit, a transformer, an output capacitor, and a control device.
As a first switching method, specifically, different working modes are selected according to an input voltage, when the input voltage is greater than or equal to a first threshold value, the flyback converter works in the first working mode, the control device controls the secondary side switch unit to be turned on once before the primary side power switch tube is turned on, and the secondary side switch unit is turned on only after the demagnetization of the transformer is finished, a negative excitation current is generated within the turn-on time, and zero-voltage turn-on of the primary side power switch tube is realized;
when the input voltage is smaller than the first threshold value, the flyback converter works in a second working mode, the control device controls the secondary side switch unit to keep an off state all the time, and the primary side power switch tube maintains normal output of the flyback converter.
As another switching method, specifically, different working modes are selected according to input voltage and output power, when the input voltage is greater than or equal to a first threshold value and the output power is greater than a second threshold value, the flyback converter works in the first working mode, the control device controls the secondary side switch unit to be turned on once before the primary side power switch tube is turned on, and the secondary side switch unit is turned on only after the demagnetization of the transformer is finished, negative excitation current is generated in the turn-on time, and zero-voltage turn-on of the primary side power switch tube is realized;
under other conditions, the flyback converter works in the second working mode, the control device controls the secondary side switch unit to keep the turn-off state all the time, and the primary side power switch tube maintains the normal output of the flyback converter.
Preferably, after the secondary side switching unit is turned on, the secondary side switching unit is turned off, and a dead time period elapses between the time when the primary side power switching tube is turned on again and the time when the secondary side switching unit is turned off.
Preferably, in the first operating mode, after demagnetization of the transformer is completed, an excitation inductor of the transformer resonates with a parasitic capacitor between a drain and a source of the primary side power switching tube, when a voltage Vds _ SP between the drain and the source of the primary side power switching tube resonates to a peak, the control device controls the secondary side switching element to be turned on once, a negative excitation current is formed in the transformer during the turn-on period of the secondary side switching element, and when the negative excitation current reaches a certain value, the secondary side switching element is turned off, and the negative excitation current participates in resonance of the excitation inductor and the parasitic capacitor C between the drain and the source of the primary side power switching tube, so that zero-voltage turn-on of the primary side power switching tube is realized.
Preferably, in the first operating mode, the amplitude of the negative excitation current is proportional to the amplitude of the input voltage.
In terms of the device, the flyback converter suitable for the device comprises a primary side power switch tube, a secondary side switch unit, a transformer and an output capacitor, wherein a control device is respectively connected with the primary side power switch tube and the secondary side switch unit and is used for receiving a drain voltage Vds _ SP detection signal of the primary side power switch tube and an output power detection signal FB and generating a first control signal and a second control signal to respectively control the on-off of the primary side power switch tube and the secondary side switch unit;
the control device obtains an input voltage detection signal Vin _ s according to a received signal, different working modes are selected according to the input voltage detection signal Vin _ s, when the input voltage detection signal Vin _ s is larger than or equal to a first threshold value, the flyback converter works in the first working mode, the control device controls the secondary side switch unit to be switched on once before the primary side power switch tube is switched on, and the secondary side switch unit is switched on only after the demagnetization of the transformer is finished, negative excitation current is generated in the switching-on time, and zero voltage switching of the primary side power switch tube is achieved;
when the input voltage detection signal Vin _ s is smaller than the first threshold value, the flyback converter works in the second working mode, the control device controls the secondary side switch unit to be always kept in the off state, and the primary side power switch tube maintains normal output of the flyback converter.
The control device comprises a primary side controller and an isolation driver, wherein the primary side controller and the isolation driver are connected in series between a primary side power switch tube and a secondary side switch unit, the primary side controller is used for receiving a drain voltage Vds _ SP detection signal of the primary side power switch tube and an output power detection signal FB and generating a first control signal and a second control signal, and the second control signal is transmitted to the secondary side switch unit through the isolation driver.
The control device comprises a primary side controller, a secondary side detection circuit and a secondary side controller, wherein the primary side controller is connected with a primary side power switch tube and is used for receiving a drain voltage Vds _ SP detection signal of the primary side power switch tube and an output power detection signal FB and generating a first control signal to control the on and off of the primary side power switch tube; the secondary side detection circuit is connected with the secondary side switch unit and used for receiving a drain-source voltage Vds _ sr detection signal and an output power detection signal FB of the secondary side switch unit, the secondary side controller generates a second control signal to control the on and off of the secondary side switch unit, and the primary side controller and the secondary side controller can work independently.
Preferably, the secondary side switching unit is used as the transformer demagnetization freewheeling loop, and is specifically a secondary side switching transistor, or the secondary side switching transistor is connected in parallel with a diode.
Preferably, the flyback converter is adapted to have a load current of less than 3A.
Compared with the prior art, the invention has the following beneficial effects:
(1) ZVS of a primary side main power switching tube under higher input voltage is realized by using reverse excitation current, and loss is reduced;
(2) meanwhile, mode switching work is adopted, and efficiency optimization under high and low input voltages and different output powers is considered;
(3) and the mode switching is realized in a low-power application scene, and the switching operation is simple.
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. 2(c) is a prior art ZVS waveform diagram for two pulses on the secondary side control;
fig. 3 is a schematic circuit diagram of a flyback converter according to a first embodiment of the present invention;
fig. 4 is a switching flowchart of the flyback converter according to the first embodiment of the present invention;
fig. 5 is a schematic switching waveform diagram of a flyback converter according to the first embodiment of the present invention;
fig. 6 is a switching flowchart of a flyback converter according to a second embodiment of the present invention;
fig. 7 is a schematic circuit diagram of a flyback converter according to a second embodiment of the present invention.
Detailed Description
The scheme of the invention is further explained in the following by combining the attached drawings.
First embodiment
As shown in fig. 3, which is a schematic circuit diagram of the first embodiment of the present invention, the flyback converter includes a primary-side power switch 150, a secondary-side switch unit 130, a transformer T1, an output capacitor C0, a secondary-side diode, and a control device 140. The transformer T1 includes an exciting inductance Lm, and the secondary-side switching unit 130 includes first and second terminals electrically connected to the transformer T1 and the output capacitor C0, respectively.
In the first embodiment, the control device 140 includes a primary side controller 141 and an isolator driver 142, wherein the primary side controller 141 generates a first control signal G _ S1 and a second control signal G _ SR to control the on and off of the primary side power switch tube 150 and the secondary side switch unit 130, respectively, and wherein the second control signal G _ SR controls the on and off of the secondary side switch unit 130 via the isolator driver 142. The secondary side switching unit 130 is an enhancement n-channel MOS transistor, and includes a drain D, a source S, and a gate G, and the source S and the drain D are electrically connected to the transformer T1 and the output capacitor C0, respectively. The secondary side diode anode and cathode are electrically connected to the source S and drain D of the secondary side switching unit 130, respectively. The secondary side switch unit 130 is a power switch or a power switch connected in parallel with a diode.
As shown in fig. 4, which is a switching flowchart of the first embodiment of the present invention, when the input voltage is greater than or equal to the first threshold, the flyback converter operates in the first operating mode, and the control device 140 controls the secondary side switch unit 130 to be turned on once before the primary side power switch tube 150 is turned on, so as to implement zero voltage turn-on (ZVS) of the primary side power switch tube 150; on the contrary, the flyback converter operates in the second operation mode, the control device 140 controls the secondary side switching unit 130 to keep the off state all the time, and the flyback converter operates in the normal flyback operation mode.
The secondary side switching unit 130 is turned on only after the demagnetization of the transformer T1 is finished, and generates a negative excitation current (as shown by the side of the excitation inductor Lm in fig. 3, the direction is a positive excitation direction) during the turn-on time, the negative excitation current participates in the resonance process of the drain-source junction capacitor Cds of the primary side power switching tube 150 and the excitation inductor Lm, and turns on the primary side power switching tube 150 after the drain-source voltage of the primary side power switching tube 150 resonates to zero, thereby realizing zero-voltage turn-on of the primary side power switching tube 150. The primary side power switch 150 is turned on after a dead time period after the secondary side switching unit 130 is turned off.
According to the switching method of the flyback converter, the first operation mode of the flyback converter can be divided into four time periods, as shown in fig. 5, and fig. 5 is a switching waveform diagram of the first embodiment of the present invention. With reference to fig. 3 to 5, the first embodiment of the present invention works as follows:
the input voltage detection signal Vin _ s is obtained by directly dividing voltage through resistance sampling, or indirectly obtained by detecting the drain voltage Vds _ SP of the primary side power switch tube 150 and the output voltage in the demagnetization stage of the transformer T1 (Vin _ s is Vds _ SP-n Vout, and n is the turn ratio of the primary side and the secondary side of the transformer T1).
The primary side controller 141 receives the signals: the primary side controller 141 generates a first control signal G _ S1 according to the received signal, and the first control signal G _ S1 controls the on and off of the primary side power switch tube 150; and generates a second control signal G _ SR to control the on and off of the secondary side switching unit 130 via the isolation driver 142.
When the input voltage detection signal Vin _ s is greater than or equal to the first threshold Vth _ Vin1, the flyback converter operates in the first operation mode, specifically divided into the following four time periods,
in a first time period, the primary-side controller 141 outputs a first control signal G _ S1 to control the primary-side power switch 150 to be turned on, and an excitation current flows in a forward direction in the primary winding of the transformer T1;
after the first time period is finished, the first control signal G _ S1 turns off the primary side power switching tube 150, the flyback converter enters a second time period, in the second time period, the secondary side switching unit 130 can be used as a demagnetization freewheeling loop of the transformer T1, both the primary side power switching tube 150 and the secondary side switching unit 130 are turned off, at this time, the flyback converter performs freewheeling through a parasitic diode or a parallel diode of the secondary side switching unit 130, the excitation current is decreased, and when the excitation current is decreased to 0, the flyback converter enters a third time period after the second time period is finished;
in a third time period, after demagnetization of the transformer T1 is finished, the magnetizing inductor Lm resonates with the drain-source parasitic capacitor Cds of the primary side power switching tube 150, and when the voltage Vds _ SP between the drain and the source of the primary side power switching tube 150 resonates to a peak, the control device 140 controls the secondary side switching unit 130 to be turned on once through the isolation driver 142, and during the turn-on period of the secondary side switching unit 130, a negative magnetizing current is formed in the transformer T1, and enters a fourth time period;
in the fourth time period, the amplitude of the negative excitation current is proportional to the amplitude of the input voltage (i.e., the driving pulse width of the secondary side switching unit 130 is proportional to the amplitude of the input voltage), the detected negative excitation current is compared with a set threshold, and when the amplitude of the negative excitation current is greater than the threshold, the secondary side switching unit 130 is controlled to turn off, and meanwhile, the primary side power switching tube 150 is turned on after a set dead time, so as to achieve zero-voltage turn-on.
When the input voltage detection signal Vin _ s is smaller than the first threshold Vth _ Vin1, the second operating mode of the flyback converter is a normal flyback operating mode, which is well known in the art and will not be described herein.
According to the scheme, the working mode of the flyback converter is an intermittent mode, the flyback converter can better cope with the condition that the load current is less than 3A, and the flyback converter can be better suitable for an RCD clamping flyback converter or an active clamping flyback converter.
Second embodiment
As shown in fig. 7, the circuit schematic diagram of the second embodiment of the present invention is different from the circuit schematic diagram of the first embodiment in that the control device includes a primary side controller 240, a secondary side controller 241 and a secondary side detection circuit, the primary side controller 240 is configured to receive a drain voltage Vds _ SP detection signal and an output power detection signal FB of the primary side power switch tube 250 and generate a first control signal G _ S1 to control the primary side power switch tube 250 to be turned on and off, the secondary side detection circuit is configured to receive a drain-source voltage Vds _ SR detection signal and an output power detection signal FB of the secondary side switch unit 230, the secondary side controller 241 generates a second control signal G _ SR to control the secondary side switch unit 230 to be turned on and off, and the primary side controller 240 and the secondary side controller 241 can be operated independently.
The circuit of the second embodiment of the present invention can adopt the switching method of the first embodiment, and the working principle is the same, which is not described herein again.
The second embodiment of the present invention may further adopt a switching method as shown in fig. 6, and compared with the switching method in the first embodiment, the difference is that when the input voltage is greater than or equal to the first threshold and the output power is greater than the second threshold, the flyback converter operates in the first operating mode; otherwise, the flyback converter operates in the second operation mode.
It should be noted that, in the third time period in the first operating mode, after the demagnetization of the transformer T1 is completed, the excitation inductor Lm resonates with the drain-source parasitic capacitance Cds of the primary-side power switch tube 150, and when the drain-source voltage Vds _ SP of the primary-side power switch tube 150 resonates to a peak (or the drain of the secondary-side switch unit 130 resonates to a valley, the source voltage Vds _ sr resonates to a valley), the control device 140 controls the secondary-side switch unit 130 to be turned on once through the isolation driver 142.
The terminology used in the above-described embodiments is for the purpose of description and illustration, and is not intended to be limiting. As the present invention may be embodied in several forms without departing from the spirit or essential characteristics thereof, it should also be understood that the above-described embodiments are not limited by any of the details of the foregoing description, but rather should be construed broadly within its spirit and scope as defined in the appended claims, and therefore all changes and modifications that fall within the meets and bounds of the claims, or equivalences of such meets and bounds are therefore intended to be embraced by the appended claims.

Claims (10)

1. A switching method of a flyback converter is suitable for the flyback converter and comprises a primary side power switch tube, a secondary side switch unit, a transformer, an output capacitor and a control device, and is characterized in that:
different working modes are selected according to the input voltage, when the input voltage is greater than or equal to a first threshold value, the flyback converter works in the first working mode, the control device controls the secondary side switch unit to be switched on once before the primary side power switch tube is switched on, and the secondary side switch unit is switched on only after the demagnetization of the transformer is finished, negative excitation current is generated in the switching-on time, and the zero-voltage switching-on of the primary side power switch tube is realized;
when the input voltage is smaller than the first threshold value, the flyback converter works in a second working mode, the control device controls the secondary side switch unit to keep an off state all the time, and the primary side power switch tube maintains normal output of the flyback converter.
2. A switching method of a flyback converter is suitable for the flyback converter and comprises a primary side power switch tube, a secondary side switch unit, a transformer, an output capacitor and a control device, and is characterized in that:
different working modes are selected according to the input voltage and the output power, when the input voltage is greater than or equal to a first threshold value and the output power is greater than a second threshold value, the flyback converter works in the first working mode, the control device controls the secondary side switch unit to be switched on once before the primary side power switch tube is switched on, the secondary side switch unit is switched on only after the demagnetization of the transformer is finished, and negative excitation current is generated in the switching-on time, so that zero-voltage switching-on of the primary side power switch tube is realized;
under other conditions, the flyback converter works in the second working mode, the control device controls the secondary side switch unit to keep the turn-off state all the time, and the primary side power switch tube maintains the normal output of the flyback converter.
3. The control method according to claim 1 or 2, characterized in that: after the secondary side switch unit is switched on, the secondary side switch unit is switched off, and a dead time period is elapsed between the secondary side switch unit switching-on time and the primary side power switch tube switching-on time.
4. The control method according to claim 1 or 2, characterized in that: in the first working mode, after demagnetization of the transformer is finished, an excitation inductor of the transformer resonates with parasitic capacitance between a drain and a source of a primary side power switch tube, when voltage Vds _ SP between the drain and the source of the primary side power switch tube resonates to a peak, the control device controls a secondary side switch unit to be turned on once, negative excitation current is formed in the transformer during the turn-on period of the secondary side switch unit, when the negative excitation current reaches a certain value, the secondary side switch unit is turned off, and the negative excitation current participates in resonance of the excitation inductor and the parasitic capacitance C between the drain and the source of the primary side power switch tube, so that zero-voltage turn-on of the primary side power switch tube is realized.
5. The control method according to claim 1 or 2, characterized in that: and in the first working mode, the amplitude of the negative excitation current is in direct proportion to the amplitude of the input voltage.
6. The utility model provides a flyback converter controlling means, the flyback converter that is applicable to include primary side power switch tube, secondary side switch unit, transformer and output capacitance, its characterized in that:
the control device is respectively connected with the primary side power switch tube and the secondary side switch unit, and is used for receiving a drain voltage Vds _ SP detection signal of the primary side power switch tube and an output power detection signal FB, and generating a first control signal and a second control signal to respectively control the on-off of the primary side power switch tube and the secondary side switch unit;
the control device obtains an input voltage detection signal Vin _ s according to a received signal, different working modes are selected according to the input voltage detection signal Vin _ s, when the input voltage detection signal Vin _ s is larger than or equal to a first threshold value, the flyback converter works in the first working mode, the control device controls the secondary side switch unit to be switched on once before the primary side power switch tube is switched on, and the secondary side switch unit is switched on only after the demagnetization of the transformer is finished, negative excitation current is generated in the switching-on time, and zero voltage switching of the primary side power switch tube is achieved;
when the input voltage detection signal Vin _ s is smaller than the first threshold value, the flyback converter works in the second working mode, the control device controls the secondary side switch unit to be always kept in the off state, and the primary side power switch tube maintains normal output of the flyback converter.
7. The control device according to claim 6, characterized in that: the primary side controller and the isolation driver are connected in series between the primary side power switch tube and the secondary side switch unit, the primary side controller is used for receiving a drain voltage Vds _ SP detection signal of the primary side power switch tube and an output power detection signal FB and generating a first control signal and a second control signal, and the second control signal is transmitted to the secondary side switch unit through the isolation driver.
8. The control device according to claim 6, characterized in that: comprises a primary side controller, a secondary side detection circuit and a secondary side controller,
the primary side controller is connected with the primary side power switch tube and used for receiving a drain voltage Vds _ SP detection signal and an output power detection signal FB of the primary side power switch tube and generating a first control signal to control the on-off of the primary side power switch tube;
the secondary side detection circuit is connected with the secondary side switch unit and used for receiving a drain-source voltage Vds _ sr detection signal and an output power detection signal FB of the secondary side switch unit, the secondary side controller generates a second control signal to control the on and off of the secondary side switch unit, and the primary side controller and the secondary side controller can work independently.
9. The control device according to claim 6, characterized in that: the secondary side switch unit is used as the demagnetization follow current loop of the transformer, and is specifically a secondary side switch transistor, or the secondary side switch transistor is connected with a diode in parallel.
10. The control device according to claim 5, characterized in that: the load current of the flyback converter is smaller than 3A.
CN202110725253.5A 2021-03-16 2021-06-29 Switching method and control device of flyback converter Withdrawn CN113708635A (en)

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Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN115441738A (en) * 2022-04-08 2022-12-06 华源智信半导体(深圳)有限公司 Power converter, power adapter and electronic equipment

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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
CN112054659A (en) * 2020-09-25 2020-12-08 杰华特微电子（杭州）有限公司 Zero-voltage-conduction flyback circuit and control method and control circuit thereof

Patent Citations (2)

* Cited by examiner, † Cited by third party
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
CN112054659A (en) * 2020-09-25 2020-12-08 杰华特微电子（杭州）有限公司 Zero-voltage-conduction flyback circuit and control method and control circuit thereof

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN115441738A (en) * 2022-04-08 2022-12-06 华源智信半导体(深圳)有限公司 Power converter, power adapter and electronic equipment
CN115441738B (en) * 2022-04-08 2024-05-28 华源智信半导体(深圳)有限公司 Power converter, power adapter and electronic equipment

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