CN112383227A - Control method and control circuit of flyback circuit - Google Patents

Control method and control circuit of flyback circuit Download PDF

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Publication number
CN112383227A
CN112383227A CN202011319057.XA CN202011319057A CN112383227A CN 112383227 A CN112383227 A CN 112383227A CN 202011319057 A CN202011319057 A CN 202011319057A CN 112383227 A CN112383227 A CN 112383227A
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China
Prior art keywords
synchronous rectifier
voltage
rectifier tube
tube
circuit
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CN202011319057.XA
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Chinese (zh)
Inventor
许祥勇
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Joulwatt Technology Hangzhou Co Ltd
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Joulwatt Technology Hangzhou Co Ltd
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Priority to CN202011319057.XA priority Critical patent/CN112383227A/en
Publication of CN112383227A publication Critical patent/CN112383227A/en
Pending legal-status Critical Current

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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
    • 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
    • H02M1/32—Means for protecting converters other than automatic disconnection

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

Abstract

The invention provides a control method and a control circuit of a flyback circuit, wherein the flyback circuit comprises a main power tube, a synchronous rectifier tube and a transformer, and a first control signal is obtained according to the drain voltage of the synchronous rectifier tube or according to the drain voltage of the synchronous rectifier tube and the output voltage of the flyback circuit during the conduction period of the main power tube; when the first control signal is larger than a first threshold value, the synchronous rectifier tube can be normally conducted after the main power tube is turned off; and setting the first threshold value according to the switching state of the last switching period of the synchronous rectifier tube. The invention can only be in one state under the critical load state, and solves the problems of noise and ripple waves of the system under the critical state.

Description

Control method and control circuit of flyback circuit
Technical Field
The invention relates to the field of power electronics, in particular to a control circuit and a control method of a flyback circuit.
Background
To prevent false turn-on when the flyback circuit oscillates in DCM, a false turn-on prevention control method is usually added. The core thought of the existing method for preventing misconduction is to distinguish the state of DCM oscillation and prevent the misconduction under the DCM oscillation. The common practice is two, one is to detect the Drain off-voltage slope of the synchronous rectification MOSFET tube, because the Drain terminal voltage slope of the MOSFET tube is lower when the DCM oscillates under normal conditions, and if the slope is smaller than a certain threshold, the synchronous rectification is not allowed to be conducted. The other method is to detect the Drain terminal voltage of the synchronous rectification MOSFET tube, subtract the system output voltage from the Drain terminal voltage and perform volt-second product on the obtained voltage at the part of the voltage larger than zero. Since the voltage-second product of the DCM oscillation is much smaller than that of the primary side conduction, the state of the DCM oscillation can be distinguished, and the error conduction under the DCM oscillation is prevented.
However, both of the two methods are less likely to meet the switching-on condition under light load, and both methods have a critical state in which some switching cycles are on and some switching cycles are not on in the synchronous rectification drive, so that the system generates a noise problem and the output ripple is increased.
Disclosure of Invention
The invention aims to provide a control circuit and a control method of a flyback circuit in one state under a critical load state, which are used for solving the problems of noise and ripple waves of a system under the critical state.
In order to achieve the above object, the present invention provides a control method of a flyback circuit, the flyback circuit including a main power transistor, a synchronous rectifier and a transformer, wherein during the conduction period of the main power transistor, a first control signal is obtained according to a drain voltage of the synchronous rectifier or according to the drain voltage of the synchronous rectifier and an output voltage of a switching circuit; when the first control signal is larger than a first threshold value, the synchronous rectifier tube can be normally conducted after the main power tube is turned off; the first threshold is a hysteresis signal value.
Optionally, the first threshold is set according to a switching state of a last switching cycle of the synchronous rectifier tube.
Optionally, in the last switching period, after the main power transistor is turned off, if the driving voltage of the synchronous rectifier is detected, the first threshold is set to be a first voltage;
in the last switching period, after the main power tube is switched off, if the driving voltage of the synchronous rectifier tube is not detected and the duration time that the drain voltage of the synchronous rectifier tube is smaller than a second threshold reaches a first time, setting the first threshold as a second voltage;
if the driving voltage of the synchronous rectifier tube is not detected, and the duration time that the drain voltage of the synchronous rectifier tube is smaller than the second threshold value does not reach the first time, the first threshold value is kept at the first voltage; the second voltage is greater than the first voltage.
Optionally, during the conduction period of the main power tube, the first control signal is obtained according to a change rate of a drain voltage of the synchronous rectifier tube.
Optionally, during the conduction period of the main power transistor, the difference between the drain voltage of the synchronous rectifier and the output voltage of the switching circuit is integrated to obtain the first control signal.
The invention also provides a control circuit of the flyback circuit, the flyback circuit comprises a main power tube, a synchronous rectifier tube and a transformer,
a first control circuit for outputting a first control signal according to a drain voltage of the synchronous rectifier tube or according to the drain voltage of the synchronous rectifier tube and an output voltage of the switching circuit;
the setting circuit is used for setting a first threshold value according to the switching state of the synchronous rectifier tube in the last switching period, wherein the first threshold value is a hysteresis signal value;
when the first control signal is larger than the first threshold value, the synchronous rectifier tube can be conducted after the main power tube is turned off.
Optionally, the setting circuit includes a detection circuit and a second control circuit, and in the last switching cycle, after the main power transistor is turned off, if the detection circuit detects the driving voltage of the synchronous rectifier transistor, the first threshold is set as a first voltage; if the voltage of the driver of the synchronous rectifier tube is not detected, the second control circuit compares the drain voltage of the synchronous rectifier tube with a second threshold value and times, and if the duration time that the drain voltage of the synchronous rectifier tube is smaller than the second threshold value reaches a first time, the first threshold value is set as the second voltage; if the duration time that the drain voltage of the synchronous rectifier tube is smaller than the second threshold value does not reach the first time, keeping the first threshold value as the first voltage; the second voltage is greater than the first voltage.
Optionally, the setting circuit further includes a first resistor, a second resistor, and a first switch, after the first resistor and the second resistor are connected in series, one end of the first resistor receives a second voltage, the other end of the first resistor is grounded through the first switch, and a voltage at a common connection end of the first resistor and the second resistor is a first threshold; when the driving voltage of the synchronous rectifier tube is detected, the first switch is conducted; when the driving voltage of the synchronous rectifier tube is not detected, and the time that the drain voltage of the synchronous rectifier tube is smaller than the second threshold value reaches the first time, the first switch is turned off.
Optionally, the first control circuit detects a drain voltage change rate of the synchronous rectifier tube to obtain the first control signal.
Optionally, during the period that the main power tube is turned on, the first control circuit integrates a difference between the drain voltage of the synchronous rectifier and the output voltage of the switching circuit to obtain the first control signal.
Compared with the prior art, the invention has the following advantages: during the conduction period of the main power tube, obtaining a first control signal according to the drain voltage of the synchronous rectifier tube or according to the drain voltage of the synchronous rectifier tube and the output voltage of the switch circuit; when the first control signal is larger than a first threshold value, the synchronous rectifier tube can be normally conducted after the main power tube is turned off; the first threshold is a hysteresis signal value, and is set according to the switching state of the synchronous rectifier tube in the last switching period. The invention has only one working state under the critical load state, and the problems of noise and ripple waves are restrained under the working state.
Drawings
Fig. 1 is a schematic diagram of a flyback circuit of the present invention;
fig. 2 is a schematic diagram of a synchronous rectification controller in the flyback circuit of the present invention;
FIG. 3 is a schematic diagram of a circuit provided in the synchronous rectification controller according to the present invention;
FIG. 4 is a waveform of a first threshold of the present invention;
FIG. 5 is a waveform diagram illustrating the EN disable state according to the present invention;
Detailed Description
Preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings, but the present invention is not limited to only these embodiments. The invention is intended to cover alternatives, modifications, equivalents and alternatives which may be included within the spirit and scope of the invention.
In the following description of the preferred embodiments of the present invention, specific details are set forth in order to provide a thorough understanding of the present invention, and it will be apparent to those skilled in the art that the present invention may be practiced without these specific details.
The invention is described in more detail in the following paragraphs by way of example with reference to the accompanying drawings. It should be noted that the drawings are in simplified form and are not to precise scale for the purpose of facilitating and clearly explaining the embodiments of the present invention.
As shown in fig. 1, a schematic diagram of a flyback circuit of the present invention is illustrated, which includes an input inductor Lk, a transformer T1, a main power tube M1 and a synchronous rectifier tube M2, wherein one end of the input inductor Lk receives an input voltage Vin, the other end of the input inductor Lk is connected to one end of a primary inductor N1 of the transformer T1, and the other end of the primary inductor N1 of the transformer is connected to the main power tube M1; the synchronous rectifier M2 is connected with the secondary inductor N2 of the transformer, and the output end of the synchronous rectifier is connected with the control end of the synchronous rectifier M2 and used for controlling the switching state of the synchronous rectifier M2.
As shown in fig. 2, a schematic diagram of the synchronous rectification controller of the present invention is illustrated, and the synchronous rectification controller includes a first control circuit U101, a setting circuit U102, a comparator U103, and a driving circuit U104, where the first control circuit U101 receives a drain voltage Vds of a synchronous rectification tube, or the drain voltage Vds and an output voltage Vo, to obtain a first control signal VT. The setting circuit U102 sets the first threshold VT _ REF according to the synchronous rectifier driving voltage Vgs _ SR and the synchronous rectifier drain voltage Vds in the last switching cycle. When the first control signal VT is larger than the first threshold VT _ REF, the synchronous rectifier tube M2 can be controlled to be normally switched on and off; otherwise, the synchronous rectifier tube is turned off. Specifically, the first control signal VT may be obtained according to a rate of change of the synchronous rectifier Vds, or obtained by integrating a difference between the drain voltage Vds and the output voltage Vo during the conduction period of the main power transistor M1.
As shown in fig. 3, a schematic diagram of a circuit provided in the synchronous rectification controller of the present invention is illustrated, and the schematic diagram includes a detection circuit, a second control circuit, a logic circuit, a first resistor R1, a second resistor R2, and a switch k, where the resistor R1, the resistor R2, and the switch k are connected in series, a first end of the series circuit receives a voltage V1, a second end of the series circuit is grounded, the switch k is controlled by a signal EN, and a voltage at a connection end of the resistors R1 and R2 is a first threshold VT _ REF. The detection circuit U201 detects the voltage Vgs _ SR of the driving end of the synchronous rectifier tube after the main power tube M1 is turned off, when a driving signal is detected, the output signal A is enabled through a high-level signal EN output by the logic circuit U203, the switch k is controlled to be turned on, and the voltage of the connecting end of the resistors R1 and R2 is V2; if the driving signal is not detected, the second control circuit U202 samples the drain-source terminal voltage Vds of the synchronous rectifier tube, when the time that Vds is smaller than the second threshold reaches the threshold time Tsec, the second control circuit U202 outputs a B signal, the low-level signal EN output by the logic circuit U203 is disabled, the switch k1 is controlled to be turned off, the voltage at the connection end of the resistors R1 and R2 is V1, the voltage V2 is the voltage of the V1 after voltage division through the resistors R1 and R2, and the voltage V1 is greater than the voltage V2.
Fig. 4 illustrates a waveform diagram of a first threshold, after the EN enable indicates that the main power tube is turned off, the synchronous rectifier tube is normally turned on, and the obtained first threshold is V2; after the EN does not enable the characterization main power tube to be turned off, the synchronous rectifier tube is not normally turned on, and the time when the drain-source voltage Vds of the synchronous rectifier tube is less than the second threshold reaches the threshold time (refer to a waveform diagram in an EN disable state, fig. 5), and the obtained first threshold is V1.
Although the embodiments have been described and illustrated separately, it will be apparent to those skilled in the art that some common techniques may be substituted and integrated between the embodiments, and reference may be made to one of the embodiments not explicitly described, or to another embodiment described.
The above-described embodiments do not limit the scope of the present invention. Any modification, equivalent replacement, and improvement made within the spirit and principle of the above-described embodiments should be included in the protection scope of the technical solution.

Claims (10)

1. A control method of a flyback circuit comprises a main power tube, a synchronous rectifier tube and a transformer, and is characterized in that: during the conduction period of the main power tube, obtaining a first control signal according to the drain voltage of the synchronous rectifier tube or according to the drain voltage of the synchronous rectifier tube and the output voltage of the switch circuit; when the first control signal is larger than a first threshold value, the synchronous rectifier tube can be normally conducted after the main power tube is turned off; the first threshold is a hysteresis signal value.
2. The method of claim 1, wherein: and setting the first threshold value according to the switching state of the last switching period of the synchronous rectifier tube.
3. The method of claim 2, wherein:
in the last switching period, after the main power tube is switched off, if the driving voltage of the synchronous rectifier tube is detected, the first threshold is set as a first voltage;
in the last switching period, after the main power tube is switched off, if the driving voltage of the synchronous rectifier tube is not detected and the duration time that the drain voltage of the synchronous rectifier tube is smaller than a second threshold reaches a first time, setting the first threshold as a second voltage;
if the driving voltage of the synchronous rectifier tube is not detected, and the duration time that the drain voltage of the synchronous rectifier tube is smaller than the second threshold value does not reach the first time, the first threshold value is kept at the first voltage; the second voltage is greater than the first voltage.
4. The method of claim 1, wherein:
and obtaining the first control signal according to the change rate of the drain voltage of the synchronous rectifier tube during the conduction period of the main power tube.
5. The method of claim 1, wherein:
and during the conduction period of the main power tube, integrating the difference value of the drain voltage of the synchronous rectifier tube and the output voltage of the switching circuit to obtain the first control signal.
6. The utility model provides a flyback circuit's control circuit, flyback circuit includes main power tube, synchronous rectifier tube and transformer, its characterized in that:
a first control circuit for outputting a first control signal according to a drain voltage of the synchronous rectifier tube or according to the drain voltage of the synchronous rectifier tube and an output voltage of the switching circuit;
the setting circuit is used for setting a first threshold value according to the switching state of the synchronous rectifier tube in the last switching period, wherein the first threshold value is a hysteresis signal value;
when the first control signal is larger than the first threshold value, the synchronous rectifier tube can be conducted after the main power tube is turned off.
7. The control circuit of the flyback circuit of claim 6, wherein: the setting circuit comprises a detection circuit and a second control circuit, and in the last switching period, after the main power tube is switched off, if the detection circuit detects the driving voltage of the synchronous rectifier tube, a first threshold value is set as a first voltage; if the voltage of the driver of the synchronous rectifier tube is not detected, the second control circuit compares the drain voltage of the synchronous rectifier tube with a second threshold value and times, and if the duration time that the drain voltage of the synchronous rectifier tube is smaller than the second threshold value reaches a first time, the first threshold value is set as the second voltage; if the duration time that the drain voltage of the synchronous rectifier tube is smaller than the second threshold value does not reach the first time, keeping the first threshold value as the first voltage; the second voltage is greater than the first voltage.
8. The control circuit of the flyback circuit of claim 6, wherein: the setting circuit further comprises a first resistor, a second resistor and a first switch, wherein after the first resistor and the second resistor are connected in series, one end of the first resistor receives a second voltage, the other end of the first resistor is grounded through the first switch, and the voltage of the common connection end of the first resistor and the second resistor is a first threshold value; when the driving voltage of the synchronous rectifier tube is detected, the first switch is conducted; when the driving voltage of the synchronous rectifier tube is not detected, and the time that the drain voltage of the synchronous rectifier tube is smaller than the second threshold value reaches the first time, the first switch is turned off.
9. The control circuit of the flyback circuit of claim 6, wherein: the first control circuit detects the change rate of the drain voltage of the synchronous rectifier tube to obtain the first control signal.
10. The control circuit of the flyback circuit of claim 6, wherein: during the conduction period of the main power tube, the first control circuit integrates the difference value of the drain voltage of the synchronous rectifier tube and the output voltage of the switch circuit to obtain the first control signal.
CN202011319057.XA 2020-11-23 2020-11-23 Control method and control circuit of flyback circuit Pending CN112383227A (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
CN202011319057.XA CN112383227A (en) 2020-11-23 2020-11-23 Control method and control circuit of flyback circuit

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
CN202011319057.XA CN112383227A (en) 2020-11-23 2020-11-23 Control method and control circuit of flyback circuit

Publications (1)

Publication Number Publication Date
CN112383227A true CN112383227A (en) 2021-02-19

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Application Number Title Priority Date Filing Date
CN202011319057.XA Pending CN112383227A (en) 2020-11-23 2020-11-23 Control method and control circuit of flyback circuit

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Country Link
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