CN112271927A - Control circuit and control method of synchronous rectifier tube and flyback voltage conversion circuit - Google Patents
Control circuit and control method of synchronous rectifier tube and flyback voltage conversion circuit Download PDFInfo
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- 238000005070 sampling Methods 0.000 claims abstract description 25
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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
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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
- H02M1/32—Means for protecting converters other than automatic disconnection
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Abstract
The invention relates to a control circuit and a control method of a synchronous rectifier tube and a flyback voltage conversion circuit. The control circuit comprises a sampling circuit connected with the synchronous rectifier tube on the secondary side and used for collecting the drain-source voltage of the synchronous rectifier tube; the detection circuit is connected with the sampling circuit and used for outputting a primary side conduction signal when detecting that the drain-source voltage is continuously greater than a first threshold value within a first preset time and outputting a primary side conduction signal when detecting that the change amplitude of the drain-source voltage is greater than an amplitude threshold value within a second preset time; the conduction control circuit is connected with the detection circuit and is used for controlling the conduction of the synchronous rectifier tube when a primary side conduction signal is detected and the drain-source voltage is smaller than a third threshold value; the primary side conduction signal is used for representing the conduction of the primary side switch. The misconduction of the synchronous rectifier tube caused by parasitic oscillation is avoided, and the purpose of accurately controlling the conduction of the synchronous rectifier switching tube is achieved.
Description
Technical Field
The invention relates to the technical field of synchronous rectification, in particular to a control circuit and a control method of a synchronous rectifying tube and a flyback voltage conversion circuit.
Background
With the development of electronic technology, synchronous rectification circuits are widely used in situations where high conversion efficiency is required due to their high conversion efficiency. The synchronous rectification circuit generally refers to a circuit that receives an input voltage at a primary side of a transformer, converts the input voltage into a desired output voltage at a secondary side of the transformer by using a synchronous rectification switching tube (i.e., a synchronous rectifier tube), and controls the on/off of the synchronous rectification switching tube through a control circuit of the synchronous rectifier tube.
In the secondary side synchronous rectification scheme, a control circuit of the synchronous rectification tube controls the on and off of the synchronous rectification switch tube according to the magnitude of the drain-source voltage of the secondary side synchronous rectification switch tube, and when the drain-source voltage of the rectification switch tube is detected to be smaller than a certain threshold value Vth1, the body diode of the synchronous rectification switch tube is considered to be conducted, so that the rectification switch tube can be controlled to be turned on. However, in this control method, if the power supply operates in a DCM Mode (Discontinuous Conduction Mode), after the primary side switching tube is turned off, the control circuit of the synchronous rectifier tube may oscillate, and parasitic oscillation of the control circuit may also cause the body diode of the synchronous rectifier switching tube to be turned on, which may cause misconduction of the synchronous rectifier switching tube, and this control circuit may not accurately control the Conduction of the synchronous rectifier switching tube, and the power supply efficiency is low.
Disclosure of Invention
Therefore, it is necessary to provide a control circuit and a control method for a synchronous rectifier and a flyback voltage converting circuit, which are used to solve the problem that the control circuit of the synchronous rectifier cannot accurately control the conduction of the synchronous rectifier.
A control circuit for a synchronous rectifier, the control circuit comprising:
the sampling circuit is connected with the synchronous rectifying tube on the secondary side and is used for collecting the drain-source voltage of the synchronous rectifying tube;
the detection circuit is connected with the sampling circuit and used for outputting a primary side conduction signal when detecting that the drain-source voltage is continuously greater than a first threshold value within a first preset time, and the detection circuit is also used for outputting a primary side conduction signal when detecting that the change amplitude of the drain-source voltage is greater than an amplitude threshold value within a second preset time;
the conduction control circuit is connected with the detection circuit and used for controlling the synchronous rectifier tube to be conducted when the primary side conduction signal is detected and the drain-source voltage is smaller than a third threshold value;
and the primary side conduction signal is used for representing the conduction of the primary side switch.
In one embodiment, the detection circuit comprises:
the first detection circuit is used for outputting the primary side conduction signal when detecting that the drain-source voltage is continuously greater than the first threshold value within the first preset time; the first detection circuit comprises
A first comparison circuit for comparing the drain-source voltage with the first threshold;
and the timing circuit is electrically connected with the first comparison circuit and is used for starting timing when the drain-source voltage is greater than the first threshold value and outputting the primary side conduction signal after a first preset time.
In one embodiment, the timing circuit includes:
the integration module is used for carrying out integration operation on time to obtain an integration signal;
the first signal comparison module is connected with the integration module and used for outputting the primary side conduction signal according to the integration signal and a first reference signal;
the first reference signal is an integration signal corresponding to the first preset time.
In one embodiment, the first comparison circuit is connected to the integration module, and the first comparison circuit is configured to control the integration module to clear the integration signal when the drain-source voltage is smaller than the first threshold.
In one embodiment, the integration module comprises a current source, an integration unit and a zero clearing switch, wherein,
the current source is connected with the integrating unit and used for providing an integrating power supply for the integrating unit;
the integration unit is used for integrating the integration power supply to time to obtain an integration signal;
the zero clearing switch is respectively connected with the current source and the integration unit and used for controlling the integration unit to integrate the integration power source with time when the integration unit is switched off and controlling the integration unit to clear the integration signal when the integration unit is switched on.
In one embodiment, the timing circuit further includes a duration configuration module, and the duration configuration module is configured to configure the first reference signal.
In one embodiment, the detection circuit comprises:
and the second detection circuit comprises a second comparison circuit which is used for comparing the drain-source voltage with a second threshold value and outputting the primary side conducting signal when the drain-source voltage is greater than the second threshold value, and the second threshold value is greater than the maximum value of the drain-source voltage when the primary side switch is in a closed state.
In one embodiment, the detection circuit comprises:
the third detection circuit is used for outputting the primary side conduction signal when detecting that the change amplitude of the drain-source voltage is larger than the amplitude threshold value in second preset time; the third detection circuit comprises a differential module for differentiating the drain-source voltage with time to obtain a differential signal; the second signal comparison module is connected with the differential module and used for outputting the primary side conduction signal according to the differential signal and a second reference signal;
the second reference signal refers to a differential signal corresponding to the second preset time.
In one embodiment, the differentiating module comprises a differentiating capacitor and a differentiating resistor, wherein,
the differential capacitor is connected with the differential resistor and is used for providing drain-source voltage for the differential resistor;
the differential resistor is used for differentiating the drain-source voltage with respect to time to obtain a differential signal.
In one embodiment, the third detection circuit further comprises a second reference signal configuration circuit for adjusting a second reference signal to configure the amplitude threshold.
In one embodiment, the control circuit further comprises:
the turn-off control circuit is connected with the sampling circuit and used for outputting a control signal for controlling the turn-off of the synchronous rectifier tube when the drain-source voltage is greater than a fourth threshold value;
the reset end of the first trigger circuit is connected with the output end of the turn-off control circuit, the position end of the first trigger circuit is connected with the output end of the turn-on control circuit, and the output end of the first trigger circuit is connected with the grid electrode of the synchronous rectifier tube;
the reset end of the second trigger circuit is connected with the output end of the first trigger circuit, the position end of the second trigger circuit is connected with the detection circuit, and the output end of the second trigger circuit is connected with the input end of the breakover circuit;
wherein the fourth threshold is greater than the third threshold.
The control circuit of the synchronous rectifier tube outputs a primary side conduction signal when detecting that the drain-source voltage of the synchronous rectifier tube is continuously greater than a first threshold value within a first preset time through a detection circuit, outputs the primary side conduction signal when detecting that the variation amplitude of the drain-source voltage is greater than an amplitude threshold value within a second preset time, and controls the synchronous rectifier tube to be conducted when detecting the primary side conduction signal and the drain-source voltage is less than a third threshold value through a conduction control circuit connected with the detection circuit; the primary side conduction signal is used for representing that the primary side switch is in a conduction state. The detection circuit in this application can accurately judge that the primary side switch is in a conduction state according to the drain-source voltage of the synchronous rectifier tube on the secondary side, then outputs the primary side conduction signal, and the conduction control circuit controls the synchronous rectifier tube to conduct when detecting the primary side conduction signal and the drain-source voltage is less than the critical value of the drain-source voltage when the body diode of the synchronous rectifier tube conducts, and considers that the body diode of the synchronous rectifier switch tube has conducted when the drain-source voltage is less than a certain threshold Vth1, and then controls the rectifier switch tube to conduct for comparison, thereby avoiding the misconduction of the synchronous rectifier tube caused by parasitic oscillation, achieving the purpose of accurately controlling the conduction of the synchronous rectifier switch tube and improving the efficiency of the power supply.
A method of controlling a synchronous rectifier, the method comprising:
obtaining the drain-source voltage of the synchronous rectifier tube on the secondary side;
outputting a primary side conduction signal when the drain-source voltage is continuously greater than a first threshold value within a first preset time;
or when the change amplitude of the drain-source voltage in a second preset time is greater than an amplitude threshold value, outputting a primary side conduction signal;
when the primary side conduction signal is detected and the drain-source voltage is smaller than a third threshold value, controlling the synchronous rectifier tube to be conducted;
the primary side conduction signal is used for representing that the primary side switch is in a conduction state.
In one embodiment, the control method further includes outputting the primary side conduction signal when the drain-source voltage is greater than a second threshold value, where the second threshold value is greater than a maximum value of the drain-source voltage when the primary side switch is in an off state.
In one embodiment, the control method further includes:
when the drain-source voltage is smaller than a fourth threshold value, controlling the synchronous rectifier tube to be turned off;
wherein the fourth threshold is greater than the third threshold.
A flyback voltage conversion circuit comprises a primary side circuit and a secondary side circuit, wherein the secondary side circuit comprises a synchronous rectifier tube and any one of the control circuits.
According to the control method of the synchronous rectifier tube and the flyback voltage conversion circuit, the primary side switch can be accurately judged to be in a conduction state according to the drain-source voltage of the secondary side synchronous rectifier tube, then a primary side conduction signal is output, when the primary side conduction signal is detected and the drain-source voltage is smaller than the critical value of the drain-source voltage when the body diode of the synchronous rectifier tube is conducted, the synchronous rectifier tube is controlled to be conducted, and compared with the situation that the body diode of the synchronous rectifier tube is considered to be conducted when the drain-source voltage is smaller than a certain threshold Vth1, the conduction of the synchronous rectifier tube caused by parasitic oscillation is avoided, the conduction of the synchronous rectifier tube is accurately controlled, and the purpose of improving the efficiency of a power supply is achieved.
A control circuit for a synchronous rectifier, the control circuit comprising:
the sampling circuit is connected with the synchronous rectifying tube on the secondary side and is used for collecting the drain-source voltage of the synchronous rectifying tube;
the detection circuit is connected with the sampling circuit and comprises at least two of the following three detection circuits:
the first detection circuit is used for outputting a primary side conduction signal when detecting that the drain-source voltage is continuously greater than a first threshold value within a first preset time;
the second detection circuit is used for outputting a primary side conduction signal when detecting that the drain-source voltage is greater than a second threshold value;
the third detection circuit is used for outputting a primary side conduction signal when detecting that the change amplitude of the drain-source voltage is larger than an amplitude threshold value within second preset time; and
the conduction control circuit is connected with the detection circuit and used for controlling the synchronous rectifier tube to be conducted when the primary side conduction signal is detected and the drain-source voltage is smaller than a third threshold value;
and the primary side conduction signal is used for representing the conduction of the primary side switch.
The control circuit of the synchronous rectifier tube outputs a primary side conduction signal when detecting that the drain-source voltage of the synchronous rectifier tube is continuously larger than a first threshold value within a first preset time through a detection circuit, or/and outputs a primary side conduction signal when detecting that the variation amplitude of the drain-source voltage is larger than an amplitude threshold value within a second preset time, or/and outputs a primary side conduction signal when detecting that the drain-source voltage is larger than a second threshold value, and controls the synchronous rectifier tube to be conducted when detecting the primary side conduction signal and the drain-source voltage is smaller than a third threshold value through a conduction control circuit connected with the detection circuit; the primary side conduction signal is used for representing the conduction of the primary side switch. The detection circuit in this application can accurately judge that the primary side switch is in a conduction state according to the drain-source voltage of the synchronous rectifier tube on the secondary side, then outputs the primary side conduction signal, and the conduction control circuit controls the synchronous rectifier tube to conduct when detecting the primary side conduction signal and the drain-source voltage is less than the critical value of the drain-source voltage when the body diode of the synchronous rectifier tube conducts, and considers that the body diode of the synchronous rectifier switch tube has conducted when the drain-source voltage is less than a certain threshold Vth1, and then controls the rectifier switch tube to conduct for comparison, thereby avoiding the misconduction of the synchronous rectifier tube caused by parasitic oscillation, achieving the purpose of accurately controlling the conduction of the synchronous rectifier switch tube and improving the efficiency of the power supply.
Drawings
In order to more clearly illustrate the technical solutions in the embodiments or the conventional technologies of the present application, the drawings used in the descriptions of the embodiments or the conventional technologies will be briefly introduced below, it is obvious that the drawings in the following descriptions are only some embodiments of the present application, and for those skilled in the art, other drawings can be obtained according to the drawings without creative efforts.
FIG. 1 is a block diagram of a control circuit of a synchronous rectifier according to an embodiment;
FIG. 2 is a block diagram of an embodiment of a detection circuit;
FIG. 3 is a circuit diagram of a first detection circuit in one embodiment;
FIG. 4 is a circuit diagram of a first detection circuit in another embodiment;
FIG. 5 is a circuit diagram of a detection circuit in another embodiment;
FIG. 6 is a circuit diagram of a third detection circuit according to an embodiment;
FIG. 7 is a schematic diagram of a control circuit according to another embodiment;
FIG. 8 is a detailed circuit diagram of a control circuit of the synchronous rectifier device according to an embodiment;
FIG. 9 is a schematic diagram illustrating a source-drain voltage Vds of the synchronous rectifier in an embodiment;
FIG. 10 is a schematic diagram illustrating a source-drain voltage Vds of a synchronous rectifier corresponding to a quasi-resonant mode in an embodiment;
fig. 11 is a schematic diagram of a source-drain voltage Vds of the synchronous rectifier tube corresponding to the continuous conduction mode in an embodiment;
fig. 12 is a schematic diagram of a source-drain voltage Vds of the synchronous rectifier tube corresponding to the critical conduction mode in an embodiment;
fig. 13 is a schematic diagram of a source-drain voltage Vds of the synchronous rectifier tube corresponding to the discontinuous conduction mode in an embodiment;
FIG. 14 is a flowchart illustrating a method for controlling a synchronous rectifier device according to an embodiment.
Detailed Description
To facilitate an understanding of the present application, the present application will now be described more fully with reference to the accompanying drawings. Embodiments of the present application are set forth in the accompanying drawings. This application may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete.
Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein in the description of the present application is for the purpose of describing particular embodiments only and is not intended to be limiting of the application.
It will be understood that, as used herein, the terms "first," "second," and the like may be used herein to describe various elements, but these elements are not limited by these terms. These terms are only used to distinguish one element from another. For example, a first resistance may be referred to as a second resistance, and similarly, a second resistance may be referred to as a first resistance, without departing from the scope of the present application. The first resistance and the second resistance are both resistances, but they are not the same resistance.
It is to be understood that "connection" in the following embodiments is to be understood as "electrical connection", "communication connection", and the like if the connected circuits, modules, units, and the like have communication of electrical signals or data with each other.
As used herein, the singular forms "a", "an" and "the" may include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms "comprises/comprising," "includes" or "including," etc., specify the presence of stated features, integers, steps, operations, components, parts, or combinations thereof, but do not preclude the presence or addition of one or more other features, integers, steps, operations, components, parts, or combinations thereof. Also, as used in this specification, the term "and/or" includes any and all combinations of the associated listed items.
Fig. 1 is a block diagram of a control circuit of a synchronous rectifier according to an embodiment.
In one embodiment, as shown in fig. 1, there is provided a control circuit for a synchronous rectifier, the control circuit comprising:
the sampling circuit 100 is connected with the secondary synchronous rectifier tube 200 and is used for collecting the drain-source voltage Vds of the synchronous rectifier tube 200; namely, the sampling circuit 100 is connected to the drain terminal d and the source terminal s of the synchronous rectifier tube 200, and is used to obtain the voltage Vds between the drain terminal and the source terminal of the synchronous rectifier tube 200;
the detection circuit 300 is connected to the sampling circuit 100, and is configured to output a primary side conduction signal when detecting that the drain-source voltage Vds is continuously greater than a first threshold within a first preset time, and the detection circuit 300 is further configured to output a primary side conduction signal when detecting that a variation amplitude of the drain-source voltage Vds is greater than an amplitude threshold within a second preset time; the primary side conduction signal is used for indicating that the primary side switch is conducted, for example, when the primary side conduction signal is an effective value such as a high level, the conduction of the primary side switch is detected.
The conduction control circuit 400 is connected to the detection circuit 300, and is configured to control the synchronous rectifier to be conducted when the primary side conduction signal is detected and the drain-source voltage Vds is smaller than a third threshold VTH 3;
in one embodiment, the third threshold VTH3 indicates a drain-source voltage when the body diode of the synchronous rectifier is turned on, the third threshold VTH3 is greater than or equal to a critical value of the drain-source voltage when the body diode of the synchronous rectifier is turned on, a time when the drain-source voltage is greater than the first threshold is less than a first preset time when the primary side switch is turned off, and a variation amplitude of the drain-source voltage in the second preset time is less than an amplitude threshold.
Fig. 2 is a block diagram of a detection circuit according to an embodiment, and fig. 3 is a circuit diagram of a first detection circuit according to an embodiment.
As shown in fig. 2 and 3, in one embodiment, the detection circuit 300 includes:
the first detection circuit is used for outputting the primary side conduction signal when detecting that the drain-source voltage Vds is continuously greater than the first threshold value VTH1 within the first preset time T1; the first detection circuit comprises
A first comparison circuit 302 for comparing the drain-source voltage Vds and the first threshold VTH 1;
and a timing circuit 304 electrically connected to the first comparing circuit 302, wherein the timing circuit 304 is configured to start timing when the drain-source voltage Vds is greater than the first threshold VTH1, and output the primary side turn-on signal after a first preset time T1.
In this embodiment, when the drain-source voltage Vds is greater than the first threshold VTH1, the first comparing circuit 302 controls the timing circuit 304 to start timing, and after the timing circuit 304 keeps timing for the first preset time T1, the primary side conducting signal is output to the conduction control circuit 400.
In one embodiment, the first threshold VTH1 is equal to the output voltage Vout of the secondary side of the synchronous rectifier 200.
As shown in fig. 3, in one embodiment, the timing circuit 304 includes:
an integrating module 3042, configured to perform an integrating operation on time t to obtain an integrated signal Vc when the drain-source voltage Vds is greater than the first threshold VTH 1;
a first signal comparing module 3044, connected to the integrating module 3042, for outputting the primary side conducting signal according to the integrated signal Vc and a first reference signal Vth _ T1;
the first reference signal Vth _ T1 is an integrated signal corresponding to the first preset time T1.
In one embodiment, the first reference signal Vth _ T1 is a preset value of the integrated signal corresponding to a first preset time T1, and if the integrated signal Vc is greater than Vth _ T1 after the first preset time T1, the primary side on signal is output.
In one embodiment, the first comparing circuit 302 is connected to the integrating module 3042, and the first comparing circuit 302 is configured to control the integrating module 3042 to zero the integrating signal Vc when the drain-source voltage Vds is smaller than the first threshold VTH1, so as to prevent interference in an oscillation period.
In one embodiment, the integration module 3042 includes a current source I1, an integration unit, and a clear switch S1, wherein,
the current source I1 is connected with the integrating unit and used for providing integrating power supply for the integrating unit;
the integration unit is used for integrating the integration power supply to time t to obtain an integration signal Vc;
the zero clearing switch S1 is connected to the current source I1 and the integrating unit, respectively, and is configured to control the integrating unit to integrate the integrating power source with respect to time t when the integrating unit is turned off, and control the integrating unit to clear the integration signal Vc when the integrating unit is turned on, where the integrating unit includes an integrating capacitor C1.
In this embodiment, at the beginning, the clear switch S1 is turned on, and the integration signal VC is zero, that is, the integration voltage loaded across the integration capacitor C1 is 0V; when the drain-source voltage Vds is greater than the first threshold VTH1, the first comparison circuit 302 outputs a low level signal for controlling the zero clearing switch S1 to be turned off, the zero clearing switch S1 is turned off, the current source I1 charges the integrating capacitor C1, the integrating signal Vc gradually increases, and when the integrating signal Vc is greater than the first reference signal VTH _ T1, the first signal comparison module 3044 outputs a primary side on signal to the on-control circuit 400. When the drain-source voltage Vds is not greater than the first threshold VTH1, the first comparison circuit 302 outputs a high level signal for controlling the zero switch S1 to be turned on, the zero switch S1 is turned off, the integrating capacitor C1 discharges, and the integrating signal Vc gradually decreases.
As shown in fig. 4, in one embodiment, the timing circuit 304 further includes a duration configuration module 3046, and the duration configuration module 3046 is configured to configure the first reference signal Vth _ T1.
By connecting the duration configuration module 3046 in series with the resistor Rcf1, the voltage across the first reference signal Vth _ T1, i.e., the duration configuration module 3046, can be adjusted.
In one implementation, the duration configuration module 3046 includes at least one of a resistor and a capacitor.
As shown in fig. 5, in one embodiment, the detection circuit 300 includes:
the second detection circuit comprises a second comparison circuit for comparing the drain-source voltage Vds with a second threshold value VTH2 and outputting the primary side conduction signal when the drain-source voltage Vds is greater than the second threshold value VTH2, and the second threshold value VTH2 is greater than the maximum value of the drain-source voltage Vds when the primary side switch is in a closed state.
In one embodiment, the second detection circuit includes a configuration module 306 and a regulation resistor Rcf2, and the magnitude of the second threshold VTH2 can be adjusted by regulating the resistor Rcf2 and the configuration module 306.
In one embodiment, the second threshold VTH2 is equal to 2 times the output voltage Vout of the secondary side of the synchronous rectifier 200.
As shown in fig. 6, in one embodiment, the detection circuit 300 includes:
the third detection circuit is used for outputting the primary side conduction signal when detecting that the change amplitude of the drain-source voltage Vds is larger than the amplitude threshold delta Vds within a second preset time T2; the third detection circuit comprises a differential module 308 for differentiating the drain-source voltage Vds with respect to time t to obtain a differential signal Vslope; the second signal comparing module 310 is connected to the differentiating module 308, and the second signal comparing module 310 is configured to output the primary side on signal according to the differentiated signal Vslope and a second reference signal Vth _ T2;
the second reference signal Vth _ T2 is a differential signal corresponding to the second predetermined time T2.
In one embodiment, the second reference signal Vth _ T2 is a preset value of a differential signal corresponding to the second preset time T2.
In one embodiment, the differentiating module 308 includes a differential capacitor C2 and a differential resistor R2, wherein,
the differential capacitor C2 is connected with the differential resistor R2 and is used for providing a drain-source voltage Vds for the differential resistor R2;
the differential resistor R2 is used for differentiating the drain-source voltage Vds with respect to time t to obtain a differential signal Vslope.
In this embodiment, the differentiating module 308 may obtain a slope of a rising edge of Vds, that is, a variation amplitude of the drain-source voltage Vds with time, and a voltage Vslope across the resistor R2 is R2C 2 (ddds/dt); vth _ T2 is equal to the preset value of the voltage across the resistor R2 corresponding to the second preset time T2. The voltage Vslope across the resistor R2 can reflect the slope of the rising edge of Vds, and if the Vslope is greater than Vth _ T2 after a second predetermined time T2, a primary side conduction signal is output.
In one embodiment, the third detection circuit further includes a second reference signal configuration circuit, the second reference signal configuration circuit includes a configuration circuit 312 and an adjusting resistor Rcf3, and the magnitude of the second reference signal Vth _ T2 can be adjusted by adjusting the resistor Rcf3 and the configuration circuit 312, so as to achieve the purpose of configuring the amplitude threshold Δ Vds.
FIG. 7 is a schematic diagram of a control circuit of a synchronous rectifier according to another embodiment.
As shown in fig. 7, in one embodiment, the control circuit further includes:
a turn-off control circuit 500, connected to the sampling circuit 100, for outputting a control signal for controlling the turn-off of the synchronous rectifier when the drain-source voltage Vds is greater than a fourth threshold VTH 4;
a reset terminal of the first trigger circuit 600 is connected to the output terminal of the turn-off control circuit 500, a set terminal of the first trigger circuit 600 is connected to the output terminal of the turn-on control circuit 400, and an output terminal of the first trigger circuit 600 is connected to the gate g of the synchronous rectifier 200;
a reset terminal of the second trigger circuit 700 is connected to the output terminal of the first trigger circuit 600, a set terminal of the second trigger circuit 700 is connected to the detection circuit 300, and an output terminal of the second trigger circuit 700 is connected to the input terminal of the turn-on circuit 400;
wherein the fourth threshold VTH4 is greater than the third threshold VTH 3.
Fig. 8 is a schematic circuit diagram of a control circuit of a synchronous rectifier according to an embodiment. The control circuit includes a sampling circuit 100, a detection circuit 300, a turn-on control circuit 400, a turn-off control circuit 500, a first trigger circuit 600, and a second trigger circuit 700.
As shown in fig. 8, the detection circuit 300 includes a first detection circuit, a second detection circuit, a third detection circuit, and a pulse output unit 314. Specifically, the structures of the modules in the detection circuit 300, the turn-on circuit 400, the turn-off control circuit 500, the first trigger circuit 600, and the second trigger circuit 700 are as follows:
the first detection circuit comprises a first comparison circuit 302 and a timing circuit 304, wherein the first comparison circuit 302 comprises a comparator A1, the positive input end of a comparator A1 is connected with the output end of the sampling circuit 100, and a sampling voltage of a drain-source voltage Vds is input; the inverting input terminal of the comparator A1 inputs the reference voltage of the first threshold VTH 1; the output end of the comparator a1 and the control end of the integrating module 3042 are connected to the timing circuit 304; the timing circuit 304 includes an integration module 3042, a first signal comparison module 3044 and a duration configuration module 3046, the integration module 3042 includes a current source I1, an integration capacitor C1 and a clear switch S1, the first signal comparison module 3044 includes a comparator a2, a control end of the clear switch S1 is an input end of the integration module 3042, a normally closed contact of the clear switch S1, one end of the integration capacitor C1 and one end of the current source I1 are commonly connected as an output end of the integration module 3042, a normally open contact of the clear switch S1 is grounded with the other end of the integration capacitor C1, an input end of the integration module 3042 is connected with an output end of the comparator a1, an output end of the integration module 3042 is connected with a forward input end of the comparator a2, an inverted input end of the comparator a2 is connected with the duration configuration module 3046, and an output end of the comparator a2 is connected with a first input end of the.
When the drain-source voltage Vds is greater than a first threshold VTH1, the comparator a1 outputs a comparison signal of a low level, the zero clearing switch S1 is turned off, the current source I1 charges the integrating capacitor C1, after a period of time (VTH _ T1 × C11/I1, i.e., T1), the voltage Vc across the integrating capacitor C1 is higher than VTH _ T1, the comparator a2 outputs an effective high level to the pulse output unit 314, and the output end of the pulse output unit 314 outputs an effective high level pulse PWM on for representing the conduction of the primary side switch; when the drain-source voltage Vds is not greater than the first threshold VTH1, the comparator a1 outputs a high-level comparison signal, the zero clearing switch S1 is turned on, the integrating capacitor C1 discharges, and the timer is cleared to achieve the purpose of preventing the interference of the oscillation period. The second detection circuit includes a second comparison circuit. The second comparison circuit includes a comparator A3, a non-inverting input terminal of the comparator A3 is connected to the output terminal of the sampling circuit 100, an inverting input terminal of the comparator A3 is set to the second threshold VTH2, and an output terminal of the comparator A3 is connected to the third input terminal of the pulse output unit 314. When Vds is greater than a second threshold TTH2, the output terminal of the comparator a4 outputs an active high level to the pulse output unit 314, and the output terminal of the pulse output unit 314 outputs an active high level pulse PWM on for indicating that the primary side switch is turned on.
The third detection circuit includes a differentiation module 308, a configuration circuit 312, and a second signal comparison module 310. The differential module 308 in the third detection circuit comprises a differential capacitor C2 and a differential resistor R2, the second signal comparison module 310 comprises a comparator a4, one end of the differential capacitor C2 is connected with the output end of the sampling circuit 100, the other end of the differential capacitor C2 is connected with the non-inverting input end of the comparator a4, one end of the differential resistor R2 is connected with the non-inverting input end of the comparator a4, the other end of the differential resistor R3538 is grounded, the inverting input end of the comparator a4 is connected with the configuration circuit 312, and the output end of the comparator a4 is connected with the third input end of the pulse output unit 314.
The voltage Vslope at the positive input terminal of the comparator a4 is equal to the voltage across the resistor R2, and is R2C 2 (ddds/dt), and the Vslope can be used to represent the rising slope of the drain-source voltage Vds, when the Vslope is greater than Vth _ T2, the output terminal of the comparator a4 outputs an active high level to the pulse output unit 314, and the output terminal of the pulse output unit 314 outputs an active high level pulse PWM on for representing the conduction of the primary side of the switch.
The pulse output unit 314 includes an OR gate OR, a first input terminal of which is a first input terminal of the pulse output unit 314, a second input terminal of which is a second input terminal of the pulse output unit 314, a third input terminal of which is a third input terminal of the pulse output unit 314, and an output terminal of which is an output terminal of the pulse output unit 314. In this way, when any one of the first detection circuit, the second detection circuit and the third detection circuit provides an effective high-level signal, the detection circuit 300 provides an effective primary side conduction signal PWM on for performing reliable synchronous rectification control on the synchronous rectifier under various conditions. In further embodiments, the detection circuit 300 includes only any two of the first detection circuit, the second detection circuit, and the third detection circuit.
The turn-on control circuit 400 includes a comparator a5 AND an AND gate AND, the turn-off control circuit 500 includes a comparator a6, the first flip-flop circuit 600 includes a flip-flop T1, AND the second flip-flop circuit 700 includes a flip-flop T2.
The set end S of the flip-flop T2 is connected with the output end of the pulse output unit 314, the reset end R of the flip-flop T2 is connected with the output end Q of the flip-flop T1, the output end Q of the flip-flop T2 is connected with the first input end of the AND gate AND, the non-inverting input end of the comparator A5 is set to be the third threshold VTH3, the inverting input end of the comparator A5 is connected with the output end of the sampling circuit 100, the output end of the comparator A5 is connected with the second input end of the AND gate AND, the output end of the AND gate AND is connected with the set end S of the flip-flop T1, the reset end R of the flip-flop T1 is connected with the output end of the comparator A6, AND the output end; the non-inverting input terminal of the comparator a6 is connected to the output terminal of the sampling circuit 100, and the inverting input terminal of the comparator a6 is set to the fourth threshold VTH 4.
When the output end of the pulse output unit 314 outputs an active high-level pulse PWM on to the set end S of the flip-flop T2 AND the drain-source voltage Vds is smaller than the third threshold VTH3, the flip-flop T2 outputs a high level to the first input end of the AND gate AND, the comparator a5 outputs a high level to the second input end of the AND gate AND, the AND gate AND outputs a high level to the set end S of the flip-flop T1, AND the flip-flop T1 outputs a high-level switching control signal to control the synchronous rectifier 200 to be turned on. When the drain-source voltage Vds is greater than the fourth threshold VTH4, the comparator a6 outputs a high level to the reset terminal R of the flip-flop T1, and the flip-flop T1 outputs a low level switching control signal to control the synchronous rectifier 200 to turn off.
The following description exemplifies that the detection circuit 300 includes a first detection circuit, a second detection circuit, a third detection circuit, and a pulse output unit 314.
Fig. 9 is a schematic diagram of a source-drain voltage Vds of the synchronous rectifier in an embodiment.
As shown in fig. 1 and 9, in the switching power supply where the control circuit of the synchronous rectifier shown in fig. 1 is located, Vin > Nps × Vout, where Vin is an input voltage of a primary side of the switching power supply, Vout is an output voltage of a secondary side of the switching power supply, Nps is a primary-secondary side transformation ratio of a transformer, a central value of parasitic oscillation is Vout during parasitic oscillation 1, an amplitude of the parasitic oscillation does not exceed Vout, a second threshold value VTH2 is set to 2Vout, when the second detection circuit detects that a source-drain voltage Vds >2 × Vout, the detection circuit 300 determines that the primary side of the switching power supply is at a PWM on time, that is, the primary side is on, the detection circuit 300 inputs a high level (PWM on) to the pulse output unit 314, and controls the synchronous rectifier to be on (SR Gate high level) when the drain-source voltage Vds is less than a third threshold value VTH 3.
Fig. 10 is a schematic diagram of a source-drain voltage Vds of the synchronous rectifier tube corresponding to the quasi-resonant mode in an embodiment.
As shown in fig. 1 and 10, in the switching power supply where the control circuit of the synchronous rectifier shown in fig. 1 is located, Vin is not more than Nps × Vout, and as can be seen from fig. 10, the rising slope of Vds is slow, but the duration T of Vds being greater than Vout is long, and the duration of Vds being greater than Vout is generally short in the parasitic oscillation. Assuming that the first threshold VTH1 is Vout, the first preset time T1 is equal to or less than the duration T that Vds is greater than Vout and is greater than the duration that Vds is greater than Vout at the parasitic oscillation. When a first detection circuit in the detection circuit 300 detects that the drain-source voltage Vds is continuously greater than the Vout within a first preset time T1, the first detection circuit determines that the primary side of the switching power supply is at a PWM on time, that is, the primary side is turned on, the detection circuit 300 inputs a high level (PWM on) to the pulse output unit 314, and when the drain-source voltage Vds is less than a third threshold VTH3, the synchronous rectifier tube is controlled to be turned on (SR Gate high level).
Fig. 11 is a schematic diagram of a source-drain voltage Vds of a synchronous rectifier corresponding to the continuous conduction mode in an embodiment; fig. 12 is a schematic diagram of a source-drain voltage Vds of a synchronous rectifier corresponding to the critical conduction mode in an embodiment; fig. 13 is a schematic diagram of a source-drain voltage Vds of the synchronous rectifier corresponding to the discontinuous conduction mode in an embodiment.
As shown in fig. 1 and 11-13, in the switching power supply where the control circuit of the synchronous rectifier shown in fig. 1 is located, Vin ≦ Nps × Vout, as can be seen from fig. 11-13, there are portions where the slope of the rising edge of Vds is steep, and the slope of Vds of parasitic oscillation is slow. When a third detection circuit in the detection circuit 300 detects that the voltage Vslope at the non-inverting input terminal of the comparator a4 is greater than Vth _ T2, the third detection circuit determines that the primary side of the switching power supply is at the PWM on time, that is, the primary side is turned on, the detection circuit 300 inputs a high level (PWM on) to the pulse output unit 314, and controls the synchronous rectifier tube to be turned on (SR Gate high level) when the drain-source voltage Vds is less than a third threshold Vth 3.
The control circuit of synchronous rectifier tube in this application is when avoiding synchronous rectifier tube to vibrate the department misconduction in the parasitism, can be applicable to different conduction mode, like quasi-resonance mode (QR mode), continuous conduction mode (CCM mode), critical conduction mode (CRM mode) and discontinuous conduction mode (DCM mode).
The control circuit of the synchronous rectifier tube outputs a primary side conduction signal when detecting that the drain-source voltage of the synchronous rectifier tube is continuously greater than a first threshold value within a first preset time through a detection circuit, outputs the primary side conduction signal when detecting that the variation amplitude of the drain-source voltage is greater than an amplitude threshold value within a second preset time, and controls the synchronous rectifier tube to be conducted when detecting the primary side conduction signal and the drain-source voltage is less than a third threshold value through a conduction control circuit connected with the detection circuit; the primary side conduction signal is used for representing that the primary side switch is in a conduction state. The detection circuit in this application can accurately judge that the primary side switch is in a conduction state according to the drain-source voltage of the synchronous rectifier tube on the secondary side, then outputs the primary side conduction signal, and the conduction control circuit controls the synchronous rectifier tube to conduct when detecting the primary side conduction signal and the drain-source voltage is less than the critical value of the drain-source voltage when the body diode of the synchronous rectifier tube conducts, and considers that the body diode of the synchronous rectifier switch tube has conducted when the drain-source voltage is less than a certain threshold Vth1, and then controls the rectifier switch tube to conduct for comparison, thereby avoiding the misconduction of the synchronous rectifier tube caused by parasitic oscillation, achieving the purpose of accurately controlling the conduction of the synchronous rectifier switch tube and improving the efficiency of the power supply.
As shown in fig. 14, in one embodiment, there is provided a control method of a synchronous rectifier tube, the control method including:
and S102, acquiring the drain-source voltage of the synchronous rectifier tube on the secondary side.
And S104, outputting a primary side conduction signal according to the drain-source voltage.
Outputting a primary side conduction signal when the drain-source voltage is continuously greater than a first threshold value within a first preset time; or when the change amplitude of the drain-source voltage in a second preset time is larger than the amplitude threshold value, outputting a primary side conduction signal. The primary side conduction signal is used for representing that the primary side switch is in a conduction state.
In one embodiment, when the primary side switch is in the off state, the time when the drain-source voltage is greater than the first threshold is less than a first preset time, and the variation amplitude of the drain-source voltage in the second preset time is less than an amplitude threshold.
And S106, controlling the synchronous rectifier tube to be conducted.
And when the primary side conduction signal is detected and the drain-source voltage is smaller than a third threshold value, controlling the synchronous rectifier tube to be conducted.
In one embodiment, the third threshold value indicates a drain-source voltage when a body diode of the synchronous rectifier tube is turned on, and the third threshold value VTH3 is greater than or equal to a critical value of the drain-source voltage when the body diode of the synchronous rectifier tube is turned on.
In one embodiment, the control method further includes outputting the primary side conduction signal when the drain-source voltage is greater than a second threshold value, where the second threshold value is greater than a maximum value of the drain-source voltage when the primary side switch is in an off state.
In one embodiment, the control method further includes:
when the drain-source voltage is smaller than a fourth threshold value, controlling the synchronous rectifier tube to be turned off;
wherein the fourth threshold is greater than the third threshold.
In one embodiment, a flyback voltage conversion circuit is provided, which includes a primary circuit and a secondary circuit, where the secondary circuit includes a synchronous rectifier and the control circuit described in any one of the above embodiments.
According to the control method of the synchronous rectifier tube and the flyback voltage conversion circuit, the primary side switch can be accurately judged to be in a conduction state according to the drain-source voltage of the secondary side synchronous rectifier tube, then a primary side conduction signal is output, when the primary side conduction signal is detected and the drain-source voltage is smaller than the critical value of the drain-source voltage when the body diode of the synchronous rectifier tube is conducted, the synchronous rectifier tube is controlled to be conducted, and compared with the situation that the body diode of the synchronous rectifier tube is considered to be conducted when the drain-source voltage is smaller than a certain threshold Vth1, the conduction of the synchronous rectifier tube caused by parasitic oscillation is avoided, the conduction of the synchronous rectifier tube is accurately controlled, and the purpose of improving the efficiency of a power supply is achieved.
In one embodiment, a control circuit for a synchronous rectifier is provided, the control circuit comprising:
the sampling circuit is connected with the synchronous rectifying tube on the secondary side and is used for collecting the drain-source voltage of the synchronous rectifying tube;
the detection circuit is connected with the sampling circuit and comprises at least two of the following three detection circuits:
the first detection circuit is used for outputting a primary side conduction signal when detecting that the drain-source voltage is continuously greater than a first threshold value within a first preset time;
the second detection circuit is used for outputting a primary side conduction signal when detecting that the drain-source voltage is greater than a second threshold value;
the third detection circuit is used for outputting a primary side conduction signal when detecting that the change amplitude of the drain-source voltage is larger than an amplitude threshold value within second preset time; and
the conduction control circuit is connected with the detection circuit and used for controlling the synchronous rectifier tube to be conducted when the primary side conduction signal is detected and the drain-source voltage is smaller than a third threshold value;
and the primary side conduction signal is used for representing the conduction of the primary side switch.
In one embodiment, the third threshold value indicates a drain-source voltage when a body diode of the synchronous rectifier tube is turned on, and the third threshold value VTH3 is greater than or equal to a critical value of the drain-source voltage when the body diode of the synchronous rectifier tube is turned on.
In one embodiment, when the primary side switch is turned off, the time when the drain-source voltage is greater than the first threshold is less than a first preset time, and the variation amplitude of the drain-source voltage in the second preset time is less than an amplitude threshold.
It should be noted that the aforementioned first detection circuit is also applicable to the first detection circuit in this embodiment, the aforementioned second detection circuit is also applicable to the second detection circuit in this embodiment, the aforementioned third detection circuit is also applicable to the third detection circuit in this embodiment, and the aforementioned turn-on control circuit is also applicable to the turn-on circuit in this embodiment, which is not repeated herein.
The control circuit of the synchronous rectifier tube outputs a primary side conduction signal when detecting that the drain-source voltage of the synchronous rectifier tube is continuously larger than a first threshold value within a first preset time through a detection circuit, or/and outputs a primary side conduction signal when detecting that the variation amplitude of the drain-source voltage is larger than an amplitude threshold value within a second preset time, or/and outputs a primary side conduction signal when detecting that the drain-source voltage is larger than a second threshold value, and controls the synchronous rectifier tube to be conducted when detecting the primary side conduction signal and the drain-source voltage is smaller than a third threshold value through a conduction control circuit connected with the detection circuit; the primary side conduction signal is used for representing the conduction of the primary side switch. The detection circuit in this application can accurately judge that the primary side switch is in a conduction state according to the drain-source voltage of the synchronous rectifier tube on the secondary side, then outputs the primary side conduction signal, and the conduction control circuit controls the synchronous rectifier tube to conduct when detecting the primary side conduction signal and the drain-source voltage is less than the critical value of the drain-source voltage when the body diode of the synchronous rectifier tube conducts, and considers that the body diode of the synchronous rectifier switch tube has conducted when the drain-source voltage is less than a certain threshold Vth1, and then controls the rectifier switch tube to conduct for comparison, thereby avoiding the misconduction of the synchronous rectifier tube caused by parasitic oscillation, achieving the purpose of accurately controlling the conduction of the synchronous rectifier switch tube and improving the efficiency of the power supply.
In the description herein, references to the description of "some embodiments," "other embodiments," "desired embodiments," etc., mean that a particular feature, structure, material, or characteristic described in connection with the embodiment or example is included in at least one embodiment or example of the invention. In this specification, a schematic description of the above terminology may not necessarily refer to the same embodiment or example.
The technical features of the embodiments described above may be arbitrarily combined, and for the sake of brevity, all possible combinations of the technical features in the embodiments described above are not described, but should be considered as being within the scope of the present specification as long as there is no contradiction between the combinations of the technical features.
The above-mentioned embodiments only express several embodiments of the present invention, and the description thereof is more specific and detailed, but not construed as limiting the scope of the invention. It should be noted that, for a person skilled in the art, several variations and modifications can be made without departing from the inventive concept, which falls within the scope of the present invention. Therefore, the protection scope of the present patent shall be subject to the appended claims.
Claims (16)
1. A control circuit for a synchronous rectifier, the control circuit comprising:
the sampling circuit is connected with the synchronous rectifying tube on the secondary side and is used for collecting the drain-source voltage of the synchronous rectifying tube;
the detection circuit is connected with the sampling circuit and used for outputting a primary side conduction signal when detecting that the drain-source voltage is continuously greater than a first threshold value within a first preset time, and the detection circuit is also used for outputting a primary side conduction signal when detecting that the change amplitude of the drain-source voltage is greater than an amplitude threshold value within a second preset time;
the conduction control circuit is connected with the detection circuit and used for controlling the synchronous rectifier tube to be conducted when the primary side conduction signal is detected and the drain-source voltage is smaller than a third threshold value;
wherein the primary side conduction signal is used to characterize the conduction of the primary side switch.
2. The control circuit of claim 1, wherein the detection circuit comprises:
the first detection circuit is used for outputting the primary side conduction signal when detecting that the drain-source voltage is continuously greater than the first threshold value within the first preset time; the first detection circuit comprises
A first comparison circuit for comparing the drain-source voltage with the first threshold;
and the timing circuit is electrically connected with the first comparison circuit and is used for starting timing when the drain-source voltage is greater than the first threshold value and outputting the primary side conduction signal after a first preset time.
3. The control circuit of claim 2, wherein the timing circuit comprises:
the integration module is used for carrying out integration operation on time to obtain an integration signal;
the first signal comparison module is connected with the integration module and used for outputting the primary side conduction signal according to the integration signal and a first reference signal;
the first reference signal is an integration signal corresponding to the first preset time.
4. The control circuit of claim 3, wherein the first comparison circuit is connected to the integration module, and the first comparison circuit is configured to control the integration module to clear the integration signal when the drain-source voltage is smaller than the first threshold.
5. The control circuit of claim 3, wherein the integration module comprises a current source, an integration unit, and a clear switch, wherein,
the current source is connected with the integrating unit and used for providing an integrating power supply for the integrating unit;
the integration unit is used for integrating the integration power supply to time to obtain an integration signal;
the zero clearing switch is respectively connected with the current source and the integration unit and used for controlling the integration unit to integrate the integration power source with time when the integration unit is switched off and controlling the integration unit to clear the integration signal when the integration unit is switched on.
6. The control circuit of claim 3, wherein the timing circuit further comprises a duration configuration module configured to configure the first reference signal.
7. The control circuit of claim 1, wherein the detection circuit comprises:
and the second detection circuit comprises a second comparison circuit which is used for comparing the drain-source voltage with a second threshold value and outputting the primary side conducting signal when the drain-source voltage is greater than the second threshold value, and the second threshold value is greater than the maximum value of the drain-source voltage when the primary side switch is in a closed state.
8. The control circuit of claim 1, wherein the detection circuit comprises:
the third detection circuit is used for outputting the primary side conduction signal when detecting that the change amplitude of the drain-source voltage is larger than the amplitude threshold value in second preset time; the third detection circuit comprises
The differential module is used for carrying out differential operation on the drain-source voltage to obtain a differential signal;
the second signal comparison module is connected with the differential module and used for outputting the primary side conduction signal according to the differential signal and a second reference signal;
the second reference signal refers to a differential signal corresponding to the second preset time.
9. The control circuit of claim 8, wherein the differential module comprises a differential capacitor and a differential resistor, wherein,
the differential capacitor is connected with the differential resistor and is used for providing drain-source voltage for the differential resistor;
the differential resistor is used for differentiating the drain-source voltage with respect to time to obtain a differential signal.
10. The control circuit of claim 8 wherein the third detection circuit further comprises a second reference signal configuration circuit for adjusting a second reference signal to configure the amplitude threshold.
11. The control circuit of claim 1, further comprising:
the turn-off control circuit is connected with the sampling circuit and used for outputting a control signal for controlling the turn-off of the synchronous rectifier tube when the drain-source voltage is greater than a fourth threshold value;
the reset end of the first trigger circuit is connected with the output end of the turn-off control circuit, the position end of the first trigger circuit is connected with the output end of the turn-on control circuit, and the output end of the first trigger circuit is connected with the grid electrode of the synchronous rectifier tube;
the reset end of the second trigger circuit is connected with the output end of the first trigger circuit, the position end of the second trigger circuit is connected with the detection circuit, and the output end of the second trigger circuit is connected with the input end of the breakover circuit;
wherein the fourth threshold is greater than the third threshold.
12. A method of controlling a synchronous rectifier, the method comprising:
obtaining the drain-source voltage of the synchronous rectifier tube on the secondary side;
outputting a primary side conduction signal when the drain-source voltage is continuously greater than a first threshold value within a first preset time;
or when the change amplitude of the drain-source voltage in a second preset time is greater than an amplitude threshold value, outputting a primary side conduction signal;
when the primary side conduction signal is detected and the drain-source voltage is smaller than a third threshold value, controlling the synchronous rectifier tube to be conducted;
and the primary side conduction signal is used for representing the conduction of the primary side switch.
13. The control method of claim 12, further comprising outputting the primary side turn-on signal when the drain-source voltage is greater than a second threshold value, the second threshold value being greater than a maximum value of the drain-source voltage when the primary side switch is in an off state.
14. The control method according to claim 12, characterized by further comprising:
when the drain-source voltage is smaller than a fourth threshold value, controlling the synchronous rectifier tube to be turned off;
wherein the fourth threshold is greater than the third threshold.
15. A flyback voltage converter circuit comprising a primary circuit and a secondary circuit, characterized in that the secondary circuit comprises a synchronous rectifier and a control circuit as claimed in any one of claims 1 to 11.
16. A control circuit for a synchronous rectifier, the control circuit comprising:
the sampling circuit is connected with the synchronous rectifying tube on the secondary side and is used for collecting the drain-source voltage of the synchronous rectifying tube;
the detection circuit is connected with the sampling circuit and comprises at least two of the following three detection circuits:
the first detection circuit is used for outputting a primary side conduction signal when detecting that the drain-source voltage is continuously greater than a first threshold value within a first preset time;
the second detection circuit is used for outputting a primary side conduction signal when detecting that the drain-source voltage is greater than a second threshold value;
the third detection circuit is used for outputting a primary side conduction signal when detecting that the change amplitude of the drain-source voltage is larger than an amplitude threshold value within second preset time; and
the conduction control circuit is connected with the detection circuit and used for controlling the synchronous rectifier tube to be conducted when the primary side conduction signal is detected and the drain-source voltage is smaller than a third threshold value; and the primary side conduction signal is used for representing the conduction of the primary side switch.
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| CN202011109063.2A CN112271927A (en) | 2020-10-16 | 2020-10-16 | Control circuit and control method of synchronous rectifier tube and flyback voltage conversion circuit |
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