CN111193407B - Synchronous rectification control method and control circuit thereof - Google Patents
Synchronous rectification control method and control circuit thereof Download PDFInfo
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- CN111193407B CN111193407B CN202010137682.6A CN202010137682A CN111193407B CN 111193407 B CN111193407 B CN 111193407B CN 202010137682 A CN202010137682 A CN 202010137682A CN 111193407 B CN111193407 B CN 111193407B
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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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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02B—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO BUILDINGS, e.g. HOUSING, HOUSE APPLIANCES OR RELATED END-USER APPLICATIONS
- Y02B70/00—Technologies for an efficient end-user side electric power management and consumption
- Y02B70/10—Technologies improving the efficiency by using switched-mode power supplies [SMPS], i.e. efficient power electronics conversion e.g. power factor correction or reduction of losses in power supplies or efficient standby modes
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Abstract
A synchronous rectification control method and a control circuit thereof belong to the technical field of switching power supplies. The method comprises the steps of detecting the drain-source voltage of the synchronous rectification switch tube in real time, setting a judgment voltage according to the peak voltage monitored in real time when the drain-source voltage of the synchronous rectification switch tube is detected to be a peak value, comparing the drain-source voltage of the synchronous rectification switch tube after the peak value arrives and a set detection time with the judgment voltage, and generating an effective grid driving signal of the synchronous rectification switch tube to turn on the synchronous rectification switch tube when the drain-source voltage of the synchronous rectification switch tube is greater than the judgment voltage and smaller than a threshold voltage. The method can accurately distinguish the waveform from the primary side to conduct flyback to the secondary side and the self-oscillation waveform of the secondary side, realizes accurate switching judgment of secondary synchronous rectification, and solves the problem of false switching caused by the traditional slope detection mode; the synchronous rectification control provided by the invention is stable and reliable, is easy to integrate, and obviously improves the conversion efficiency of a power supply system.
Description
Technical Field
The invention belongs to the technical field of switching power supplies, and relates to a synchronous rectification control method and a control circuit for realizing the synchronous rectification control method.
Background
Fig. 1 shows a partial structure of an AC-DC switching power supply system, a primary winding of a transformer is connected to a switching tube Q1, a secondary winding of the transformer is connected to a diode D1, and a secondary side of a conventional flyback converter has only one diode D1, however, since energy efficiency requirements are higher and higher, forward voltage drops of the diodes are generally more than 0.7V, power consumption of the conventional scheme is particularly high, and it is more and more difficult to meet energy consumption requirements.
Therefore, it is proposed to replace diode D1 in the conventional structure with an SR (synchronous rectification) chip in the switching power supply to achieve high energy efficiency. As shown in fig. 2, a control architecture of a typical SR (synchronous rectification) chip re-switching power supply is shown, and the synchronous rectification technology is to use a synchronous rectification control chip (SR controller) in combination with a synchronous rectification switching tube (MOS tube QSR) to replace an original diode D1, so as to reduce a diode voltage drop and improve overall efficiency. As shown in fig. 2, the synchronous rectification control chip samples the secondary VSEN voltage to generate a gate driving signal VG for controlling the synchronous rectification switch tube QSR to be turned on and off, and VDS is a voltage difference between a VSEN pin and a GND pin of the synchronous rectification control chip and is also a drain-source voltage of the synchronous rectification switch tube QSR.
However, the conventional synchronous rectification control technology has some problems, as shown in fig. 3, when the secondary side freewheeling and VDS becomes a negative voltage and is lower than VDS _ n, the synchronous rectification switch tube QSR should be turned on, but when the secondary side current is 0, the drain-source voltage VDS of the secondary side synchronous rectification switch tube oscillates and may also oscillate (oscillation of the excitation inductance and the parasitic capacitance) to be negative, and at this time, the synchronous rectification switch tube QSR should not be turned on, that is, the SR chip does not generate an effective Gate drive signal. Therefore, how to correctly distinguish secondary-side freewheeling from oscillation becomes the key for controlling the SR Gate (i.e. controlling the Gate drive of the synchronous rectification switch tube).
The conventional synchronous rectification control technology generally controls the SR Gate by detecting the slope of the falling edge of the drain-source voltage VDS of the synchronous rectification switch tube, but under the condition of light load (or small secondary-side follow current), the difference between the normal falling edge of the drain-source voltage VDS of the synchronous rectification switch tube and oscillation is not large, so that the conventional synchronous rectification control technology cannot distinguish secondary-side follow current from oscillation, and false operation is easily caused. In addition, for the starting of the winding with the auxiliary group, the control mode of increasing the efficiency by injecting energy in a short time and forcibly adjusting the amplitude of the resonance of the excitation inductor cannot be used. Fig. 4 shows a case where the auxiliary winding is included on the side of the switching power supply transformer, because in the case of energy injection, after the Q2 connected to the auxiliary winding is controlled to be turned on by the Q2_ DRV signal, the falling edge of the drain-source voltage VDS of the synchronous rectification switching tube is very steep, and there is inevitable false turn-on of the synchronous rectification switching tube QSR.
Disclosure of Invention
Aiming at the problem that false start caused by incapability of distinguishing secondary side follow current and oscillation exists when synchronous rectification control is carried out by detecting the slope of the falling edge of the drain-source voltage VDS of the synchronous rectification switch tube, the invention provides the control method of the synchronous rectification circuit.
The technical scheme of the invention is as follows:
the invention provides a synchronous rectification control method, which is characterized in that the current of the output side of a switching power supply is rectified by controlling the on and off of a synchronous rectification switching tube;
the synchronous rectification control method comprises the following steps:
step one, detecting the drain-source voltage of the synchronous rectification switch tube in real time, wherein the drain-source voltage of the synchronous rectification switch tube can represent the output voltage information of the switch power supply, and turning to step two when the drain-source voltage of the synchronous rectification switch tube is detected to be a peak value;
comparing the drain-source voltage of the synchronous rectification switch tube detected in real time with a judgment voltage after a set detection time from the time when the peak value of the drain-source voltage of the synchronous rectification switch tube is detected in the step one, wherein the judgment voltage is obtained by sampling and holding the peak value of the drain-source voltage of the synchronous rectification switch tube detected in the step one and multiplying the peak value by a coefficient N, and the coefficient N is greater than 0 and not greater than 1;
and step three, when the drain-source voltage of the synchronous rectification switch tube is lower than the threshold voltage and the comparison result of the step two is that the drain-source voltage of the synchronous rectification switch tube is larger than the judgment voltage after the set detection time, the synchronous rectification switch tube is turned on, otherwise, the synchronous rectification switch tube is turned off.
Specifically, the coefficient N is less than 1.
Specifically, the threshold voltage is set according to the drain-source voltage of the synchronous rectification switch tube when the secondary current of the switching power supply continues flowing.
The invention also provides a synchronous rectification control circuit which can realize the synchronous rectification control method and is used for generating a grid driving signal of a synchronous rectification switching tube to control the on and off of the synchronous rectification switching tube in the switching power supply so as to rectify the current at the output side of the switching power supply;
the synchronous rectification control circuit comprises a peak value detection module, a timer, a sampling module, a first comparator, a second comparator and an AND gate;
the peak value detection module is used for detecting the drain-source voltage of the synchronous rectification switch tube and generating an effective peak value updating signal when the peak value of the drain-source voltage of the synchronous rectification switch tube is detected;
the sampling module is used for sampling and holding the drain-source voltage of the synchronous rectification switch tube under the control of the peak value updating signal to obtain the peak value voltage of the drain-source voltage of the synchronous rectification switch tube;
the timer starts timing under the control of the peak value updating signal and stops timing under the control of a reset signal, and the timer generates an enabling signal of the first comparator when timing is stopped each time;
the first input end of the first comparator is connected with the drain-source voltage of the synchronous rectification switch tube, and the second input end of the first comparator is connected with the output signal of the sampling module;
the first input end of the second comparator is connected with the drain-source voltage of the synchronous rectification switch tube, and the second input end of the second comparator is connected with the threshold voltage;
two input signals of the AND gate are respectively an output signal of the first comparator and an output signal of the second comparator, and the output end of the AND gate generates a gate driving signal of the synchronous rectification switching tube;
when the first comparator compares that the drain-source voltage of the synchronous rectification switch tube is greater than the output signal of the sampling module, and the second comparator compares that the drain-source voltage of the synchronous rectification switch tube is less than the threshold voltage, the AND gate outputs an effective gate driving signal of the synchronous rectification switch tube to turn on the synchronous rectification switch tube.
Specifically, the synchronous rectification switch tube is an NMOS tube, the first comparator outputs a high level when the drain-source voltage of the synchronous rectification switch tube is greater than the output signal of the sampling module, and the second comparator outputs a high level when the drain-source voltage of the synchronous rectification switch tube is less than the threshold voltage.
Specifically, the synchronous rectification control circuit further comprises an SR flip-flop and an or gate, and an output signal of the first comparator is used as an input signal of the and gate after passing through the SR flip-flop;
the S input end of the SR trigger is connected with the output end of the first comparator, the R input end of the SR trigger is connected with the output end of the OR gate, and the output end of the SR trigger is connected with one input end of the AND gate;
the first input end of the OR gate is connected with the grid driving signal of the synchronous rectification switching tube, and the second input end of the OR gate is connected with the peak value updating signal.
Specifically, the peak update signal is a pulse signal.
Specifically, a multiplier is further arranged between the sampling module and the first comparator, and the output signal of the sampling module is multiplied by a coefficient N in the multiplier and then connected to the second input end of the first comparator, wherein the coefficient N is greater than 0 and smaller than 1.
The invention has the beneficial effects that: according to the invention, the judgment voltage is set through real-time peak value monitoring, and the drain-source voltage of the synchronous rectification switch tube is compared with the judgment voltage after the detection time, so that whether the drain-source voltage of the synchronous rectification switch tube is a platform voltage or not is effectively identified, thus the waveform of the primary side conducted to be flyback to the secondary side and the waveform of the secondary side self oscillation are accurately distinguished, the accurate opening judgment of the secondary synchronous rectification is realized, and the problem of false opening caused by the traditional slope detection mode is solved; the synchronous rectification control provided by the invention is stable and reliable, is easy to integrate, and obviously improves the conversion efficiency of a power supply system.
Drawings
Fig. 1 is a schematic diagram of a portion of an AC-DC switching power supply system, including a primary side structure and a secondary side structure.
Fig. 2 is a block diagram of a synchronous rectification technique using a synchronous rectification control chip (SR controller) in combination with a MOS transistor QSR in low-side driving of a switching power supply.
Fig. 3 is a waveform diagram of key nodes in the conventional synchronous rectification control technology.
Fig. 4 is a schematic diagram of synchronous rectification control including an auxiliary winding on one side of a switching power supply transformer.
Fig. 5 is a waveform diagram of some key nodes when the synchronous rectification control method provided by the invention is adopted.
Fig. 6 is a partial flowchart of a synchronous rectification control method according to the present invention.
Fig. 7 is a partial flowchart of a synchronous rectification control method according to the present invention.
Fig. 8 is a schematic diagram of the application of the present invention to high-side driving of a switching power supply.
Fig. 9 is an implementation architecture diagram of a synchronous rectification control circuit according to the present invention.
Detailed Description
The technical solution of the present invention is described in detail below with reference to the accompanying drawings and specific embodiments.
The synchronous rectification control method and the control circuit provided by the invention are suitable for switching power supplies including flyback switching power supplies, forward switching power supplies, LLC (logical Link control), and the like.
Referring to fig. 2 and 8, the schematic diagram of the application of the present invention to the low-side drive and the high-side drive of the switching power supply is shown, the primary side of the switching power supply includes a primary side winding and a switching tube Q1, and the secondary side includes a secondary side winding, a capacitor C1 and a synchronous rectification switching tube QSR. When the primary side switching tube Q1 is turned off, the secondary side of the switching power supply continues current, that is, current is generated on the output side of the switching power supply, and when the secondary side flyback voltage is negative, the synchronous rectification switching tube QSR needs to be turned on. The two types can be accurately distinguished by the synchronous rectification control method provided by the invention, as shown in fig. 5, the waveform diagrams of some key nodes when the synchronous rectification control method provided by the invention is adopted comprise the waveform diagram of the secondary flyback voltage, namely the drain-source voltage VDS of the synchronous rectification switching tube, the waveform of the Gate driving signal of the primary switching tube Q1 and the waveform diagram of the synchronous rectification control signal SR Gate generated by the invention, when the primary switching tube Q1 is conducted, the waveform of the secondary flyback voltage is square, the voltage Spike is removed, the waveform is approximate to a square, and when the secondary side is self-resonant, the waveform of the secondary voltage is arc. The synchronous rectification control method provided by the invention judges whether the voltage waveform of the secondary side is circular arc or square in a platform detection mode so as to distinguish the waveform of the primary side conducted from flyback to the secondary side and the waveform of self oscillation of the secondary side, and further distinguish whether the primary side is started or not, thereby controlling whether a synchronous rectification switching tube should be started or not. If the primary side is opened, the synchronous rectification switching tube is opened when the secondary side flyback voltage is negative, and if the primary side is not opened, the synchronous rectification switching tube is not opened when the secondary side flyback voltage is negative.
Fig. 6 and 7 show a flow chart of a synchronous rectification control method proposed by the present invention, which includes the following steps:
and step A, detecting the drain-source voltage VDS of the synchronous rectification switch tube, wherein the drain-source voltage VDS of the synchronous rectification switch tube can represent output voltage information of the switching power supply, and when the drain-source voltage VDS of the synchronous rectification switch tube is detected to be a peak value, the step B and the step C are simultaneously carried out.
Step B, when the peak value comes, the peak voltage Vpk of the drain-source voltage of the synchronous rectification switch tube is sampled and held, as shown in fig. 9, a pulse signal is generated by using the peak detection module when the peak value comes, and the drain-source voltage VDS (i.e., the voltage of the pin VSEN) of the synchronous rectification switch tube is sampled under the control of the pulse signal, so as to obtain the effective peak voltage Vpk. Setting a judgment voltage of the platform by using the peak voltage Vpk, wherein the judgment voltage is the peak voltage Vpk multiplied by a coefficient N, and N can be 1, namely the peak voltage Vpk is directly used as the judgment voltage; n can also be a number greater than 0 and less than 1, indicating that a certain voltage drop is tolerated and that this arrangement enables a greater immunity to interference.
And step C, when the peak value comes, timing by using a timer, wherein the timing time is the set detection time, and the detection time can be set according to the characteristics of the circuit, and the order of magnitude is generally hundreds nS-uS. And acquiring the drain-source voltage VDS of the synchronous rectification switch tube at the moment when the peak value comes and the set detection time passes.
And D, comparing the drain-source voltage VDS of the synchronous rectification switching tube after the detection time obtained in the step C with the judgment voltage Vpk N set in the step B, and controlling the synchronous rectification switching tube QSR according to the comparison result.
The timer sets detection time to judge the width of the secondary side flyback voltage platform, and when the detection time is over, the drain-source voltage VDS of the synchronous rectification switch tube is compared to judge whether the voltage Vpk N is greater or not, so that whether the platform exists or not is judged.
If Vpk N < VDS, the platform voltage of the secondary side voltage is still in, and the width of the platform voltage is larger than the set detection time, the primary side starting state is indicated, and the synchronous rectification starting is effective.
If Vpk × N > VDS, the platform voltage of the secondary side voltage is not present, or the platform is too short, or the secondary side oscillates, the condition of starting the synchronous rectification switching tube is not met, and the synchronous rectification is started ineffectively.
And E, comparing the drain-source voltage VDS of the synchronous rectification switch tube with a set threshold voltage Vds _ n, and combining the further judgment standard obtained in the steps to obtain accurate judgment of the secondary synchronous rectification starting of the switching power supply. The threshold voltage Vds _ n is a determination signal for determining the secondary follow current of the switching power supply, is a fixed value, and is determined by the switching power supply itself, such as-0.1V. When the drain-source voltage VDS of the synchronous rectification switch tube is a negative value and is smaller than the threshold voltage Vds _ N, and Vpk N is smaller than VDS after the detection time, an effective grid driving signal VG of the synchronous rectification switch tube can be generated, and the synchronous rectification switch tube QSR is started.
If only judging whether the drain-source voltage VDS of the synchronous rectification switch tube is smaller than the set threshold voltage Vds _ N, namely the waveform shown in figure 3, the waveform of the primary side conducted to the secondary side and the waveform of the self oscillation of the secondary side can not be distinguished, therefore, the invention provides a platform detection mode, the peak value of the drain-source voltage VDS of the synchronous rectification switch tube is used for setting the judgment voltage Vpk _ N, the detection time is set to obtain the drain-source voltage VDS of the synchronous rectification switch tube after the detection time is passed, and then the drain-source voltage VDS of the synchronous rectification switch tube is compared with the judgment voltage Vpk _ N, so that whether the drain-source voltage VDS of the synchronous rectification switch tube is a platform voltage in the detection time is known, the waveform of the drain-source voltage VDS of the synchronous rectification switch tube is a square shape from the primary side to the secondary side in a flyback manner or an arc shape from the secondary side to the self resonance manner.
Fig. 9 shows an implementation form of the synchronous rectification control circuit provided by the present invention, which is used for generating a gate driving signal VG of a synchronous rectification switching tube QSR to control the on and off of the synchronous rectification switching tube QSR in a switching power supply, so as to rectify a current at an output side of the switching power supply. As shown in fig. 9, the synchronous rectification control circuit includes a peak detection module, a timer, a sampling module, a first comparator, a second comparator, and an and gate; the peak value detection module is used for detecting the drain-source voltage of the synchronous rectification switching tube QSR, the input end of the peak value detection module can be connected with the VSEN pin of the SR chip, and an effective peak value updating signal Vpk _ t is generated when the peak value of the drain-source voltage of the synchronous rectification switching tube QSR is detected; the sampling module is used for sampling and holding the drain-source voltage of the synchronous rectification switching tube QSR under the control of the peak value updating signal Vpk _ t to obtain the peak value voltage VPK of the drain-source voltage of the synchronous rectification switching tube QSR; the timer starts timing under the control of the peak value updating signal Vpk _ T, stops timing under the control of the reset signal RST, and generates an enabling signal T _ trigger of the first comparator when timing is stopped each time; the first input end of the first comparator is connected with the drain-source voltage of the synchronous rectification switching tube QSR, and the second input end of the first comparator is connected with the output signal VPK of the sampling module; the first input end of the second comparator is connected with the drain-source voltage of the synchronous rectification switching tube QSR, and the second input end of the second comparator is connected with the threshold voltage Vds _ n; two input signals of the AND gate are respectively an output signal of the first comparator and an output signal of the second comparator, and the output end of the AND gate generates a gate driving signal VG of the synchronous rectification switching tube QSR; when the first comparator compares that the drain-source voltage of the synchronous rectification switch tube QSR is greater than the output signal of the sampling module, and the second comparator compares that the drain-source voltage of the synchronous rectification switch tube QSR is less than the threshold voltage, the AND gate outputs an effective gate drive signal VG of the synchronous rectification switch tube QSR to turn on the synchronous rectification switch tube QSR.
Taking the synchronous rectification switch tube QSR as an NMOS tube with an effective high level as an example, when the drain-source voltage of the synchronous rectification switch tube QSR is greater than the output signal of the sampling module, the first comparator outputs a high level, when the drain-source voltage of the synchronous rectification switch tube QSR is less than the threshold voltage, the second comparator outputs a high level, and the output of the and gate is high to turn on the synchronous rectification switch tube QSR only when the first comparator and the second comparator both output a high level.
In some embodiments, the synchronous rectification control circuit further comprises an SR flip-flop and an or gate, and an output signal of the first comparator is used as an input signal of the and gate after passing through the SR flip-flop; the S input end of the SR trigger is connected with the output end of the first comparator, the R input end of the SR trigger is connected with the output end of the OR gate, and the output end of the SR trigger is connected with one input end of the AND gate; the first input terminal of the or gate is connected to the gate driving signal VG of the synchronous rectification switching tube QSR, and the second input terminal thereof is connected to the peak update signal Vpk _ t, which may be a pulse signal.
A multiplier can be arranged between the sampling module and the first comparator, the output signal VPK of the sampling module is multiplied by a coefficient N in the multiplier, and then the output signal VPK is connected with the second input end of the first comparator, wherein the coefficient N is larger than 0 and smaller than 1.
The operation of the circuit in this embodiment is described in detail below: the input end of the synchronous rectification control circuit is connected with a VSEN pin of the SR chip and inputs a drain-source voltage VDS of the synchronous rectification switch tube, the peak detection module always monitors whether the drain-source voltage VDS of the synchronous rectification switch tube has a peak value, and an effective peak updating signal Vpk _ t is generated when the peak value of the drain-source voltage VDS of the synchronous rectification switch tube is detected. After a peak value updating signal Vpk _ t is sent out, a sampling module carries out sampling, holding and updating on the peak value voltage VPK of the drain-source voltage VDS of the synchronous rectification switch tube; meanwhile, a peak value updating signal Vpk _ T controls a timer to return to zero and count again, a timer external resistor RST pin is used for setting timing time, after the timing time is finished, an effective first comparator enabling signal T _ trigger is generated to trigger a first comparator, two input signals of the first comparator are respectively a judgment voltage VPK N and a synchronous rectification switch tube drain-source voltage VDS, namely VSEN pin voltage, the two signals are compared after the detection time set by the timer, and if VPK N is smaller than the VSEN at the moment, the first comparator outputs an effective signal; the active signal of the first comparator causes the output signal SR _ EN of the SR flip-flop U1 to be high; meanwhile, the second comparator compares the drain-source voltage VDS of the synchronous rectification switch tube, namely the voltage of a VSEN pin, with the threshold voltage Vds _ n, when the VSEN is lower than the negative threshold voltage Vds _ n, the output signal Vds _ neg of the second comparator is valid, the output signal of the AND gate U2, namely the gate driving signal VG of the synchronous rectification switch tube is valid, and the synchronous rectification switch tube QSR is started. The SR flip-flop U1 may be cleared by the falling edge of the synchronous rectified switching tube gate drive signal VG or the peak update signal Vpk _ t signal.
In summary, the present embodiment has been described by taking the secondary synchronous rectification of the flyback controller as an example, and discloses a control method and a control circuit for synchronous rectification, in which the present invention sets a determination voltage by performing peak monitoring in real time, sets a detection time providing platform, compares the drain-source voltage of the synchronous rectification switch tube with the determination voltage after the detection time, and effectively identifies whether the drain-source voltage of the synchronous rectification switch tube is a platform voltage within the detection time, thereby accurately distinguishing the waveform of the drain-source voltage of the synchronous rectification switch tube, and implementing accurate turn-on determination of the secondary synchronous rectification.
The synchronous rectification control method and the control circuit provided by the present invention are described in detail above, and the principle and the implementation manner of the present invention are explained by applying specific embodiments in the present invention, and the description of the above embodiments is only used to help understanding the method and the core idea of the present invention, and should not be construed as limiting the present invention; meanwhile, for a person skilled in the art, according to the idea of the present invention, there may be variations in the specific implementation method and the application scope, and the variations should fall within the protection scope of the present invention.
Claims (8)
1. A synchronous rectification control method is characterized in that current on the output side of a switching power supply is rectified by controlling the on and off of a synchronous rectification switching tube;
the synchronous rectification control method is characterized by comprising the following steps of:
step one, detecting the drain-source voltage of the synchronous rectification switch tube in real time, wherein the drain-source voltage of the synchronous rectification switch tube can represent the output voltage information of the switch power supply, and turning to step two when the drain-source voltage of the synchronous rectification switch tube is detected to be a peak value;
comparing the drain-source voltage of the synchronous rectification switch tube detected in real time with a judgment voltage after a set detection time from the time when the peak value of the drain-source voltage of the synchronous rectification switch tube is detected in the step one, wherein the judgment voltage is obtained by sampling and holding the peak value of the drain-source voltage of the synchronous rectification switch tube detected in the step one and multiplying the peak value by a coefficient N, and the coefficient N is greater than 0 and not greater than 1;
and step three, when the drain-source voltage of the synchronous rectification switch tube is lower than the threshold voltage and the comparison result of the step two is that the drain-source voltage of the synchronous rectification switch tube is larger than the judgment voltage after the set detection time, the synchronous rectification switch tube is turned on, otherwise, the synchronous rectification switch tube is turned off.
2. The synchronous rectification control method of claim 1, wherein the factor N is less than 1.
3. The synchronous rectification control method of claim 1, wherein the threshold voltage is set according to a drain-source voltage of the synchronous rectification switch tube when the switching power supply secondarily freewheels.
4. A synchronous rectification control circuit is used for generating a grid electrode driving signal of a synchronous rectification switching tube to control the on and off of the synchronous rectification switching tube in a switching power supply so as to rectify current on the output side of the switching power supply;
the synchronous rectification control circuit comprises a peak value detection module, a timer, a sampling module, a first comparator, a second comparator and an AND gate;
the peak value detection module is used for detecting the drain-source voltage of the synchronous rectification switch tube and generating an effective peak value updating signal when the peak value of the drain-source voltage of the synchronous rectification switch tube is detected;
the sampling module is used for sampling and holding the drain-source voltage of the synchronous rectification switch tube under the control of the peak value updating signal to obtain the peak value voltage of the drain-source voltage of the synchronous rectification switch tube;
the timer starts timing under the control of the peak value updating signal and stops timing under the control of a reset signal, and the timer generates an enabling signal of the first comparator when timing is stopped each time;
the first input end of the first comparator is connected with the drain-source voltage of the synchronous rectification switch tube, and the second input end of the first comparator is connected with the output signal of the sampling module;
the first input end of the second comparator is connected with the drain-source voltage of the synchronous rectification switch tube, and the second input end of the second comparator is connected with the threshold voltage;
two input signals of the AND gate are respectively an output signal of the first comparator and an output signal of the second comparator, and the output end of the AND gate generates a gate driving signal of the synchronous rectification switching tube;
when the first comparator compares that the drain-source voltage of the synchronous rectification switch tube is greater than the output signal of the sampling module, and the second comparator compares that the drain-source voltage of the synchronous rectification switch tube is less than the threshold voltage, the AND gate outputs an effective gate driving signal of the synchronous rectification switch tube to turn on the synchronous rectification switch tube.
5. The synchronous rectification control circuit of claim 4, wherein the synchronous rectification switch tube is an NMOS tube, the first comparator outputs a high level when the drain-source voltage of the synchronous rectification switch tube is greater than the output signal of the sampling module, and the second comparator outputs a high level when the drain-source voltage of the synchronous rectification switch tube is less than the threshold voltage.
6. The synchronous rectification control circuit of claim 5, further comprising an SR flip-flop and an OR gate, wherein an output signal of the first comparator is used as an input signal of the AND gate after passing through the SR flip-flop;
the S input end of the SR trigger is connected with the output end of the first comparator, the R input end of the SR trigger is connected with the output end of the OR gate, and the output end of the SR trigger is connected with one input end of the AND gate;
the first input end of the OR gate is connected with the grid driving signal of the synchronous rectification switching tube, and the second input end of the OR gate is connected with the peak value updating signal.
7. The synchronous rectification control circuit of any one of claims 4 to 6, wherein the peak update signal is a pulse signal.
8. The synchronous rectification control circuit of claim 4, wherein a multiplier is further disposed between the sampling module and the first comparator, and the output signal of the sampling module is multiplied by a coefficient N in the multiplier and then connected to the second input terminal of the first comparator, wherein the coefficient N is greater than 0 and smaller than 1.
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| US9595874B2 (en) | 2012-04-12 | 2017-03-14 | On-Bright Electronics (Shanghai) Co., Ltd. | Systems and methods for regulating power conversion systems with output detection and synchronized rectifying mechanisms |
| US10622902B2 (en) | 2012-04-12 | 2020-04-14 | On-Bright Electronics (Shanghai) Co., Ltd. | Systems and methods for regulating power conversion systems with output detection and synchronized rectifying mechanisms |
| CN111146961B (en) | 2020-01-20 | 2022-04-12 | 昂宝电子（上海）有限公司 | Control circuit and method for controlling synchronous rectification system |
| CN111697838B (en) | 2020-05-29 | 2023-09-26 | 昂宝电子（上海）有限公司 | Synchronous rectification control circuit, method and switching power supply system |
| CN111953184A (en) * | 2020-07-17 | 2020-11-17 | 上海百功半导体有限公司 | Isolated power supply synchronous rectification device and method |
| CN112234837B (en) * | 2020-10-30 | 2024-06-18 | 上海新进芯微电子有限公司 | Synchronous rectification circuit and flyback switching power supply |
| CN112366953B (en) * | 2020-11-17 | 2022-04-19 | 成都芯源系统有限公司 | Synchronous rectification circuit and control method thereof |
| CN112865541B (en) * | 2021-01-22 | 2022-03-29 | 成都启臣微电子股份有限公司 | Synchronous rectification controller, synchronous rectification system and synchronous rectification control method |
| CN113141117B (en) * | 2021-04-08 | 2022-05-31 | 昂宝电子（上海）有限公司 | Flyback switching power supply and synchronous rectification controller thereof |
| CN113541514B (en) * | 2021-07-21 | 2023-03-14 | 艾科微电子(深圳)有限公司 | Synchronous rectification controller and control method thereof |
| CN113572364B (en) * | 2021-07-29 | 2023-08-15 | 昂宝电子（上海）有限公司 | Switching power supply system and synchronous rectification controller thereof |
| CN113765404A (en) * | 2021-09-27 | 2021-12-07 | 江苏慧易芯科技有限公司 | Method for judging turn-on time of secondary side switch and switch power supply circuit thereof |
| CN114123789B (en) * | 2021-11-12 | 2023-07-07 | 深圳市卓芯微科技有限公司 | Synchronous rectification converter |
| CN115065221B (en) * | 2022-08-16 | 2022-11-04 | 成都利普芯微电子有限公司 | Synchronous rectification dynamic accelerating circuit, control circuit and switching power supply |
| CN118100660B (en) * | 2024-04-17 | 2024-07-02 | 成都利普芯微电子有限公司 | Synchronous rectification control circuit, chip and switching power supply |
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| CN109274272B (en) * | 2018-10-19 | 2020-11-17 | 成都芯源系统有限公司 | Switching power supply circuit, synchronous rectification control circuit and control method thereof |
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