CN106941321B - A kind of control circuit of synchronous rectifier - Google Patents
A kind of control circuit of synchronous rectifier Download PDFInfo
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- CN106941321B CN106941321B CN201710173147.4A CN201710173147A CN106941321B CN 106941321 B CN106941321 B CN 106941321B CN 201710173147 A CN201710173147 A CN 201710173147A CN 106941321 B CN106941321 B CN 106941321B
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
- H02M3/00—Conversion of dc power input into dc power output
- H02M3/22—Conversion of dc power input into dc power output with intermediate conversion into ac
- H02M3/24—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters
- H02M3/28—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac
- H02M3/325—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal
- H02M3/335—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal using semiconductor devices only
- H02M3/33569—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal using semiconductor devices only having several active switching elements
- H02M3/33576—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal using semiconductor devices only having several active switching elements having at least one active switching element at the secondary side of an isolation transformer
- H02M3/33592—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal using semiconductor devices only having several active switching elements having at least one active switching element at the secondary side of an isolation transformer having a synchronous rectifier circuit or a synchronous freewheeling circuit at the secondary side of an isolation transformer
-
- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
- H02M1/00—Details of apparatus for conversion
- H02M1/36—Means for starting or stopping converters
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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
Abstract
The invention discloses a kind of control circuits of synchronous rectifier, including voltage slope detection circuit, transformer and synchronous rectifier output-stage circuit, logic circuit and driving circuit, the voltage slope detection circuit, logic circuit, driving circuit and transformer and synchronous rectifier output-stage circuit are sequentially connected.The present invention passes through setting voltage slope detection circuit, detect the slope of the voltage change of synchronous rectifier drain electrode, accurately distinguish its drain terminal voltage change be due to caused by the shutdown of primary side main power tube or synchronous rectifier turn off after caused by resonance, it is opened so as to avoid synchronous rectifier from being opened by mistake due to resonance, further realizes the correct unlatching of synchronous rectifier.
Description
Technical field
The present invention relates to power tube drive area, in particular to a kind of control circuit of synchronous rectifier.
Background technique
Requirement of the switch power technology to efficiency is increasingly harsh, in order to improve the efficiency of switching circuit, mostly uses at present same
Step rectifies metal-oxide-semiconductor to substitute freewheeling diode.
But in the case where devices and primary side main switch signal do not communicate, how correctly to open synchronization
Rectifying metal-oxide-semiconductor becomes key technology.
The moment after shutdown of primary side main power tube, secondary side transformer start afterflow by the body diode of synchronous rectifier,
Synchronous rectifier needs quickly to open the time of afterflow for reducing body diode and improves efficiency at the same time.Existing synchronizing power pipe
Opening technology is exactly to open synchronous function after synchronous rectifier drain-source both end voltage drop becomes negative voltage from positive voltage by detecting
Rate pipe.
But this opening technology has the drawback that, it can fault open synchronizing power pipe.Terminate it in secondary side current stream
Synchronous rectifier turns off afterwards, and it is whole that the resonance that the parasitic capacitance and primary side inductance of primary side main power tube drain electrode generate synchronizes secondary side
Flow tube drain-source both ends generate same resonant voltage waveforms, this voltage can be similarly pressed between negative voltage from higher positive electricity to shake
It swings, middle Vds waveform is from t4 time point to the variation at t5 time point as shown in Fig. 3.In this case, synchronous rectifier can be
After current stream, again due to resonance and can be by fault open.
In order to solve fault open phenomenon caused by above-mentioned resonance, a kind of method is, after synchronous rectifier shutdown
Certain time interval inner shield synchronous rectifier is again turned on.If but this shielding time is too short, can not play
The effect of full-shield, or can be by the unlatching of mistake after the shielding time terminates；If the shielding time is too long, there can be mistake
It accidentally shields, normal open signal is shielded, cause secondary side electric current to pass through the body diode afterflow of synchronous rectifier, further
System output voltage is caused to reduce.
Thus the prior art could be improved and improve.
Summary of the invention
Place in view of above-mentioned deficiencies of the prior art, the purpose of the present invention is to provide a kind of control of synchronous rectifier electricity
Road, can accurately distinguish the variation of synchronous rectifier drain-source voltage is due to causing or synchronizing whole after the shutdown of primary side main power tube
Resonance causes after flow tube shutdown, to realize the correct unlatching to synchronous rectifier.
In order to achieve the above object, this invention takes following technical schemes:
A kind of control circuit of synchronous rectifier, comprising:
Voltage slope detection circuit, for detecting the slope of the voltage change at synchronous rectifier drain-source both ends and exporting control
Signal；
Transformer and synchronous rectifier output-stage circuit；
Logic circuit, the control signal for exporting to voltage slope detection circuit carry out logic calculation and output driving letter
Number control synchronous rectifier on-off；
Driving circuit, the on-off of the driving signal driving synchronous rectifier for being exported according to logic circuit；
The voltage slope detection circuit, logic circuit, driving circuit transformer and synchronous rectifier output-stage circuit
It is sequentially connected.
In the control circuit of the synchronous rectifier, the transformer and synchronous rectifier output-stage circuit include primary side
Transformer, primary side main power tube, primary side sampling resistor, secondary side transformer, output capacitance and synchronous rectifier, the primary side transformation
One end of device connects power input, and the other end of the primary side transformer connects the drain electrode of the primary side main power tube, described
The source electrode of primary side main power tube is grounded by the primary side sampling resistor, and the grid of the primary side main power tube receives main driving letter
Number, one end of one end connection power output end and output capacitance of the secondary transformer, the other end of the secondary transformer
The drain electrode of the synchronous rectifier is connected, the source electrode ground connection of the synchronous rectifier also connects the other end of the output capacitance,
The grid of the synchronous rectifier connects the driving circuit.
In the control circuit of the synchronous rectifier, the voltage slope detection circuit includes:
First voltage threshold detection unit, for detecting the high threshold part of synchronous rectifier drain-source both end voltage, and it is defeated
First comparison signal out；
Second voltage threshold detection unit, for detecting the Low threshold part of synchronous rectifier drain-source both end voltage, and it is defeated
Second comparison signal out；
Time detection unit is used for generation time reference quantity, and exports third comparison signal；
Signal processing unit for carrying out logic calculation processing to the second comparison signal and third comparison signal, and exports
Signal is controlled to the logic circuit；
The first voltage threshold detection unit, time detection unit and signal processing unit are sequentially connected, the signal
Processing unit is also connected with the second voltage threshold detection unit.
In the control circuit of the synchronous rectifier, the first voltage threshold detection unit includes first resistor,
Two resistance and first comparator, one end of the first resistor are signal receiving end, receive the drain-source electricity of the synchronous rectifier
Pressure also connects the second voltage threshold detection unit, one end of the other end connection second resistance of the first resistor and institute
The inverting input terminal of first comparator is stated, the positive input terminal of the first comparator A1 inputs the first predetermined reference voltage, described
The output end of first comparator connects the time detection unit, the other end ground connection of the second resistance.
In the control circuit of the synchronous rectifier, the second voltage threshold detection unit include the first metal-oxide-semiconductor and
Second comparator, the drain electrode of first metal-oxide-semiconductor connect one end of the first resistor, also receive the leakage of the synchronous rectifier
Source voltage, the source electrode of first metal-oxide-semiconductor connect the inverting input terminal of second comparator, the grid of first metal-oxide-semiconductor
VDD power supply is connected, the positive input terminal of second comparator inputs the second predetermined reference voltage, the output of second comparator
End connects the signal processing unit.
In the control circuit of the synchronous rectifier, the time detection unit includes current source, the first phase inverter, height
First switch, the low level that the first comparison signal exported by the first comparator that level conducting, low level disconnect is controlled
The second switch controlled by first inverter output signal, first capacitor and the third comparator that conducting, high level disconnect,
One end of the current source connects VDD power supply, and the other end of the current source connects one end of the first switch, and described first
The output end of comparator exports the first comparison signal and controls being turned on or off for the first switch, the first switch it is another
End is grounded by the second switch, also connects the inverting input terminal of the third comparator and one end of first capacitor, described
The other end of first capacitor is grounded, and the positive input terminal of the third comparator inputs third predetermined reference voltage, the third ratio
The signal processing unit is connected compared with the output end of device, the input terminal of first phase inverter connects the defeated of the first comparator
The output end output signal control second switch of outlet, first phase inverter is turned on or off.
In the control circuit of the synchronous rectifier, the signal processing unit includes the second phase inverter, third reverse phase
Device, the 4th phase inverter, first and door and the first trigger, the input terminal of second phase inverter connect second comparator
The input terminal of output end and the 4th phase inverter, the output end of second phase inverter connect the input of the third phase inverter
End, the output end of the third phase inverter connect the second input terminal of described first Yu door, and described first inputs with the first of door
End connects the output end of the third comparator, and described first connect the end S of first trigger with the output end of door, described
The end R of first trigger connects the output end of the 4th phase inverter, and the end Q of first trigger connects the logic electricity
Road.
In the control circuit of the synchronous rectifier, the logic circuit includes the second trigger, second triggering
The end S of device connects the end Q of first trigger, and the end R of second trigger inputs cut-off signals, second trigger
The end Q connect the driving circuit.
In the control circuit of the synchronous rectifier, the input terminal of the driving circuit connects the end Q of the second trigger,
The output end of the driving circuit connects the grid of the synchronous rectifier.
Compared to the prior art, the control circuit of a kind of synchronous rectifier provided by the invention, including voltage slope detection
Circuit, transformer and synchronous rectifier output-stage circuit, logic circuit and driving circuit, the voltage slope detection circuit are patrolled
It collects circuit, driving circuit and transformer and synchronous rectifier output-stage circuit is sequentially connected.The present invention passes through setting voltage slope
Detection circuit, the slope of the voltage change of detection synchronous rectifier drain electrode, accurately distinguishing its drain terminal voltage change is due to primary side
After still synchronous rectifier turns off caused by main power tube shutdown caused by resonance, so as to avoid synchronous rectifier due to humorous
It shakes and is opened by mistake and opened, further realize the correct unlatching of synchronous rectifier.
Detailed description of the invention
Fig. 1 is the structural block diagram of the control circuit of synchronous rectifier provided by the invention.
Fig. 2 is the schematic diagram of the control circuit of synchronous rectifier provided by the invention.
Fig. 3 is the electric current and voltage waveform view when the synchronous rectifier that the present invention controls works.
Fig. 4 is the schematic diagram of the voltage slope detection circuit in the control circuit of synchronous rectifier provided by the invention.
Specific embodiment
The present invention provides a kind of control circuit of synchronous rectifier, and by the way that voltage slope detection circuit is arranged, detection is synchronized
The slope of the voltage change of rectifying tube drain electrode, accurately distinguishing its drain terminal voltage change is due to caused by the shutdown of primary side main power tube
Or it avoids synchronous rectifier caused by resonance after synchronous rectifier shutdown and is opened due to resonance by opening by mistake.
To make the purpose of the present invention, technical solution and effect clearer, clear and definite, right as follows in conjunction with drawings and embodiments
The present invention is further described.It should be appreciated that described herein, specific examples are only used to explain the present invention, is not used to
Limit the present invention.
Referring to Fig. 1, a kind of control circuit of synchronous rectifier provided by the invention, including voltage slope detection circuit
10, transformer and synchronous rectifier output-stage circuit 20, logic circuit 30 and driving circuit 40.
Wherein, the voltage slope detection circuit 10 is used to detect the slope of the voltage change at synchronous rectifier drain-source both ends
And control signal is exported, specifically, the voltage slope detection circuit 10 can detect two different voltage thresholds respectively,
The time quantum between two voltage thresholds can also be detected simultaneously, according to the variation deltaV's of voltage and time quantum deltaT
Ratio can obtain the variation slope of voltage, while the voltage slope detection circuit 10 also exports control signal and gives logic electricity
Road 30, by the on-off for further controlling synchronous rectifier after the progress logic calculation of logic circuit 30.
The transformer and the synchronous pipe output-stage circuit 20 that arranges are the switching circuit with synchronous rectifier, including primary side
Transformer L1, primary side main power tube M3, primary side sampling resistor Rcs, secondary side transformer L2, output capacitance Cout and synchronous rectifier
One end of M2, the primary side transformer L1 receive input voltage vin, and the other end of the primary side transformer L1 connects the primary side
The source electrode of the drain electrode of main power tube M3, the primary side main power tube M3 is grounded by the primary side sampling resistor Rcs, the primary side
The grid of main power tube M3 receives main driving signal, and one end of the secondary transformer L2 exports output voltage Vout, and connects
One end of output capacitance Cout, the other end of the secondary transformer L2 connects the drain electrode of the synchronous rectifier M2, described same
The source electrode ground connection for walking rectifying tube M2, also connects the other end of the output capacitance Cout, and the grid of the synchronous rectifier M2 connects
Connect the driving circuit 40.
Furthermore, it is understood that secondary side corresponds to after starting afterflow referring to Fig. 3, Fig. 3 is after the primary side power tube M3 is turned off
Electric current and voltage waveform.Wherein Isec indicates secondary side transformer current waveform, that is, passes through the electric current of synchronous rectifier M2
Waveform；Vds indicates that the synchronous rectifier M2 drain-source both ends correspond to the voltage waveform of electric current Isec.It can by Vds voltage waveform
To obtain, voltage descending slope of the voltage from t1 to t2 in the time is obviously greater than descending slope of the voltage from t4 to t5, and Vds
Waveform it is from time t1 to time t2 decline be as the primary side main power tube M3 shutdown caused by, and Vds waveform from time t4 to
The decline of time t5 is that the resonance generated by the drain terminal parasitic capacitance of the primary side main power tube M3 and the primary side transformer L1 draws
It rises, so can judge that drain-source voltage variation is due to primary side by detecting the voltage slope at synchronous rectifier M2 drain-source both ends
Caused by main power tube turns off or after synchronous rectifier shutdown caused by resonance, so as to avoid synchronous rectifier due to
Resonance and opened by opening by mistake.
Control signal progress logic calculation that the logic circuit 30 is used to export voltage slope detection circuit 10 is simultaneously defeated
The on-off of driving signal control synchronous rectifier out, when the signal of the voltage slope detection circuit 10 output is high level,
30 output drive signal of logic circuit opens synchronous rectifier M2, when the letter of the voltage slope detection circuit 10 output
Number be low level when, 30 output drive signal of logic circuit make synchronous rectifier M2 turn off.
The on-off for the driving signal driving synchronous rectifier M2 that the driving circuit 40 is used to be exported according to logic circuit 30.
When it is implemented, the voltage slope detection circuit 10, logic circuit 30, driving circuit 40 and transformer and synchronous
Rectifying tube output-stage circuit 20 is sequentially connected.
Please refer to Fig. 1, Fig. 2 and Fig. 4, the voltage slope detection circuit 10 include first voltage threshold detection unit 101,
Second voltage threshold detection unit 103, time detection unit 102 and signal processing unit 104.
Wherein, the first voltage threshold detection unit 101 is used to detect the height of synchronous rectifier M2 drain-source both end voltage
Threshold portion, and export the first comparison signal comp1.
The second voltage threshold detection unit 102 is used to detect the Low threshold portion of synchronous rectifier M2 drain-source both end voltage
Point, i.e. negative pressure part, and the second comparison signal comp2 of output.
The time detection unit 103 is used for generation time reference quantity Tref, and exports third comparison signal comp3.
The signal processing unit 104 is used to carry out logic to the second comparison signal comp2 and third comparison signal comp3
Calculation processing, and output control signals to the logic circuit 30.
When it is implemented, the first voltage threshold detection unit 101, time detection unit 103 and signal processing unit
104 are sequentially connected, and the signal processing unit 104 is also connected with the second voltage threshold detection unit 102.
Please continue to refer to Fig. 2 and Fig. 4, the first voltage threshold detection unit 101 includes first resistor R1, second resistance
One end of R2 and first comparator A1, the first resistor R1 are signal receiving end, receive the drain-source of the synchronous rectifier M2
Voltage also connects the second voltage threshold detection unit 102, the other end connection second resistance R2's of the first resistor R1
The positive input terminal of the inverting input terminal of one end and the first comparator A1, the first comparator A1 inputs the first preset reference
The output end of voltage Vref1, the first comparator A1 connect the time detection unit 103, and the second resistance R2's is another
One end ground connection.
Specifically, the drain-source voltage Vds of the synchronous rectifier M2 is divided by first resistor R1 and second resistance R2
High threshold part Vds_h=Vref1* (R1+R2)/R2 of drain-source voltage Vds is obtained, to detect the leakage of synchronous rectifier M2
The high threshold part of source voltage Vds, while when the drain-source voltage Vds of synchronous rectifier M2 is lower than its high threshold voltage Vds_h,
The output voltage of the first comparator A1 increases, i.e. the first comparison signal comp1 of its output is high level.
Please continue to refer to Fig. 2 and Fig. 4, the second voltage threshold detection unit 102 includes the ratio of the first metal-oxide-semiconductor M1 and second
Compared with device A2, the drain electrode of first metal-oxide-semiconductor connects one end of the first resistor, also receives the drain-source of the synchronous rectifier M2
Voltage, the source electrode of the first metal-oxide-semiconductor M1 connect the inverting input terminal of the second comparator A2, the first metal-oxide-semiconductor M1's
Grid connects VDD power supply, positive input terminal input the second predetermined reference voltage Vref2 of the second comparator A2, and described second
The output end of comparator A2 connects the signal processing unit 104.
Specifically, the first metal-oxide-semiconductor M1 plays the role of protecting internal low-voltage device, when the leakage of synchronous rectifier M2
When the voltage input of source, Low threshold part Vds_l=Vref2 of drain-source voltage Vds is obtained by the first metal-oxide-semiconductor M1, to detect
The Low threshold part of the drain-source voltage Vds of synchronous rectifier M2 out, while when the drain-source voltage Vds of synchronous rectifier M2 is reduced to
Lower than its low threshold voltage Vds_l, the second comparison signal of the second comparator A2 output switchs to high level by low level.
Please continue to refer to Fig. 2 and Fig. 4, the time detection unit 103 includes current source I1, the first phase inverter A4, high electricity
First switch K1 that the first comparison signal comp1 exported by the first comparator A1 that flat conducting, low level disconnect is controlled,
Second switch K2, the first capacitor C1 controlled by the first phase inverter A4 output signal that high level conducting, low level disconnect
With third comparator A3, one end of the current source I1 connects VDD power supply, the other end connection described first of the current source I1
One end of switch K1, the output end of the first comparator A1 export the first comparison signal comp1 and control the first switch K1
Be turned on or off, the other end of the first switch K1 is grounded by the second switch K2, is also connected the third and is compared
The inverting input terminal of device A3 and one end of first capacitor C1, the other end ground connection of the first capacitor C1, the third comparator
The positive input terminal of A3 inputs third predetermined reference voltage Vref3, and the output end of the third comparator A3 connects at the signal
Unit 103 is managed, the input terminal of the first phase inverter A4 connects the output end of the first comparator A1, first phase inverter
The output end output signal control second switch K2 of A4 is turned on or off.
Specifically, when the drain-source voltage Vds of synchronous rectifier M2 falls below Vds_h, the first comparator A1
Output voltage increase so that the first switch K1 in the time detection circuit 102 be closed, otherwise the first phase inverter A4 is exported
Signal make second switch K2 disconnect, the current source I1 start give capacitor C1 charging, at this time third comparator A3 output
Third comparison signal comp3 remains high level, when the reverse side voltage of third comparator A3 reaches internal reference voltage ref3
When, the third comparison signal comp3 of third comparator A3 output becomes low level from high level, therefore can be charged according to capacitor C1
Time and time period in synchronous rectifier M2 drain-source voltage variation detect synchronous rectifier drain-source voltage variation it is oblique
Rate, thus further accurately distinguish its drain terminal voltage change be due to primary side main power tube shutdown caused by or synchronous rectifier
After shutdown caused by resonance.
Please continue to refer to Fig. 2 and Fig. 4, the signal processing unit 104 include the second phase inverter A6, third phase inverter A7,
4th phase inverter A8, first and door A5 and the first trigger A9, the input terminal connection of the second phase inverter A6 second ratio
The output end of the input terminal of output end and the 4th phase inverter A8 compared with device A2, the second phase inverter A6 connects the third
The output end of the input terminal of phase inverter A7, the third phase inverter A7 connects the second input terminal of described first Yu door A5, described
First connect the output end of the third comparator A3 with the first input end of door A5, and described first connect with the output end of door A5
The end R at the end S of the first trigger A9, the first trigger A9 connects the output end of the 4th phase inverter A8, described
The end Q of first trigger A9 connects the logic circuit 103.
Specifically, the first trigger A9 is rest-set flip-flop, when the second comparison signal comp2 and third comparison signal
When comp3 is high level simultaneously, first with door A5 export high level, i.e. the set end S of rest-set flip-flop be height, clear terminal R be it is low,
The output end Q of rest-set flip-flop is high level, i.e. the control signal of voltage slope detection circuit output is high level；Compare when second
Have in signal comp2 and third comparison signal comp3 one for low level when, first exports low level, i.e. RS triggering with door A5
The set end S of device be it is low, the output end Q of rest-set flip-flop is low level, i.e. the control signal of voltage slope detection circuit output is
Low level, therefore only the second comparison signal comp2 and third comparison signal comp3 is simultaneously when being high level, voltage slope detection
The control signal of circuit output is just high level, and the synchronous rectifier M2 can be just turned on, and otherwise can not be opened.
Please continue to refer to Fig. 2, the logic circuit 30 includes the second trigger A10, the end S of the second trigger A10
The end Q of the first trigger A9 is connected, the end R of the second trigger A10 inputs cut-off signals OFF, second triggering
The end Q of device A10 connects the driving circuit 40.
Please continue to refer to Fig. 2, the input terminal of the driving circuit 40 connects the end Q of the second trigger A10, the drive
The output end of dynamic circuit 40 connects the grid of the synchronous rectifier M2, to be driven according to the driving signal that logic circuit 30 exports
The on-off of dynamic synchronous rectifier M2, when the driving signal that logic circuit 30 exports is high level, the driving of driving circuit 40 is synchronized
Rectifying tube M2 is opened, and when the driving signal that logic circuit 30 exports is low level, driving circuit 40 drives synchronous rectifier M2
It disconnects, to realize the correct unlatching of synchronous rectifier M2.
In order to better understand the present invention, it elaborates below in conjunction with attached drawing to technical solution of the present invention:
When Vd2 waveform changes from t1 to t2 in analysis chart 3 first, Vds voltage falls below its high threshold when the t1 moment
Vd2_h, the first comparator A1 output voltage are high level, and the current source I1 in the time detection circuit 102 is opened at this time
Begin to be that capacitor C1 charges, when time t2, since the capacitor C1 is not charged to the reference voltage Vref 3, third ratio yet
High level is remained compared with signal comp3 signal, but Vds voltage has been reduced to lower than its low threshold voltage Vd2_l, at this time at this time
Second comparison signal comp2 of the second comparator A2 output switchs to high level by low level, so, when the second comparison signal
When comp2 and third comparison signal comp3 is high simultaneously, the control signal of the output of the signal processing circuit 104 is high electricity
Flat, the synchronous rectifier M2 can be turned on.
Secondly when Vds waveform changes from t4 to t5 in analysis chart 3, Vds voltage falls below its high threshold when the t4 moment
The first comparison signal comp1 of Vd2_h, the first comparator A1 output are high level, at this time the time detection circuit 102
In current source I1 start for capacitor C1 charging, when time t5, due to the capacitor C1 be charged to it is described with reference to electricity
Vref3 is pressed, third compares comp3 signal and switchs to low level, but Vds voltage does not fall below its low threshold voltage still at this time
Vd2_l, the second comparison signal comp2 of the output of the second comparator A2 remains low level at this time, compares letter when second
Number comp2 and third comparison signal comp3 is non-concurrent when being high, and the output signal ON of the signal processing circuit 104 is remained
Low level opens phenomenon to efficiently avoid the synchronous rectifier M2 due to caused by resonance signal and open by mistake.
In conclusion the present invention passes through setting voltage slope detection circuit, the voltage change of detection synchronous rectifier drain electrode
Slope, accurately distinguish its drain terminal voltage change be due to primary side main power tube shutdown caused by or synchronous rectifier turn off after
It caused by resonance, is opened so as to avoid synchronous rectifier from being opened by mistake due to resonance, is further realizing synchronous rectifier just
Really open.
It, can according to the technique and scheme of the present invention and its hair it is understood that for those of ordinary skills
Bright design is subject to equivalent substitution or change, and all these changes or replacement all should belong to the guarantor of appended claims of the invention
Protect range.
Claims (7)
1. a kind of control circuit of synchronous rectifier characterized by comprising
Voltage slope detection circuit, for detecting the slope of the voltage change at synchronous rectifier drain-source both ends and exporting control letter
Number；
Transformer and synchronous rectifier output-stage circuit；
Logic circuit, the control signal for exporting to voltage slope detection circuit carry out logic calculation and output drive signal control
The on-off of synchronous rectifier processed；
Driving circuit, the on-off of the driving signal driving synchronous rectifier for being exported according to logic circuit；
The voltage slope detection circuit, logic circuit, driving circuit and transformer and synchronous rectifier output-stage circuit are successively
Connection；
The transformer and synchronous rectifier output-stage circuit include transformer primary winding, primary side main power tube, primary side sampling
One end connection of resistance, transformer secondary winding, output capacitance and synchronous rectifier, the transformer primary winding receives input
Voltage, the other end of the transformer primary winding connect the drain electrode of the primary side main power tube, the primary side main power tube
Source electrode is grounded by the primary side sampling resistor, and the grid of the primary side main power tube receives main driving signal, the transformer
One end of vice-side winding exports output voltage, and connects one end of output capacitance, and the other end of the transformer secondary winding connects
The drain electrode of the synchronous rectifier is connect, the source electrode ground connection of the synchronous rectifier also connects the other end of the output capacitance, institute
The grid for stating synchronous rectifier connects the driving circuit；
The voltage slope detection circuit includes:
First voltage threshold detection unit for detecting the high threshold part of synchronous rectifier drain-source both end voltage, and exports the
One comparison signal；
Second voltage threshold detection unit for detecting the Low threshold part of synchronous rectifier drain-source both end voltage, and exports the
Two comparison signals；
Time detection unit is used for generation time reference quantity, and exports third comparison signal；
Signal processing unit for carrying out logic calculation processing to the second comparison signal and third comparison signal, and exports control
Signal is to the logic circuit；
The first voltage threshold detection unit, time detection unit and signal processing unit are sequentially connected, the signal processing
Unit is also connected with the second voltage threshold detection unit.
2. the control circuit of synchronous rectifier according to claim 1, which is characterized in that the first voltage threshold test
Unit includes first resistor, second resistance and first comparator, and one end of the first resistor is signal receiving end, described in reception
The drain-source voltage of synchronous rectifier also connects the second voltage threshold detection unit, the other end connection of the first resistor
The positive input terminal input first of the inverting input terminal of one end of second resistance and the first comparator, the first comparator is pre-
If reference voltage, the output end of the first comparator connects the time detection unit, another termination of the second resistance
Ground.
3. the control circuit of synchronous rectifier according to claim 2, which is characterized in that the second voltage threshold test
Unit includes the first metal-oxide-semiconductor and the second comparator, and the drain electrode of first metal-oxide-semiconductor connects one end of the first resistor, also connects
The drain-source voltage of the synchronous rectifier is received, the source electrode of first metal-oxide-semiconductor connects the inverting input terminal of second comparator,
The grid of first metal-oxide-semiconductor connects VDD power supply, and the positive input terminal of second comparator inputs the second predetermined reference voltage,
The output end of second comparator connects the signal processing unit.
4. the control circuit of synchronous rectifier according to claim 3, which is characterized in that the time detection unit includes
The the first comparison signal control exported by the first comparator that current source, the first phase inverter, high level conducting, low level disconnect
The second switch controlled by first inverter output signal that the first switch of system, high level conducting, low level disconnect, the
One capacitor and third comparator, one end of the current source connect VDD power supply, the other end connection described first of the current source
One end of switch, what the output end of the first comparator exported that the first comparison signal controls the first switch leads on-off
It opens, the other end of the first switch is grounded by the second switch, also connects the inverting input terminal of the third comparator
It is grounded with the other end of one end of first capacitor, the first capacitor, the positive input terminal input third of the third comparator is pre-
If reference voltage, the output end of the third comparator connects the signal processing unit, the input terminal of first phase inverter
The output end of the first comparator is connected, the output end output signal control second switch of first phase inverter leads on-off
It opens.
5. the control circuit of synchronous rectifier according to claim 4, which is characterized in that the signal processing unit includes
Second phase inverter, third phase inverter, the 4th phase inverter, first and door and the first trigger, the input terminal of second phase inverter
Connect the output end of second comparator and the input terminal of the 4th phase inverter, the output end connection of second phase inverter
The input terminal of the third phase inverter, the output end of the third phase inverter connect the second input terminal of described first Yu door, institute
State the first output end that the third comparator is connect with the first input end of door, described first connect with the output end of door described in
The end S of first trigger, the end R of first trigger connect the output end of the 4th phase inverter, first trigger
The end Q connect the logic circuit.
6. the control circuit of synchronous rectifier according to claim 5, which is characterized in that the logic circuit includes second
Trigger, the end S of second trigger connect the end Q of first trigger, and the end R of second trigger inputs shutdown
The end Q of signal, second trigger connects the driving circuit.
7. the control circuit of synchronous rectifier according to claim 6, which is characterized in that the input terminal of the driving circuit
The end Q of the second trigger is connected, the output end of the driving circuit connects the grid of the synchronous rectifier.
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| CN109713921B (en) * | 2018-12-21 | 2021-07-06 | 西安矽力杰半导体技术有限公司 | Synchronous rectification control circuit, control method and switching circuit |
| CN109980946B (en) * | 2019-04-18 | 2020-02-14 | 深圳南云微电子有限公司 | Synchronous rectification control circuit and control method thereof |
| CN110445403B (en) * | 2019-08-12 | 2021-04-20 | 上海南芯半导体科技有限公司 | SR false-open prevention control method |
| TWI774980B (en) * | 2019-08-29 | 2022-08-21 | 偉詮電子股份有限公司 | Synchronous rectification controller, method of adaptively setting a slew-rate threshold, and relevant control methods |
| CN110855131B (en) * | 2019-12-09 | 2021-10-15 | 成都芯源系统有限公司 | Drive circuit of synchronous rectifier |
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| CN113746358A (en) * | 2021-08-16 | 2021-12-03 | 西安鼎芯微电子有限公司 | Synchronous rectification switch control circuit |
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