CN112398315A - Synchronous rectification control circuit and power converter - Google Patents

Synchronous rectification control circuit and power converter Download PDF

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Publication number
CN112398315A
CN112398315A CN202011324665.XA CN202011324665A CN112398315A CN 112398315 A CN112398315 A CN 112398315A CN 202011324665 A CN202011324665 A CN 202011324665A CN 112398315 A CN112398315 A CN 112398315A
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CN
China
Prior art keywords
voltage
circuit
synchronous rectifier
rectifier tube
synchronous
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CN202011324665.XA
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Chinese (zh)
Inventor
文鹏
曾强
林官秋
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Shenzhen Biyi Microelectronics Co Ltd
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Shenzhen Biyi Microelectronics Co Ltd
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Priority to CN202011324665.XA priority Critical patent/CN112398315A/en
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    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M1/00—Details of apparatus for conversion
    • H02M1/08—Circuits specially adapted for the generation of control voltages for semiconductor devices incorporated in static converters
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • 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
    • 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
    • H03—ELECTRONIC CIRCUITRY
    • H03K—PULSE TECHNIQUE
    • H03K17/00—Electronic switching or gating, i.e. not by contact-making and –breaking
    • H03K17/04—Modifications for accelerating switching
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02B—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO BUILDINGS, e.g. HOUSING, HOUSE APPLIANCES OR RELATED END-USER APPLICATIONS
    • Y02B70/00—Technologies for an efficient end-user side electric power management and consumption
    • Y02B70/10—Technologies improving the efficiency by using switched-mode power supplies [SMPS], i.e. efficient power electronics conversion e.g. power factor correction or reduction of losses in power supplies or efficient standby modes

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

Abstract

Disclosed are a synchronous rectification control circuit and a power converter, the power converter including the synchronous rectification control circuit, the synchronous rectification control circuit including: the main control circuit is used for controlling the on and off of the synchronous rectifier tube; and the voltage regulating circuit is used for reducing the voltage of the control end of the synchronous rectifier tube before the synchronous rectifier tube is turned off in the on time of the synchronous rectifier tube. The synchronous rectification control circuit and the power converter provided by the invention can reduce the voltage variation when the synchronous rectification tube is turned off, reduce the turn-off delay of the synchronous rectification tube and improve the reliability and stability of synchronous rectification control.

Description

Synchronous rectification control circuit and power converter
Technical Field
The invention relates to the technical field of electronic circuits, in particular to a synchronous rectification control circuit and a power converter.
Background
A power converter, such as the flyback voltage converter shown in fig. 1, includes a primary circuit 101 and a secondary circuit 102, where the primary circuit 101 and the secondary circuit 102 are isolated by a transformer T. The primary switch Q of the primary circuit 101 transfers energy to the secondary circuit 102 by switching. The secondary circuit 102 includes a rectifying device D, which is turned on when the primary switch Q is turned off, and is used to supply power to the output capacitor C0 and the load through the freewheeling current, and is turned off when the freewheeling current drops to zero, and is used to supply power to the load through the output capacitor C0.
In order to improve the power efficiency, the rectifier device D on the secondary side usually employs a synchronous rectifier (with lower resistance, lower loss and higher efficiency) and the high-efficiency rectification function is realized by timely controlling the on and off of the synchronous rectifier. However, the on and off of the synchronous rectifier is controlled according to the control voltage of the gate, the voltage jumps from one level to another level with a certain delay, which causes the off delay of the synchronous rectifier, and the off delay will cause the synchronous rectifier of the secondary circuit 102 and the primary switch Q to be in common, which causes the reliability and stability of the system.
Disclosure of Invention
In view of the above problems, an object of the present invention is to provide a synchronous rectification control circuit and a power converter, so as to reduce the turn-off delay effect of a synchronous rectifier tube and improve the reliability and stability of synchronous rectification control.
According to an aspect of the present invention, there is provided a synchronous rectification control circuit including:
the main control circuit comprises a drain-source voltage input end of the synchronous rectifier tube and a driving signal output end of the synchronous rectifier tube, wherein the driving signal output end of the synchronous rectifier tube is coupled to the control end of the synchronous rectifier tube and controls the on and off of the synchronous rectifier tube;
a voltage regulating circuit comprising a synchronous rectifier drain-source voltage input and a regulated voltage output coupled to a control terminal of said synchronous rectifier, wherein,
the adjusting voltage of the adjusting voltage output end is changed in stages according to the drain-source voltage of the synchronous rectifier tube, and the voltage of the control end of the synchronous rectifier tube is gradually reduced before the synchronous rectifier tube is turned off.
Optionally, the stepwise variation of the regulation voltage comprises at least two phases.
Optionally, the voltage regulating circuit includes at least one voltage regulating unit, each of the voltage regulating units includes a detection circuit and a voltage bleeder circuit, the detection circuit controls the opening of a bleeder path of the voltage bleeder circuit according to the drain-source voltage of the synchronous rectifier, and a bleeder input end of the voltage bleeder circuit is coupled to the control end of the synchronous rectifier.
Optionally, the detection circuit includes a comparator, an output terminal of the comparator is coupled to the control terminal of the voltage bleeder circuit, an input terminal of the comparator receives the drain-source voltage of the synchronous rectifier and the reference voltage, and a bleeder path of the voltage bleeder circuit is opened when the drain-source voltage of the synchronous rectifier is higher than the reference voltage.
Optionally, the voltage bleeding circuit comprises:
the diode, the switch and the voltage source, the anode of the diode is the bleeder input end, the cathode of the diode is coupled to the first end of the switch, the second end of the switch is coupled to the positive end of the voltage source, the negative end of the voltage source is grounded, and the control end of the switch is the control end of the voltage bleeder circuit.
Optionally, the voltage bleeding circuit comprises:
the gate of the PMOS tube receives a threshold voltage and is turned off when the voltage of the bleeding input end is lower than the threshold voltage, and the gate of the second NMOS tube is a control end of the voltage bleeding circuit;
the first NMOS tube is coupled between the bleeder input end and the ground in a positive direction, and the grid electrode of the first NMOS tube is coupled to the source electrode of the second NMOS tube.
Optionally, the main control circuit comprises:
the PWM signal generating circuit is used for generating a PWM signal according to the drain-source voltage of the synchronous rectifier tube;
and the driving circuit is connected with the PWM signal generating circuit and provides the synchronous rectifier tube driving signal according to the PWM signal.
Optionally, the PWM signal generation circuit includes:
the conduction detection circuit is used for comparing the drain-source voltage of the synchronous rectifier tube with a conduction threshold value and providing a conduction signal;
the turn-off detection circuit is used for comparing the drain-source voltage of the synchronous rectifier tube with a turn-off threshold value and providing a turn-off signal;
and the logic circuit is connected with the turn-on detection circuit and the turn-off detection circuit and is used for providing the PWM signal according to the turn-on signal and the turn-off signal.
According to another aspect of the present invention, there is provided a power converter comprising a primary circuit and a secondary circuit coupled by a transformer, for transferring energy from the primary circuit to the secondary circuit, the secondary circuit comprising a synchronous rectifier tube connected in series in a secondary current path, wherein the power converter further comprises:
the invention provides a synchronous rectification control circuit.
The invention provides a synchronous rectification control circuit, which comprises a main control circuit and a voltage regulating circuit, wherein the main control circuit controls the on and off of a synchronous rectifier tube, the voltage regulating circuit provides regulating voltage which is changed in stages according to drain-source voltage of the synchronous rectifier tube at a regulating voltage output end of the voltage regulating circuit, the control end voltage of the synchronous rectifier tube can be gradually reduced between the off of the synchronous rectifier tube, the voltage change amplitude of the control end of the synchronous rectifier tube during the off of the synchronous rectifier tube is reduced, the speed of reducing the control end voltage of the synchronous rectifier tube to an off threshold value is improved, the off delay time of the synchronous rectifier tube controlled by synchronous rectification is reduced, and the reliability and the stability of synchronous rectification control are improved.
The voltage regulation comprises at least two stages, the voltage of the control end corresponding to the synchronous rectifier tube is changed for a plurality of times in the conduction time and is gradually reduced, the voltage of the control end of the synchronous rectifier tube is gradually changed, the change of the conduction current of the synchronous rectifier tube is smoother, the change of the drain-source voltage of the synchronous rectifier tube is smoother, the judgment of the turn-off point of the judgment of the synchronous rectification control according to the drain-source voltage of the synchronous rectifier tube is more accurate, and the synchronous rectification effect is better.
The power converter provided by the invention comprises the synchronous rectification control circuit provided by the invention, the turn-off delay of the synchronous rectification tube is short, the turn-off of the synchronous rectification tube is rapid and accurate, and the reliability and the stability of the power converter can be improved.
Drawings
The above and other objects, features and advantages of the present invention will become more apparent from the following description of the embodiments of the present invention with reference to the accompanying drawings, in which:
fig. 1 shows a schematic diagram of a flyback power converter according to the prior art;
FIG. 2 is a schematic diagram of a synchronous rectification control circuit according to an embodiment of the present invention;
FIG. 3 shows a timing diagram of a portion of signals of a synchronous rectification control circuit according to an embodiment of the present invention;
fig. 4 is a schematic diagram of another voltage regulating unit of the synchronous rectification control circuit according to the embodiment of the invention.
Detailed Description
Various embodiments of the present invention will be described in more detail below with reference to the accompanying drawings. Like elements in the various figures are denoted by the same or similar reference numerals. For purposes of clarity, the various features in the drawings are not necessarily drawn to scale.
The following detailed description of embodiments of the present invention is provided in connection with the accompanying drawings and examples.
The term "connected" or "coupled" in this specification includes both direct and indirect connections. An indirect connection is a coupling via an intermediary, such as a conductor, wherein the electrically conductive medium may include parasitic inductance or parasitic capacitance, or via an intermediary circuit or component as described in the embodiments of the specification; indirect connections may also include coupling through other active or passive devices that perform the same or similar function, such as coupling through signal amplification circuitry, follower circuitry, logic processing circuitry, and so on.
Fig. 2 is a schematic diagram illustrating a structure of a synchronous rectification control circuit according to an embodiment of the present invention.
As shown in fig. 2, the synchronous rectification control circuit 200 of the embodiment of the present invention includes a main control circuit 210 and a voltage regulation circuit 220.
The main control circuit 210 includes a drain-source voltage input terminal of the synchronous rectifier, receives the drain-source voltage Vds of the synchronous rectifier, and a synchronous rectification control signal output terminal thereof is coupled to a control terminal (gate) of the synchronous rectifier SR, and provides a synchronous rectification control signal to control the on/off of the synchronous rectifier SR.
The voltage regulating circuit 220 includes a drain-source voltage input terminal of the synchronous rectifier tube and a regulated voltage output terminal coupled to the control terminal of the synchronous rectifier tube SR, and is configured to provide a step-change regulated voltage according to the drain-source voltage Vds of the synchronous rectifier tube SR, so as to gradually reduce the control terminal voltage of the synchronous rectifier tube SR before the synchronous rectifier tube SR is turned off, and reduce the control terminal voltage to a lower level immediately before the synchronous rectifier tube SR is turned off, so that the level change of the control terminal voltage of the synchronous rectifier tube SR when the synchronous rectifier tube SR is turned off is reduced, and at the same level reduction speed, the control terminal voltage of the synchronous rectifier tube SR is more quickly reduced to a level threshold required for turn-off, thereby reducing the turn-off delay of the synchronous rectifier tube SR, improving the accuracy of time control of the synchronous rectifier control, and improving the reliability and stability of the synchronous rectifier control. Meanwhile, the follow current is reduced to lower current when being turned off, so that the switching loss is reduced, and the system efficiency is improved.
The main control circuit 210 includes an on detection comparator U11, an off detection comparator U22, an SR flip-flop T1, and a driving circuit 211.
The conduction detection comparator U11 forms a conduction detection circuit, the non-inverting input end of the conduction detection comparator U11 receives a conduction threshold Vref11, the inverting input end receives a drain-source voltage Vds of the synchronous rectifier tube, the output end provides a conduction signal, and the conduction signal is effective when the drain-source voltage Vds of the synchronous rectifier tube is smaller than the conduction threshold Vref 11.
The turn-off detection comparator U22 forms a turn-off detection circuit, the inverting input end of the turn-off detection comparator U22 receives a turn-off threshold Vref22, the non-inverting input end receives a drain-source voltage Vds of the synchronous rectifier tube, the output end provides a turn-off signal, and the turn-off signal is effective when the drain-source voltage Vds of the synchronous rectifier tube is greater than the turn-off threshold Vref 22.
Wherein the off threshold Vref22 is greater than the on threshold Vref 11.
The SR flip-flop T1 is a logic circuit, and provides a PWM (Pulse Width Modulation) signal according to the on signal and the off signal, the set terminal of the SR flip-flop T1 is connected to the output terminal of the conduction detection comparator U11, receives the on signal, and sets the output terminal of the SR flip-flop T1 to 1 when the on signal is valid; the reset terminal of the SR flip-flop T1 is connected to the output terminal of the shutdown detection comparator U22, receives the shutdown signal, and resets the output terminal of the SR flip-flop T1 to 0 when the shutdown signal is valid.
The input end of the driving circuit 211 is connected to the output end of the SR flip-flop T1, the output end is coupled to the control end of the synchronous rectifier SR, the PWM signal is converted into a synchronous rectifier driving signal capable of driving the synchronous rectifier SR to turn on and off, and when the PWM signal is 0, the output end of the driving circuit 211 is grounded, the control end of the synchronous rectifier SR is grounded, and turn-off control of the synchronous rectifier SR is ensured.
The voltage regulating circuit 220 includes at least one voltage regulating unit, and in the present embodiment, n voltage regulating units are taken as an example.
The first voltage adjusting unit includes a first comparator U1, a first diode D1, a first switch S1, and a first voltage source V1.
The first diode D1, the first switch S1, and the first voltage source V1 are connected in sequence to form a bleed path of the voltage bleed circuit. The anode of the first diode D1 is a bleeding input terminal, coupled to the control terminal of the synchronous rectifier SR, and the cathode is connected to the first terminal of the first switch S1; a second terminal of the first switch S1 is connected to the positive terminal of the first voltage source V1, and a control terminal is connected to the output terminal of the first comparator U1; the negative terminal of the first voltage source V1 is grounded, and when the first switch S1 is turned on, the voltage at the control terminal of the synchronous rectifier SR is pulled down to the positive terminal level of the first voltage source V1.
The first comparator U1 is a first detection circuit, the non-inverting input terminal of the first comparator U1 receives the drain-source voltage Vds of the synchronous rectifier, the inverting input terminal receives the first reference voltage Vref1, the output terminal provides the first detection signal to the first switch S1, and when the drain-source voltage Vds of the synchronous rectifier is greater than the first reference voltage Vref1, the first detection signal is valid, and the first switch S1 is turned on.
The second voltage regulating unit includes a second comparator U2, a second diode D2, a second switch S2, and a second voltage source V2, the nth voltage regulating unit includes an nth comparator Un, an nth diode Dn, an nth switch Sn, and an nth voltage source Vn, and circuit structures of the second to nth voltage regulating units are the same as those of the first voltage regulating unit, and will not be described in detail herein. The first reference voltage Vref1, the second reference voltage Vref2 to the nth reference voltage Vrefn correspond to the first voltage source V1, the second voltage source V2 to the nth voltage source Vn one to one, the levels of the first reference voltage Vref1, the second reference voltage Vref2 to the nth reference voltage Vrefn are gradually increased, the levels provided by the first voltage source V1, the second voltage source V2 to the nth voltage source Vn are gradually decreased, the level of the first reference voltage Vref1 is greater than the level of the turn-on threshold Vref11, and the level of the nth reference voltage Vrefn is less than the level of the turn-off threshold Vref 22.
In the on-time of the synchronous rectifier tube SR, the drain-source voltage Vds of the synchronous rectifier tube gradually increases (changes from a negative value to 0), the discharge path of the voltage discharge circuit of the voltage regulating unit is sequentially opened, the control end voltage of the synchronous rectifier tube SR is stepped down (from V1 to Vn) until the drain-source voltage Vds of the synchronous rectifier tube reaches a turn-off threshold Vref22, the control end voltage of the synchronous rectifier tube SR is changed from the level value of the nth voltage source Vn to the ground level, the level variation is small, the time delay is short, and the jump from the on-state to the off-state is rapid. The output voltage of the nth voltage source Vn is greater than the lowest breakover voltage of the synchronous rectifier SR.
Fig. 3 shows a timing diagram of a part of signals of the synchronous rectification control circuit according to the embodiment of the invention.
As shown in fig. 3, a timing diagram of the drain-source voltage Vds, the PWM signal, and the gate voltage VG (the control terminal voltage of the synchronous rectifier SR) of the synchronous rectifier 200 of the synchronous rectifier control circuit 200 according to the embodiment of the present invention is shown.
At time t1, the drain-source voltage Vds of the synchronous rectifier is smaller than the turn-off threshold Vref22 and is reduced to the turn-on threshold Vref11, the PWM signal is set to 1, and the gate voltage VG of the synchronous rectifier starts to be raised by the driving circuit 211 and gradually raised to the driving power voltage VCC, wherein when the gate voltage VG of the synchronous rectifier reaches the lowest turn-on voltage of the synchronous rectifier SR, the synchronous rectifier SR is turned on.
The driving power source voltage VCC is higher, so as to rapidly increase the control terminal voltage of the synchronous rectifier SR and rapidly turn on the synchronous rectifier SR.
After the synchronous rectifier SR is turned on, the drain-source voltage Vds of the synchronous rectifier gradually increases, and at the time of t2, the drain-source voltage Vds of the synchronous rectifier increases to the first reference voltage Vref1, the first switch S1 of the first voltage adjustment unit is turned on, the discharge path of the first voltage adjustment circuit is turned on, the gate voltage VG of the synchronous rectifier is gradually reduced by the driving power voltage VCC, and is limited by the first power supply V1, and the gate voltage VG of the synchronous rectifier is stabilized after being reduced to the level V1 of the first voltage supply V1.
The drain-source voltage Vds of the synchronous rectifier tube continues to increase, and when the time is t2, the drain-source voltage Vds of the synchronous rectifier tube increases to a second reference voltage Vref2, a second switch S2 of the second voltage adjusting unit is turned on, a drain path of the second voltage adjusting circuit is turned on, the gate voltage VG of the synchronous rectifier tube is gradually reduced from the level of the first voltage source V1, and is limited by the second voltage source V2, and the gate voltage VG of the synchronous rectifier tube is stabilized after being reduced to the level V2 of the second voltage source V2. At this time, the leakage path of the first voltage regulating unit is still turned on, but the level of the regulated voltage output terminal of the voltage regulating circuit 220 is based on the lowest limit level in the leakage path, so that the level of the control terminal of the synchronous rectifier SR can be gradually reduced.
At the time t4, the drain-source voltage Vds of the synchronous rectifier tube is raised to the turn-off threshold Vref22, the PWM signal value is 0, the output end of the driving circuit 211 outputs the ground level, so that the control end of the synchronous rectifier tube SR is connected to the ground level, the gate voltage VG of the synchronous rectifier tube is rapidly changed from the level of the second voltage source V2 to the ground level, and the synchronous rectifier tube SR is rapidly turned off.
Before the synchronous rectifier SR is turned off, the voltage at the control end of the synchronous rectifier SR is gradually reduced, at least two stages are arranged to be gradually reduced, the change between the stages also needs certain time, the arrangement of the at least two stages can avoid the superposition of the relaxation time and the turn-off time of the conversion between the stages, the effect of the conversion between the stages is reduced, the voltage at the control end of the synchronous rectifier SR can be ensured to be stably reduced to a set target value before the control end of the synchronous rectifier SR is turned off, and the rapid turn-off of the synchronous rectifier SR is ensured.
Fig. 4 is a schematic diagram of another voltage regulating unit of the synchronous rectification control circuit according to the embodiment of the invention.
As shown in fig. 4, another voltage regulating unit of the synchronous rectification control circuit according to the embodiment of the present invention is different from the voltage regulating unit of the synchronous rectification control circuit 200 shown in fig. 2 in the voltage dropping circuit 221, and the details of the other parts are not described herein.
The voltage bleeder circuit 221 of this embodiment includes a first NMOS (N-Metal-Oxide-Semiconductor) transistor N1, a second NMOS transistor N2, a PMOS (P-Metal-Oxide-Semiconductor) transistor P, and a resistor R.
The source of the second NMOS transistor N2 is grounded through a resistor R, the drain is connected to the drain of the PMOS transistor P, the gate is the control terminal of the voltage bleeder circuit 221, and the second NMOS transistor N2 is turned on when the drain-source voltage Vds of the synchronous rectifier reaches the corresponding reference voltage.
The source of the PMOS transistor P is a bleeding input terminal of the voltage bleeding circuit 221, and the gate thereof receives a threshold voltage VP, and turns off the PMOS transistor P when the voltage at the bleeding input terminal is lower than the threshold voltage VP.
The first NMOS transistor N1 is connected in series between the drain input terminal of the voltage bleeder circuit 221 and ground in the forward direction, the gate is connected to the source of the second NMOS transistor N2, and after the second NMOS transistor N2 is turned on, the drain input terminal of the voltage bleeder circuit 221 is turned on through the control terminal voltage of the synchronous rectifier SR connected to the ground drain input terminal of the first NMOS transistor N1, when the control terminal voltage of the synchronous rectifier SR decreases to the threshold voltage VP, the PMOS transistor P is turned off, the gate of the first NMOS transistor N1 is turned off from the control terminal of the synchronous rectifier SR at the drain input terminal, the level is ground, the first NMOS transistor N1 is also turned off, the voltage drain path of the voltage bleeder circuit 221 is turned off, and the control terminal circuit of the synchronous rectifier SR is maintained at the threshold voltage VP.
The voltage bleeder circuit 221 of this embodiment provides a threshold voltage VP for the gate of the PMOS transistor P, and controls the bleeder final voltage of the voltage bleeder circuit 221, the threshold voltage VP does not depend on a dedicated voltage source, and for the voltage regulator circuit 220 provided with a plurality of voltage regulator units, only one voltage source and a plurality of voltage divider circuits may be used, so that a plurality of gradually changing threshold voltages VP may be provided.
The invention provides a synchronous rectification control circuit, which comprises a main control circuit and a voltage regulating circuit, wherein the main control circuit controls the on and off of a synchronous rectifier tube, the voltage regulating circuit provides regulating voltage which is changed in stages according to drain-source voltage of the synchronous rectifier tube at a regulating voltage output end of the voltage regulating circuit, the control end voltage of the synchronous rectifier tube can be gradually reduced between the off of the synchronous rectifier tube, the voltage change amplitude of the control end of the synchronous rectifier tube during the off of the synchronous rectifier tube is reduced, the speed of reducing the control end voltage of the synchronous rectifier tube to an off threshold value is improved, the off delay time of the synchronous rectifier tube controlled by synchronous rectification is reduced, and the reliability and the stability of synchronous rectification control are improved.
While embodiments in accordance with the invention have been described above, these embodiments are not intended to be exhaustive or to limit the invention to the precise embodiments described. Obviously, many modifications and variations are possible in light of the above teaching. The embodiments were chosen and described in order to best explain the principles of the invention and the practical application, to thereby enable others skilled in the art to best utilize the invention and various embodiments with various modifications as are suited to the particular use contemplated. The invention is limited only by the claims and their full scope and equivalents.

Claims (9)

1. A synchronous rectification control circuit, comprising:
the main control circuit comprises a drain-source voltage input end of the synchronous rectifier tube and a driving signal output end of the synchronous rectifier tube, wherein the driving signal output end of the synchronous rectifier tube is coupled to the control end of the synchronous rectifier tube and controls the on and off of the synchronous rectifier tube;
a voltage regulating circuit comprising a synchronous rectifier drain-source voltage input and a regulated voltage output coupled to a control terminal of said synchronous rectifier, wherein,
the adjusting voltage of the adjusting voltage output end is changed in stages according to the drain-source voltage of the synchronous rectifier tube, and the voltage of the control end of the synchronous rectifier tube is gradually reduced before the synchronous rectifier tube is turned off.
2. The synchronous rectification control circuit of claim 1,
the stepwise variation of the regulating voltage comprises at least two phases.
3. The synchronous rectification control circuit of claim 1,
the voltage regulating circuit comprises at least one voltage regulating unit, each voltage regulating unit comprises a detection circuit and a voltage bleeder circuit, the detection circuit controls the opening of a bleeder path of the voltage bleeder circuit according to the drain-source voltage of the synchronous rectifier tube, and the bleeder input end of the voltage bleeder circuit is coupled to the control end of the synchronous rectifier tube.
4. The synchronous rectification control circuit of claim 3,
the detection circuit comprises a comparator, the output end of the comparator is coupled to the control end of the voltage bleeder circuit, the input end of the comparator receives the drain-source voltage and the reference voltage of the synchronous rectifier tube, and the bleeder path of the voltage bleeder circuit is opened when the drain-source voltage of the synchronous rectifier tube is higher than the reference voltage.
5. The synchronous rectification control circuit of claim 4, wherein the voltage bleed circuit comprises:
the diode, the switch and the voltage source, the anode of the diode is the bleeder input end, the cathode of the diode is coupled to the first end of the switch, the second end of the switch is coupled to the positive end of the voltage source, the negative end of the voltage source is grounded, and the control end of the switch is the control end of the voltage bleeder circuit.
6. The synchronous rectification control circuit of claim 4, wherein the voltage bleed circuit comprises:
the gate of the PMOS tube receives a threshold voltage and is turned off when the voltage of the bleeding input end is lower than the threshold voltage, and the gate of the second NMOS tube is a control end of the voltage bleeding circuit;
the first NMOS tube is coupled between the bleeder input end and the ground in a positive direction, and the grid electrode of the first NMOS tube is coupled to the source electrode of the second NMOS tube.
7. The synchronous rectification control circuit of claim 1, wherein the main control circuit comprises:
the PWM signal generating circuit is used for generating a PWM signal according to the drain-source voltage of the synchronous rectifier tube;
and the driving circuit is connected with the PWM signal generating circuit and provides the synchronous rectifier tube driving signal according to the PWM signal.
8. The synchronous rectification control circuit of claim 7, wherein the PWM signal generation circuit comprises:
the conduction detection circuit is used for comparing the drain-source voltage of the synchronous rectifier tube with a conduction threshold value and providing a conduction signal;
the turn-off detection circuit is used for comparing the drain-source voltage of the synchronous rectifier tube with a turn-off threshold value and providing a turn-off signal;
and the logic circuit is connected with the turn-on detection circuit and the turn-off detection circuit and is used for providing the PWM signal according to the turn-on signal and the turn-off signal.
9. A power converter comprising a primary circuit and a secondary circuit coupled by a transformer for transferring energy from the primary circuit to the secondary circuit, the secondary circuit comprising a synchronous rectifier tube connected in series in a secondary current path, the power converter further comprising:
a synchronous rectification control circuit as claimed in any one of claims 1 to 8.
CN202011324665.XA 2020-11-23 2020-11-23 Synchronous rectification control circuit and power converter Pending CN112398315A (en)

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