CN112134465A - Synchronous rectification control circuit and voltage converter - Google Patents
Synchronous rectification control circuit and voltage converter Download PDFInfo
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- 238000010586 diagram Methods 0.000 description 8
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
- H02M3/00—Conversion of dc power input into dc power output
- H02M3/22—Conversion of dc power input into dc power output with intermediate conversion into ac
- H02M3/24—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters
- H02M3/28—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac
- H02M3/325—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal
- H02M3/335—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal using semiconductor devices only
- H02M3/33569—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal using semiconductor devices only having several active switching elements
- H02M3/33576—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal using semiconductor devices only having several active switching elements having at least one active switching element at the secondary side of an isolation transformer
- H02M3/33592—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal using semiconductor devices only having several active switching elements having at least one active switching element at the secondary side of an isolation transformer having a synchronous rectifier circuit or a synchronous freewheeling circuit at the secondary side of an isolation transformer
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
- H02M1/00—Details of apparatus for conversion
- H02M1/0048—Circuits or arrangements for reducing losses
- H02M1/0054—Transistor switching losses
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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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- Dc-Dc Converters (AREA)
Abstract
The first comparator compares the drain-source voltage of the synchronous rectifier tube with a first reference signal and provides a first control signal, the second comparator compares the drain-source voltage of the synchronous rectifier tube with a second reference signal and provides a third control signal to a second input end of the first trigger, and the delay circuit delays the first control signal and provides the second control signal to a first input end of the first trigger. The delay time of the delay circuit of the synchronous rectification control circuit is a threshold value for judging whether a body diode of the rectification tube is in normal conduction or parasitic oscillation conduction, namely, whether the effective starting time of the third control signal is before or after the effective starting time of the second control signal is judged, the effective starting time is set into two output states respectively corresponding to the first trigger before the original output state is maintained, and the synchronous rectification tube is controlled to be in timely conduction and disconnection.
Description
Technical Field
The invention relates to the technical field of electronic circuits, in particular to a synchronous rectification control circuit and a voltage converter.
Background
As shown in fig. 1, the flyback voltage converter includes a primary circuit and a secondary circuit, the primary circuit and the secondary circuit are isolated by a transformer T, the primary circuit includes a primary switch Q on an electrical loop, energy can be transferred to the secondary circuit by a switching operation of the primary switch Q, the secondary circuit includes an output capacitor C0 connected in series with a secondary side of the transformer T and a synchronous rectifier SR disposed between the secondary side of the transformer T and the output capacitor C0, and two ends of the output capacitor are coupled to a load. In order to improve the power efficiency, the synchronous rectifier on the secondary side usually uses a synchronous rectifier with lower resistance than a diode or a body diode and low synchronous conduction state loss, and the high-efficiency rectification function is realized by timely controlling the conduction and the disconnection of the synchronous rectifier.
In the voltage-controlled synchronous rectifier, the conduction time of the synchronous rectifier is generally determined by detecting the drain-source voltage Vds of the synchronous rectifier SR, and as shown in fig. 2, when Vds is detected to be smaller than the second threshold voltage Vth2, the body diode of the synchronous rectifier is considered to be turned on, and the synchronous rectifier can be controlled to be turned on.
In the prior art, when the circuit operates in a DCM (Discontinuous Conduction Mode), the circuit may generate parasitic oscillation, which may also cause the body diode of the synchronous rectifier SR to be turned on, and further erroneously turn on the synchronous rectifier SR under the parasitic oscillation, as shown in fig. 2, in the prior art, a PWM (Pulse Width Modulation) signal correspondingly controls the synchronous rectifier SR to be turned on, and a Blank signal follows the PWM signal, and the Blank signal corresponds to the parasitic oscillation time, and controls the synchronous rectifier SR to be kept off, so as to prevent erroneous Conduction of the synchronous rectifier SR. However, if the power supply needs to be compatible with CCM (Continuous Conduction Mode), QR (quadrature-resonance) Mode, and DCM operation, the Blank time of the Blank signal may prevent the synchronous rectifier SR from normally conducting in the QR and CCM operation modes, thereby reducing the power supply efficiency.
Disclosure of Invention
In view of the above problems, it is an object of the present invention to provide a synchronous rectification control circuit and a voltage converter, thereby improving power supply efficiency.
According to an aspect of the present invention, a synchronous rectification control circuit is provided, which includes a drain-source voltage receiving terminal of a synchronous rectifier and a gate control signal output terminal of the synchronous rectifier, and includes:
the first comparator comprises an input end coupled with the drain-source voltage receiving end of the synchronous rectifier tube, a first reference signal input end and a first control signal output end;
a delay circuit comprising an input coupled to the first control signal output and a second control signal output;
the second comparator comprises an input end coupled with the drain-source voltage receiving end of the synchronous rectifier tube, a second reference signal input end and a third control signal output end;
a first flip-flop having a first input terminal coupled to the second control signal output terminal of the delay circuit, a second input terminal coupled to the third control signal output terminal of the second comparator, and an output terminal coupled to the gate control signal output terminal of the synchronous rectification transistor,
wherein a level of the first reference signal is higher than a level of the second reference signal.
Optionally, the delay circuit comprises:
the first end of the capacitor is coupled with the output end of the current source, and the second end of the capacitor is grounded;
a switch connected in series across the capacitor, the switch including a switch control terminal coupled to the first control signal output terminal;
a third comparator comprising an input coupled to the first terminal of the capacitor, a third reference signal input, and an output, the output of the third comparator being the second control signal output.
Optionally, a third reference signal input terminal of the delay circuit is coupled to a third reference signal output terminal of an external third reference signal configuration circuit.
Optionally, the delay circuit further comprises an inverter, the inverter being coupled in a forward direction between the first control signal output terminal and the switch control terminal of the switch;
the switch is an NMOS tube, and the grid electrode of the NMOS tube is the switch control end.
Optionally, the method further comprises:
an or gate coupled between the second control signal output and the first input of the first flip-flop, the or gate including a first input, a second input, and an output, the second input of the or gate being coupled to the second control signal output, the output of the or gate being coupled to the first input of the first flip-flop;
a pulse generator, an input terminal of the pulse generator being coupled to the first control signal output terminal, and a pulse output terminal of the pulse generator being coupled to the first input terminal of the or gate.
Optionally, the method further comprises:
and the AND gate comprises a first input end coupled with the first control signal output end, a second input end coupled with the output end of the first trigger and an output end coupled with the grid control signal output end of the synchronous rectifier tube.
Optionally, the method further comprises:
a set end of the second trigger is coupled to an output end of the AND gate, and an output end of the second trigger is coupled to a gate control signal output end of the synchronous rectifier tube;
and the synchronous rectifier tube turn-off detection module comprises an input end coupled with the drain-source voltage receiving end of the synchronous rectifier tube and a synchronous rectifier tube turn-off signal output end coupled with the reset end of the second trigger.
Optionally, the method further comprises:
a set end of the second trigger is coupled to an output end of the first trigger, an output end of the second trigger is coupled to a grid control signal output end of the synchronous rectifier tube, and the second trigger is a reset leading trigger;
and the synchronous rectifier tube turn-off detection module comprises an input end coupled with the drain-source voltage receiving end of the synchronous rectifier tube and a synchronous rectifier tube turn-off signal output end coupled with the reset end of the second trigger.
Optionally, the synchronous rectifier tube turn-off detection module includes:
and the fourth comparator comprises an input end coupled with the drain-source voltage receiving end of the synchronous rectifier tube, a fourth reference signal input end and a synchronous rectifier tube turn-off signal output end coupled with the reset end of the second trigger.
Optionally, the first trigger is an RS trigger, a position end of the RS trigger is a first input end of the first trigger, a reset end of the RS trigger is a second input end of the first trigger, and an inverted output end of the RS trigger is an output end of the first trigger.
According to another aspect of the present invention, there is provided a voltage converter including:
the transformer is connected with the primary side circuit and the secondary side circuit, and the secondary side circuit comprises a synchronous rectifier tube;
according to the synchronous rectification control circuit provided by the invention, a synchronous rectification tube grid control signal output end of the synchronous rectification control circuit is coupled with a grid of the synchronous rectification tube.
The invention provides a synchronous rectification control circuit, which comprises a first trigger, a first comparator, a second comparator and a delay circuit, wherein the first comparator compares the drain-source voltage of a synchronous rectifier tube with a first reference signal to provide a first control signal, the second comparator compares the drain-source voltage of the synchronous rectifier tube with a second reference signal to provide a third control signal, the delay circuit delays the first control signal to provide the second control signal, the second control signal is provided for a first input end of the first trigger, and the third control signal is provided for a second input end of the first trigger, wherein the delay time of the delay circuit is a threshold value for judging whether a body diode of the rectifier tube is in normal conduction or parasitic oscillation conduction, namely the effective starting time of the third control signal is before or after the effective starting time of the second control signal, and the two output states are respectively set by the first trigger before the original output state is maintained, respectively corresponding to the on and off of the synchronous rectifier tube.
The time delay circuit determines the time delay time through the time from the charging of the first end of the capacitor to the level of the third reference signal, the performance of the capacitor is stable, and the time delay is simple and effective.
The third reference signal is configured by an external third reference signal configuration circuit, can be externally adjusted, and can adjust the delay time after the circuit design is completed so as to be suitable for the synchronous rectification specifications of different voltage converters, and is matched with the delay time control design of a capacitor, and can also be suitable for parameter change caused by device aging, and the adjustment of the third reference signal can compensate errors caused by aging, and the practicability is improved.
The charge and discharge of a capacitor of the delay circuit are controlled by a switch, and the NMOS tube is selected by the switch, so that the response speed is high, and the delay time precision is high.
The design of the OR gate and the pulse generator provides a narrow pulse when the first control signal is effectively started, and the narrow pulse is provided to the first input end of the first trigger after being subjected to OR logic with the second control signal, so that the inverting output end of the first trigger can be initialized to 0, the synchronous rectifier tube is correspondingly turned off, and the false turn-on of the synchronous rectifier tube is avoided.
The AND gate is arranged to execute the output state of the first control signal and the inverted output end of the first trigger and control the synchronous rectifier tube to be opened after logic, so that the first trigger can be prevented from mistakenly outputting an effective synchronous rectifier tube grid control signal due to the interference of other signals in the time when the output state is unknown, and the synchronous rectifier tube is prevented from being mistakenly opened in the time.
The second trigger and the synchronous rectifier tube turn-off detection module which are mainly reset are arranged, the output end of the synchronous rectifier tube turn-off detection module is coupled to the reset end of the second trigger, the turn-off of the synchronous distillation section is controlled independently, the turn-off of the synchronous rectifier tube is guaranteed within the time of the turn-off of the synchronous rectifier tube, and the error conduction is avoided.
The voltage converter provided by the invention comprises a primary circuit and a secondary circuit which are connected by a transformer, wherein the secondary circuit comprises a synchronous rectifier tube, and the synchronous rectifier tube is controlled by adopting the synchronous rectifier control circuit provided by the invention, so that the synchronous rectifier tube can be prevented from being conducted in parasitic oscillation time, and the working efficiency of the voltage converter is 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 voltage converter according to the prior art;
FIG. 2 shows a timing diagram of control signals for a synchronous rectifier according to the prior art;
FIG. 3 is a schematic diagram of a synchronous rectification control circuit according to an embodiment of the present invention;
FIG. 4 shows a timing diagram of the operation of a pulse generator according to an embodiment of the invention;
fig. 5 shows a partial timing diagram of a synchronous rectification control circuit according to an embodiment of the present 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. 3 is a schematic diagram of a synchronous rectification control circuit according to an embodiment of the present invention.
As shown in fig. 3, the synchronous rectification control circuit 100 according to the embodiment of the invention includes a second flip-flop T2, a synchronous rectifier turn-on detection module 110 and a synchronous rectifier turn-off detection module 120, the synchronous rectifier drain-source voltage Vds is from a synchronous rectifier drain-source voltage receiving terminal (not shown in the figure), the synchronous rectifier turn-on detection module 110 and the synchronous rectifier turn-off detection module 120 detect a voltage value of the synchronous rectifier drain-source voltage Vds, respectively output a synchronous rectifier turn-on signal (a second flip-flop set signal T2S) to a set terminal of the second flip-flop T2 and output a synchronous rectifier turn-off signal (a second flip-flop reset signal T2R) to a reset terminal of the second flip-flop T2, an output terminal Q of the second flip-flop T2 is coupled to a gate of the synchronous rectifier SR, the synchronous rectifier SR is controlled to be turned on and off according to the second flip-flop set signal T2S and the second flip-flop reset signal T2R. The second flip-flop T2 is a reset dominant flip-flop, and when the second flip-flop reset signal T2R is active 1, the output terminal Q outputs a low level to turn off the synchronous rectifier SR.
The synchronous rectifier tube turn-on detection module 110 includes a first comparator COMP1, a pulse generator 111, a first flip-flop T1, an and gate 115, a second comparator COMP2, an or gate 114, a third comparator COMP4, a reference value configuration circuit (a third reference signal configuration circuit) 112, a capacitor C1, a switch S1, a resistor Rcf, a current source I1, and an inverter 113. The first flip-flop T1 is a normal RS flip-flop, and maintains an original output state when both the set terminal and the reset terminal are 1.
In the embodiment, the first flip-flop T1 is an RS flip-flop, the set terminal of the RS flip-flop is the first input terminal of the first flip-flop T1, the reset terminal of the RS flip-flop is the second input terminal of the first flip-flop T1, and the inverted output terminal of the RS flip-flop is the output terminal of the first flip-flop T1.
An input end of the first comparator COMP1 is coupled to a drain-source voltage receiving end of the synchronous rectifier tube, that is, an inverting input end receives a drain-source voltage Vds of the synchronous rectifier tube; comprises a first reference signal input terminal, namely a non-inverting input terminal for receiving a first reference signal Vth 1; the first control signal output terminal outputs a first control signal CU 1.
The inverter 113, the switch S1, the current source I1, the capacitor C1, and the third comparator COMP4 form a delay circuit, which includes an input terminal coupled to the first control signal output terminal, a third reference signal input terminal, and a third control signal output terminal, receives the first control signal CU1, and outputs the second control signal CU4 after delaying for a certain time.
The delay time may be controlled by a third reference signal Vth _ conf, the third reference signal Vth _ conf is configured by the reference value configuration circuit 112, the reference value configuration circuit 112 is a third reference signal configuration circuit, which outputs the third reference signal Vth _ conf at the third reference signal output end, and the other end is grounded through a resistor Rcf, the third reference signal configuration circuit is an external circuit, the voltage value of the third reference signal at the output point may be adjusted through an external resistor, a capacitor, and other elements, the slope of the ramp voltage Vramp provided by the first end of the capacitor C1 during charging is fixed, the time when the ramp voltage Vramp rises to the level value of the third reference signal Vth _ conf is the delay time, and the effective start time of the second control signal CU4 delays the effective start time of the first control signal CU1 by one delay time.
In the delay circuit, the input end of the inverter 113 receives a first control signal CU1, and the output end is coupled to the switch control end of the switch S1 to control the on/off of the switch S1; the first end of the capacitor C1 is coupled to the output end of the current source I1, and the second end is grounded; the switch S1 is connected in series across the capacitor C1; the third comparator COMP4 includes an input terminal coupled to the first terminal of the capacitor C1, a third reference signal input terminal, which is an inverting input terminal of the third comparator COMP4 and receives a third reference signal Vth _ conf, and a second control signal output terminal, which is a non-inverting input terminal of the third comparator COMP4 and receives the ramp voltage signal Vramp, and an output terminal of the third comparator COMP4 is a second control signal output terminal, and provides a second control signal CU 4; the second control signal CU4 is coupled to the second input terminal of the or gate 114, and the first input terminal of the or gate 114 is coupled to the Pulse output terminal of the Pulse generator 111, and the second control signal CU4 and the Pulse signal Pulse1 are used as the set signal T1S of the first flip-flop T1 after being subjected to or logic.
The second comparator COMP2 includes an input terminal (inverting input terminal) coupled to the drain-source voltage receiving terminal of the synchronous rectifier for receiving the drain-source voltage Vds of the synchronous rectifier, a second reference signal input terminal (non-inverting input terminal) for receiving a second reference signal Vth2, and a third control signal output terminal, where the third control signal is the reset signal T1R of the first flip-flop T1. The output signal TU1 of the inverting output terminal (Q not terminal) of the first flip-flop T1 can be used as a gate control signal of the synchronous rectifier to control the on and off of the synchronous rectifier, i.e., the inverting output terminal of the first flip-flop T1 can be directly coupled to the gate control signal output terminal of the synchronous rectifier.
The synchronous rectifier turn-off detection module 120 includes a fourth comparator COMP3, where the fourth comparator COMP3 includes an input terminal, a fourth reference signal input terminal, and a synchronous rectifier turn-off signal output terminal, that is, the non-inverting input terminal of the fourth comparator receives the synchronous rectifier drain-source voltage Vds, the inverting input terminal receives the fourth reference signal Vth3, when the synchronous rectifier drain-source voltage Vds is greater than the level of the fourth reference signal Vth3, an effective synchronous rectifier turn-off signal is output, that is, the reset signal T2R of the second flip-flop T2 is effective, the second flip-flop T2 is a reset dominant flip-flop, the output terminal (Q terminal) of the reset dominant flip-flop is reset to a low level, the synchronous rectifier SR is turned off, and the synchronous rectifier drain-source voltage Vds and the voltage converter secondary side voltage rise synchronously.
Fig. 4 shows a timing diagram of the operation of the pulse generator according to an embodiment of the invention.
As shown in fig. 4, the pulse generator according to the embodiment of the present invention outputs a pulse signal in synchronization with the rising edge of the input signal, and immediately outputs a narrow pulse signal when the input signal becomes a high level.
Fig. 5 shows a partial timing diagram of a synchronous rectification control circuit according to an embodiment of the present invention.
Referring to fig. 5 and fig. 3, Vth1>0> Vth3> Vth2, time T4 to T9 is in the parasitic oscillation time, when Vds > Vth3, the fourth comparator outputs a high level, the reset signal T2R of the second flip-flop T2 is active as 1, the output end of the second flip-flop T2 is reset to 0, and the gate of the synchronous rectification tube is at a low level and remains off. Here, the high level may be understood as 1, and the low level may be understood as 0.
At time T1, the drain-source voltage Vds of the synchronous rectifier tube drops to the level of the first reference signal Vth1, the first control signal CU1 changes to high level, the Pulse signal Pulse1 output by the Pulse generator outputs a narrow Pulse, so that the set signal T1S of the first flip-flop T1 is temporarily set to 1 and then maintained to 0, and the inverting output terminal of the first flip-flop T1 can be set to 0, that is, the inverting output terminal of the first flip-flop T1 is initialized to 0 and then maintained to 0; vds > Vth2, T1R is 0; so that the output signal TU1 at the inverting output terminal of the first flip-flop T1 is 0 from time T1 to time T2; the switch S1 is turned off, the capacitor C1 starts to charge, the ramp voltage Vramp starts to rise, but is lower than the level of the third reference signal Vth _ conf, and the level of CU4 is maintained at 0 after the Pulse1 Pulse ends.
The CU1 controls the on/off of the switch S1 through the inverter 113, the switch S1 may be an NMOS (N-Metal-Oxide-Semiconductor) transistor, a gate of the NMOS transistor is a switch control end, a gate control signal of the NMOS transistor is at a low level at time t1, the NMOS transistor is turned off, the switch S1 is turned off, the NMOS transistor is fast in response, and time control is accurate.
At time T2, the Vds signal is decreased to Vth2, the second comparator outputs a high level, the reset signal T1R of the first flip-flop is set to 1, the ramp voltage Vramp is still lower than the level of the third reference signal Vth _ conf, the set signal T1S of the first flip-flop T1 is equal to CU4 and is 0, the output signal TU1 at the inverting output terminal of the first flip-flop T1 is controlled by the reset signal T1R to 1, Vds is lower than Vth3, T2R is 0, T2S is 1, the output terminal of the second flip-flop T2 is a high level, and the synchronous rectifier is turned on. the time t 1-t 2 is the first time Vds is reduced from Vth1 to Vth 2.
At time T3, the ramp Vramp of the first terminal of the capacitor C1 is raised to the level of the third reference signal Vth _ conf, CU4 goes high, the set signal and the reset signal of the first flip-flop T1 are 1 and 1 respectively, the output state is maintained, i.e., TU1 is maintained at 1, and the synchronous rectifier is maintained to be on. the time t1 to t3 is a delay time.
At time T4, Vds rises to Vth2, and is smaller than Vth1, T1R becomes low, T1S is high, the set terminal of the first flip-flop T1 is enabled, the reset terminal is disabled, TU1 becomes 0, and the rectifying tube can be controlled to be turned off. After TU1 and CU1 are subjected to logic summation, the logic summation is provided to a set terminal of a second flip-flop T2, a reset terminal of the second flip-flop T2 is controlled by the synchronous rectifier off detection module 120, Vds is smaller than Vth3 at time T4, an output terminal of the second flip-flop T2 is maintained at 1, TU1 is maintained at 0, T2S is maintained at 0, an output terminal signal of the second flip-flop T2 cannot be set to 1, the synchronous rectifier can be maintained to be off during parasitic oscillation time from T4 to T9, and the off start time is after time T4 and Vds is greater than Vth3, that is, the synchronous rectifier is turned off by using Vth3 as a reference standard and is turned on during time T2 to T4 except for turning off.
At time T5, during the parasitic oscillation time, Vds rises back to Vth1, CU1 goes low, switch S1 is closed, the first end of capacitor C1 is grounded, ramp voltage Vramp is at ground level, CU4 goes low, the set end of first flip-flop T1 is 0, the reset end is also 0, and TU1 at the inverting output end is 0. If Vds in the parasitic oscillation time is smaller than Vth1, the ramp voltage Vramp is continuously charged, so that the CU4 signal is continuously at a high level, after time t5, the TU1 is continuously set to 0, the synchronous rectifier is kept turned off, and the false turn-on can be avoided.
At time T6, Vds of the parasitic oscillation decreases to Vth1, CU1 becomes high, the pulse generator outputs a narrow pulse, the set end of the first flip-flop T1 is temporarily set to 1, the first flip-flop T1 is initialized, TU1 is 0, the switch S1 is opened, the capacitor C1 starts to charge, and the ramp voltage Vramp starts to rise.
At time T7, the ramp Vramp rises to the level of the third reference signal Vth _ conf, CU4 goes high, the set terminal of the first flip-flop T1 is 1, Vds has not yet decreased to Vth2 at this time, TIR is 0, the inverted output terminal of the first flip-flop T1 is set to 0, TU1 is 0, the set terminal of the second flip-flop T2 is set to 0, the output terminal of the second flip-flop T2 is not set to 1, 0 is output, and the synchronous rectifier is kept off.
In the time from t5 to t7 when the Pulse time of Pulse1 is eliminated, the set end and the reset end of the first flip-flop are both 0, the output state is unknown, the TU1 signal at the inverting output end is maintained at 0 without other interference, the TU1 signal and the CU1 signal are executed and logically through the and gate 115 to control the conduction of the synchronous rectifier tube, so that the interference of the interference signal to the output state of the first flip-flop in the time when the output state of the first flip-flop is unknown can be avoided, and the synchronous rectifier tube is prevented from being conducted by mistake.
At time T8, Vds is decreased to Vth2, the signal T1R changes to 1, the reset terminal of the first flip-flop T1 is set to 1, the set terminal of the first flip-flop T1 is maintained to 1, the output state of the first flip-flop T1 is maintained to be the original state, TU1 is maintained to be 0, and the synchronous rectifier is maintained to be off.
The time from T1 to T3 is equal to the time from T6 to T7, which is a delay time, the first time from T1 to T2 is the time from Vth1 to Vth2 when the body diode of the drain-source voltage of the synchronous rectifier is normally turned on, the second time from T6 to T8 is the time from Vth1 to Vth2 when the body diode of the drain-source voltage of the synchronous rectifier is turned on in the parasitic oscillation time, the first time < delay time < second time, after the delay time, the set signal T1S of the first flip-flop T1 is 1, after the first time or the second time passes, the reset signal T1R of the first flip-flop T1 is 1, and the first flip-flop T1 maintains the output state when the set end and the reset end of the first flip-flop are both 1.
When the body diode corresponding to the synchronous rectifier tube is normally conducted, Vds is reduced from Vth1 to Vth2, the first time is shorter than the delay time, namely before the first trigger T1 maintains the original state, the reset signal T1R of the first trigger T1 is effective, the output signal TU1 of the inverting output end of the first trigger T1 is reset to 1, after the delay time passes, the TU1 maintains 1, and the synchronous rectifier tube is conducted.
The body diode corresponding to the synchronous rectifier tube is conducted in parasitic oscillation time, Vds is reduced to Vth2 slowly from Vth1, the second time is longer than delay time, before the first trigger T1 maintains the original state, a set signal T1S of the first trigger T1 is effective, an output signal TU1 at the inverting output end of the first trigger T1 is set to 0, after the second time passes, a reset signal T1R of the first trigger T1 is 1, an output signal TU1 at the inverting output end of the first trigger T1 is maintained to 0, in time from T4 to T7, a TU1 signal is set to 0 by CU4 and maintained to 0, the synchronous rectifier tube is in an off state, and can be maintained to be off after time T7, and false conduction of the synchronous rectifier tube in the parasitic oscillation time is avoided.
The re-conduction of the synchronous rectifier tube requires that Vds is reduced from Vth1 to Vth2 under the condition that the body diode of the synchronous rectifier tube is normally conducted, namely, the synchronous rectifier control circuit can control the synchronous rectifier tube to be conducted under the condition that the body diode of the synchronous rectifier tube is normally conducted, and can effectively avoid the false conduction of the synchronous rectifier tube in the parasitic oscillation time.
The synchronous rectification control circuit is provided with delay time, after the delay time passes, the position end of a first trigger is 1, the first trigger is a common trigger, a reset signal of a reset end of the first trigger is determined by the speed of reducing the level of a first reference signal to the level of a second reference signal according to the drain-source voltage of a synchronous rectifier tube, wherein the body diode corresponding to the synchronous rectifier tube with high speed is normally conducted, the reset signal is effective before the position signal is 1, the inverted output end of the first trigger is reset to 1, and is maintained to 1 after the delay time passes, and the synchronous rectifier tube is controlled to be started; the body diode corresponding to the synchronous rectifier tube with low speed is conducted in the parasitic oscillation time, the reset signal is effective after the set signal is 1, the inverted output end of the first trigger is set to be 0 and then maintained to be 0, and the synchronous rectifier tube is prevented from being conducted in error in the parasitic oscillation time.
Those skilled in the art should understand that the logic controls of "high" and "low", "set" and "reset", "and" or "," in-phase "and" reverse "in the above logic controls can be interchanged or changed, and the subsequent logic controls can be adjusted to achieve the same functions or purposes as those of the above embodiments.
The descriptions related to the effects or advantages in the specification may not be reflected in practical experimental examples due to uncertainty of specific condition parameters or influence of other factors, and the descriptions related to the effects or advantages are not used for limiting the scope of the invention.
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 (11)
1. The utility model provides a synchronous rectification control circuit, includes synchronous rectifier tube drain-source voltage receiving terminal and synchronous rectifier tube grid control signal output part, its characterized in that includes:
the first comparator comprises an input end coupled with the drain-source voltage receiving end of the synchronous rectifier tube, a first reference signal input end and a first control signal output end;
a delay circuit comprising an input coupled to the first control signal output and a second control signal output;
the second comparator comprises an input end coupled with the drain-source voltage receiving end of the synchronous rectifier tube, a second reference signal input end and a third control signal output end; and
a first flip-flop, a first input of which is coupled to the second control signal output of the delay circuit, a second input of which is coupled to the third control signal output of the second comparator, and an output of which is coupled to the gate control signal output of the synchronous rectification transistor, wherein a level of the first reference signal is higher than a level of the second reference signal.
2. The synchronous rectification control circuit of claim 1, wherein the delay circuit comprises:
the first end of the capacitor is coupled with the output end of the current source, and the second end of the capacitor is grounded;
a switch connected in parallel across the capacitor, the switch including a switch control terminal coupled to the first control signal output terminal;
a third comparator comprising an input coupled to the first terminal of the capacitor, a third reference signal input, and an output, the output of the third comparator being the second control signal output.
3. The synchronous rectification control circuit of claim 2,
the delay circuit comprises a third reference signal input end which is coupled with a third reference signal output end of an external third reference signal configuration circuit.
4. The synchronous rectification control circuit of claim 2,
the delay circuit further comprises an inverter coupled in a forward direction between the first control signal output terminal and a switch control terminal of the switch;
the switch is an NMOS tube, and the grid electrode of the NMOS tube is the switch control end.
5. The synchronous rectification control circuit of claim 1, further comprising:
an or gate coupled between the second control signal output and the first input of the first flip-flop, the or gate including a first input, a second input, and an output, the second input of the or gate being coupled to the second control signal output, the output of the or gate being coupled to the first input of the first flip-flop;
a pulse generator, an input terminal of the pulse generator being coupled to the first control signal output terminal, and a pulse output terminal of the pulse generator being coupled to the first input terminal of the or gate.
6. The synchronous rectification control circuit of claim 1, further comprising:
and the AND gate comprises a first input end coupled with the first control signal output end, a second input end coupled with the output end of the first trigger and an output end.
7. The synchronous rectification control circuit of claim 6, further comprising:
a set end of the second trigger is coupled to an output end of the AND gate, and an output end of the second trigger is coupled to a gate control signal output end of the synchronous rectifier tube;
and the synchronous rectifier tube turn-off detection module comprises an input end coupled with the drain-source voltage receiving end of the synchronous rectifier tube and a synchronous rectifier tube turn-off signal output end coupled with the reset end of the second trigger.
8. The synchronous rectification control circuit of claim 1, further comprising:
a set end of the second trigger is coupled to an output end of the first trigger, an output end of the second trigger is coupled to a grid control signal output end of the synchronous rectifier tube, and the second trigger is a reset leading trigger;
and the synchronous rectifier tube turn-off detection module comprises an input end coupled with the drain-source voltage receiving end of the synchronous rectifier tube and a synchronous rectifier tube turn-off signal output end coupled with the reset end of the second trigger.
9. The synchronous rectification control circuit of claim 7 or 8, wherein the synchronous rectification tube turn-off detection module comprises:
and the fourth comparator comprises an input end coupled with the drain-source voltage receiving end of the synchronous rectifier tube, a fourth reference signal input end and a synchronous rectifier tube turn-off signal output end coupled with the reset end of the second trigger.
10. The synchronous rectification control circuit of claim 1,
the first trigger is an RS trigger, the position end of the RS trigger is the first input end of the first trigger, the reset end of the RS trigger is the second input end of the first trigger, and the reverse phase output end of the RS trigger is the output end of the first trigger.
11. A voltage converter, comprising:
the transformer is connected with the primary side circuit and the secondary side circuit, and the secondary side circuit comprises a synchronous rectifier tube;
the synchronous rectification control circuit of any one of claims 1 to 8, wherein a synchronous rectifier gate control signal output of the synchronous rectification control circuit is coupled to a gate of the synchronous rectifier.
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| CN113162440A (en) * | 2021-04-25 | 2021-07-23 | 深圳市力生美半导体股份有限公司 | Switching power supply and synchronous rectification control circuit thereof |
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