CN110995013A - Synchronous rectification control circuit of switching power supply - Google Patents
Synchronous rectification control circuit of switching power supply Download PDFInfo
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- CN110995013A CN110995013A CN201911384094.6A CN201911384094A CN110995013A CN 110995013 A CN110995013 A CN 110995013A CN 201911384094 A CN201911384094 A CN 201911384094A CN 110995013 A CN110995013 A CN 110995013A
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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
- H02M7/00—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output
- H02M7/02—Conversion of ac power input into dc power output without possibility of reversal
- H02M7/04—Conversion of ac power input into dc power output without possibility of reversal by static converters
- H02M7/12—Conversion of ac power input into dc power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
- H02M7/21—Conversion of ac power input into dc power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal
- H02M7/217—Conversion of ac power input into dc power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02B—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO BUILDINGS, e.g. HOUSING, HOUSE APPLIANCES OR RELATED END-USER APPLICATIONS
- Y02B70/00—Technologies for an efficient end-user side electric power management and consumption
- Y02B70/10—Technologies improving the efficiency by using switched-mode power supplies [SMPS], i.e. efficient power electronics conversion e.g. power factor correction or reduction of losses in power supplies or efficient standby modes
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Abstract
The invention discloses a switching power supply synchronous rectification control circuit, which comprises a power tube and a synchronous rectification controller, wherein the synchronous rectification controller comprises a primary side conduction sensing unit, a voltage averaging unit and a volt-second balancing module; the voltage averaging unit generates a second reference voltage equal to the average voltage of the first signal in a switching period; the volt-second balance module is coupled to the primary side conduction sensing unit and the voltage averaging unit, and calculates the conduction time and the cut-off time of the power tube in a switching period based on a volt-second balance principle. The switching power supply synchronous rectification control circuit accurately calculates the on-time and the off-time of the power tube according to the on-time of the primary side switching tube, the power tube has two states in a switching period, the power tube and the primary side switching tube are alternately conducted in the whole switching period, and the switching power supply synchronous rectification control circuit is suitable for an inductive current discontinuous conduction mode and an inductive current continuous conduction mode.
Description
Technical Field
The invention relates to the technical field of switching power supplies, in particular to a synchronous rectification control circuit of a switching power supply.
Background
Compared with the traditional linear power supply, the switching power supply has the characteristics of small volume and high conversion efficiency, and is widely applied to electronic equipment needing alternating current-direct current conversion, such as mobile phone chargers, notebook computer adapters and the like. Fig. 1 shows a typical power conversion circuit with synchronous rectification function in the prior art, which includes an input dc Vin output by a rectifier bridge, where the dc Vin is connected to one end of a primary winding of a transformer, a switching tube S1 is connected between the other end of the primary winding and a primary ground, a secondary winding of the transformer is connected to a synchronous rectification switch S2 and an output capacitor C, and the synchronous rectification switch S2 is controlled by a synchronous rectification controller to be turned on or off. The switch tube S1 and the synchronous rectifier switch S2 are alternately turned on, and when the switch tube S2 is turned on, the synchronous rectifier switch S2 is turned off, the dc Vin supplies power to the primary winding of the transformer, and the current in the primary winding starts to increase, at this time, because the synchronous rectifier switch S2 is turned off, energy is stored in the primary winding coil. The switching tube S1 is turned off, the synchronous rectifier switch is turned on, the primary current is reduced from the maximum value, and the energy in the primary winding coil is transferred to the load through the secondary winding.
In order to avoid the loss of conversion efficiency and the switch burnout, the switching tube S2 of the primary winding of the transformer and the synchronous rectifier switch S2 of the secondary winding need to be strictly controlled to be alternately conducted. Chinese patent publication No. CN101826810B discloses a synchronous rectification circuit for a switching power supply, in which a control circuit generates a control signal for controlling the on/off of a synchronous rectification switch (i.e., a power tube) according to a voltage state across the synchronous rectification switch. When the body diode of the power tube is converted from reverse bias to forward bias, the control circuit enables the power tube to be conducted; after the power tube is conducted, when the forward bias voltage of a body diode of the power tube is reduced to be lower than a set threshold value, the control circuit enables the power tube to be turned off for a certain time; when the parasitic body diode is changed from forward bias to reverse bias, the control circuit enables the power tube to be in a turn-off state. In the technical scheme, the power tube works in three states under the control of the control circuit: in the state 1, a primary winding switch is switched on, and a power tube is switched off; in the state 2, the primary winding switch is turned off, and the power tube is turned on; and in the state 3, the primary winding switch and the power tube are simultaneously turned off. Based on this, the technical scheme is only suitable for an inductive current Discontinuous Conduction Mode (DCM), and the condition that a primary winding switch and a power tube are simultaneously conducted exists in the inductive current Continuous Conduction Mode (CCM), so that the conversion efficiency of the switching power supply is influenced, and even the power tube is burnt in severe cases. On the other hand, the technical scheme cannot accurately calculate the on-time and the off-time of the power tube.
Disclosure of Invention
The technical problem to be solved by the invention is to provide a synchronous rectification control circuit of a switching power supply, which accurately calculates the conduction time and the cut-off time of a power tube according to the conduction time of a primary side switching tube and is simultaneously suitable for an inductive current discontinuous conduction mode and an inductive current continuous conduction mode.
In order to solve the above technical problem, the present invention provides a synchronous rectification control circuit for a switching power supply, comprising,
the power tube is connected between a secondary winding of a transformer of the switching power supply and an output capacitor of the switching power supply;
the synchronous rectification controller is connected with the output stage of the switching power supply and is used for generating a control signal to control the power tube to be switched on or switched off;
the synchronous rectification controller comprises a synchronous rectification controller and a synchronous rectification control circuit,
a primary side conduction sensing unit for sensing conduction time T in the switching period of the primary side winding switching tube of the transformer according to the voltage difference between two ends of the power tubeonAnd a cut-off time Toff(ii) a Generating a first signal according to the voltage difference between two ends of the power tube; wherein, when the voltage difference between the two ends of the power tube exceeds the threshold voltage, a first reference voltage V is generatedref1(ii) a Otherwise, generating a ground potential;
a voltage averaging unit coupled to the output terminal of the primary side conduction sensing unit for generating a second reference voltage V equal to the average voltage of the first signal in a switching periodref2(ii) a Wherein,
a voltage-to-current control source configured to convert the first reference voltage Vref1Is converted into a first current source Iref1The second reference voltage V is used for converting the second reference voltage V into the second reference voltage Vref2Is converted into a second current source Iref2(ii) a The first current source Iref1And a second current sourceIref2After being connected in series, the grounding is carried out;
a first switch connected in series to the first current source Iref1And a second current source Iref2And is controlled by the first signal;
a timing capacitor having a first end connected to the output end of the primary side conduction sensing unit and a second end connected to the first switch and coupled to a second current source Iref2One end of (a);
the timing capacitor is in the on time TonThe synchronous rectification controller generates a control signal to conduct the power tube when the timing capacitor is charged to a high position; said timing capacitor being at said cut-off time ToffAnd internal discharge, wherein the synchronous rectification controller generates a control signal to turn off the power tube when the timing capacitor discharges to a low position.
In a preferred embodiment of the present invention, the synchronous rectification controller further comprises a second switch, the second switch is connected in parallel with the timing capacitor, and the second switch is turned on when the pulse generator generates the trigger pulse; the pulse generator is controlled by the first signal and generates a trigger pulse when the first signal is converted from a low potential to a high potential.
In a preferred embodiment of the present invention, the second switch is a transistor, a control terminal of the transistor is connected to the output terminal of the primary side conduction sensing unit, and the second switch is turned on for a time TonInternal turn-off, at off-time ToffAnd conducting internally.
In a preferred embodiment of the present invention, the synchronous rectification controller further comprises a timing comparator, an inverting input terminal of the timing comparator is connected to the first terminal of the timing capacitor and the output terminal of the primary side conduction sensing unit, and a non-inverting input terminal of the timing comparator is connected to the second terminal of the timing capacitor and the first switch, and the first switch is coupled to the second current source Iref2And the output end of the first switch is connected with the logic driving unit.
In a preferred embodiment of the present invention, the logic driving unit further comprises,
the input end of the first NOT gate is connected with the output end of the primary side conduction sensing unit;
the input end of the second NOT gate is connected with the output end of the timing comparator;
one end of the NAND gate is connected with the output end of the first NOT gate, and the other end of the NAND gate is connected with the output end of the second NOT gate;
an input end S of the SR flip-flop is connected with the output end of the first NOT gate, and an input end R of the SR flip-flop is connected with the output end of the NAND gate;
and the driver receives the output signal of the SR trigger and drives the power tube to be switched on or switched off.
In a preferred embodiment of the present invention, the primary side conduction sensing unit further includes a conduction sensing comparator, a voltage difference between two ends of the power tube is connected to a positive phase input terminal of the conduction sensing comparator, and a negative phase input terminal of the conduction sensing comparator is connected to a threshold voltage VA(ii) a The output end of the conduction sensing comparator generates the first signal; when the voltage difference between two ends of the power tube exceeds the threshold voltage, the conduction sensing comparator outputs a first reference voltage Vref1(ii) a Otherwise, the conduction sense comparator outputs ground potential.
In a preferred embodiment of the present invention, the voltage averaging unit is a circuit including a low-pass filter.
In a preferred embodiment of the present invention, the low pass filter is an RC filter, an RL filter or an LC filter.
In a preferred embodiment of the present invention, the power transistor is a MOS transistor.
The invention has the beneficial effects that:
the invention relates to a synchronous rectification control circuit of a switching power supply, which accurately calculates the on-time and the off-time of a power tube according to the on-time of a primary side switching tube, wherein the power tube has two states in a switching period: in the first state, when the primary side switching tube is conducted, the power tube is turned off; in the second state, when the primary side switching tube is turned off, the power tube is conducted, the power tube and the primary side switching tube are conducted alternately in the whole switching period, and the secondary side switching tube is suitable for an inductive current discontinuous conduction mode and an inductive current continuous conduction mode.
Drawings
Fig. 1 is a block diagram of a power conversion circuit with a synchronous rectification function in the prior art;
fig. 2 is a circuit schematic diagram of a synchronous rectification control circuit of the switching power supply in the preferred embodiment of the invention;
FIG. 3 is a circuit diagram of a buck-boost regulator;
FIG. 4 is a graph of a voltage current waveform associated with the buck-boost regulator of FIG. 3;
FIG. 5 is a graph of an inductor current waveform for the voltage regulator operating in CCM mode;
FIG. 6 is a circuit diagram of a volt-second balancing module;
FIG. 7 is a waveform diagram illustrating charging and discharging of the timing capacitor in the volt-second balance module shown in FIG. 6;
fig. 8 is a waveform diagram related to the synchronous rectification control circuit shown in fig. 2.
The reference numbers in the figures illustrate:
10-a primary side conduction sensing unit, 20-a voltage averaging unit, 30-a volt-second balancing module, 40-a logic driving unit and 50-a pulse generator;
41-first not gate, 42-second not gate, 43-nand gate, 44-SR flip-flop, 45-driver.
Detailed Description
The present invention is further described below in conjunction with the following figures and specific examples so that those skilled in the art may better understand the present invention and practice it, but the examples are not intended to limit the present invention.
Examples
The present embodiment discloses a synchronous rectification control circuit of a switching power supply, which is shown in fig. 2 and 8, and includes a power tube S2 and a synchronous rectification controller, where the power tube S2 is connected to a secondary winding of a transformer T of the switching power supply and an output capacitor C of the switching power supply0To (c) to (d); the synchronous rectification controller is connected with an output stage of the switching power supply and is used for generating a control signal to control the power tube S2 to be switched on or switched off. In the technical solution of this embodiment, the power tube S2 is preferably selectedThe MOS tube is used, and compared with a rectifier diode in the traditional technology, the MOS tube can improve the conversion efficiency of the switching power supply.
In the synchronous rectification controller in the technical solution of this embodiment, the on-time and the off-time of the power tube S2 in the switching period can be accurately calculated according to the voltage difference between the drain and the source of the power tube S2, so that the power tube S2 and the switching tube S1 of the primary winding of the transformer are alternately turned on, and the power tube S2 is ensured to only work in two working states in the whole switching period:
in the first state, when the switch tube S1 is turned on, the power tube S2 is turned off;
in the second state, when the switch tube S1 is turned off, the power tube S2 is turned on.
Referring to fig. 2, the synchronous rectification controller includes a primary side conduction sensing unit 10, a voltage averaging unit 20, a logic driving unit 40, and a volt-second balancing module 30 designed based on a volt-second balancing principle.
The primary side conduction sensing unit 10 senses the conduction time T of the switching tube S1 of the primary side winding of the transformer in a switching period according to the voltage difference between the two ends of the drain and the source of the power tube S2onAnd a cut-off time Toff(ii) a Generating a first signal according to a voltage difference between the drain and the source of the power tube S2; wherein, the voltage difference between the drain and the source of the power tube S2 exceeds the threshold voltage VAGenerating a first reference voltage Vref1(ii) a Otherwise, a ground potential is generated. That is, the voltage difference across the drain and the source of the power tube S2 exceeds the threshold voltage VAWhen the first signal is the first reference voltage Vref1(ii) a Otherwise, the first signal is ground potential. In the technical solution of this embodiment, the following circuit design is preferably used to implement the above function of the primary side conduction sensing unit 10: the primary side conduction sensing unit 10 includes a conduction sensing comparator COMP1, a voltage difference between two drain and source terminals of the power transistor S2 is connected to a positive phase input terminal of the conduction sensing comparator COMP1, and a negative phase input terminal of the conduction sensing comparator COMP1 is connected to a threshold voltage VA(ii) a The output terminal of the conduction sense comparator COMP1 generates the first signal. When the circuit is in steady state and the switch tube S1 is turned on, the drain-source voltage V isds1At a low potential; at the moment, the power tube S2 is cut offIts drain-source voltage Vds1Compared with the threshold voltage VAWhen the voltage is at a high level, the conduction sense comparator COMP1 outputs a first signal at a first reference voltage Vref1(ii) a On the contrary, when the switch tube S1 is turned off and the power tube S2 is turned on, the drain-source voltage V of the power tube S2ds1Compared with the threshold voltage VAAt low potential, the voltage of the conduction sense comparator COMP1 outputting the first signal is zero (i.e., ground). Above, the first reference voltage V is setref1The voltage deviation can be cancelled out.
As above, the conduction sensing comparator COMP1 outputs the first reference voltage Vref1Is the conduction time T in the switching period of the switching tube S1onThe time when the output voltage of the conduction sensing comparator COMP1 is zero is the cut-off time T in the switching period of the switching tube S1off。
The voltage averaging unit 20 is coupled to the output terminal of the primary side conduction sensing unit 10, and generates a second reference voltage V equal to an average voltage of the first signal during a switching periodref2(ii) a Wherein,
in the present embodiment, the above function of the voltage averaging unit 20 is realized by designing a low-pass filter, which is one of an RC filter, an RL filter, and an LC filter, and as one of the technical solutions of the present embodiment, referring to fig. 2, the function of the voltage averaging unit 20 is realized by an RC filter coupled by a resistor and a capacitor in series-parallel. Of course, in other technical solutions, the function of the voltage averaging unit 20 may also be implemented by a digital circuit, which receives the first signal and converts the first signal into the second reference voltage V equal to its average voltage in the switching periodref2Satisfy the following requirements
This application designs volt-second balance module 30 based on volt-second balance principle, and in the known art, volt-second balance principle does: in the inductor in a stable state, the volt-second number of the switch on time (current rising segment) must be equal to the volt-second number of the switch off (current falling segment) in value, which also means that the area of the inductor voltage versus time curve is plotted, and the area of the on-period curve must be equal to the area of the off-period curve.
The volt-second balance module 30 designed based on the volt-second balance principle is introduced as follows for the volt-second balance principle: referring to fig. 3, a basic circuit architecture diagram of the buck-boost type voltage regulator is shown, wherein the basic circuit architecture diagram comprises a power switch element S, a power diode D, a filter inductor L, a filter capacitor C and a load RLIn FIG. 4, TSIn the switching period, Ton is the conduction cell, and the duty period D defines the parameters:
from the principle of volt-second or flux linkage balance of the inductor, it can be seen that the inductive voltage V is at times of a steady stateLEffective area of waveform (FIG. 4V)LInclined portion) is 0.
Referring to fig. 5, the ripple current of the inductor is:
the slope of ripple current of the inductor in the interval from 0 to dTs is m1, the slope in the interval from dTs is m2, and the slopes m1 and m2 can be expressed as:
finishing formulas 1 to 6:
let Vref1＝(m1-m2),Vref2＝-m2In the range of 0 to dTsThe slope of the interval inductance current is Vref1-Vref2At dTs～TsThe slope of the interval inductance current is-Vref2And V is given by the formula (7)ref2＝D·Vref1。
As can be seen from the principle equation (2) of volt-seconds or flux linkage balance of the inductor,
the volt-second balance module 30 designed based on the above volt-second balance principle considers that an inductor is difficult to integrate in a semiconductor chip, and the capacitor C is used for timing1Alternative inductors:
from the capacitor definition, it can be seen that:
as shown in FIGS. 7 to 8,
and
and Δ v(+)＝Δv(-)And order Iref1＝K1·Vref1And Iref2＝K2·Vref2Can obtain the product
If K1＝K2Then, then
Therefore, it can be seen that formula (10) is the same as formula (8).
The volt-second balancing module 30 of the present application implements a volt-second balancing process implemented by a timing capacitor through the following structural design: the volt-second balancing module 30 comprises a voltage-to-current control source and a first switch SW1And a timing capacitor C1And a timing comparator COMP 2.
The voltage-to-current control source is configured to convert the first reference voltage V into the first reference voltage Vref1Is converted into a first current source Iref1The second reference voltage V is used for converting the second reference voltage V into the second reference voltage Vref2Is converted into a second current source Iref2(ii) a The first current source Iref1And a second current source Iref2And after being connected in series, the power is grounded.
The first switch SW1Is connected in series with the first current source Iref1And a second current source Iref2And is controlled by the first signal.
The timing capacitor C1Has a first end connected to the output end of the conduction sensing comparator COMP1, and a second end connected to the first switch SW1Coupled to a second current source Iref2To one end of (a).
The inverting input end of the timing comparator COMP2 is connected with the timing capacitor C1And an output terminal of the conduction sense comparator COMP1, a non-inverting input terminal of which is connected to the timing capacitor C1And a first switch SW1Coupled to a second current source Iref2And an output terminal thereof is connected to the logic driving unit 40.
The timing capacitor C1At the above-mentioned on-time TonInternal charging, the synchronous rectification controller is arranged in a timing capacitor C1Charging to high (V)ref1-Vref2) Generating a control signal to turn on the power transistor S2; the timing capacitor C1At the above-mentioned cut-off time ToffInternal discharge, said synchronous rectification controller being in timing capacitor C1Discharge to low level (V)ref2) A control signal is generated to turn off the power transistor S2.
The logic driving unit 40 includes a first not gate 41, a second not gate 42, a nand gate 43, an SR flip-flop 44, and a driver 45.
The input end of the first not gate 41 is connected to the output end of the conduction sensing comparator COMP 1;
the input end of the second not gate 42 is connected with the output end of the timing comparator COMP 2;
one end of the nand gate 43 is connected to the output end of the first not gate 41, and the other end is connected to the output end of the second not gate 42;
the input terminal S of the SR flip-flop 44 is connected to the output terminal of the first not gate 41, and the input terminal R thereof is connected to the output terminal of the nand gate 43;
the driver 45 receives the output signal of the SR flip-flop 44, and drives the power transistor S2 to turn on or off.
The synchronous rectification controller also comprises a second switch SW2The second switch SW2And the above-mentioned timing capacitor C1In parallel, the second switch SW2Conducting when the pulse generator 50 generates a trigger pulse; the pulse generator 50 is controlled by the first signal, and converts the low potential (0) into the high potential (V) when the first signal is changedref1) A trigger pulse is generated, i.e. the pulse generator 50 generates a trigger pulse at the instant when the switch tube S1 is turned on, to ensure complete clearing of the timing capacitor C1Integrated charge on.
Preferably, the second switch S isW2Is a transistor, the control terminal of the transistor is connected with the output terminal of the conduction sensing comparator COMP1, and the second switch SW2At the on time TonInternal turn-off, at off-time ToffAnd conducting internally.
Considering that the input terminal of the timing comparator COMP2 has a lower gain and a slower response speed if it is operated at a voltage close to 0V. In order to solve the technical problem, in the technical solution of this embodiment, the first current source I is providedref1And a second current source Iref2In series, and the first current source Iref1And (4) grounding. By the design, the input end of the timing comparator COMP2 can be operatedAt a high potential.
The above-mentioned embodiments are merely preferred embodiments for fully illustrating the present invention, and the scope of the present invention is not limited thereto. The equivalent substitution or change made by the technical personnel in the technical field on the basis of the invention is all within the protection scope of the invention. The protection scope of the invention is subject to the claims.
Claims (9)
1. A synchronous rectification control circuit of a switching power supply comprises,
the power tube is connected between a secondary winding of a transformer of the switching power supply and an output capacitor of the switching power supply;
the synchronous rectification controller is connected with the output stage of the switching power supply and is used for generating a control signal to control the power tube to be switched on or switched off;
the method is characterized in that: the synchronous rectification controller comprises a synchronous rectification controller and a synchronous rectification control circuit,
a primary side conduction sensing unit for sensing conduction time T in the switching period of the primary side winding switching tube of the transformer according to the voltage difference between two ends of the power tubeonAnd a cut-off time Toff(ii) a Generating a first signal according to the voltage difference between two ends of the power tube; wherein, when the voltage difference between the two ends of the power tube exceeds the threshold voltage, a first reference voltage V is generatedref1(ii) a Otherwise, generating a ground potential;
a voltage averaging unit coupled to the output terminal of the primary side conduction sensing unit for generating a second reference voltage V equal to the average voltage of the first signal in a switching periodref2(ii) a Wherein,
a voltage-to-current control source configured to convert the first reference voltage Vref1Is converted into a first current source Iref1The second reference voltage V is used for converting the second reference voltage V into the second reference voltage Vref2Is converted into a second current source Iref2(ii) a The first current source Iref1And a second current source Iref2After being connected in series, the grounding is carried out;
a first switch connected in seriesAt the first current source Iref1And a second current source Iref2And is controlled by the first signal;
a timing capacitor having a first end connected to the output end of the primary side conduction sensing unit and a second end connected to the first switch and coupled to a second current source Iref2One end of (a);
the timing capacitor is in the on time TonThe synchronous rectification controller generates a control signal to conduct the power tube when the timing capacitor is charged to a high position; said timing capacitor being at said cut-off time ToffAnd internal discharge, wherein the synchronous rectification controller generates a control signal to turn off the power tube when the timing capacitor discharges to a low position.
2. The switching power supply synchronous rectification control circuit according to claim 1, wherein: the synchronous rectification controller also comprises a second switch, the second switch is connected with the timing capacitor in parallel, and the second switch is conducted when the pulse generator generates a trigger pulse; the pulse generator is controlled by the first signal and generates a trigger pulse when the first signal is converted from a low potential to a high potential.
3. The switching power supply synchronous rectification control circuit according to claim 2, wherein: the second switch is a transistor, the control end of the transistor is connected with the output end of the primary side conduction sensing unit, and the second switch is in conduction time TonInternal turn-off, at off-time ToffAnd conducting internally.
4. The switching power supply synchronous rectification control circuit according to claim 1, wherein: the synchronous rectification controller also comprises a timing comparator, wherein the inverting input end of the timing comparator is connected with the first end of the timing capacitor and the output end of the primary side conduction sensing unit, and the non-inverting input end of the timing comparator is connected with the second end of the timing capacitor and the first switch which are coupled to the second current source Iref2And the output end of the first switch is connected with the logic driving unit.
5. The switching power supply synchronous rectification control circuit according to claim 4, wherein: the logic driving unit includes a logic driving unit including,
the input end of the first NOT gate is connected with the output end of the primary side conduction sensing unit;
the input end of the second NOT gate is connected with the output end of the timing comparator;
one end of the NAND gate is connected with the output end of the first NOT gate, and the other end of the NAND gate is connected with the output end of the second NOT gate;
an input end S of the SR flip-flop is connected with the output end of the first NOT gate, and an input end R of the SR flip-flop is connected with the output end of the NAND gate;
and the driver receives the output signal of the SR trigger and drives the power tube to be switched on or switched off.
6. The switching power supply synchronous rectification control circuit according to claim 1, wherein: the primary side conduction sensing unit comprises a conduction sensing comparator, the voltage difference between two ends of the power tube is connected to the positive phase input end of the conduction sensing comparator, and the negative phase input end of the conduction sensing comparator is connected to the threshold voltage VA(ii) a The output end of the conduction sensing comparator generates the first signal; when the voltage difference between two ends of the power tube exceeds the threshold voltage, the conduction sensing comparator outputs a first reference voltage Vref1(ii) a Otherwise, the conduction sense comparator outputs ground potential.
7. The switching power supply synchronous rectification control circuit according to claim 1, wherein: the voltage averaging unit is a circuit composed of a low-pass filter.
8. The switching power supply synchronous rectification control circuit according to claim 7, wherein: the low-pass filter is an RC filter, an RL filter or an LC filter.
9. The switching power supply synchronous rectification control circuit according to any one of claims 1 to 8, wherein: the power tube is an MOS tube, a BJT or an IGBT.
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| CN111697838A (en) * | 2020-05-29 | 2020-09-22 | 昂宝电子（上海）有限公司 | Synchronous rectification control circuit and method and switching power supply system |
| CN112379204A (en) * | 2020-11-18 | 2021-02-19 | 苏州美思迪赛半导体技术有限公司 | Drive port state detection circuit and method of drive circuit |
| CN114337299A (en) * | 2021-12-22 | 2022-04-12 | 连云港杰瑞电子有限公司 | Control system of secondary rectifier tube |
| CN116345906A (en) * | 2023-03-28 | 2023-06-27 | 苏州海鹏科技有限公司 | Control method based on bidirectional direct current converter circuit |
| US11764684B2 (en) | 2012-04-12 | 2023-09-19 | On-Bright Electronics (Shanghai) Co., Ltd. | Systems and methods for regulating power conversion systems with output detection and synchronized rectifying mechanisms |
| US11764697B2 (en) | 2020-01-20 | 2023-09-19 | On-Bright Electronics (Shanghai) Co., Ltd. | Systems and methods for controlling synchronous rectification |
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| US12047007B2 (en) | 2021-03-11 | 2024-07-23 | On-Bright Electronics (Shanghai) Co., Ltd. | Systems and methods for controlling gate voltage increase on primary side to reduce voltage spike on secondary side of switching power supplies |
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| US12095379B2 (en) | 2021-07-07 | 2024-09-17 | On-Bright Electronics (Shanghai) Co., Ltd. | Systems and methods for controlling synchronous rectification with variable voltage regulation |
| CN114337299B (en) * | 2021-12-22 | 2023-09-15 | 上海杰瑞兆新信息科技有限公司 | Control system of secondary rectifying tube |
| CN114337299A (en) * | 2021-12-22 | 2022-04-12 | 连云港杰瑞电子有限公司 | Control system of secondary rectifier tube |
| CN116345906A (en) * | 2023-03-28 | 2023-06-27 | 苏州海鹏科技有限公司 | Control method based on bidirectional direct current converter circuit |
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