CN111786560A - Synchronous rectification control method, control circuit and switching power supply - Google Patents

Synchronous rectification control method, control circuit and switching power supply Download PDF

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Publication number
CN111786560A
CN111786560A CN202010582833.9A CN202010582833A CN111786560A CN 111786560 A CN111786560 A CN 111786560A CN 202010582833 A CN202010582833 A CN 202010582833A CN 111786560 A CN111786560 A CN 111786560A
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synchronous rectification
voltage
signal
pull
source
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CN202010582833.9A
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Chinese (zh)
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苏志勇
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Joulwatt Technology Hangzhou Co Ltd
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Joulwatt Technology Hangzhou Co Ltd
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    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M3/00—Conversion of dc power input into dc power output
    • H02M3/22—Conversion of dc power input into dc power output with intermediate conversion into ac
    • H02M3/24—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters
    • H02M3/28—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac
    • H02M3/325—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal
    • H02M3/335—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal using semiconductor devices only
    • H02M3/33569—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal using semiconductor devices only having several active switching elements
    • H02M3/33576—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal using semiconductor devices only having several active switching elements having at least one active switching element at the secondary side of an isolation transformer
    • H02M3/33592—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal using semiconductor devices only having several active switching elements having at least one active switching element at the secondary side of an isolation transformer having a synchronous rectifier circuit or a synchronous freewheeling circuit at the secondary side of an isolation transformer
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M1/00—Details of apparatus for conversion
    • H02M1/0048—Circuits or arrangements for reducing losses
    • H02M1/0054—Transistor switching losses
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02B—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO BUILDINGS, e.g. HOUSING, HOUSE APPLIANCES OR RELATED END-USER APPLICATIONS
    • Y02B70/00—Technologies for an efficient end-user side electric power management and consumption
    • Y02B70/10—Technologies improving the efficiency by using switched-mode power supplies [SMPS], i.e. efficient power electronics conversion e.g. power factor correction or reduction of losses in power supplies or efficient standby modes

Abstract

The invention discloses a synchronous rectification control method, a control circuit and a switching power supply, wherein when the drain-source voltage of a synchronous rectification switching tube is reduced to a set second threshold voltage, the gate-source voltage of the synchronous rectification switching tube is subjected to pull-up processing through a pulse type pull-up signal, and the duty ratio of the pulse type pull-up signal is adjusted according to the drain-source voltage of the synchronous rectification switching tube. The scheme of the stepped pull-up gate source voltage can prevent the phenomenon that the drain source voltage of the synchronous rectification switch tube reaches the turn-off threshold value in advance and the synchronous rectification switch tube is turned off in advance due to the fact that the pull-up is too fast, can quickly adjust the gate source voltage and has good applicability.

Description

Synchronous rectification control method, control circuit and switching power supply
Technical Field
The invention relates to the field of switching power supplies, in particular to a synchronous rectification control method, a control circuit and a switching power supply.
Background
A flyback switching power supply is an isolated switching power supply widely used for alternating current/direct current (AC/DC) and direct current/direct current (DC/DC) conversion to provide insulation between an input stage and an output stage. The flyback switching power supply generally comprises a main power switching tube, a transformer and a secondary rectifier tube, wherein the transformer comprises a primary winding and a secondary winding, the main power switching tube is connected with the primary winding, the secondary rectifier tube is connected with the secondary winding, a capacitor and a switching tube are connected between a drain electrode of the primary main power switching tube and an input power supply, and as shown in fig. 1, the drain voltage of the primary main power switching tube is clamped through an active clamping circuit, so that the aim of reducing the turn-off loss of the main power switching tube is fulfilled. In order to further improve the conversion efficiency of the flyback switching power supply, a synchronous rectification switch tube is usually used as the secondary side rectification tube, such as the synchronous rectification switch tube M1 in fig. 1.
Referring to fig. 1-1, which is a working waveform diagram of the active clamp flyback switching power supply in fig. 1, in the working process of the active clamp flyback switching power supply, after the secondary side synchronous rectification switching tube M1 is turned on, along with the change of the current Ids flowing through the drain-source both ends of the synchronous rectification switching tube, like the sinusoidal waveform in fig. 1-1, the voltage Vds across the drain-source both ends of the synchronous rectification switching tube also changes, and when it is detected that the voltage Vds across the drain-source both ends of the synchronous rectification switching tube reaches the preset first threshold voltage Vth1, the gate-source voltage Vgs of the synchronous rectification switching tube is pulled down through a pull-down circuit, and the gate-source voltage Vgs is reduced and maintained near the turn-on voltage (Vgs (th)) of the synchronous rectification switching tube. Because the gate-source voltage Vgs is maintained at a value close to the turn-on voltage (Vgs (th)), the on-resistance of the synchronous rectification switch tube is relatively large, the current Ids at the two ends of the drain and the source of the synchronous rectification switch tube is increased, and the voltage Vds at the two ends of the drain and the source is also increased, which undoubtedly increases the loss of the synchronous rectification switch tube and affects the power efficiency.
Disclosure of Invention
In view of the above, the present invention provides a synchronous rectification control method, a control circuit and a switching power supply, so as to solve the technical problems of high loss and low efficiency of a switching tube in the prior art.
The technical solution of the present invention is to provide a synchronous rectification control method for controlling a synchronous rectification switching tube in a switching power supply, including,
detecting the voltage at two ends of the drain source of the synchronous rectification switch tube, outputting a pull-down signal by the signal regulating circuit to pull down the grid-source voltage of the synchronous rectification switch tube when the voltage at two ends of the drain source of the synchronous rectification switch tube is detected to be more than or equal to a preset first threshold voltage,
when the voltage of the two ends of the drain source of the synchronous rectification switch tube is detected to be smaller than a preset second threshold voltage, the signal regulating circuit outputs a pulse type pull-up signal to pull up the gate source voltage of the synchronous rectification switch tube until the voltage of the two ends of the drain source of the synchronous rectification switch tube is larger than the preset second threshold voltage or until the gate source voltage of the synchronous rectification switch tube reaches a maximum driving voltage value.
Preferably, the duty ratio of the pulse type pull-up signal is adaptively adjusted according to the drain-source voltage of the synchronous rectification switching tube.
Preferably, one duty cycle of the pulsed pull-up signal comprises a first time period and a second time period,
during a first time period, the signal value of the pulsed pull-up signal is maintained at a constant value,
in a second time period, the signal value of the pulsed pull-up signal is zero,
and the time constant of the second time period is set according to the voltages of the two drain and source ends of the synchronous rectification switch tube.
Preferably, in the second time period of each working cycle, the voltage across the drain and the source of the synchronous rectifier tube is compared with the second threshold voltage,
when the voltage at the two ends of the drain and the source of the synchronous rectifier tube is smaller than the second threshold voltage, the pulse type pull-up signal of the next period is output,
and when the voltage at two ends of the drain and the source of the synchronous rectifier tube is greater than or equal to the second threshold voltage, prolonging the time constant of a second time period of the pulse type pull-up signal.
Preferably, the preset first threshold voltage is set to a voltage value before the synchronous rectifier tube reaches turn-off,
the value of the second threshold voltage is less than the value of the first threshold voltage.
The invention relates to a synchronous rectification control circuit for controlling a synchronous rectification switch tube in a switching power supply, which comprises,
the signal regulating circuit detects voltages at two ends of a drain source of the synchronous rectification switch tube, when the voltage at the two ends of the drain source of the synchronous rectification switch tube is detected to be larger than or equal to a preset first threshold voltage, the signal regulating circuit outputs a pull-down signal to pull down a grid source voltage of the synchronous rectification switch tube,
when the voltage of the two ends of the drain source of the synchronous rectification switch tube is detected to be smaller than a preset second threshold voltage, the signal regulating circuit outputs a pulse type pull-up signal to pull up the gate source voltage of the synchronous rectification switch tube until the voltage of the two ends of the drain source of the synchronous rectification switch tube is larger than the preset second threshold voltage or until the gate source voltage of the synchronous rectification switch tube reaches a maximum driving voltage value.
Preferably, the duty ratio of the pulse type pull-up signal is adaptively adjusted according to the gate-source voltage of the synchronous rectification switching tube.
Preferably, the preset first threshold voltage is set to a voltage value before the synchronous rectification switch tube reaches turn-off,
and, the value of the first threshold voltage is greater than the value of the second threshold voltage.
Preferably, the signal conditioning circuit comprises a detection circuit, a pulse circuit and a pull-up circuit,
the detection circuit is used for detecting the voltage at two ends of the drain source of the synchronous rectifier tube to output a switch signal to be transmitted to the pulse circuit,
the pulse circuit is used for generating an enabling pulse signal to the pull-up circuit, the pulse circuit receives the switching signal to adjust the duty ratio of the enabling pulse signal according to the effective state of the switching signal,
the pull-up circuit outputs the pulse type pull-up signal according to the enabling pulse signal.
Preferably, the enable pulse signal includes an active high state and an inactive low state, wherein a time constant of the inactive low state is adjusted according to an active state of the switching signal.
Preferably, the pull-up circuit includes a field effect transistor, a control terminal of the field effect transistor receives the enable pulse signal, a drain terminal of the field effect transistor receives a power supply, and an output signal of the source terminal is used as the pulse type pull-up signal.
The switching power supply comprises a primary side main power switching tube, a secondary side synchronous rectification switching tube and a clamping circuit, wherein the clamping circuit is connected between the main power switching tube and a power supply input end, and the synchronous rectification control circuit is used for controlling the secondary side synchronous rectification switching tube.
As described above, according to the synchronous rectification control method, the control circuit, and the switching power supply of the present invention, when the drain-source voltage of the synchronous rectification switching tube decreases to the set lower threshold voltage, the gate-source voltage of the synchronous rectification switching tube is pulled up by the pulse-type pull-up signal, the drain-source voltage of the synchronous rectification switching tube is detected, and once the drain-source voltage is detected to increase to the set lower threshold voltage, the inactive state of the pulse-type pull-up signal is extended. By the scheme of the stepped pull-up gate source voltage, the phenomenon that the drain source voltage of the synchronous rectification switch tube reaches the turn-off threshold value in advance and the synchronous rectification switch tube is turned off in advance due to the fact that the pull-up is too fast is avoided, and the size of the gate source voltage can be adjusted rapidly.
Drawings
Fig. 1 is a block diagram of the structure of an active clamp flyback switching power supply;
fig. 1-1 is a waveform diagram of the operation of the active clamp flyback switching power supply in fig. 1;
FIG. 2 is a block circuit diagram of the synchronous rectification control circuit of the present invention;
FIG. 2-1 is a circuit configuration diagram of the pull-up circuit of FIG. 2;
fig. 2-2 are diagrams of operating waveforms of the synchronous rectification switching tube in fig. 2.
Detailed Description
The preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings, but the present invention is not limited to these embodiments. The invention encompasses any and all alternatives, modifications, and equivalent methods and arrangements which fall within the spirit and scope of the invention.
In the following description of the preferred embodiments of the present invention, specific details are set forth in order to provide a thorough understanding of the present invention, and it will be apparent to those skilled in the art that the present invention may be practiced without these specific details.
The invention is described in more detail in the following paragraphs by way of example with reference to the accompanying drawings. It should be noted that the drawings are simplified in form and are not to precise scale, which is only used for convenience and clarity to assist in describing the embodiments of the present invention.
The synchronous rectification control method according to the present invention is used for controlling a synchronous rectification switching tube in a switching power supply, and preferably, is used for controlling a secondary synchronous rectification switching tube in an active clamp flyback switching power supply, as shown in fig. 2, and is a circuit block diagram of a common active clamp flyback switching power supply, a power stage circuit is the same as that in the background technology, and the secondary synchronous rectification switching tube is M1. Specifically, the control method detects the voltage V between the drain and the source of the synchronous rectification switching tube M1DSWhen the voltage V at the two ends of the drain and the source of the synchronous rectification switch tube is detectedDSWhen the voltage is larger than or equal to a preset first threshold voltage Vth1, the signal regulating circuit outputs a pull-down signal Id2 to pull down a gate-source voltage V of the synchronous rectifier tubeGSWhen the voltage V at the two ends of the drain and the source of the synchronous rectification switch tube is detectedDSWhen the voltage is less than a preset second threshold voltage Vth2, the signal regulating circuit outputs a pulse type pull-up signal Id1 to pull up the grid-source voltage V of the synchronous rectification switch tubeGSUp to the voltage V at the two drain-source ends of the synchronous rectification switch tubeDSGreater than a predetermined second threshold voltage Vth2, where the predetermined first threshold voltage Vth1 is set to a voltage value before the synchronous rectifier reaches off, for example, when the voltage across the drain and source of the synchronous rectifier switch VDSWhen the synchronous rectifier tube is turned off when a certain value is reached, for example, -10mv, the first threshold voltage Vth1 is set to be smaller than the certain value, for example, -40mv, so that the synchronous rectifier tube reaches a state before the synchronous rectifier tube is turned off, wherein the value of the second threshold voltage Vth2 is smaller than the value of the first threshold voltage Vth1, the second threshold voltage is set to be a lower threshold voltage, the purpose of quick adjustment can be ensured to be achieved when the synchronous rectifier tube is required to be turned off, and the second threshold voltage can be set to be between-40 mv and-80 mv.
The following is combined with the following figures 2 and 2-1The control method of the present invention is explained for the circuit block diagram of the synchronous rectification control circuit of the present invention and the circuit block diagram of the pull-up circuit. As shown in fig. 2, the synchronous rectification control circuit includes a signal conditioning circuit 1, and the signal conditioning circuit 1 detects a voltage V across the drain and the source of the synchronous rectification switch tube M1DSTo output a pull-down signal and a pulse-type pull-up signal to the gate of the synchronous rectification switch tube M2 for adjusting the gate-source voltage V of the synchronous rectification switch tubeGS。
In an embodiment of the present invention, the control method further includes that one duty cycle of the pulsed pull-up signal includes a first time period Δ t1 and a second time period Δ t2, a signal value of the pulsed pull-up signal is maintained at a constant value (which may be denoted as an active state) in the first time period Δ t1, a signal value of the pulsed pull-up signal is zero (which may be denoted as an inactive state) in the second time period Δ t2, and a quotient of the second time period Δ t2 and a sum of the first time period Δ t1 and the second time period Δ t2 is a duty ratio of the pulsed pull-up signal. And in the second time period delta t2 of each working cycle, comparing the voltage V between the drain and the source of the synchronous rectification switch tubeDSThe voltage V between the drain and the source of the synchronous rectification switch tube is equal to the second threshold voltage Vth2DSAnd when the voltage at two ends of a drain and a source of the synchronous rectification switch tube is greater than or equal to the second threshold voltage, or the gate-source voltage of the synchronous rectification switch tube reaches the maximum driving voltage value, the time constant of a second time period of the pulse type pull-up signal is prolonged. The control method leads the grid-source voltage of the synchronous rectification switch tube to be in a step-type rise through controlling the duty ratio of the pulse type pull-up signal, thus being capable of strictly monitoring the voltage V at two ends of the drain source of the synchronous rectification switch tubeDSThe change is not less than the second threshold voltage Vth2, the turn-off threshold of the synchronous rectification switching tube is not reached, the size of the duty ratio can be rapidly adjusted according to the circuit structure, the adaptability is good, the control method has good reliability, and the control result is accurate.
Specifically, referring to fig. 2 and fig. 2-1, the invention is explained in conjunction with a specific circuit embodiment, the signal conditioning circuit includes a detection circuit 1-1 and a pull-up circuit 1-2, the pull-up circuit includes a pulse circuit 1-2-1 and a current source circuit 1-2-2, the detection circuit 1-1 is configured to detect a voltage across a drain and a source of the synchronous rectifier tube to output a switching signal Vf for transmission to the pull-up circuit, and the detection circuit may be implemented by a comparator or the like.
The pulse circuit 1-2-1 generates an enable pulse signal GEN to the current source circuit 1-2-2, receives the switching signal Vf, and determines and adjusts a duty ratio of the enable pulse signal GEN according to an effective state of the switching signal Vf, and specifically, in a previous cycle, when the enable pulse signal GEN is at a low level, and when the switching signal Vf is at an effective state, the low-level invalid state of the enable pulse signal is extended.
The current source circuit 1-2-2 receives the enable pulse signal GEN to output the pulsed pull-up signal Id1 according to the enable pulse signal state. In this embodiment, the current source circuit includes a field effect transistor M3, a control terminal of the field effect transistor M3 receives the enable pulse signal GEN, a drain terminal of the field effect transistor M3 receives a power supply Vcc, and an output signal of a source terminal of the field effect transistor M3 is used as the pulse type pull-up signal Id 1.
In addition, in the control method, the step of: when the voltage of the two ends of the drain source of the synchronous rectification switch tube is detected to be larger than or equal to a preset first threshold voltage, the signal regulating circuit outputs a pull-down signal to pull down the grid source voltage of the synchronous rectification switch tube. Here, the voltage V across the drain and the source of the synchronous rectification switch tube may be received by the detection circuitDSAnd preA first threshold voltage Vth1 when the voltage V between the drain and the sourceDSWhen the voltage reaches a first threshold voltage Vth1, the gate-source voltage of the synchronous rectification switch tube is pulled down through a pull-down circuit, so that the voltage V at the two ends of the drain and the source of the synchronous rectification tubeDSIs maintained around the first threshold voltage Vth 1. In this embodiment, when the gate-source voltage of the synchronous rectifying tube drops to a preset voltage value, the pull-down signal is controlled to decrease, and when it is detected that the voltage across the drain and the source of the synchronous rectifying tube is equal to a preset first threshold voltage, the gate-source voltage value of the synchronous rectifying tube is recorded as a first voltage value, the preset voltage value is greater than an inherent voltage value and less than or equal to the first voltage value, wherein the inherent voltage value is one of 0.5V to 0.7V.
Referring now to fig. 2-2, a waveform diagram of the operation of the synchronous rectification switch tube of fig. 2 is shown. At the time t0, the secondary side synchronous rectification switch tube M1 is turned on, and the drain-source current I of the synchronous rectification switch tube M1DSStarting to change according to quasi-sine, and reaching the time t1, the voltage V between the drain and the source of the synchronous rectification switch tube M1DSWhen the voltage reaches a first threshold voltage Vth1, the signal regulating circuit outputs the pull-down signal to pull down the grid voltage of the synchronous rectification switching tube M1, the grid-source voltage of the synchronous rectification switching tube M1 is pulled down to be close to a turn-off threshold value, and the voltage V at two ends of the drain and the source of the synchronous rectification switching tube M1DSStarting to drop, and reaching the time t2, the voltage V between the drain and the source of the synchronous rectification switch tube M1DSAnd the voltage drops to a second threshold voltage Vth2, at this time, the switching signal Vf output by the detection circuit 1-1 is in a high-level effective state, the pulse circuit 2-2-1 receives the switching signal Vf and outputs an enable pulse signal GEN to the field effect transistor M3, the field effect transistor M3 is turned on, and the gate-source voltage of the synchronous rectification switching tube M1 is pulled up through the power supply voltage Vcc. One working period of the enabling pulse signal GEN comprises a high-level effective state and a low-level ineffective state, and in the previous working period of the enabling pulse signal GEN, in a low-level time period, the voltage V at two ends of a drain source of the synchronous rectification switch tube is detectedDSThe second threshold voltage Vth2, when the drain of the synchronous rectification switch tubeVoltage V across the sourceDSWhen the switching signal is in an active state less than the second threshold voltage Vth2, the pulse circuit outputs an enable pulse signal GEN of the next period to the synchronous rectification switch tube M1, and the cycle is repeated, so that it can be understood that the source voltage signal of the synchronous rectification switch tube M1, i.e., the pull-up signal, is a pulse signal. As shown in fig. 2-2, the gate-source current I of the synchronous rectification switch tube is in the time period of t2-t3DSFor pulse signals, after the pull-up is carried out for a plurality of cycles, the detection circuit detects the voltage V at two ends of the drain and the source of the synchronous rectification switch tube to the time t3DSWhen the voltage is higher than the second threshold voltage Vth2, the switching signal is in an inactive state, and the pulse circuit extends the inactive state of the enable pulse signal. Then, in the stage of t3-t4, the voltage V between the grid and the source of the synchronous rectification switch tubeGSMaintaining the voltage V at two ends of drain and source of synchronous rectification switch tube at a value greater than the turn-off threshold valueDSWith drain-source current IDSThe variation of (2) will fluctuate a little, as shown in fig. 2-2, and the voltage V between the drain and the source of the synchronous rectification switch tube is reduced a little by t4DSWhen the turn-off threshold value is reached, the voltage V at the two ends of the grid source of the synchronous rectification switch tube is pulled downGSAnd turning off the switching tube. According to the switching characteristic of the synchronous rectification switching tube, when the voltage V is applied to the two ends of the grid source of the synchronous rectification switching tubeGSWhen the voltage is pulled up to the maximum driving voltage value, the grid source voltage does not need to be pulled up any more, and the enable pulse signal is kept in a low-level invalid state.
It can be seen from the above process that, according to the embodiment, after the drain-source voltage of the synchronous rectification switch tube is decreased to the set lower threshold voltage, the gate-source voltage of the synchronous rectification switch tube is pulled up by the pulse-type pull-up signal, and the drain-source voltage of the synchronous rectification switch tube is monitored all the time, and once the drain-source voltage is detected to be increased to the set lower threshold voltage, the invalid state of the pulse-type pull-up signal is prolonged. By the scheme of the stepped pull-up gate source voltage, the phenomenon that the drain-source voltage of the synchronous rectification switch tube reaches the turn-off threshold value in advance and the synchronous rectification switch tube is turned off in advance due to the fact that the pull-up is too fast is avoided, the pull-up signal of the circuit can be adjusted in a self-adaptive mode according to the drain-source voltage, the circuit is adjusted fast, and the adaptability is good.
Finally, the invention discloses a switching power supply, which comprises a primary side main power switching tube, a secondary side synchronous rectification switching tube and a clamping circuit, wherein the clamping circuit is connected between the main power switching tube and a power supply input end, and the synchronous rectification control circuit is used for controlling the secondary side synchronous rectification switching tube. By utilizing the synchronous rectification control scheme, the phenomenon that the drain-source voltage of the synchronous rectification switch tube reaches the turn-off threshold value in advance due to the fact that the synchronous rectification switch tube is pulled up too fast can be prevented, the synchronous rectification switch tube is turned off in advance, the stability and the efficiency of the switch power supply are improved, the adjusting time is fast, and the effect is good.
It is known to those skilled in the art that the synchronous rectification control circuit and the control method of the embodiment of the present invention can be applied to any suitable switching power supply circuit, such as an LLC resonant switching circuit.
The above-described embodiments do not limit the scope of the present invention. Any modification, equivalent replacement, and improvement made within the spirit and principle of the above-mentioned embodiments should be included in the protection scope of the technical solution.

Claims (12)

1. A synchronous rectification control method is used for controlling a synchronous rectification switching tube in a switching power supply and is characterized by comprising the following steps,
detecting the voltage at two ends of the drain source of the synchronous rectification switch tube, when detecting that the voltage at two ends of the drain source of the synchronous rectification switch tube is larger than or equal to a preset first threshold voltage, the signal regulating circuit outputs a pull-down signal to pull down the grid source voltage of the synchronous rectification switch tube,
when the voltage of the two ends of the drain source of the synchronous rectification switch tube is detected to be smaller than a preset second threshold voltage, the signal regulating circuit outputs a pulse type pull-up signal to pull up the grid source voltage of the synchronous rectification switch tube until the voltage of the two ends of the drain source of the synchronous rectification switch tube is larger than the preset second threshold voltage or until the grid source voltage of the synchronous rectification switch tube reaches a maximum driving voltage value.
2. The control method according to claim 1, wherein the duty cycle of the pulsed pull-up signal is adaptively adjusted according to the drain-source voltage of the synchronous rectification switch tube.
3. The control method of claim 2, wherein one duty cycle of the pulsed pull-up signal comprises a first time period and a second time period,
during a first time period, the signal value of the pulsed pull-up signal is maintained at a constant value,
in a second time period, the signal value of the pulsed pull-up signal is zero,
and the time constant of the second time period is set according to the voltage at the two ends of the drain and the source of the synchronous rectification switch tube.
4. The control method of claim 3, wherein during the second period of each duty cycle, comparing the magnitude of the voltage across the drain and the source of the synchronous rectifier tube with the second threshold voltage,
when the voltage at the two ends of the drain and the source of the synchronous rectifier tube is smaller than the second threshold voltage, the pulse type pull-up signal of the next period is output,
and when the voltage at two ends of the drain and the source of the synchronous rectifier tube is greater than or equal to the second threshold voltage, prolonging the time constant of a second time period of the pulse type pull-up signal.
5. The control method according to claim 1, wherein the preset first threshold voltage is set to a voltage value before the synchronous rectifier tube reaches an OFF state,
the value of the second threshold voltage is less than the value of the first threshold voltage.
6. A synchronous rectification control circuit is used for controlling a synchronous rectification switching tube in a switching power supply and is characterized by comprising,
the signal regulating circuit detects the voltage at two ends of the drain source of the synchronous rectification switch tube, when the voltage at two ends of the drain source of the synchronous rectification switch tube is detected to be larger than or equal to a preset first threshold voltage, the signal regulating circuit outputs a pull-down signal to pull down the gate-source voltage of the synchronous rectification switch tube,
when the voltage of the two ends of the drain source of the synchronous rectification switch tube is detected to be smaller than a preset second threshold voltage, the signal regulating circuit outputs a pulse type pull-up signal to pull up the grid source voltage of the synchronous rectification switch tube until the voltage of the two ends of the drain source of the synchronous rectification switch tube is larger than the preset second threshold voltage or until the grid source voltage of the synchronous rectification switch tube reaches a maximum driving voltage value.
7. The control circuit of claim 6, wherein a duty cycle of the pulsed pull-up signal is adaptively adjusted according to a gate-source voltage of the synchronous rectification switch tube.
8. The control circuit of claim 6, the preset first threshold voltage is set to a voltage value before the synchronous rectification switching tube reaches turn-off,
and, the value of the first threshold voltage is greater than the value of the second threshold voltage.
9. The control circuit of claim 7, wherein the signal conditioning circuit comprises a detection circuit, a pulse circuit, and a pull-up circuit,
the detection circuit is used for detecting the voltage at two ends of the drain source of the synchronous rectifier tube to output a switching signal to be transmitted to the pulse circuit,
the pulse circuit is used for generating an enabling pulse signal to the pull-up circuit, the pulse circuit receives the switching signal so as to adjust the duty ratio of the enabling pulse signal according to the effective state of the switching signal,
the pull-up circuit outputs the pulse type pull-up signal according to the enabling pulse signal.
10. The control circuit of claim 9, wherein the enable pulse signal comprises an active high state and an inactive low state,
wherein the time constant of the low level invalid state is adjusted according to the valid state of the switching signal.
11. The control circuit of claim 10, wherein the pull-up circuit comprises a field effect transistor, a control terminal of the field effect transistor receives the enable pulse signal, a drain terminal of the field effect transistor receives a power supply, and an output signal of a source terminal of the field effect transistor is used as the pulse-type pull-up signal.
12. A switching power supply comprising a primary side main power switching tube, a secondary side synchronous rectification switching tube and a clamp circuit, said clamp circuit being connected between said main power switching tube and a power supply input terminal, characterized by further comprising a synchronous rectification control circuit as claimed in any of claims 6-11, said synchronous rectification control circuit being adapted to control said secondary side synchronous rectification switching tube.
CN202010582833.9A 2020-06-23 2020-06-23 Synchronous rectification control method, control circuit and switching power supply Pending CN111786560A (en)

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Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN114094855A (en) * 2021-11-25 2022-02-25 深圳市必易微电子股份有限公司 Rectifier control circuit and power supply conversion system and control method thereof
TWI786781B (en) * 2021-07-21 2022-12-11 大陸商艾科微電子（深圳）有限公司 Synchronous rectifier controller and control method thereof
CN115864858A (en) * 2023-03-01 2023-03-28 恩赛半导体(成都)有限公司 Auxiliary power supply, power supply system and electronic device
US11817792B2 (en) 2020-10-30 2023-11-14 Joulwatt Technology Co., Ltd. Switching-type regulation driver and regulation driving method thereof

Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US11817792B2 (en) 2020-10-30 2023-11-14 Joulwatt Technology Co., Ltd. Switching-type regulation driver and regulation driving method thereof
TWI786781B (en) * 2021-07-21 2022-12-11 大陸商艾科微電子（深圳）有限公司 Synchronous rectifier controller and control method thereof
CN114094855A (en) * 2021-11-25 2022-02-25 深圳市必易微电子股份有限公司 Rectifier control circuit and power supply conversion system and control method thereof
CN115864858A (en) * 2023-03-01 2023-03-28 恩赛半导体(成都)有限公司 Auxiliary power supply, power supply system and electronic device
CN115864858B (en) * 2023-03-01 2023-05-05 恩赛半导体(成都)有限公司 Auxiliary power supply, power supply system and electronic device

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