CN116054580A - Synchronous rectification control circuit, method and flyback power conversion circuit system - Google Patents

Synchronous rectification control circuit, method and flyback power conversion circuit system Download PDF

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Publication number
CN116054580A
CN116054580A CN202211556263.1A CN202211556263A CN116054580A CN 116054580 A CN116054580 A CN 116054580A CN 202211556263 A CN202211556263 A CN 202211556263A CN 116054580 A CN116054580 A CN 116054580A
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CN
China
Prior art keywords
synchronous rectification
rectification device
condition
adjustable control
turned
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CN202211556263.1A
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Chinese (zh)
Inventor
文鹏
张波
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Shenzhen Biyi Microelectronics Co ltd
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Shenzhen Biyi Microelectronics Co ltd
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Priority to CN202211556263.1A priority Critical patent/CN116054580A/en
Publication of CN116054580A publication Critical patent/CN116054580A/en
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    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • 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
    • H02M1/08—Circuits specially adapted for the generation of control voltages for semiconductor devices incorporated in static converters
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • 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
    • 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
    • H02M7/2176—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 comprising a passive stage to generate a rectified sinusoidal voltage and a controlled switching element in series between such stage and the output
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02B—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO BUILDINGS, e.g. HOUSING, HOUSE APPLIANCES OR RELATED END-USER APPLICATIONS
    • Y02B70/00—Technologies for an efficient end-user side electric power management and consumption
    • Y02B70/10—Technologies improving the efficiency by using switched-mode power supplies [SMPS], i.e. efficient power electronics conversion e.g. power factor correction or reduction of losses in power supplies or efficient standby modes

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  • Engineering & Computer Science (AREA)
  • Power Engineering (AREA)
  • Rectifiers (AREA)

Abstract

The invention provides a synchronous rectification control circuit, a flyback power supply conversion circuit system and a control method. The synchronous rectification control circuit turns on the synchronous rectification device and enters an adjustable control section when the first condition is met, the synchronous rectification device is not allowed to be turned off in the adjustable control section or is turned off only when the second condition is met, wherein the duration of the adjustable control section changes along with the follow current time length of the synchronous rectification device, and if the synchronous rectification device is not turned off in the adjustable control section, the synchronous rectification device is turned off when the third condition is met after the adjustable control section is finished. The self-adaptive control method is used for adaptively adjusting the adjustable control interval, preventing the synchronous rectification from being turned off in advance and preventing the synchronous rectification from being turned off too late, improving the power efficiency and the system reliability, and is suitable for different power systems.

Description

Synchronous rectification control circuit, method and flyback power conversion circuit system
Technical Field
The present invention relates to the field of electronics, and in particular, but not exclusively, to a control circuit, method and flyback power conversion circuitry for controlling synchronous rectification devices.
Background
Fig. 1 shows a conventional flyback power conversion circuit system, which transmits power of a primary side to a secondary side through a switching operation of a primary side switch Q, and outputs an output voltage Vo driving a load at the secondary side through rectification of a secondary side rectifying device SR. In order to reduce the power consumption of the rectifying device, a synchronous rectifying tube can be selectively used, and when the follow current flows through the rectifying device SR, the rectifying device SR is controlled to work in a switch conducting state so as to reduce the conducting resistance and the power consumption.
Fig. 2 shows a conventional operation waveform diagram corresponding to fig. 1 for explaining the state of synchronous rectification operation. When the primary side switch Q is turned off, the voltage on the secondary side winding L2 turns over, the voltage Vds at two ends of the rectifying device SR drops sharply, the rectifying device SR starts to freewheel, and the freewheel current I sd at the secondary side rises. At time t1, when it is detected that the Vds voltage is lower than the reference voltage, the gate control signal SR PWM is converted to a high level, and the synchronous rectification device SR is turned on for reducing power consumption. Normally, when the freewheel is over, the Vds voltage rises to another reference value, pulling the signal SR PWM low, turning off the synchronous rectifying device SR. However, due to the influence of parasitic parameters such as leakage inductance of the transformer, the oscillation exists in the initial freewheeling current I sd of the freewheeling, the oscillation also exists in the Vds voltage, and when the Vds voltage oscillation is serious, the SR controller may misjudge and turn off the synchronous rectifier device SR by mistake. The loss is increased during follow current due to early false turn-off, heating is aggravated, and the system performance and reliability are affected. To avoid early turn-off of the synchronous rectifier device SR, a minimum on-time LEB (leading edge blanking time) is typically set after synchronous rectification on, during which time the synchronous rectifier device SR is not allowed to be turned off, thereby avoiding being turned off by mistake.
However, for different systems, the oscillation and the change of the freewheel time may be caused by the conditions of different input voltages, frequencies, load changes and the like, for a fixed LEB time, false triggering may not be avoided for some application occasions, and for another application occasion, if the freewheel time is too short, synchronous rectification cannot be started, so that the power consumption is reduced. In order to effectively avoid false triggering and effectively rectify, different front edge blanking time is required to be set for different power supply systems or power supply systems with different working frequencies. The front blanking time is typically adjusted by designing configuration pins, by connecting different resistors or capacitors on the configuration pins, but this approach increases the pin count of the package and external components. Or multiple chip versions can be set for different parameters, but the multiple versions increase material management and control cost and design management and control cost.
In addition, in a single-ended flyback PFC (power factor correction) circuit system, the freewheel time of the rectifying device has a great change along with the change of the input voltage, and a fixed leading edge blanking time cannot be applied.
In view of this, there is a need to provide a new architecture or control method in order to solve at least some of the above problems.
Disclosure of Invention
At least in view of one or more problems in the background art, the present invention provides a synchronous rectification control circuit, a flyback power conversion circuit system and a control method.
According to an aspect of the present invention, a synchronous rectification control circuit turns on a synchronous rectification device and enters an adjustable control section in which the synchronous rectification device is not allowed to be turned off or is turned off only when a second condition is satisfied, when it is detected that the first condition is satisfied, wherein a duration of the adjustable control section changes along with a freewheel time length in one switching cycle of the synchronous rectification device, and turns off the synchronous rectification device when the third condition is satisfied after the end of the adjustable control section if the synchronous rectification device is not turned off in the adjustable control section, wherein the first condition, the second condition, and the third condition are different from each other.
In one embodiment, the synchronous rectification device comprises a diode and a switching device connected in parallel, wherein the first condition comprises a current flowing in the diode when detected.
In one embodiment, the synchronous rectification device comprises a MOSFET (metal oxide semiconductor field effect transistor) having a body diode, the first condition comprising a drain-source voltage of the MOSFET falling below a first reference voltage, the second condition comprising the drain-source voltage of the MOSFET rising above a second reference voltage, and the third condition comprising the drain-source voltage of the MOSFET rising above a third reference voltage.
In one embodiment, the second reference voltage is greater than the third reference voltage.
In one embodiment, the control circuit is used in a single-ended flyback PFC converter, wherein the synchronous rectification device is disabled from conducting for a period of time when the freewheel time of the synchronous rectification device is less than a preset threshold.
In one embodiment, the duration of the adjustable control interval is between a minimum preset value and a maximum preset value.
According to another aspect of the present invention, a control circuit for controlling a synchronous rectification device receives a sampling signal indicative of a voltage difference across the synchronous rectification device, the control circuit comprising: the conduction detection circuit compares the sampling signal with a conduction reference signal and provides a conduction control signal for controlling the conduction of the synchronous rectification device; the adjustable control interval control circuit generates an adjustable control interval signal based on the follow current time in one switching period of the synchronous rectification device, and adjusts the duration of the adjustable control interval; and a turn-off detection circuit coupled to the adjustable control interval control circuit, the turn-off detection circuit comparing the sampling signal with a turn-off reference signal and providing a turn-off control signal for controlling turn-off of the synchronous rectification device, wherein the turn-off control signal is masked for maintaining the synchronous rectification device on or stepping the turn-off reference signal to a second reference signal when the adjustable control interval signal is a valid value.
In one embodiment, the synchronous rectification device includes a MOSFET transistor having a body diode, the sampling signal characterizing a drain-source voltage of the MOSFET transistor, the second reference signal being greater than the off reference signal.
In one embodiment, the length of the adjustable control interval increases when the freewheel time of the synchronous rectification device increases, and decreases when the freewheel time of the synchronous rectification device decreases.
In one embodiment, the control circuit is used in a single-ended flyback PFC converter, wherein the synchronous rectification device is disabled from conducting for a period of time when the freewheel time of the synchronous rectification device is less than a preset threshold.
According to still another aspect of the present invention, a synchronous rectification control circuit turns on a synchronous rectification device when detecting that a drain-source voltage of the synchronous rectification device falls below a first reference voltage, enters an adjustable control section in which the synchronous rectification device is not allowed to be turned off or is turned off only when the drain-source voltage rises above a second reference voltage, and turns off the synchronous rectification device when the drain-source voltage rises above a third reference voltage after the adjustable control section is finished, wherein the second reference voltage is greater than the third reference voltage, and a length of the adjustable control section changes with a freewheel time length if the synchronous rectification device is not turned off in the adjustable control section.
According to yet another aspect of the present invention, a flyback power conversion circuit system includes a primary side switch, a transformer, and a synchronous rectification device and a synchronous rectification control circuit as described in any of the embodiments above.
According to another aspect of the present invention, a synchronous rectification control method includes: when the first condition is detected to be met, the synchronous rectification device is conducted and enters an adjustable control interval; controlling the duration of the adjustable control interval, in which the synchronous rectification device is not allowed to be turned off or is turned off only when the second condition is satisfied, to be changed along with the length of the freewheel time in one switching cycle of the synchronous rectification device; and if the synchronous rectifying device is not turned off in the adjustable control interval, when the third condition is met after the adjustable control interval is finished, turning off the synchronous rectifying device, wherein the first condition, the second condition and the third condition are different from each other.
In one embodiment, the synchronous rectification device comprises a MOSFET, the first condition comprises a drain-source voltage of the MOSFET falling below a first reference voltage, the second condition comprises the drain-source voltage of the MOSFET rising above a second reference voltage, and the third condition comprises the drain-source voltage of the MOSFET rising above a third reference voltage.
In one embodiment, the second reference voltage is greater than the third reference voltage.
The synchronous rectification control circuit, the flyback power supply conversion circuit system and the control method provided by the invention can adaptively adjust the adjustable control interval, can prevent the synchronous rectification from being turned off in advance due to misjudgment, improve the power supply efficiency, can prevent the synchronous rectification from being turned off too late, improve the system reliability, can be suitable for different power supply systems, and has the advantages of simple system and low material management and control cost.
Drawings
The accompanying drawings are included to provide a further understanding of the invention, and together with the description serve to explain the embodiments of the invention, and do not constitute a limitation of the invention. In the drawings:
FIG. 1 illustrates a prior art flyback power conversion circuitry;
FIG. 2 illustrates a prior art operational waveform diagram corresponding to FIG. 1;
FIG. 3 shows a control circuit block diagram for controlling a synchronous rectification device in accordance with an embodiment of the present invention;
FIG. 4 shows a schematic diagram of a synchronous rectification control circuit according to an embodiment of the present invention;
FIG. 5 shows a control signal waveform schematic according to an embodiment of the invention;
FIG. 6 illustrates a control circuit schematic according to an embodiment of the present invention;
FIG. 7 shows a schematic diagram of a control circuit according to another embodiment of the invention;
fig. 8 shows a schematic diagram of signal waveforms with synchronous rectification control for a single-ended flyback PFC converter according to an embodiment of the present invention;
fig. 9 shows a flow chart of a control method for controlling a synchronous rectification device according to an embodiment of the present invention;
fig. 10 shows a flowchart of a control method for controlling a synchronous rectification control device according to another embodiment of the present invention.
Detailed Description
For a further understanding of the present invention, preferred embodiments of the invention are described below in conjunction with the examples, but it should be understood that these descriptions are merely intended to illustrate further features and advantages of the invention, and are not limiting of the claims of the invention.
The description of this section is intended to be illustrative of only a few exemplary embodiments and the invention is not to be limited in scope by the description of the embodiments. Combinations of the different embodiments, and alternatives of features from the same or similar prior art means and embodiments are also within the scope of the description and protection of the invention.
"coupled" or "connected" in the specification includes both direct and indirect connections. An indirect connection is a connection via an intermediary, such as a connection via an electrically conductive medium, such as a conductor, where the electrically conductive medium may contain parasitic inductance or parasitic capacitance, or may be a connection via an intermediary circuit or component described in the embodiments of the specification; indirect connections may also include connections through other active or passive devices, such as through circuits or components such as switches, signal amplification circuits, follower circuits, and the like, that may perform the same or similar functions. "plurality" or "multiple" means two or more.
Fig. 3 shows a block diagram of a control circuit 10 for controlling a synchronous rectification device SR according to an embodiment of the present invention.
After the synchronous rectifying device SR is turned on, the adjustable control interval ACR is entered, and the duration of the adjustable control interval ACR changes along with the increase and decrease of the follow current time Tdem of the synchronous rectifying device SR, so as to ensure that the synchronous rectifying device SR is not turned off in advance to reduce the power conversion efficiency, and is not turned off in a delayed manner to cause the reverse current generated by synchronous rectification to affect the reliability of the system. When the synchronous rectification follow current time Tdem is increased, the duration of the adjustable control interval ACR is increased; when the synchronous rectification freewheel time Tdem decreases, the duration of the adjustable control interval ACR decreases. The synchronous rectification freewheel time Tdem refers to the duration of the current flowing across the synchronous rectification device SR in one switching cycle, or the demagnetizing time of the transformer or the inductor in the power conversion circuit. Specifically, in one embodiment, the control circuit 10 may switch on the synchronous rectification device SR and enter the adjustable control interval ACR when it is detected that the on condition is satisfied, where the synchronous rectification device SR is not allowed to be turned off, and the adjustable control interval ACR is a leading edge blanking time, where the duration of the adjustable control interval ACR changes along with the freewheel time length Tdem in one switching cycle of the synchronous rectification device SR, and when the off condition is satisfied after the adjustable control interval ACR is completed, the synchronous rectification device SR is turned off. In another embodiment, the synchronous rectification device SR is allowed to be turned off in the adjustable control interval ACR, but the off condition is different from the off condition after exiting the adjustable control interval ACR, so as to strengthen the interference on the resonance signal, i.e. in the adjustable control interval ACR, the synchronous rectification device SR can be turned off when the second condition is detected to be satisfied; if the synchronous rectification device SR is not turned off in the adjustable control interval ACR, when the third condition is satisfied after the adjustable control interval is finished, the synchronous rectification device SR is turned off, wherein the first condition, the second condition and the third condition are different from each other.
In the illustrated embodiment, the synchronous rectification device SR includes a MOSFET (metal oxide semiconductor field effect transistor) having a body diode. In one embodiment, the on condition (or first condition) includes the drain-source voltage Vds of the MOSFET falling below the first reference voltage Vref1, the second condition includes the drain-source voltage Vds of the MOSFET rising above the second reference voltage Vref2, and the third condition includes the drain-source voltage Vds of the MOSFET rising above the third reference voltage Vref3. In a preferred embodiment, the second reference voltage Vref2 is greater than the third reference voltage Vref3.
In another embodiment, the synchronous rectification device may include a discrete diode and switching device connected in parallel, wherein the on condition/first condition includes when a current flowing in the diode is detected. Detecting the current flowing through the diode may be performed by detecting the current, detecting a voltage difference across the diode, or the like. The switching device may be a MOSFET, a JFET (junction field effect transistor), an IGBT (insulated gate bipolar transistor), or the like. The detection of the freewheel time length Tdem within one switching period of the synchronous rectification device SR may take place by any existing or other feasible detection method. In one embodiment, detecting the freewheel time Tdem may be achieved by detecting a time from when the voltage across the synchronous rectification device SR is smaller than the first reference voltage Vref1 to when the voltage across it is larger than the third reference voltage Vef 3. In another embodiment, the detection of the freewheel time Tdem may be performed by detecting a time length during which the control signal SR PWM of the synchronous rectification device SR is at a high level. Detecting the freewheel time Tdem may also detect the time of the current Isd from being greater than the first threshold to being less than a threshold by any other means.
The synchronous rectifying device can be used in a secondary side circuit of a flyback power supply conversion circuit and is used for providing a follow current function and simultaneously ensuring stable low power consumption and reliability. The flyback power conversion circuit can refer to the structure of fig. 1, and comprises a primary side switch Q, a transformer T, a synchronous rectification device SR and a control circuit for controlling the synchronous rectification device SR. Synchronous rectification devices may also be used in other types of power conversion circuits, such as Buck circuits, boost circuits, and the like.
In a voltage conversion system, the maximum value and the minimum value can be set for the duration of the adjustable control interval ACR, so that the duration of the adjustable control interval ACR is between the minimum preset value and the maximum preset value, and the reliability of the system is improved.
Fig. 4 shows a schematic diagram of a synchronous rectification control circuit according to an embodiment of the present invention. The control circuit receives a sampling signal Vds that characterizes the voltage difference across the synchronous rectification device. Preferably, the sampling signal Vds is a divided signal of a drain-source voltage of the MOSFET rectifier. The control circuit includes a conduction detection circuit 41, a turn-off detection circuit 42, and an adjustable control section control circuit 43, wherein the conduction detection circuit 41 detects the arrival of the conduction condition of the synchronous rectification device based ON the sampling signal Vds, and provides a conduction control signal ON for controlling the conduction of the synchronous rectification device. Preferably, the drain-source voltage sampling signal Vds representing the synchronous rectifier MOSFET is compared with the conduction reference signal, and when the sampling signal Vds falls below the conduction reference signal, the conduction detection circuit 41 outputs an effective conduction control signal ON for controlling the conduction of the synchronous rectifier; the adjustable control section control circuit 43 generates an adjustable control section signal ACR based on the freewheel time Tdem in one switching period of the synchronous rectification device and adjusts the duration of the adjustable control section. The adjustable control section control circuit 43 may include a freewheel time detection circuit 431 for detecting a freewheel time Tdem and an adjustable control section adaptive adjustment circuit 432 for adjusting the duration of the adjustable control section according to the freewheel time length Tdem. In one embodiment, the duration of the adjustable control interval reflected by the adjustable control interval signal ACR increases when the freewheel time Tdem of the synchronous rectification device increases, and the duration of the adjustable control interval reflected by the adjustable control interval signal ACR decreases when the freewheel time Tdem of the synchronous rectification device decreases. The turn-OFF detection circuit 42 is coupled to the adjustable control interval control circuit 43, and the turn-OFF detection circuit 42 provides a turn-OFF control signal OFF for controlling the turn-OFF of the synchronous rectification device based on the sampling signal Vds and the adjustable control interval signal ACR generated by the adjustable control interval control circuit 43. In one embodiment, the shutdown detection circuit 42 compares the sampling signal Vds with a shutdown reference signal, and shuts down the synchronous rectification device when the sampling signal Vds is greater than the shutdown reference signal. In one embodiment, when the adjustable control interval signal ACR is a valid value, the OFF control signal OFF is masked, that is, an inactive state is maintained, the synchronous rectification device is not allowed to be turned OFF, and the on state of the synchronous rectification device is maintained until the adjustable control interval signal ACR is finished, and when an OFF condition is satisfied, the valid OFF control signal OFF is generated for turning OFF the synchronous rectification device. In another embodiment, when the adjustable control interval signal ACR is a valid value, the off reference signal is stepped to the second reference signal, so that the off threshold of the synchronous rectification device is raised. In one embodiment, the second reference signal is greater than the off reference signal. The control circuit may further comprise a logic driving circuit 44 for generating a driving signal SR PWM adapted to drive the synchronous rectification device based ON the OFF control signal OFF and the ON control signal ON.
In one embodiment, the control circuit is fabricated on a semiconductor substrate to form a control chip. In one embodiment, the control circuit is fabricated in an electronic package to form an electronic chip, and the electronic chip can be automatically adapted to different control systems and applications without introducing different parameter configurations by using additional pins, so that not only can the higher power efficiency be ensured, but also the generation of reverse current can be prevented, the high reliability is realized, and the requirements of different systems can be adaptively met.
Fig. 5 shows a control signal waveform diagram according to an embodiment of the present invention. The signal SR PWM characterizes a control signal controlling the synchronous rectification device, the duration of which during one switching cycle represents the freewheel duration of the synchronous rectification device. In the two switching cycles illustrated, the freewheel lengths are T1 and T2, respectively. The signal ACR is an adjustable control interval signal, and in two switching periods shown in the figure, the duration of the adjustable control interval is Tc0 and Tc1 respectively, wherein the duration Tc0 of the adjustable control interval can be adjusted based on the freewheel time of the previous switching period or periods. The adjustable control interval duration Tc1 may be based on an adjustment of the freewheel time of the preceding switching cycle or cycles. In a preferred embodiment, the adjustable control interval duration Tc1 is controlled by the last switching cycle freewheel duration T1. When the length of the time length T1 is increased relative to the last period, the adjustable control interval time length Tc1 is increased, and when the length of the time length T1 is shortened, the adjustable control interval time length Tc1 is reduced. In one embodiment, the freewheel period is a time when the gate voltage of the synchronous rectifier is high or the synchronous rectifier is operated in a switch on state. In another embodiment, the freewheel period is a time when the current in the rectifier tube is greater than a certain reference value, such as a zero value, the current including the current flowing through the diode and through the synchronous rectifier tube.
Fig. 6 shows a schematic diagram of a control circuit according to an embodiment of the invention. The logic gate 64 and the flip-flop circuit 65 may be regarded as part of a logic driving circuit of the control circuit. The logic gate 64 may also be considered part of the turn-off detection circuit. The adjustable control interval signal ACR output from the adjustable control interval control circuit 63 is input to both input terminals of the logic gate 64 together with the signal at the output terminal of the OFF detection circuit 62, and the output terminal of the logic gate 64 provides the OFF control signal OFF. When the adjustable control interval signal ACR is an active value (e.g., high level), the OFF control signal OFF is in an inactive state (low level) for masking the active (high level) signal output from the OFF detection circuit 62, so that the synchronous rectification device remains on. In one embodiment, the ON detection circuit 61 receives the drain-source voltage sampling signal Vds of the synchronous rectification device, and when detecting that the drain-source voltage of the synchronous rectification device drops to be less than the first reference voltage, the ON detection circuit 61 outputs an active ON control signal ON, and the trigger circuit 65 is set, and the signal SR PWM is at a high level, for turning ON the synchronous rectification device. Preferably, the on detection circuit 61 includes a comparison circuit for comparing the drain-source voltage sampling signal Vds with the on reference signal vth_on. When the ON control signal ON is an active value, the trigger circuit 65 outputs a high level signal SR PWM for turning ON the synchronous rectification device. Meanwhile, the ON control signal ON or the signal SR PWM may be transmitted to the adjustable control section control circuit 63, and the adjustable control section signal ACR is set to a high level active state, and enters the adjustable control section. At this time, the OFF signal OFF of the output of the logic gate 64 is kept at a low level, and the synchronous rectification device is not allowed to be turned OFF. Wherein the time length of the adjustable control interval varies with the length of the freewheel time Tdem. After the adjustable control time is over, the adjustable control interval signal ACR is switched to a low level. At this time, when the drain-source voltage rises to be greater than the third reference voltage, the OFF detection circuit 62 outputs a high level signal, and the OFF control signal OFF output by the logic gate 64 is high level, so as to reset the trigger circuit 65, and the signal SR PWM is low level, and turn OFF the synchronous rectification device. Preferably, the OFF detection circuit 62 includes a comparison circuit for comparing the drain-source voltage sampling signal Vds with the OFF reference signal vth_off, and outputs the OFF control signal OFF of a high level when the signal Vds is greater than the reference signal vth_off. The control circuit may further comprise a driving circuit for amplifying the signal output by the triggering circuit 65 to an amplitude suitable for driving the synchronous rectification device.
Fig. 7 shows a schematic diagram of a control circuit according to another embodiment of the invention. In contrast to the embodiment of fig. 6, in this embodiment, the control circuit does not include a logic gate, but the OFF detection circuit 72 includes an OFF threshold adjustment circuit 721, an input terminal of the OFF threshold adjustment circuit 721 is coupled to an output terminal of the adjustable control interval control circuit 73, and an output terminal of the OFF threshold adjustment circuit 721 provides an OFF reference signal vth_off for comparison with the drain-source voltage sampling signal Vds of the synchronous rectification device to generate an OFF control signal OFF. In one embodiment, when the adjustable control interval signal ACR outputted by the adjustable control interval control circuit 73 is an invalid value, the shutdown reference signal vth_off provided by the shutdown threshold adjusting module 721 is a first reference value, and when the adjustable control interval signal ACR is an valid value, the shutdown reference signal vth_off provided by the shutdown threshold adjusting module 721 is stepped to a second reference value. Preferably, the second reference value is greater than the first reference value. When the drain-source voltage sampling signal Vds of the synchronous rectification device is detected to be reduced to be smaller than the conduction reference signal vth_on (the drain-source voltage of the corresponding synchronous rectification device is reduced to be smaller than the first reference voltage), the synchronous rectification device is turned on, and the synchronous rectification device enters an adjustable control interval, and an adjustable control interval signal ACR is an effective value. In the adjustable control interval, the turn-off reference signal vth_off rises to a second reference value, and is turned off when the drain-source voltage rises to a value that is greater than the second reference value (corresponding to the drain-source voltage being greater than the second reference voltage), if the synchronous rectification device is not turned off in the adjustable control interval, the adjustable control interval signal ACR is an invalid value after the adjustable control time is over, the turn-off reference signal vth_off falls to a first reference value, and the synchronous rectification device is turned off when the drain-source voltage sampling signal Vds rises to a value that is greater than the first reference value (corresponding to the drain-source voltage rising to a value that is greater than the third reference voltage, wherein the second reference voltage is greater than the third reference voltage). In one embodiment, the off reference signal vth_off in the adjustable control interval is a fixed value, and the signal providing manner is simpler. In another embodiment, the off reference signal vth_off within the adjustable control interval varies with the freewheel time Tdem, increasing the false trigger prevention performance and reliability of the system.
Fig. 8 shows a schematic diagram of signal waveforms with synchronous rectification control for a single-ended flyback PFC converter according to an embodiment of the present invention. In order to obtain a good power factor, the conduction time of a primary side main power tube and a secondary side rectifying tube of the single-ended flyback PFC converter changes along with the magnitude of an input voltage Vbus, so that the input current follows the input voltage to form a sine wave rectifying waveform. In the single-ended flyback PFC conversion circuit system, the follow current time variation amplitude of the synchronous rectification device is huge. The single-ended flyback PFC converter can adopt the control circuit in any embodiment to control the synchronous rectifying device, so that the duration of the adjustable control interval ACR of the synchronous rectifying tube can be adaptively adjusted in a power frequency period, the LEB time of the synchronous rectification can be changed along with the increase and decrease of the follow current time of the synchronous rectification, the synchronous rectification can be ensured to be neither turned off in advance nor turned off in a delayed manner, and the synchronous rectification can obtain optimal efficiency and highest reliability. In one embodiment, in the adjustable control interval ACR, the turn-off threshold of the synchronous rectifying device is increased, so that false triggering is prevented, and the synchronous rectifying tube is turned off in advance, thereby improving rectifying efficiency. In one embodiment, when the freewheel time of the synchronous rectifying device is smaller than a preset threshold value, the synchronous rectifying device is prohibited from being conducted in a period of time, and the diode is used for rectifying, so that the switching tube is prevented from being frequently opened and closed, the switching loss is reduced, and the reliability is improved.
Fig. 9 shows a flow chart of a control method for controlling a synchronous rectification device according to an embodiment of the present invention. The control method flow chart shows the control logic in one switching cycle. Of course, the power conversion circuit typically includes a plurality of switching cycles. The control method of controlling the synchronous rectification device may include the following steps. In step 901, it is detected whether a first condition is satisfied. In one embodiment, the synchronous rectification device includes a MOSFET, and detecting whether the first condition is met includes detecting whether a drain-source voltage of the MOSFET drops below a first reference voltage. Of course, the first condition may also include detecting whether the current signal flowing across the rectifying device exceeds a threshold value. When it is detected that the first condition is satisfied, the synchronous rectification device is turned on and enters the adjustable control interval ACR in step 902. The control method further includes controlling the duration Tacr of the adjustable control interval to vary with the length of the freewheel time Tdem within one switching cycle of the synchronous rectification device at step 902. Preferably, when the freewheel time length increases, the length of the adjustable control interval increases. In step 903, it is determined whether the adjustable control interval ACR has ended, in which the synchronous rectification device is not allowed to be turned off. If it is detected that the adjustable control interval has ended (the timing from the start of turning on the synchronous rectification device is greater than Tacr), in step 904, it is determined whether the off condition is satisfied. In one embodiment, the off condition includes a drain-source voltage of the MOSFET rising above a third reference voltage. Of course, the off condition may also be obtained by other means, such as by detecting that the current signal is smaller than a preset value, etc. When the off condition (third condition) is satisfied, the synchronous rectification device is turned off.
Fig. 10 shows a flowchart of a control method for controlling a synchronous rectification control device according to another embodiment of the present invention. Steps 1001, 1002, 1005 and 1006 may be referred to as steps 901, 902, 904 and 905. When entering the adjustable control interval ACR, the control method of the embodiment includes determining whether the second condition is satisfied in step 1003. If the second condition is satisfied, the process proceeds to step 1006, where the synchronous rectification device is turned off, and the operation of the present switching cycle is completed. In one embodiment, the second condition includes the drain-source voltage of the MOSFET rising above a second reference voltage, wherein the second reference voltage is greater than the off threshold voltage after the end of the adjustable control interval. If the synchronous rectification device is not turned off in the adjustable control interval, after the adjustable control interval is finished (Tacr is finished), it is detected in step 1005 whether a third condition is satisfied, and if the third condition is satisfied, step 1006 is entered to turn off the synchronous rectification device. In one embodiment, the third condition includes the drain-source voltage of the MOSFET rising above a third reference voltage. Preferably, the second reference voltage is greater than the third reference voltage. Wherein the first condition, the second condition, and the third condition are different from each other.
Through such control, the LEB time or the synchronous rectification turn-off condition is changed along with the change of the follow current time, so that the synchronous rectification can be performed immediately, the power efficiency is improved, false triggering can be avoided, the reliability of the system is improved, the situation that extra pins are arranged outside a packaging device or a large number of versions are added to meet different applications can be avoided, the method is suitable for single-ended flyback PFC application with the change of the follow current time greatly, and meanwhile, the system is simplified.
It will be appreciated by those skilled in the art that the logic controls of the "high" and "low", "set" and "reset", "and" or "," in-phase input "and" anti-phase input "among the logic controls described in the specification or drawings may be interchanged or changed, and that the same functions or purposes as those of the above embodiments may be achieved by adjusting the subsequent logic controls.
The description and applications of the present invention herein are illustrative and are not intended to limit the scope of the invention to the embodiments described above. The relevant descriptions of effects, advantages and the like in the description may not be presented in practical experimental examples due to uncertainty of specific condition parameters or influence of other factors, and the relevant descriptions of effects, advantages and the like are not used for limiting the scope of the invention. Variations and modifications of the embodiments disclosed herein are possible, and alternatives and equivalents of the various components of the embodiments are known to those of ordinary skill in the art. It will be clear to those skilled in the art that the present invention may be embodied in other forms, structures, arrangements, proportions, and with other assemblies, materials, and components, without departing from the spirit or essential characteristics thereof. Other variations and modifications of the embodiments disclosed herein may be made without departing from the scope and spirit of the invention.

Claims (15)

1. A synchronous rectification control circuit turns on a synchronous rectification device and enters an adjustable control section in which the synchronous rectification device is not allowed to be turned off or is turned off only when a second condition is satisfied, wherein the duration of the adjustable control section changes along with the freewheel time length of the synchronous rectification device, and turns off the synchronous rectification device when a third condition is satisfied after the adjustable control section is completed if the synchronous rectification device is not turned off in the adjustable control section, wherein the first condition, the second condition, and the third condition are different from each other.
2. The control circuit of claim 1, wherein the synchronous rectification device comprises a diode and a switching device in parallel, wherein the first condition comprises a current flowing in the diode when detected.
3. The control circuit of claim 1, wherein the synchronous rectification device comprises a MOSFET (metal oxide semiconductor field effect transistor) having a body diode, the first condition comprising a drain-source voltage of the MOSFET falling below a first reference voltage, the second condition comprising a drain-source voltage of the MOSFET rising above a second reference voltage, and the third condition comprising a drain-source voltage of the MOSFET rising above a third reference voltage.
4. The control circuit of claim 3, wherein the second reference voltage is greater than the third reference voltage.
5. The control circuit of claim 1, for use in a single-ended flyback PFC converter, wherein the synchronous rectification device is disabled from conducting for a period of time when a freewheel time of the synchronous rectification device is less than a preset threshold.
6. The control circuit of claim 1, wherein the adjustable control interval has a duration between a minimum preset value and a maximum preset value.
7. A control circuit for synchronous rectification that receives a sampling signal indicative of a voltage difference across a synchronous rectification device, the control circuit comprising:
the conduction detection circuit compares the sampling signal with a conduction reference signal and provides a conduction control signal for controlling the conduction of the synchronous rectification device;
the adjustable control interval control circuit generates an adjustable control interval signal based on the follow current time in one switching period of the synchronous rectification device, and adjusts the duration of the adjustable control interval; and
and the turn-off detection circuit is coupled with the adjustable control interval control circuit, compares the sampling signal with the turn-off reference signal, and provides a turn-off control signal for controlling the turn-off of the synchronous rectification device, wherein when the adjustable control interval signal is an effective value, the turn-off control signal is shielded for maintaining the turn-on of the synchronous rectification device or stepping the turn-off reference signal to the second reference signal.
8. The control circuit of claim 7, wherein the synchronous rectification device comprises a MOSFET having a body diode, the sampling signal characterizing a drain-source voltage of the MOSFET, the second reference signal being greater than the off reference signal.
9. The control circuit of claim 7, wherein the length of the adjustable control interval increases when the freewheel time of the synchronous rectification device increases, and the length of the adjustable control interval decreases when the freewheel time of the synchronous rectification device decreases.
10. The control circuit of claim 7, for use in a single-ended flyback PFC converter, wherein the synchronous rectification device is disabled from conducting for a period of time when a freewheel time of the synchronous rectification device is less than a preset threshold.
11. A synchronous rectification control circuit turns on a synchronous rectification device when detecting that the drain-source voltage of the synchronous rectification device falls below a first reference voltage, and enters an adjustable control interval, wherein the synchronous rectification device is not allowed to be turned off or is only turned off when the drain-source voltage rises above a second reference voltage in the adjustable control interval, if the synchronous rectification device is not turned off in the adjustable control interval, the synchronous rectification device is turned off when the drain-source voltage rises above a third reference voltage after the adjustable control time is over, the second reference voltage is greater than the third reference voltage, and the length of the adjustable control interval changes along with the length of a follow current time.
12. A flyback power conversion circuitry comprising a primary side switch, a transformer and a synchronous rectification device and synchronous rectification control circuit as claimed in any one of claims 1 to 11.
13. A synchronous rectification control method, comprising:
when the first condition is detected to be met, the synchronous rectification device is conducted and enters an adjustable control interval;
controlling the duration of the adjustable control interval, in which the synchronous rectification device is not allowed to be turned off or is turned off only when the second condition is satisfied, to be changed along with the length of the freewheel time in one switching cycle of the synchronous rectification device; and
if the synchronous rectifying device is not turned off in the adjustable control interval, when the third condition is met after the adjustable control interval is finished, the synchronous rectifying device is turned off, wherein the first condition, the second condition and the third condition are different from each other.
14. The control method of claim 13, wherein the synchronous rectification device comprises a MOSFET, the first condition comprises a drain-source voltage of the MOSFET falling below a first reference voltage, the second condition comprises the drain-source voltage of the MOSFET rising above a second reference voltage, and the third condition comprises the drain-source voltage of the MOSFET rising above a third reference voltage.
15. The control method of claim 14, wherein the second reference voltage is greater than the third reference voltage.
CN202211556263.1A 2022-12-06 2022-12-06 Synchronous rectification control circuit, method and flyback power conversion circuit system Pending CN116054580A (en)

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CN202211556263.1A CN116054580A (en) 2022-12-06 2022-12-06 Synchronous rectification control circuit, method and flyback power conversion circuit system

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