CN114123789A - Synchronous rectification converter - Google Patents

Synchronous rectification converter Download PDF

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Publication number
CN114123789A
CN114123789A CN202111351147.1A CN202111351147A CN114123789A CN 114123789 A CN114123789 A CN 114123789A CN 202111351147 A CN202111351147 A CN 202111351147A CN 114123789 A CN114123789 A CN 114123789A
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voltage
tube
module
resistor
current
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CN202111351147.1A
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CN114123789B (en
Inventor
吴智星
梅亚康
李柳霖
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Shenzhen Zhuoxin Micro Technology Co ltd
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Shenzhen Zhuoxin Micro Technology 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
    • H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
    • H02H7/00—Emergency protective circuit arrangements specially adapted for specific types of electric machines or apparatus or for sectionalised protection of cable or line systems, and effecting automatic switching in the event of an undesired change from normal working conditions
    • H02H7/10—Emergency protective circuit arrangements specially adapted for specific types of electric machines or apparatus or for sectionalised protection of cable or line systems, and effecting automatic switching in the event of an undesired change from normal working conditions for converters; for rectifiers
    • H02H7/12—Emergency protective circuit arrangements specially adapted for specific types of electric machines or apparatus or for sectionalised protection of cable or line systems, and effecting automatic switching in the event of an undesired change from normal working conditions for converters; for rectifiers for static converters or rectifiers
    • H02H7/1213—Emergency protective circuit arrangements specially adapted for specific types of electric machines or apparatus or for sectionalised protection of cable or line systems, and effecting automatic switching in the event of an undesired change from normal working conditions for converters; for rectifiers for static converters or rectifiers for DC-DC 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
    • 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
    • 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)
  • Dc-Dc Converters (AREA)

Abstract

The invention discloses a synchronous rectification converter which comprises a comparison module, a conduction module, a turn-off module, a protection module and a control module which are sequentially connected, wherein the conduction module prevents an SR (thyristor) from being based on a drain-source voltage V at the starting moment of the SR at the time of starting the SR after the SR is starteddsSetting a minimum on-time T1 for a false trigger signal generated by fluctuation, prohibiting the SR tube from being turned off within T1 time, and turning off the SR tube when a drain-source voltage V is detecteddsWhen the voltage is negative, the comparator judges that the SR tube is resonance of DCM dead time or conduction rectification of the SR tube to generate a shielding signal T2, the comparator is prevented from turning over in the dead time to trigger the SR tube to be turned on, the normal and reliable operation of the SR tube is ensured by the timing mode of the conduction module and the turn-off module, the current detection unit, the voltage amplification unit, the phase shift unit, the zero comparison unit and the optical coupling isolation unit are arranged in the protection module, and the problem of loop can be solvedThe method has the advantages of reducing energy consumption and improving the working stability of the synchronous rectification converter due to the flow problem.

Description

Synchronous rectification converter
Technical Field
The invention relates to the technical field of converter rectification, in particular to a synchronous rectification converter.
Background
With the development of electronic products and the increasing demand of the market on the electronic products, the working frequency of the switching power supply is higher and higher, and in order to reduce power consumption, the working voltage of the power supply needs to be reduced, so that the loss of the secondary rectifier diode can also quickly rise in proportion under the low-voltage and high-current output state of the switching power supply. However, most of the applications in the field of medium and low power supply modules adopt a diode rectification mode, the problem of rectification loss occurs under the condition of low output voltage, and a converter adopting a synchronous rectification technology can generate reverse circulation current under the condition of light load, so that energy loss is caused, and the working efficiency of a power supply is reduced.
Disclosure of Invention
In view of the above, the present invention provides a synchronous rectification converter capable of shielding false triggering signals caused by instantaneous voltage surge of a synchronous rectification transistor switch, improving system operation reliability, and reducing energy consumption, so as to solve the above technical problems, and is implemented by the following technical solutions.
The invention provides a synchronous rectification converter, comprising:
a comparison module including two comparators for generating an on signal and an off signal for a drain-source voltage V by setting different flip threshold voltages to the comparators, respectivelydsSampling the changes in (a);
the conduction module is used for avoiding that the SR tube is based on the drain-source voltage V at the starting moment after the SR tube is starteddsA false trigger signal generated by fluctuation sets a minimum conduction time T1, and the SR tube is forbidden to be switched off within the time T1;
a turn-off module for turning off the power supply when the drain-source voltage V is detecteddsWhen the voltage is negative, the comparator judges that the SR tube is resonance of DCM dead time or conduction rectification of the SR tube, and generates a shielding signal T2 to prevent the comparator from turning over to trigger the SR tube to be turned on in the dead time;
the protection module starts a protection action cut-off circuit to work when the voltage is reduced to critical working voltage, the protection module comprises a current detection unit, a voltage amplification unit, a phase forward-shift unit, a zero comparison unit and an optical coupling isolation unit, the current detection unit comprises a current transformer CT and a resistor R1, high-frequency resonant current of an output capacitor and a transformer secondary inductor is sampled by the current transformer CT and then induced to a secondary side, and the current of the secondary side generates corresponding voltage drop on a resistor R1 and is output to the next unit; the voltage amplification unit comprises an operational amplifier OPA1, a resistor R2 and a resistor R3, wherein the positive phase end of the operational amplifier OPA1 is grounded, the negative phase end of the operational amplifier OPA1 is connected with the output voltage of the current detection module through the resistor R2, a resistor R3 is connected between the output end and the reverse phase end of the operational amplifier OPA1, the operational amplifier amplifies the output voltage of a current transformer in the previous unit, the ratio of the R2 to the R3 is a voltage amplification factor, and the input voltage signal is subjected to reverse transformation; the phase shifting unit comprises an operational amplifier OPA2, a resistor R4, a resistor R5, an adjustable resistor R6 and a capacitor C1, an input signal is input from the positive phase end of a remote amplifier OPA2, the resistor R4, the resistor R5 and the capacitor C1 are connected in series and then are connected to the negative end of an OPA2, the resistor R6 is added between the output end of the R5 and the output end of the OPA2, and the R6 is used for adjusting the phase shifting time; the zero point comparison unit comprises a comparator COM and a resistor R7, the adjusted phase advancing signal is accessed to a positive-phase end of the comparator COM through the resistor R7, a negative-phase end of the COM is grounded, the signal of the positive-phase end is compared with zero voltage, and the input resonant current is converted into a square wave signal; the optical coupling isolation unit comprises an optical coupler OPT, a current limiting resistor R8 and a pull-up resistor R9, a square wave signal is connected to the light emitting side of the optical coupler OPT through a resistor R8, a current limiting protection diode R8 outputs a current signal at the triode side of the OPT, and the current signal is connected to the control module to become a trigger signal of the reverse moment of the secondary current in synchronous rectification;
and the control module is used for processing the shielding signals T2 and T1 generated by the switch-on module and the switch-off module, judging whether a new synchronous rectification cycle is started or not, and endowing the driving circuit with an initial state, wherein the SR gate driving voltage of the rectification switch tube is low in the initial state, and the SR tube is switched off.
As a further improvement of the above technical solution, the synchronous rectification converter further includes:
the reference module is used for providing a preset reference voltage for the synchronous rectification converter, and the preset voltage is kept stable in a high-temperature area so as to enable the circuit to normally operate;
and the power supply module generates a voltage lower than the power supply voltage as the power supply voltage of the circuit when the voltage of the external circuit is not established.
As a further improvement of the above technical solution, the synchronous rectification converter further includes:
the driving module is used for providing driving current to rapidly start the SR tube by using a push-pull structure of a pull-up PMOS and a pull-down NMOS to the SR tube;
and the output module is used for detecting the overshoot or undershoot condition of the output voltage and controlling the overshoot or undershoot condition.
As a further improvement of the above technical solution, the operation process of the synchronous rectification converter includes:
after the system is started to work and before the power supply voltage is formally established, the parasitic diode in the SR tube realizes rectification;
with the gradual operation of the system, the power voltage is increased to a critical value, the synchronous rectification converter starts to be powered on and starts a synchronous rectification mode, and when the T1 timing is ended, if the system detects Vds<-350mV, making the SR tube conductive;
after the SR tube is conducted, the shutdown of the SR tube is subjected to error shutdown detection, and the system shuts down the SR tube after T2 timing is finished;
in the synchronous rectification process, if the power supply voltage is detected to be reduced to the turn-off voltage of the protection module, the system will disconnect the SR tube, at the moment, the parasitic body diode replaces the SR tube to finish rectification, the system returns to the synchronous rectification mode after knowing that the direct-current power supply voltage is increased to the turn-on voltage of the protection module.
As a further improvement of the above technical solution, when the secondary side inductance current of the transformer flows through zero, the current detection unit generates a trigger signal and turns off the rectifying MOS transistor, thereby suppressing the generation of reverse circulation current.
As a further improvement of the technical scheme, the timing time of the SR tube starts from VdsThe voltage value reaches the conduction threshold value for the first timeAnd when the voltage V1 is pressed, determining that the T1 is the minimum on-time, judging that the switching signal detected in the T1 time period is not valid, and after the timing is finished, enabling the switching signal to reach the driving stage to control the SR tube and conducting or shutting off the SR tube.
As a further improvement of the technical scheme, when the SR tube is in a turn-off state, VdsWhen the surge voltage generates a false trigger signal, the shutdown module judges the validity of the surge voltage;
if the signal is detected as invalid, the shutdown operation is not performed, and if the voltage signal V is detected as invalidds<350mV is judged as invalid, and the grid GATE keeps a low level state before the time T2 is timed out;
when the timing time is over, the GATE is waken up to high level from the locking state, and the system starts normal switching action.
Compared with the prior art, the invention provides a synchronous rectification converter, which has the following beneficial effects:
the comparison module, the conduction module, the turn-off module, the protection module and the control module are sequentially connected, and the conduction module is used for avoiding that the SR tube is based on the drain-source voltage V at the starting moment after the SR tube is starteddsSetting a minimum on-time T1 for a false trigger signal generated by fluctuation, forbidding the SR tube to be turned off in the time T1, and turning off the module when the drain-source voltage V is detecteddsWhen the voltage is negative, the comparator judges that the SR tube is resonance of DCM dead time or conduction rectification of the SR tube, and generates a shielding signal T2 to prevent the comparator from turning over to trigger the SR tube to be turned on in the dead time, and the normal and reliable operation of the SR tube is ensured by adopting a timing mode of the conduction module and the turn-off module, so that the working efficiency of the synchronous rectification converter is improved. The protection module is internally provided with a current detection unit, a voltage amplification unit, a phase advancing unit, a zero point comparison unit and an optical coupling isolation unit, the control module allows the rectifier tube to be conducted reversely when detecting that an inductive current signal is reduced from the positive direction and begins to be negative reversely, the drive module allows the rectifier tube to be conducted reversely, the energy of the circulating part is fully recovered through multiple LC resonances, one part of the energy is fed back to an input power supply, the other part of the energy is transmitted to the output module through the second opening of the rectifier tube in a uniform period, and the current detection unit, the voltage amplification unit, the phase advancing unit, the zero point comparison unit and the optical coupling isolation unit are arranged in the circuitThe circulating current energy is recycled without loss, so that the circuit structure is simplified, the circulating current problem can be solved, the energy consumption is reduced, and the working stability of the synchronous rectification converter is improved.
Drawings
In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings needed to be used in the embodiments will be briefly described below, it should be understood that the following drawings only illustrate some embodiments of the present invention and therefore should not be considered as limiting the scope, and for those skilled in the art, other related drawings can be obtained according to the drawings without inventive efforts.
Fig. 1 is a block diagram of a synchronous rectification converter according to an embodiment of the present invention;
fig. 2 is a circuit diagram of a synchronous rectification converter according to an embodiment of the present invention;
fig. 3 is a circuit diagram of a protection module according to an embodiment of the present invention;
fig. 4 is a flowchart of the operation of the synchronous rectification converter according to the embodiment of the present invention.
The main element symbols are as follows:
10-a synchronous rectifier converter; 11-a comparison module; 12-a conducting module; 13-a shut-down module; 14-a protection module; 141-a current detection unit; 142-a voltage amplification unit; 143-a phase advancing unit; 144-zero comparison unit; 145-optical coupling isolation unit; 15-a control module; 16-a reference module; 17-a power supply module; 18-a drive module; 19-output module.
Detailed Description
Reference will now be made in detail to embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein like or similar reference numerals refer to the same or similar elements or elements having the same or similar function throughout. The embodiments described below with reference to the accompanying drawings are illustrative only for the purpose of explaining the present invention, and are not to be construed as limiting the present invention.
It will be understood that when an element is referred to as being "secured to" another element, it can be directly on the other element or intervening elements may also be present. When an element is referred to as being "connected" to another element, it can be directly connected to the other element or intervening elements may also be present. In contrast, when an element is referred to as being "directly on" another element, there are no intervening elements present. The terms "vertical," "horizontal," "left," "right," and the like as used herein are for illustrative purposes only.
In the present invention, unless otherwise expressly stated or limited, the terms "mounted," "connected," "secured," and the like are to be construed broadly and can, for example, be fixedly connected, detachably connected, or integrally formed; can be mechanically or electrically connected; either directly or indirectly through intervening media, either internally or in any other relationship. The specific meanings of the above terms in the present invention can be understood by those skilled in the art according to specific situations.
Referring to fig. 1, 2 and 3, the present invention provides a synchronous rectification converter 10, including:
a comparison module 11 including two comparators for generating an on signal and an off signal for the drain-source voltage V by setting different flip threshold voltages to the comparators, respectivelydsSampling the changes in (a);
the conduction module 12 is used for avoiding that the SR tube is based on the drain-source voltage V at the starting moment after the SR tube is starteddsA false trigger signal generated by fluctuation sets a minimum conduction time T1, and the SR tube is forbidden to be switched off within the time T1;
a shutdown module 13 for shutting down the power supply when the drain-source voltage V is detecteddsWhen the voltage is negative, the comparator judges that the SR tube is resonance of DCM dead time or conduction rectification of the SR tube, and generates a shielding signal T2 to prevent the comparator from turning over to trigger the SR tube to be turned on in the dead time;
the protection module 14 starts a protection action cut-off circuit to work when the voltage is reduced to a critical working voltage, the protection module 14 comprises a current detection unit 141, a voltage amplification unit 142, a phase shift unit 143, a zero point comparison unit 144 and an optical coupling isolation unit 145, the current detection unit 141 comprises a current transformer CT and a resistor R1, high-frequency resonant current of an output capacitor and a transformer secondary inductor is sampled by the current transformer CT and then induced to a secondary side, and the current of the secondary side generates a corresponding voltage drop on the resistor R1 and is output to a next unit; the voltage amplifying unit 142 comprises an operational amplifier OPA1, a resistor R2 and a resistor R3, wherein the positive phase end of the operational amplifier OPA1 is grounded, the negative phase end is connected to the output voltage of the current detection module through the resistor R2, a resistor R3 is connected between the output end and the negative phase end of the operational amplifier OPA1, the operational amplifier amplifies the output voltage of the current transformer in the previous unit, the ratio of the R2 to the R3 is the voltage amplification factor, and the input voltage signal is reversely converted; the phase shifting unit 143 includes an operational amplifier OPA2, a resistor R4, a resistor R5, an adjustable resistor R6 and a capacitor C1, an input signal is input from a positive phase end of the remote amplifier OPA2, the resistor R4, the resistor R5 and the capacitor C1 are connected in series and grounded and then connected to a negative end of the OPA2, the resistor R6 is added between the output ends of the R5 and the OPA2, and the R6 is used for adjusting the phase shifting time; the zero point comparison unit 144 includes a comparator COM and a resistor R7, the adjusted phase advance signal is connected to the positive phase terminal of the comparator COM through the resistor R7, the negative phase terminal of the COM is grounded, the signal at the positive phase terminal is compared with the zero voltage, and the input resonant current is converted into a square wave signal; the optical coupling isolation unit 145 comprises an optical coupler OPT, a current limiting resistor R8 and a pull-up resistor R9, a square wave signal is connected to the light emitting side of the optical coupler OPT through a resistor R8, a current limiting protection diode R8 outputs a current signal at the triode side of the OPT, and the current signal is connected to the control module 15 to become a trigger signal of the reverse moment of the secondary current in synchronous rectification;
the control module 15 processes the shielding signals T2 and T1 generated by the turn-on module 12 and the turn-off module 13, determines whether to start a new synchronous rectification cycle, and assigns an initial state to the driving circuit, wherein the SR gate driving voltage of the rectification switch tube is low and the SR tube is turned off in the initial state.
In this embodiment, synchronous rectifier converter 10 is used on the secondary side of a switching converter by generating a standard level or logic level signalThe N-channel power MOS tube is driven to realize a rectification function and is applied to an isolation switch power supply with low-voltage output. When the primary side main switch tube SW of the transformer is opened, the primary side inductor stores energy, the SR tube is switched off by the control module 15 at the moment, and the capacitor C0Providing energy to the load. When the SW is switched off, the voltage at the synonym end of the primary winding can be quickly reduced to zero, at the same time, the voltage at the synonym end of the secondary winding, namely the drain voltage of the SR tube is also quickly reduced, and when the drain voltage is reduced to be less than the source voltage of the SR tube, the parasitic body diode of the SR tube is conducted to supply the capacitor C0And (6) charging. The control module 15 monitors the change of the drain-source voltage of the SR tube caused before and after the SW switch through the VD end to generate a driving signal, and controls the SR tube to be switched on or switched off. The synchronous rectification converter 10 further includes a reference module 16 and a power supply module 17, the reference module 16 provides a preset reference voltage for the synchronous rectification converter 10, and the preset voltage is maintained stable in a high temperature region, so that the circuit operates normally, and the power supply module 17 generates a voltage lower than the power supply voltage as the power supply voltage of the circuit when the voltage of the external circuit is not established. The synchronous rectification converter 10 further includes a driving module 18 and an output module 19, the driving module 18 is a push-pull structure using a pull-up PMOS and a pull-down NMOS to the SR transistor to provide a driving current to rapidly turn on the SR transistor, and the output module 19 is configured to detect and control an overshoot or undershoot condition of the output voltage.
It should be noted that the comparing module 11 adopts a two-comparator structure, and compares the voltages of the turn-on signal and the turn-off signal to achieve the drain-source voltage VdsVarying the purpose of accurate sampling. The conduction module 12 is a minimum conduction time module, and can well avoid the leakage-source voltage V of the SR tube at the moment of starting the SR tube after the SR tube is starteddsThe minimum conduction time T1 is set, and the SR is prohibited from being turned off in the time T1, so that the SR tube can work safely and reliably in one period. The turn-off module 13 is a minimum turn-off time module, i.e., a false turn-on detection module, and generates a shielding signal T2 to prevent the SR tube from being turned on due to false triggering caused by comparator flipping during dead time. The reference module 16 is a band-gap reference module, and provides a reference voltage of 1.2V for the whole chip, and the voltage is in a high-temperature regionThe domain can be maintained stable so that the circuit can operate normally. R6 in the phase advancing unit 143 is an adjustable resistor for adjusting the advancing time of the phase when R6When the resistance value of the rectifier MOS is increased, the forward displacement of the phase is correspondingly increased, otherwise, the smaller the forward displacement of the phase is, the adjusting time is influenced by the delay time of the driving module, the SR tube and the control module 15, and the switching state of the rectifier MOS is ensured to be changed at the moment when the resonant current crosses zero after the adjusting time. The MOS has bidirectional conductivity, so that when the synchronous rectification converter uses synchronous rectification, when the load current gradually decreases, the synchronous rectification converter cannot enter DCM autonomously, but will be conducted reversely, so that the circuit enters a forced continuous operation mode FCCM, and the driving control mode is to control the gate driving voltage of the rectifier SR by using a suitable control module 15, so that the rectifier SR is turned off before entering the FCCM mode, and the generation of reverse circulation current can be suppressed.
It should be understood that the MOS in the SR transistor is a high voltage-withstanding MOS, and the diode connected to the source of the MOS transistor is a low voltage-withstanding schottky diode, which makes the circuit have better forward conduction characteristics. When the system is subjected to synchronous rectification, loss can be obviously reduced under the condition of heavy load, but reverse circulation problem is caused due to bidirectional conductivity of the MOS tube under the condition of light load, circulation loss is generated, additional loss caused when the system is applied to heavy load is partial loss of the rectification MOS tube, and additional reverse circulation loss is caused under the condition of light load. The control loop current suppression circuit of the protection module 14 can more accurately detect the time when the secondary current of the transformer drops to zero and timely turn off the rectifier tube to prevent reverse loop current from being generated, so that the circuit can be effectively simplified and the integration level of a chip can be improved.
Referring to fig. 4, optionally, the operation of the synchronous rectification converter includes:
s1: after the system is started to work and before the power supply voltage is formally established, the parasitic diode in the SR tube realizes rectification;
s2: with the gradual operation of the system, the power voltage is increased to a critical value, the synchronous rectification converter starts to be powered on and starts a synchronous rectification mode, and when the T1 timing is ended, if the system detects Vds<-350mV, making the SR tube conductive;
s3: after the SR tube is conducted, the shutdown of the SR tube is subjected to error shutdown detection, and the system shuts down the SR tube after T2 timing is finished;
s4: in the synchronous rectification process, if the power supply voltage is detected to be reduced to the turn-off voltage of the protection module, the system will disconnect the SR tube, at the moment, the parasitic body diode replaces the SR tube to finish rectification, the system returns to the synchronous rectification mode after knowing that the direct-current power supply voltage is increased to the turn-on voltage of the protection module.
In this embodiment, the circuit directly samples the drain-source voltage V of the SR tube through the VD enddsWhen the secondary demagnetization of the transformer begins, the current on the secondary side flows through the body diode, and the voltage VdsWill drop to about-700 mV, which is below the turn-on threshold voltage V1 of the SR tube, i.e., -350mV, and if this negative voltage is detected at terminal D, the driving output voltage V0 is pulled high, turning on the SR tube after a delay time of about 100 ns. After the SR tube is turned on, a minimum on-time of T1 of 1.9 μ s is set to shield the false turn-off signal caused by the secondary side high frequency oscillation. As the transformer continues to demagnetize, the drain voltage continues to rise, and when the drain voltage rises to a value above-5 mV of the SR transistor turn-off threshold voltage V2, zero current is detected, and at this time, the driving voltage V0 is pulled down to the ground quickly, turning off the SR transistor quickly within a short delay time of about 75ns at T2.
When the secondary side inductance current of the transformer flows through zero, the current detection unit generates a trigger signal to cut off the rectifying MOS transistor, thereby suppressing the generation of reverse circulation. The timing time of the SR tube starts from VdsWhen the voltage value reaches a turn-on threshold voltage V1 for the first time, determining T1 as the minimum turn-on time, determining that the switching signal detected in the time period T1 cannot be determined to be valid, and after the timing is finished, enabling the switching signal to reach a driving stage to control the SR tube and conducting or turning off the SR tube. When the SR tube is in OFF state, VdsIs falsely triggered when surge voltage occursThe signal is judged by the turn-off module for effectiveness; if the signal is detected as invalid, the shutdown operation is not performed, and if the voltage signal V is detected as invalidds<350mV is judged as invalid, and the grid GATE keeps a low level state before the time T2 is timed out; when the timing time is over, the GATE is waken up to high level from the locking state, and the system starts normal switching action.
It should be understood that when V is detecteddsWhen the electric tower is lowered to the conduction threshold voltage of the SR tube, the SR tube is driven to be conducted, the parasitic body diode is short-circuited, the secondary side current passes through the SR tube to form a loop and is gradually reduced, and when the secondary side inductive current is lowered, the corresponding V isdsThe voltage will increase linearly in the pair VdsWhen detection is carried out, the SR tube can be disconnected after the value exceeds the disconnection threshold voltage, the inductive current under the threshold voltage is close to a zero value, and when or after the SR tube is disconnected, a smaller secondary side current passes through the body diode, the conduction of the SR tube continues to flow continuously until the secondary side inductive current is attenuated to the zero value, the corresponding body diode is cut off after the secondary side inductive current is reduced to the zero value, and the corresponding V corresponds to the VdsThe voltage begins to ring. The conduction module and the turn-off module ensure that the SR tube does not have multiple times of wrong turn-on or turn-off operations in a rectification period, and the reliability of the system can be improved.
The invention provides a synchronous rectification converter, which is characterized in that a comparison module, a conduction module, a turn-off module, a protection module and a control module are sequentially connected, and the conduction module is used for avoiding that an SR (thyristor) is based on a drain-source voltage V at the starting moment of the SR after the SR is starteddsSetting a minimum on-time T1 for a false trigger signal generated by fluctuation, forbidding the SR tube to be turned off in the time T1, and turning off the module when the drain-source voltage V is detecteddsWhen the voltage is negative, the comparator judges that the SR tube is resonance of DCM dead time or conduction rectification of the SR tube, and generates a shielding signal T2 to prevent the comparator from turning over to trigger the SR tube to be turned on in the dead time, and the normal and reliable operation of the SR tube is ensured by adopting a timing mode of the conduction module and the turn-off module, so that the working efficiency of the synchronous rectification converter is improved. The protection module is provided with a current detection unit, a voltage amplification unit and a phase frontThe circuit comprises a moving unit, a zero point comparison unit and an optical coupling isolation unit, wherein when the control module detects that an inductive current signal is reduced from the positive direction and begins to be negative in the reverse direction, the driving module allows the rectifier tube to be conducted in the reverse direction, the energy of the circulating current part is fully recovered through multiple LC resonances, one part of the energy is fed back to an input power supply, the other part of the energy is transmitted to the output module through the second starting of the rectifier tube in a unified period, the circulating current energy in the circuit is not lost and is recycled, the circuit structure is simplified, the circulating current problem can be solved, the energy consumption is reduced, the working stability of the synchronous rectification converter is improved, and the hardware cost is reduced.
In all examples shown and described herein, any particular value should be construed as merely exemplary, and not as a limitation, and thus other examples of example embodiments may have different values.
It should be noted that: like reference numbers and letters refer to like items in the following figures, and thus, once an item is defined in one figure, it need not be further defined and explained in subsequent figures.
The above examples are merely illustrative of several embodiments of the present invention, and the description thereof is more specific and detailed, but not to be construed as limiting the scope of the invention. It should be noted that, for a person skilled in the art, several variations and modifications can be made without departing from the inventive concept, which falls within the scope of the present invention.

Claims (7)

1. A synchronous rectifier converter, comprising:
a comparison module including two comparators for generating an on signal and an off signal for a drain-source voltage V by setting different flip threshold voltages to the comparators, respectivelydsSampling the changes in (a);
the conduction module is used for avoiding that the SR tube is based on the drain-source voltage V at the starting moment after the SR tube is starteddsSetting a minimum conduction time T1 for false triggering signals generated by fluctuation, and forbidding the SR tube in the time T1Turning off;
a turn-off module for turning off the power supply when the drain-source voltage V is detecteddsWhen the voltage is negative, the comparator judges that the SR tube is resonance of DCM dead time or conduction rectification of the SR tube, and generates a shielding signal T2 to prevent the comparator from turning over to trigger the SR tube to be turned on in the dead time;
the protection module starts a protection action cut-off circuit to work when the voltage is reduced to critical working voltage, the protection module comprises a current detection unit, a voltage amplification unit, a phase forward-shift unit, a zero comparison unit and an optical coupling isolation unit, the current detection unit comprises a current transformer CT and a resistor R1, high-frequency resonant current of an output capacitor and a transformer secondary inductor is sampled by the current transformer CT and then induced to a secondary side, and the current of the secondary side generates corresponding voltage drop on a resistor R1 and is output to the next unit; the voltage amplification unit comprises an operational amplifier OPA1, a resistor R2 and a resistor R3, wherein the positive phase end of the operational amplifier OPA1 is grounded, the negative phase end of the operational amplifier OPA1 is connected with the output voltage of the current detection module through the resistor R2, a resistor R3 is connected between the output end and the reverse phase end of the operational amplifier OPA1, the operational amplifier amplifies the output voltage of a current transformer in the previous unit, the ratio of the R2 to the R3 is a voltage amplification factor, and the input voltage signal is subjected to reverse transformation; the phase shifting unit comprises an operational amplifier OPA2, a resistor R4, a resistor R5, an adjustable resistor R6 and a capacitor C1, an input signal is input from the positive phase end of a remote amplifier OPA2, the resistor R4, the resistor R5 and the capacitor C1 are connected in series and then are connected to the negative end of an OPA2, the resistor R6 is added between the output end of the R5 and the output end of the OPA2, and the R6 is used for adjusting the phase shifting time; the zero point comparison unit comprises a comparator COM and a resistor R7, the adjusted phase advancing signal is accessed to a positive-phase end of the comparator COM through the resistor R7, a negative-phase end of the COM is grounded, the signal of the positive-phase end is compared with zero voltage, and the input resonant current is converted into a square wave signal; the optical coupling isolation unit comprises an optical coupler OPT, a current limiting resistor R8 and a pull-up resistor R9, a square wave signal is connected to the light emitting side of the optical coupler OPT through a resistor R8, a current limiting protection diode R8 outputs a current signal at the triode side of the OPT, and the current signal is connected to the control module to become a trigger signal of the reverse moment of the secondary current in synchronous rectification;
and the control module is used for processing the shielding signals T2 and T1 generated by the switch-on module and the switch-off module, judging whether a new synchronous rectification cycle is started or not, and endowing the driving circuit with an initial state, wherein the SR gate driving voltage of the rectification switch tube is low in the initial state, and the SR tube is switched off.
2. The synchronous rectified converter according to claim 1, further comprising:
the reference module is used for providing a preset reference voltage for the synchronous rectification converter, and the preset voltage is kept stable in a high-temperature area so as to enable the circuit to normally operate;
and the power supply module generates a voltage lower than the power supply voltage as the power supply voltage of the circuit when the voltage of the external circuit is not established.
3. The synchronous rectified converter according to claim 1, further comprising:
the driving module is used for providing driving current to rapidly start the SR tube by using a push-pull structure of a pull-up PMOS and a pull-down NMOS to the SR tube;
and the output module is used for detecting the overshoot or undershoot condition of the output voltage and controlling the overshoot or undershoot condition.
4. The synchronous rectification converter according to claim 1, wherein the operation of the synchronous rectification converter comprises:
after the system is started to work and before the power supply voltage is formally established, the parasitic diode in the SR tube realizes rectification;
with the gradual operation of the system, the power voltage is increased to a critical value, the synchronous rectification converter starts to be powered on and starts a synchronous rectification mode, and when the T1 timing is ended, if the system detects Vds<-350mV, making the SR tube conductive;
after the SR tube is conducted, the shutdown of the SR tube is subjected to error shutdown detection, and the system shuts down the SR tube after T2 timing is finished;
in the synchronous rectification process, if the power supply voltage is detected to be reduced to the turn-off voltage of the protection module, the system will disconnect the SR tube, at the moment, the parasitic body diode replaces the SR tube to finish rectification, the system returns to the synchronous rectification mode after knowing that the direct-current power supply voltage is increased to the turn-on voltage of the protection module.
5. The synchronous rectification converter according to claim 1, wherein when the secondary side inductance current of the transformer flows through zero, the current detection unit generates a trigger signal and turns off the rectification MOS transistor, thereby suppressing the generation of reverse circulation current.
6. The synchronous rectification converter of claim 1 wherein the SR tube is clocked starting at VdsWhen the voltage value reaches a turn-on threshold voltage V1 for the first time, determining T1 as the minimum turn-on time, determining that the switching signal detected in the time period T1 cannot be determined to be valid, and after the timing is finished, enabling the switching signal to reach a driving stage to control the SR tube and conducting or turning off the SR tube.
7. The synchronous rectification converter of claim 1 wherein when the SR transistor is off, VdsWhen the surge voltage generates a false trigger signal, the shutdown module judges the validity of the surge voltage;
if the signal is detected as invalid, the shutdown operation is not performed, and if the voltage signal V is detected as invalidds<350mV is judged as invalid, and the grid GATE keeps a low level state before the time T2 is timed out;
when the timing time is over, the GATE is waken up to high level from the locking state, and the system starts normal switching action.
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