CN113804945B - Current detection circuit, detection method and control method for synchronous rectification in high-frequency LLC (logical Link control) - Google Patents

Current detection circuit, detection method and control method for synchronous rectification in high-frequency LLC (logical Link control) Download PDF

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CN113804945B
CN113804945B CN202111094177.9A CN202111094177A CN113804945B CN 113804945 B CN113804945 B CN 113804945B CN 202111094177 A CN202111094177 A CN 202111094177A CN 113804945 B CN113804945 B CN 113804945B
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current
current transformer
capacitor
voltage
llc
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CN113804945A (en
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魏高昊
王康平
杨旭
魏吉文
吴佳芮
陈乔梁
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Longteng Semiconductor Co ltd
Xian Jiaotong University
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Longteng Semiconductor Co ltd
Xian Jiaotong University
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R19/00—Arrangements for measuring currents or voltages or for indicating presence or sign thereof
    • G01R19/0092—Arrangements for measuring currents or voltages or for indicating presence or sign thereof measuring current 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
    • 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
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02B—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO BUILDINGS, e.g. HOUSING, HOUSE APPLIANCES OR RELATED END-USER APPLICATIONS
    • Y02B70/00—Technologies for an efficient end-user side electric power management and consumption
    • Y02B70/10—Technologies improving the efficiency by using switched-mode power supplies [SMPS], i.e. efficient power electronics conversion e.g. power factor correction or reduction of losses in power supplies or efficient standby modes

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Abstract

The invention discloses a current detection circuit, a detection method and a control method for synchronous rectification in a high-frequency LLC (logical Link control), and a resistor R1One end of each of which is connected to a resistor R2Is connected to one end of a capacitor C, a resistor R1The other end of the current transformer and the current transformer CT1Is connected with the same name end of the current transformer CT1The different name end of the capacitor C is respectively connected with the other end of the capacitor C and the current transformer CT2Is connected with the same name end of the current transformer CT2The synonym terminal and the resistor R2The other end of the first and second connecting rods is connected; current transformer CT1Resonant inductor L for use in high frequency LLCrIs connected with the magnetic core of the current transformer CT1End of same name and resonant inductor LrThe same-name ends of the two groups are positioned at the same side; current transformer CT2Excitation inductor L used in high-frequency LLCmIs connected with the magnetic core of the current transformer CT2End of same name and excitation inductance LmAre located on the same side. The method is suitable for cycle-by-cycle synchronous rectification control of the LLC resonant converter under the condition of high frequency and large current.

Description

Current detection circuit, detection method and control method for synchronous rectification in high-frequency LLC (logical Link control)
Technical Field
The invention belongs to the technical field of power electronics, and particularly relates to a current detection circuit, a detection method and a control method for synchronous rectification in a high-frequency LLC.
Background
The application of the synchronous rectification technology can further reduce the loss of synchronous rectification and improve the overall efficiency, and is particularly important in the scenes of low output voltage and large output current. The on-time and off-time of the synchronous rectification need to be precisely controlled. However, for a high switching frequency, large output current LLC resonant converter, accurate control of the on-time and off-time of synchronous rectification is a very difficult problem.
The currently popular synchronous rectification control methods mainly include: firstly, based on a method for detecting the current of a synchronous tube; second, a method for controlling the turn-on time of a diode based on a synchronous body. For the first method, a current transformer, a rogowski coil, a hall sensor, etc. are generally used to detect the current of the synchronous tube, and this detection method needs to be connected in series in a circuit or wound on a conducting wire, which will result in an increase in leakage inductance and resistance of the secondary side of the transformer, and an increase in voltage spike and power loss of the secondary side of the transformer, which is not favorable for achieving high efficiency and high reliability. With respect to the second method, since this method is not a cycle-by-cycle control method, during complex transient processes such as sudden load change, soft start, short circuit, etc., the synchronous rectification control signal needs to be carefully adjusted and checked, which is time-consuming and increases the complexity of control.
Disclosure of Invention
Aiming at the problems in the prior art, the invention provides a current detection circuit, a detection method and a control method for synchronous rectification in a high-frequency LLC, which can detect the resonant current and the exciting current in the high-frequency LLC resonant converter under the condition of less passive devices so as to obtain the synchronous rectification current and are suitable for cycle-by-cycle synchronous rectification control of the LLC resonant converter under the condition of high-frequency large current.
In order to solve the technical problems, the invention is realized by the following technical scheme:
a current detection circuit for synchronous rectification in high frequency LLC comprises a resistor R1Resistance R2Capacitor C and current transformer CT1And current transformer CT2Said resistance R1One end of each of the resistors R2And at one end ofOne end of the capacitor C is connected, and the resistor R1And the other end of the current transformer CT1Is connected with the same name end of the current transformer CT1The different name end of the capacitor C is respectively connected with the other end of the capacitor C and the current transformer CT2Is connected with the same name end of the current transformer CT2And the resistor R2The other end of the first and second connecting rods is connected; the current transformer CT1Resonant inductor L for use in high frequency LLCrIs connected with the magnetic core of the current transformer CT1And the resonant inductor LrThe same-name ends of the two groups are positioned at the same side; the current transformer CT2Excitation inductor L used in high-frequency LLCmIs connected with the magnetic core of the current transformer CT2End of same name as the excitation inductor LmThe synonyms of (a) are located on the same side.
Further, note: the resonant inductor LrAnd the current transformer CT1Has a ratio of N turns11, preparing a catalyst; the excitation inductance LmAnd the current transformer CT2Has a ratio of N turns2:1；
Then
Figure BDA0003268481940000021
Further, the current transformer CT1Resonant inductor L in high frequency LLCrThe magnetic cores of the current transformer CT are connected by magnetic coupling2And excitation inductance L in high-frequency LLCmThe magnetic cores of (1) are connected by magnetic coupling.
Further, the resistor R1And the resistance R shown2Is in the kiloohm range.
A current detection method for synchronous rectification in a high-frequency LLC adopts the detection circuit to detect, and comprises the following steps:
the current transformer CT1Resonant inductor L in high-frequency LLCrIs connected with the magnetic core of the current transformer CT2And heightExcitation inductance L in frequency LLCmThe magnetic core of (2) is connected;
then the process of the first step is carried out,
Figure BDA0003268481940000022
wherein,
ISR＝N2(ILr-ILm)
in the formula ILrFor flowing through the resonant inductor LrThe current of (a); i isLmFor flowing through the excitation inductance LmThe current of (a); vsIs the voltage across the capacitor C; n is a radical of11 is the resonant inductor LrAnd the current transformer CT1The ratio of the number of turns of (c); n is a radical of21 is the excitation inductance LmAnd the current transformer CT2The ratio of the number of turns of (c); I.C. ASRFor synchronous rectified current in a high frequency LLC.
Further, the voltage V at two ends of the capacitor C is adjustedsAnd obtaining direct current voltage after rectification and filtration, and detecting the output current of the high-frequency LLC by using the direct current voltage.
A control method for synchronous rectification in a high-frequency LLC (logical Link control), based on the voltage V at two ends of a capacitor C obtained by the current detection methodsAnd performing control, including:
the voltage V at two ends of the capacitor CsRespectively comparing the voltage with a preset positive voltage threshold value and a preset negative voltage threshold value;
when the voltage V across the capacitor CsWhen the voltage is larger than the positive voltage threshold value, the synchronous tube SR in the high-frequency LLC is controlled2Drive signal V ofgsSR2Outputting a positive level;
when the voltage V at both ends of the capacitor CsWhen the voltage is less than the negative voltage threshold value, the synchronous tube SR in the high-frequency LLC is controlled1Drive signal V ofgsSR1A positive level is output.
Furthermore, by reducing the amplitude of the preset positive voltage threshold, the synchronous tube SR in the high-frequency LLC is realized2Drive signal V ofgsSR2Output the outputThe duration of the positive level increases; by increasing the amplitude of a preset negative voltage threshold, the synchronous tube SR in the high-frequency LLC is realized1Drive signal V ofgsSR1The duration of the output positive level increases.
Further, still include: by reducing the resistance R2Change the voltage V across the capacitor CsThereby reducing the synchronous tube SR1Actual on-time and synchronous tube SR1Drive signal V ofgsSR1Time difference of positive level time, and reducing synchronous tube SR2Actual on-time and synchronous tube SR2Drive signal V ofgsSR2Time difference of positive level time.
Compared with the prior art, the invention has at least the following beneficial effects: the invention provides a current detection circuit for synchronous rectification in a high-frequency LLC resonant converter, which is applied as follows:
(1) compared with the traditional synchronous rectification control method of the LLC resonant converter, the synchronous rectification control method of the LLC resonant converter has higher bandwidth, has higher accuracy and advantages when detecting the current of the converter with higher frequency, and has stronger anti-interference capability under the scenes of low output voltage and large output current. Therefore, the method is more suitable for the LLC resonant converter with high switching frequency and large output current, and the synchronous rectification control method of the LLC resonant converter provided by the invention is a cycle-by-cycle synchronous rectification control method; the method can detect the resonant current and the exciting current in the high-frequency LLC resonant converter under the condition of fewer passive devices, thereby obtaining the synchronous rectification current, and is suitable for cycle-by-cycle synchronous rectification control of the LLC resonant converter under the condition of high-frequency large current.
(2) In the detection circuit of the present invention, the resistor R1And R2Is in the order of kiloohms, which allows a flow through the resistor R with a fixed gain L/NRC1And R2The current of (2) is very small, the loss in the detection circuit is very low, and the influence on the efficiency of the high-power density converter can be ignored;
(3) the invention aims at the drive delay of synchronous rectification and can reduce R2To compensate for synchronous rectificationThe driving delay improves the accuracy of synchronous rectification and the efficiency of the circuit at the synchronous rectification position;
(4) the invention detects the voltage V at two ends of the capacitor C in the circuitsAfter rectification and filtering, the output current can be further calculated, and subsequent current sampling can be carried out through the output current.
In order to make the aforementioned and other objects, features and advantages of the present invention comprehensible, preferred embodiments accompanied with figures are described in detail below.
Drawings
In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings used in the description of the embodiments will be briefly introduced below, and it is obvious that the drawings in the following description are some embodiments of the present invention, and it is obvious for those skilled in the art that other drawings can be obtained according to the drawings without creative efforts.
FIG. 1 is a topological diagram of an LLC resonant circuit of the current detection circuit for synchronous rectification in a high frequency LLC according to the invention;
FIG. 2 is a schematic diagram of a single turn detection coil of the current detection circuit for synchronous rectification in high frequency LLC according to the invention;
FIG. 3 is a graph showing the amplitude-frequency and phase-frequency characteristics of the current detection circuit for synchronous rectification in high frequency LLC according to the invention;
FIG. 4 is a connection mode of the current detection circuit for synchronous rectification in high frequency LLC according to the invention;
FIG. 5 is a graph of the relationship between the output current signal and the output current obtained in the current detection circuit for synchronous rectification in high frequency LLC according to the invention;
FIG. 6 is a diagram of the voltage V across the capacitor C in the current detection circuit for synchronous rectification in high frequency LLC according to the inventionsObtaining a schematic diagram of a driving signal of a synchronous tube;
FIG. 7 is a compensation waveform for the synchronous rectification delay of the current sense circuit for synchronous rectification in high frequency LLC according to the invention;
FIG. 8 is the present inventionThe current detection method for synchronous rectification in the high-frequency LLC measures the resonance current ILrAnd measuring the resonant current I using a capacitive shunt methodLrA waveform to be compared;
FIG. 9 shows the measured resonance current I using the method proposed by the present inventionLrExciting current ILmAnd a synchronous rectified current ISRThe waveform of (a);
fig. 10 is a waveform of a current signal detected by the current detection method of synchronous rectification proposed by the present invention controlling synchronous rectification in an actual circuit.
Detailed Description
To make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings, and it is apparent that the described embodiments are some, but not all embodiments of the present invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
As shown in FIG. 1, the present invention provides a current detection circuit for synchronous rectification in a high frequency LLC resonant converter, which comprises a resistor R1Resistance R2Capacitor C and current transformer CT1And current transformer CT2Resistance R1One end of each of which is connected to a resistor R2Is connected to one end of a capacitor C, a resistor R1And the other end of the current transformer CT1Is connected with the same name end of the current transformer CT1The different name end of the capacitor C is respectively connected with the other end of the capacitor C and the current transformer CT2Is connected with the same name end of the current transformer CT2The synonym terminal and the resistor R2The other end of the connecting rod is connected; current transformer CT1Resonant inductor L for resonant converter with high frequency LLCrMagnetic core magnetic coupling connection of (2), and current transformer CT1End of same name and resonant inductor LrThe same-name ends of the two groups are positioned at the same side; current transformer CT2Excitation inductor L for resonant converter with high-frequency LLCmAre magnetically coupled to each other and are in current flow communication with each otherSensor CT2End of same name and excitation inductance LmThe synonyms of (a) are located on the same side.
Wherein, remember: resonant inductor LrTurn number of and current transformer CT1Has a ratio of N turns11, preparing a catalyst; excitation inductance LmTurn number of and current transformer CT2Has a ratio of N turns2:1；
Then
Figure BDA0003268481940000061
The circuit structure within the dashed box in fig. 1 is a circuit topology of a high frequency LLC resonant converter.
The invention discloses a method for detecting synchronous rectification current in a high-frequency LLC resonant converter, which is used for detection by using a detection circuit of the invention and specifically comprises the following steps:
current transformer CT1Resonant inductor L in resonant converter with high-frequency LLCrIs connected with the magnetic core of the current transformer CT2Excitation inductor L in resonant converter with high-frequency LLCmThe magnetic core of (2) is connected;
then the user can use the device to make a visual display,
Figure BDA0003268481940000062
wherein,
ISR＝N2(ILr-ILm)
in the formula ILrFor flowing through the resonant inductor LrThe current of (a); i isLmFor passing through the excitation inductance LmThe current of (a); vsIs the voltage across the capacitor C; n is a radical of11 is a resonant inductor LrTurn number of and current transformer CT1The ratio of the number of turns of (c); n is a radical of21 is an excitation inductor LmTurn number of and current transformer CT2The number of turns of (c); I.C. ASRThe current is rectified synchronously in the high frequency LLC resonant converter.
In order to facilitate a better understanding of the present disclosure, a more detailed explanation is provided below.
Fig. 2(a) shows a single turn detection coil schematic. Fig. 2(b) shows a schematic diagram of a simplified circuit of a single-turn detection coil. A single-turn detection coil is wound on the magnetic core of the inductor to form an N:1 transformer. N is the number of winding turns of the inductor. The resistor and the capacitor are connected in series on the detection coil. From FIG. 2(b), a detected current signal, i.e., the voltage V across the capacitor C, can be obtainedsThe expression of (a) is:
Figure BDA0003268481940000071
wherein due to Ls/N2R<<1, and 1/RCs<<1, Ls/N can be ignored2R and 1/RCs. Because G is VsI, so the expression for gain G can be derived from the above:
Figure BDA0003268481940000072
fig. 3 shows a graph of amplitude-frequency and phase-frequency characteristics of the proposed synchronous rectified current detection method. At a lower limit frequency of 1/2 pi RC and an upper limit frequency of N2Voltage V across capacitor C in the range of R/2 pi LsProportional to the inductor current and without phase difference between the two, as shown in fig. 3. It can be seen that the method has a very wide frequency range, suitable for applications in high frequency scenarios. In the inductor, L is the inductance value L of the resonant inductorr(ii) a In the transformer, L is the inductance value L of the transformer exciting inductancem。
By adopting the method, the resonant inductor current I can be respectively detectedLrAnd transformer exciting current ILm. Synchronous rectification current ISRIs the difference of N2And (4) doubling.
ISR＝N2(ILr-ILm)
Fig. 4 shows the connection mode of the detection circuit of the proposed synchronous rectification current detection method. By exchanging the terminals of the detection coil, eitherTo vary the voltage V across the capacitor CsOf (c) is used. The resonant current I is realized by connecting the circuits in the manner shown in FIG. 4LrAnd an excitation current ILmAnd can reduce the passive element capacitors by one. According to the circuit superposition theorem, the voltage V across the capacitor CsIs a resonant inductor current ILrAnd transformer exciting current ILmSum of excitation results of (a). The voltage V at two ends of the capacitor C can be obtainedsThe expression of (c):
Figure BDA0003268481940000081
by adjusting R1And R2A value of (a) can ensure that I in the above formulaLrAnd ILmAre equal, i.e. R1And R2The following relationship is satisfied:
Figure BDA0003268481940000082
when R is1And R2Satisfies the relationship of the above expression, then the voltage V across the capacitor CsWith synchronous rectification of current ISRAnd (4) in proportion.
Figure BDA0003268481940000083
As a preferred embodiment, FIG. 5 shows the voltage V across the capacitor CsAnd the output current IoThe relationship (2) of (c). The synchronous rectification current I can be known from the basic knowledge of the circuitSRThe average of the absolute values being equal to the output current IoI.e. avg (| I)SR|)＝Io. Thus, the voltage V across the capacitor C can be measuredsObtaining an output current I after correction and filteringoI.e. by pairing avg (| V)sI) to obtain an output current Io. Avg (| V) can be deriveds|)/Io＝avg(|G ISR/N2|)/Io＝G/N2. FIG. 9 shows k.avg (| V)sI) with IoCan be seen to have good linearity. k.avg (| V)s|)/IoThe slope of (d) is 0.016 and the calculated result k.G/N21.5 × 0.056/5 is close to 0.017. The coefficient k is V during correction and filteringsThe value of (a) is equal to 1.5. This further demonstrates the accuracy of the detection method.
A control method for synchronous rectification in a high-frequency LLC resonant converter is based on the voltage V at two ends of a capacitor C obtained by the current detection methodsThe control method specifically comprises the following steps:
as shown in FIG. 6(a), the voltage V across the capacitor C is measuredsRespectively comparing the voltage with a preset positive voltage threshold value and a preset negative voltage threshold value;
as shown in fig. 6(b), when the voltage V across the capacitor C is appliedsWhen the voltage is larger than the positive voltage threshold value, the synchronous tube SR in the high-frequency LLC resonant converter is controlled2Drive signal V ofgsSR2Outputting a positive level; when the voltage V across the capacitor CsWhen the voltage is smaller than a negative voltage threshold value, controlling a synchronous tube SR in the high-frequency LLC resonant converter1Drive signal V ofgsSR1A positive level is output.
As a preferred embodiment, the synchronous tube SR in the high-frequency LLC resonant converter is realized by reducing the amplitude of the preset positive voltage threshold2Drive signal V ofgsSR2The duration of the output positive level increases; by increasing the amplitude of a preset negative voltage threshold, the synchronous tube SR in the high-frequency LLC resonant converter is realized1Drive signal V ofgsSR1The duration of the output positive level increases.
As a preferred embodiment, the method further comprises: due to the drive delay in the circuit for a certain time, this will result in the actual on-time of the synchronous tube lagging behind the given time of the synchronous rectification control signal. In the present invention, by reducing the resistance R2Change the voltage V across the capacitor CsThereby reducing the synchronous tube SR1Actual on-time and synchronous tube SR1Drive signal V ofgsSR1Time difference of positive level, and reduced synchronizationTube SR2Actual on-time and synchronous tube SR2Drive signal V ofgsSR2Time difference of positive level. As shown in fig. 7, with R2The curve has a tendency to slope to the left, thereby causing the voltage V across the capacitor C to be reducedsThe waveform of (a) is shifted to the left to compensate for the drive delay.
Furthermore, if the detection coil is very close to the winding, the detection signal may be disturbed by a high dv/dt. At this time, a shielding layer may be added between the detection coil and the winding, and then the shielding layer is connected to a stable potential point. The shielding layer can bypass noise and prevent the detection signal from being interfered.
FIG. 8 shows the measurement of the resonant current I using a capacitive shunt methodLrThe resonant current I is measured by the current detection circuit, the detection method and the control method for synchronous rectification in the high-frequency LLCLrThe waveforms are compared. Respectively measuring and providing the resonant current I of the LLC resonant converter under three working conditions, namely that the switching frequency is less than the resonant frequency and equal to the resonant frequency and is greater than the resonant frequencyLrWaveform of (2) and resonant current I at a switching frequency of 600kHzLrThe waveform of (2).
FIG. 9 shows the measured resonance current I using the method proposed by the present inventionLrExciting current ILmAnd a synchronous rectified current ISR. Respectively measuring and providing the resonant current I of the LLC resonant converter under three working conditions, namely that the switching frequency is less than the resonant frequency, equal to the resonant frequency and greater than the resonant frequencyLrExciting current ILmAnd a synchronous rectified current ISRThe waveform of (2).
Fig. 10 shows waveforms of current signals detected by the current detection method of synchronous rectification proposed by the present invention to control synchronous rectification in an actual circuit. The synchronous rectification control signal is obtained by detecting the voltage V across the capacitor CsCompared with a preset threshold voltage. Meanwhile, in the case of a short circuit of the load, the switching frequency of the LLC resonant converter needs to be increased to limit the output current within a desired range. Under the working condition, the synchronous rectification control signal can still be goodIs given in (1).
Finally, it should be noted that: although the present invention has been described in detail with reference to the foregoing embodiments, it should be understood by those skilled in the art that the following descriptions are only illustrative and not restrictive, and that the scope of the present invention is not limited to the above embodiments: any person skilled in the art can modify or easily conceive the technical solutions described in the foregoing embodiments or equivalent substitutes for some technical features within the technical scope of the present disclosure; such modifications, changes or substitutions do not depart from the spirit and scope of the embodiments of the present invention, and they should be construed as being included therein. Therefore, the protection scope of the present invention shall be subject to the protection scope of the claims.

Claims (8)

1. A current detection circuit for synchronous rectification in a high-frequency LLC circuit is characterized by comprising a resistor R1Resistance R2Capacitor C and current transformer CT1And current transformer CT2Said resistance R1One end of each of the resistors R2Is connected to one end of the capacitor C, the resistor R1And the other end of the current transformer CT1Is connected with the same name end of the current transformer CT1The different name end of the capacitor C is respectively connected with the other end of the capacitor C and the current transformer CT2Is connected with the same name end of the current transformer CT2And the resistor R2The other end of the connecting rod is connected; the current transformer CT1Resonant inductor L for use in high frequency LLCrIs connected with the magnetic core of the current transformer CT1And the resonant inductor LrThe same-name ends of the two groups are positioned at the same side; the current transformer CT2Excitation inductor L used in high-frequency LLCmIs connected with the magnetic core of the current transformer CT2End of same name as the excitation inductor LmThe different named ends of the two groups are positioned at the same side;
the resistor R1And the resistance R shown2Is in the kiloohm range.
2. The current sense circuit of claim 1, wherein said current sense circuit further comprises: the resonant inductor LrAnd the current transformer CT1Has a ratio of N turns11, preparing a catalyst; the excitation inductance LmAnd the current transformer CT2Has a ratio of N turns2:1；
Then
Figure FDA0003623782010000011
3. The current detection circuit for synchronous rectification in high frequency LLC according to claim 1, wherein said current transformer CT1Resonant inductor L in high frequency LLCrThe magnetic cores of the two magnetic circuits are connected by magnetic coupling, and the current transformer CT2And excitation inductance L in high-frequency LLCmThe magnetic cores of (1) are connected by magnetic coupling.
4. A method for detecting a current of synchronous rectification in a high frequency LLC, wherein the detection is performed by the detection circuit of claim 1, comprising:
the current transformer CT1Resonant inductor L in high frequency LLCrIs connected with the magnetic core of the current transformer CT2And excitation inductance L in high-frequency LLCmThe magnetic core of (2) is connected;
then the process of the first step is carried out,
Figure FDA0003623782010000021
wherein,
ISR＝N2(ILr-ILm)
in the formula ILrFor flowing through the resonant inductor LrThe current of (a); i isLmFor flowing through the excitation inductance LmThe current of (a); vsIs the voltage across the capacitor C; n is a radical of11 is the resonant inductor LrAnd the current transformer CT1The ratio of the number of turns of (c); n is a radical of21 is the excitation inductance LmAnd the current transformer CT2The ratio of the number of turns of (c); i isSRFor synchronous rectified current in a high frequency LLC.
5. A method as claimed in claim 4, wherein the voltage V across the capacitor C is measuredsAnd obtaining direct current voltage after rectification and filtration, and detecting the output current of the high-frequency LLC by using the direct current voltage.
6. A control method of synchronous rectification in high frequency LLC, characterized in that, based on the voltage V at two ends of the capacitor C obtained by the current detection method of claim 4sAnd performing control, including:
voltage V across the capacitor CsRespectively comparing the voltage with a preset positive voltage threshold value and a preset negative voltage threshold value;
when the voltage V at both ends of the capacitor CsWhen the voltage is larger than the positive voltage threshold value, the synchronous tube SR in the high-frequency LLC is controlled2Drive signal V ofgsSR2Outputting a positive level;
when the voltage V at both ends of the capacitor CsWhen the voltage is less than the negative voltage threshold value, the synchronous tube SR in the high-frequency LLC is controlled1Drive signal V ofgsSR1A positive level is output.
7. The method as claimed in claim 6, wherein the amplitude of the preset positive voltage threshold is reduced to realize SR (synchronous transistor) of the synchronous tube in the high frequency LLC2Drive signal V ofgsSR2The duration of the output positive level increases; by increasing the amplitude of a preset negative voltage threshold, the synchronous tube SR in the high-frequency LLC is realized1Drive signal V ofgsSR1The duration of the output positive level increases.
8. The method of claim 6, further comprising: by reducing the resistance R2Change the voltage V across the capacitor CsThereby reducing the synchronous tube SR1Actual on-time and synchronous tube SR1Drive signal V ofgsSR1Time difference of positive level time, and reducing synchronous tube SR2Actual on-time and synchronous tube SR2Drive signal V ofgsSR2Time difference of positive level time.
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