CN117420348A - Resonant current detection circuit - Google Patents
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- CN117420348A CN117420348A CN202311748830.8A CN202311748830A CN117420348A CN 117420348 A CN117420348 A CN 117420348A CN 202311748830 A CN202311748830 A CN 202311748830A CN 117420348 A CN117420348 A CN 117420348A
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- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
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Abstract
The invention discloses a resonant current detection circuit, which belongs to the technical field of electric energy conversion and is used for detecting the resonant current of a resonant circuit, wherein the resonant circuit comprises a resonant inductor and a resonant capacitor, and comprises a first operational amplifier, a first capacitor and a first resistor, wherein the first end of the resonant capacitor is connected with the input positive end of the first operational amplifier, the first end of the first capacitor is connected with the second end of the resonant capacitor, the second end of the first capacitor is connected with the input negative end of the first operational amplifier, the first end of the first resistor is connected with the input negative end of the first operational amplifier, and the second end of the first resistor is connected with the output end of the first operational amplifier. The resonant current detection circuit disclosed by the invention has fewer peripheral devices, and is beneficial to improving the efficiency and power density of a system.
Description
Technical Field
The present invention relates to the field of power conversion technology, and in particular, to a resonant current detection circuit.
Background
Along with the continuous improvement of functions and performances of electronic devices, requirements on power supply devices for supplying power to the electronic devices are also higher and higher, and in particular, requirements on high power density, high efficiency, high dynamic performance, high reliability and the like are met. To meet these requirements, a control mode with high dynamic characteristics is required for power supply design. Therefore, a current signal is needed to be added into the power supply module as input signals of the control circuit and the protection circuit to control the power supply, so that the circuit works more stably and reliably. In order to control using the current signal in the circuit, the current needs to be sampled.
For a resonant circuit, the resonant current in the sampling circuit is controlled and is important for the operation of the whole circuit. The common resonant current detection circuit includes an external resistance detection circuit, an inductance direct current resistance detection circuit (DCR detection circuit), a capacitance shunt detection circuit and the like.
The following describes three common resonant current detection circuits using an LLC half-bridge resonant circuit as an example.
As shown in FIG. 1, the external resistor detection circuit is formed by serially connecting a resistor R to the primary side of an LLC half-bridge resonance circuit 1 Through an operational amplifier A 1 Resistance to R 1 The voltage across the resistor R is amplified proportionally 1 The current of (a) is the resonant currenti Lr Resistance R 1 The voltage across it is:
，
the resonant current can be obtained according to the above formulai Lr . However, an additional resistor R 1 Additional losses can be incurred, reducing system efficiency. To reduce losses, resistor R 1 The value is usually smaller, so that the detected signal is smaller and is easily influenced by switching noise, thereby influencing the detection precision.
As shown in fig. 2, the inductance-dc resistance detection circuit uses a resonant inductance L r Parasitic resistance R of (2) Lr Sampling current information at resonance inductance L r And parasitic resistance R Lr The two ends are connected in parallel with a group of RC branches connected in series, and the capacitor C can be obtained according to the principle of equal voltage and voltage division of the parallel circuit 1 The voltages across are as follows:
，
，
regulating resistor R 2 And capacitor C 1 Take on a value of L r /R Lr = R 2 C 1 The above method can be simplified into
，
Thereby, through an operational amplifier A 2 Counter capacitor C 1 The voltage at both ends is amplified to detect the resonant currenti Lr . However, in practical application, due to the resonant inductance L r And parasitic resistance R Lr The inductance and direct current resistance detection circuit is only at L r /R Lr = R 2 C 1 The current can be accurately detected under the condition of (1), otherwise, the sampling precision is greatly affected. At the same time, the detection circuit requires more peripheral separation devices, such as a resistor R 2 Capacitance C 1 In some cases, the capacitor C may be used to adjust the current sampling resistor 1 A set of shunt resistors are connected in parallel, thus reducing the power density of the system. In addition, due to parasitic resistance R Lr Smaller, resonant currenti Lr Through parasitic resistance R Lr The voltage drop generated by the high-voltage-drop circuit is only tens of millivolts, and the signal is a ripple signal working at the switching frequency, so that a high-precision and high-bandwidth operational amplifier is required to be used for current mode control and overcurrent protection after sampling, and the input end of the operational amplifier is required to bear high common-mode voltage, so that the difficulty and cost of design are increased, and the power density and the control cost are not improved.
As shown in fig. 3, the capacitance shunt detection circuit is formed by a resonance capacitor C r Two ends of the resonant capacitor are connected in parallel with a group of RC branches in series, and the flow flows through the resonant capacitor C r Is set to be equal to or greater than the resonance current of the (a)i Lr Shunt to obtain the resonance currenti Lr And the weak current signals with the same phase are connected into an amplifying circuit. Resistor R 3 The voltage across the terminals is as follows:
，
when C 2 R 3 <<T sw In this case, the above formula can be simplified as:
，
when selecting a proper resistor R 3 Capacitance C 2 In time, according to resistance R 3 The voltage at both ends can detect the resonant currenti Lr . However, in the actual operation process, the switching frequency is continuously adjusted along with the input voltage and the load current, when the switching frequency is higher, the switching frequency is higherBecomes non-negligible, thereby causing a sampling coefficient change, and there is a phase difference between the sampling signal and the actual resonance current, and the sampling accuracy is greatly reduced.
Disclosure of Invention
In order to solve the above problems, the present invention provides a resonant current detection circuit.
In order to achieve the above purpose, the technical scheme of the invention is as follows:
a resonance current detection circuit is used for detecting resonance current of a resonance circuit, the resonance circuit comprises a resonance inductor and a resonance capacitor, the resonance circuit comprises a first operational amplifier, a first capacitor and a first resistor, a first end of the resonance capacitor is connected with an input positive end of the first operational amplifier, a first end of the first capacitor is connected with a second end of the resonance capacitor, a second end of the first capacitor is connected with an input negative end of the first operational amplifier, a first end of the first resistor is connected with an input negative end of the first operational amplifier, and a second end of the first resistor is connected with an output end of the first operational amplifier.
Further, the resonant current detection circuit further comprises a second capacitor and a second resistor, wherein a first end of the resonant capacitor is connected with the input positive end of the first operational amplifier through the second capacitor, a first end of the second resistor is grounded, and a second end of the second resistor is connected with the input positive end of the first operational amplifier.
Further, the value of the first capacitance is equal to the value of the second capacitance.
Further, the value of the first resistor is equal to the value of the second resistor.
Further, the resonant current detection circuit further comprises a first direct current voltage, wherein the positive electrode of the first direct current voltage is connected with the first end of the second resistor, and the negative electrode of the first direct current voltage is grounded.
Further, the resonant current detection circuit further comprises a third resistor, wherein a first end of the third resistor is connected with the first end of the resonant capacitor, and a second end of the third resistor is connected with the input positive end of the first operational amplifier.
In a specific embodiment of the present invention, the resonant circuit includes a first switch, a second switch, a resonant inductor, a resonant capacitor, a transformer, a first diode, a second diode and a third capacitor, where a source of the first switch is connected to a drain of the second switch, a source of the second switch is grounded, the resonant inductor, the resonant capacitor and a primary winding of the transformer are connected in series and then connected in parallel between the source of the first switch and ground, a first end of a first secondary winding of the transformer is connected to an anode of the first diode, a second end of the first secondary winding of the transformer is connected to a first end of a second secondary winding of the transformer, a second end of the second secondary winding of the transformer is connected to an anode of the second diode, a cathode of the first diode is connected to a cathode of the second diode, and the third capacitor is connected in parallel between the cathode of the first diode and the second end of the first secondary winding of the transformer.
Further, the drain electrode of the first switch is connected with the positive electrode of the input voltage, and the source electrode of the second switch is connected with the negative electrode of the input voltage.
Further, a source electrode of the first switch is connected with a first end of the resonant inductor, a second end of the resonant inductor is connected with a first end of a primary winding of the transformer, a second end of the primary winding of the transformer is connected with a second end of the resonant capacitor, and the first end of the resonant capacitor is connected with a source electrode of the second switch.
Further, a source electrode of the first switch is connected with a first end of the resonant capacitor, a second end of the resonant capacitor is connected with a first end of the resonant inductor, a second end of the resonant inductor is connected with a first end of a primary winding of the transformer, and a second end of the primary winding of the transformer is connected with a source electrode of the second switch.
The resonant current detection circuit has the beneficial effects that only the voltage on the resonant capacitor is required to be sampled, no extra loss is caused, fewer peripheral devices are required, and the efficiency and the power density of the system are improved; the primary side resonance current can be accurately sampled, and current control and rapid protection are facilitated; the required peripheral devices are common, and the design and cost control are facilitated in practical application; compared with the traditional capacitance shunt detection, the decoupling of the sampling coefficient and the switching frequency is realized; at any switching frequency, the RC value does not bring a phase difference between the sampling signal and the resonance current, and the sampling coefficient is kept unchanged.
In order to make the above features and advantages of the present invention more comprehensible, embodiments accompanied with figures are described in detail below.
Drawings
FIG. 1 is a schematic circuit diagram of an external resistor detection circuit.
Fig. 2 is a circuit schematic diagram of an inductance-direct current resistance detection circuit.
Fig. 3 is a circuit schematic diagram of the capacitive shunt detection circuit.
Fig. 4 is a circuit diagram of a resonant current detection circuit according to a first embodiment of the present invention.
Fig. 5 is a circuit diagram of a resonant current detection circuit according to a second embodiment of the present invention.
Fig. 6 is a circuit diagram of a resonant current detection circuit according to a third embodiment of the present invention.
FIG. 7 (a) is f r2 <f s <f r1 The waveform diagram of the operation of the LLC half-bridge resonant circuit in FIG. 4.
FIG. 7 (b) is f s =f r1 The waveform diagram of the operation of the LLC half-bridge resonant circuit in FIG. 4.
FIG. 7 (c) is f s ＞f r1 The waveform diagram of the operation of the LLC half-bridge resonant circuit in FIG. 4.
FIG. 8 (a) is f r2 <f s <f r1 The working process simulation waveform diagram of the LLC half-bridge resonant circuit in fig. 4.
FIG. 8 (b) is f s =f r1 The working process simulation waveform diagram of the LLC half-bridge resonant circuit in fig. 4.
FIG. 8 (c) is f s ＞f r1 The working process simulation waveform diagram of the LLC half-bridge resonant circuit in fig. 4.
FIG. 9 f r2 <f s <f r1 The working process simulation waveform diagram of the LLC half-bridge resonant circuit in FIG. 5.
FIG. 10 f r2 <f s <f r1 The working process simulation waveform diagram of the LLC half-bridge resonant circuit in FIG. 6.
Detailed Description
In order to make the purpose and technical solutions of the embodiments of the present invention more clear, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. It will be apparent that the described embodiments are some, but not all, embodiments of the invention. All other embodiments, which can be made by a person skilled in the art without creative efforts, based on the described embodiments of the present invention fall within the protection scope of the present invention.
In the resonant circuit, the resonant current is a periodically variable quantity, the resonant current charges and discharges the resonant capacitor, and according to the relation between the capacitor voltage and the current, the voltage at two ends of the resonant capacitor is sampled and differentiated, so that the current waveform flowing through the resonant capacitor can be obtained. The sampled current small signal can be used for control and protection after being amplified by a high-speed and high-precision operational amplifier.
The LLC half-bridge resonant circuit is taken as an example to describe the resonant current detection circuit.
Fig. 4 is a circuit diagram of a resonant current detection circuit according to a first embodiment of the present invention. As shown in fig. 4, the LLC half-bridge resonant circuit includes a switch Q 1 Switch Q 2 Inductance L r Capacitance C r Transformer T r Diode D 1 And diode D 2 Switch Q 1 Source connection switch Q 2 Drain of switch Q 1 Is connected with the input voltage V in Positive electrode of switch Q 2 Is connected with the input voltage V in Is input with voltage V in Is grounded at the negative electrode of the switch Q 1 Source electrode connection inductance L of (a) r Inductance L of the first end of (a) r Is connected to the transformer T r Primary winding N of (a) p First end, primary winding N p The second end of (C) is connected with a capacitor C r Capacitor C r Is connected with the switch Q 2 Source electrode of excitation inductance L m Parallel to primary winding N p Two ends. Transformer T r Is a secondary winding N s1 The first end is connected with a diode D 1 Anode, secondary winding N s1 The second end is connected with a transformer T r Is a secondary winding N s2 First end, secondary winding N s2 The second end is connected with a diode D 2 Anode of diode D 1 Cathode connection diode D 2 Cathode of diode D 1 Cathode and secondary winding N s1 A capacitor C connected in parallel between the second ends of (2) o Capacitance C o Two ends of parallel resistor R o Resistance R o The voltage at two ends is the output voltage V o . Wherein the input voltage V in Is a direct current voltage.
Further, the resonant current detection circuit includes an operational amplifier A 4 Capacitance C 3 Resistance R 4 And resistance R 5 Capacitance C 3 Is connected with the first end of (a)Capacitor C r Capacitor C 3 The second end of (a) is connected with the operational amplifier A 4 Is the negative input terminal of (1), resistance R 4 Is connected with the capacitor C r Resistance R 4 The second end of (a) is connected with the operational amplifier A 4 Input positive terminal of (a), resistance R 5 Is connected with the operational amplifier A 4 Is the negative input terminal of (1), resistance R 5 The second end of (a) is connected with the operational amplifier A 4 An operational amplifier A 4 Output terminal of (2) outputs voltagev 4 。
Further, resistance R 4 Is a balancing resistor for reducing errors caused by static input voltage formed by the input bias current of the operational amplifier.
More specifically, the primary side switching network is formed by switch Q 1 Switch Q 2 Composition, switch Q 1 Switch Q 2 Complementary conduction, input voltage V in And becomes a square wave signal as an input to the resonant cavity. Switch Q 1 Switch Q 2 Sufficient dead time should be provided between the drive signals to ensure implementation of the soft switch to improve conversion efficiency.
More specifically, the resonant cavity is formed by inductance L r Transformer T r Exciting inductance L of (1) m And capacitor C r Composition is prepared. Capacitor C r And inductance L r Forming a low-pass filter to filter out high-frequency components of the square wave signal, so that the current flowing into the resonant cavity is approximately sine wave, and the switch Q is changed 1 Switch Q 2 The gain of the resonant cavity can be changed, so that stable output of voltage is realized. Transformer T r Has isolation function, and the transformation ratio N is the input voltage V in And output voltage V o Is a ratio of (2).
More specifically, diode D 1 Diode D 2 Capacitance C o And forming a rectifying and filtering network.
The LLC half-bridge resonant circuit in fig. 4 has two resonant frequencies:
，
。
according to the switching frequency f s And resonant frequency f r1 Resonant frequency f r2 The relationship between these can divide the operating state of an LLC half-bridge resonant circuit into three types: f (f) r2 <f s <f r1 、f s =f r1 、f s ＞f r1 . In different operating states, key waveforms of the LLC half-bridge resonant circuit during operation are shown in fig. 7 (a) to 7 (c). FIG. 7 (a) is f r2 <f s <f r1 The waveform diagram of the working process of the LLC half-bridge resonant circuit in FIG. 4 is shown in FIG. 7 (b) as f s =f r1 The waveform diagram of the working process of the LLC half-bridge resonant circuit in FIG. 4 is shown in FIG. 7 (c) as f s ＞f r1 The waveform diagram of the working process of the LLC half-bridge resonant circuit in FIG. 4, wherein V gs1 Is a switch Q 1 On signal of V gs2 Is a switch Q 2 On signal of V ds1 Is a switch Q 1 Drain-source voltage of V ds2 Is a switch Q 2 Is used for the voltage control of the drain-source electrode,i Lr for the resonant current to be a resonant current,i Lm for the excitation current to be sufficient,i D1 for flowing through diode D 1 Is used for the current flow of (a),i D2 for flowing through diode D 2 Is set in the above-described range).
The operation in FIG. 7 (a) is divided into 8 phases, the first four phases t 0 -t 4 And the last four phases t 4 -t 8 Is completely symmetrical, and only the first four phases are used for analysis.
[t 0 -t 1 ]Stage: at t 0 Before the moment due to the resonant currenti Lr Without abrupt change, i.e. resonant currenti Lr Through switch Q 1 Follow current of body diode of (1), switch Q 1 The voltage at two ends is zero, thereby providing a condition for zero voltage turn-on of a primary side switching device of the LLC half-bridge resonance circuit. At t 0 Time of day, switch Q 1 The voltage between the two points A, B is the inputVoltage V of in . Resonant currenti Lr According to sine law, the exciting current is increasedi Lm And increases linearly. Diode D of secondary side 1 Turn on, output voltage V o Through transformer T r Added to excitation inductance L m Two ends, excitation inductance L m The voltage across the terminals is clamped to N x V o . At this stage, only the capacitor C r And inductance L r Takes part in resonance, excitation inductance L m Does not participate in resonance, and the resonance currenti Lr And exciting currenti Lm All from negative to positive until the resonant currenti Lr And exciting currenti Lm Equal.
[t 1 -t 2 ]Stage: at t 1 Time of day, switch Q 1 Is still kept on, exciting currenti Lm Equal to the resonant currenti Lr Through transformer T r The primary side current is zero, the transformer T r No energy is transferred to the secondary side, diode D of the secondary side 1 The zero current turn-off is realized because the current flowing through the switch is gradually zero. In this process, the inductance L r Exciting inductance L m Capacitance C r All participate in resonance, but the resonance frequency is much smaller than the switching frequency.
[t 2 -t 3 ]Stage: switch Q 1 Turn off, enter dead time stage, resonant currenti Lr For switch Q 1 Junction capacitance charging, switch Q 2 Is discharged by the junction capacitance of switch Q 1 Voltage at both ends rises, switch Q 2 The voltage across the terminals drops. Due to capacitance C r Far greater than switch Q 1 Switch Q 2 Junction capacitance of (2), switch Q 1 Switch Q 2 The junction capacitor can be charged and discharged rapidly, and the switching device can be turned on at zero voltage in the next stage as long as the junction capacitor is charged and discharged in dead time.
[t 3 -t 4 ]Stage: at t 3 At the moment, the junction capacitor has completed charging and discharging, switch Q 1 Switch Q 2 In the off-phase due to resonant currenti Lr No abrupt change of current through switch Q 2 Freewheeling of the body diode of (1) so that the switch Q 2 Zero voltage turn-on is realized.
The working of the first four stages is finished, and the working processes of the last four stages and the first four stages are symmetrical, and are not repeated.
f s =f r1 The LLC half-bridge resonant circuit operates in the state shown in FIG. 7 (b), which can be regarded as f r2 <f s <f r1 Is a special working procedure of only resonant currenti Lr And exciting currenti Lm Equal phase does not exist, inductance L r Capacitance C r And excitation inductance L m The course of the common resonance is shortened to a moment, i.e. there is no [ t ] in FIG. 7 (a) 1 -t 2 ]Working procedure of stage, rest procedure and f r2 <f s <f r1 The working process is the same, and the resonant currenti Lr Almost sine wave, lowest harmonic distortion and current of secondary sidei D1 Current flowi D2 In a critical continuous state. When the LLC half-bridge resonant circuit operates at a resonant frequency, the voltage gain is unity and the transfer function is independent of the load.
f s ＞f r1 The state of operation of the LLC half-bridge resonant circuit is shown in fig. 7 (c). Inductance L r And capacitor C r Resonance, excitation inductance L m Does not participate in resonance, excitation inductance L m The voltage across the terminals is clamped at + -N x V o Diode D of secondary side 1 Diode D 2 Is always on. During the commutation process, the resonant currenti Lr Can change sharply, and bring about larger turn-off loss. When the switching frequency is high, the resonant currenti Lr The peak is high and the current stress of the device is high.
The resonant current detection circuit in fig. 4 samples the resonant capacitor C r The voltage at two ends is connected into a differential conditioning circuit, and the finally obtained voltage signal is proportional to the resonant current, so that the resonant current of the LLC half-bridge resonant circuit is realizedi Lr Sampling may be used for subsequent control and protection.
In the three operating states of the LLC half-bridge resonant circuit, due to the inductance L r And capacitor C r All are in series connection to obtain a capacitor C r Voltage of (2)v Cr And resonant currenti Lr The relationship of (2) is as follows:
。
capacitor C is coupled through the resonant current detection circuit of FIG. 4 r The voltage across the two terminals is differentiated to obtain the following relationship:
。
the two formulas can be obtained by combining:
，
it can be seen that the voltagev 4 And resonant currenti Lr proportional-R 5 C 3 /C r Operational amplifier A 4 Output voltage of (2)v 4 Can accurately reflect the resonance currenti Lr Is the resonant current at this timei Lr is-R 5 C 3 /C r 。
In different operation states, the simulation waveforms of the LLC half-bridge resonant circuit during operation are shown in fig. 8 (a) to 8 (c). FIG. 8 (a) is f r2 <f s <f r1 FIG. 4 shows a waveform of simulation of the operation of the LLC half-bridge resonant circuit, FIG. 8 (b) is f s =f r1 FIG. 4 shows a waveform of simulation of the operation of the LLC half-bridge resonant circuit, FIG. 8 (c) is f s ＞f r1 The simulation waveform diagram of the working process of the LLC half-bridge resonant circuit in FIG. 4, wherein V gs1 Is a switch Q 1 On signal of V gs2 Is a switch Q 2 On signal of V ds1 Is a switch Q 1 Drain-source voltage of V ds2 Is a switch Q 2 Is used for the voltage control of the drain-source electrode,i Lr for the resonant current to be a resonant current,i Lm for the excitation current to be sufficient,v 4 is an operational amplifier A 4 Is set, the output voltage of which is set. As can be seen from the figure, in the switch Q 1 On conduction, resonant currenti Lr From negative to positive direction, resonant currenti Lr Increase, corresponding voltagev 4 A reduction; at switch Q 2 On conduction, resonant currenti Lr From positive to negative direction, resonant currenti Lr Reduction of the corresponding voltagev 4 Increasing. Operational amplifier A in three operating states 4 Output voltage of (2)v 4 Can follow the resonant currenti Lr And the linear change realizes accurate sampling.
To sum up, the circuit in fig. 4 only needs to be applied to the capacitor C r The voltage is sampled, so that extra loss is avoided, fewer peripheral devices are needed, and the efficiency and the power density of the system are improved; the primary side resonance current can be accurately sampled, and current control and rapid protection are facilitated; the required peripheral devices are common, and the design and cost control are facilitated in practical application; compared with the traditional capacitance shunt detection, the decoupling of the sampling coefficient and the switching frequency is realized; at any switching frequency, the RC value does not bring a phase difference between the sampling signal and the resonance current, and the sampling coefficient is kept unchanged.
Fig. 5 is a circuit diagram of a resonant current detection circuit according to a second embodiment of the present invention, suitable for use in the capacitor C r There is no shorting to ground. As shown in fig. 5, the LLC half-bridge resonant circuit includes a switch Q 1 Switch Q 2 Inductance L r Capacitance C r Transformer T r Diode D 1 And diode D 2 Switch Q 1 Source connection switch Q 2 Drain of switch Q 1 Is connected with the input voltage V in Positive electrode of switch Q 2 Is connected with the input voltage V in Is input with voltage V in Is grounded at the negative electrode of the switch Q 1 Source connection capacitor C of (2) r Capacitor C r Is connected to the inductor L r Inductance L of the first end of (a) r Is connected to the transformer T r Primary winding N of (a) p First end, primary winding N p Second end connection switch Q 2 Source electrode of excitation inductance L m Parallel to primary winding N p Two ends. Transformer T r Is a secondary winding N s1 The first end is connected with a diode D 1 Anode, secondary winding N s1 The second end is connected with a transformer T r Is a secondary winding N s2 First end, secondary winding N s2 The second end is connected with a diode D 2 Anode of diode D 1 Cathode connection diode D 2 Cathode of diode D 1 Cathode and secondary winding N s1 A capacitor C connected in parallel between the second ends of (2) o Capacitance C o Two ends of parallel resistor R o Resistance R o The voltage at two ends is the output voltage V o . Wherein the input voltage V in Is a direct current voltage.
Further, the resonant current detection circuit includes an operational amplifier A 4 Capacitance C 3 Capacitance C 4 Resistance R 5 And resistance R 6 Capacitance C r Is passed through capacitor C 4 Connected with an operational amplifier A 4 Capacitance C at the input positive terminal of (2) r Is passed through capacitor C 3 Connected with an operational amplifier A 4 Is the negative input terminal of (1), resistance R 6 Is grounded, resistance R 6 The second end of (a) is connected with the operational amplifier A 4 Input positive terminal of (a), resistance R 5 Is connected with the operational amplifier A 4 Is the negative input terminal of (1), resistance R 5 The second end of (a) is connected with the operational amplifier A 4 An operational amplifier A 4 Output terminal of (2) outputs voltagev 5 。
More specifically, resistance R 5 Resistance R 6 Capacitance C 3 Capacitance C 4 The values of (2) satisfy the following relationship:
C 3 = C 4 = C s ，
R 5 = R 6 = R s 。
when the capacitor C r When not grounded, the capacitor C is required r The voltage at both ends is differentially sampled and is used as an operational amplifier A in a differential mode 4 Is input to the computer. The virtual short and virtual break of the operational amplifier can be obtained:
，
wherein,v Cr+ is a capacitor C r The voltage value at the first end of the capacitor,v Cr- is a capacitor C r The voltage value of the second end is simplified to obtain
，
I.e.
。
As can be seen from the above, the voltagev 5 And resonant currenti Lr In proportion R s C s /C r Through an operational amplifier A 4 Output voltage of (2)v 5 The resonant current can be determinedi Lr 。
FIG. 9 f r2 <f s <f r1 The simulation waveform diagram of the working process of the LLC half-bridge resonant circuit in FIG. 5, wherein V gs1 Is a switch Q 1 On signal of V gs2 Is a switch Q 2 On signal of V ds1 Is a switch Q 1 Drain-source voltage of V ds2 Is a switch Q 2 Is used for the voltage control of the drain-source electrode,i Lr for the resonant current to be a resonant current,i Lm for the excitation current to be sufficient,v 5 is an operational amplifier A 4 Is set, the output voltage of which is set. As can be seen from the figure, in the switch Q 1 On conduction, resonant currenti Lr From negative to positive direction, resonant currenti Lr Increase, corresponding voltagev 5 An increase; at switch Q 2 On conduction, resonant currenti Lr From positive to negative direction, resonant currenti Lr Reduction of the corresponding voltagev 5 And (3) reducing. Operational amplifier A 4 Output voltage of (2)v 5 Can follow the resonant currenti Lr The same proportion is changed, and accurate sampling is realized.
To sum up, the circuit in fig. 5 only needs to be applied to the capacitor C r The voltage is sampled, so that extra loss is avoided, fewer peripheral devices are needed, and the efficiency and the power density of the system are improved; the primary side resonance current can be accurately sampled, and current control and rapid protection are facilitated; the differential sampling mode is suitable for resonance capacitors at any positions, and the influence of switching noise on sampling signals can be reduced; the resonant current detection circuit is not limited by the position of the resonant capacitor in the circuit, and can be applied to more circuits.
From the simulation waveforms of FIG. 9, the voltage can be seenv 5 Is of positive and negative symmetrical waveform, usually voltagev 5 The latter controller is accessed for control and protection. If the pins of the controller cannot bear negative pressure, the resistor R is needed 6 A direct current voltage V is connected between the ground dc Thus in the operational amplifier A 4 Output voltage of (2)v 5 Introducing DC bias, lifting sampling signal, and finally obtaining voltagev 6 The positive pressure is shown in fig. 6.
FIG. 6 is a circuit diagram of a resonant current detection circuit according to a third embodiment of the invention, based on the circuit of FIG. 5, with a resistor R 6 A direct current voltage V is connected in series between the ground dc More specifically, the direct current voltage V dc Positive electrode connection resistor R of (a) 6 Is a first end of the DC voltage V dc Is grounded, operational amplifier A 6 Output terminal of (2) outputs voltagev 6 。
Thereby obtaining a voltagev 6 And resonant currenti Lr The relationship of (2) is as follows:
。
FIG. 10 f r2 <f s <f r1 The working process simulation waveform of LLC half-bridge resonant circuit in FIG. 6, wherein V gs1 Is a switch Q 1 On signal of V gs2 Is a switch Q 2 On signal of V ds1 Is a switch Q 1 Drain-source voltage of V ds2 Is a switch Q 2 Is used for the voltage control of the drain-source electrode,i Lr for the resonant current to be a resonant current,i Lm for the excitation current to be sufficient,v 6 is an operational amplifier A 4 Is set, the output voltage of which is set. As can be seen from the figure, the voltagev 6 Can follow the resonant currenti Lr The accurate sampling is realized by changing the same proportion; and voltage throughout the switching cyclev 6 And more than 0, which is beneficial to the design and realization of the later-stage controller.
It should be noted that the resonant current detection circuit of the present invention is applicable not only to LLC half-bridge resonant circuits, but also to various resonant circuits, such as LCC resonant conversion circuits, series resonant conversion circuits, parallel resonant conversion circuits, and the like, and various quasi-resonant conversion circuits.
Although the present invention has been described with reference to the above embodiments, it should be understood that the invention is not limited thereto, but rather is capable of modification and variation without departing from the spirit and scope of the present invention.
Claims (10)
1. The resonant current detection circuit is used for detecting resonant current of a resonant circuit and comprises a resonant inductor and a resonant capacitor, and is characterized by comprising a first operational amplifier, a first capacitor and a first resistor, wherein a first end of the resonant capacitor is connected with an input positive end of the first operational amplifier, a first end of the first capacitor is connected with a second end of the resonant capacitor, a second end of the first capacitor is connected with an input negative end of the first operational amplifier, a first end of the first resistor is connected with an input negative end of the first operational amplifier, and a second end of the first resistor is connected with an output end of the first operational amplifier.
2. The resonant current detection circuit of claim 1, further comprising a second capacitor and a second resistor, wherein a first end of the resonant capacitor is connected to the input positive terminal of the first operational amplifier through the second capacitor, a first end of the second resistor is grounded, and a second end of the second resistor is connected to the input positive terminal of the first operational amplifier.
3. A resonant current detection circuit according to claim 2, wherein the value of the first capacitance is equal to the value of the second capacitance.
4. A resonant current detection circuit according to claim 3, wherein the value of the first resistor is equal to the value of the second resistor.
5. The resonant current detection circuit of claim 4, further comprising a first dc voltage, wherein a positive electrode of the first dc voltage is coupled to the first end of the second resistor, and wherein a negative electrode of the first dc voltage is coupled to ground.
6. The resonant current detection circuit of claim 1, further comprising a third resistor, a first terminal of the third resistor connected to the first terminal of the resonant capacitor, and a second terminal of the third resistor connected to the input positive terminal of the first operational amplifier.
7. The resonant current detection circuit according to any one of claims 1-6, wherein the resonant circuit comprises a first switch, a second switch, a resonant inductor, a resonant capacitor, a transformer, a first diode, a second diode, and a third capacitor, a source of the first switch is connected to a drain of the second switch, a source of the second switch is grounded, the resonant inductor, the resonant capacitor, a primary winding of the transformer are connected in series and then connected in parallel between the source of the first switch and ground, a first end of a first secondary winding of the transformer is connected to an anode of the first diode, a second end of the first secondary winding of the transformer is connected to a first end of the second secondary winding of the transformer, a second end of the second secondary winding of the transformer is connected to an anode of the second diode, a cathode of the first diode is connected to a cathode of the second diode, and the cathode of the first secondary winding of the first diode is connected to a third capacitor between the second end of the first secondary winding of the transformer in parallel.
8. The resonant current detection circuit of claim 7, wherein the drain of the first switch is connected to the positive pole of the input voltage and the source of the second switch is connected to the negative pole of the input voltage.
9. The resonant current detection circuit of claim 8, wherein the source of the first switch is connected to a first terminal of the resonant inductor, the second terminal of the resonant inductor is connected to a first terminal of a primary winding of the transformer, the second terminal of the primary winding of the transformer is connected to a second terminal of the resonant capacitor, and the first terminal of the resonant capacitor is connected to the source of the second switch.
10. The resonant current detection circuit of claim 8, wherein a source of the first switch is connected to a first terminal of the resonant capacitor, a second terminal of the resonant capacitor is connected to a first terminal of the resonant inductor, a second terminal of the resonant inductor is connected to a first terminal of a primary winding of the transformer, and a second terminal of the primary winding of the transformer is connected to a source of the second switch.
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| CN202311748830.8A CN117420348A (en) | 2023-12-19 | 2023-12-19 | Resonant current detection circuit |
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| CN202311748830.8A CN117420348A (en) | 2023-12-19 | 2023-12-19 | Resonant current detection circuit |
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