Magnetic isolation feedback circuit

Abstract

The embodiment of the invention provides a magnetic isolation feedback circuit which comprises an error amplifier unit, a modulator unit and a demodulator unit. The magnetic isolation feedback circuit is used for transmitting an error signal of an output voltage sampling signal Vos of a secondary side of the LLC resonant triode converter to a primary side of the LLC resonant converter so as to control the duty ratio of a first primary side switching tube QH and a second primary side switching tube QL of the LLC resonant converter; the error amplifier unit is used for amplifying an error signal of the output voltage sampling signal Vos to generate an amplified error signal; the modulator unit is used for modulating the input amplified error signals into square wave signals with the same amplitude; and the demodulator unit is used for demodulating the modulated square wave signal into a direct current signal with the same amplitude. According to the scheme, the forward converter is used as a modulator, so that a magnetic isolation feedback circuit with good temperature characteristics and radiation resistance characteristics is provided.

Description

Technical Field

[0001] The invention relates to the technical field of switching power supplies, and in particular to a magnetic isolation feedback circuit. Background Art

[0002] In situations where power supply safety requirements are high, a transformer is required to achieve electrical isolation between the primary and secondary sides of the switching power supply. In this case, an isolated converter is required. In order to achieve output voltage stability, the control signal of the secondary side needs to be transmitted to the primary side. In this case, an isolated feedback circuit is required. Common isolation feedback methods include optocoupler isolation and magnetic isolation. Although optocoupler isolation has simple parameter design and low cost, it is sensitive to temperature and radiation and has a large transmission delay. Therefore, it is not suitable for situations where high reliability and fast dynamic response are required for power electronic converters.

[0003] Magnetic isolation feedback has good temperature and radiation stability, and through reasonable design, the transformer can work at high frequency, which can effectively reduce the size of the transformer. Currently, the integrated magnetic isolation feedback chips on the market mainly include TI's UC3901 and ADI's adum3190. These chips are expensive and limit the input and output voltage range, which causes many inconveniences in loop design. Summary of the invention

[0004] In view of this, the embodiments of this specification provide a magnetic isolation feedback circuit to meet the isolation feedback requirements of the control signal of the isolated converter in the switching power supply, and to provide a magnetic isolation feedback circuit with good temperature characteristics and radiation resistance characteristics.

[0005] The embodiments of this specification provide the following technical solutions:

[0006] A magnetic isolation feedback circuit, comprising:

[0007] An error amplifier unit, a modulator unit and a demodulator unit, wherein the output of the error amplifier unit is used as an input of the modulator unit, and the output of the modulator unit is used as an input of the demodulator unit;

[0008] The magnetic isolation feedback circuit is used to sample the output voltage signal V of the secondary side of the LLC resonant converter. os The error signal is transmitted to the primary side of the LLC resonant converter to control the first primary switch tube Q of the LLC resonant converter. H And the second primary switch tube Q L Duty cycle;

[0009] The error amplifier unit is used to convert the output voltage sampling signal V os amplifying the error signal to generate an amplified error signal;

[0010] The modulator unit is used to modulate the input amplified error signal into a square wave signal with equal amplitude;

[0011] The demodulator unit is used to demodulate the modulated square wave signal into a DC signal with equal amplitude.

[0012] Further, the error amplifier unit comprises:

[0013] Operational amplifier OP1, a first resistor R1, a second resistor R2, a first capacitor C1 and a second capacitor C2;

[0014] One end of the first resistor R1 is connected to the output voltage sampling signal V os The other end of the first resistor R1 is connected to the inverting end of the operational amplifier OP1, one end of the first capacitor C1 and one end of the second capacitor C2 respectively, the other end of the first capacitor C1 is connected to one end of the second resistor R2, the other end of the second resistor R2 and the other end of the second capacitor C2 are both connected to the output end of the operational amplifier OP1, and the non-inverting end of the operational amplifier OP1 is connected to the output voltage sampling signal V os The reference voltage V ref are connected.

[0015] Further, the error amplifier unit comprises:

[0016] Digital controller;

[0017] The output voltage sampling signal V is obtained by the ADC unit of the digital controller. os The digital signal is converted into a digital signal and sent to the digital controller. The DAC unit of the digital controller converts the calculated digital signal into an output voltage error signal V EA .

[0018] Further, the modulator unit comprises:

[0019] It includes a first NPN transistor Q1, a second NPN transistor Q2, a magnetic isolation transformer T1 and a first diode D1;

[0020] The base of the first NPN transistor Q1 is connected to the output of the error amplifier, the collector of the first NPN transistor Q1 is connected to the power supply VCC of the secondary side of the LLC resonant converter, the emitter of the first NPN transistor Q1 is connected to the same-name end of the first primary winding N1 of the magnetic isolation transformer T1, the other end of the first primary winding N1 is connected to the collector of the second NPN transistor Q2, the emitter of the second NPN transistor Q2 is connected to the secondary ground SGND of the LLC resonant converter, and the base of the second NPN transistor Q2 is connected to the secondary ground SGND of the LLC resonant converter. The pole is connected to the same-name end of the secondary winding of the LLC resonant converter, one end of the second primary winding N2 of the magnetic isolation transformer T1 is connected to the primary ground PGND, the other end of the second primary winding N2 of the magnetic isolation transformer T1 is connected to the demodulator, one end of the auxiliary winding N3 of the magnetic isolation transformer T1 is connected to the secondary power supply VCC of the LLC resonant converter, the other end of the auxiliary winding N3 of the magnetic isolation transformer T1 is connected to the cathode of the first diode D1, and the anode of the first diode D1 is connected to the secondary ground SGND.

[0021] Further, the demodulator unit comprises:

[0022] A second diode D2, a third capacitor C3 and a third resistor R3;

[0023] The anode end of the second diode D2 is connected to one end of the second primary winding N2 of the modulator unit, and the cathode end of the second diode D2 is connected to one end of the third capacitor C3 and the third resistor R3 respectively, and the other ends of the third capacitor C3 and the third resistor R3 are connected to the primary ground PGND.

[0024] Further, the demodulator unit comprises:

[0025] A second operational amplifier OP2, a third diode D3, a fourth capacitor C4 and a fourth resistor R4;

[0026] The in-phase end of the second operational amplifier OP2 is connected to one end of the primary winding N2 in the modulator unit, the anode end of the third diode D3 is connected to the output end of the second operational amplifier OP2, the cathode end of the third diode D3 is connected to the reverse end of the second operational amplifier OP2, the fourth capacitor C4 and one end of the fourth resistor R4, and the other end of the fourth capacitor C4 and the fourth resistor R4 is connected to the primary ground PGND.

[0027] Further, the demodulator unit comprises:

[0028] a third NMOS transistor Q3, a fourth PMOS transistor Q4, a fourth diode D4, a fifth capacitor C5, a sixth capacitor C6, a fourth resistor R4, a fifth resistor R5, a sixth resistor R6 and a seventh resistor R7;

[0029] The cathode end of the fourth diode D4 and the drain end of the fourth PMOS tube Q4 are connected to one end of the primary winding N2 in the modulator, the anode end of the fourth diode D4 and one end of the fifth resistor R5 are connected to the gate end of the third NMOS tube Q3, the other end of the fifth resistor R5 and the other end of the primary winding N2 are both connected to the primary ground PGND, the fifth capacitor C5 is connected to the fourth diode D4 in parallel, the source end of the third NMOS tube Q3 is connected to the primary ground PGND, the drain end of the third NMOS tube Q3 is connected to the gate end of the fourth PMOS tube Q4, the source end of the fourth PMOS tube Q4 is connected to one end of the seventh resistor R7, the other end of the seventh resistor R7 is connected to one end of the sixth capacitor C6 and the sixth resistor R6, and the other end of the sixth capacitor C6 and the sixth resistor R6 are connected to the primary ground PGND.

[0030] Furthermore, one end of the magnetic isolation feedback circuit is connected to the controller of the LLC resonant converter, and the other end of the magnetic isolation feedback circuit is connected to the output end of the LLC resonant converter.

[0031] Compared with the prior art, the at least one technical solution adopted in the embodiments of this specification can achieve the following beneficial effects:

[0032] Aiming at the isolated feedback demand of the control signal of the isolated converter in the switching power supply, a magnetic isolation feedback circuit with good temperature characteristics and radiation resistance characteristics is provided, which can effectively reduce the cost, improve the reliability of the converter and increase the dynamic response speed. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0034] Figure 1 It is a structural schematic diagram of a magnetic isolation feedback circuit according to an embodiment of the present invention applied to a Buck+LLC resonant converter;

[0035] Figure 2 It is a schematic diagram of the structure of a magnetic isolation feedback circuit according to an embodiment of the present invention;

[0036] Figure 3 It is a structural schematic diagram of a demodulator unit of a magnetic isolation feedback circuit according to a second embodiment of the present invention;

[0037] Figure 4 It is a structural schematic diagram of a demodulator unit of a magnetic isolation feedback circuit according to a third embodiment of the present invention;

[0038] Figure 5 1 is a working waveform diagram of the magnetic isolation feedback circuit according to the embodiment of the present invention. DETAILED DESCRIPTION

[0039] The embodiments of the present application are described in detail below with reference to the accompanying drawings.

[0040] It should be noted that, in the absence of conflict, the embodiments and features in the embodiments of the present application can be combined with each other. The present invention will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0041] Reference Figure 1 As shown, the magnetic isolation feedback circuit of the present invention is used in the LLC resonant converter. The LLC resonant converter is an isolated converter, and its primary ground PGND and secondary ground SGND are not grounded together. Therefore, the circuit is used to transmit the error signal of the secondary output voltage sampling signal of the LLC resonant converter to the primary control chip to control the primary switch tube Q of the LLC resonant converter. H and Q L The duty cycle of the output voltage is thus controlled in a closed loop. Figure 1 As shown, one end of the magnetic isolation feedback circuit is connected to the controller of the LLC resonant converter, and the other end of the magnetic isolation feedback circuit is connected to the output end of the LLC resonant converter.

[0042] The magnetic isolation feedback circuit of the embodiment of the present invention is an isolation feedback method and circuit suitable for isolating control signals in an isolation converter. The isolation feedback method can effectively reduce costs, improve the reliability of the converter, and increase the dynamic response speed.

[0043] like Figure 2 As shown, the magnetic isolation feedback circuit includes three units: an error amplifier, a modulator unit and a demodulator unit.

[0044] The error amplifier unit amplifies the error signal sampled by the output voltage, and can be composed of an operational amplifier and its peripheral circuits. The output of the error amplifier unit serves as the input of the modulator unit.

[0045] The modulator unit modulates the input amplified error signal into a square wave signal with equal amplitude. It adopts a forward converter with a magnetic reset winding, in which the first NPN transistor Q1 works in the linear region, plays the role of impedance isolation, and converts the voltage error signal output by the error amplifier unit into a current signal flowing into the transformer winding. The second NPN transistor Q2 works in the switching state, which is equivalent to the switch tube of the forward converter. Its driving signal can be obtained by the voltage division of the secondary winding voltage of the isolation converter to achieve the switching synchronization of the magnetic isolation feedback circuit and the main circuit switch tube, avoiding the generation of beat frequency phenomenon. The output of the modulator unit is transmitted from the secondary side to the primary side through the transformer as the input of the demodulator unit.

[0046] If the error amplifier is implemented using analog devices, such as Figure 2 As shown in part A of FIG. 1 , the error amplifier unit includes: an operational amplifier OP1, a first resistor R1, a second resistor R2, a first capacitor C1, and a second capacitor C2. One end of the first resistor R1 is connected to the output voltage sampling signal V os The other end of the first resistor R1 is connected to the inverting end of the operational amplifier OP1, one end of the first capacitor C1 and one end of the second capacitor C2 respectively, the other end of the first capacitor C1 is connected to one end of the second resistor R2, the other end of the second resistor R2 and the other end of the second capacitor C2 are both connected to the output end of the operational amplifier OP1, and the non-inverting end of the operational amplifier OP1 is connected to the output voltage sampling signal V os The reference voltage V ref The error amplifier can change the proportional integral coefficient of the voltage regulator by adjusting the parameter values ​​of the first resistor R1, the second resistor R2, the first capacitor C1 and the second capacitor C2, thereby achieving the purpose of adjusting the loop.

[0047] Optionally, the error amplifier unit can also be implemented by a digital controller. Figure 2 As shown in part B, the ADC unit of the digital controller outputs the voltage sampling signal V os The analog signal is converted into a digital signal, and the digital signal is sent to the digital controller for digital control loop calculation. The calculated digital signal is converted into the output voltage error signal V by the DAC unit of the digital controller (which converts the digital signal into an analog signal). EA .

[0048] The modulator unit includes: a first NPN transistor Q1, a second NPN transistor Q2, a magnetic isolation transformer T1 and a first diode D1. The magnetic isolation transformer has three windings, namely N1, N2 and N3, wherein N1 is a secondary feedback winding, N2 is a primary winding, and N3 is an auxiliary winding for magnetic reset. The base of the first NPN transistor Q1 is connected to the output of the error amplifier, the collector of the first NPN transistor Q1 is connected to the power supply VCC of the secondary side of the LLC resonant converter, the emitter of the first NPN transistor Q1 is connected to the same-name end of the first primary winding N1 of the magnetic isolation transformer T1, the other end of the first primary winding N1 is connected to the collector of the second NPN transistor Q2, the emitter of the second NPN transistor Q2 is connected to the secondary ground SGND of the LLC resonant converter, and the base of the second NPN transistor Q2 is connected to the secondary ground SGND of the LLC resonant converter. The pole is connected to the same-name end of the secondary winding of the LLC resonant converter, one end of the second primary winding N2 of the magnetic isolation transformer T1 is connected to the primary ground PGND, the other end of the second primary winding N2 of the magnetic isolation transformer T1 is connected to the demodulator, one end of the auxiliary winding N3 of the magnetic isolation transformer T1 is connected to the secondary power supply VCC of the LLC resonant converter, the other end of the auxiliary winding N3 of the magnetic isolation transformer T1 is connected to the cathode of the first diode D1, and the anode of the first diode D1 is connected to the secondary ground SGND.

[0049] The demodulator unit is essentially a peak detection circuit. The demodulator unit realizes demodulating the modulated square wave into a DC signal with the same amplitude. In one embodiment of the present invention, Figure 2 As shown, the demodulator unit includes: a second diode D2, a third capacitor C3 and a third resistor R3. The anode end of the second diode D2 is connected to one end of the second primary winding N2 of the modulator unit, the cathode end of the second diode D2 is connected to one end of the third capacitor C3 and the third resistor R3 respectively, and the other ends of the third capacitor C3 and the third resistor R3 are connected to the primary ground PGND.

[0050] Alternatively, in another embodiment of the present invention, Figure 3 As shown, the demodulator unit includes: a second operational amplifier OP2, a third diode D3, a fourth capacitor C4 and a fourth resistor R4. The in-phase terminal of the second operational amplifier OP2 is connected to one end of the primary winding N2 in the modulator unit, the anode terminal of the third diode D3 is connected to the output terminal of the second operational amplifier OP2, the cathode terminal of the third diode D3 is connected to the reverse terminal of the second operational amplifier OP2, the fourth capacitor C4 and one end of the fourth resistor R4, and the other end of the fourth capacitor C4 and the fourth resistor R4 is connected to the primary ground PGND.

[0051] Optionally, the second diode D2 in the peak detection circuit can be replaced by a MOS tube to eliminate the influence of the diode voltage drop on the loop. Figure 4 The specific circuit is given. The demodulator unit includes: a third NMOS transistor Q3, a fourth PMOS transistor Q4, a fourth diode D4, a fifth capacitor C5, a sixth capacitor C6, a fourth resistor R4, a fifth resistor R5, a sixth resistor R6 and a seventh resistor R7. The cathode end of the fourth diode D4 and the drain end of the fourth PMOS tube Q4 are connected to one end of the primary winding N2 in the modulator, the anode end of the fourth diode D4 and one end of the fifth resistor R5 are connected to the gate end of the third NMOS tube Q3, the other end of the fifth resistor R5 and the other end of the primary winding N2 are both connected to the primary ground PGND, the fifth capacitor C5 is connected to the fourth diode D4 in parallel, the source end of the third NMOS tube Q3 is connected to the primary ground PGND, the drain end of the third NMOS tube Q3 is connected to the gate end of the fourth PMOS tube Q4, the source end of the fourth PMOS tube Q4 is connected to one end of the seventh resistor R7, the other end of the seventh resistor R7 is connected to one end of the sixth capacitor C6 and the sixth resistor R6, and the other end of the sixth capacitor C6 and the sixth resistor R6 are connected to the primary ground PGND.

[0052] Figure 5 This is a working waveform diagram of the magnetic isolation feedback circuit of the present invention. Figure 5 The working principle of the magnetic isolation feedback circuit of the embodiment of the present invention is described in detail. When the magnetic isolation feedback circuit is used, the steps are as follows:

[0053] Step 1: The first NPN transistor Q1 works in the linear region and acts as a voltage follower, and the second NPN transistor works in the saturation region and cutoff region and acts as a switch. Figure 5 As shown, at time t0, the second NPN transistor Q2 is turned on, and the voltage V applied to the primary side of the transformer is p =V EA –V BE The voltage Vs1 converted to the secondary side N2 is greater than the output voltage V o , at this time, the second diode D2 of the demodulator unit is turned on, and current will flow into the third capacitor C3 in a short time to charge it. p The peak current is I pp , which is mainly limited by the base current and current amplification factor of the first NPN transistor Q1.

[0054] Step 2: [t1, t2]: During this period, the voltage applied to the primary side of the transformer is still V p ,i p Increases linearly. Then:

[0055]

[0056] The transformer magnetic flux Φ increases linearly, the increase is ΔΦ (+) for:

[0057]

[0058] Where Di is the duty cycle of the second NPN transistor Q2, T si is the switching period. In this embodiment, the driving signal of the second NPN transistor Q2 is taken from the secondary winding of the LLC resonant converter. Therefore, its duty cycle is approximately 50%. si The switching cycle is the same as that of the LLC resonant converter, which realizes the synchronization of the switching frequency of the main power circuit and the control circuit, avoids the beat frequency phenomenon, and is beneficial to the stability of the control loop.

[0059] Step 3: [t2, t3]: At t2, the second NPN transistor Q2 is turned off, and the transformer is demagnetized through the reset winding. In this mode, the voltage v N3 =-V cc , then:

[0060]

[0061] The transformer magnetic flux Φ decreases by ΔΦ (-) for:

[0062]

[0063] Where, T r is the time for the magnetic flux to decrease to zero, and D reset =T r / T si .

[0064] Step 4: [t3, t4]: At t3, the transformer excitation current decreases to 0, so the voltage applied to the primary side of the transformer is 0. In this mode, the third capacitor C3 is still discharged.

[0065] In order for the transformer to complete magnetic reset, ΔΦ needs to be satisfied. (+) =ΔΦ (-) , then from equation (2) and equation (4) we can get:

[0066]

[0067] In order to enable the transformer to complete magnetic reset, D reset <1–D i . And V p Maximum V cc , combined with formula (5), we can get the following expression:

[0068]

[0069] According to the [t2, t4] time period, the output voltage drop can be expressed as:

[0070]

[0071] By increasing the third capacitor C3, the output voltage drop can be reduced. When the third capacitor C3 is large, ΔV s Approximately 0.

[0072] Therefore, the output voltage V s It can be expressed as:

[0073] V s =V p =V EA -V BE ≈V EA (8);

[0074] Thus, an approximately smooth DC voltage V is obtained. s , its amplitude is related to the secondary input signal V EA Approximately equal.

[0075] Beneficial effects of the embodiments of the present invention:

[0076] A magnetic isolation feedback circuit is constructed by discrete components, with a basic forward converter as the modulator. There is no need for an output filter inductor, which simplifies the circuit, makes the implementation method simple and low-cost, and achieves synchronization between the frequency of the control circuit and the main power switch frequency, which is beneficial to the stability of the control loop and has a faster dynamic response speed. The magnetic isolation feedback circuit utilizes the characteristic of the forward converter that can effectively transmit isolated signals, and is improved on this basis. There is no need for an output filter inductor, and the transformer is operated at a high frequency, which further reduces the volume of the magnetic components. Finally, discrete devices are used to implement magnetic isolation feedback. This method can effectively reduce costs and improve reliability. It has a small size and a small transmission delay, and is suitable for working environments with high temperatures and strong radiation. At the same time, it can effectively reduce costs, improve the reliability of the converter, and improve the dynamic response speed.

[0077] The above is only a specific embodiment of the present invention, and cannot be used to limit the scope of the invention. Therefore, the replacement of equivalent components, or equivalent changes and modifications made according to the scope of protection of the patent of the present invention, should still fall within the scope of this patent. In addition, the technical features of the present invention can be freely combined with each other, with each other, and with each other.

Claims

1. A magnetic isolation feedback circuit, characterized in that: include: An error amplifier unit, a modulator unit and a demodulator unit, wherein the output of the error amplifier unit is used as the input of the modulator unit, and the output of the modulator unit is used as the input of the demodulator unit; The magnetic isolation feedback circuit is used to sample the output voltage signal V of the secondary side of the LLC resonant converter. os The error signal is transmitted to the primary side of the LLC resonant converter to control the first primary side switch tube Q of the LLC resonant converter. H And the second primary switch tube Q L Duty cycle; The error amplifier unit is used to convert the output voltage sampling signal V os amplifying the error signal to generate an amplified error signal; The modulator unit is used to modulate the input amplified error signal into a square wave signal with equal amplitude; The demodulator unit is used to demodulate the modulated square wave signal into a DC signal with equal amplitude.

2. The magnetic isolation feedback circuit according to claim 1, characterized in that: The error amplifier unit comprises: Operational amplifier OP1, a first resistor R1, a second resistor R2, a first capacitor C1 and a second capacitor C2; One end of the first resistor R1 is connected to the output voltage sampling signal V os The other end of the first resistor R1 is connected to the inverting end of the operational amplifier OP1, one end of the first capacitor C1 and one end of the second capacitor C2 respectively, the other end of the first capacitor C1 is connected to one end of the second resistor R2, the other end of the second resistor R2 and the other end of the second capacitor C2 are both connected to the output end of the operational amplifier OP1, and the non-inverting end of the operational amplifier OP1 is connected to the output voltage sampling signal V os The reference voltage V ref are connected.

3. The magnetic isolation feedback circuit according to claim 1, characterized in that: The error amplifier unit comprises: Digital controller; The output voltage sampling signal V is converted by the ADC unit of the digital controller os The digital signal is converted into a digital signal, and the digital signal is sent to the digital controller, and the DAC unit of the digital controller converts the calculated digital signal into an output voltage error signal V EA .

4. The magnetic isolation feedback circuit according to claim 1, characterized in that: The modulator unit comprises: It includes a first NPN transistor Q1, a second NPN transistor Q2, a magnetic isolation transformer T1 and a first diode D1; The base of the first NPN transistor Q1 is connected to the output of the error amplifier, the collector of the first NPN transistor Q1 is connected to the power supply VCC of the secondary side of the LLC resonant converter, the emitter of the first NPN transistor Q1 is connected to the same-name end of the first primary winding N1 of the magnetic isolation transformer T1, the other end of the first primary winding N1 is connected to the collector of the second NPN transistor Q2, the emitter of the second NPN transistor Q2 is connected to the secondary ground SGND of the LLC resonant converter, and the base of the second NPN transistor Q2 is connected to the secondary ground SGND of the LLC resonant converter. The pole is connected to the same-name end of the secondary winding of the LLC resonant converter, one end of the second primary winding N2 of the magnetic isolation transformer T1 is connected to the primary ground PGND, the other end of the second primary winding N2 of the magnetic isolation transformer T1 is connected to the demodulator, one end of the auxiliary winding N3 of the magnetic isolation transformer T1 is connected to the secondary power supply VCC of the LLC resonant converter, the other end of the auxiliary winding N3 of the magnetic isolation transformer T1 is connected to the cathode of the first diode D1, and the anode of the first diode D1 is connected to the secondary ground SGND.

5. The magnetic isolation feedback circuit according to claim 1, characterized in that: The demodulator unit comprises: A second diode D2, a third capacitor C3 and a third resistor R3; The anode end of the second diode D2 is connected to one end of the second primary winding N2 of the modulator unit, and the cathode end of the second diode D2 is respectively connected to one end of the third capacitor C3 and the third resistor R3, and the other ends of the third capacitor C3 and the third resistor R3 are connected to the primary ground PGND.

6. The magnetic isolation feedback circuit according to claim 1, characterized in that: The demodulator unit comprises: A second operational amplifier OP2, a third diode D3, a fourth capacitor C4 and a fourth resistor R4; The in-phase end of the second operational amplifier OP2 is connected to one end of the primary winding N2 in the modulator unit, the anode end of the third diode D3 is connected to the output end of the second operational amplifier OP2, the cathode end of the third diode D3 is connected to the reverse end of the second operational amplifier OP2, the fourth capacitor C4 and one end of the fourth resistor R4, and the other end of the fourth capacitor C4 and the fourth resistor R4 is connected to the primary ground PGND.

7. The magnetic isolation feedback circuit according to claim 1, characterized in that: The demodulator unit comprises: a third NMOS transistor Q3, a fourth PMOS transistor Q4, a fourth diode D4, a fifth capacitor C5, a sixth capacitor C6, a fourth resistor R4, a fifth resistor R5, a sixth resistor R6 and a seventh resistor R7; The cathode end of the fourth diode D4 and the drain end of the fourth PMOS tube Q4 are connected to one end of the primary winding N2 in the modulator, the anode end of the fourth diode D4 and one end of the fifth resistor R5 are connected to the gate end of the third NMOS tube Q3, the other end of the fifth resistor R5 and the other end of the primary winding N2 are both connected to the primary ground PGND, the fifth capacitor C5 is connected to the fourth diode D4 in parallel, the source end of the third NMOS tube Q3 is connected to the primary ground PGND, the drain end of the third NMOS tube Q3 is connected to the gate end of the fourth PMOS tube Q4, the source end of the fourth PMOS tube Q4 is connected to one end of the seventh resistor R7, the other end of the seventh resistor R7 is connected to the sixth capacitor C6 and one end of the sixth resistor R6, and the other end of the sixth capacitor C6 and the sixth resistor R6 are connected to the primary ground PGND.

8. The magnetic isolation feedback circuit according to any one of claims 1 to 7, characterized in that: One end of the magnetic isolation feedback circuit is connected to the controller of the LLC resonant converter, and the other end of the magnetic isolation feedback circuit is connected to the output end of the LLC resonant converter.

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