CN206865350U - A kind of filter circuit and power supply adaptor - Google Patents

Abstract

The embodiment of the utility model discloses a filter circuit and a power adapter. The filter circuit includes: a DC input terminal, a differential mode interference suppression module and a common mode interference suppression module; wherein, the differential mode interference suppression module is connected to the DC input terminal , for performing differential-mode interference suppression on the DC signal input by the DC input terminal; the common-mode interference suppression module is connected to the DC input terminal through the differential-mode interference suppression module, and is used for common-mode interference suppression for the DC signal Mode interference suppression. Since the filter circuit provided by this implementation model does not need to increase the discharge resistance, the no-load loss of the power supply can be reduced by using the above circuit, the average efficiency of the power supply can be improved, and the design of the circuit can also be simplified under the condition of meeting the European Union VI energy efficiency requirements. .

Description

A filter circuit and power adapter

technical field

The embodiment of the utility model relates to the field of power supply technology, in particular to a filter circuit and a power adapter.

Background technique

As the global energy becomes more and more tense, energy conservation and emission reduction has become a common goal pursued by people. It is also particularly important to improve the average efficiency of the switching power supply, reduce the loss of the power supply when it is no-load, and reduce the power consumption when the terminal system is in standby. All of these drive the continuous development of electronic products in the direction of "high efficiency and low standby power consumption". As the "heart" and power source of electronic products, the power supply is the key to improving the efficiency of electronic products while reducing power consumption.

Since the power supply itself will generate EMI (Electromagnetic Interference, electromagnetic interference) to other surrounding equipment, it will also be subjected to electromagnetic interference generated by other equipment and propagated through the power supply. Therefore, the EMI filter circuit will play a very important role in the use of the power supply. In the prior art, an X capacitor (CX1) is used in the EMI filter circuit to suppress differential mode interference. Usually the X capacitor is a safety capacitor, which is connected between the AC L line (live line) and the N line (neutral line), and is used to suppress the differential mode interference noise at the AC incoming line end. Since the X capacitor is located at the AC terminal in front of the rectifier bridge, when the power is cut off, the X capacitor will still store a certain amount of charge. Therefore, a discharge resistor must be added below the X capacitor to meet the discharge test requirements defined by the safety regulations, thereby avoiding The electric shock hazard caused by the charge stored in the X capacitor to the contacts of the power supply equipment after power failure.

However, due to the increase of the bleeder resistance, the no-load loss after the power supply is turned off increases, and it is difficult to meet the no-load loss requirement in the sixth-level energy efficiency, which increases the difficulty of design.

Utility model content

The embodiment of the utility model provides a filter circuit and a power adapter, which can reduce the no-load loss after the power is cut off while satisfying EMI filtering.

The embodiment of the utility model provides a filtering circuit, which includes: a DC input terminal, a differential mode interference suppression module and a common mode interference suppression module; wherein,

The differential-mode interference suppression module is connected to the DC input terminal, and is used to suppress differential-mode interference on the DC signal input by the DC input terminal;

The common-mode interference suppression module is connected to the DC input terminal through the differential-mode interference suppression module, and is used for suppressing the common-mode interference on the DC signal.

Further, the differential-mode interference suppression module includes two electrolytic capacitors, and the common-mode interference suppression module includes a common-mode inductor; wherein,

Both ends of the first electrolytic capacitor are connected between the two DC input ends, and are respectively connected to the two input ends of the common mode inductor;

Both ends of the second electrolytic capacitor are respectively connected to the two output ends of the common mode inductor.

The embodiment of the utility model provides a power adapter, which includes a rectifier circuit, a transformer, and a filter circuit; the DC input terminal of the filter circuit is connected to the output terminal of the rectifier circuit, and the output terminal of the filter circuit is connected to the output terminal of the rectifier circuit. connected to the input of the transformer.

Further, the transformer includes a primary coil, an auxiliary coil and a secondary coil; wherein,

The primary coil is connected to the output end of the filter circuit for providing an input voltage signal;

The secondary coil is connected to the load, and is used to output a power supply voltage according to the input voltage signal to supply power to the load;

The auxiliary coil and the primary coil are arranged at the same terminal, and are used to convert the supply voltage into an auxiliary voltage signal according to the transformer turn ratio.

Further, the power adapter also includes: a start-up circuit connected to the filter circuit for generating a start-up voltage signal according to the filtered electrical signal;

a sampling circuit, connected to the auxiliary coil of the transformer, for detecting the auxiliary voltage signal and generating a sampling voltage signal;

An IC chip, connected to the start-up circuit, for obtaining the start-up voltage signal, and working under the drive of the start-up voltage signal; the IC chip is connected with the sampling circuit and the primary coil of the transformer, for obtaining The sampling voltage signal, and according to the sampling voltage signal, the MOS transistor packaged in the IC chip performs chopping on the rectified DC voltage signal to obtain a pulse voltage signal, so as to adjust the input voltage signal, and through the transformer, the Adjust the output voltage of the secondary coil.

Further, the power adapter also includes: an RCD absorbing circuit, connected to the IC chip, for absorbing the voltage spike generated by the MOS tube during the off period;

The secondary rectifying and filtering circuit is connected to the secondary coil of the transformer, and is used to rectify the supply voltage to obtain a DC signal to supply power to the load.

Further, the rectification circuit is a full-wave rectification circuit, wherein the rectification circuit further includes a fuse, a varistor and a thermistor for protecting the power adapter.

Further, the starting circuit includes a starting resistor and a third capacitor, wherein,

The starting resistor is connected in series with the third capacitor, and is connected between the DC positive output terminal of the filter circuit and the ground wire;

The positive end of the third capacitor is connected to the IC chip, and is used to drive the IC chip to work when the third capacitor is charged to form a starting voltage signal. Further, the sampling circuit includes a first resistor, a second resistor and a first diode; wherein,

The circuit in which the first resistor and the second resistor are connected in series is connected in parallel at both ends of the auxiliary coil of the transformer;

The positive end of the first diode is connected to the auxiliary coil of the transformer, and the negative end of the first diode is connected to the positive end of the third capacitor;

The connection point between the first resistor and the second resistor is used as a sampling point, connected to the IC chip, and used for obtaining a sampling voltage signal from the sampling point.

Further, the RCD absorbing circuit includes: a fourth capacitor, a third resistor, and a fourth resistor connected in parallel in sequence, and connected in series with the second diode; wherein,

The first terminal of the fourth capacitor and the positive terminal of the second diode are respectively connected to the primary coil of the transformer, and the negative terminal of the second diode is connected to the second terminal of the fourth capacitor. connected;

At the same time, the anode terminal of the second diode is connected to the drain terminal of the MOS transistor.

Further, the secondary rectification and filtering circuit includes a third diode, an RC snubber circuit, a fifth capacitor and a sixth capacitor; wherein,

The positive terminal of the third diode is connected to the secondary coil of the transformer, and the negative terminal of the third diode is connected to the positive terminal of the fifth capacitor;

The RC snubber circuit is connected in parallel at both ends of the third diode;

The negative terminal of the fifth capacitor is connected to the secondary ground;

The sixth capacitor is connected in parallel with both ends of the fifth capacitor.

The embodiment of the utility model provides a filter circuit and a power adapter, which are connected to the DC input terminal through a differential mode interference suppression module, and can perform differential mode interference suppression on the DC signal input by the DC input terminal; by using the common mode interference suppression module, The differential mode interference suppression module is connected to the DC input terminal, and is used for suppressing the common mode interference of the DC signal. Since the differential mode interference suppression module is not directly connected to the AC input terminal in the filter circuit provided by this implementation model, it is connected to the DC input terminal, so after the power is cut off, there will be no accumulated charge, and there is no need to increase the discharge Therefore, the no-load loss of the power supply can be reduced, and the average efficiency of the power supply can be improved at the same time, and the circuit design can also be simplified under the condition of meeting the European Union VI energy efficiency requirements.

Description of drawings

FIG. 1 is a schematic structural diagram of a filter circuit provided by Embodiment 1 of the present invention;

Fig. 2 is a kind of preferred EMI filtering circuit that the utility model embodiment one provides;

Fig. 3a is a structural block diagram of a power adapter provided by Embodiment 2 of the present invention;

Figure 3b is a preferred rectification and EMI filter circuit diagram provided by Embodiment 2 of the present invention;

Fig. 4 is a schematic structural diagram of a power adapter circuit provided by Embodiment 3 of the present invention;

FIG. 5 is a schematic diagram of a preferred power adapter circuit provided by Embodiment 3 of the present invention.

detailed description

Below in conjunction with accompanying drawing and embodiment the utility model is described in further detail. It can be understood that the specific embodiments described here are only used to explain the utility model, rather than limit the utility model. In addition, it should be noted that, for the convenience of description, only some structures related to the present utility model are shown in the drawings but not all structures.

Embodiment one

Fig. 1 is a schematic structural diagram of a filter circuit provided by Embodiment 1 of the present invention; the circuit can be integrated into a power adapter or an open switching power supply to supply power to terminal equipment. As shown in FIG. 1 , the circuit specifically includes: a DC input terminal 110 , a differential mode interference suppression module 120 and a common mode interference suppression module 130 .

Among them, the differential mode interference suppression module 120 is connected to the DC input terminal 110, and is used for differential mode interference suppression on the DC signal input by the DC input terminal; the common mode interference suppression module 130 is connected to the DC input terminal through the differential mode interference suppression module 120 , for common-mode interference suppression of DC signals.

Among them, differential-mode interference and common-mode interference signals belong to EMI interference. Exemplarily, when a switching power supply is working or other electronic devices are in a switching state, noise will appear at the input end of the power supply, resulting in radiated and conducted interference, that is, EMI interference. EMI interference also enters the AC grid and interferes with other electronic equipment again. Therefore, it is necessary to take effective measures to suppress EMI interference, so as to ensure the normal and effective operation of electronic equipment. The embodiment of the utility model improves the EMI filter circuit containing the X capacitor in the prior art through the differential mode interference suppression module and the common mode interference suppression module, and realizes the suppression of EMI interference. In the filter circuit provided by the embodiment of the present invention, the differential mode interference suppression module is not directly connected to the AC input terminal, but is connected to the DC input terminal, so after the power is cut off, there will be no accumulated charge, so the power supply space can be reduced. load loss, improve the average efficiency of the power supply, and simplify the circuit design while meeting the EU VI energy efficiency requirements.

Exemplarily, the differential-mode interference suppression module includes two electrolytic capacitors C1 and C2, and the common-mode interference suppression module includes a common-mode inductor LF1; wherein, both ends of the first electrolytic capacitor C1 are connected between two DC input terminals , and are respectively connected to the two input terminals of the common mode inductor LF1; both ends of the second electrolytic capacitor C2 are respectively connected to the two output terminals of the common mode inductor LF1. FIG. 2 is a preferred EMI filter circuit provided by Embodiment 1 of the present invention. As shown in Figure 2, by matching C1, C2 and LF1, the filtering of EMI interference in the circuit can be realized.

Exemplarily, the filter circuit provided in this embodiment can be integrated into a power adapter to filter out EMI interference in the power adapter circuit.

This embodiment provides a filter circuit, including a DC input terminal, a differential mode interference suppression module, and a common mode interference suppression module. Differential-mode interference suppression; common-mode interference suppression module, which is connected to the DC input through the differential-mode interference suppression module, can realize common-mode interference suppression on DC signals. Since the filter circuit provided by this implementation model does not need to increase the discharge resistor, it can reduce the no-load loss of the power supply, improve the average efficiency of the power supply, and simplify the circuit design under the condition of meeting the European Union VI energy efficiency requirements.

Embodiment two

Fig. 3a is a structural block diagram of a power adapter provided by Embodiment 2 of the present invention. This embodiment can integrate the filter circuit provided by the above embodiments. As shown in FIG. 3 a , the power adapter 200 includes a rectifier circuit 210 , a filter circuit 220 and a transformer 230 . in,

The DC input end 221 of the filter circuit 220 is connected with the output end of the rectification circuit 210, and the output end of the filter circuit 220 is connected with the input end of the transformer 230.

It should be noted that the transformer 230 preferably includes a primary coil, an auxiliary coil and a secondary coil; wherein, the primary coil is connected to the output end of the filter circuit for providing an input voltage signal; the secondary coil is connected to a load for The voltage signal outputs the power supply voltage to supply power to the load; the auxiliary coil and the primary coil are set according to the same terminal, and are used to convert the power supply voltage into an auxiliary voltage signal according to the transformer turn ratio. The auxiliary voltage signal can be used for sampling or other auxiliary processing functions. Since the transformer is between the primary and secondary of the power adapter, it can isolate the primary high voltage from the secondary low voltage.

Exemplarily, the rectification circuit in this embodiment may be a full-wave rectification circuit. Fig. 3b is a circuit diagram of a preferred rectification and EMI filter provided by Embodiment 2 of the present invention. As shown in Figure 3b, when the output terminal of the rectifier circuit is connected to the input terminal of the filter circuit, since the diode in the rectifier circuit is in the reverse cut-off state, the charge stored in the electrolytic capacitor of the filter circuit Under the circumstances, it cannot be fed back to the secondary coil end of the transformer. Therefore, after the power is cut off, it can also avoid the phenomenon that the contactor will be shocked by touching the power adapter. The safety of the power adapter can be effectively improved.

Further, as shown in FIG. 3 b , the rectifier circuit may also include a fuse F1 , a piezoresistor MOV1 and a thermistor NTC1 . The above-mentioned device can be used as a protection device for a circuit against 4KV lightning strike, so the safety of the circuit can be further improved by using the above-mentioned device.

This embodiment provides a power adapter, which can obtain a DC voltage by rectifying the AC voltage input from the power grid through a rectifier circuit, and then filter the DC voltage through a filter circuit to filter out EMI interference in the circuit, and then use a transformer as an energy conversion The device supplies power to the load. By adopting the above circuit, the power adapter can supply power to the terminal equipment.

Embodiment three

Fig. 4 is a schematic structural diagram of a power adapter circuit provided by Embodiment 3 of the present invention. This embodiment is further optimized on the basis of the above embodiments. As shown in Fig. 4, the power adapter 300 includes a rectifier circuit 310 , filter circuit 320 , startup circuit 330 , RCD absorption circuit 340 , transformer 350 , sampling circuit 360 , IC chip 370 and secondary rectification filter circuit 380 . Each circuit is described in detail below:

(1) The start-up circuit 330 is connected to the filter circuit 320, and is used to generate a start-up voltage signal according to the electric signal after filtering;

Exemplarily, FIG. 5 is a schematic diagram of a preferred power adapter circuit provided by Embodiment 3 of the present invention. As shown in Figure 5, the start-up circuit 330 includes a start-up resistor 331 and a third capacitor C3; wherein the start-up resistor 331 is connected in series with the third capacitor C3, and is connected between the DC positive output terminal of the filter circuit and the ground wire; the third capacitor The positive end of C3 is connected to the IC chip 370, and is used to drive the IC chip 370 to work when the third capacitor C3 is charged to form a starting voltage signal. Specifically, the starting resistor 331 may include an eighth resistor R8, a ninth resistor R9 and a tenth resistor R10.

It should be noted that when the circuit is working normally, there will be some loss in the starting resistor. If the total resistance value of the starting resistor is defined as Rin, and the rectified DC high voltage is defined as V _dc , then the loss of the starting resistor Rin is:

Therefore, in the case of properly reducing the capacity of the third capacitor C3, by increasing the resistance of the starting resistor, the loss in the starting resistor can be reduced, thereby reducing the no-load loss of the power adapter and improving the efficiency of the power supply. Preferably, the value of the third capacitor C3 is 6.8 μF.

(2) The sampling circuit 360 is connected to the auxiliary coil of the transformer, and is used to detect the auxiliary voltage signal and generate a sampling voltage signal.

Exemplarily, as shown in FIG. 5, the sampling circuit 360 includes a first resistor R1, a second resistor R2, and a first diode D1; wherein, the circuit in which the first resistor R1 and the second resistor R2 are connected in series is connected in parallel to the transformer The two ends of the auxiliary coil; the positive terminal of the first diode D1 is connected to the auxiliary coil of the transformer, and the negative terminal of the first diode D1 is connected to the positive terminal of the third capacitor C3. The connection point between the first resistor R1 and the second resistor R2 is used as a sampling point, which is connected to the IC chip, and is used for obtaining a sampling voltage signal from the sampling point.

It should be noted that after the IC chip is started, the auxiliary winding of the transformer charges the third capacitor C3 to maintain the working state of the IC chip. As shown in FIG. 5, since the third capacitor is an electrolytic capacitor and needs to work in a DC circuit, the AC signal of the auxiliary winding of the transformer can be rectified into a DC signal through the first diode D1 to charge the third capacitor C3.

Further, the sampling circuit 360 may further include an eighth capacitor C8, and the two ends of the eighth capacitor C8 are connected in parallel to the two ends of the transformer auxiliary coil for filtering out EMC (Electro Magnetic Compatibility, electromagnetic compatibility) interference in the circuit.

Further, the sampling circuit 360 may further include a ninth capacitor C9, and the two ends of the ninth capacitor C9 are connected in parallel with the two ends of the first resistor R1 to prevent the interference signal in the circuit from entering the IC chip, thereby ensuring the normal operation of the IC chip. Work.

(3) IC chip 370 is connected with the starting circuit 330 for obtaining the starting voltage signal and works under the drive of the starting voltage signal; the IC chip 370 is connected with the sampling circuit 360 and the primary coil of the transformer for obtaining the sampling voltage signal , and according to the sampling voltage signal, the DC voltage is chopped through the MOS transistor packaged in the IC chip to obtain a pulse voltage to adjust the input voltage signal, and the voltage output by the secondary coil is adjusted through the transformer.

Further, the two parallel resistors R11 and R12 can be connected to the current detection pin of the IC chip that functions as overcurrent protection, and the primary peak current flowing through the MOS tube is converted into voltage feedback to the IC chip through the current detection resistors R11 and R12 The current detection pin realizes the effect of overcurrent protection.

The working principle of the startup circuit, the sampling circuit and the IC chip is described in detail below:

When the high-voltage signal rectified by the rectifier circuit passes through the start-up resistor, it can charge the third capacitor C3, as shown in Figure 5, since the positive terminal of the third capacitor C3 is connected to the power supply pin VDD of the IC chip, therefore, when the VDD terminal After the voltage reaches the starting voltage of the IC chip, the IC chip will start and drive the entire power system to work. When the IC chip is started, power is supplied to the IC chip through the auxiliary coil of the transformer through the third capacitor C3.

Since the MOS tube is packaged in the IC chip, the IC chip can realize the chopping of the voltage by controlling the opening and closing of the MOS tube, that is, the DC voltage input to the primary coil is chopped into a pulse voltage. Wherein, the amplitude of the pulse voltage is equal to the amplitude of the input DC voltage. Since the feedback terminal of the IC chip is connected between the first resistor R1 and the second resistor R2, the voltage of the auxiliary coil of the transformer can be detected through the first resistor R1 and the second resistor R2, and a sampled voltage signal is generated and fed back to the IC chip. Since there is a certain proportional relationship between the voltage at both ends of the auxiliary coil of the transformer and the output voltage at both ends of the secondary coil of the transformer, the IC chip can detect the output voltage of the transformer according to the sampling voltage signal, and adjust the duty cycle according to the sampling voltage signal, thereby controlling the MOS The turn-on time and turn-off time of the tube to ensure a stable output voltage of the transformer. For example, when the output voltage of the secondary coil of the transformer is too high, the sampling voltage obtained through R1 and R2 is also relatively high. If the sampling voltage is greater than the preset reference voltage of the IC chip, the IC chip will reduce the duty cycle, Then reduce the conduction time of the MOS tube to reduce the output voltage of the transformer. By adopting the above technical solution, a stable voltage can be output through the transformer to supply power to the load.

(4) The RCD absorbing circuit 340 is connected to the IC chip 370 and is used to absorb the voltage spike generated by the MOS transistor during the turn-off period.

Specifically, the RCD absorbing circuit 340 includes: a fourth capacitor C4, a third resistor R3, a fourth resistor R4, and a second diode D2 connected in parallel in sequence; wherein, the first end of the fourth capacitor C4 and the second diode The positive end of D2 is connected to the primary coil of the transformer respectively, the negative end of the second diode D2 is connected to the second end of the fourth capacitor C4 ; meanwhile, the positive end of the second diode D2 is connected to the IC chip 370 .

Exemplarily, the value range of R3 and R4 is preferably 200KΩ-390KΩ, and the value range of the fourth capacitor C4 is preferably: 1nF-2.2nF.

The function of the RCD absorption circuit is to absorb the voltage peak generated by the leakage inductance of the transformer at the drain of the MOS tube when the MOS tube is turned off, and avoid the voltage peak from breaking down the MOS tube. Therefore, the RCD absorption circuit can ensure the safe operation of the MOS tube and improve the circuit performance. reliability.

(5) The secondary rectification and filtering circuit 380 is connected to the secondary coil of the transformer, and is used to rectify the supply voltage to obtain a DC signal to supply power to the load.

Specifically, the secondary rectification and filtering circuit 380 includes a third diode D3, an RC snubber circuit 381, a fifth capacitor C5, and a sixth capacitor C6; wherein, the positive end of the third diode D3 is connected to the secondary coil of the transformer , the negative end of the third diode D3 is connected to the positive end of the fifth capacitor C5; the RC snubber circuit 381 is connected in parallel to both ends of the rectifier diode D3; the negative end of the fifth capacitor C5 is connected to the secondary ground; the sixth capacitor C6 is connected in parallel at both ends of the fifth capacitor C5.

Wherein, the third diode D3 serves as a path through which the power device can carry a large current. Since reducing the loss on the diode is an important part of realizing the overall six-level energy efficiency of the power supply, the third diode D3 should be a low-drop diode.

Specifically, the RC snubber circuit 381 includes a seventh capacitor C7 and a fifth resistor R5; wherein, the seventh capacitor C7 and the fifth resistor R5 are connected in series. The function of the RC absorption circuit is to absorb the reverse voltage peak of the third diode D3 during the turn-off period of the MOS transistor, so that the reverse peak voltage of the third diode D3 works below its specification value, so as to ensure that the third diode D3 D3 safe work. Preferably, the value range of the fifth resistor R5 is preferably 10Ω-68Ω, and the value range of the seventh capacitor C7 is preferably 220pF˜1000pF.

It should be noted that the secondary rectification filter circuit can rectify the voltage induced by the secondary coil of the transformer through the third diode D3, and then obtain a smooth and stable DC voltage after filtering by the filter capacitors (C5 and C6). The use of end products provides high-precision and stable power supply.

This embodiment provides a power adapter circuit. On the basis of the above embodiments, this embodiment can combine the startup circuit, sampling circuit and IC chip with the rectifier circuit, filter circuit and transformer provided by the above embodiments. The voltage output by the secondary coil of the transformer is fed back to the IC chip, and the IC chip adjusts the duty cycle to control the opening and closing of the internal MOS tube, thereby stabilizing the output voltage of the transformer. The RCD absorbing circuit can absorb the voltage spike generated by the leakage inductance of the transformer at the drain of the MOS tube during the turn-off period of the MOS tube, so as to avoid the failure of the MOS tube. At the same time, after processing by the secondary rectification and filtering circuit, a smooth and stable DC voltage can be obtained to provide a stable power supply for the load. The power adapter circuit provided by this new implementation embodiment not only meets the basic requirements of the European Union VI energy efficiency, but also has the characteristics of high energy efficiency and low power consumption, and has high reliability.

Note that the above are only preferred embodiments of the present invention and the applied technical principles. Those skilled in the art will understand that the utility model is not limited to the specific embodiments described here, and various obvious changes, readjustments and substitutions can be made by those skilled in the art without departing from the protection scope of the utility model. Therefore, although the utility model has been described in detail through the above embodiments, the utility model is not limited to the above embodiments, and can also include more other equivalent embodiments without departing from the concept of the utility model. The scope of the present invention is determined by the appended claims.

Claims (10)

1. A filter circuit, characterized in that it comprises: a DC input terminal, a differential mode interference suppression module and a common mode interference suppression module; wherein, The differential-mode interference suppression module is connected to the DC input terminal, and is used to suppress differential-mode interference on the DC signal input by the DC input terminal; The common-mode interference suppression module is connected to the DC input terminal through the differential-mode interference suppression module, and is used for suppressing the common-mode interference on the DC signal. 2. The circuit according to claim 1, wherein the differential-mode interference suppression module includes two electrolytic capacitors, and the common-mode interference suppression module includes a common-mode inductor; wherein, Both ends of the first electrolytic capacitor are connected between the two DC input ends, and are respectively connected to the two input ends of the common mode inductor; Both ends of the second electrolytic capacitor are respectively connected to the two output ends of the common mode inductor. 3. A power adapter, comprising a rectifier circuit and a transformer, characterized in that it also includes the filter circuit according to claim 1 or 2; the DC input end of the filter circuit is connected to the output end of the rectifier circuit, and the The output terminal of the filter circuit is connected with the input terminal of the transformer. 4. The power adapter according to claim 3, wherein the transformer comprises a primary coil, an auxiliary coil and a secondary coil; wherein, The primary coil is connected to the output end of the filter circuit for providing an input voltage signal; The secondary coil is connected to the load, and is used to output a power supply voltage according to the input voltage signal to supply power to the load; The auxiliary coil and the primary coil are arranged at the same terminal, and are used to convert the supply voltage into an auxiliary voltage signal according to the transformer turn ratio. 5. The power adapter according to claim 4, further comprising: The starting circuit is connected to the filter circuit, and is used to generate a starting voltage signal according to the filtered electrical signal; a sampling circuit, connected to the auxiliary coil of the transformer, for detecting the auxiliary voltage signal and generating a sampling voltage signal; An IC chip, connected to the start-up circuit, for obtaining the start-up voltage signal, and working under the drive of the start-up voltage signal; the IC chip is connected with the sampling circuit and the primary coil of the transformer, for obtaining The sampling voltage signal, and according to the sampling voltage signal, the MOS transistor packaged in the IC chip performs chopping on the rectified DC voltage signal to obtain a pulse voltage signal, so as to adjust the input voltage signal, and through the transformer, the Adjust the output voltage of the secondary coil. 6. The power adapter according to claim 5, further comprising: The RCD absorbing circuit is connected with the IC chip and is used to absorb the voltage spike generated by the MOS tube during the off period; The secondary rectifying and filtering circuit is connected to the secondary coil of the transformer, and is used to rectify the supply voltage to obtain a DC signal to supply power to the load. 7. The power adapter according to claim 5, wherein the startup circuit includes a startup resistor and a third capacitor; wherein, The starting resistor is connected in series with the third capacitor, and is connected between the DC positive output terminal of the filter circuit and the ground wire; The positive end of the third capacitor is connected to the IC chip, and is used to drive the IC chip to work when the third capacitor is charged to form a starting voltage signal. 8. The power adapter according to claim 7, wherein the sampling circuit comprises a first resistor, a second resistor and a first diode; wherein, The circuit in which the first resistor and the second resistor are connected in series is connected in parallel at both ends of the auxiliary coil of the transformer; The positive end of the first diode is connected to the auxiliary winding of the transformer, and the negative end of the first diode is connected to the positive end of the third capacitor; The connection point between the first resistor and the second resistor is used as a sampling point, connected to the IC chip, and used for obtaining a sampling voltage signal from the sampling point. 9. The power adapter according to claim 6, wherein the RCD snubbing circuit comprises: a fourth capacitor, a third resistor, and a fourth resistor connected in parallel in sequence, and connected in series with the second diode; wherein, The first terminal of the fourth capacitor and the positive terminal of the second diode are respectively connected to the primary coil of the transformer, and the negative terminal of the second diode is connected to the second terminal of the fourth capacitor. connected; At the same time, the anode terminal of the second diode is connected to the drain terminal of the MOS transistor. 10. The power adapter according to claim 6, wherein the secondary rectification filter circuit comprises a third diode, an RC snubber circuit, a fifth capacitor and a sixth capacitor; wherein, The positive terminal of the third diode is connected to the secondary coil of the transformer, and the negative terminal of the third diode is connected to the positive terminal of the fifth capacitor; The RC snubber circuit is connected in parallel at both ends of the third diode; The negative terminal of the fifth capacitor is connected to the secondary ground; The sixth capacitor is connected in parallel with both ends of the fifth capacitor.