CN106783099A - A kind of transformer and power supply adaptor - Google Patents

Abstract

The embodiment of the present invention discloses a transformer and a power adapter. The transformer includes: a skeleton, a primary coil reversely wound on the skeleton, an auxiliary coil and a shielding coil, and a secondary winding forwardly wound on the skeleton Coil; wherein, the primary coil is used to receive the voltage signal output by the power supply, and provide an input voltage signal to the secondary coil according to the voltage signal; the secondary coil is connected to a 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 set according to the terminal with the same name, and are used to convert the power supply voltage into an auxiliary voltage signal according to the transformer turn ratio; the shielding coil is grounded, as the shielding layer of the transformer, used to adjust the The parasitic capacitance of the above-mentioned transformer, and suppress EMI interference. Therefore, by using the transformer provided in this embodiment, there is no need to add a Y capacitor in the circuit, and at the same time, EMI interference can be effectively suppressed. The reliability of the power supply is improved.

Description

Transformer and power adapter

technical field

Embodiments of the present invention relate to the technical field of power supplies, and in particular, to a transformer 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, the Y capacitor, as a safety capacitor, has a certain inhibitory effect on EMI interference between the primary and secondary sides of the power supply. At the same time, the existence of the secondary common-mode inductance can cooperate with the Y capacitor to suppress EMI interference on terminal equipment ground. Through the Y capacitor and the secondary common mode inductance, the EMI index of the power supply can meet the requirements of the safety standard.

However, the existence of Y capacitors has potential risks to the safety of users, and it will also have adverse effects on many products. The main reason is that although the Y capacitor is a safety device, it cannot guarantee the possibility that it will never fail. Since the Y capacitor is connected across the primary and secondary of the power supply (that is, between high and low voltage), once it fails, it will change from the previous high impedance to low impedance, and directly connect the primary high voltage of the power supply to the secondary ground, and then pass the power ground to the secondary ground. When the terminal product is connected, high voltage appears on the shell or port of the terminal product, which will endanger the personal safety of the user. In addition, due to the existence of the Y capacitor, the leakage current of the power supply will increase sharply, and the leakage current will affect the normal use of terminal equipment such as medical equipment or voice calls, resulting in a decrease in the performance of the terminal equipment. Therefore, the presence of Y capacitors reduces the reliability of the power supply.

Contents of the invention

Embodiments of the present invention provide a transformer and a power adapter, which improve power supply reliability while implementing EMI filtering.

In the first aspect, an embodiment of the present invention provides a transformer, including: a bobbin, a primary coil wound on the bobbin in reverse, an auxiliary coil and a shielding coil, and a secondary coil wound forward on the bobbin ;in,

The primary coil is used to receive a voltage signal output by a power supply, and provide an input voltage signal to the secondary coil according to the 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 end, and are used to convert the supply voltage into an auxiliary voltage signal;

The shielding coil is grounded and used as a shielding layer of the transformer for adjusting the parasitic capacitance of the transformer and suppressing EMI interference.

Further, the transformer is a vertical skeleton structure, and the magnetic core of the transformer is grounded, which is used to shield the common mode noise of the primary coil, the secondary coil and the magnetic core, and suppress EMI interference at the same time.

Further, the ratio of the number of turns of the primary coil to the number of turns of the secondary coil ranges from 7 to 8;

The number of turns of the shielding coil is 1.5 turns.

In the second aspect, an embodiment of the present invention provides a power adapter, the power adapter includes a rectifier circuit and a filter circuit, and also includes a transformer; wherein,

The input end of the rectification circuit is connected to the power supply, and is used to rectify the AC signal output by the power supply into a DC signal;

The input end of the filter circuit is connected to the output end of the rectification circuit, and is used to filter the direct current signal and suppress EMI interference in the circuit;

The input terminal of the transformer is connected to the output terminal of the filter circuit, and is used to obtain the filtered high-voltage electrical signal and convert it into a low-voltage electrical signal to supply power to the terminal equipment.

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, chopping the rectified DC voltage signal through the MOS transistor packaged in the IC chip to obtain a pulse voltage signal, so as to adjust the input voltage signal, and through the transformer, The voltage output by the secondary coil is adjusted.

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 filter circuit includes two electrolytic capacitors and a common mode inductor; wherein,

Both ends of the first electrolytic capacitor are connected to the two output ends of the rectification circuit, and 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.

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.

An embodiment of the present invention provides a transformer and a power adapter, the transformer includes a bobbin, a primary coil reversely wound on the bobbin, an auxiliary coil and a shielding coil, and a secondary coil wound forward on the bobbin . In the embodiment of the present invention, by setting the winding direction of the transformer coil, adding a shielding coil, and grounding the shielding coil, the parasitic capacitance generated by the transformer can be adjusted, so that the parasitic capacitance can realize the function of the Y capacitor in the prior art, and can also effectively suppress EMI. interference. Therefore, by using the transformer provided in this embodiment, there is no need to add a Y capacitor in the circuit, and the reliability of the power supply is improved on the premise of meeting the European Union VI energy efficiency requirements.

Description of drawings

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

FIG. 2 is a structural schematic diagram of a transformer provided in Embodiment 1 of the present invention;

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

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

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

FIG. 6 is a schematic diagram of a preferred power adapter circuit provided by Embodiment 3 of the present invention.

detailed description

The present invention will be further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described here are only used to explain the present invention, but not to limit the present invention. In addition, it should be noted that, for the convenience of description, only some structures related to the present invention are shown in the drawings but not all structures.

Embodiment one

FIG. 1 is a schematic structural diagram of a transformer provided by Embodiment 1 of the present invention. The transformer can be integrated into a power adapter or an open-type switching power supply for powering terminal equipment. As shown in Figure 1, the transformer 100 specifically includes: a bobbin N0, a primary coil N1 reversely wound on the bobbin N0, an auxiliary coil N2 and a shielding coil N4, and a secondary coil N3 forward wound on the bobbin N0 . in,

The primary coil N1 is used to receive the voltage signal output by the power supply, and provide an input voltage signal to the secondary coil according to the voltage signal; the secondary coil N3 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 N2 and the primary coil N1 are set according to the same terminal, and are used to convert the supply voltage into an auxiliary voltage signal; the shielding coil N4 is grounded, as the shielding layer of the transformer 100, and is used to adjust the parasitic capacitance of the transformer 100 and suppress EMI interference.

Preferably, the structure of the transformer can preferably be a vertical frame structure, and the winding direction is defined as follows: when the coil is being wound forward, the top of the frame faces the winding machine; when the coil is rewinding, the PIN needle of the frame faces the winding machine.

Preferably, the magnetic core of the transformer is grounded for shielding the common mode noise of the primary coil, the secondary coil and the magnetic core while suppressing EMI interference.

FIG. 2 is a schematic structural diagram of a transformer provided in Embodiment 1 of the present invention. The winding process of the transformer coil is specifically described below in conjunction with Figure 2:

The primary coil N1 of the transformer starts from the fourth pin 4 of the transformer, and takes up the wire from the first pin 1 of the transformer; the secondary coil N3 of the transformer starts from the sixth pin 6 of the transformer, and takes up the wire from the seventh pin 7; The auxiliary coil N2 starts from the 5th pin of the transformer, and takes up the wire from the 3rd pin; the shielding coil N4 of the transformer starts from the third pin 3 (primary ground) of the transformer, and the other end is suspended (NC). The magnetic core shielding design also starts from the third pin 3 of the transformer during the implementation process, that is, the pin3 pin in Figure 2 is connected to the magnetic core. Preferably, the part of the enameled wire in contact with the magnetic core is connected to the magnetic core by tin plating. The parasitic capacitance generated by the transformer can be further adjusted through the shielding design of the magnetic core, so as to realize the function of the Y capacitor in the prior art and also have the effect of anti-EMI interference.

Specifically, two layers of insulating tape are arranged between the primary coil N1 and the auxiliary coil N2, the auxiliary coil N2 and the secondary coil N3, and the secondary coil N3 and the shielding coil N4. Coils N1, N2 and N3 are put on Teflon sleeves at the inlet and outlet of coils; Teflon sleeves are added at the inlet of N4. Among them, the length of the Teflon sleeve at the inlet and outlet of the coils N1 and N2 extends into the wire package is 3mm; the length of the Teflon sleeve at the inlet of the coil N4 extends into the wire package is 3mm; the length of the coil N3 The inner length of the Teflon bushing at the end and the outlet is 6.5mm.

The above-mentioned shielding layer of the primary coil and the secondary coil of the transformer does not need to use copper foil shielding, but can be realized through the auxiliary coil of the transformer. The parasitic capacitance generated by the transformer can be adjusted through the shielding layer, so that the parasitic capacitance can realize the function of the Y capacitor in the existing circuit. By combining the winding direction of the transformer coil, the EMI interference in the circuit can be further suppressed, thereby improving the reliability of the power supply.

Further, since the turn ratio of the transformer (that is, the ratio of the number of turns of the primary coil to the secondary coil) has a very large impact on the switching frequency and switching loss of the power supply, for example, when the turn ratio is too large, the switch that will cause the power supply to work As the frequency increases, the switching loss will increase accordingly, and the average efficiency of the power supply will therefore decrease. Therefore, the switching frequency and transformer inductance of the power supply can be controlled by rationally optimizing the turn ratio of the transformer, thereby reducing the switching loss of the power supply and improving the efficiency of the power supply.

Exemplarily, for a power supply with 12V output, the range of its turn ratio can be set as: 7-8; for a power supply with 5V output, the range of its turn ratio can be set as: 12-16 values. Preferably, the primary coil can be wound 80 times, and the secondary coil can be wound 11 times; at the same time, in order to cooperate with the primary coil and the secondary coil to better improve the efficiency of the power supply, the shielding coil can preferably be wound 1.5 times to assist The coil can be wound 13 turns.

Embodiment 1 of the present invention provides a transformer, which includes a skeleton, a primary coil wound on the bobbin in reverse, an auxiliary coil and a shielding coil, and a secondary coil wound forward on the bobbin. In the embodiment of the present invention, by setting the winding direction of the transformer coil, adding a shielding coil, and grounding the shielding coil, and cooperating with the magnetic core shielding technology, the parasitic capacitance generated by the transformer can be adjusted, so that the parasitic capacitance realizes the function of the Y capacitor in the prior art, At the same time, it can effectively suppress EMI interference. Therefore, by using the transformer provided in this embodiment, there is no need to add Y capacitors in the circuit, which improves the reliability of the power supply and simplifies the design of the circuit.

Embodiment two

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

The input terminal of the rectification circuit 210 is connected to the power supply, and is used to rectify the AC signal output by the power supply into a DC signal; the input terminal of the filter circuit 220 is connected to the output terminal of the rectification circuit 210, and is used to filter the DC signal, suppressing the EMI interference; the input terminal of the transformer 230 is connected to the output terminal of the filter circuit 220, used to obtain the filtered high-voltage electrical signal, and convert it into a low-voltage electrical signal to supply power to the terminal equipment.

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, FIG. 4 is a circuit diagram of a preferred rectification and EMI filter provided by Embodiment 2 of the present invention. As shown in FIG. 4, the rectification circuit in this embodiment may be a full-wave rectification circuit. Preferably, the filter circuit may include two electrolytic capacitors C1 and C2, and a common mode inductor LF1. Wherein, the two ends of the first electrolytic capacitor C1 are connected to the two output ends of the rectifier circuit, and are connected to the two input ends of the common mode inductor LF1; the two ends of the second electrolytic capacitor C2 are connected to the two output ends of the common mode inductor LF1 respectively connected. By matching C1, C2 and LF1, the filtering of EMI interference in the circuit can be realized. By using the above circuit, 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 will It cannot be fed back to the secondary coil end of the transformer. Therefore, after the power is cut off, it can also prevent the contactor from being shocked by the power adapter. The safety of the power adapter can be effectively improved.

Further, as shown in FIG. 4 , the rectifier circuit may further include a fuse F1 , a piezoresistor MOV1 and a thermistor NTC1 for protecting the power adapter and improving the reliability of the power supply.

This embodiment provides a power adapter, which can obtain a DC voltage by rectifying the AC voltage output from the power grid through a rectification circuit, and then filter the DC voltage through a filter circuit to filter out EMI interference in the circuit. The use of the transformer can not only serve as an energy conversion device to supply power to the load, but also eliminate the need to add Y capacitors and secondary common-mode inductance to the power adapter circuit, which effectively suppresses EMI interference and improves the reliability of the power supply.

Embodiment Three

FIG. 5 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. IC chip 370 and secondary rectification and filtering 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 filtered electrical signal.

Exemplarily, FIG. 6 is a schematic diagram of a preferred power adapter circuit provided by Embodiment 3 of the present invention. As shown in Figure 6, 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. 6, 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 starts up, the auxiliary winding of the transformer charges the third capacitor C3 in order to maintain the working state of the IC chip. As shown in FIG. 6, 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 sampled 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 with overcurrent protection function to adjust the current in the MOS tube packaged in the IC chip, and the primary peak current flowing through the MOS tube Through the current detection resistors R11 and R12, it is converted into a voltage and fed back to the current detection pin of the IC chip to achieve 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 6, 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 applied technical principles. Those skilled in the art will understand that the present invention is not limited to the specific embodiments described herein, and that various obvious changes, readjustments and substitutions can be made by those skilled in the art without departing from the protection scope of the present invention. Therefore, although the present invention has been described in detail through the above embodiments, the present invention is not limited to the above embodiments, and can also include more other equivalent embodiments without departing from the concept of the present invention, and the present invention The scope is determined by the scope of the appended claims.

Claims (10)

1. A transformer, comprising: the transformer comprises a framework, a primary coil, an auxiliary coil, a shielding coil and a secondary coil, wherein the primary coil, the auxiliary coil and the shielding coil are reversely wound on the framework; wherein,

the primary coil is used for receiving a voltage signal output by a power supply and providing an input voltage signal to the secondary coil according to the voltage signal;

the secondary coil is connected with a load and used for outputting power supply voltage according to the input voltage signal and supplying power to the load;

the auxiliary coil and the primary coil are arranged according to the same name end and are used for converting the power supply voltage into an auxiliary voltage signal according to the turn ratio of the transformer;

the shielding coil is grounded and used as a shielding layer of the transformer for adjusting the parasitic capacitance of the transformer and inhibiting EMI interference.

2. The transformer of claim 1,

the transformer is of a vertical skeleton structure, and meanwhile, a magnetic core of the transformer is grounded and used for shielding common-mode noise of the primary coil, the secondary coil and the magnetic core and inhibiting EMI interference.

3. The transformer of claim 2,

the ratio range of the number of winding turns of the primary coil to the number of winding turns of the secondary coil is 7-8;

the number of winding turns of the shielding coil is 1.5.

4. A power adapter comprising a rectifying circuit and a filtering circuit, further comprising a transformer according to any one of claims 1 to 3; wherein,

the input end of the rectifying circuit is connected with a power supply and is used for rectifying an alternating current signal output by the power supply into a direct current signal;

the input end of the filter circuit is connected with the output end of the rectifying circuit and is used for filtering the direct current signal and inhibiting EMI interference in the circuit;

the input end of the transformer is connected with the output end of the filter circuit and used for acquiring the high-voltage electric signal after filtering processing and converting the high-voltage electric signal into a low-voltage electric signal to supply power to the terminal equipment.

5. The power adapter as claimed in claim 4, further comprising:

the starting circuit is connected with the filter circuit and used for generating a starting voltage signal according to the electric signal after the filtering processing;

the sampling circuit is connected with the auxiliary coil of the transformer and used for detecting the auxiliary voltage signal and generating a sampling voltage signal;

the IC chip is connected with the starting circuit and used for acquiring the starting voltage signal and working under the driving of the starting voltage signal; the IC chip is connected with the sampling circuit and the primary coil of the transformer and used for acquiring the sampling voltage signal, chopping the rectified direct-current voltage signal through an MOS (metal oxide semiconductor) tube packaged in the IC chip according to the sampling voltage signal to obtain a pulse voltage signal so as to adjust the input voltage signal, and adjusting the voltage output by the secondary coil through the transformer.

6. The power adapter as claimed in claim 4, further comprising:

the RCD absorption circuit is connected with the IC chip and used for absorbing a voltage spike generated by the MOS tube during the turn-off period;

and the secondary rectification filter circuit is connected with a secondary coil of the transformer and used for rectifying the power supply voltage to obtain a direct current signal to supply power to a load.

7. The power adapter of claim 4, the filter circuit comprising two electrolytic capacitors and a common mode inductor; wherein,

two ends of the first electrolytic capacitor are connected with two output ends of the rectifying circuit and two input ends of the common mode inductor;

and two ends of the second electrolytic capacitor are respectively connected with two output ends of the common mode inductor.

8. The power adapter as claimed in claim 5, wherein: the starting circuit comprises a starting resistor and a third capacitor; wherein,

the starting resistor is connected with the third capacitor in series and is connected between the direct-current positive electrode output end of the filter circuit and the ground wire;

and the positive end of the third capacitor is connected with the IC chip and used for driving the IC chip to work when the third capacitor is charged to form a starting voltage signal.

9. The power adapter as claimed in claim 5, wherein: the sampling circuit comprises a first resistor, a second resistor and a first diode; wherein,

a circuit formed by connecting the first resistor and the second resistor in series is connected in parallel to two ends of the auxiliary coil of the transformer;

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

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

10. The power adapter as claimed in claim 6, wherein: the secondary rectifying and filtering circuit comprises a third diode, an RC absorption circuit, a fifth capacitor and a sixth capacitor; wherein,

the positive end of the third diode is connected with the secondary coil of the transformer, and the negative end of the third diode is connected with the positive end of the fifth capacitor;

the RC absorption circuit is connected in parallel to two ends of the third diode;

the negative electrode of the fifth capacitor is connected with the secondary ground;

and the sixth capacitor is connected in parallel at two ends of the fifth capacitor.