CN110808680A - Direct current EMI filter structure for power adapter - Google Patents

Abstract

This invention discloses a DC EMI filter structure for a power adapter, comprising a rectifier module, a filter module, and a transformer module. The rectifier module, the filter module, and the transformer module are electrically connected in sequence. The filter module includes a first capacitor and a choke coil. The first capacitor is connected in parallel with the rectifier module and in parallel with the first and second ends of the choke coil. The third and fourth ends of the choke coil are connected in parallel with the transformer module. This achieves filtering on the DC side, occupies less space, reduces the size of the filter, and simultaneously reduces power loss.

Description

A DC EMI filter structure for power adapter

technical field

The present invention relates to the technical field of filters, in particular to a DC EMI filter structure for a power adapter.

Background technique

The demand for high power density power adapters in the market is rapidly increasing, which requires smaller form factor designs. Corresponding to the smaller volume, the allowable releasable power loss is correspondingly smaller. This requires us to design smaller devices to achieve higher efficiency.

The filter volume in the power adapter is often too large, so a filter that reduces power loss and volume is urgently needed.

SUMMARY OF THE INVENTION

The purpose of the present invention is to provide a DC EMI filter structure for a power adapter, aiming to solve the problem that a filter with reduced power loss and volume is urgently needed.

In order to achieve the above object, the present invention provides a DC EMI filter structure for a power adapter, including a rectifier module, a filter module and a transformer module, wherein the rectifier module, the filter module and the transformer module are electrically connected in sequence. The filter module includes a first capacitor and a choke coil, the first capacitor is connected in parallel with the rectifier module, and is connected in parallel with the first end and the second end of the choke coil, and the choke coil is connected in parallel. The third end and the fourth end of the transformer are connected in parallel with the transformer module.

The rectifier module includes a first diode, a second diode, a third diode and a fourth diode, and the anode of the first diode is connected to the anode of the power supply and the anode of the second diode. The negative electrode is connected, the negative electrode of the first diode is connected to the negative electrode of the third diode and the first end of the first capacitor, the positive electrode of the fourth diode is connected to the positive electrode of the second diode and the The second end of the first capacitor is connected, and the cathode of the fourth diode is connected to the anode of the third diode and the cathode of the power supply.

The transformer module further includes a transformer, a third capacitor, a first resistor, a fifth diode, a field effect transistor, a sixth diode, a fourth capacitor, a second resistor and a fifth capacitor. The transformer A primary winding and a secondary winding are arranged on it, and the first end of the primary winding is connected to the third end of the choke coil, the first end of the third capacitor and the first end of the first resistor, The cathode of the fifth diode is connected to the second end of the third capacitor and the second end of the first resistor, and the second end of the primary winding is connected to the anode of the fifth diode and the second end of the first resistor. The drain of the field effect transistor is connected to the drain, the first end of the secondary winding is connected to the anode of the sixth diode, and the cathode of the sixth diode is connected to the first end of the fourth capacitor connected to the first end of the second resistor, the second end of the secondary winding is connected to the second end of the fourth capacitor, the second end of the second resistor and the first end of the fifth capacitor The source of the field effect transistor is connected to the second end of the fifth capacitor and the fourth end of the choke coil.

The filter module further includes a first inductor and a second capacitor, the first end of the first inductor is connected to the third end of the choke coil, and the second end of the first inductor is connected to the third end of the choke coil. The first end of the second capacitor is connected to the first end of the third capacitor, and the second end of the second capacitor is connected to the fourth end of the choke coil and the source of the field effect transistor.

The filter module further includes a first inductor and a second capacitor, the first end of the first inductor is connected to the first end of the first capacitor, and the second end of the first inductor is connected to the choke The first end of the second capacitor is connected to the third end of the choke coil, the second end of the second capacitor is connected to the fourth end of the choke coil and the third end of the choke coil. The source of the field effect transistor is connected.

The filter module further includes a first inductor, the first end of the first inductor is connected to the third end of the choke coil, and the second end of the first inductor is connected to the third end of the third capacitor. connected at one end.

The filter module further includes a first inductor and a second capacitor, the first end of the first inductor is connected to the third end of the choke coil and the first end of the second capacitor, and the first end of the first inductor is connected to the third end of the choke coil and the first end of the second capacitor. The second end of an inductor is connected to the first end of the third capacitor, and the second end of the second capacitor is connected to the fourth end of the choke coil and the source of the field effect transistor.

In a structure of a DC EMI filter for a power adapter of the present invention, the rectifier module, the filter module and the transformer module are electrically connected in sequence, the first capacitor is connected in parallel with the rectifier module, and The first end and the second end of the choke coil are connected in parallel, the third end and the fourth end of the choke coil are connected in parallel with the transformer module, and the first capacitor and the choke coil are placed in On the DC side, the size of the DC bus filter is much smaller than that of the AC line filter, reducing the size of the adapter and reducing power loss.

Description of drawings

In order to explain the embodiments of the present invention or the technical solutions in the prior art more clearly, the following briefly introduces the accompanying drawings that need to be used in the description of the embodiments or the prior art. Obviously, the accompanying drawings in the following description are only These are some embodiments of the present invention. For those of ordinary skill in the art, other drawings can also be obtained according to these drawings without creative efforts.

1 is a schematic circuit diagram of a first embodiment of the present invention;

2 is a schematic circuit diagram of a second embodiment of the present invention;

3 is a schematic circuit diagram of a third embodiment of the present invention;

4 is a schematic circuit diagram of a fourth embodiment of the present invention;

Figure 5 is a comparison chart of the inductor current waveform of the choke coil;

Fig. 6 is the filter size comparison chart under the same noise attenuation situation;

In the figure: 10-rectifier module, 20-filter module, 30-transformer module, D1-first diode, D2-second diode, D3-third diode, D4-fourth diode , C1-first capacitor, CM-choke coil, C2-second capacitor, L1-first inductor, C3-third capacitor, R1-first resistor, D5-fifth diode, T1-transformer, Q1 - Field effect transistor, D6-sixth diode, C4-fourth capacitor, C5-fifth capacitor, R2-second resistor.

Detailed ways

The following describes in detail the embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein the same or similar reference numerals refer to the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary, and are intended to explain the present invention and should not be construed as limiting the present invention.

Please refer to FIG. 1 , which is a schematic circuit diagram of a first embodiment of the structure of a DC EMI filter for a power adapter provided by the present invention. The DC EMI filter structure for the power adapter includes a rectifier module, a filter module and a transformer module, the rectifier module, the filter module and the transformer module are electrically connected in sequence, and the filter module includes a first A capacitor and a choke coil, the first capacitor is connected in parallel with the rectifier module, and is connected in parallel with the first end and the second end of the choke coil, and the third end and the fourth end of the choke coil are connected with the The transformer modules are connected in parallel.

The rectifier module includes a first diode, a second diode, a third diode and a fourth diode, and the anode of the first diode is connected to the anode of the power supply and the cathode of the second diode , the cathode of the first diode is connected to the cathode of the third diode and the first end of the first capacitor, the anode of the fourth diode is connected to the anode of the second diode and the The second end of the first capacitor is connected, and the cathode of the fourth diode is connected to the anode of the third diode and the cathode of the power supply.

The transformer module further includes a transformer, a third capacitor, a first resistor, a fifth diode, a field effect transistor, a sixth diode, a fourth capacitor, a second resistor and a fifth capacitor, and the transformer is provided with There are primary windings and secondary windings, the first end of the primary winding is connected with the third end of the choke coil, the first end of the third capacitor and the first end of the first resistor, the The cathode of the fifth diode is connected to the second end of the third capacitor and the second end of the first resistor, and the second end of the primary winding is connected to the anode of the fifth diode and the second end of the first resistor. The drain of the field effect transistor is connected to the drain of the field effect transistor, the first end of the secondary winding is connected to the anode of the sixth diode, and the cathode of the sixth diode is connected to the first end of the fourth capacitor and all The first end of the second resistor is connected, and the second end of the secondary winding is connected to the second end of the fourth capacitor, the second end of the second resistor and the first end of the fifth capacitor , the source of the field effect transistor is connected to the second end of the fifth capacitor and the fourth end of the choke coil.

The filter module further includes a first inductor and a second capacitor, the first end of the first inductor is connected to the third end of the choke coil, and the second end of the first inductor is connected to the second capacitor The first end of the capacitor is connected to the first end of the third capacitor, and the second end of the second capacitor is connected to the fourth end of the choke coil and the source of the field effect transistor.

In this embodiment, the rectifier module is used to rectify the circuit on the AC side, the first diode, the second diode, the third diode and the fourth diode The tube forms a rectifier bridge through the unidirectional conduction principle of the diode, which converts the alternating current into direct current. The third capacitor and the first resistor are connected in parallel at both ends of the primary winding, and it is difficult for a DC signal or a low-frequency signal to pass through, while an AC signal or a high-frequency signal is easier to pass through, achieving the effect of filtering, and at the same time with the The fifth diode is connected in series, the fifth diode allows the current to pass in a single direction, and is blocked when reversed, the third capacitor is used to absorb energy and suppress voltage spikes, and the first resistor is used to In order to dissipate energy and weaken the oscillation process, the fifth diode generates resonance in order to prevent the energy absorbed on the third capacitor from charging the parasitic inductance reversely, so that the voltage oscillation can be effectively suppressed. The transformer is a device that uses the principle of electromagnetic induction to change the AC voltage, and realizes voltage transformation according to circuit requirements. The fourth capacitor and the second resistor are connected in parallel with the sixth diode. The fourth capacitor is used to absorb energy and suppress voltage spikes. The second resistor is used to consume energy and weaken the oscillation process. In order to prevent the energy absorbed on the fourth capacitor from charging the parasitic inductance in the reverse direction, the sixth diode generates resonance, so it can effectively suppress the oscillation of the voltage and play the role of filtering. The field effect transistor is conducted by majority carriers, and it is also a unipolar transistor. It belongs to a voltage-controlled semiconductor device and can be used for current amplification. It has high input resistance, low noise, low power consumption, large dynamic range, and easy The advantages of integration, no secondary breakdown phenomenon, and wide safe working area. The fifth capacitor plays the role of anti-interference and time delay. In order to reduce common-mode noise in traditional power adapters, two common-mode choke coils with different inductances are located on the AC side, namely before the rectifier module, for low-frequency and high-frequency common-mode noise attenuation. The work of the diode bridge has a very high peak value. In order to avoid saturation, a large-sized magnetic core needs to be used; at the same time, in order to reduce the differential mode noise of the traditional power adapter, a capacitor is applied between the line and the neutral line, and the capacitor is film capacitance, and the leakage inductance of the choke is applied as a common mode inductance. Most of the traditional power adapters are occupied by large-sized capacitors and choke coils. For example, one capacitor has an area of 108mm ² and a volume of 1296mm ³ ; the other capacitor has an area of 60mm ² and a volume of 660mm ³ ; the choke The circle has an area of 293 mm ² and a volume of 3550 mm ³ ; a total area of 461 mm ² and a total volume of 5506 mm ³ .

The first capacitor, the choke coil, the first inductor and the second capacitor of the DC EMI filter structure for the power adapter are placed on the DC side, that is, after the rectifier module. The value of the choke coil is much smaller than the capacitor of the traditional power adapter, so the current ripple on the AC side mainly flows through the first capacitor, and at the same time due to the existence of the first inductance, the switching current ripple mainly flows through the second capacitor. Therefore, the current flowing through the choke coil is almost a constant DC component with a small peak value, which means that it will not saturate the magnetic core. Figure 5 is a comparison diagram of the inductor current waveform of the choke coil. Therefore, a magnetic core with a much smaller size compared with the AC line filter can be used. In addition, the second capacitor adopts a ceramic capacitor, which has the same capacitance value as the film capacitor in the traditional power adapter and is far in size. It is smaller than the film capacitor. Figure 6 is a comparison diagram of the filter size under the same noise attenuation condition. The size of the DC bus filter is much smaller than that of the AC line filter, the occupied area is reduced by 75%, and the volume is reduced by 91%. At the same time, the RMS current on the AC side is generally much larger than the RMS value on the DC side. In this way, the same filter inductance will reduce a lot of power loss on the DC side, which is beneficial to the heat dissipation of the adapter and the temperature rise of the chassis. Small filters require small filters. Core material and small copper wire, the cost is also reduced, and there is no impact on filtering.

Please refer to FIG. 2 , which is a schematic circuit diagram of a second embodiment of the structure of a DC EMI filter for a power adapter provided by the present invention. The DC EMI filter structure for the power adapter includes a rectifier module, a filter module and a transformer module, the rectifier module, the filter module and the transformer module are electrically connected in sequence, and the filter module includes a first A capacitor and a choke coil, the first capacitor is connected in parallel with the rectifier module, and is connected in parallel with the first end and the second end of the choke coil, and the third end and the fourth end of the choke coil are connected with the The transformer modules are connected in parallel.

The rectifier module and the transformer module have the same structures and functions as those of the first embodiment, which will not be repeated here.

The filter module further includes a first inductor and a second capacitor, the first end of the first inductor is connected to the first end of the first capacitor, and the second end of the first inductor is connected to the choke coil The first end of the second capacitor is connected to the third end of the choke coil, the second end of the second capacitor is connected to the fourth end of the choke coil and the field The source of the effect transistor is connected.

In this embodiment, the first capacitor, the first inductor, the choke coil and the second capacitor are placed on the DC side, that is, after the rectifier module, the current pulsation on the AC side mainly flows through all the At the same time, due to the existence of the first inductor, the switching current ripple mainly flows through the second capacitor, so the current flowing through the choke coil is almost a constant DC component with a small peak value, which means Since it does not saturate the magnetic core, it is possible to use a magnetic core that is much smaller in size compared with the AC line filter. In addition, the second capacitor uses a ceramic capacitor, which has the same characteristics as the film capacitor in the traditional power adapter. The capacitance value of the filter is much smaller than that of the film capacitor, and the RMS current on the AC side is generally much larger than the RMS value on the DC side. In this way, the same filter inductance will reduce a lot of power loss on the DC side, which is beneficial to the heat dissipation of the adapter and the temperature of the case. A small filter requires a small core material and small copper wire, and the cost is correspondingly reduced, and there is no impact on the filtering.

Please refer to FIG. 3 , which is a circuit schematic diagram of the third embodiment of the structure of the DC EMI filter for the power adapter provided by the present invention. The DC EMI filter structure for the power adapter includes a rectifier module, a filter module and a transformer module, the rectifier module, the filter module and the transformer module are electrically connected in sequence, and the filter module includes a first A capacitor and a choke coil, the first capacitor is connected in parallel with the rectifier module, and is connected in parallel with the first end and the second end of the choke coil, and the third end and the fourth end of the choke coil are connected with the The transformer modules are connected in parallel.

The rectifier module and the transformer module have the same structures and functions as those of the first embodiment, which will not be repeated here.

The filter module further includes a first inductor, the first end of the first inductor is connected to the third end of the choke coil, and the second end of the first inductor is connected to the first end of the third capacitor connect.

In this embodiment, the first capacitor, the first inductor and the choke coil are placed on the DC side, that is, after the rectifier module, the current pulsation on the AC side mainly flows through the first capacitor, and at the same time Due to the existence of the first inductance, the current flowing through the choke coil is almost a constant DC component with a small peak value, which means that it does not saturate the core and can be used in a size comparable to that of an AC line filter. The magnetic core is much smaller, and the RMS current on the AC side is generally much larger than the RMS value on the DC side. In this way, the same filter inductance will reduce a lot of power loss on the DC side, which is beneficial to the heat dissipation of the adapter and the temperature rise of the case. The filter requires small magnetic core material and small copper wire, the cost is also reduced accordingly, and there is no impact on the filtering.

Please refer to FIG. 4 , which is a schematic circuit diagram of a fourth embodiment of the structure of a DC EMI filter for a power adapter provided by the present invention. The DC EMI filter structure for the power adapter includes a rectifier module, a filter module and a transformer module, the rectifier module, the filter module and the transformer module are electrically connected in sequence, and the filter module includes a first A capacitor and a choke coil, the first capacitor is connected in parallel with the rectifier module, and is connected in parallel with the first end and the second end of the choke coil, and the third end and the fourth end of the choke coil are connected with the The transformer modules are connected in parallel.

The rectifier module and the transformer module have the same structures and functions as those of the first embodiment, which will not be repeated here.

The filter module further includes a first inductor and a second capacitor, the first end of the first inductor is connected to the third end of the choke coil and the first end of the second capacitor, the first inductor The second end of the capacitor is connected to the first end of the third capacitor, and the second end of the second capacitor is connected to the fourth end of the choke coil and the source of the field effect transistor.

In this implementation manner, in this implementation manner, the first capacitor, the first inductor, the choke coil and the second capacitor are placed on the DC side, that is, after the rectifier module, the AC side The current ripple mainly flows through the first capacitor, and at the same time, due to the existence of the first inductor, the switching current ripple mainly flows through the second capacitor, so the current flowing through the choke coil is almost a constant DC component, The peak value is very small, which means that it does not saturate the magnetic core, and a magnetic core that is much smaller in size compared to the AC line filter can be used. In addition, the second capacitor is a ceramic capacitor, which is different from the thin film in the traditional power adapter. Compared with capacitors, they have the same capacitance value, and their volume is much smaller than that of film capacitors. At the same time, the RMS current on the AC side is generally much larger than the RMS value on the DC side. In this way, the same filter inductance will reduce a lot of power loss on the DC side, which is beneficial to The heat dissipation of the adapter and the temperature rise of the chassis, the small filter requires small magnetic core material and small copper wire, and the cost is also reduced accordingly, and it has no effect on the filtering.

The above disclosure is only a preferred embodiment of the present invention, and of course, it cannot limit the scope of rights of the present invention. Those of ordinary skill in the art can understand that all or part of the process for realizing the above-mentioned embodiment can be realized according to the rights of the present invention. The equivalent changes required to be made still belong to the scope covered by the invention.

In a structure of a DC EMI filter for a power adapter of the present invention, the rectifier module, the filter module and the transformer module are electrically connected in sequence, the first capacitor is connected in parallel with the rectifier module, and The first end and the second end of the choke coil are connected in parallel, the third end and the fourth end of the choke coil are connected in parallel with the transformer module, and the first capacitor and the choke coil are placed in On the DC side, the size of the DC bus filter is much smaller than that of the AC line filter, reducing the size of the adapter and reducing power loss.

Claims (7)

1. a direct current EMI filter structure for power adapter, is characterized in that, It includes a rectifier module, a filter module and a transformer module. The rectifier module, the filter module and the transformer module are electrically connected in sequence. The filter module includes a first capacitor and a choke coil. The first capacitor is connected to the The rectifier modules are connected in parallel with the first end and the second end of the choke coil, and the third end and the fourth end of the choke coil are connected in parallel with the transformer module. 2. The DC EMI filter structure for a power adapter according to claim 1, wherein the rectifier module comprises a first diode, a second diode, a third diode and a fourth second diode The anode of the first diode is connected to the anode of the power supply and the cathode of the second diode, the cathode of the first diode is connected to the cathode of the third diode and the first end of the first capacitor connected, the anode of the fourth diode is connected to the anode of the second diode and the second end of the first capacitor, the cathode of the fourth diode is connected to the third diode The positive pole and the negative pole of the power supply are connected. 3. The DC EMI filter structure for a power adapter according to claim 1, wherein the transformer module further comprises a transformer, a third capacitor, a first resistor, a fifth diode, and a field effect transistor , a sixth diode, a fourth capacitor, a second resistor and a fifth capacitor, the transformer is provided with a primary winding and a secondary winding, the first end of the primary winding and the third end of the choke coil , the first end of the third capacitor is connected to the first end of the first resistor, the cathode of the fifth diode is connected to the second end of the third capacitor and the second end of the first resistor terminal, the second terminal of the primary winding is connected to the anode of the fifth diode and the drain of the field effect transistor, the first terminal of the secondary winding is connected to the anode of the sixth diode The anode is connected, the cathode of the sixth diode is connected to the first end of the fourth capacitor and the first end of the second resistor, and the second end of the secondary winding is connected to the fourth capacitor. The second end, the second end of the second resistor and the first end of the fifth capacitor are connected, and the source of the field effect transistor is connected to the second end of the fifth capacitor and the first end of the choke coil. The fourth end is connected. 4. The DC EMI filter structure for a power adapter according to claim 3, wherein the filter module further comprises a first inductor and a second capacitor, and the first end of the first inductor is connected to the The third end of the choke coil is connected, the second end of the first inductor is connected to the first end of the second capacitor and the first end of the third capacitor, and the second end of the second capacitor is connected to the The fourth terminal of the choke coil is connected to the source of the field effect transistor. 5. The DC EMI filter structure for a power adapter according to claim 3, wherein the filter module further comprises a first inductor and a second capacitor, and the first end of the first inductor is connected to the The first end of the first capacitor is connected, the second end of the first inductor is connected to the first end of the choke coil, and the first end of the second capacitor is connected to the third end of the choke coil , the second end of the second capacitor is connected to the fourth end of the choke coil and the source of the field effect transistor. 6 . The DC EMI filter structure for a power adapter according to claim 3 , wherein the filter module further comprises a first inductor, the first end of the first inductor is connected to the end of the choke coil. 7 . The third terminal is connected, and the second terminal of the first inductor is connected to the first terminal of the third capacitor. 7. The DC EMI filter structure for a power adapter according to claim 3, wherein the filter module further comprises a first inductor and a second capacitor, and the first end of the first inductor is connected to the The third end of the choke coil is connected to the first end of the second capacitor, the second end of the first inductor is connected to the first end of the third capacitor, and the second end of the second capacitor is connected to the The fourth terminal of the choke coil is connected to the source of the field effect transistor.

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