CN1556581A - A method for suppressing common-mode interference of power converters - Google Patents

Abstract

A power converter common mode interference suppression method is composed of a rectification filter circuit and a boost (Boost) circuit, in the boost circuit, the inductance is changed from the positive bus of the DC input to the negative bus of the DC input , the diode is changed to a common anode diode, and it is connected from the positive bus of the DC output to the negative bus of the DC output. The present invention directly connects the nodes on the direct current input positive bus, so the potential is stable, and the distributed capacitance of the MOSFET drain to the ground and the distributed capacitance of the nodes on the positive bus have little influence on the common mode interference. And because the circuit can output a stable DC voltage when it is in normal working state, the influence of the common-anode diode distributed capacitance on the common-mode interference can be ignored. The distributed capacitance of wires that has a greater impact on common-mode interference can be reduced through reasonable wiring of the printed circuit board, thereby achieving the purpose of suppressing common-mode interference. The invention is simple and practical, and can be applied to some existing topologies of power converters.

Description

A method for suppressing common-mode interference of power converters

technical field

The present invention relates to a common-mode electromagnetic interference (EMI) suppression method for a power converter.

Background technique

The source of the power converter's conducted common-mode electromagnetic interference is mainly caused by the displacement current generated in the distributed capacitance of the electric node in the circuit whose potential changes drastically with time and flows through the ground loop.

Usually, the drain of a metal oxide field effect transistor (MOSFET) is fixed on an external heat sink through its heat dissipation metal shell through an insulating gasket, and the heat sink is grounded. Therefore, there is a large distributed capacitance between the drain of the MOSFET and the ground. In the same way, for common diodes, the heat-dissipating metal shell of the package is connected to the cathode of the diode, and is also fixed on the external heat sink through an insulating gasket, that is, the distributed capacitance of the cathode of the diode to ground is formed. In addition, the wires in the circuit also have distributed capacitance to the ground.

In this circuit, the potential of the node connected to the drain of the MOSFET changes drastically with the on-off state of the MOSFET, that is, the du/dt is very large. The ground-distributed capacitance of the MOSFET and the ground-distributed capacitance of the wire connected to it will generate a large displacement current, which will flow into the ground loop through the radiator to form a common-mode interference current.

Generally, the distributed capacitance generated by wires can be reduced through reasonable wiring of the printed circuit board, but the distributed capacitance existing to the drain of the MOSFET to the ground cannot be reduced.

In order to suppress the common-mode interference in this circuit, many scholars have proposed some methods, such as: the common-mode current anti-phase offset method, which requires an additional winding and a MOSFET, which increases the cost; common-mode current passive elimination method, which still requires an additional winding and an additional capacitor; the method of dynamic node balancing, which is difficult to apply to a boost power factor correction (Boost PFC) circuit, increases the dynamic node in the circuit, and increases the printed circuit board Wiring difficulty.

Contents of the invention

The purpose of the present invention is to reduce the influence of the MOSFET drain on the sub-capacitance existing in the ground by constructing a steady-state node in the circuit, that is, to provide a power converter with a stable potential of the wire node and a small influence of the distributed capacitance on the common-mode interference Common mode interference suppression method.

The purpose of the present invention is achieved by the following scheme: it is composed of a rectification filter circuit and a boost (Boost) circuit, in which the inductance is changed from the positive bus of the DC input to the negative of the DC input. On the bus, the diode is changed to a common anode diode whose heat dissipation metal shell is connected to the anode, and it is connected from the positive bus of the DC output to the negative bus of the DC output.

Since the present invention connects the inductance on the positive bus of DC input to the negative bus of DC input and removes the diode on the positive bus of DC output, a common anode diode is used to connect the negative bus of DC output, while the DC input and DC There are no components on the positive bus of the output, so the potential of the wire node is stable, and the distributed capacitance of the drain of the MOSFET to the ground and the distributed capacitance of the node on the positive bus have little influence on the common mode interference. And because the output DC voltage is stable in the normal working state, the distributed capacitance of the anode of the common anode diode to the ground and the partial capacitance of the DC output terminal of the negative bus to the ground have negligible influence on the common mode interference. At this time, when the MOSFET switches, only the node connecting the inductor and the cathode of the common anode diode in the circuit has a high potential change rate, and the distributed capacitance of this node to the ground will become the main factor affecting the common mode interference, but through the printed circuit Reasonable layout of the board can easily reduce the distributed capacitance of the node to the ground. And it is simple and practical, and can be applied to some existing power converter topologies, such as boost power factor correction (Boost PFC) circuit, step-down (Buck) circuit, step-down (Buck-Boost) circuit, etc.

Description of drawings

Fig. 1 is a schematic circuit diagram of the present invention;

Figure 2 is a prior art reference diagram.

Detailed ways

With reference to Fig. 1, the present invention is made up of rectification filter circuit and booster circuit. The rectification filter circuit consists of 4 diode bridge rectifiers connected in parallel with capacitor _C1 , and there are connection nodes n5 and n6 in the circuit. The boost circuit is composed of metal oxide field effect transistor (MOSFET) Q, radiator T, inductor L, common anode diode D and capacitor _C2 . MOSFET has connection nodes n1 and n2 in the circuit, its drain d is connected to the positive bus, and its drain d has a large distributed capacitance C _m to the ground; the inductance L is connected between nodes n6 and n2. Capacitor _C2 has connection nodes n3, n4 in the circuit. A common anode diode D is connected between nodes n2 and n4. The heat dissipation metal shells of the MOSFET and the common anode diode D are respectively fixed on the heat dissipation pipe T through insulating gaskets. At this time, the distributed capacitance C _d of the positive anode diode D to the heat pipe T is actually the distributed capacitance of the diode anode to the ground. C _p1 , C _p2 , C _p3 and C _p4 in the circuit are the partial capacitances of the wires connected to the nodes n1, n2, n3 and n4 to the ground respectively. It can be seen that the nodes n1 and n3 are directly connected to the DC input positive bus, so their potentials are stable, and the distributed capacitances C _m , C _p1 and C _p3 have little influence on the common mode interference. At the same time, the output DC voltage is stable when the circuit is working normally, so the potential of node n4 is also stable, and the influence of distributed capacitance C _d and C _p4 on common mode interference can be ignored. At this time, when the metal oxide field effect transistor Q switches, only the node n2 potential in the circuit has a high du/dt, and the capacitance C _p2 becomes the main factor affecting the common mode interference. This is achieved through the reasonable wiring of the printed circuit board. This capacitance can be easily reduced, thereby achieving the purpose of suppressing the common mode interference of the circuit.

Claims (1)

1, a kind of power converter common-mode interference suppressing method, it is made of rectification filter circuit and boost (Boost) circuit, it is characterized in that: in described boost circuit, its inductance (L) is reconnected to direct current On the negative bus of the input, its diode is changed to a common anode diode (D), which is connected to the negative bus of the DC output.

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