DC power supply EMI filter with reverse connection protection and starting impact current suppression functions

Abstract

The utility model provides a DC power supply EMI filter with reverse connection protection and starting impact current suppression functions. Comprising an input reverse connection protection circuit, a starting impact current suppression circuit and an EMI filter circuit which are connected in sequence, the input reverse connection protection circuit comprises a field effect transistor Q2, a grid electrode of the field effect transistor Q2 is connected with a voltage input end positive UIN +, and a drain electrode of the field effect transistor Q2 is connected with a voltage input end negative UIN-; the starting impact current suppression circuit comprises a field effect transistor Q1, the grid electrode and the source electrode of the field effect transistor Q1 are connected with a capacitor C27 in parallel, the grid electrode of the field effect transistor Q1 is connected to the voltage input end UIN +, and the source electrode of the field effect transistor Q1 is connected with the source electrode of a field effect transistor Q2; the EMI filter circuit comprises a pi-type filter circuit and a common-mode filter circuit. According to the utility model, the anti-reverse connection design is adopted, when positive and negative lines are reversely connected, the MOS tube is cut off, a power line loop is disconnected, and the damage to post-stage equipment is prevented.

Description

Technical Field

[0001] The utility model relates to a direct current power supply EMI filter with both reverse connection protection and startup impact current suppression functions. Background Art

[0002] The DC power supply EMI filter is a passive bidirectional network with one end connected to the power supply and the other end connected to the load device. Its function is to filter out the interference caused by the load device on the power line when it is working and to filter out the interference on the power grid itself, so as to provide pure power for the load device.

[0003] The existing DC power supply EMI filter has a single function and does not meet the requirements of avoiding startup impact current and reverse connection protection in existing equipment. In actual use, in order to achieve reverse connection protection or startup impact current suppression, it is necessary to add a reverse connection protection circuit and a startup impact suppression circuit between the input power supply and the filter. In this case, not only is the layout difficult, but it is also more likely to cause the electromagnetic interference in the equipment to be coupled to the anti-reverse circuit and the startup impact suppression circuit again, resulting in interference leakage.

[0004] For example, a method for manufacturing a military-grade small EMI DC power supply filter disclosed in publication number CN106559959B uses a four-stage common-mode filtering structure composed of a good capacitor and an inductor, each stage targeting interference in a different frequency band. However, it only has a filtering function and cannot avoid the impact of the starting current. In addition, when the line is connected incorrectly, there is no reverse connection protection function, which will cause circuit damage. Utility Model Content

[0005] In order to solve the above technical problems, the utility model provides a DC power supply EMI filter with both reverse connection protection and startup impact current suppression functions.

[0006] The utility model is realized through the following technical solutions.

[0007] The utility model provides a DC power supply EMI filter with both reverse connection protection and startup impact current suppression functions; it comprises an input reverse connection protection circuit, a startup impact current suppression circuit, and an EMI filtering circuit which are connected in sequence, the input reverse connection protection circuit comprises a field effect tube Q2, the gate of the field effect tube Q2 is connected to the positive voltage input terminal U_IN+, and the drain is connected to the negative voltage input terminal U_IN-; the startup impact current suppression circuit comprises a field effect tube Q1, the gate and source of the field effect tube Q1 are connected in parallel with a capacitor C27, the gate of the field effect tube Q1 is connected to the positive voltage input terminal U_IN+, and the source is connected to the source of the field effect tube Q2; the EMI filtering circuit comprises a π-type filtering circuit and a common mode filtering circuit.

[0008] Resistors R1 to R6 are connected in series in sequence between the positive voltage input terminal U_IN+ and the gate of the field effect transistor Q2. The source and gate of the field effect transistor Q2 are also connected in parallel with the voltage stabilizing diode Z1 and the resistor R7.

[0009] The rear electrodes of the positive voltage input terminal U_IN+ and the negative voltage input terminal U_IN- are also grounded through two parallel capacitors respectively.

[0010] Resistors R8 to R13 are connected in series in sequence between the positive voltage input terminal U_IN+ and the gate of the field effect transistor Q1 , and a voltage stabilizing diode Z2 and a resistor R14 are connected in parallel at both ends of the capacitor C27 .

[0011] The source and drain of the field effect transistor Q1 are also connected in parallel with the resistor R15 and the resistor R16.

[0012] The π-type filter circuit includes a differential mode inductor L1, which is connected to the positive voltage input terminal U_IN+ line. The front pole of the differential mode inductor L1 has capacitors C5 and C6 connected between the positive voltage input terminal U_IN+ and the negative voltage input terminal U_IN-, and the rear pole has capacitors C9, C10, C13, C11, and C12 connected between the positive voltage input terminal U_IN+ and the negative voltage input terminal U_IN-.

[0013] The two ends of the connection point between the capacitor C6 and the negative voltage input terminal U_IN- are also connected to capacitors C7 and C8 respectively, and the other ends of capacitors C7 and C8 are grounded. The two ends of the connection point between the capacitor C10 and the positive voltage input terminal U_IN+ are also connected to capacitors C14 and C15 respectively, and the other ends of capacitors C14 and C15 are grounded.

[0014] The common-mode filtering circuit includes a common-mode inductor L2, the two poles of the input end of the common-mode inductor L2 are respectively connected to the two ends of the capacitor C12, and capacitors C19, C23, C24, C25, and C26 are connected in parallel between the two poles of the output end, and the two ends of the capacitor C26 are also respectively connected to the positive voltage output terminal U_OUT+ and the negative voltage output terminal U_OUT-, and the capacitors C19, C23, and C24 are also grounded through a capacitor.

[0015] The beneficial effects of the utility model are:

[0016] 1) Multi-function: The reverse connection protection circuit, startup impact suppression circuit and filter circuit are integrated, so that the filter not only has EMI filtering function but also reverse connection protection and impact current suppression functions;

[0017] 2) High safety: With anti-reverse connection design, when the positive and negative lines are reversed, the MOS tube is cut off and the power line loop is disconnected to prevent damage to the subsequent equipment. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 This is a schematic diagram of the circuit principle of the utility model. DETAILED DESCRIPTION

[0019] The technical solution of the utility model is further described below, but the scope of protection required is not limited to the description.

[0020] A DC power supply EMI filter with both reverse connection protection and startup impact current suppression functions; comprising an input reverse connection protection circuit, a startup impact current suppression circuit, and an EMI filtering circuit connected in sequence, wherein the input reverse connection protection circuit comprises a field effect tube Q2, the gate of the field effect tube Q2 is connected to the positive voltage input terminal U_IN+, and the drain is connected to the negative voltage input terminal U_IN-; the startup impact current suppression circuit comprises a field effect tube Q1, the gate and source of the field effect tube Q1 are connected in parallel with a capacitor C27, the gate of the field effect tube Q1 is connected to the positive voltage input terminal U_IN+, and the source is connected to the source of the field effect tube Q2; the EMI filtering circuit comprises a π-type filtering circuit and a common mode filtering circuit. The input reverse connection protection circuit, the startup current impact suppression circuit, and the filtering circuit respectively play the functions of anti-reverse connection protection, impact current suppression, and EMI filtering.

[0021] like Figure 1 As shown, resistors R1 to R6 are connected in series between the positive voltage input terminal U_IN+ and the gate of the field effect tube Q2. The source and gate of the field effect tube Q2 are also connected in parallel with the voltage zener diode Z1 and the resistor R7. The positive electrode of the voltage zener diode Z1 is connected to the source of the field effect tube Q2, and the negative electrode is connected to the gate of the field effect tube Q1. The current of the positive voltage input terminal U_IN+ is divided by R1 to R7 in series and then stabilized to 15V by the voltage zener tube before being connected to the gate of Q2. At this time, the gate voltage of Q2 is higher than the source voltage, Q2 is turned on, and the power line loop is in normal working state. When U_IN+ is a negative voltage and U_IN- is a positive voltage, that is, the positive and negative lines of the power supply are connected in reverse, there is no voltage difference between the gate and source of Q2, the MOS tube is cut off, and the power supply loop is in a disconnected state, which plays a protective role.

[0022] The rear electrodes of the positive voltage input terminal U_IN+ and the negative voltage input terminal U_IN- are also grounded through two parallel capacitors respectively.

[0023] Resistors R8 to R13 are connected in series between the positive voltage input terminal U_IN+ and the gate of the field effect transistor Q1, and a voltage zener diode Z2 and a resistor R14 are connected in parallel at both ends of the capacitor C27, the positive electrode of the voltage zener diode Z2 is connected to the source of the field effect transistor Q1, and the negative electrode is connected to the gate of the field effect transistor Q2. The source and drain of the field effect transistor Q1 are also connected in parallel with resistors R15 and R16.

[0024] For energy storage and filtering, there are usually large-capacity capacitors (X capacitors) between the positive and negative lines of the power supply. When the power is turned on, these capacitors will charge and generate a large charging current, which is called the starting surge current. This type of current needs to be suppressed.

[0025] As attached Figure 1 The startup impulse suppression circuit is composed of resistors R8~R16, capacitor C27, voltage-stabilizing diode Z2 and field effect transistor Q1. Its working principle is as follows: when the input is turned on, due to the delay effect of capacitor C27, the threshold voltage between the gate and source of Q1 MOS tube does not reach within the set time, Q1 is not turned on, and the X capacitor is charged through R7 and R8 current limiting. By designing the resistance value of R15 and R16, the maximum charging current is limited to the required range. After the capacitor is fully charged, the voltage across capacitor C27 rises to the threshold voltage of the gate and source of Q1, Q1 starts to turn on, and the power line loop works normally.

[0026] The π-type filter circuit removes the differential mode interference signal on the power line, and the common mode inductor and the grounding capacitor filter out the common mode interference signal. The filtering effect is related to the capacitance value and the inductance value. The larger the capacitance and inductance value, the greater the insertion loss of the filter circuit, and the better the filtering effect.

[0027] The π-type filter circuit includes a differential mode inductor L1, which is connected to the positive voltage input terminal U_IN+ line. The front pole of the differential mode inductor L1 has capacitors C5 and C6 connected between the positive voltage input terminal U_IN+ and the negative voltage input terminal U_IN-, and the rear pole has capacitors C9, C10, C13, C11, and C12 connected between the positive voltage input terminal U_IN+ and the negative voltage input terminal U_IN-.

[0028] The two ends of the connection point between the capacitor C6 and the negative voltage input terminal U_IN- are also connected to capacitors C7 and C8 respectively, and the other ends of capacitors C7 and C8 are grounded. The two ends of the connection point between the capacitor C10 and the positive voltage input terminal U_IN+ are also connected to capacitors C14 and C15 respectively, and the other ends of capacitors C14 and C15 are grounded.

[0029] The common-mode filter circuit includes a common-mode inductor L2, the two poles of the input end of the common-mode inductor L2 are respectively connected to the two ends of the capacitor C12, and the two poles of the output end are connected in parallel with capacitors C19, C23, C24, C25, and C26. The two ends of capacitor C26 are also respectively connected to the positive voltage output terminal U_OUT+ and the negative voltage output terminal U_OUT-. One end of the capacitor C19, C23, and C24 is respectively connected to capacitors C16 to C18, and the other end is respectively connected to capacitors C20 to C22. The capacitor adopts a 2000V high-voltage Y capacitor. The total capacity of the high-voltage Y capacitor is less than 0.02uF, the capacity of the X capacitor is more than 10uF, and the capacitance design value of the Y capacitor is about 500 times smaller than that of the X capacitor. When the housing contacts or senses high voltage between the positive and negative lines, the Y capacitor is quickly fully charged, and the potential is concentrated on the Y capacitor, thereby protecting the X capacitor.

[0030] Embodiment: A design scheme that integrates the reverse connection protection circuit, the startup impact current suppression circuit and the filter circuit on a PCB, and then seals and installs it on a metal shell. It mainly includes capacitors, inductors, MOS tubes, PCB boards, aluminum alloy shells, input connectors, output connectors, etc. There are 4 metallized mounting holes on the PCB, which are fixed to the shell through metal support columns to form multi-point grounding. The structural sealing design prevents electromagnetic interference from being transmitted inside and outside. X capacitors and Y capacitors use low-ESL ceramic capacitors, and adopt parallel and multi-point grounding design. Y capacitors use a withstand voltage of 2000V to improve lightning protection and anti-static capabilities. The functions of reverse connection protection and startup impact current suppression are achieved by controlling the on and off of MOS.

[0031] Compared with the single filtering function of the existing DC power supply EMI filter, the utility model DC power supply EMI filter not only has a good filtering effect, but also has the functions of reverse connection protection and startup impact current suppression. The 2000V high-voltage Y capacitor is used to give it a certain lightning protection and anti-static ability, and it is highly safe. It meets the requirements of electromagnetic compatibility, startup impact current and reverse connection protection in existing equipment.

Claims

1. A DC power supply EMI filter with both reverse connection protection and startup surge current suppression functions, characterized in that: It includes an input reverse connection protection circuit, a startup impact current suppression circuit, and an EMI filter circuit which are connected in sequence. The input reverse connection protection circuit includes a field effect tube Q2, the gate of the field effect tube Q2 is connected to the positive voltage input terminal U_IN+, and the drain is connected to the negative voltage input terminal U_IN-; the startup impact current suppression circuit includes a field effect tube Q1, the gate and source of the field effect tube Q1 are connected in parallel with a capacitor C27, the gate of the field effect tube Q1 is connected to the positive voltage input terminal U_IN+, and the source is connected to the source of the field effect tube Q2; the EMI filter circuit includes a π-type filter circuit and a common-mode filter circuit.

2. The DC power supply EMI filter with both reverse connection protection and startup surge current suppression functions as claimed in claim 1, characterized in that: Resistors R1 to R6 are connected in series in sequence between the positive voltage input terminal U_IN+ and the gate of the field effect transistor Q2. The source and gate of the field effect transistor Q2 are also connected in parallel with the voltage stabilizing diode Z1 and the resistor R7.

3. The DC power supply EMI filter with both reverse connection protection and startup surge current suppression functions as claimed in claim 1, characterized in that: The rear electrodes of the positive voltage input terminal U_IN+ and the negative voltage input terminal U_IN- are also grounded through two parallel capacitors respectively.

4. The DC power supply EMI filter with both reverse connection protection and startup surge current suppression functions as claimed in claim 1, characterized in that: Resistors R8 to R13 are connected in series in sequence between the positive voltage input terminal U_IN+ and the gate of the field effect transistor Q1 , and a voltage stabilizing diode Z2 and a resistor R14 are connected in parallel at both ends of the capacitor C27 .

5. The DC power supply EMI filter with both reverse connection protection and startup surge current suppression functions as claimed in claim 1, characterized in that: The source and drain of the field effect transistor Q1 are also connected in parallel with the resistor R15 and the resistor R16.

6. The DC power supply EMI filter with both reverse connection protection and startup surge current suppression functions as claimed in claim 1, characterized in that: The π-type filter circuit includes a differential mode inductor L1, which is connected to the positive voltage input terminal U_IN+ line. The front pole of the differential mode inductor L1 has capacitors C5 and C6 connected between the positive voltage input terminal U_IN+ and the negative voltage input terminal U_IN-, and the rear pole has capacitors C9, C10, C13, C11, and C12 connected between the positive voltage input terminal U_IN+ and the negative voltage input terminal U_IN-.

7. The DC power supply EMI filter with both reverse connection protection and startup surge current suppression functions as claimed in claim 6, characterized in that: The two ends of the connection point between the capacitor C6 and the negative voltage input terminal U_IN- are also connected to capacitors C7 and C8 respectively, and the other ends of capacitors C7 and C8 are grounded. The two ends of the connection point between the capacitor C10 and the positive voltage input terminal U_IN+ are also connected to capacitors C14 and C15 respectively, and the other ends of capacitors C14 and C15 are grounded.

8. The DC power supply EMI filter with both reverse connection protection and startup surge current suppression functions as claimed in claim 1, characterized in that: The common-mode filtering circuit includes a common-mode inductor L2, the two poles of the input end of the common-mode inductor L2 are respectively connected to the two ends of the capacitor C12, and capacitors C19, C23, C24, C25, and C26 are connected in parallel between the two poles of the output end, and the two ends of the capacitor C26 are also respectively connected to the positive voltage output terminal U_OUT+ and the negative voltage output terminal U_OUT-, and the capacitors C19, C23, and C24 are also grounded through a capacitor.

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