EMC (Electro Magnetic Compatibility) protection and overvoltage protection circuit of direct current power supply equipment

Abstract

The invention discloses an EMC (Electro Magnetic Compatibility) protection and overvoltage protection circuit of direct current power supply equipment. The overvoltage protection circuit at least comprises a primary EMC protection unit and an overvoltage protection unit, the primary EMC protection unit comprises an overcurrent protection subunit, a common-mode interference processing subunit and a differential-mode interference processing subunit; the overcurrent protection subunit is used for preventing equipment damage caused by abnormal increase of current; and the overvoltage protection unit is used for monitoring the condition of an external input voltage range in real time and quickly acting when the voltage exceeds a set value to cut off the whole power supply loop, so that equipment is effectively protected from being damaged. The EMC performance and the overvoltage protection capability of the direct current power supply equipment can be remarkably improved, especially under the conditions that extra EMC protection is not arranged and an AC-to-DC adapter with isolation is used, interference signals introduced by the equipment to a power grid through a power line can be effectively restrained, the energy does not exceed the threshold value of the standard requirement, and the power supply efficiency is improved. Therefore, other equipment working on the public power grid is prevented from being interfered.

Description

Technical Field

[0001] The invention belongs to the technical field of circuit design, and relates to an EMC protection and overvoltage protection circuit for direct current power supply equipment. Background Art

[0002] EMC, the full name of which is Electromagnetic Compatibility, refers to the ability of a device or system to work normally in its electromagnetic environment and not cause unbearable electromagnetic disturbance to anything in the environment. Simply put, EMC includes two requirements: on the one hand, it means that the electromagnetic disturbance (Emission) generated by the device to the environment in normal operation cannot exceed a certain limit; on the other hand, it means that the device has a certain degree of immunity (Immunity) to the electromagnetic disturbance in the environment, that is, electromagnetic sensitivity.

[0003] With the rapid development of electronic technology and the trend of miniaturization and integration of electronic equipment, DC power supply equipment has been widely used in various fields. However, the power ports of these electronic devices generally lack effective EMC protection or have unreasonable EMC design problems, which causes the equipment to fail to work properly in the electromagnetic environment or interfere with other equipment. Therefore, it is also forced that the power ports of the equipment must be equipped with an external AC-DC adapter with strong EMC protection and isolation during relevant EMC (surge, pulse group, power conduction emission, etc.) experiments and in actual use.

[0004] At the same time, the input power of DC power supply equipment may generate overvoltage due to grid fluctuations, lightning strikes, switching operations, etc. If these overvoltages are not properly protected, they may directly act on the internal circuits of the equipment, causing serious consequences such as component damage and circuit short circuits. However, overvoltage protection is often lacking or oversimplified, and over-reliance on TVS (transient suppression diodes) as the only overvoltage protection method. This practice may expose serious safety hazards when facing extreme voltage conditions, especially when the power of the TVS tube is not enough to cope with excessively high voltages, which may lead to catastrophic consequences such as fire.

[0005] Therefore, designing a DC power supply device with EMC protection and overvoltage protection circuit is of great significance for improving the electromagnetic compatibility of the equipment, protecting the equipment from electromagnetic interference, ensuring the safe operation of the equipment under overvoltage conditions, meeting relevant standards and regulations, and enhancing product competitiveness. Summary of the invention

[0006] In order to solve the above technical problems, the present application proposes an EMC protection and overvoltage protection circuit for a DC power supply device.

[0007] The present invention comprises at least a primary EMC protection unit and an overvoltage protection unit; The first-level EMC protection unit includes an overcurrent protection subunit, a common mode interference processing subunit and a differential mode interference processing subunit; The overcurrent protection subunit is used to prevent damage to the equipment caused by abnormal increase of current; The differential mode interference processing subunit is used to suppress and discharge differential mode interference, and is composed of a first varistor and a first air discharge tube connected in series, and is arranged between the positive and negative electrodes of the DC power supply; The common mode interference processing subunit is used to suppress and discharge common mode interference, and is composed of a second varistor, a third varistor and a second air discharge tube connected in series; one end of the second varistor is connected to the negative pole of the DC power supply, and one end of the third varistor is connected to the positive pole of the DC power supply; the other end of the second varistor and the other end of the third varistor are connected to one end of the second air discharge tube, and the other end of the second air discharge tube is connected to the metal shell ground; The overvoltage protection unit is used to monitor the external input voltage range in real time, and to act quickly when the voltage exceeds the set value to cut off the entire power supply circuit, thereby effectively protecting the device from damage.

[0008] Furthermore, it also includes a secondary EMC protection unit, which is located after the primary EMC protection unit and is used to suppress residual electromagnetic interference after passing through the primary EMC protection unit.

[0009] Preferably, the secondary EMC protection unit includes a common-mode inductor for suppressing common-mode interference. The common-mode inductor uses ferrite as a magnetic core, and is composed of two coils of the same size and the same number of turns symmetrically wound on the ferrite ring core, and the winding directions of the coils are opposite.

[0010] Preferably, the secondary EMC protection unit further comprises two high-voltage capacitors connected in series, which are arranged between the positive and negative electrodes of the DC power supply, and the middle of the two high-voltage capacitors connected in series is connected to the metal shell ground for discharging common-mode interference.

[0011] Preferably, two capacitors are further included, which are arranged at both ends of the common mode inductor and bridged between the positive and negative electrodes of the DC power supply.

[0012] Preferably, a third-level EMC protection unit is located after the second-level EMC protection unit, including a differential mode inductor and a TVS tube. The differential mode inductor is used to suppress differential mode interference, and the TVS tube is used to limit the transient high voltage in the circuit to a predetermined voltage level to protect subsequent circuits from the impact of transient high voltage.

[0013] Furthermore, the overvoltage protection unit also includes an anti-reverse connection protection subunit in the form of a rectifier bridge.

[0014] Preferably, the overvoltage protection unit includes a voltage regulator diode and a MOS tube. When the input power of the DC power supply device exceeds the preset threshold of the voltage regulator diode, the gate voltage of the MOS tube is lowered, so that the MOS tube is in an open circuit state, thereby playing an overvoltage cut-off function.

[0015] Preferably, lowering the gate voltage of the MOS tube is achieved by a transistor, the emitter of the transistor is connected to the source of the MOS tube, the base is connected to the positive electrode of the voltage-stabilizing diode through a current-limiting resistor, and the collector is connected to the gate of the MOS tube.

[0016] Preferably, a Schottky diode is connected between the base and the emitter of the transistor.

[0017] Beneficial effects of the present invention: The present invention can significantly improve the EMC performance and overvoltage protection capability of DC power supply equipment, especially when no additional EMC protection is provided and an isolated AC-to-DC adapter is used, and can effectively suppress interference signals introduced by the equipment into the power grid through the power line, and these energies do not exceed the limit value required by the standard, thereby ensuring that other equipment working on the public power grid is free from interference. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 This is a schematic diagram of the structure of an embodiment of the present application; Figure 2 This is a schematic diagram of the circuit of the embodiment of the present application; Figure 3 The figure is a graph of power supply conducted emission (CE) after using the embodiment of the present application. DETAILED DESCRIPTION

[0019] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0020] like Figure 1 As shown, an EMC protection and overvoltage protection circuit of a DC power supply device provided in an embodiment of the present application includes: a primary EMC protection unit, a secondary EMC protection unit, a tertiary EMC protection unit, an anti-reverse protection and an overvoltage protection unit.

[0021] like Figure 1 and Figure 2As shown, the first pin of the power external port J1 is the positive pole of the DC power supply, the second pin is the negative pole of the DC power supply, the first pin of J1 is connected to one end of the fuse F1, the second pin of the power external port J1 is connected to the negative pole of the power supply (DC-), and the third pin of the power external port J1 is connected to the metal shell ground. The other end of the F1 fuse is respectively connected to one end of the varistor RV1 and the varistor RV3 and the first pin of the common mode inductor T1; the other end of the varistor RV1 is connected to one end of the air discharge tube G2, and the other end of the air discharge tube G2 is connected to the negative pole of the DC power supply. One end of the varistor RV2 is connected to the negative pole of the DC power supply, and the other end is respectively connected to one end of the varistor RV3 and one end of the gas discharge tube G1, and the other end of the gas discharge tube G1 is connected to the metal shell ground. The above parts constitute the first-level EMC protection and overcurrent protection.

[0022] Furthermore, the slow-blow fuse F1 constitutes an overcurrent protection subunit. When the current in the circuit increases abnormally and exceeds the rated current of the circuit or device, the fuse will quickly blow, thereby cutting off the circuit and preventing the current from continuing to damage the circuit or device.

[0023] Furthermore, the varistors RV2, RV3 (i.e., the second varistors and the third varistors) and the air discharge tube G1 (i.e., the second air discharge tube) constitute a common-mode interference processing subunit. The common-mode interference suppression and discharge are at the positive and negative ports of the DC power supply, respectively through the varistors RV2, RV3, and then connected to the metal casing ground through the air discharge tube G1.

[0024] Furthermore, RV1 and the air discharge tube G2 constitute a differential mode interference processing subunit, and differential mode interference suppression and discharge are achieved by connecting the varistor RV1 (i.e., the first varistor) and the air discharge tube G2 (the first air discharge tube) in series between the positive and negative electrodes of the DC power supply.

[0025] When an external signal without common-mode or differential-mode interference is input, the varistor and the gas discharge tube are in a disconnected state (the impedance is very high, similar to an open circuit). In order to enhance the insulation capability and avoid aging of the varistor during long-term use, the varistor and the gas discharge tube are connected in series.

[0026] When the external common-mode or differential-mode interference exceeds the threshold voltage of the varistor and gas discharge tube, its internal resistance drops sharply and turns on quickly to discharge the interference and clamp the voltage at a fixed value, thereby protecting the back end from damage caused by overvoltage.

[0027] like Figure 1 and Figure 2As shown, the two ends of capacitor C1 are respectively connected between the positive and negative poles of the DC power supply, the first pin of the common-mode inductor T1 is connected to the positive pole of the DC power supply, the second pin of the common-mode inductor T1 is connected to the negative pole of the DC power supply, and the third pin of the common-mode inductor T1 is respectively connected to one end of capacitor C2 and high-voltage capacitor C4. The fourth pin of the common-mode inductor T1 is respectively connected to the other end of capacitor C2 and high-voltage capacitor C3. The other ends of high-voltage capacitors C3 and C4 are connected to the metal shell, and the above parts constitute the secondary EMC protection. The secondary EMC protection unit is located after the first level of protection to further suppress the residual electromagnetic interference after the first level of protection.

[0028] Furthermore, the common-mode inductor T1 uses a common-mode interference suppression device with a ferrite core, etc. It consists of two coils of the same size and number of turns symmetrically wound on the same ferrite ring core, and the winding directions of the coils are opposite. When a differential-mode current flows through the two wires, two magnetic fields are generated to cancel each other out, that is, the differential-mode signal has no attenuation, and when a common-mode current flows, the magnetic flux in the magnetic ring is superimposed on each other, at this time the inductance is large, and the coil presents a high impedance, thereby suppressing the common-mode interference.

[0029] Furthermore, high-voltage capacitors C3 and C4 are respectively connected between the positive electrode of the DC power supply and the metal casing ground, and between the negative electrode and the metal casing ground, and have a strong discharge effect on high-frequency common-mode interference.

[0030] Furthermore, capacitors C1 and C2 are placed at both ends of the common-mode inductor and bridged between the positive and negative poles of the DC power supply, which have a strong discharge effect on high-frequency differential-mode interference. At the same time, capacitors C1 and C2 and the leakage inductance of the common-mode inductor form a π-type filter to effectively filter out differential-mode interference.

[0031] like Figure 1 and Figure 2 As shown, one end of the differential mode inductor L1 is connected to one end of the fourth pin of the common mode inductor T1, the other end of the differential mode inductor L1 is connected to one end of the TVS tube D2, and the other end of the TVS tube D2 is connected to the third pin of the common mode inductor T1. The above parts constitute a three-level EMC protection unit.

[0032] The three-level EMC protection unit further suppresses the electromagnetic interference that still exists after the first two levels of protection, ensuring that important equipment can operate in a stable electromagnetic environment. TVS tubes with higher sensitivity and faster response speed are selected. This EMC protection unit is mainly used for differential mode interference suppression and discharge.

[0033] When there is a sudden differential-mode interference on the differential-mode inductor L1 (the current suddenly increases), a large impedance will be presented on the coil, thereby suppressing the differential-mode interference.

[0034] Furthermore, TVS tube D2 uses a 5.0 SMDJ high-power device with large current flow, extremely fast response time, and high-precision clamping voltage. It can limit the transient high voltage in the circuit to a predetermined voltage level, protecting subsequent circuits from the impact of transient high voltage, thereby ensuring the stability and reliability of the circuit.

[0035] like Figure 1 and Figure 2 As shown, the first pin and the second pin of the rectifier bridge D1 are respectively connected to the two ends of the TVS tube D2, the third pin of the rectifier bridge D1 is respectively connected to the voltage-stabilizing diode D3 and one end of the resistor R3, the fourth pin of the rectifier bridge D1 is respectively connected to the resistor R1, the Schottky diode D4, the voltage-dividing resistor R4, one end of the filter capacitor C5, and the emitter of the transistor Q1 and the source of the NMOS tube Q2. The other end of the voltage-stabilizing diode D3 is respectively connected to one end of the resistor R2 and the other end of the resistor R1. The other end of the resistor R2 is respectively connected to the other end of the Schottky diode D4 and the base of the transistor Q1. The collector of the transistor Q1 is respectively connected to the voltage-dividing resistors R3, R4, the filter capacitor C5, and the gate of the NMOS tube, and the drain of the NMOS tube is connected to the rear end protection unit, and the above parts constitute the anti-reverse protection and overvoltage protection unit.

[0036] Among them, the rectifier bridge D1 constitutes the anti-reverse connection protection sub-unit. It is composed of four diodes arranged in a bridge circuit, which converts the power input into a non-polarity input. No matter how the positive and negative poles of the power supply are connected in reverse, the circuit board can work normally to avoid the current backflow caused by the reverse connection of the power supply, thereby protecting the normal operation of the circuit and equipment and preventing them from being damaged by reverse current.

[0037] The overvoltage protection circuit includes a voltage-stabilizing diode D3, current-limiting resistors R1 and R2, a Schottky diode D4, a transistor Q1, voltage-dividing resistors R3 and R4, a filter capacitor C5, and an NMOS tube Q2. When the input power of the DC power supply device exceeds the preset threshold of the voltage-stabilizing diode D3, the voltage-stabilizing diode D3 is in the reverse breakdown region, and then the current passes through the current-limiting resistor R1 and the resistor R2 respectively, and then flows into the base of the transistor Q1 after passing through the current-limiting resistor R2. The transistor Q1 is in the on state, so that the gate voltage VGS of the NMOS tube Q2 is 0V. At this time, the NMOS tube Q2 is in the open circuit state, thereby playing the overvoltage cutoff function.

[0038] On the contrary, when the input power of the DC power supply device is lower than the preset threshold of the voltage-stabilizing diode D3, the voltage-stabilizing diode D3 is in the cut-off state, and no current flows through the current-limiting resistors R1, R2 and the base of the transistor Q1, and the transistor Q1 is in the cut-off state. Because the resistors R3 and R4 are connected across the positive and negative ends of the power supply, the voltage divided by the resistors R3 and R4 in series is equal to the voltage of VGS, that is, the NMOS tube is always in the on state. It can be seen from this that this part of the circuit can monitor the external input voltage range in real time, and act quickly when the voltage exceeds the set value to cut off the entire power supply circuit, thereby effectively protecting the equipment from damage.

[0039] like Figure 3 As shown, after the power port of the DC power supply device is equipped with the EMC protection of the DC power supply device according to the embodiment of the present application, the electromagnetic compatibility is significantly improved. Specifically: Figure 3 The middle curves correspond to the quasi-peak detection curve (red) and the average detection curve (blue). When performing power supply conducted emission tests, the quasi-peak value measured by the QP Detector should not exceed the specified QP Limit. Similarly, the average value measured by the AV Detector should not exceed the specified AV Limit. This ensures that the emission level of the device is within an acceptable range. Figure 3 It can be seen that the EMC multi-level protection circuit of the present invention effectively suppresses the interference signals emitted outward through the power line when the device is working, and these energies do not exceed the limit value required by the standard, thereby ensuring that other devices working on the public power grid are free from interference, thereby meeting safety regulations and complying with the electromagnetic compatibility of electronic products.

[0040] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. An EMC protection and overvoltage protection circuit for a DC power supply device, characterized in that: At least include a first-level EMC protection unit and an overvoltage protection unit; The first-level EMC protection unit includes an overcurrent protection subunit, a common mode interference processing subunit and a differential mode interference processing subunit; The overcurrent protection subunit is used to prevent damage to the equipment caused by abnormal increase of current; The differential mode interference processing subunit is used to suppress and discharge differential mode interference, and is composed of a first varistor and a first air discharge tube connected in series, and is arranged between the positive and negative electrodes of the DC power supply; The common mode interference processing subunit is used to suppress and discharge common mode interference, and is composed of a second varistor, a third varistor and a second air discharge tube connected in series; one end of the second varistor is connected to the negative pole of the DC power supply, and one end of the third varistor is connected to the positive pole of the DC power supply; the other end of the second varistor and the other end of the third varistor are both connected to one end of the second air discharge tube, and the other end of the second air discharge tube is connected to the metal shell ground; The overvoltage protection unit is used to monitor the external input voltage range in real time, and to quickly act when the voltage exceeds the set value to cut off the entire power supply circuit, thereby effectively protecting the device from damage.

2. The EMC protection and overvoltage protection circuit of a DC power supply device according to claim 1, characterized in that: It also includes a secondary EMC protection unit, which is located after the primary EMC protection unit and is used to suppress residual electromagnetic interference after passing through the primary EMC protection unit.

3. The EMC protection and overvoltage protection circuit of a DC power supply device according to claim 2, characterized in that: The secondary EMC protection unit includes a common mode inductor for suppressing common mode interference. The common mode inductor uses ferrite as a magnetic core, and is composed of two coils of the same size and the same number of turns symmetrically wound on the ferrite ring core, and the winding directions of the coils are opposite.

4. The EMC protection and overvoltage protection circuit of a DC power supply device according to claim 2, characterized in that: The secondary EMC protection unit also includes two high-voltage capacitors connected in series, which are arranged between the positive and negative electrodes of the DC power supply. The middle of the two high-voltage capacitors connected in series is connected to the metal shell ground for discharging common mode interference.

5. The EMC protection and overvoltage protection circuit of a DC power supply device according to claim 3, characterized in that: It also includes two capacitors, which are arranged at both ends of the common mode inductor and bridged between the positive and negative electrodes of the DC power supply.

6. An EMC protection and overvoltage protection circuit for a DC power supply device according to any one of claims 2 to 5, characterized in that: It also includes a third-level EMC protection unit located after the second-level EMC protection unit, including a differential mode inductor and a TVS tube. The differential mode inductor is used to suppress differential mode interference, and the TVS tube is used to limit the transient high voltage in the circuit to a predetermined voltage level to protect subsequent circuits from the impact of transient high voltage.

7. The EMC protection and overvoltage protection circuit of a DC power supply device according to claim 1, characterized in that: The overvoltage protection unit also includes an anti-reverse connection protection subunit in the form of a rectifier bridge.

8. The EMC protection and overvoltage protection circuit of a DC power supply device according to claim 1 or 7, characterized in that: The overvoltage protection unit includes a voltage regulator diode and a MOS tube. When the input power of the DC power supply device exceeds the preset threshold of the voltage regulator diode, the gate voltage of the MOS tube is lowered, so that the MOS tube is in an open circuit state, thereby playing the overvoltage cutoff function.

9. The EMC protection and overvoltage protection circuit of a DC power supply device according to claim 8, characterized in that: The gate voltage of the MOS tube is pulled down by a triode, the emitter of the triode is connected to the source of the MOS tube, the base is connected to the positive electrode of the voltage-stabilizing diode through a current-limiting resistor, and the collector is connected to the gate of the MOS tube.

10. The EMC protection and overvoltage protection circuit of a DC power supply device according to claim 9, characterized in that: A Schottky diode is also connected between the base and emitter of the transistor.

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