Device for measuring the common-mode voltage of conducted interference

Abstract

This utility model relates to the field of electromagnetic compatibility (EMC) of electronic equipment and can be used in the development and debugging of pulsed power supplies (PMS) to isolate the common-mode component of conducted interference and assess its level during preliminary compliance testing with emission standards. The proposed device for measuring the common-mode component of conducted interference comprises input connectors, a differential-mode suppression circuit implemented using a resistive circuit, an amplification stage, a buffer amplifier, and an output connector for connection to an oscilloscope operating in fast Fourier transform mode.The technical result consists in providing the ability to measure the common-mode component of conductive interference directly at the workstation of the development engineer using a standard digital oscilloscope without the use of expensive specialized laboratory equipment, in an operating frequency range of up to 30 MHz.

Description

[0001] FIELD OF TECHNOLOGY

[0002] This utility model relates to electromagnetic compatibility (EMC), and is specifically designed to isolate common-mode interference from the conducted interference spectrum and evaluate it during the debugging of switched-mode power supplies (SMPS) to ensure compliance with emission standards. The device can be used in research and production laboratories, design bureaus, and for educational purposes when studying conducted interference measurement methods.

[0003] STATE OF THE ART

[0004] A prior art invention includes an "Electromagnetic Interference Noise Separator" (patent US8125291B2, issued February 28, 2012, classification index H03H 7 / 38). This device separates conducted interference into common-mode and differential-mode components using two wideband chokes. The differential choke has a high impedance for the differential component of the interference, allowing it to output common-mode interference. The common-mode choke, in turn, passes the differential component, significantly attenuating the common-mode component of the interference signal. The wide bandwidth requirements for the chokes are driven by the need to measure interference in the range of up to 30 MHz without distortion.

[0005] The disadvantage of this method is the increased requirements for the bandwidth of the chokes and the PCB layout, since the wave impedance of the printed conductors must be 50 ohms in order to prevent distortion.

[0006] The "Soft separation method of conducted electromagnetic interference noise based on blind signal processing technology" is known, patent CN101799494B, 10.08.2011 cl. G01R 23 / 16, G01R 31 / 00. This method evaluates and compensates the spectral components of two current probes. Next, using a dual-channel oscilloscope and the said probes, electromagnetic interference signals are simultaneously measured in the time domain in the phase and neutral wires that supply the switching power supply. Next, computer post-processing is performed using the Fast ICA algorithm for "blind" separation of electromagnetic interference and comparison of the separated signal with reference signals of the common-mode and differential modes.

[0007] The disadvantages of this method are the need for digital post-processing of the signals received by the oscilloscope, which significantly complicates the measurement process and increases the time spent by the developer on noise separation, as well as the requirement to compensate for the spectral components of the current probes in order to ensure measurement accuracy.

[0008] The prototype and closest analogue of the proposed measuring device can be a differential interference suppression circuit consisting of five resistors (see H. Ott Electromagnetic compability engineering, New Jersey: J. Wiley and Sons, 2009, ISBN: 978-0-470-50851-0).

[0009] This circuit mixes the input signals from two power supply network (PSN) devices, LISN-1 and LISN-2, suppressing the differential component and producing a common-mode interference voltage at the output. A spectrum analyzer or oscilloscope can be used as the signal receiver. For effective interference suppression, the input impedance of the signal receiver should be 50 ohms.

[0010] The disadvantage of the prototype is that when connecting an oscilloscope to the output of this circuit, it is necessary to amplify the received common-mode interference voltage due to the insufficient sensitivity of the oscilloscopes, which leads to distortion of the amplitude of the measured voltage.

[0011] ESSENCE OF THE UTILITY MODEL

[0012] The essence of the utility model is the creation of a device for measuring the common-mode voltage of conductive interference, which ensures the formation of a common-mode interference signal at the output, the level and spectral composition of which is suitable for direct measurement by a digital oscilloscope without additional processing.

[0013] The technical result of this utility model is the ability to measure common-mode interference from conducted interference voltage using an oscilloscope directly at the design engineer's workstation. This allows for the identification of optimal solutions for reducing the conducted interference emissions of SMPSs. This reduces the time spent on expensive laboratory equipment and accelerates SMPS development. This technical result is achieved by a device for measuring the common-mode component of conducted interference voltage comprising input connectors, a differential-mode interference suppression circuit, an amplifier stage, a buffer amplifier, and an output connector directly connected to an oscilloscope operating in fast Fourier transform (FFT) mode.The differential component suppression circuit is implemented as a resistive circuit of five resistors, providing summation of signals from the measuring outputs of two electronic amplifiers and suppression of the differential component; the amplification stage is implemented on a high-frequency bipolar transistor using a common-base circuit; the buffer amplifier is implemented on a similar transistor using an emitter-follower circuit, and the device is powered by a battery with a nominal voltage of 12 V.

[0014] The utility model is new compared to the prototype, since it additionally contains an amplification stage and a buffer amplifier, as well as an autonomous power supply for the circuit.

[0015] BRIEF DESCRIPTION OF DRAWINGS

[0016] The essence of the device is explained in Fig. 1-2.

[0017] Fig. 1 - schematic diagram of a device for measuring the common-mode voltage of conductive interference, where:

[0018] X1, X2 - input connectors of the device for connection to the measuring outputs of the ESP;

[0019] X3 - connector for connecting the device's power source (12 V battery);

[0020] X4 - device output connector for connecting to an oscilloscope;

[0021] R1-R5 - resistors of the differential component suppression circuit of conductive interference;

[0022] R6 - the base bias resistor of the amplifier stage transistor, which sets the operating point for direct current;

[0023] R7 - resistor that sets the gain;

[0024] R8 - resistor that sets the input resistance of the amplifier stage;

[0025] R9 - emitter load resistor of the buffer amplifier transistor, which forms the output voltage of the device;

[0026] C1 - blocking capacitor in the emitter circuit of the transistor of the amplification stage, eliminating negative feedback on alternating current;

[0027] C2, C3 - filter capacitors in the power supply circuit of the device;

[0028] C4 - output circuit decoupling capacitor, preventing the DC component of the signal from passing to the device output;

[0029] L1 - a choke that provides attenuation of low-frequency components of the input signal;

[0030] VT1 - transistor of the amplification stage, providing voltage gain of the common-mode component of conductive interference;

[0031] VT2 - transistor of the buffer amplifier, designed according to the emitter follower circuit;

[0032] Fig. 2 - circuit diagram of the device for measuring common mode interference voltage using an oscilloscope, where:

[0033] 1 - storage battery (AKB);

[0034] 2 - measuring device;

[0035] 3 - oscilloscope;

[0036] 4 - test SMPS;

[0037] 5 - load;

[0038] LISN 1, LISN 2 - power supply network equivalents through which alternating supply voltage is supplied to the SMPS and from whose measuring outputs the conducted interference voltage is removed.

[0039] DETAILED DESCRIPTION OF THE UTILITY MODEL

[0040] Fig. 1 shows the circuit diagram of a device for measuring the common-mode voltage of conducted interference. The differential-mode interference suppression circuit is implemented using resistors R1-R5. Resistor R8 sets the amplifier's input impedance. Inductor L1 attenuates low-frequency components of the input signal. Transistor VT1 provides voltage gain for the input signal. Resistor R7 adjusts the gain. Resistor R6 sets the initial base bias of VT1 and stabilizes the transistor's operating point with DC current. Bypass capacitor C1 eliminates negative AC feedback.

[0041] The emitter follower transistor VT2 serves as a buffer amplifier and ensures a constant amplitude-frequency response (AFR) in the range above 20 MHz. R9 converts the VT2 emitter current into an output voltage. C2 and C3 filter the supply voltage. Output capacitor C4 serves as a decoupling capacitor and prevents the DC component of the signal from reaching the device output. X1 and X2 are the device input connectors for connecting to the electronic control system. X3 is the 12 V battery connector. X4 is the output connector for connecting the device to an oscilloscope. The transistors used should be high-frequency, which allows the device to operate in an extended frequency range and also reduces measurement error in the 20-30 MHz range.For example, SS9018 type transistors or their functional analogs can be used as high-frequency transistors, providing a cutoff frequency of at least 1 GHz and a sufficient voltage gain in the operating frequency range.

[0042] Fig. 2 shows the circuit diagram for the device for measuring the common-mode voltage of conducted interference. The alternating supply voltage is fed through the LISN-1 and LISN-2 power supply network equivalents to the input of the tested pulse power supply 4, which operates on a resistive load 5. From the measuring outputs of the power supply network equivalents, the conducted interference voltage is applied to the inputs of the measuring device 2. The measuring device 2 is powered from the storage battery 1 with a nominal voltage of 12 V. The isolated common-mode component of the conducted interference from the output of the measuring device 2 is fed to the input of the oscilloscope 3.

[0043] The device for measuring the common-mode voltage of conducted interference operates as follows. The conducted interference voltage, read from the ESP measurement outputs relative to the phase and neutral, respectively, is applied to the device's input terminals X1 and X2. A resistive differential-mode suppression circuit, formed by resistors R1-R5, isolates the common-mode voltage, which is fed to the input of a transistor amplifier on VT1. The amplified signal is then fed through a buffer amplifier on VT2 to the device's output terminal X4 and then to oscilloscope 3, operating in FFT mode. The development engineer analyzes the obtained harmonic amplitude of the common-mode component of the conducted interference spectrum and, by comparing the obtained results with the conducted interference spectrum, determines which type of interference (common-mode or differential) predominates in the spectrum at various frequencies.

[0044] The proposed device's positive effect is to increase the efficiency of developing pulsed voltage converters and reduce the time spent on expensive EMC laboratory equipment. This positive effect is achieved by using an oscilloscope directly at the developer's workstation to preliminarily assess the level of common-mode interference and promptly select technical solutions for its suppression.

[0045] Such technical solutions may include changing the printed circuit board topology, adjusting the filter circuit at the input and output of the SMPS, selecting the parameters of common-mode chokes and capacitors, as well as optimizing grounding and shielding.

Claims

1. A device for measuring the common-mode component of conductive interference voltage, comprising input connectors for connection to the measuring outputs of two power supply network equivalents, a differential component suppression circuit, and an output connector for connecting a measuring instrument, characterized in that it additionally comprises an amplification stage and a buffer amplifier, wherein the differential component suppression circuit is implemented in the form of a resistive circuit of five resistors connected to the input connectors, the output of the resistive network is connected to the input of the amplification stage, the output of the amplification stage is connected to the input of a buffer amplifier implemented according to an emitter follower circuit, the output of which is connected to the output connector of the device, and the power supply of the amplification stage and the buffer amplifier is carried out from an autonomous DC source with a nominal voltage of 12 V.

2. The device according to paragraph 1, characterized in that the transistors of the amplifying stage and the buffer amplifier are selected to be high-frequency with a cutoff frequency of at least 1 GHz to ensure a range of operating frequencies of the device of up to 30 MHz and to reduce the measurement error of the common-mode component of conductive interference in the 20-30 MHz subrange.

Images