Measurement of noise source impedance of SMPS usingtwo current probes

An EMI noise solution scheme by independent component measurement

“…This can be implemented by two current probe method [4] (see Fig.5), where the noise source impedance is calculated through measuring voltages across two current probes under the conditions of short circuit, standard resistor connected, and noise source connected at load terminal respectively. The impedance is calculated by …”

Multi-Channel Time-Domain EMI Evaluation of Dominant Mode Interference for Optimized Filter Design in Three-Phase Systems

“…Components that define the common mode (CM) noise source impedance are the unintentional capacitance between the switching device and the heat sink, parasitic capacitance between the heat sink and the grounded chassis, and parasitic capacitance between other parts of the setup, which carry pulsating current, and the grounded chassis; components that define the differential mode (DM) noise source impedance is the turned-on resistance of the rectifying diodes, the equivalent series resistance and the equivalent series inductance of the bulk capacitor [5]. At lower frequencies (below 1 MHz), interference is mainly DM while at higher frequencies it is mainly CM [6] because parasitic effects create a low-impedance pass for interference.…”

“…Thus, knowing the noise source and the load impedances, we can design a perfect filter for each particular case. Various approaches for in-situ impedance measurements were devel-oped previously [5], [9]- [12]. However, all of the proposed approaches are time-consuming, due to the pre-measurement calibration process and require expensive equipment which is not always available.…”