Abstract
In the electrostatic discharge (ESD) immunity testing specified by the IEC 61000-4-2, an ESD generator simulating a human ESD is normally used for contact discharges, while air discharge testing is also being accepted despite the fact that the testing is likely to provide inconsistent test results from the poor reproducibility of discharge current waveforms. To confirm to what extent air discharges affect the discharge currents with respect to charge voltages and approach speeds, we measured the discharge currents through a hand-held metal piece with fast and slow approaches from a male subject charged from 1000 V to 8000 V, which were calculated from two equivalent circuits. An equivalent circuit with an ideal switch in view of a spark was used to show the limit waveform of the discharge current through the inverse Fourier transform from the measured human impedance. The other equivalent circuit consisting of a time varying spark resistance and lumped circuit parameters derived from the human body impedance was used to estimate the discharge current based on a spark resistance formula. As a result, we found that the first equivalent circuit provides the maximum current peak and minimum rise time of discharge currents regardless of the charge voltages or approach speeds, while under an appropriate spark length according to the charge voltage the second equivalent circuit gives the discharge current waveform that approximately coincides with the measured result.
