Investigation on mechanism of radiated emissions from fan unit model

Pulse width modulation (PWM) is used to drive fan units in order to control them precisely. It creates a need to maintain the technology suppressing radiated emissions. Many studies are carried out to suppress emissions from PCB. However, mechanism of radiated emissions from an interface cable is not yet studied enough. In this paper, the radiation mechanism is studied using the fan unit model constructed with the fans and the drive circuit. The places of radiation source were investigated from the radiated electric field. The results show that the sources were placed at the interface cable connecting the drive circuit with the fan. The model was presented by the wire grid and the radiated electric field was calculated when the common mode current on the interface cable was the same as measured one. The results show that the calculation results almost agree with the measured one. The results also suggest that the radiation source was the drive pulse on the interface cable and the electric field was radiated from the interface cables and the AC-mains cables. The effect of the improving ground between the drive circuit and the fans was investigated from both the experiment and the analysis. The results indicated that the improvement of the ground was effective to reduce the radiation level.