EMI Suppression Filters (EMC and Noise Suppression) Example of noise suppression in the power circuits of devices mounted in vehicles

Various electronic devices are now mounted in vehicles. These automotive devices contain power circuits in order to create the voltages required to power these devices.
The power circuits use a switching system that increases efficiency, but is also a source of problematic noise. Noise suppression measures for the power circuits (DC-DC converter) of devices mounted in vehicles are described below.

The noise suppression measures and products introduced here are not limited to vehicles and can also be used with industrial and other equipment.

Evaluation model power circuit

Evaluation was performed using a 12 V → 5 V step-down DC-DC converter as the model circuit.

  • Iin ≒ 0.3A、Iout ≒ 0.7A
  • Switching frequency≒400kHz

Investigation of noise conditions

The initial noise conditions were confirmed and the types of noise were isolated.

Noise was measured for the following three patterns.

  • Conducted noise (150 kHz to 108 MHz)
  • Radiated noise (150 kHz to 30 MHz)
  • Radiated noise (30 kHz to 300 MHz)

Implementation of noise suppression measures

The methods for suppressing noise were decided and the noise reduction effects were confirmed for each of the three patterns.