Design of a power supply filter for avionics displays: a case study

The design of a power supply filter for an active matrix liquid crystal display (AMLCD) for avionics applications is discussed. Determining the relative dominance of the differential-mode and common-mode noise currents is the key to an effective design of the filter. Equivalent circuits representing the effects of the various filter elements on the differential-mode and common-mode currents are obtained and a general rule for determining these for other filter configurations is given.