Design of transient voltage suppressors for digital inputs of avionics devices in indirect lightning tests according to ED-14/DO-160

Transients due to lightning strikes on an aircraft´s fuselage impose stress on the input filters of electronic equipment. Permanent damage can occur if the voltage handling capabilities of components are exceeded. In ED-14/DO-160, section 22, a number of waveforms and levels are defined that are used to check the airworthiness of avionics equipment. Depending on procedure and level, Y-capacitors are stressed by transient voltages that exceed their dielectric strength. The design engineer´s task is to properly select the type and voltage rating of capacitors. With moderate simplifications, an equivalent LCR-series network can be justified which enabled the calculation of maximum current and energy into the suppression element.