When designing airborne systems, compliance to certain parameters of the MIL-STD-704 (A-F) or DO-160 (A-G) standards will be required. Systems that are connected to and derive their power from the aircraft’s electrical power bus are called Utilization Equipment. Many electric power parameters must be considered for the proper operation of the utilization equipment that is connected to the power bus.
This white paper will help system designers to understand better the terminology and requirements specific to the parameter commonly referred to as “holdup”. A Transfer operation as defined in MIL-STD-704 is a switching operation that transfers the aircraft’s electrical
power feed from one source to another. In executing the power transfer, there will be a momentary interruption in electrical power supplied to utilization equipment. It is sometimes a requirement that utilization equipment continues to operate during the resultant power interruption. This capability is defined as a holdup function. Simply stated, the utilization equipment must ride through a power interrupt without interrupting its intended function. In such systems, the power supply within the equipment must have sufficient energy stored in reserve to draw upon during these dropout events. A holdup requirement can be applicable to systems of various power levels, and holdup time durations can range from 50 mS up to 1 second in some systems.