SEH based independent APU overspeed protection circuit and its bit design

In order to address the issue of APU rotator overspeed, which can lead to a hazardous failure condition, it is necessary to develop an APU Electronics Control Unit (ECU) with Design Assurance Level (DAL) B. The development of such a unit is essential for mitigating this risk. However, it should be noted that the cost and time required for developing DAL B software or hardware are much higher compared to non-DAL required. Therefore, this paper aims to propose a method for designing an APU rotator overspeed protection circuit using Simple Electronics Hardware (SEH) technic, thus avoiding the process certification mandated by DO-254. This circuit comprises four modules: signal conditioning, reference signal generation, overspeed detection, and overspeed protection. Simulation results will validate the functionality of the circuit, while failure rate calculations will confirm its compliance with regulatory requirements.