Tech Briefs

An integrated approach to prediction tools enables faults to be diagnosed accurately.

Electronic systems such as electronic controls, onboard computers, communications, navigation, and radar perform many critical functions onboard military and commercial aircraft. All of these systems depend on electrical power supplies for direct current (DC) power at a constant (regulated) voltage to drive solid-state electronics. With these power supplies playing an important role in the operation of aircraft systems and subsystems, flight and ground crews need health state awareness and prediction tools that diagnose faults accurately, predict failures, and project life remaining of these components.

A Physics of Failure Model was used to demonstrate gate-oxide breakdown, one of the major concerns regarding MOSFET devices. Damage to the gate oxide can result in excessive leakage current, increased standby power, and a decrease in response time.
An integrated approach to switching mode power supply health management was developed that implements techniques from engineering disciplines including statistical reliability modeling, damage accumulation models, physics of failure modeling, and sensor-based condition monitoring using automated reasoning algorithms. Using model-based assessments in the absence of fault indications, and updating the model-based assessments with sensed information when it becomes available, provides health state awareness at any point in time. The diagnostic techniques, and prognostic models, have been demonstrated through accelerated failure testing of switching mode power supplies.

Switch-mode power supplies (SMPSs) are commonly used aboard aircraft where their weight, size, and efficiency make them preferable to conventional transformer-based power supplies. In addition to regulating the voltage of DC power, these novel circuits can also serve as DC-to-DC converters that can step down (“bucking” design) voltage like conventional supplies or step up (“boost” or “flyback” design) voltage. However, early SMPS designs suffered from sudden and catastrophic failures or generated excessive electromagnetic interference (EMI). More recent SMPS designs employ protective circuits to isolate sensitive components from damaging events.

The DC-DC converter at the heart of SMPSs uses a switching element, along with capacitors and inductors, to step up or step down voltage and current accordingly. High-speed switching enables the transfer of energy packets from the input filter capacitor to the output filter capacitor. The last stage filters out any high-frequency components from the DC output. Finally, the output is feedback into a control circuit that stabilizes the DC/DC converter.