Abstract: Aircraft Auxiliary Power Unit (APU) controllers and related methods are described herein. An example APU controller includes a sensor interface to receive a signal from a speed sensor. The signal includes pulses representing a rotational speed of an engine of an APU. The APU controller also includes an overspeed detection circuit including a counter to count a number of pulses from the signal occurring within a time interval, a digital-to-analog converter (DAC) to convert the number of pulses into an analog voltage signal and a comparator to: compare the analog voltage signal to an overspeed threshold signal and generate a shutdown command in response to the analog voltage signal exceeding the overspeed threshold signal. The APU controller also includes a valve driver to, in response to receiving the shutdown command, cause a fuel shutoff valve to cease fuel flow to the engine of the APU.

Abstract: A battery depassivation system includes a depassivation circuit, a battery connect/disconnect circuit, and a processor. The depassivation circuit is adapted to be electrically coupled in series with a battery. The depassivation circuit is also coupled to receive an ENABLE signal and is configured, upon receipt thereof, to draw current from the battery. The battery connect/disconnect circuit is adapted to be electrically coupled in series between the battery and one or more battery-powered electronic circuits. The battery connect/disconnect circuit is coupled to receive an ISOLATE signal and is configured, upon receipt thereof, to electrically disconnect the one or more battery-powered electronic circuits from the battery. The processor is adapted to couple to the battery and is configured, upon being coupled thereto, to determine if the battery needs depassivation and implement a depassivation routine if the battery is determined to need depassivation.

Abstract: A battery depassivation system includes a depassivation circuit, a battery connect/disconnect circuit, and a processor. The depassivation circuit is adapted to be electrically coupled in series with a battery. The depassivation circuit is also coupled to receive an ENABLE signal and is configured, upon receipt thereof, to draw current from the battery. The battery connect/disconnect circuit is adapted to be electrically coupled in series between the battery and one or more battery-powered electronic circuits. The battery connect/disconnect circuit is coupled to receive an ISOLATE signal and is configured, upon receipt thereof, to electrically disconnect the one or more battery-powered electronic circuits from the battery. The processor is adapted to couple to the battery and is configured, upon being coupled thereto, to determine if the battery needs depassivation and implement a depassivation routine if the battery is determined to need depassivation.