US Patent 7181340 Engine control circuit

An engine control circuit includes a battery voltage detector, a signal supervisor, and a processor that operates in a normal mode and a power-down mode. The battery voltage detector senses the output voltage of a battery that supplies current to the engine, and asserts a detection signal when the voltage is below a predetermined value. The signal supervisor measures the length of time for which the detection signal remains asserted. The processor switches from the normal mode to the power-down mode when the measured length of time reaches a predetermined value. This scheme avoids loss of engine control when the battery voltage drops briefly and then recovers.