Processor supervisory circuit and method having increased range of power-on reset signal stability

A power supply, comprising:

• AC-to-DC voltage conversion circuitry;
• a storage capacitor, coupled to an output of said conversion circuitry, for receiving and storing unregulated electrical power received from said conversion circuitry;
• a voltage regulator, coupled to said storage capacitor, for regulating said unregulated electrical power received from said storage capacitor;
• and
• a processor supervisory circuit, coupled to said voltage regulator, comprising:
• a power-on reset circuit, comprising:
• an adaptive, nonlinear voltage divider having a voltage input and a voltage output, said divider dividing an unscaled, unregulated voltage received at said voltage input by a factor that varies as a function of said unscaled, unregulated voltage to produce a scaled, unregulated voltage at said voltage output, and
• a comparison circuit for comparing said scaled, unregulated voltage with a scaled, regulated voltage to produce a power-on reset (RESET) signal when said scaled, regulated voltage exceeds said scaled, unregulated voltage, said divider being adaptive and nonlinear to ensure that said comparison circuit continuously produces said RESET signal when said scaled, regulated voltage exceeds said scaled, unregulated voltage and thereby avoid premature activation of a processor couplable to said power-on reset circuit, said comparison circuit employing positive feedback to obtain transfer characteristics with hysteresis, and
• a power-fail sense circuit, coupled to said voltage regulator, for producing a power-fail sense (PFS) signal.