Early power failure detection circuit

A method, performed by an electrical circuit in an electronic device, for providing an early power failure (EPF) indication for the electronic device energized by an alternating current (AC) input mains voltage, the method comprising:

• applying the AC input mains voltage to a full wave bridge rectifier coupled to a voltage divider that is coupled to a threshold detector of the electronic device, wherein the threshold detector reacts to a positive threshold voltage to activate an opto-coupled transistor to provide a pulse to a processor when the positive threshold voltage is exceeded;
• measuring, by the processor, a duration of the pulse, which is indicative of a length of time of a corresponding portion of a period of the AC input mains voltage, when, during the period portion, an instantaneous magnitude of the AC input mains voltage exceeds the positive threshold voltage;
• and
• providing, by the processor, the EPF indication in accordance with the length of time of the pulse, wherein the EPF indication initiates and the processor performs an orderly power shutdown of the electronic device.