Patent ID: 7750816

Claim:
A surge current alarm circuit comprising: a detecting circuit to detect a surge current and convert the surge current into a digital signal with a pulse width corresponding to a duration of an over value part of the surge current when the surge current is over a limitative current value; a processing circuit connected to the detecting circuit to receive the digital signal and generate an alarm signal when the pulse width of the digital signal is over a limitative time; and an alarm circuit connected to the processing circuit to give an alarm upon receiving the alarm signal from the processing circuit, wherein the detecting circuit comprises: an input port with an anode and a grounded cathode; an output port with an anode and a grounded cathode; a detecting resistor connected between the anodes of the input port and the output port; a Zener diode having a cathode connected to the anode of the input port and an anode grounded via a first resistor; and a comparator having a non-inverting terminal connected to the anode of the input port via a second resistor and grounded via a third resistor and the first resistor in turn, an inverting terminal connected to the anode of the input port via a fourth resistor and the detecting resistor in turn and grounded via a fifth resistor and the first resistor in turn, and an output terminal connected to the processing circuit.