Patent ID: 7397643

Claim:
A protection circuit, coupled between a secondary winding of a transformer and a load, comprising: a first impedance having a first end coupled to a first end of the secondary winding and a second end coupled to a first end of the load, and a second end of the secondary winding coupled to ground; a second impedance having a first end coupled to the first end of the secondary winding; a third impedance having a first end coupled to the second end of the first impedance; a temperature-controlled variable resistor having a first end coupled to a second end of the second impedance; and a switch comprising a first node, a second node, a third node and a fourth node, wherein the first node is coupled to a second end of the temperature-controlled variable resistor, the second node is coupled to a second end of the third impedance, the third node is coupled to a second end of the load, and the fourth node is coupled to the ground.