Fault protection scheme for CCFL integrated circuits

A method of operating a power supply for a cold cathode fluorescent lamp, the method comprising:

• operating the power supply and producing an operating current;
• producing a reference current with a reference component;
• producing a replica current proportional to the operating current;
• comparing the replica current to the reference current;
• and
• signaling a fault if the replica current and the reference current are unequal.

A power supply for a cold cathode fluorescent lamp, comprising:

• A first power transistor having a first node, second node and gate node, the first node coupled to a power supply;
• A second power transistor having a first node, second node and gate node, the second power transistor matched to the first power transistor, the first node coupled to a power supply;
• A third power transistor having a first node, second node and gate node, the first node coupled to the second node of the first power transistor, the second node coupled to ground;
• A fourth power transistor having a first node, second node and gate node, the fourth power transistor matched to the third power transistor, the first node coupled to the second node of the second power transistor, the second node coupled to ground;
• A replica transistor formed proportional to the third and fourth power transistors, having a first node, second node and gate node, the second node coupled to ground, the first node regulated to match the first node of the third and fourth power transistors in alternation;
• A current mirror, the current mirror coupled to the first node of the replica transistor;
• And
• A reference terminal, the reference terminal coupled to the current mirror.