Patent ID: 7372218

Claim:
An open protection circuit for a backlight module that includes a plurality of fluorescent lamps, the open protection circuit comprising: a pulse width modulator having a control port, the control port being configured to disable the pulse width modulator according to a predetermined signal; a switch having a gate terminal, and a source terminal connected to the control port; a first input circuit including a first diode, a first positive terminal of the first diode connected to the gate terminal of the switch, and a first negative terminal of the first diode connected to ground; a second input circuit including a first input resistor, one end of the first input resistor connected to the control port; a first detecting circuit including a first sampling resistor, one end of the first sampling resistor connected to a first one of the fluorescent lamps and the first negative terminal of the first diode, and another end of the first sampling resistor connected to ground; and a second detecting circuit including a second sampling resistor, one end of the second sampling resistor connected to a second one of the fluorescent lamps, and to the control port via the first input resistor, and another end of the second sampling resistor connected to ground; wherein the control port is pulled to a low voltage state when either of the first or second fluorescent lamps has an open circuit.