Patent ID: 6667584
Filing Date: 2003-12-23
Classification: H05B

Abstract:
A ballast circuit adapted to be connected to at least one fluorescent lamp, each lamp having two ends with a filament at each end, each filament connected to a lamp electrode, further comprising:a circuit part for generating a supply voltage; a preheating circuit powered by the supply voltage, configured to preheat the lamp electrodes; a protection circuit, configured to detect short-circuit conditions in the preheating circuit, and comprising: a sensing resistor coupled to the preheating circuit, configured to sense a current flowing through the preheating circuit; a control signal circuit connected across the sensing resistor, configured to convert the sensed current into a control signal, comprising a low-pass filter, configured to prevent transitory currents from triggering a control means; and a rectifying diode; the control means connected between said preheating circuit and the sensing resistor, configured to disable the supply voltage when the control signal exceeds the value of a preset trigger level.