초록 ▼

A series resonant ballast safety control circuit for controlling the operation of a ballast when a lamp is removed from a lamp fixture. The safety control circuit senses a diode clamp current and activates a transistor to ground one of the terminals of a dimming control circuit. The dimming control

A series resonant ballast safety control circuit for controlling the operation of a ballast when a lamp is removed from a lamp fixture. The safety control circuit senses a diode clamp current and activates a transistor to ground one of the terminals of a dimming control circuit. The dimming control circuit reduces the duty cycle of one of the inverter transistors to decrease the available output voltage and reduce the through-lamp leakage current to safe levels. Once the lamp is replaced in the lamp fixture, the safety control circuit no longer controls the dimming control circuit and the ballast returns to normal operation. In another embodiment, the safety control circuit is used with a boost power factor correction circuit in a non-dimming ballast system to reduce the current provided to the lamp load. The safety control circuit is connected to the boost power factor correction circuit so that when the safety control circuit senses a diode clamp current, the safety control circuit disables the boost power factor correction circuit. This prevents the boosted voltage from being supplied to the inverter, which in turn reduces the output voltage provided to the removed lamp and results in a reduced through-lamp leakage current.

대표청구항 ▼

[ What is claimed is:] [1.] A ballast circuit for controlling one or more fluorescent lamps connected to a pair of lamp terminals of a lamp fixture comprising:a DC power supply;an inverter connected to the DC power supply and to the lamp fixture;a safety control means for reducing a through-lamp lea

[ What is claimed is:] [1.] A ballast circuit for controlling one or more fluorescent lamps connected to a pair of lamp terminals of a lamp fixture comprising:a DC power supply;an inverter connected to the DC power supply and to the lamp fixture;a safety control means for reducing a through-lamp leakage current to eliminate a shock hazard when a lamp is removed from the lamp terminals;wherein the safety control means is activated by an electrical signal produced by a clamping current flowing through a clamping circuit when the lamp is removed; andwherein the inverter continues to operate while the safety control means is activated.