Patent ID: 6011358
Filing Date: 2000-01-04
Classification: H05B

Abstract:
An electronic ballast for operation of at least two low-pressure gas discharge lamps, comprising:a DC voltage source which supplies current to at least said gas discharge lamps,at least one half bridge, which is connected to said DC voltage source and supplies an AC voltage at an output terminal, wherein said output terminal is connected to said gas discharge lamps via coupling means,a driving circuit connected via control terminals to said half bridge, said driving circuit driving said half bridge at a settable frequency, and having a supply voltage input connected to a supply voltage,wherein if said supply voltage exceeds a threshold value the driving circuit adopts an active operating mode and drives said half bridge at a given frequency, andwherein if said supply voltage falls below a second threshold value said driving circuit adopts a passive operating mode and blocks said half bridge,a first controlled switch with a self-holding characteristic and which is connected to said supply voltage against a frame, said first controlled switch reducing said voltage below said second threshold value when it is closed,wherein said first controlled switch is connected in series with a circuit for generating a potential offset when said first controlled switch is closed, said first controlled switch alternatively controlled by a voltage monitoring circuit for monitoring said gas discharge lamps so that said first controlled switch is closed when said voltage monitoring circuit detects an impermissible state at at least one of said gas discharge lamps, whereby said supply voltage is lowered to below said second threshold value, anda second controlled switch, which can alternatively assume a non-conducting state and a conducting state, in which it switches said first controlled switch to said non-conducting state, and whose control input is connected to a detector circuit which is assigned to said respective gas discharge lamp, and which detects a connection of a gas discharge lamp to said electronics ballast.