Adaption circuit for operating a high-pressure discharge lamp

Claim 1

An adaptation circuit for operating a high-pressure discharge lamp comprising: first and second input terminals for connection to a source of supply voltage via a series ballast impedance, first and second output terminals for connection to terminals of a discharge lamp connectable to said output terminals, means connecting a first controlled semiconductor switch between the first input terminal and the first output terminal, means connecting the second input terminal to the second output terminal, a voltage-division circuit coupled between said first input terminal and one of said output terminals so that the first semiconductor switch and the voltage-division circuit provide two parallel paths for current to flow between said first and second input terminals, wherein at least one of said current paths includes a discharge lamp when connected to said output terminals, said voltage division circuit having first and second branches with a junction point therebetween, said first branch including a capacitor, means including a voltage-responsive switch for connecting a control electrode of the first semiconductor switch to said junction point, and wherein the second branch of the voltage-division circuit includes a voltage source whose voltage is primarily determined by the lamp voltage and whose polarity is the same as that of a voltage developed across the voltage division circuit, whereby the firing angle of the first semiconductor switch varies with the lamp voltage in a sense to maintain lamp power constant despite variations in the supply voltage or variations in the lamp operating voltage.