Patent ID: 7339321

Claim:
A ballast for a discharge lamp in particular for a vehicle lighting/signalling device, comprising: (a) input terminals receiving a DC voltage coming from a supply source of the vehicle, (b) a chopping supply circuit, functioning at a predetermined chopping frequency, in order to supply an output voltage to the discharge lamp, and (c) a filtering device disposed at the input to the ballast, the filtering device is configured to reduce radio interference produced by the chopping supply circuit and comprising: (i) at least one first filtering capacitor connected between the input terminals, (ii) a filtering choke connected in series between one of the input terminals and the chopping supply circuit, and (iii) at least one second filtering capacitor in series with an additional choke, the second capacitor being configured with the additional choke to form a resonant circuit disposed between the input terminals and tuned to the chopping frequency.