Patent ID: 7057355

Claim:
A drive circuit for operating at least one lamp (La) in an associated load circuit, in which the terminals for the at least one lamp are arranged, having two switches (S 1 , S 2 ) in a half-bridge arrangement, each switch (S 1 , S 2 ) comprising a cascode circuit of a bipolar transistor (B 2 ) having a control, a working and a reference electrode, and a field-effect transistor (F 2 ) having a control, a working and a reference electrode, the center point of the half-bridge arrangement being coupled to the at least one load circuit, and each cascode circuit of this type having an input circuit (E 1 , E 2 ), in which a diode (D 21 ) and a secondary winding (L 2 ) of a transformer, connected in series, are arranged in parallel with the control electrode of the bipolar transistor (B 2 ) and the reference electrode of the field-effect transistor (F 2 ), the primary winding (L 0 ) of said transformer being arranged in the load circuit such that the load circuit current (I L ) flows through it when operating the at least one lamp (La), wherein the diode (D 21 ) is arranged such that, in the case of an npn-bipolar transistor (B 2 ), it prevents a positive base current (I B ) from flowing away via the secondary winding (L 2 ), and, in the case of a pnp-bipolar transistor, it prevents a negative base current from flowing away via the secondary winding.