A controller circuit is specified, having a step-up controller, a resonant converter connected downstream of the step-up controller on the output side, a transformer, a rectifier, which rectifier is connected to the secondary winding of the transformer on the input side, and a CLL resonant circuit connected to the resonant converter and to the primary winding of the transformer, which CLL resonant circuit has a resonance capacitance and a first and a second resonance inductance. In order to reduce the switching losses, the CLL resonant circuit is embodied as a “T” circuit.