A resonant circuit inverter with a rectifier, a DC link circuit and an inverter including controllable switches. The resonant circuit inverter has a first control means, with which the operating point (Ap) of the resonant circuit inverter determined by a phase angle between an output current (Iist) and a voltage (Uist) at the output of the resonant circuit inverter is controlled. The first control means determines frequency of the output current (Iist). The resonant circuit inverter has a phase detector for determining an actual phase angle as a function of a zero crossing of the output current (Iist). The resonant circuit inverter has means for detecting a zero crossing of the output current (Iist). For determining the actual phase angle, the difference (Ti−Tt) is determined from measured time (Ti) and a known dead time (Tt).