The invention relates to a control means for a transistor switch circuit controlling a power supply circuit for providing electric power to a load, comprising: a power supply stage having a transistor bridge circuit and an LC circuit with an inductor and filter capacitors, and a control stage. The control stage comprises a monitor circuit for monitoring a bridge voltage of a connection between two semiconductor members and the current through the inductor, said monitor circuit comprising a first comparator for comparing when the current through the inductor exceeds a reference value and a second comparator for comparing when the bridge voltage changes polarity towards the corresponding rail polarity; and a drive circuit adapted to provide a firing pulse to one of said switchable members of said semiconductor members for initiating the conduction thereof. The control drive circuit is adapted to terminate the conduction of said switchable member when said first comparator determines that the current through the inductor exceeds said reference value, and to provide another firing pulse when said second comparator determines that the bridge voltage changes polarity towards the corresponding rail polarity. According to the invention, a logic circuit is incorporated in the monitor circuit and connected to the outputs of first and second comparators, said logic circuit being adapted to respond to the first firing edge of a signal from the second comparator only, when the signal from the first comparator permits firing.