A method for controlling a voltage transformer for operating a switchable load having at least one inductance and a switch, which is activated by a digital control device. When the switch is closed, a magnetizing current flows through the inductance. When the switch is open, a demagnetizing current flows through the inductance. The method comprises the steps of measuring the demagnetizing time of the inductance and, when a maximum value of the demagnetizing time of the inductance is exceeded, storing such an occurrence as a fault. The load is disconnected by the control device when a predetermined maximum frequency of faults is exceeded.