A dc input circuit receives a dc input voltage. At least four rectification elements are coupled to each other in a diode bridge configuration, where an input of the diode bridge configuration is coupled to the dc input circuit to receive the dc input voltage. At least one of the rectification elements includes a transistor. A decision circuit indicates, as a function of one of collector current and emitter current of the transistor, that the received dc input voltage has normal or reversed polarity. Other embodiments are also described and claimed.