The device (16) has a discharge circuit that connects power output to reference potential via controlled switch. A control circuit includes charge or discharge timing circuit having relaxation time. One input of logic circuit is connected to main control input of power supply device, and other input is connected to output of timing circuit. The logic circuit is adapted so that controlled switch is only turned on when no activation signal is present on main control input and output of first timing circuit reaches value greater than or equal to relaxation time of timing circuit.
