Switched-mode power supply with a function for detecting a broken feedback loop

A switched-mode power supply, comprising:

• a primary coil;
• a switching element connected in series with said primary coil for applying a direct voltage to said primary coil as determined by a drive signal;
• a secondary circuit coupled to said primary coil with output terminals for providing an output voltage;
• and
• a drive circuit for providing the drive signal, said drive circuit being supplied with a feedback signal, the feedback signal depending on the output voltage;
• said drive circuit having a signal generating circuit for generating the drive signal and having a protective circuit, said protective circuit inhibiting said signal generating circuit depending on a comparison of the feedback signal with a first reference signal;
• said protective circuit gating out the feedback signal during a period after a start of said drive circuit so that inhibiting of said signal generating circuit based on the comparison of the feedback signal with the first reference signal is prevented during the period;
• and
• said protective circuit inhibiting said signal generating circuit after the period has elapsed, after elapse of a shorter delay than the period, as soon as the feedback signal reaches the first reference signal.