serious regulator malfunction

27 Jan 2011

Hi!

Today I had some strange problems with the regulator that makes 3,3V from the 4,5-9V input. What happened: the mbed wouldn't boot and the lights remained off. Then I measured the output voltage on Vout pin. There was about 4,1V on the ouput! Luckily my 3,3V sensors (very expensive tilt compensated compass) still function. Then about an hour later it functioned normal once, but after removing the batteries and connecting them again it went wrong again. And after I added some large capacitors to the input and output the problem seems to be solved.

What can this be?

27 Jan 2011

Depending on the load it may appear on regulator as parasite oscillations that can be removed by some capacitors. Thermal behaviour of the regulator is also modified in this case.