I am going to power up a micro-controller from a supply that fluctuations can expect so I need some circuits to keep 5V stable output supply though the input has fluctuations. Input fluctuation can be expected less than 5 V too. Any suggestions ??
Most circuits are powered from a 5V voltage regulator IC.
Most voltage regulator ICs need an input of 7V or more. A "low-dropout" IC needs an input of only 5.3V or more.