If you atre doing a lot of LED's and they are going to draw a lot of power, ranging from all on to all off, then 2 separate power converters will work. Low power one to drive the microcontroller, and a separate one with an enable to do the LED drive voltage. When they are all off the power supply is switched off with the enable, otherwise you enable it. As an advantage you can choose LED drive voltage to have multiple series strings, if the LED's are always going to be on like that, and if so then you can also use LED driver converters to do both the drive and current control, and save on power converter and switches, using LED drivers with dimming and enable as needed.