I have 1 circuit composed from 3 little very simple circuits I want to power them all from a 5V@1A power source.
All of these 3 circuits must be powered at different voltages.
Their current draw I measured for each of them.
A=4V @10mA, B=3.4V @1.6mA, C= 5V @24mA
What can you suggest?
Thank you.

 

Are the current draws constant? If so, then just use dropping resistors.
From a 5.0 volt source:
4.0 volts @ 10 mA would require a 100 ohm resistor
3.4 volts @ 1.6 mA would require a 1000 ohm resistor
5 volts @24 mA would be powered direct.

 

LDO linear regulators, there are a ton on Digikey, Mouser, etc.. Power the 3.4V from the output of the 4V so you don't pay the penalty twice. If power efficiency is a major issue (is it battery powered?) then you can look at switching regulators, but linear LDO will be cheaper and easier to implement. Get them sized for your use (don't get a whopper 10A one for 1.5mA) and check the datasheets for idle current, if energy efficiency is important. Also check for minimum current requirements.

 

Thank you !