The electronics devices works in dc power supply comes with different voltage specifications. Some devices works in battery power with voltages ranging from 1.5V to 9V, but majority of the devices can be directly plugged into a power plug. Such devices have a built in AC to low voltage DC converter inside it and the voltage output of that converter will be corresponding to the design of the entire circuit. The design of a circuit actually begins with considering the value of the voltage which will be supplied to it.The circuits which work in 5V power supply are most common which contains 5V TTL devices, but there is other category of TTL devices which works in 3.3V supply. Apart from these two categories there are CMOS based circuits and there is all kind of analog circuits which are designed to work on different voltages. Those who are interested in working with all these kind of circuits should have a variable power supply source. 

The electronics devices works in dc power supply comes with different voltage specifications. Some devices works in battery power with voltages ranging from 1.5V to 9V, but majority of the devices can be directly plugged into a power plug. Such devices have a built in AC to low voltage DC converter inside it and the voltage output of that converter will be corresponding to the design of the entire circuit. The design of a circuit actually begins with considering the value of the voltage which will be supplied to it. The circuits which work in 5V power supply are most common which contains 5V TTL devices, but there is other category of TTL devices which works in 3.3V supply. Apart from these two categories there are CMOS based circuits and there is all kind of analog circuits which are designed to work on different voltages. Those who are interested in working with all these kind of circuits should have a variable power supply source.