If you work with IC TTL (Transistor Transistor Logic IC) you will often find that a logic 1 will lead to a voltage approximately 5 volts and a logic 0 will lead to voltage 0 volts. In my area is very difficult to find a transformer that outputs 5 volt.Usually be easy to use zener diodes to issue a voltage of 5 volts, but typically it will issue a zener diode voltage over 5 volts (5.1-5.2Volt). In order for the output voltage actually 5 volts then I use the IC 7805. So by the IC regulator will be very helpful in the works associated with TTL IC. You just need to source voltage of greater than 5 volts and the output must be 5 volts.