Logic power control of analog regulator can be useful in application where a digital circuit/controller need to control power source, such as in EEPROM programmer or other power controls.  This is a circuit provide ON-OFF control  for 78xx regulator using digital (TTL or CMOS) signal level. This circuit uses transistors in series with the 78XX regulator,  which it’s base is controlled by logic level input. Here is the schematic diagram of the  circuit:

 

Logic Control Of 78xx Regulator circuit schematic