The available voltage from a voltage source that is usually not appropriate to the needs. It is necessary for a voltage regulator that functions to maintain the constant voltage value on a certain value. Voltage regulator chip is usually a code with the 78xx or 79xx. For the 79xx series is used for DC negative voltage regulator. xx indicates the regulator output voltage. For example, the system needs is a -5 volt negative, the regulator used is 7905. Chip regulator consists of three pins, namely input, output and ground. In this IC uses the input voltage must be greater several percent (depending on the data sheet) from the value output voltage.
