There are basically two types of Three Terminal Fixed Voltage regulator ICs are available. One is positive output voltage and other has negative output voltage; but the output voltage is fixed.
There are two IC series.
1. 78XX series:
This is a positive regulator. The first two digits i.e.78 indicates that the output voltage is positive. The second two digits 'XX' indicates output voltage of the regulator. The available ICs of this series are 7805(+5V), 7812 (+12V), 7815(+15V) etc. The output voltages are shown in brackets.
2. 79XX series:
This is a negative voltage regulator. The first two digits i.e.79 indicates that the output voltage is negative. The second two digits 'XX' indicates output voltage of the regulator. The available ICs of this series are 7905(-5V), 7912 (-12V), 7915(-15V) etc. The output voltages are shown in brackets.
These ICs are provided with adequate heat sinking and can deliver output currents more than 1A. These ICs require less external components. These are provided with internal thermal shut down, overload and short circuit protection.
These two series are available in two versions, like low power and high power. The low power versions are available in plastic and metal packages like transistors.
The high power versions are packaged in TO-3 type metal can or in T-220 type modulated plastic packages like power transistors. The typical value of output resistance is 8mΩ.
Typical connections of IC 7805 regulator are shown below.