Voltage Regulator (regulator), usually
having three legs, converts
varying input voltage and produces a constant regulated output
voltage. They are available in a variety of outputs.
The most common part numbers start with the numbers 78 or 79 and finish
with two digits indicating the output voltage. The number 78
represents positive voltage and 79 negative one. The 78XX series
of voltage regulators are designed for positive input. And the
79XX series is designed for negative input.
5V DC Regulator Name: LM7805
-5V DC Regulator Name: LM7905
6V DC Regulator Name: LM7806
-9V DC Regulator Name: LM7909 or MC7909
The LM78XX series typically has the ability to drive current up to 1A.
For application requirements up to 150mA, 78LXX can be used. As mentioned
above, the component has three legs: Input leg which can hold up to
36VDC Common leg (GND) and an output leg with the regulator's
voltage. For maximum voltage regulation, adding a capacitor
in parallel between the common leg and the output is usually
recommended. Typically a 0.1MF capacitor is used. This eliminates any high frequency AC
voltage that could otherwise combine with the output voltage.
See below circuit diagram which represents a typical use of a voltage
As a general rule the input voltage should be limited to 2 to 3 volts
above the output voltage. The LM78XX series can handle up to 36
volts input, be advised that the power difference between the input
and output appears as heat. If the input voltage is
unnecessarily high, the regulator will overheat. Unless
sufficient heat dissipation is provided through heat sinking, the regulator will shut