Voltage Regulators in detail
A voltage regulator is an element that can stabilize a voltage at a fixed value, which is necessary for the electronic assemblies in need of a voltage that does not fluctuate, even if that bit. In this article i discussed the concept of voltage regulation with necessary examples.
Voltage Regulation:-
In the literature, you will often find the term "stabilized voltage" or "voltage regulated". The difference between the two is important? Rarely, because in both cases is desired the same thing, ie a voltage that departs as little as possible of the value we want to give it. The definition of control in the technical field is "Maintain a magnitude between two limits" while in physiological (living) they say "Ensuring the consistency of the characters of an indoor environment despite changes in external environment". The definition of stability is itself "Allowing a system to return to an established position after being sidelined by an external action" or "To maintain sustainable without profound changes". In all cases there is reference to a desired state (the voltage value in our case) and a low range of variation that must be accepted because perfection does not exist. I myself have always used the two terms without actually making any distinction, so do not be surprised when I write "stabilized voltage regulator output".Regulators fixed:-
Regulators are still so called because they were designed to deliver a DC voltage of a given value, which can not be changed without artifice. There are many kinds, but most common are undoubtedly those of series LM78xx and LM79xx. There are very easy to implement, and it takes very little knowledge to know which to use, stating their name for itself by what it is. To learn more, break down the name of these regulators:
LM = prefix used by the manufacturer. It may also involve uA, or MC.
= 78 means it is a positive regulator
= 79 means it is a negative regulator
xx = fixed output voltage (integer value)
Current values ??available: 5V, 6V, 9V, 10V, 12V, 15V, 18V, 24V (some of these values ??were less common in the past than now).
Example of use with a controller type 7812, when a capacitor was added to the controller input, and a second at its exit (you can sometimes do without it for positive regulators, but it is advisable to keep the good reflex of the plan): 
This type of regulator has an input (two son), and an outlet (also son of two). As a son of two of the input is common to a son of the two output (mass), we find only three legs of the components: input, output and ground. Applying the voltage to be regulated between the tab and the tab input mass, and recovering the regulated voltage output between the tab and the lug mass.
Pin assignment: he must be very careful, broaching negative regulators is not the same as the pin positive regulators! Below is the pinout of the most common fixed regulators LM78xx / LM79xx in case TO220 (components shown from the front, visible references). 
Offset of the output voltage of a fixed regulator:-
It is possible to obtain an output voltage with a non-standard voltage regulator fixed in the desired value, by means of a Zener diode placed between ground and ground terminal of the integrated controller. For example, to obtain an output voltage of 10V, it is possible to insert a 5.1 V zener between terminal "Ground" of a 5V regulator and Ground "real", as shown in the diagram below (in theory, the output voltage should be 10.1 V, but the tolerance on the values ??of the Zener and the output voltage of the regulator are that the value may differ slightly): 
Similarly, for a voltage close to 9V and if you do not find LM7809, you can use a 5V regulator (LM7805) in combination with a 3.9 V zener (5V +3.9 V = 8.9 V, in practice it fits perfectly in most cases).
Of course, this method can be used if you already have a fixed voltage regulator on hand that you absolutely want to use. For if this is not the case, I would strongly advise you to use an adjustable voltage regulator. Regulators adjustable (programmable):-
Adjustable regulators are designed in order to provide an output voltage that can assume any value within a certain range determined, and whose value can be determined easily. In most cases, the output voltage of an adjustable voltage regulator is determined by the value of two additional resistors. The diagram below shows an embodiment based on a LM317 (LM317 is a positive regulator, the LM337 is its "complementary" if negative). 
As the regulator sets, the controller has an adjustable leg input and an output pin. The difference lies in the use of the third leg, which is no longer a tab mass, but a reference tab. On this leg we will "play" to bring out the desired voltage to the regulator. Let us at once that for almost all the regulators, the minimum output voltage is 1.25 V, and can not go below without using a negative voltage source or by using a trick that really complicates the scheme. The two resistors R1 and R2 in the previous diagram can therefore "programmed" the output voltage. The formula for determining the value of these resistors is:
Vout (positive output voltage) = 1.25 * (1 + (R2 / R1)).
Very important! The resistor R1 must be mounted as close to the regulator, especially for the leg side controller output. It is indeed necessary to ensure that the voltage drop introduced between the controller output and the leg of this resistance is as low as possible to minimize variations in output voltage versus current consumption (the risk is all greater than the current drawn at the output is important).
The diagram above shows how easy it is to achieve a regulated power supply to the fixed value that we want, so very simple. To adjust the output voltage, replace the resistor R2 by a potentiometer, which will vary the voltage ratio between the output terminal of the regulator and Adjust. 
It is not recommended to place a potentiometer so if you want a fixed output voltage but perfectly adjusted. There is a big difference between wanting to fit accurately a fixed output voltage (eg 15.0 V) and want to have a variable output voltage (eg from 3 to 24V). In the first case, it is preferable to replace the trimmer by a potentiometer connected in series with a limiting resistor. This limits the range of variation and thus make it more precise. Under these conditions, no need for an expensive multiturn potentiometer, a simple potentiometer adjustable 3/4 laps of Carbon Track is enough.
Montages presented above are simple. But in practice, we must recognize that the addition of some components can improve the overall functioning and avoid unpleasant surprises. The following diagram shows an embodiment more "concrete". 
The capacitor C1 is the main filter, do not we extend it. Three capacitors were added from the database schema: C2, C3 and C4. C2 and C4 contribute to a better stability of the assembly and severely limit the risk of occurrence of parasitic oscillation in controller output. The capacitor C3 in turn helps to improve the ripple rejection of the alternative (read: less hum out), its value is generally between 10 uF and 100 uF. These additional capacitors are not required if the connections are short, and are recommended if the connections exceeds a few cm.
Note the negative regulator LM337: the capacitor placed at the output (the equivalent of C4 in the previous diagram) must be a few uF of tantalum or electrolytic few tens or hundreds of uF (although in the audio is not recommended tantalum and that he prefers a higher value chemical). Avoid the latter to use a ceramic capacitor and film.
Broaching: these adjustable regulators adopt the same box that regulators fixed (TO220 and TO3 are the two most répendus), and for this reason, we must remain cautious for the pinouts, which differ from each other. Below is the pinout of the most common adjustable regulators LM317 / LM337 in TO220 casing (components shown from the front, visible references).