Voltage regulator serves

Rectifier circuit is good enough if its voltage ripple is small, but there are stability issues. If the voltage PLN up / down, then the output voltage will also rise / fall. As rectifier circuit above, if the flow the greater the voltage dc discharge was also dropped. For some applications a voltage change is quite annoying, so it requires the active component that can regulate the output voltage becomes stable.

Voltage regulator serves as a filter voltage to suit. Therefore, usually in a series of power supply then the voltage regulator IC is always used for stable voltage outputan.

Here the composition of the regulator IC legs.


For example 7805 is a voltage regulator to get a +5 volt, +12 volt voltage regulator 7812 and beyond. While the 79XX series is the 7905 and 7912 such that a row is a voltage regulator -5 and -12 volts.

Apart from a fixed voltage regulators have a voltage regulator ICs also can be arranged. The principle is the same as the OP-amp regulator packaged in a single IC for regulators such as LM317 LM337 variable positive and negative variables for the regulator. The difference resistors R1 and R2 are outside the IC, so the output voltage can be set via external resistors.

The most simple regulator circuit shown in Figure 6. In this circuit, the zener breakdown work on the area, thus producing the same output voltage with a zener or a voltage Vout = Vi. However, this circuit is only useful if the load current not exceeding 50mA.
The principle that the power supply circuit is called a shunt regulator, one of his trademark is the component parallel to the load regulator. Another feature of the shunt regulator is susceptible to short-circuit. Notice when Vout connected short (short-circuit) then the current is fixed I = Vin/R1. In addition to a shunt regulator, there are also called series regulator. The main principle of such series regulator circuit in figure 7 below. In this circuit the output voltage is:

Vout = VZ + VBE

VBE is the base-emitter voltage of transistor Q1 which is between 0.2 - 0.7 volts depending on the type of transistor used. By ignoring the current IB flowing in the transistor base, a large resistance R2 can be calculated that is needed is:

R2 = (Vin - Vi) / Iz

Iz is the current minimum required by the zener diode to achieve the zener breakdown voltage. These large currents can be determined from the magnitude datasheet approximately 20 mA.



If necessary supply a larger current, base current IB of the calculations on the above circuit can not be ignored anymore. Where as it is known, a large flow of IC will be directly proportional to the flow defined by IB or IC = BIB. For this purpose, the transistor Q1 is used can be replaced with a Darlington transistor which typically has a value of b is large enough. With a Darlington transistor, the current small base that could produce a greater current IC.

Techniques that better regulation is to use the Op-Amp to drive a transistor Q, as in a series of figure 8. Zener diodes are not here to give direct feedback to the transistor Q, but as a reference voltage for the Op-amp IC1. Feedback on the negative pin of op-amp is an excerpt from the voltage regulator out, namely:

Vin (-) = (R2 / (R1 + R2)) Vout

If the voltage Vout rising out, the voltage Vin (-) will also be rising until the voltage is equal to the reference voltage Vi. And vice versa if the voltage Vout decreases exit, for example because of supply current to the load increases, the op-amp will maintain stability in Vi with a reference point to give the current IB to the transistor Q1. So at all times maintain the stability of the Op-amp:

Vin (-) = ½


By ignoring the VBE voltage of transistor Q1 and mensubsitusi formula (11) into the formula (10) of the obtained mathematical relationship:

Vout = ((R1 + R2) / R2) ½

In this circuit the output voltage can be set by adjusting R1 and R2 large.

Now it should no longer need to painstakingly search for the op-amp, transistors and other components to realize the regulator circuit as above. Because this kind of circuit has been packaged into a single fixed voltage regulator IC. Are now widely known as the 78XX series components of the voltage regulator to remain positive and 79XX series which is a voltage regulator to remain negative. In fact, these components are usually already equipped with current limiting (current limiter) and also limiting the temperature (thermal shutdown). This component is only three pins and by adding some components alone can be a series of power supply regulation was good.