Senin, 13 Februari 2012

regulator IC

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

Voltage regulators voltage serves as a filter to suit. Therefore, it is usually in a series of power supply the voltage regulator IC is always used for stabilizing the voltage out put.

The following arrangement 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 IC is also adjustable. The principle is the same as the OP-amp regulator packaged in a single IC for regulators such as LM317 and LM337 variable positive to negative variable regulator. The difference between resistor R1 and R2 are outside the IC, so the output voltage can be set via external resistors.

The simplest regulator circuit shown in figure 6. In this circuit, zener breakdown work in the area, thereby producing an output voltage equal to or zener voltage Vout = Vi. But this series is only useful if the load current not exceeding 50mA.

The principle of the power supply circuit is called a shunt regulator, one of his trademark is the component parallel to the load regulator. Another characteristic of the shunt regulator is susceptible to short-circuit. Note if Vout connected short (short-circuit) then the current is fixed I = Vin/R1. Besides the shunt regulator, there is also called a 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 IB currents flowing in the transistor base, R2 can be calculated of the prisoners are required are:

R2 = (Vin - Vi) / Iz

Iz is the minimum flow required by the zener diode breakdown voltage zener to achieve it. Large currents can be known from the datasheet that the amount of approximately 20 mA.

If needed supply a larger current, base current IB of the calculations in the above circuit can not be ignored anymore. Where as 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 usually has a value of b is large enough. With a Darlington transistor, the current small base current can produce a larger IC.

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

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

If the voltage Vout ascending out, the voltage Vin (-) will also be upward until the voltage is equal to the reference voltage Vi. And vice versa if the voltage Vout decreases exit, such as the supply current to the load increases, the op-amp will maintain stability in a given reference point Vi IB flows to the transistor Q1. So at all times maintain the stability of Op-amp:

Vin (-) = ½

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

Vout = ((R1 + R2) / R2) ½

In this circuit the output voltage can be set to adjust the R1 and R2.

Now it should no longer have to laboriously search for op-amps, transistors and other components to realize the regulator circuit as above. Because these circuits are packed into a fixed voltage regulator IC. Are now widely known as the 78XX series parts stayed positive voltage regulator and the 79XX series is a negative regulator for a fixed voltage. In fact, these components are usually already equipped with current limiting (current limiter) and also the limiting temperature (thermal shutdown). This component is only three pins, and by adding some components alone can be a power supply circuit that was a good regulation.

It's just note that the IC regulator circuit can work, the input voltage must be greater than the output voltage regulators. Usually the difference in voltage Vin to Vout recommended in the datasheet component. Use of heat sink (aluminum coolers) is recommended if these components are used for supply large currents. In the datasheet, this component can pass through the flow reaches a maximum of 1 A.

1 komentar:

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