DC Voltage Regulator

Build The DC Voltage Regulator

How to Build A Variable Voltage Regulator

In several previous articles some positive regulators constructed using linear voltage regulator IC that provides fixed output voltage. Now I want to explain how to build a variable voltage regulator that is more flexible because the output voltage can be set as needed.

In this article the regulator IC to be selected is a type LM317 adjustable regulator. The reason this election is already very popular DC voltage regulator IC which is a family of three terminal positive regulator. This IC has a configuration input, adj and output. So this will be easy for the beginner to understand the construction.

LM317 regulator IC is an integrated circuit designed to supply more than 1.5A load current with a voltage range can be set from 1.2V to 37V. So IC LM317 is a voltage regulator IC that can be programmed. Internally it has been installed IC circuit current limiting, short-circuit and over-thermal protection. So this feature would eliminate the worries will be fewer mistakes in construction.

Variable Voltage Regulator Circuit Formula

Here is the basic circuit of a regulator IC LM317 (datasheet), where the calculation of the components that will be used to follow the following formula:

VOut = 1.25V (1 + R 2 / R 1) + IadjR2,

in practice negligible IadjR2 is intended for current under 100uA. The Variable voltage regulator circuit below will set the output voltage range of 1.5V to 12V as below.
Variable Voltage Regulator - Table
Variable Voltage Regulator - Table
In the circuit R1 value is 100R (Ohm), while the output voltage changes according to changes in the value of R2 value (Vout) follow the formula above. From the calculation, where the overall R2 using a variable resistor 1K Ohm. Value of the input voltage that can be achieved is at 13.75V (R2 = 1000 Ohm), 12V (R2 = 860 Ohm), 3V (R2 = 140 Ohm), with a minimum value of 1.25V (R2 = 0).
LM317(T) Variable Regulator Circuit
LM317(T) Variable Regulator Circuit
So the value calculation and test circuit obtained results are not much different to the formula, the output voltage increases proportionally with the decrease in the value of resistor R2 in the voltage range of 1.25V-13.75V. Hopefully with practice you are doing you can understand how to build a variable voltage regulator using LM317 (T).

Low Dropout 5V Voltage Regulator

The 5V voltage regulator is found various electronic circuits, especially in applications of audio-video, radio frequency and robotic or microcontroller. Whatever the application is constructed or designed, a voltage regulator should be able to provide a stable voltage with good quality. Excess heat in a voltage regulator IC cause unwanted voltage drop. While this will not have a serious impact on some electronic applications, but at least you need to add a heatsink to reduce the heat that arises.

Features of the LM2940 Regulator IC

In the following circuit is a 5V regulator using a low dropout regulator IC LM2940CT-5.0. It provides a fixed output voltage of 5 V at 1A current with dropout voltage of typically 0.5V and a maximum of 1V over the entire temperature range. The IC regulator is equipped with a quiescent current reduction circuit serves to reduce ground current, when the voltage difference between the input voltage and the output voltage above 3V.

All regulated circuitry are protected from reverse battery installations or 2-battery jumps. During line transients, such as load dump when the input voltage can momentarily exceed the specified maximum operating voltage, the regulator will automatically shut down to protect internal circuits and the load. It also features a 7805 regulator IC is short-circuited and thermal overload protection.

5V Voltage Regulator Circuit

This DC voltage regulator circuit is basically the same as the circuit for IC 7805. Regulator IC is compatible with the PCB that uses a three-terminal positive regulator. Even to increase the capacity of the load current is not different from the IC's circuit family. You can opt for the fixed 5V output voltage according to the last digit "5" as in ML2940CT-5.

Low Dropout 5V Voltage Regulator
Low Dropout 5V Voltage Regulator - LM2940CT-5.0
The following circuit provides output voltage regulator 9V to 6A load current.
9V 6A Low Dropout Voltage Regulator
9V 6A Low Dropout Voltage Regulator - LM2940CT-9.0
Hopefully the above example circuit is useful for the hobby to work requires a low DC voltage drop, especially using a 5V voltage regulator.

How to Test DC Voltage Regulator IC

It is simple way to test DC voltage regulator. We will test a DC voltage regulator IC, the output voltage level. For example we want to do testing on a 7805 regulator. IC 7805 regulator designed provide a fixed output voltage of 5V, if the good results it will be measured at the pin (3) the amount of output voltage of 5 volts DC.

To perform the test we need a DC power supply panel equipped with a voltmeter, a DC voltmeter, regulator IC 7805 and the black and red wires as needed. Red and black wires are used as a link between positive polarity (+) and negative (-) of the voltage source to the input pin (1) and ground (2) the regulator IC. Output pin (3) and ground (2) of the 7805 IC to be connected to the positive polarity (+) and negative (-) on the voltmeter.

Diagram of DC Voltage Regulator IC Testing

Test DC Voltage Regulator 7805
Test DC Voltage Regulator 7805
The things you should know and be prepared prior to testing or measuring voltage regulator is:
  • A type of three-terminal regulator IC regulator will work fine if input voltage is greater than the output voltage around 3V. It should be remembered that 7805 was a positive linear type regulator which will be different pinout configurations with IC 7905.
  • Turn on the DC power supply and adjust the output voltage of about 8V or slightly larger. Or alternatively you can use a battery 9V-12V as voltage source. Look at the voltmeter panel when you set the voltage
  • Prepare a DC voltmeter readings on voltage range 50V to measure the output voltage of the IC 7805.
  • Perform the red and black cable connections are correct, red for positive polarity (+) and pin (1) IC, black for polarity (-) and pin (2) IC.
The test results of IC 7805 is good if the pin (3) read positive DC voltage 5V. And you can do it over and over to ensure that the condition of IC 7805 is still functioning well. Do a test for another DC voltage regulator IC..

High Current 7812 Voltage Regulator

High current 7812 voltage regulator can be constructed by adding a transistor to increase load current capability. As contained in the manual 78/79xx three terminal voltage regulators, positive type of regulator used to use NPN transistors, and otherwise negative type use PNP transistors.

Here is an example of 12V DC voltage regulator circuit using IC 7812 which aims to improve the load current of 1A IC 7812 higher (15A). The more external transistor used the higher load currents.

7812 Voltage Regulator Circuit

The voltage regulator circuit below has a current capability up to 15A load by adding three complementary transistors MJ2955. The load current capability can be changed by adding or reducing the number of MJ2955. Resistor 100R or lower can serve to prevent current swamping so as to stabilize the incoming voltage to the IC 7812.
High Current 7812 Voltage Regulator
High Current 7812 Voltage Regulator
Since 7812 no load current capability greater than 1A needs to be given as a safety fuse 1A output current over the IC, and protect it from high current transients. In IC 7812 and MJ2955 transistor heatsink should be installed so that there is enough heat reduction of the load current is used.

As the above circuit design can be applied to the negative regulator 7912. You need to replace the transistor MJ2955 with other types such as MJ3055, 2N3055 or TIP3055. Hopefully this brief overview is useful in increasing the load current of the 7812 voltage regulator.

How to Choose A Linear Voltage Regulator IC

One of the users preferred the linear voltage regulator IC is easy to use and cheap. It is not denied that in practice only by connecting a DC input voltage and provides some additional components to the IC pin, you are ready to operate a specific application. However this only applies to fixed positive and negative voltage with maximum load current 1A. (See the 7805 voltage regulator)

There are some factors in an effort known as easy to choose a voltage regulator IC. It concerns the flexibility to determine the suitability of voltage and current to the load current. Simply put the IC regulator selected should operate the application you want.

Types of Linear Voltage Regulator IC

Basically there are several types of linear voltage regulator that can be used very well and each type has its own characteristics. The selection of each type depends on the needs of the design with the performance and cost considerations. Type of the voltage regulators are as follows:
  • Positive Output Regulator, providing a fixed regulated output voltage positive.
  • Negative Output Regulator, providing a fixed regulated output voltage negative.
  • Fixed Output Regulator, providing fixed regulated output voltages for both types of regulators.
  • Adjustable Regulator, providing a regulated output voltage as needed.
Linear Voltage Regular IC
Linear Voltage Regular IC - Fixed Outputs
On the positive and negative voltage regulator which is used in accordance with the polarity of each type. Positive type is set positive voltage, and reverse negative type is negative voltage. The difference between the two types lies in the input voltage pin configuration. The difference in the two types of input pin regulator can be seen in the picture. By adjusting the grounding system will be obtained an opposite voltage.

The configuration above is easy and cheap to do, but it is limited to fixed output voltage and load current up to 1A. However, the products from several other manufacturers have allowed the available capabilities to over 1A load current.

In the above explanation, the three-terminal fixed regulator is the same type of adjustable voltage regulator. The advantages of this type on the flexibility of the output voltage can be adjusted to the needs of the design. The output voltage can be easily adjusted or adjusted by adding two external resistors as a voltage divider. The output voltage can be adjusted from 1.2V up to 40V maximum voltage available. The ability of this type of regulator load current is available up to 3A.

Choosing Voltage Regulator IC

If a DC voltage regulator type has been determined, then choose the specific device. To provide a higher current than is available from monolithic technologies, in fact regulator IC is more often used as a driver for amplifying the transistor. It will be overlap and complicate the selection and design tasks. So there is no definite steps were ideal to choose a particular type of regulator in certain applications that could be the best solution. Levels of complexity, performance and cost and size will be the things that should be considered together.

So it is better to choose the regulator that meets the requirements for line and load regulation, output voltage and temperature operating ranges. So there is no concern with the ability of a voltage regulator IC in terms of output voltage, operating temperature and output load current.