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The LM317 voltage regulator is a very easy to use three-pin device. In its smallest configuration, a couple of resistors are enough to obtain the voltage you want (although, as you will see, it is convenient to add a few extra components in order to improve the output provided by the LM317 voltage regulator).
The virtues of LM317 do not end there. In addition to how simple it is to use it, it has its own protection system in case the maximum output current of this component (1.5A) is exceeded or its working temperature is exceeded (remember that in devices of this type it is usually useful to use heatsinks).
As you can imagine, it is one of the most common components in any electronic laboratory. This is not simply due to its use as a voltage regulator. With the LM317 you can build: variable voltage regulators, logic level regulators, current regulators, power trackers, etc.
In this post I’m just going to teach you how to use this element as a simple voltage regulator but it will not be the only thing you write about this device, without a doubt.
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1 Basic Characteristics of the LM317 Voltage Regulator
1.2 Extra Information
Basic Characteristics of the LM317 Voltage Regulator
As it is the first post dedicated to this device, before starting with the assembly I will show you the basic characteristics of the LM317, so that you can get an idea of the circuits in which you can use this element:
Output voltage from 1.2V to 37V.
Tolerance of the output voltage of 1%.
Output current of up to 1.5A.
The current limitation does not depend on the temperature.
Protection against noise at the entrance (RR = 80dB).
It can work at high temperatures (125ºC).
Nominal voltage (Vref) of 1.25V.
I hope you understand that these few data can not replace the information that is going to provide you with the datasheet of this device. They are simply put in an orientative way.
Depending on the range of voltages you are going to work with (it may be worth a range of 10V to 20V and you do not need to go from 1.2V to 37V), of the output current you want to power your circuit and even from the distance that the components are between each other, you can do without some elements. However, with the idea of making this post a little more generic, I have decided to explain the LM317 voltage regulator in its full version, with all the components.
1 x LM317.
1 x 5kΩ potentiometer.
1 x Resistance of 240Ω.
2 x Diode 1N4002 or similar.
1 x 10μF electrolytic condenser (capacitor).
1 x 25μF electrolytic condenser (capacitor).
I’m going to show you the circuit diagram of this version of the LM317 voltage regulator. Remember that this circuit is designed for a range of output voltages from 1.2V to 37V. In case the range of tensions with which you go to work is different, it is possible that you can save some components (you will see later).
In case you had any problem to understand this scheme, you can look at the following image where the same montage is shown on a Breadboard.
Voltage Regulator with LM317
As I have already mentioned before, it is possible that in your assembly you do not need some components. Here I show you a small list with some tips so you can see which components you should use and how:
Although the LM317 internally limits the power dissipation, do not exceed 20W.
The entrance must be at least 1.5V higher than the exit.
The 10μF capacitor is useful in case the source or battery with which you feed the LM317 voltage regulator varies.
The 25μF capacitor serves to stabilize the output (although the output of this voltage regulator is already quite stable) and the value you need may vary depending on what you connect this circuit to.
The diodes are used to discharge the capacitors and are only necessary if you are going to regulate voltages of more than 25V.
As in the rest of circuits, you must ensure that your components support the voltage, current and power values to which you are subjecting them. Be especially careful when selecting capacitors. They must always bear a little more of the voltage that is going to pass through them.
This has been all for this post about the LM317 voltage regulator. I hope you liked it and, as always, I would like to receive your comment.