LM317 - This is a very common, versatile and convenient integrated voltage regulator that can be used in a variety of designs and assemblies. You can even assemble a very simple one using this microcircuit. In addition to voltage regulation LM317 can be used as a current regulator. One example is the brightness control of a line of LEDs. The microcircuit can be used in a power source with a fixed output voltage, or used as a basis with the ability to adjust the output voltage over a wide range. It is especially convenient to use LM317 when you need to make a stabilized power supply for any non-standard voltage or a regulated power supply.
Features of LM317
- The microcircuit can operate in a wide range of output voltages from 1.2 to 37 V.
- The microcircuit provides an output current of up to 1.5 A.
- Maximum power dissipation up to 20 W.
- The microcircuit has built-in protection against overcurrent and short circuit.
- Built-in overheat protection.
Minimum turn-on involves the use of two external resistors. The ratio of the resistances of these resistors sets the output voltage of the regulator and the two capacitors at the input and output of the microcircuit.
The most important electrical parameters of the microcircuit are the reference voltage Vref and that in the control output circuit Iadj. The reference voltage is the voltage that the microcircuit strives to maintain across resistor R1, that is, if we short-circuit resistor R2, then at the output of the regulator we will receive this same reference voltage. This voltage may vary slightly from instance to instance and is 1.2 ... 1.3 V (on average 1.25V.) The higher the voltage drop across resistor R2, the higher the output voltage of the regulator. The output voltage is easy to calculate; it is equal to the voltage drop across R2 + 1.25 (Vref).
R2=R1*((Uout/Uop)-1)
Then clarify the values in real conditions in a working circuit.
Here is an example of ratings for a pair of standard voltages:
For 5V voltage R1 = 120 Ohm, R2 = 360 Ohm
For 12V voltage R1 = 240 Ohm, R2 = 2000 Ohm
However, for typical voltages like 5, 12, 15, etc. volts it is easier and more convenient to use fixed voltage regulators like 7805 or 7812. It is better to use 317 for these purposes only if a fixed voltage regulator is not at hand, and you need to make a power source urgently.
Pin configuration of the LM317 chip in different packages
Soft start power supply. As you can see, a PNP bipolar transistor, a 50 kOhm resistor, a silicon diode and a 25 μF electrolytic capacitor are added to the standard circuit. When such a source is turned on, there is a minimum voltage at its output, which smoothly increases to the set 15V as capacitor C1 charges.
It is also easy to make a source with several fixed voltages on this chip, which can be switched programmatically using a microcontroller. To do this, we include chains of transistors and resistors in the control circuit, as shown in the figure below. We connect the transistor bases to the microcontroller ports. When a high level is applied to each subsequent transistor, it will connect another additional resistor in parallel with R2 and the output voltage will decrease:
Using the LM317 you can make a simple charger for batteries with a nominal voltage of 12V. The values of resistors R1 and R2 set the final voltage on the battery being charged, and resistor Rs sets the maximum charging current. This is a diagram from the datasheet for the microcircuit.
The microcircuit has been a hit among novice radio amateurs for decades due to its simplicity and reliability. Based on this chip, you can assemble an adjustable power supply based on LM317, a current stabilizer, an LED driver and other power supplies. This will require several external radio components; for LM317, the switching circuit works immediately, no configuration is required.
The LM317 and LM317T datasheet microcircuits are completely identical, differing only in the housing. There are no differences or differences, not at all.
I also wrote reviews and datasheets of other popular ICs. With good illustrations, clear and simple diagrams.
- 1. Characteristics
- 2. Analogues
- 3. Typical connection diagrams
- 4. Calculators
- 5. Connection circuits
- 6. Radio constructors
- 7. Datasheet
Characteristics
The main purpose is to stabilize positive voltage. The adjustment occurs in a linear manner, unlike pulse converters.
The LM317T is also popular, I haven’t come across it, so I had to search for a long time for the correct datasheet for it. It turned out that they are completely identical in parameters; the letter “T” at the end of the marking indicates the TO-220 1.5 Ampere housing.
Download datasheets:
- full ;
Characteristics
Even with integrated protection systems, it should not be operated at its maximum capacity. If it fails, it is not known how many volts will be at the output, it will be possible to burn an expensive load.
I will give the main electrical characteristics from the LM317 datasheet in Russian. Not everyone knows technical terms in English.
The datasheet indicates a huge scope of application; it’s easier to write where it is not used.
Analogs
There are many microcircuits that have almost the same functionality, domestic and foreign. I will add more powerful analogues to the list to avoid including several in parallel. The most famous LM317 analogue is the domestic KR142EN12.
- LM117 LM217 – extended operating temperature range from -55° to +150°;
- LM338, LM138, LM350 - analogues for 5A, 5A and 3A, respectively;
- LM317HV, LM117HV - output voltage up to 60V, if the standard 40V is not enough for you.
Complete analogues:
- GL317;
- SG317;
- UPC317;
- ECG1900.
Typical connection diagrams
Regulator 1.25 - 20 Volts with adjustable current
Calculators
To make calculations as easy as possible based on the LM317T, many LM317 calculator programs and online calculators have been developed. By specifying the initial parameters, you can immediately calculate several options and see the characteristics of the required radio components.
A program for calculating voltage and current sources taking into account LM317 characteristics of LM317T. Calculation of circuits for switching on powerful converters using transistors, TL431, M5237. Also IC 7805, 7809, 7812.
Connection schemes
The LM317 stabilizer has proven itself to be a universal microcircuit capable of stabilizing voltage and Amperes. Over decades, hundreds of LM317T switching circuits for various applications have been developed. The main purpose is a voltage stabilizer in power supplies. To increase the number of amperes at the output there are several options:
- connection in parallel;
- installing power transistors at the output, we get up to 20A;
- replacement with powerful analogues LM338 up to 5A or LM350 up to 3A.
To build a bipolar power supply, negative voltage stabilizers LM337 are used.
I think that parallel connection is not the best option due to the difference in the characteristics of the stabilizers. It is impossible to set several pieces to exactly the same parameters in order to distribute the load evenly. Due to the spread, one will always have more load than the others. The probability of failure of a loaded element is higher; if it burns, the load on others, which may not be able to withstand it, will sharply increase.
In order not to connect in parallel, it is better to use transistors at the output for the power part of the DC-DC voltage converter. They are designed for high current and have better heat dissipation due to their large size.
Modern pulse chips are inferior in popularity, but their simplicity is hard to beat. The lm317 current stabilizer for LEDs is easy to set up and calculate, and is currently still used in small-scale production of electronic components.
Bipolar power supply LM317 and LM337, for obtaining positive and negative voltage.
Radio constructors
For beginner radio amateurs, I can recommend radio designers from the Chinese on Aliexpress. Such a constructor is the best way to assemble a device according to the switching diagram; there is no need to make a board and select parts. Any designer can be modified at your own discretion, the main thing is that there is a board. The cost of the designer starts from 100 rubles with delivery, the ready-made module assembled from 50 rubles.
Datasheet
The microcircuit is very popular, produced by many manufacturers, including Chinese. My colleagues came across LM317 with poor parameters that do not draw the declared current. We bought it from the Chinese, who like to fake and copy everything, while worsening the characteristics.
Let's consider the simplest option for making an LED driver with your own hands with minimal time investment. To calculate the current stabilizer on LM317 for LEDs, we use a calculator, which needs to indicate the required current strength for LED diodes. First draw up a circuit for switching on the LEDs, taking into account the maximum power of the microcircuit and the unit. Look for a cooling system for the entire structure in advance.
- 1. Connection diagram
- 2. Example of calculations and assembly
- 3. Basic electrical characteristics
- 4. Pulse drivers
Calculator
Connection diagram
To make a current stabilizer on LM317 with the ability to regulate, instead of a constant resistor, install a powerful variable resistance. The variable resistance rating can be calculated by specifying the control limits to the calculator. The resistance can be from 1 to 110 Ohms, this corresponds to the maximum and minimum. But I recommend that you refuse to adjust the Amperes in the load with variable resistance. It will be difficult to implement correctly and the heating will be too high.
The power of a constant resistor for heat dissipation should be with a reserve, calculated by the formula:
- I² * R = Pw
current squared multiplied by the resistance of the resistor.
A transformer or switching voltage source with polar voltage can be used as a power supply. As a rectifier, it is better to use a classic diode bridge, after which a large capacitor is installed.
The current regulator does not operate on a linear principle, so it can get quite hot due to its low efficiency. Having a decent radiator is a must. If the heating control shows a low heating temperature, it can be reduced.
If the number of Amperes required is more than 1.5A, then a couple of elements must be added to the standard circuit. You can get up to 10A by installing a powerful KT825A transistor and a 10-ohm resistor.
This option is suitable for those who do not have an LM338 or LM350 on hand.
The 3A version of the current stabilizer is made on the KT818 transistor. The amperes in the load are regulated and calculated in all circuits the same way on a calculator.
Example of calculations and assembly
If you really want to assemble it but don’t have a suitable power supply, then there are several options to solve this. Barter with a neighbor or connect the circuit to a 9V battery like Krona. The photo shows the entire circuit assembled with an LED.
If 1A is required for LEDs, then we indicate this in the calculator and get a result of 1.25 ohms. There is no resistor of exactly the same value, so we install a suitable one with a value in the direction of increasing Ohm. The second option is to use parallel and series connection of resistors. By correctly connecting several resistances we get the required number of Ohms.
Your LM317 current stabilizers will be similar to the products below.
And if you suffer from complete LED fanaticism, it will look like this.
Basic electrical characteristics
I strongly recommend not to operate the LM317 at extreme conditions; Chinese microcircuits do not have a safety margin. Of course, there is built-in protection against short circuits and overheating, but don’t expect it to work every time.
As a result of an overload, not only the LM317 can burn out, but also what is connected to it, and this is a completely different kind of damage.
Main parameters of LM317:
If a load of 1A is not enough for you, then you can use more powerful models of stabilizers LM338 and LM350, 5A and 3A, respectively.
To improve heat transfer, the TO-3 case was enlarged, this is often found in Soviet transistors. But it is also available in a small TO-220 case, designed for lighter loads.
LM338 parameters:
Pulse Drivers
Thanks to Chinese hard work, power supplies, current and voltage stabilizers can be bought in foreign online stores for 50-150 rubles. The adjustment is driven by a small variable resistance; at 2-3 Amps they do not require a radiator to cool the driver controller. You can order, for example, on the popular bazaar Aliexpress.com. The main drawback is the wait for 2-4 weeks, but the price is the lowest, you can buy half a kilo at once.
I often search on Avito in my city for a quick and inexpensive method. I and many others order stabilizers with a reserve, in case they turn out to be faulty. Then they sell the excess through advertisements, and you can always bargain.
Welcome, dear visitor to this Internet page. We would like to draw your attention to the fact that there are many circuits and options for manufacturing an LED driver using a simple current stabilizer on the LM317. The most labor-intensive and materially costly, they represent additional schematic solutions that make it possible to preserve the most expensive electronic components during critical drops in voltage and current.
Scheme and principle of operation of the stabilizer up to 1.5A
To make a current stabilizer on LM317, we will use the following circuit.
The minimum resistance of the resistor between the control electrode and the output electrode corresponds to a value of 1 Ohm, and the maximum value is 120 Ohms. The resistance of the resistor can be selected experimentally, or calculated using the formula.
I stabilization = 1.25/R
The power of the resistor when dissipating the generated heat should be enough not only for dissipation, but also take into account the possibility of overheating, so a power value with a good margin is used. To calculate it, you must use the following formula:
Pw = I² * R.
As can be seen from the formula, the power is equal to the square of the current multiplied by the resistance of the resistor. For rectification, the most effective solution is to use a standard diode bridge. At the output of the diode bridge, a capacitor with a large capacity is installed. When adjusting the current on the LM317, the LM317 uses a linear operating principle. In this regard, they can become very hot due to their low efficiency. Therefore, the cooling system must be thoughtful and efficient, that is, it must have a radiator that can cool electronic components well. If a low temperature is detected while monitoring the heating temperature, a less powerful cooling system can be used.
Current stabilizer up to 10A
The stabilization current can be increased to 10 Amps if a transistor labeled KT825A and a resistance of 12 Ohms are added to the circuit. This distribution of electronic components is used by radio amateurs who do not have an LM338 or LM350. The circuit with a current of 3A is assembled based on the KT818 transistor. Load amperes in any of the circuits are calculated identically.
If a radio amateur has a great desire to make a driver, but does not have the necessary power supply, then you can use alternative options.
You can use the option of connecting resistors in series or parallel.
If the LEDs require a current equal to one ampere, then when calculating we get a resistance equal to 1.25 Ohms. You won’t be able to select a resistor with this value, because they are not produced, so you need to take the first closest one, with a slightly higher resistance.
Invite a radio amateur you know to replace a power supply with suitable parameters for the radio component or electronic circuit he needs. Connect a 9V Krona battery or one with similar parameters to power the assembled circuit. If there is no Krona, connect 6 1.5 V batteries of any size in series and connect them to the circuit.
We strongly advise you not to use the LM317 beyond its permissible limits. Electronic elements produced in China have a small safety margin. Of course, there is protection against short circuits or overheating, but it works successfully, not in all critical modes and situations. In such situations, other electronic components besides LM317 may burn out, and this is not at all desirable.
Main parameters LM317: Input voltage up to 40 V, load up to 1.5 A; maximum operating temperature +125°C, short circuit protection.
power unit - This is an indispensable attribute in the amateur radio workshop. I also decided to build myself an adjustable power supply, because I was tired of buying batteries every time or using random adapters. Here is its brief description: The power supply regulates the output voltage from 1.2 Volts to 28 Volts. And it provides a load of up to 3 A (depending on the transformer), which is most often enough to test the functionality of amateur radio designs. The circuit is simple, just right for a beginner radio amateur. Assembled on the basis of cheap components - LM317 And KT819G.LM317 regulated power supply circuit
List of circuit elements:
- Stabilizer LM317
- T1 - transistor KT819G
- Tr1 - power transformer
- F1 - fuse 0.5A 250V
- Br1 - diode bridge
- D1 - diode 1N5400
- LED1 - LED of any color
- C1 - electrolytic capacitor 3300 uF*43V
- C2 - ceramic capacitor 0.1 uF
- C3 - electrolytic capacitor 1 µF * 43V
- R1 - resistance 18K
- R2 - resistance 220 Ohm
- R3 - resistance 0.1 Ohm*2W
- P1 - construction resistance 4.7K
Pinout of the microcircuit and transistor
The case was taken from the computer's power supply. The front panel is made of PCB, it is advisable to install a voltmeter on this panel. I haven't installed it because I haven't found a suitable one yet. I also installed clamps for the output wires on the front panel.
I left the input socket to power the power supply itself. A printed circuit board made for surface-mounted mounting of a transistor and a stabilizer chip. They were secured to a common radiator through a rubber gasket. The radiator was solid (you can see it in the photo). It needs to be taken as large as possible - for good cooling. Still, 3 amperes is a lot!
