Quite often there is a need for a simple voltage stabilizer. This article provides a description and examples of the use of an inexpensive (prices for LM317) integrated voltage stabilizer LM317.

The list of tasks solved by this stabilizer is quite extensive - this includes powering various electronic circuits, radio devices, fans, motors and other devices from the mains or other voltage sources, such as a car battery. The most common circuits are voltage-regulated.

In practice, with the participation of LM317, you can build a voltage stabilizer for an arbitrary output voltage in the range of 3...38 volts.

Specifications:

• Stabilizer output voltage: 1.2... 37 volts.
• Load-bearing current up to 1.5 amperes.
• Stabilization accuracy 0.1%.
• There is internal protection against accidental short circuit.
• Excellent protection of the integrated stabilizer from possible overheating.

Power dissipation and input voltage of the LM317 stabilizer

The voltage at the stabilizer input should not exceed 40 volts, and there is also one more condition - the minimum input voltage should exceed the desired output voltage by 2 volts.

The LM317 microcircuit in the TO-220 package is capable of stable operation at a maximum load current of up to 1.5 amperes. If you do not use a high-quality heat sink, this value will be lower. The power released by the microcircuit during its operation can be determined approximately by multiplying the output current and the difference between the input and output potential.

The maximum permissible power dissipation without a heat sink is approximately 1.5 W at an ambient temperature of 30 degrees Celsius or less. If good heat dissipation from the LM317 case is ensured (no more than 60 g), the power dissipation can be 20 watts.

When placing a microcircuit on a radiator, it is necessary to isolate the microcircuit body from the radiator, for example, with a mica gasket. It is also advisable to use thermal conductive paste for effective heat removal.

Selection of resistance for stabilizer LM317

For accurate operation of the microcircuit, the total value of resistances R1...R3 must create a current of approximately 8 mA at the required output voltage (Vo), that is:

R1 + R2 + R3 = Vo / 0.008

This value should be taken as ideal. In the process of selecting resistances, a slight deviation (8...10 mA) is allowed.

The value of variable resistance R2 is directly related to the output voltage range. Typically, its resistance should be approximately 10...15% of the total resistance of the remaining resistors (R1 and R2), or you can select its resistance experimentally.

The location of the resistors on the board can be arbitrary, but for better stability it is advisable to place it away from the heatsink of the LM317 chip.

Circuit stabilization and protection

Capacitance C2 and diode D1 are optional. The diode protects the LM317 stabilizer from possible reverse voltage that appears in the designs of various electronic devices.

Capacitance C2 not only slightly reduces the response of the LM317 microcircuit to voltage changes, but also reduces the influence of electrical interference when the stabilizer board is placed near places with powerful electromagnetic radiation.

The LM317 adjustable three-terminal current regulator provides a load of 100 mA. The output voltage range is from 1.2 to 37 V. The device is very easy to use and requires only a pair of external resistors to provide the output voltage. Plus, the instability in terms of performance indicators has better parameters than similar models with a fixed output voltage supply.

Description

LM317 is a current and voltage stabilizer that operates even when the ADJ control pin is disconnected. During normal operation, the device does not need to be connected to additional capacitors. The exception is when the device is located at a considerable distance from the primary filter supply. In this case, you will need to install an input shunt capacitor.

The output analog allows you to improve the performance of the LM317 current stabilizer. As a result, the intensity of transient processes and the value of the pulsation smoothing coefficient increase. Such an optimal indicator is difficult to achieve in other three-terminal analogues.

The purpose of the device in question is not only to replace stabilizers with a fixed output indicator, but also for a wide range of applications. For example, the LM317 current stabilizer can be used in high-voltage power supply circuits. In this case, the individual system of the device affects the difference between the input and output voltage. The operation of the device in this mode can continue indefinitely until the difference between the two indicators (input and output voltage) exceeds the maximum permissible point.

Peculiarities

It is worth noting that the LM317 current stabilizer is convenient for creating simple adjustable pulse devices. They can be used as a precision stabilizer by connecting a fixed resistor between the two outputs.

The creation of secondary power sources that operate during short-term short circuits has become possible thanks to the optimization of the voltage indicator at the control output of the system. The program keeps it at the input within 1.2 volts, which is very low for most loads. The LM317 current and voltage stabilizer is manufactured in a standard TO-92 transistor core, operating temperatures range from -25 to +125 degrees Celsius.

Characteristics

The device in question is excellent for designing simple regulated blocks and power supplies. In this case, the parameters can be adjusted and specified in terms of load.

The adjustable current stabilizer on the LM317 has the following technical characteristics:

• The output voltage range is from 1.2 to 37 volts.
• Maximum load current is 1.5 A.
• There is protection against possible short circuit.
• The circuit is protected against overheating.
• The output voltage error is no more than 0.1%.
• Integrated circuit housing - type TO-220, TO-3 or D2PAK.

Current stabilizer circuit on LM317

The device in question is most often used in LED power supplies. The following is a simple circuit that involves a resistor and a microcircuit.

The input voltage is supplied by the power source, and the main contact is connected to the output analogue using a resistor. Next, aggregation occurs with the anode of the LED. The most popular current stabilizer circuit, LM317, described above, uses the following formula: R = 1/25/I. Here I is the output current of the device, its range varies between 0.01-1.5 A. The resistor resistance is allowed in sizes 0.8-120 Ohms. The power dissipated by the resistor is calculated by the formula: R = IxR (2).

The information received is rounded up. Fixed resistors are produced with a small variation in final resistance. This affects the receipt of calculated indicators. To resolve this problem, an additional stabilizing resistor of the required power is connected to the circuit.

Pros and cons

As practice shows, during operation it is better to increase the dispersion area by 30%, and in the low convection compartment - by 50%. In addition to a number of advantages, the LM317 LED current stabilizer has several disadvantages. Among them:

• Low efficiency.
• The need to remove heat from the system.
• Current stabilization over 20% of the limit value.

The use of pulse stabilizers will help to avoid problems in operating the device.

It is worth noting that if you need to connect a powerful LED element with a power of 700 milliamps, you will need to calculate the values ​​using the formula: R = 1.25/0.7 = 1.78 Ohm. The dissipated power will accordingly be 0.88 watts.

Connection

The calculation of the LM317 current stabilizer is based on several connection methods. Below are the basic diagrams:

1. If you use a powerful transistor like Q1, you can get an output current of 100 mA without a microassembly heatsink. This is quite enough to control the transistor. As a safety net against excess charge, protective diodes D1 and D2 are used, and a parallel electrolytic capacitor performs the function of reducing extraneous noise. When using transistor Q1, the maximum output power of the device will be 125 W.
2. Another circuit ensures current limitation and stable operation of the LED. A special driver allows you to power elements from 0.2 watts to 25 volts.
3. The next design uses a step-down transformer from an alternating network from 220 W to 25 W. Using a diode bridge, the alternating voltage is transformed into a constant value. In this case, all interruptions are smoothed out by a capacitor of type C1, which ensures stable operation of the voltage regulator.
4. The following connection diagram is considered one of the simplest. The voltage comes from the secondary winding of the transformer at 24 volts, is rectified when passing through the filter, and the output is a constant reading of 80 volts. This avoids exceeding the maximum voltage supply threshold.

It is worth noting that a simple charger can also be assembled based on the microcircuit of the device in question. You will get a standard linear stabilizer with an adjustable output voltage. The microassembly of the device can function in a similar role.

Analogues

The powerful stabilizer on the LM317 has a number of analogues in the domestic and foreign markets. The most famous of them are the following brands:

• Domestic modifications of KR142 EH12 and KR115 EH1.
• Model GL317.
• Variations of SG31 and SG317.
• UC317T.
• ECG1900.
• SP900.
• LM31MDT.

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:

1. 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.

Analogues

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.

1. LM117 LM217 – extended operating temperature range from -55° to +150°;
2. LM338, LM138, LM350 - analogues for 5A, 5A and 3A, respectively;
3. 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:

1. connection in parallel;
2. installing power transistors at the output, we get up to 20A;
3. 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 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.

Recently, interest in current stabilizer circuits has grown significantly. And first of all, this is due to the emergence of artificial lighting sources based on LEDs as leading positions, for which a stable current supply is a vital point. The simplest, cheapest, but at the same time powerful and reliable current stabilizer can be built on the basis of one of the integrated circuits (IM): lm317, lm338 or lm350.

Datasheet for lm317, lm350, lm338

Before moving directly to the circuits, let's consider the features and technical characteristics of the above linear integrated stabilizers (LIS).

All three IMs have a similar architecture and are designed to build on their basis simple current or voltage stabilizer circuits, including those used with LEDs. The differences between the microcircuits lie in the technical parameters, which are presented in the comparison table below.

	LM317	LM350	LM338
Adjustable output voltage range	1.2…37V	1.2…33V	1.2…33V
Maximum current load	1.5A	3A	5A
Maximum permissible input voltage	40V	35V	35V
Indicator of possible stabilization error	~0,1%	~0,1%	~0,1%
Maximum power dissipation*	15-20 W	20-50 W	25-50 W
Operating temperature range	0° - 125°С	0° - 125°С	0° - 125°С
Datasheet	LM317.pdf	LM350.pdf	LM338.pdf

* - depends on the manufacturer of the IM.

All three microcircuits have built-in protection against overheating, overload and possible short circuit.

Integrated stabilizers (IS) are produced in a monolithic package of several variants, the most common being TO-220. The microcircuit has three outputs:

1. ADJUST. Pin for setting (adjusting) the output voltage. In current stabilization mode, it is connected to the positive of the output contact.
2. OUTPUT. A pin with low internal resistance to generate output voltage.
3. INPUT. Output for supply voltage.

Schemes and calculations

The greatest application of ICs is found in power supplies for LEDs. Let's consider the simplest current stabilizer (driver) circuit, consisting of only two components: a microcircuit and a resistor.
The voltage of the power source is supplied to the input of the MI, the control contact is connected to the output contact through a resistor (R), and the output contact of the microcircuit is connected to the anode of the LED.

If we consider the most popular IM, Lm317t, then the resistor resistance is calculated using the formula: R = 1.25/I 0 (1), where I 0 is the output current of the stabilizer, the value of which is regulated by the passport data for LM317 and should be in the range of 0.01 -1.5 A. It follows that the resistor resistance can be in the range of 0.8-120 Ohms. The power dissipated by the resistor is calculated by the formula: P R =I 0 2 ×R (2). Switching on and calculating IM lm350, lm338 are completely similar.

The resulting calculated data for the resistor is rounded up, according to the nominal series.

Fixed resistors are manufactured with a small variation in resistance value, so it is not always possible to obtain the desired output current value. For this purpose, an additional trimming resistor of appropriate power is installed in the circuit.
This slightly increases the cost of assembling the stabilizer, but ensures that the required current is received to power the LED. When the output current stabilizes at more than 20% of the maximum value, a lot of heat is generated on the microcircuit, so it must be equipped with a heatsink.

Online calculator lm317, lm350 and lm338

Required output voltage (V):

R1 rating (Ohm): 240 330 470 510 680 750 820 910 1000

Additionally

Load current (A):

Input voltage (V):

The LM317 is more suitable than ever for the design of simple, regulated sources and electronics with a variety of output characteristics, both variable output voltage and fixed voltage output. electric shock loads.

To facilitate the calculation of the required output parameters, there is a specialized LM317 calculator, which can be downloaded from the link at the end of the article along with the LM317 datasheet.

Technical characteristics of the stabilizer LM317:

• Providing output voltage from 1.2 to 37 V.
• Load current up to 1.5 A.
• Availability of protection against possible short circuit.
• Reliable protection of the microcircuit from overheating.
• Output voltage error 0.1%.

This inexpensive integrated circuit is available in TO-220, ISOWATT220, TO-3, and also D2PAK packages.

Purpose of the microcircuit pins:

Online calculator LM317

Below is an online calculator for calculating a voltage stabilizer based on LM317. In the first case, based on the required output voltage and the resistance of resistor R1, resistor R2 is calculated. In the second case, knowing the resistances of both resistors (R1 and R2), you can calculate the voltage at the output of the stabilizer.

For a calculator for calculating the current stabilizer on LM317, see.

Examples of application of the LM317 stabilizer (connection circuits)

Current stabilizer

Given current stabilizer can be used in circuits of various battery chargers or regulated power supplies. The standard charger circuit is shown below.

This connection circuit uses a direct current charging method. As can be seen from the diagram, the charge current depends on the resistance of resistor R1. The value of this resistance ranges from 0.8 Ohm to 120 Ohm, which corresponds to a charging current from 10 mA to 1.56 A:

5 Volt power supply with electronic switching

Below is a diagram of a 15 volt power supply with soft start. The required smoothness of switching on the stabilizer is set by the capacitance of capacitor C2:

Switching circuit with adjustable output voltage