Unusual circuits for the lm317 chip. Integral stabilizer LM317. Selection of resistance for the stabilizer LM317

Welcome dear visitor of this web page. We want to draw your attention to the fact that there are many schemes and manufacturing options LED driver, by means of a simple current regulator on the LM317. The most time-consuming and materially costly, they are additional schematic solutions that allow, in case of critical voltage and current drops, to save the most expensive electronic components.

Scheme and principle of operation of the stabilizer up to 1.5A

To make a current stabilizer on the LM317, use the following diagram.
The minimum resistance of the resistor between the control electrode and the output corresponds to a value of 1 ohm, and the maximum value is 120 ohms. The resistance of the resistor can be selected empirically, or calculated by 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 to 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:

P W \u003d 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 efficient solution is to use a standard diode bridge. At the output of the diode bridge, a capacitor with a large capacity is installed. The LM317 LM317 uses a linear principle of operation when adjusting the current. In this regard, their strong heating is possible, due to their low efficiency. Therefore, the cooling system must be thoughtful and efficient, that is, have a radiator that can cool the electronic components well. If during the monitoring of the heating temperature, a low temperature, in which case you can use less powerful system cooling.

Current stabilizer up to 10A

The stabilization current can be increased to 10 amperes if a transistor marked KT825A and a resistance with a value 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 strength of 3A is assembled on the basis of the KT818 transistor. Load amperes in any of the circuits are calculated identically.

If the radio amateur has a great desire to make a driver, but the necessary power supply is not available, then you can use alternative options.

You can use the option of series or parallel connection of resistors.

If the LEDs require a current equal to one ampere, then in the calculation we get a resistance equal to 1.25 Ohm. You will not be able to choose a resistor with such a value, because they are not produced, so you need to take the first near one, with a slightly higher resistance.

Invite a familiar radio amateur to change the power supply that is suitable for the parameters for the radio component or electronic circuit he needs. For food assembled circuit connect a Krona battery or similar in terms of parameters to 9V. If there is no Krona, connect 6 batteries of any size at 1.5 V in series and connect them to the circuit.

We strongly advise you not to use the LM317 beyond its limits. Made in China electronic elements, have a low margin of safety. Of course, there is protection from short circuit or from overheating, but it works successfully, not in all critical modes and situations. In such situations, in addition to the LM317, other electronic components may burn out, and this is not at all desirable.

Main parameters LM317: Input voltage up to 40V, load up to 1.5A; maximum operating temperature +125°С, short circuit protection.

A high-quality power supply with adjustable output voltage is the dream of every novice radio amateur. In everyday life, such devices are used everywhere. For example, take any charger for a phone or laptop, a power supply for a children's toy, game console, landline phone, many other household appliances.

As for the circuit implementation, The design of sources can be different:

• with power transformers, a full-fledged diode bridge;
• pulse converters mains voltage with adjustable output voltage.

But in order for the source to be reliable, durable, it is better to choose a reliable element base for it. This is where difficulties begin to arise. For example, choosing as regulating, stabilizing components domestic production, the low voltage threshold is limited to 5 V. But what if 1.5 V is required? In this case, it is better to use imported analogues. Moreover, they are more stable and practically do not heat up during operation. One of the most widely used is integral stabilizer lm317t.

Main characteristics, chip topology

The lm317 chip is universal. It can be used as a stabilizer with a constant output voltage and as an adjustable regulator with high efficiency. MS has high practical characteristics, making it possible to use it in various charger circuits or laboratory power supplies. At the same time, you do not even have to worry about the reliability of operation under critical loads, because the microcircuit is equipped with internal short circuit protection.

This is a very good addition, because the maximum output current of the stabilizer on lm317 is no more than 1.5 A. But the presence of protection will not allow you to unintentionally burn it. To increase the stabilization current, it is necessary to use additional transistors. Thus, currents up to 10 A or more can be regulated by using appropriate components. But we'll talk about this later, and in the table below we present main characteristics of the component.

Circuit pinout

An integrated circuit was made in a standard TO-220 package with a heat sink mounted on a radiator. As for the numbering of the conclusions, they are located according to GOST from left to right and have the following meaning:

Pin 2 is connected to the heatsink without an insulator, so in devices, if the heatsink is in contact with the case, mica insulators must be used or any other heat-conducting material. This important point, because you can accidentally short-circuit the conclusions, and there will simply be nothing at the output of the microcircuit.

Analogs lm317

Sometimes it is not possible to find the specifically required microcircuit on the market, then you can use similar ones. Among the domestic components on the lm317, the analogue is quite powerful and productive. It is chip KR142EN12A. But when using it, it is worth considering the fact that it is unable to provide a voltage of less than 5 V at the output, so if this is important, you will again have to use an additional transistor or find exactly the required component.

In terms of form factor, the CR has as many pins as the lm317 has. Therefore, you do not even have to redo the circuit of the finished device in order to adjust the parameters of the voltage regulator or constant stabilizer. When performing integrated circuit wiring it is recommended to install it on a radiator with good heat dissipation and cooling system. Which is quite often observed in the manufacture of a powerful LED lamp. But at rated load, the device generates some heat.

In addition to the domestic integrated circuit KR142EN12, more powerful imported analogues are produced, the output currents of which are 2-3 times higher. These chips include:

• lm350at, lm350t - 3 A;
• lm350k - 3 A, 30 W in another case;
• lm338t, lm338k - 5 A.

The manufacturers of these components guarantee higher output voltage stability, low regulation current, increased power with the same minimum output voltage of no more than 1.3 V.

Connection Features

On the lm317t, the switching circuit is quite simple, it consists of a minimum number of components. However, their number depends on the purpose of the device. If a voltage stabilizer is being manufactured, it will require the following details:

Rs is a shunt resistance that also acts as a ballast. Select around 0.2 ohm if maximum output current up to 1.5A is required.

Resistive divide with R1, R2, connected to the output and the case, and the regulating voltage comes from the midpoint, forming a deep feedback. Due to this, a minimum ripple coefficient and high stability of the output voltage are achieved. Their resistance is selected based on the ratio 1:10: R1=240 Ohm, R2=2.4 kOhm. This is a typical voltage regulator circuit with an output voltage of 12 V.

If you want to design a current stabilizer, this will require even fewer components:

R1, which is a shunt. They set the output current, which should not exceed 1.5 A.

In order to correctly calculate the circuit of one or another device, always you can use calculator lm317. As for the calculation of Rs, it can be determined by the usual formula: Iout. = Uop/R1. On lm317, the LED current stabilizer turns out to be of sufficient quality, which can be made in several types depending on the power of the LED:

• to connect a single-watt LED with a current consumption of 350mA, you must use Rs = 3.6 Ohm. Its power is selected at least 0.5 W;
• to power three-watt LEDs, you will need a 1.2 ohm resistor, the current will be 1 A, and the dissipation power will be at least 1.2 watts.

On lm317, the LED current stabilizer is quite reliable, but it is important to correctly calculate the resistance of the shunt and choose its power. A calculator will help in this matter. Also, on the basis of LEDs and on the basis of this MS, various powerful lamps and home-made spotlights are made.

Building powerful regulated power supplies

The internal transistor lm317 is not powerful enough, to increase it you will have to use external additional transistors. In this case, components are selected without restrictions, because their control requires much lower currents, which the microcircuit is quite capable of providing.

An lm317 regulated power supply with an external transistor is not much different from a regular power-on. Instead of constant R2, a variable resistor is installed, and the base of the transistor is connected to the input of the microcircuit through an additional limiting resistor that turns off the transistor. Used as a control bipolar key with p-n-p conductivity. In this design, the microcircuit operates with currents of the order of 10 mA.

When designing bipolar power supplies you will need to use a complementary pair of this chip, which is lm337. And to increase the output current, a transistor with n-p-n conductivity is used. In the reverse arm of the stabilizer, the components are connected in the same way as in the upper one. The primary circuit is a transformer or impulse block, which depends on the quality of the circuit and its efficiency.

Some features of working with the lm317 chip

When designing power supplies with a small output voltage, at which the difference between the input and output value does not exceed 7 V, it is better to use other, more sensitive microcircuits with an output current of up to 100 mA - LP2950 and LP2951. At low incidence, lm317 is not able to provide the necessary stabilization coefficient, which can lead to unwanted pulsations during operation.

Other practical circuits on lm317

In addition to conventional stabilizers and voltage regulators based on this microcircuit, there are also can be made digital regulator voltage. This will require the microcircuit itself, a set of transistors and several resistors. By turning on the transistors and upon the arrival of a digital code from a PC or other device, the resistance R2 changes, which also leads to a change in the circuit current within the voltage range from 1.25 to 1.3 V.

Hello. I bring to your attention a review of the integrated linear adjustable voltage (or current) stabilizer LM317 at a price of 18 cents apiece. In a local store, such a stabilizer costs an order of magnitude more, which is why I was interested in this lot. I decided to check what is sold at such a price and it turned out that the stabilizer is quite high quality, but more on that below.
In the review, testing in the mode of a voltage and current stabilizer, as well as checking protection against overheating.
Interested please...

A little theory:

Review hero:

Testing:
Similar stabilizers are produced by many manufacturers, here.
The location of the legs is as follows:
1 - adjustment;
2 - exit;
3 - entrance.
We collect the simplest voltage stabilizer according to the scheme from the manual:


Here is what we managed to get with 3 positions of the variable resistor:
The results, frankly speaking, are not very good. It does not turn out to be called a stabilizer.
Next, I loaded the stabilizer with a 25 ohm resistor and the picture completely changed:

Next, I decided to check the dependence of the output voltage on the load current, for which I set the input voltage to 15V, set the trimmer resistor output voltage about 5V, and the output is loaded with a variable 100 ohm wire resistor. Here's what happened:
It was not possible to obtain a current of more than 0.8A, because the input voltage began to drop (the PSU is weak). As a result of this testing, the stabilizer with a radiator heated up to 65 degrees:

To test the operation of the current stabilizer, the following circuit was assembled:


Instead of a variable resistor, I used a constant one, here are the test results:
Current stabilization is also good.
Well, how can a review be without burning the hero? To do this, I assembled the voltage stabilizer again, applied 15V to the input, set the output to 5V, i.e. 10V fell on the stabilizer, and loaded it by 0.8A, i.e. 8W of power was allocated on the stabilizer. Removed the radiator.
The result is shown in the following video:

Outcome:

On this, let me take my leave, good luck!

The product was provided for writing a review by the store. The review is published in accordance with clause 18 of the Site Rules.