Current stabilizers for lm317, lm338, lm350 and their use for LEDs. Connection diagrams lm317

connection circuit, characteristics and an adjustable stabilizer based on it

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

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

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

But in order for the source to be reliable and durable, it is better to choose a reliable element base for it. This is where difficulties begin to arise. For example, choosing domestically produced components as regulating, stabilizing components, the lower 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 the lm317t integrated stabilizer.

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 stabilizer with high efficiency. MS has high practical characteristics that make it possible to use it in various charger circuits or laboratory power supplies. At the same time, you don’t even have to worry about reliable 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 the lm317 is no more than 1.5 A. But the presence of protection will prevent you from unintentionally burning it. To increase the stabilization current, it is necessary to use additional transistors. Thus, currents of up to 10 A or more can be regulated when using the appropriate components. But we’ll talk about this later, and in the table below we present the main characteristics of the component.

Microcircuit pinout

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

Pin 2 is connected to a heat sink without an insulator, so in devices where the heat sink is in contact with the body, it is necessary to use insulators made of mica or any other heat-conducting material. This is an important point, because you can accidentally short-circuit the pins, 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 based on lm317, there is an analogue that is quite powerful and productive. It is the KR142EN12A microcircuit. But when using it, it is worth considering the fact that it is unable to provide a voltage 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.

As for the form factor, the KR has the same number of pins as the lm317 has. Therefore, you don’t even have to redo the circuit of the finished device in order to adjust the parameters of the voltage regulator or unchangeable stabilizer. When installing an integrated circuit, it is recommended to install it on a radiator with good heat dissipation and a cooling system. This is quite often observed in the manufacture of powerful LED lamps. But at rated load the device generates a little 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. Such microcircuits include:

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

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 and 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 parts:

Rs is a shunt resistance, which also acts as a ballast. Select a value of about 0.2 Ohm if you want to provide a maximum output current of up to 1.5 A.

The resistive divides with R1, R2, connected to the output and the housing, and the regulating voltage comes from the middle point, forming 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, you will need even fewer components:

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

To correctly calculate the circuit of a particular device, you can always use the lm317 calculator. As for the calculation of Rs, it can be determined using the usual formula: Iout. = Uop/R1. On lm317, the LED current stabilizer is of quite high quality, which can be made of 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 to be at least 0.5 W;
• To power three-watt LEDs, you will need a resistor with a resistance of 1.2 Ohm, the current will be 1 A, and the dissipation power will be at least 1.2 W.

With lm317, the LED current stabilizer is quite reliable, but it is important to correctly calculate the shunt resistance and select its power. A calculator will help in this matter. Also, various powerful lamps and homemade spotlights are made using LEDs and based on this MS.

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.

The lm317 regulated power supply with an external transistor is not much different from the usual one. Instead of a 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. A bipolar switch with p-n-p conductivity is used as a controlled switch. In this design, the microcircuit operates with currents of about 10 mA.

When designing bipolar power supplies, you will need to use the 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 arm. The primary circuit is a transformer or a pulse unit, 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 low output voltage, at which the difference between the input and output values ​​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 a low drop, lm317 is not able to provide the required stabilization coefficient, which can lead to unwanted ripples during operation.

Other practical circuits on lm317

In addition to conventional stabilizers and voltage regulators, a digital voltage regulator can also be manufactured based on this microcircuit. To do this, you will need the microcircuit itself, a set of transistors and several resistors. By turning on the transistors and upon receipt 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.

instrument.guru

Correct circuit and board for stabilizers on LM317, LM337, LM350 chips

While researching topics regarding the use of LM series 3-terminal voltage regulators, I couldn't find a recommended PCB design anywhere. Therefore, we will fill the gap and give several rules that allow us to achieve high parameters from the stabilizer. We present our design for the placement of elements, a prototype circuit assembled on a breadboard and measurement results. We are sure that this will be useful not only for beginners, since LM317, LM337, LM350 are very often used in different power supplies, both separately and as part of devices.

Stabilizer connection diagram

So, we needed a linear stabilizer of symmetrical voltage +/- 5 V at a current of about 2 A to power the analog circuit. A cheap 9 V, 3 A switching power supply is used at the stabilizer input.

Unfortunately, the output voltages of switching power supplies contain significant ripple - for a 2 A load the ripple amplitude is about 0.1 V.

What to pay attention to

1. Thanks to the use of SMD ceramic capacitors, they can be placed very close to the terminals of the LM3xx chip (capacitors C2 and C4 in 0805 packages can even be soldered directly on the stabilizer solder fields.
2. Elements R2 and D2 should be placed in exactly this sequence (R2 is closer to U1).
3. The lower terminal of resistor R1 is not connected directly to ground, only ends with a solder field. It is necessary to connect as close to ground as possible, then the voltage drop on the ground wires will be compensated.
4. It may be worth using Schottky diodes as diodes D1 and D3.

After assembly according to this scheme, it was not possible to notice any pulsations at the output on the oscilloscope at a load current of up to 2.5 A, even in the range of 50 mV/cm. The voltage drop is not noticeable with or without load.

Printed circuit board for LM3XX

Here is the recommended type of PCB for LM317 (LM350 is a higher current version of LM317).

A capacitor at the output that is too large has a big impact on the possible excitation of the circuit. In some datasheet it was even written that the output could have a maximum of 10 µF low ESR, preferably tantalum. We once convinced ourselves of this when the LM317 worked as a current source. The output voltage jumped from zero to maximum. Reducing the output capacitance to 10 µF effectively eliminated this defect. Additionally, a large output capacitor can cause large current surges in the load when something goes wrong. On the other hand, the absence of a capacitor causes inertia when the load current changes.

Please note that for the LM350 chip the currents are quite high, which causes a noticeable voltage drop across the traces. Read more in the datasheet for LM350.

The job of diode D1 is to discharge the output capacitor in a situation where the voltage on LM3xx has become higher than before (for example, during adjustment).

Another important point is that in the power supply, diodes D1 and D3 must be selected appropriately for the fuse so that it is the fuse that burns, and not them. The easiest way is to install them with the highest current available (according to the 6A6 circuit for 6 amperes).

2shemi.ru

Current stabilizer on lm317 - application, connection diagram, assembly, characteristics

Nowadays, when technological processes for the development of electrical appliances are rapidly improving, it is quite difficult to do without special equipment for connecting equipment at home. The power supply plays an important role in stabilizing the electric current supply. Every lover of modern electronic devices should learn how to assemble converters themselves.

We offer a detailed look at how to assemble a current stabilizer for lm317 with your own hands. The device has a wide range of applications, primarily with LEDs, so before the development process you should first study its features and operating principle.

Technical features

The converter for the lm 317 regulator acts as an important element for the correct operation of any technical equipment. The operating process is as follows: the device converts the supply of electricity coming from a centralized network into the voltage required by the user, which allows connecting one or another electrical appliance. With all this, the converter device additionally performs a protective function against the possibility of a short circuit.

Power supplies are divided into 2 types:

• adjustable current stabilizer on lm317;
• impulse.

In addition, the schematic data used to create a given unit can have significant differences, from the most elementary diagrams to complex ones.

If you have minimal experience and knowledge, you should start by making a voltage stabilizer for lm317 according to simple drawings. This will allow you to thoroughly study the functioning process and subsequently create a more complex design.

Approximate diagram

If you trust the reviews of “home” craftsmen, this device is several times superior in functionality to purchased modifications, both in functionality and service life.

VIDEO: LM317 current stabilizer LED DRIVER

Operating principle

In order for the device to correctly regulate the voltage and be able to correctly measure the power of the current emanating from the electrical network, you need to understand its operating principle.

The lm317t converter is characterized by actions such as normalizing the intensity of current flow to the output voltage, which helps reduce the power of electricity. The decrease in electric current occurs in the resistor itself, which has a value of 1.25V.

Working power supply

It is very important that the soldering areas are molded. If the connection is made incorrectly, there is a possibility of a short circuit. You should also use high-quality components only from well-known manufacturers.

Remember that the regulator assembly diagram, which contains the lm317 chip, has limiting frames. The lowest barrier is considered to be 0.8 Ohm, the highest is 120 Ohm. It turns out that in order for this system to work stably, it is necessary to apply the formula 0.8

Scope of application

A voltage stabilization unit on lm317, specializing in changing the power and intensity of electric current, is used in the following situations:

1. If there is a need to connect various electrical equipment to a 220V power supply.
2. Testing of devices in a personal technical laboratory.
3. Design of a lighting system using LED lamps and strips.

Characteristics

The voltage stabilizer lm317, based on the operation of a microcircuit of this modification, has the following characteristics:

• The product allows you to independently adjust the output voltage level within 1.2-28V.
• The intensity of the electric current load can vary up to 3A.

Chip

You should pay attention to the load indicator; it is more than enough for testing electrical appliances of your own production. A current and voltage stabilizer manufactured according to the most elementary circuit can provide these parameters.

Preparatory work

To work, you will need a number of elements and parts that can be purchased at a specialized store or taken from another device:

• Current stabilizer lm317;
• R-3 – resistance 0.1 Ohm * 2 W;
• TR-1 – power type transformer device;
• T-1 – transistor type KT-81-9G;
• R-2 – resistance action 220 Ohm;
• F-1 – fuse element 0.5 A and 250V;
• R-1 – resistance 18K;
• D-1 – LED IN-54-00;
• P-1 – resistance 4.7 K;
• BR-1 – LED barrier;
• LED-1 – color diode;
• C-1 – modified capacitor device with parameters 3,300 µF*43V;
• C-3 – capacitor device modification 1uF*43V;
• C-2 – 0.1 µF ceramic capacitor element.

The list may vary depending on the type of connection scheme used.

Before assembling the lm317t converter, you must first purchase all the components from the above list.

Select high-quality, proven elements; the functioning of not only the unit of your own production, but also the equipment that is planned to be connected will depend on this.

The main part of the product is a transformer, which can be removed from any electrical device: a stereo system, a TV or a small radio. It can also be purchased; experts recommend giving preference to the TBK110 modification. However, the model can only produce an output voltage of 9V.

Assembling the apparatus

When the design scheme has been selected and all the necessary spare parts have been prepared, you can safely begin creating a current stabilizer for lm317. The production process, the connection diagram should be carried out as follows:

1. The selected type of transformer unit is installed.
2. The cascade circuit and rectifier equipment are being assembled.
3. All semiconductor LEDs are soldered.

It is important to know! The type of rectifier element can be full-wave or single-wave equipment with double and triple bridges. To manufacture the device according to the standard design, a bridge straightening option should be used.

1. The pins on the system are determined. There are only three of them: weight, output, input. In order not to get confused in the process, you need to designate the parameters on the elements with the corresponding numbers, from 1 to 3.
2. Turn the unit over so that the numbering you indicate starts on the left side.
3. Adjust the voltage to stabilize the parameters. To do this, apply a minus to pin “2” while simultaneously removing the configured current intensity value from the third element.
4. Based on the scheme you have chosen, install the remaining spare parts and place them in a durable plastic or aluminum case.

The shape of the product can be different, it all depends on the user’s preferences and the dimensional parameters of the component parts.

If you choose the circuit correctly, follow the connection rules and carry out the process step by step, the result can be a high-quality current stabilizer on the lm317 microcircuit. This device will serve as an indispensable unit in every “home” laboratory specialized in the creation of electrical devices.

VIDEO: Homemade voltage stabilizer for LEDs

www.diodgid.ru

Integrated voltage stabilizer LM317. Description and Application

Quite often there is a need for a simple voltage stabilizer. This article provides a description and examples of the use of an inexpensive (price 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 power supply circuits are based on LM317 with voltage regulation.

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 heat-conducting 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 resistance value of variable resistor 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.

As mentioned above, the maximum possible load current limit for the LM317 is 1.5 amperes. There are types of stabilizers that are similar in operation to the LM317 stabilizer, but are designed for a higher load current. For example, the LM350 stabilizer can withstand current up to 3 amperes, and LM338 up to 5 amperes.

To facilitate the calculation of stabilizer parameters, there is a special calculator:

Download calculator for LM317 (downloads: 5,588)

Download datasheet LM317 (downloads: 1,795)

fornk.ru

Adjustable power supply based on voltage regulator LM317 |

A novice radio amateur simply cannot do without at least a simple power supply. When developing or configuring a device, an adjustable power supply is an indispensable attribute. But if you are a beginner radio amateur and cannot afford an expensive fancy power supply, then this article will help you fill your need

Power supply on LM317T chip, diagram:

There are countless diagrams of various power supplies on the Internet. But even at first glance, simple schemes turn out to be not so easy during the setup process. I recommend that you consider a very easy to set up, cheap and reliable power supply circuit based on the LM317T stabilizer chip, which regulates voltage from 1.3 to 30 V and provides a current of 1A (usually this is enough for simple amateur radio circuits) Figure No. 1.

Figure No. 1 – Electrical circuit diagram of an regulated power supply.

R1 - about 18 KOhm (you need to select it for the LED current). R2 - You don’t have to solder it in - it is necessary if you need to obtain non-standard voltage regulation limits. You simply select it in such a way that the sum R2 + R3 = 5KOhm.

R3 - 5.6 Com. R4 – 240 Ohm. C1 – 2200 µF (electrolytic)

C2 - 0.1 µF C3 - 10 µF (electrolytic) C4 - 1 µF (electrolytic) DA1 – LM317T

The main element in the circuit is the LM317T microcircuit; you can easily look at all its characteristics in the manual for the microcircuit. The only thing that should be separately noted is that it must be attached to the radiator (Figure No. 2) so that the microcircuit does not fail.

According to the documentation, its maximum current is 1.5 A - but I do not recommend driving it into such extreme operating modes. I also recommend using the transformer with a current reserve (current 3A), so that in the event of a sudden surge of current it does not fail. Every radio amateur does printed circuit boards as he pleases - but if you are too lazy to trace it - you can use my version of the printed circuit board, figure No. 3, which is available at this link or at this link. The files can be opened using the Sprint-Layout 5 program.

Before you start making my version of the board layout, review and analyze it again!!! I traced the board for the photolithography method, so unfold it as needed. I tried to make the board the most universal for this circuit and made it to suit my needs. If you do not solder resistor R2, then you just need a jumper instead.

P.S.: I tried to clearly show and describe not tricky tips. I hope that at least something is useful to you. But this is not everything that can be imagined, so go ahead and study the site http://bip-mip.com/

It is best to set all resistances in the circuit to half a watt, this is almost a guarantee of stable operation of the circuit, even under extreme operating conditions. Resistor R2 can be completely excluded from the circuit; I left a place for it for those cases when it is necessary to receive a non-standard voltage. And also, after digging around on the Internet, I found a special calculator for recalculating LM317, namely resistors in the voltage regulation control circuit.

Window of a special calculator for calculating LM317 Control voltage divider

Resistors R3 and R4 are an ordinary voltage divider, so we can match it to the resistors that we have at hand (within specified limits) - this is very convenient and allows us to easily adjust the operation of the LM317T to any voltage (upper limit can vary from 2 to 37 V). For example, you can choose resistors so that your power supply is regulated from 1.2 to 20V - it all depends on the recalculation of the divider R3 and R4. You can find out the formula by which the calculator works by reading the datasheet on the LM317T. Otherwise, if everything is assembled correctly, the power supply is immediately ready for use.

bip-mip.com

LM217, LM317 - Adjustable Voltage Stabilizers - DataSheet

Description

LM217, LM317 - monolithic integrated circuits in TO-220, TO-220FP and D²PAK packages intended for use as voltage stabilizers. Can support a load current of more than 1.5 A and an adjustable voltage ranging from 1.2 V to 37 V. The rated output voltage is selected using a resistive divider, which makes the device very easy to use. The domestic analogue is the KR142EN12A microcircuit.

Properties

• Output voltage from 1.2 V to 37 V
• Output current 1.5 A
• 0.1% adjustment deviation in line and load
• Variable control for high voltages
• Full set of protection: current limitation; overheat shutdown; SOA quality control

Marking

Pin layout

You can buy LM317 here.

Maximum values

Scheme

Electrical characteristics

Electrical characteristics of LM217

VI - VO = 5 V, IO = 500 mA, IMAX = 1.5 A and PMAX = 20 W, TJ = - 55 to 150 °C unless otherwise noted.

Electrical characteristics of LM317

VI - VO = 5 V, IO = 500 mA, IMAX = 1.5 A and PMAX = 20 W, TJ = 0 to 150 °C unless otherwise noted.

1. CADJ is connected between the control pin and ground.

LM317B Electrical Specifications

VI - VO = 5 V, IO = 500 mA, IMAX = 1.5 A and PMAX = 20 W, TJ = -40 to 150 °C unless otherwise noted.

1. CADJ is connected between the control pin and ground.

Typical characteristics

Application

Stabilizers of the LM217, LM317 series support a reference voltage of 1.25 V between the output and the control pin. It is used to maintain a constant current through a voltage divider (see Fig. 6), which gives an output voltage VO calculated by the formula:

VO = VREF (1 + R2/R1) + IADJ R2

Regulators were designed to reduce the IADJ current and keep it constant in the line as the load changes. Generally, the deviation IADJ × R2 can be neglected. To meet the above requirements, the stabilizer returns the quiescent current to the output pin to maintain the minimum load current. If the load is insufficient, the output voltage will rise. Since LM217, LM317 regulators have an ungrounded "floating" output and only see the difference between the input and output voltage, for sources with very high voltage relative to ground, it is possible to stabilize the voltage for as long as possible until the maximum difference between the input and output voltage is exceeded. In addition, you can easily assemble a programmable stabilizer. By connecting a constant resistor between the output and the control, the device can be used as a precision current stabilizer. Performance can be improved by adding containers as described below:

• There is a 1 µF capacitor at the bypass input.
• There is a 10 µF capacitor on the control pin to improve ripple suppression by 15 dB (CADJ).
• Tantalum electrolytic capacitor at the output to improve transient response. In addition to capacitors, you can add protective diodes, as shown in Fig. 7. D1 is used to protect the stabilizer against input short circuit, D2 to protect against output short circuit and capacitance discharge.

IO = (VREF / R1) + IADJ = 1.25 V / R1

R2 corresponds to the maximum output voltage value

RS sets the output charging resistance, calculated by the formula ZO = RS (1 + R2/R1). The use of RS makes it possible to reduce the charge level when the battery is fully charged.

*R3 sets the maximum current (0.6 A for 1 Ohm).

If you find an error, please select a piece of text and press Ctrl+Enter.

rudatasheet.ru

Current stabilizer for lm317, lm338, lm350 for LEDs

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.

* - 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 use 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/I0 (1), where I0 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 using the formula: PR=I02×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 necessary current is obtained 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

Let's say you need to connect a powerful LED with a current consumption of 700 milliamps. According to formula (1) R=1.25/0.7= 1.786 Ohm (the closest value from the series E2-1.8 Ohm). The dissipated power according to formula (2) will be: 0.7×0.7×1.8 = 0.882 Watt (the closest standard value is 1 Watt).

Phase control relay designation on the diagram

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