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If the circuit requires a stabilizer for some non-standard voltage, then an excellent solution is to use the popular integrated stabilizer LM317T with the following characteristics:
- capable of operating in the output voltage range from 1.2 to 37 V;
- output current can reach 1.5 A;
- maximum power dissipation 20 W;
- built-in current limitation for short circuit protection;
- built-in overheating protection.
For the LM317T microcircuit, the minimum connection circuit assumes the presence of two resistors, the resistance values of which determine the output voltage, an input and output capacitor.
The stabilizer has two important parameters: the reference voltage (Vref) and the current flowing from the adjustment pin (Iadj).
The value of the reference voltage can vary from instance to instance from 1.2 to 1.3 V, and on average is 1.25 V. The reference voltage is the voltage that the stabilizer chip strives to maintain across resistor R1. Thus, if resistor R2 is closed, then the output of the circuit will be 1.25 V, and the greater the voltage drop across R2, the greater the output voltage will be. It turns out that 1.25 V on R1 adds up with the drop on R2 and forms the output voltage.
But I would advise using the LM317T in the case of typical voltages, only when you urgently need to do something on your knees, and a more suitable microcircuit like 7805 or 7812 is not at hand.
And here is the pinout location of the LM317T:
- Adjusting
- Day off
- Input
By the way, the domestic analogue of LM317 - KR142EN12A - has exactly the same connection circuit.
It’s easy to make an adjustable power supply on this chip: replace the constant R2 with a variable one, add a network transformer and a diode bridge.
You can also make a soft start circuit on LM317: add a capacitor and a current amplifier on a bipolar pnp transistor.
The connection circuit for digital control of the output voltage is also not complicated. We calculate R2 for the maximum required voltage and add chains of a resistor and transistor in parallel. Turning on the transistor will add, in parallel to the conductivity of the main resistor, the conductivity of the additional one. And the output voltage will decrease.
The current stabilizer circuit is even simpler than the voltage stabilizer, since only one resistor is needed. Iout = Uop/R1.
For example, in this way we get a current stabilizer for LEDs from lm317t:
- for single-watt LEDs I = 350 mA, R1 = 3.6 Ohm, power of at least 0.5 W.
- for three-watt LEDs I = 1 A, R1 = 1.2 Ohm, power of at least 1.2 W.
It’s easy to make a charger for 12 V batteries based on the stabilizer, that’s what the datasheet offers us. Rs can be used to set the current limit, while R1 and R2 determine the voltage limit.
If the circuit needs to stabilize voltages at currents of more than 1.5 A, then the LM317T can still be used, but in conjunction with a powerful bipolar transistor of the pnp structure.
If we need to build a bipolar adjustable voltage stabilizer, then an analogue of the LM317T will help us, but working in the negative arm of the stabilizer - LM337T.
But this chip also has limitations. It is not a low-dropout regulator; on the contrary, it only starts to work well when the difference between the output and output voltage exceeds 7 V.
If the current does not exceed 100mA, then it is better to use low-dropout ICs LP2950 and LP2951.
Powerful analogs of LM317T - LM350 and LM338
If the output current of 1.5 A is not enough, then you can use:
- LM350AT, LM350T - 3 A and 25 W (TO-220 package)
- LM350K - 3 A and 30 W (TO-3 package)
- LM338T, LM338K - 5 A
The manufacturers of these stabilizers, in addition to increasing the output current, promise a reduced control input current to 50 μA and improved accuracy of the reference voltage.
But the switching circuits are suitable for LM317.
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:
- ADJUST. Pin for setting (adjusting) the output voltage. In current stabilization mode, it is connected to the positive of the output contact.
- OUTPUT. A pin with low internal resistance to generate output voltage.
- 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/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 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
Vin (input voltage): 3-40 Volts
Vout (output voltage): 1.25-37 Volts
Output current: up to 1.5 Amps
Maximum power dissipation: 20 Watt
Formula to calculate output (Vout) voltage: Vout = 1.25 * (1 + R2/R1)
*Resistance in Ohms
*Voltage values are obtained in Volts
This simple circuit allows you to rectify alternating voltage into direct voltage thanks to a diode bridge made of diodes VD1-VD4, and then use an accurate substring resistor of the SP-3 type to set the voltage you need within the limits of the integrated stabilizer chip.
I used old ones as rectifier diodes FR3002, which once upon a time fell out of an ancient computer from the year 1998. Despite their impressive size (DO-201AD housing), their characteristics (Ureverse: 100 Volts; Idirect: 3 Amps) are not impressive, but that’s enough for me. For them, we even had to widen the holes in the board, their pins are too thick (1.3mm). If you slightly change the board in the layout, you can immediately solder a ready-made diode bridge.
A radiator to remove heat from the 317 chip is required; it’s even better to install a small fan. Also, at the junction of the TO-220 chip case substrate with the heatsink, drop a little thermal paste. The degree of heating will depend on how much power the chip dissipates, as well as on the load itself.
Microcircuit LM317T I did not install it directly on the board, but brought out three wires from it, with the help of which I connected this component to the others. This was done so that the legs would not become loose and, as a result, would not be broken, because this part will be attached to the heat dissipator.
To be able to use the full voltage of the microcircuit, that is, adjust from 1.25 and right up to 37 Volts, we set the substring resistor with a maximum resistance of 3432 kOhm (in the store the closest value is 3.3 kOhm). Recommended type of resistor R2: interlinear multi-turn (3296).
The LM317T stabilizer chip itself and others like it are produced by many, if not all, companies producing electronic components. Buy only from trusted sellers, because there are Chinese counterfeits, especially often the LM317HV microcircuit, which is designed for an input voltage of up to 57 Volts. You can identify a fake microcircuit by its iron backing; in a fake, it has a lot of scratches and an unpleasant gray color, as well as incorrect markings. It should also be said that the microcircuit has protection against short circuits and overheating, but don’t count on them too much.
Do not forget that this (LM317T) integrated stabilizer is capable of dissipating power with a radiator only up to 20 Watts. The advantages of this common microcircuit are its low price, limitation of internal short circuit current, internal thermal protection
The scarf can be drawn with high quality even with an ordinary parchment marker, and then etched in a solution of copper sulfate/ferric chloride...
Photo of the finished board.
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 the circuit implementation, The design of the sources may 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 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 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 lm317 is no more than 1.5 A. But having protection will prevent you from accidentally 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’ll present 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 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 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 on lm317, there is an analogue that is quite powerful and productive. He is microcircuit KR142EN12A. 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 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 need 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.
To correctly calculate the circuit of a particular device, always you can 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.
On 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 one. 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 low drop, lm317 is not able to provide the required 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 chip, there are also Can you make a digital voltage regulator?. 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.
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!
