Voltage stabilizer on the lm317t chip. Linear Voltage or Current Regulator LM317

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

The list of tasks to be solved by this stabilizer is quite extensive - this is the power supply of 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 with voltage regulation.

In practice, with the participation of the LM317, it is possible to build a voltage regulator for an arbitrary output voltage in the range of 3 ... 38 volts.

Specifications:

• Stabilizer output voltage: 1.2 ... 37 volts.
• Withstanding current up to 1.5 amps.
• Stabilization accuracy 0.1%.
• There is an internal protection against accidental short circuit.
• Excellent protection of the integral stabilizer from possible overheating.

Power dissipation and input voltage of the LM317 stabilizer

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

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

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

When placing a chip on a heatsink, it is necessary to isolate the chip body from the heatsink, for example, with a mica gasket. Also, for efficient heat dissipation, it is desirable to use heat-conducting paste.

Selection of resistance for the stabilizer LM317

For accurate operation of the microcircuit, the total value of the 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 is allowed (8 ... 10 mA).

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

The location of the resistors on the board can be arbitrary, but it is desirable for better stability to place them 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 chip to voltage changes, but also reduces the effect 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 varieties of stabilizers 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 amps, and LM338 up to 5 amps.

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

(downloaded: 5 916)

(downloaded: 1 904)

Component references (or datasheets) are essential
in the development of electronic circuits. However, they have one, but an unpleasant feature.
The fact is that the documentation for any electronic component (for example, a microcircuit)
should always be ready before this chip is released.
As a result, we actually have a situation where microcircuits are already on sale,
and yet not a single product based on them has been created.
And, therefore, all the recommendations and especially the application schemes given in the datasheets,
are theoretical and recommendatory in nature.
These circuits mainly demonstrate the working principles of electronic components,
but they have not been tested in practice and should therefore not be blindly taken into account
during development.
This is a normal and logical state of affairs, if only over time and as
accumulating experience, changes and additions are made to the documentation.
Practice shows the opposite - in most cases, all circuit solutions,
given in the datasheet remain at the theoretical level.
And, unfortunately, often these are not just theories, but blunders.
And even more regrettable is the discrepancy between the real (and most important)
chip parameters stated in the documentation.

As a typical example of such datasheets, here is a guide to the LM317,-
three-pin adjustable voltage regulator, which, by the way, is available
already 20 years old. And the schemes and data in his datasheet are still the same ...

So, the shortcomings of the LM317, like microcircuits and errors in the recommendations for its use.

1. Protective diodes.
Diodes D1 and D2 serve to protect the regulator, -
D1 for input short circuit protection and D2 for over discharge protection
capacitor C2 "through the low output impedance of the regulator" (quote).
In fact, diode D1 is not needed, since there is never a situation where
The voltage at the input of the regulator is less than the voltage at the output.
Therefore, diode D1 never opens, and therefore does not protect the regulator.
Except, of course, the case of a short circuit at the input. But this is an unrealistic situation.
Diode D2 can open, of course, but capacitor C2 discharges just fine
and without it, through the resistors R2 and R1 and through the load resistance.
And somehow there is no need to specifically discharge it.
Also, the mention in the Datasheet of "discharge C2 through the output of the regulator"
nothing more than an error, because, as the circuit of the output stage of the regulator -
This is an emitter follower.
And the capacitor C2 simply cannot be discharged through the output of the regulator.

2. Now - about the most unpleasant, namely, the discrepancy between real
electrical characteristics declared.

Datasheets of all manufacturers have an Adjustment Pin Current parameter
(current at the tuning input). The parameter is very interesting and important, determining,
in particular, the maximum value of the resistor in the Adj input circuit.
As well as the value of the capacitor C2. The declared typical current Adj is 50 μA.
Which is very impressive and would completely suit me as a circuit engineer.
If in fact it would not be 10 times larger, i.e. 500 uA.

This is a real discrepancy, tested on chips from different manufacturers.
and for many years.
And it all started with bewilderment - why is it such a low-resistance divider at the output in all circuits?
And that's why it's low-resistance, because otherwise it's impossible to get at the output of LM317
minimum voltage level.

The most interesting thing is that in the technique for measuring the current Adj, the low-resistance divider
the output is also present. Which actually means that this divider is on
in parallel with the electrode Adj.
Only with such a cunning approach can one “fit” into the framework of a typical value of 50 μA.
But this is a rather elegant, but trick. "Special Measurement Conditions".

I understand that it is very difficult to achieve a stable current of the declared value of 50 μA.
So don't write linden in the Datasheet. Otherwise, it is a fraud of the buyer. And honesty is the best policy.

3. More about the most unpleasant.

The Datasheets LM317 has a Line Regulation parameter that defines
operating voltage range. And the range indicated is still not bad - from 3 to 40 volts.
Here is just one small BUT...
The inside of the LM317 contains a current regulator that uses
a zener diode for a voltage of 6.3 V.
Therefore, effective regulation starts with an Input-Output voltage of 7 Volts.
In addition, the output stage of the LM317 is an npn transistor connected according to the circuit
emitter follower. And on the “buildup” he has the same repeaters.
Therefore, efficient operation of the LM317 at a voltage of 3 V is not possible.

4. About circuits that promise to get an adjustable voltage from zero Volt at the output of the LM317.

The minimum voltage value at the output of the LM317 is 1.25 V.
It would be possible to get even less if it were not for the built-in protection circuit against
short circuit at the output. Not the best plan to say the least...
In other microcircuits, the short circuit protection circuit is triggered when the load current is exceeded.
And in the LM317 - when the output voltage drops below 1.25 V. Simple and tasteful -
the transistor closed itself at a base-emitter voltage below 1.25 V and that's it.
That's why, all application schemes that promise to get the output
LM317 adjustable voltage, starting from zero volts - do not work.
All these circuits suggest connecting the Adj pin through a resistor to the source
negative voltage.
But already when the voltage between the output and the Adj contact is less than 1.25 V
the short circuit protection circuit will operate.
All these schemes are pure theoretical fantasy. Their authors do not know how the LM317 works.

5. The output short circuit protection method used in the LM317 also imposes
known restrictions on the launch of the regulator - in some cases, the launch will be difficult,
since it is not possible to distinguish between short-circuit mode and normal-on mode,
when the output capacitor is not yet charged.

6. Recommendations for capacitor ratings at the output of the LM317 are very impressive, -
this range is from 10 to 1000 uF. What in combination with the value of the output resistance
a regulator of the order of one thousandth of an ohm is complete nonsense.
Even students know that the capacitor at the input of the stabilizer is essential,
to put it mildly, more effective than the output.

7. About the principle of regulating the output voltage of LM317.

LM317 is an operational amplifier in which the regulation
output voltage is carried out on the NOT inverting input Adj.
In other words, through the Positive Feedback Circuit (PIC).

Why is it bad? And the fact that all interference from the regulator output through the Adj input passes inside the LM317,
and then back to load. It’s good that the transmission coefficient along the PIC circuit is less than one ...
And then we would get an autogenerator.
And it is not surprising in this regard that it is recommended to put a capacitor C2 in the Adj circuit.
At least somehow filter out interference and increase resistance to self-excitation.

It is also very interesting that in the POS circuit, inside the LM317,
There is a 30pF capacitor. Which increases the level of ripple on the load with increasing frequency.
True, this is honestly shown on the Ripple Rejection chart. But why this capacitor?
It would be very useful if the regulation was carried out along the chain
negative feedback. And in the value of POS, it only worsens stability.

By the way, with the very concept of Ripple Rejection, not everything is “according to concepts”.
In the conventional sense, this value means how well the regulator
filters the ripple from the INPUT.
And for the LM317, it actually means the degree of its own inferiority
and shows how well the LM317 fights ripples, which itself
takes it from the exit and again drives it inside itself.
In other regulators, regulation is carried out along the chain
Negative feedback, which maximizes all parameters.

8. About the minimum load current for LM317.

The Datasheet specifies a minimum load current of 3.5 mA.
At a lower current, the LM317 is inoperative.
A very strange feature for a voltage stabilizer.
So, it is necessary to monitor not only the maximum load current, but also the minimum one too?
This also means that at a load current of 3.5 mA, the efficiency of the regulator does not exceed 50%.
Thank you so much developers...

1. Recommendations for the use of protective diodes for LM317 are of a general theoretical nature and consider situations that do not happen in practice.
And, since it is proposed to use powerful Schottky diodes as protective diodes, we get a situation where the cost of (unnecessary) protection exceeds the price of the LM317 itself.

2. In Datasheets LM317, the parameter for the current input Adj is incorrect.
It is measured in "special" conditions when connecting a low-resistance output divider.
This measurement method does not correspond to the generally accepted concept of "input current" and shows the inability to achieve the specified parameters during the manufacture of the LM317.
And also it is a deception of the buyer.

3. The Line Regulation parameter is specified as a range from 3 to 40 Volts.
In some application circuits, the LM317 "works" at an input-output voltage of as much as two volts.
In fact, the range of effective regulation is 7 - 40 Volts.

4. All circuits for obtaining an adjustable voltage at the output of the LM317, starting from zero volts, are practically inoperative.

5. The LM317 short circuit protection method is sometimes used in practice.
It's simple, but not the best. In some cases, the start of the regulator will be impossible at all.

7. The LM317 implements a flawed principle of output voltage regulation, -
through a positive feedback loop. It should be worse, but nowhere.

8. The limitation on the minimum load current indicates poor circuit design of the LM317 and clearly limits its use cases.

Summing up all the shortcomings of the LM317, recommendations can be made:

a) To stabilize constant "typical" voltages of 5, 6, 9, 12, 15, 18, 24 V, it is advisable to use three-pin stabilizers of the 78xx series, and not LM317.

b) To build really effective voltage regulators, you should use microcircuits like LP2950, ​​LP2951, capable of operating at an input-output voltage of less than 400 millivolts.
Combined with powerful transistors when needed.
The same microcircuits effectively work as current stabilizers.

c) In most cases, an operational amplifier, a zener diode and a powerful transistor (especially a field effect transistor) will give much better parameters than an LM317.
And certainly - the best adjustment, as well as the widest range of types and values ​​​​of resistors and capacitors.

G). And, don't blindly trust Datasheets.
Any microcircuits are made and, characteristically, sold by people ...

In amateur radio practice, microcircuits of adjustable stabilizers are widely used. LM317 and LM337. They have earned their popularity due to their low cost, availability, easy-to-install design, and good parameters. With a minimum set of additional parts, these microcircuits allow you to build a stabilized power supply with an adjustable output voltage from 1.2 to 37 V at a maximum load current of up to 1.5A.

But! It often happens that with an illiterate or inept approach, radio amateurs fail to achieve high-quality operation of microcircuits, to obtain the parameters declared by the manufacturer. Some manage to drive microcircuits into generation.

How to get the most out of these microcircuits and avoid common mistakes?

About this in order:

Chip LM317 is an adjustable stabilizer POSITIVE voltage, and the microcircuit LM337- adjustable stabilizer NEGATIVE voltage.

I draw special attention to the fact that the pinouts of these microcircuits various!

Zoom on click

The output voltage of the circuit depends on the value of the resistor R1 and is calculated by the formula:

Uout=1.25*(1+R1/R2)+Iadj*R1

where Iadj is the control output current. According to the datasheet, it is 100 μA, as practice shows, the real value is 500 μA.

For the LM337 chip, you need to change the polarity of the rectifier, capacitors and output connector.

But the meager datasheet description does not reveal all the intricacies of using these microcircuits.

So, what does a radio amateur need to know to get from these microcircuits MAXIMUM!
1. To get the maximum suppression of input voltage ripple, you must:

• Increase (within reasonable limits, but at least up to 1000 uF) the capacitance of the input capacitor C1. By suppressing the ripple at the input as much as possible, we get a minimum of ripple at the output.
• Shunt the control output of the microcircuit with a 10 microfarad capacitor. This increases ripple suppression by 15-20dB. Setting the capacity more than the specified value does not give a tangible effect.

The scheme will take the form:

2. With output voltage more than 25V in order to protect the microcircuit , for fast and safe discharge of capacitors, it is necessary to connect protective diodes:

Important: for LM337 microcircuits, the polarity of the diodes must be reversed!

3. To protect against high-frequency interference, electrolytic capacitors in the circuit must be shunted with small film capacitors.

We get the final version of the scheme:

Zoom on click

4. If you look internal structure of microcircuits, you can see that 6.3V zener diodes are used inside in some nodes. So the normal operation of the microcircuit is possible at the input voltage not lower than 8V!

Although the datasheet says that the difference between the input and output voltages should be at least 2.5-3 V, one can only guess how stabilization occurs when the input voltage is less than 8V.

5. Particular attention should be paid to the installation of the microcircuit. The diagram below shows the wiring diagram:

Zoom on click

Explanations for the scheme:

1. length of conductors (wires) from the input capacitor C1 to the input of the microcircuit (A-B) should not exceed 5-7 cm. If for some reason the capacitor is removed from the stabilizer board, it is recommended to install a 100 uF capacitor in the immediate vicinity of the microcircuit.
2. to reduce the effect of the output current on the output voltage (increasing current stability), resistor R2 (point D) must be connected directly to the output pin of the microcircuit or separate track/ conductor (section C-D). Connecting resistor R2 (point D) to the load (point E) reduces the stability of the output voltage.
3. the conductors to the output capacitor (C-E) should also not be made too long. If the load is far away from the stabilizer, then on the load side it is necessary to connect a bypass capacitor (100-200 uF electrolyte).
4. also, in order to reduce the influence of the load current on the stability of the output voltage, the "ground" (common) wire must be separated "star" from the common terminal of the input capacitor (point F).

Successful creativity!

14 comments on “LM317 and LM337 adjustable stabilizers. Application Features”

1. Chief Editor:
   August 19, 2012

   Domestic analogues of microcircuits:

   LM317 - 142EN12

   LM337 - 142EN18

   The 142EN12 chip was produced with different pinout options, so be careful when using them!

   Due to the wide availability and low cost of original microcircuits

   Better not to waste time, money and nerves.

   Use LM317 and LM337.

2. Sergei Khraban:
   March 9, 2017

   Hello, dear Editor-in-Chief! I am registered with you and I also really want to read the entire article, study your recommendations on the use of LM317. But, unfortunately, something I can not view the entire article. What do I need to do? Please give me a complete article.

   Sincerely, Sergey Khraban

3. Chief Editor:
   March 10, 2017

   Now happy?

4. Sergei Khraban:
   March 13, 2017

   I am very grateful to you, thank you very much! All the best!

5. Oleg:
   July 21, 2017

   Dear Chief Editor! I assembled two polar explorers on lm317 and lm337. Everything works fine except for the difference in tension in the shoulders. The difference is not great, but there is sediment. Could you tell me how to achieve equal voltages, and most importantly, what is the reason for such a bias. Thank you in advance for your answer. With wishes of creative success Oleg.

6. Chief Editor:
   July 21, 2017

   Dear Oleg, the difference in tension in the shoulders is due to:

   2. deviation of the values ​​of the setting resistors. It should be remembered that resistors have tolerances of 1%, 5%, 10% and even 20%. That is, if 2 kOhm is written on the resistor, its actual resistance can be in the region of 1800-2200 Ohm (with a tolerance of 10%)

   Even if you put multi-turn resistors in the control circuit and use them to accurately set the required values, then ... when the ambient temperature changes, the voltages will still float away. Since the resistors are not the fact that they will warm up (cool down) the same way or change by the same amount.

   You can solve your problem by using op-amp circuits that monitor the error signal (output voltage difference) and make the necessary correction.

   Consideration of such schemes is beyond the scope of this article. Google to the rescue.

7. Oleg:
   July 27, 2017

   Dear editor! Thank you for the detailed answer, which prompted clarifications - how critical is power supply with a difference in the shoulders of 0.5-1 volt for ULF, preliminary cascades? Regards, Oleg

8. Chief Editor:
   July 27, 2017

   The voltage difference in the arms is primarily fraught with asymmetric signal limitation (at high levels) and the appearance of a constant component at the output, etc.

   If the path does not have isolation capacitors, then even a slight DC voltage that appears at the output of the first stages will be repeatedly amplified by subsequent stages and become a significant value at the output.

   For power amplifiers powered by (usually) 33-55V, the voltage difference in the arms can be 0.5-1V, for pre-amplifiers it is better to keep within 0.2V.

9. Oleg:
   August 7, 2017

   Dear editor! Thank you for your detailed, thorough replies. And, if I may, another question: Without load, the voltage difference in the arms is 0.02-0.06 volts. When the load is connected, the positive shoulder is +12 volts, the negative is -10.5 volts. What is the reason for this shift? Is it possible to adjust the equality of the output voltages not at idle, but under load. Regards, Oleg

10. Chief Editor:
    August 7, 2017

    If everything is done correctly, then the stabilizers must be adjusted under load. The MINIMUM load current is indicated in the datasheet. Although, as practice shows, it turns out at idle.

    But the fact that the negative shoulder sags as much as 2B is wrong. Is the load the same?

    There are either installation errors, or the left (Chinese) microcircuit, or something else. No doctor will make a diagnosis by phone or correspondence. I can't heal from a distance either!

    Did you notice that LM317 and LM337 have different pin arrangement! Maybe this is the problem?

11. Oleg:
    August 8, 2017

    Thank you for your reply and patience. I'm not asking for a detailed answer. We are talking about possible reasons, nothing more. Stabilizers need to be adjusted under load: that is, conditionally, I connect a circuit to the stabilizer that will be powered from it and set equal voltages in the shoulders. Do I understand the process of setting the stabilizer correctly? Regards, Oleg

12. Chief Editor:
    August 8, 2017

    Oleg, not really! So you can burn the scheme. At the output of the stabilizer, you need to attach resistors (of the required power and rating), adjust the output voltages, and only after that connect the powered circuit.

    According to the datasheet, the LM317 has a minimum output current of 10mA. Then, with an output voltage of 12V, you need to hang a 1kΩ resistor on the output and adjust the voltage. At the input of the stabilizer, there must be at least 15V!

    By the way, how are the stabilizers powered? From one transformer / winding or different ones? When the load is connected, the minus sags by 2V - but how are things at the input of this shoulder?

13. Oleg:
    August 10, 2017

    Good health, dear editor! Trans wound himself, at the same time two windings with two wires. The output on both windings is 15.2 volts. On filter capacitors of 19.8 volts. Today, tomorrow I will conduct an experiment and unsubscribe.

    By the way, I had an incident. I assembled a stabilizer for 7812 and 7912, powered them with tip35 and tip36 transistors. As a result, up to 10 volts, the voltage regulation in both arms went smoothly, the voltage equality was ideal. But above... it was something. The voltage was regulated by jumps. And rising in one shoulder, in the second it went down. The reason turned out to be tip36, which I ordered in China. I replaced the transistor with another one, the stabilizer began to work perfectly. I often buy parts in China and came to the following conclusion: You can buy, but you need to choose suppliers who sell radio components made in factories, and not in the shops of some incomprehensible individual entrepreneur. It comes out a little more expensive, but the quality is appropriate. Regards, Oleg.

14. Oleg:
    August 22, 2017

    Good evening, dear editor! Only today there was time. Trance with a midpoint, the voltage on the windings is 17.7 volts. I hung resistors of 1 kw 2 watts at the output of the stabilizer. The voltage in both shoulders set 12.54 volts. I disconnected the resistors, the voltage remained the same - 12.54 volts. I connected the load (10 pieces of ne5532), the stabilizer works fine.

    Thank you for your advice. Regards, Oleg.

Add a comment

Spammers, do not waste your time - all comments are moderated!!!
All comments are moderate!

You must to leave a comment.

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, a game console, a landline phone, and 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 of mains voltage with output regulated 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 domestic production as regulatory, stabilizing components, 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 is an 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 middle point, 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. A bipolar key with p-n-p conductivity is used as a controlled one. 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 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 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 you can make a digital voltage regulator. 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.

The current stabilizer for LEDs is used in many fixtures. Like all diodes, LEDs have a non-linear volt-ampere dependence. What does it mean? When the voltage rises, the current slowly begins to gain power. And only when the threshold value is reached, the brightness of the LED becomes saturated. However, if the current does not stop growing, the lamp may burn out.

The correct operation of the LED can only be ensured by a stabilizer. This protection is also necessary because of the variation in LED voltage thresholds. When connected in parallel, the light bulbs can simply burn out, as they have to pass an amount of current that is unacceptable for them.

Types of stabilizing devices

According to the method of limiting the current strength, devices of a linear and pulse type are distinguished.

Since the voltage across the LED is a constant value, current regulators are often considered LED power regulators. In fact, the latter is directly proportional to the change in voltage, which is typical for a linear relationship.

The linear regulator heats up the more, the more voltage is applied to it. This is his main shortcoming. The advantages of this design are due to:

• lack of electromagnetic interference;
• simplicity;
• low cost.

More economical devices are stabilizers based on a pulse converter. In this case, power is pumped in portions - as needed for the consumer.

Line device diagrams

The simplest stabilizer circuit is a circuit built on the basis of an LM317 for an LED. The latter are an analogue of a zener diode with a certain operating current that it can pass. Given the low current strength, you can assemble a simple device yourself. The simplest driver for LED lamps and strips is assembled in this way.

The LM317 chip has been a hit with beginner radio amateurs for decades due to its simplicity and reliability. Based on it, you can assemble an adjustable driver unit and other PSUs. This will require several external radio components, the module works immediately, no settings are required.

The integral stabilizer LM317, like no other, is suitable for creating simple regulated power supplies for electronic devices with different characteristics, both with adjustable output voltage and with specified load parameters.

The main purpose is the stabilization of the given parameters. The adjustment takes place in a linear way, in contrast to pulse converters.

LM317 are produced in monolithic cases, made in several variations. The most common model TO-220 marked LM317T.

Each output of the microcircuit has its own purpose:

• ADJUST. Input for output voltage regulation.
• OUTPUT. Input for generating the output voltage.
• INPUT. Input for supplying voltage.

Technical indicators of the stabilizer:

• The output voltage is within 1.2–37 V.
• Overload and short circuit protection.
• Output voltage error 0.1%.
• Switching circuit with adjustable output voltage.

Power dissipation and device input voltage

The maximum “bar” of the input voltage should be no more than the specified one, and the minimum one should be 2 V higher than the desired output voltage.

The microcircuit is designed for stable operation at a maximum current of up to 1.5 A. This value will be lower if a good heat sink is not used. The maximum allowable power dissipation without the latter is approximately 1.5 W at an ambient temperature of not more than 30 0 С.

When installing a microcircuit, it is required to isolate the case from the radiator, for example, using a mica gasket. Also, efficient heat dissipation is achieved through the use of heat-conducting paste.

Short description

Briefly describe the advantages of the LM317 electronic module used in current stabilizers as follows:

• the brightness of the luminous flux is provided by the output voltage range 1, - 37 V;
• output indicators of the module do not depend on the frequency of rotation of the motor shaft;
• maintaining the output current up to 1.5 A allows you to connect several electrical receivers;
• fluctuation error of output parameters is 0.1% of the nominal value, which is a guarantee of high stability;
• there is a protection function for limiting current and cascading shutdown in case of overheating;
• the microcircuit housing replaces the ground, therefore, with external fastening, the number of mounting cables is reduced.

Switching schemes

Of course, the simplest way to limit current for LED lamps will be to connect an additional resistor in series. But this tool is only suitable for low-power LEDs.

The simplest stabilized power supply

To make a current stabilizer you will need:

• microchip LM317;
• resistor;
• mounting tools.

We assemble the model according to the scheme below:

The module can be used in circuits of different chargers or regulated IS.

Power supply on an integrated stabilizer

This option is more practical. LM317 limits the current consumption, which is set by the resistor R.

Remember that the maximum current you need to drive the LM317 is 1.5A with a good heatsink.

Scheme of a stabilizer with an adjustable power supply

Below is a circuit with a regulated output voltage of 1.2-30V / 1.5A.

The alternating current is converted to direct current by a bridge rectifier (BR1). Capacitor C1 filters the ripple current, C3 improves the transient response. This means that the voltage regulator can work perfectly with DC at low frequencies. The output voltage is adjusted by the P1 slider from 1.2 volts to 30 V. The output current is about 1.5 A.

The selection of resistors at face value for the stabilizer must be carried out according to an accurate calculation with a tolerance (small). However, arbitrary placement of resistors on the circuit board is allowed, but it is advisable to place them away from the LM317 heatsink for better stability.

Application area

The LM317 chip is an excellent option for use in the stabilization mode of the main technical indicators. It is characterized by simplicity in execution, inexpensive cost and excellent performance. The only downside is that the voltage threshold is only 3V. The TO220 style case is one of the most affordable models that dissipates heat fairly well.

The microcircuit is applicable in devices:

• current stabilizer for LED (including LED strips);
• Adjustable .

The stabilizing circuit based on the LM317 is simple, cheap, and at the same time reliable.