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!
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 with 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 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 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.
Quite often there is a need for a simple voltage stabilizer. This article provides a description and examples of the use of an inexpensive (prices for LM317) integrated voltage stabilizer LM317.
The list of tasks solved by this stabilizer is quite extensive - this includes powering various electronic circuits, radio devices, fans, motors and other devices from the mains or other voltage sources, such as a car battery. The most common circuits are voltage-regulated.
In practice, with the participation of LM317, you can build a voltage stabilizer for an arbitrary output voltage in the range of 3...38 volts.
Specifications:
- Stabilizer output voltage: 1.2... 37 volts.
- Load-bearing current up to 1.5 amperes.
- Stabilization accuracy 0.1%.
- There is internal protection against accidental short circuit.
- Excellent protection of the integrated stabilizer from possible overheating.
Power dissipation and input voltage of the LM317 stabilizer
The voltage at the stabilizer input should not exceed 40 volts, and there is also one more condition - the minimum input voltage should exceed the desired output voltage by 2 volts.
The LM317 microcircuit in the TO-220 package is capable of stable operation at a maximum load current of up to 1.5 amperes. If you do not use a high-quality heat sink, this value will be lower. The power released by the microcircuit during its operation can be determined approximately by multiplying the output current and the difference between the input and output potential.
The maximum permissible power dissipation without a heat sink is approximately 1.5 W at an ambient temperature of 30 degrees Celsius or less. If good heat dissipation from the LM317 case is ensured (no more than 60 g), the power dissipation can be 20 watts.
When placing a microcircuit on a radiator, it is necessary to isolate the microcircuit body from the radiator, for example, with a mica gasket. It is also advisable to use 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 value of variable resistance R2 is directly related to the output voltage range. Typically, its resistance should be approximately 10...15% of the total resistance of the remaining resistors (R1 and R2), or you can select its resistance experimentally.
The location of the resistors on the board can be arbitrary, but for better stability it is advisable to place it away from the heatsink of the LM317 chip.
Circuit stabilization and protection
Capacitance C2 and diode D1 are optional. The diode protects the LM317 stabilizer from possible reverse voltage that appears in the designs of various electronic devices.
Capacitance C2 not only slightly reduces the response of the LM317 microcircuit to voltage changes, but also reduces the influence of electrical interference when the stabilizer board is placed near places with powerful electromagnetic radiation.
In amateur radio practice, adjustable stabilizer microcircuits 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 with 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 and obtain the parameters declared by the manufacturer. Some manage to get 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 would like to draw special attention to the fact that the pinouts of these microcircuits are various!
Click to enlarge
The output voltage of the circuit depends on the value of resistor R1 and is calculated by the formula:
Uout=1.25*(1+R1/R2)+Iadj*R1
where Iadj is the current of the control output. 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 subtleties of using these microcircuits.
So, what does a radio amateur need to know to get from these microcircuits? MAXIMUM!
1. To obtain maximum input voltage ripple suppression, you must:
- Increase (within reasonable limits, but at least up to 1000 μF) the capacitance of the input capacitor C1. Having suppressed ripple at the input as much as possible, we will get a minimum of pulsation at the output.
- Bypass the control pin of the microcircuit with a 10 µF capacitor. This increases ripple suppression by 15-20dB. Setting a capacity larger than the specified value does not produce a noticeable effect.
The diagram will look like:
2. At output voltage more than 25V to protect the chip , To quickly and safely discharge capacitors, it is necessary to connect protective diodes:
Important: for LM337 microcircuits, the polarity of the diodes should be changed!
3. To protect against high-frequency interference, the electrolytic capacitors in the circuit must be bypassed with small-capacity film capacitors.
We get the final version of the scheme:
Click to enlarge
4. If you look internal structure of the microcircuits, you can see that 6.3V zener diodes are used inside some nodes. So 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. Below is a diagram taking into account the wiring:
Click to enlarge
Explanations for the diagram:
- length of conductors (wires) from 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 µF capacitor in the immediate vicinity of the microcircuit.
- to reduce the influence 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.
- The conductors to the output capacitor (C-E) should also not be made too long. If the load is removed from the stabilizer, then a bypass capacitor (electrolyte 100-200 µF) must be connected on the load side.
- 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).
Happy creativity!
14 comments to “Adjustable stabilizers LM317 and LM337. Features of application"
- Chief Editor:
August 19, 2012Domestic 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 chips
It’s better not to waste time, money and nerves.
Use LM317 and LM337.
- Sergey Khraban:
March 9, 2017Hello, dear Editor-in-Chief! I am registered with you and I also really want to read the entire article and study your recommendations for using the LM317. But, unfortunately, I can’t view the entire article. What do I need to do? Please give me the full article.
Sincerely, Sergey Khraban
- Chief Editor:
March 10, 2017Are you happy now?
- Sergey Khraban:
March 13, 2017I am very grateful to you, thank you very much! All the best!
- Oleg:
July 21, 2017Dear Editor-in-Chief! I assembled two polar explorers on lm317 and lm337. Everything works great except for the difference in tension in the shoulders. The difference is not great, but there is a sediment. Could you tell me how to achieve equal voltages, and most importantly, what is the reason for such a imbalance? Thank you in advance for your answer. With wishes of creative success Oleg.
- Chief Editor:
July 21, 2017Dear Oleg, the difference in tension in the shoulders is due to:
2. deviation of the values of the setting resistors. Remember that resistors have tolerances of 1%, 5%, 10% and even 20%. That is, if the resistor says 2kOhm, its actual resistance can be in the region of 1800-2200 Ohms (with a tolerance of 10%)
Even if you install 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 resistors are not guaranteed to warm up (cool down) the same way or change by the same amount.
You can solve your problem by using circuits with operational amplifiers that monitor the error signal (difference in output voltages) and make the necessary adjustments.
Consideration of such schemes is beyond the scope of this article. Google to the rescue.
- Oleg:
July 27, 2017Dear editor! Thank you for your detailed answer, which prompted clarification - how critical is it for amplifier, preliminary stages, power supply with a difference in the arms of 0.5-1 volt? Regards, Oleg
- Chief Editor:
July 27, 2017The voltage difference in the arms is fraught, first of all, with asymmetrical limitation of the signal (at high levels) and the appearance of a constant component at the output, etc.
If the path does not have coupling capacitors, then even a small DC voltage that appears at the output of the first stages will be amplified many times over by subsequent stages and will become a significant value at the output.
For power amplifiers with a power supply (usually) 33-55V, the voltage difference in the arms can be 0.5-1V; for preamplifiers it is better to keep within 0.2V.
- Oleg:
August 7, 2017Dear editor! Thank you for your detailed, thorough answers. And, if you allow, another question: Without load, the voltage difference in the arms is 0.02-0.06 volts. When the load is connected, the positive arm is +12 volts, the negative arm is -10.5 volts. What is the reason for this imbalance? Is it possible to adjust the equality of output voltages not at idle, but under load? Regards, Oleg
- Chief Editor:
August 7, 2017If you do everything correctly, then the stabilizers need to be adjusted under load. The MINIMUM load current is indicated in the datasheet. Although, as practice shows, it also works at idle.
But the fact that the negative leverage sags by as much as 2B is wrong. Is the load the same?
There are either errors in installation, or a left-handed (Chinese) microcircuit, or something else. No doctor will make a diagnosis over the phone or by correspondence. I also don’t know how to heal from a distance!
Have you noticed that LM317 and LM337 have different pin locations! Maybe this is the problem?
- Oleg:
August 8, 2017Thank you for your response 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 the voltages in the shoulders to be equal. Do I understand the process of setting up the stabilizer correctly? Regards, Oleg
- Chief Editor:
August 8, 2017Oleg, not very much! This way you can burn the circuit. You need to attach resistors (of the required power and rating) to the output of the stabilizer, adjust the output voltages, and only then connect the powered circuit.
According to the datasheet, LM317 has a minimum output current of 10mA. Then, with an output voltage of 12V, you need to attach a 1kOhm resistor to 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? When a load is connected, the minus drops by 2V - but how are things at the input of this arm?
- Oleg:
August 10, 2017Good health, dear editor! The trans wound itself, simultaneously two windings with two wires. The output on both windings is 15.2 volts. The filter capacitors are 19.8 volts. Today and tomorrow I will conduct an experiment and report back.
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 proceeded smoothly, the voltage equality was ideal. But above...it was something. The voltage was regulated intermittently. Moreover, while rising in one shoulder, it went down in the second. 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 have come to the following conclusion: You can buy, but you need to choose suppliers who sell radio components made in factories, and not in the workshops of some obscure individual entrepreneur. It turns out to be a little more expensive, but the quality is appropriate. Regards, Oleg.
- Oleg:
August 22, 2017Good evening, dear editor! Only today there was time. Trans with a midpoint, the voltage on the windings is 17.7 volts. I hung 1 kohm 2 watt resistors at the output of the stabilizer. The voltage in both shoulders was set to 12.54 volts. I disconnected the resistors, the voltage remained the same - 12.54 volts. I connected the load (10 pieces ne5532) and the stabilizer works great.
Thank you for your advice. Regards, Oleg.
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