The LM317 adjustable three-terminal positive voltage regulator provides a load current of 100mA over an output voltage range of 1.2V to 37V. The regulator is very easy to use and requires only two external resistors to provide the output voltage. In addition, the voltage and current instability of the LM317 stabilizer has better performance than traditional stabilizers with a fixed output voltage value.
The advantage of IS LM317 is also that it is produced in a standard TO-92 transistor package, which is convenient for installation and installation. In addition to improved performance over traditional fixed-output voltage regulators, the LM317L provides full IC-only protection against overload, including built-in internal current limiting, overheating, and safe area correction. work.
All regulator overload protection functions also when the control output (ADJ) is disconnected. Under normal working conditions, stabilizer LM317. Does not require connection of additional capacitors, except when the regulator IC is installed far from the primary power filter capacitor; in such a situation, an input shunt capacitor is required. An alternative output capacitor improves the performance of transients in the stabilizer, and shunting the control output of the IC by the capacitor increases the value of the voltage ripple smoothing factor, which is difficult to achieve in other known three-terminal stabilizers.
In addition to replacing traditional fixed voltage regulators, the LM317 is suitable for a wide range of possible applications. So, in particular, the "floating" mode of operation of the stabilizer according to the real drop in the output voltage, in which the IC is affected only by the difference between the input and output voltage, allows it to be used in circuits with a high-voltage stabilized power supply, and the operation of the stabilizer in such a circuit can continue indefinitely , as long as the difference between the input and output voltage does not exceed the maximum allowable value.
In addition, the LM317 is useful for building very simple adjustable switching regulators, programmable output regulators, or for creating a precision current regulator based on the LM317 by connecting a fixed resistor between the control and output pins of the IC. The creation of secondary power supplies that remain operational during episodic short circuits of the output circuits is possible due to fixing the voltage level at the control output of the IC relative to ground, which programs the output voltage to be held at 1.2 V (for this voltage level, the current is quite small for the vast majority of types of loads ). The LM317 IC is produced in a standard TO-92 transistor package, and operates in a temperature range of -25 +125 "C.
The diagram of the charger on the LM317 is shown below. It uses a constant current charging method. The charge current depends on the resistance R1. The resistance rating must be in the range from 0.8 ohms to 120 ohms, which is equal to the charging current from 10 mA to 1.56 A:
Stabilized 5 Volt power supply with electronic switching:
15 volt power supply with soft start. The necessary smoothness of switching on is set by the capacitance level of capacitor C2:
Scheme of an adjustable power supply for 2-30 Volts on the LM317
The output voltage can be adjusted from 1.2 to 37 volts.
A powerful Darlington transistor Q1 is needed to increase the current of the LM317, because without a heatsink, the microassembly can only output 100 mA current, but it is quite enough to control the transistor. D1 and D2 are protective diodes against overcharging of capacitances. 100 nF capacitors are installed in parallel with electrolytic capacitors to reduce RF noise. It is desirable to put the transistor Q1 on a radiator, the maximum output power of the PSU is 125 watts.
Programmable power supply on LM317 circuit |
The circuit shown in the figure below allows you to change the output voltage by turning the transistors on and off. When the transistor is turned on, the resistance R will be connected to ground, which affects U out. The maximum circuit voltage is 27 volts at an input level of 28 V.
As bipolar transistors T1-T4, you can use 2N2222 or their analogues. The table on the left shows the output voltage of the circuit and the corresponding resistance R when one of the contacts A-D is connected to the U input.
This circuit limits the current and ensures the normal operation of the LED. This driver can power 0.2-5 watt LEDs from 9-25 volts
Not without the help of a transformer, we lower the voltage from an alternating 220 Volt to 25 Volts (you can use a transformer to another voltage convenient for you), then the alternating voltage turns into a constant one using the "diode bridge" spell and is smoothed out by the capacitor C1, then to a highly stable regulator voltage
The scheme of the device is quite simple. The voltage coming from the secondary windings of the 24-volt transformer is rectified and the output of the filter is a constant voltage of 80V, which is supplied to the voltage stabilizer, a constant voltage of 52 Volts is obtained from its output so as not to exceed the maximum threshold voltage on the microcircuit
In this electronic guide, among other usefulness, there is a calculation of the integral voltage regulator LM317
A fairly simple automatic-type memory can be assembled on the LM317 chip, which is a typical linear voltage regulator with adjustable output voltage. The microassembly can also work as a current stabilizer.
Welcome dear visitor of this web page. We would like to draw your attention to the fact that there are many schemes and options for manufacturing an LED driver using a simple current regulator on the LM317. The most time-consuming and materially costly, they are additional schematic solutions that allow, in case of critical voltage and current drops, to save the most expensive electronic components.
Scheme and principle of operation of the stabilizer up to 1.5A
To make a current stabilizer on the LM317, use the following diagram.
The minimum resistance of the resistor between the control electrode and the output corresponds to a value of 1 ohm, and the maximum value is 120 ohms. The resistance of the resistor can be selected empirically, or calculated by the formula.
I stabilization = 1.25/R
The power of the resistor when dissipating the generated heat should be enough, not only for dissipation, but also to take into account the possibility of overheating, so a power value with a good margin is used. To calculate it, you must use the following formula:
P W \u003d I² * R.
As can be seen from the formula, the power is equal to the square of the current multiplied by the resistance of the resistor. For rectification, the most efficient solution is to use a standard diode bridge. At the output of the diode bridge, a capacitor with a large capacity is installed. The LM317 LM317 uses a linear principle of operation when adjusting the current. In this regard, their strong heating is possible, due to their low efficiency. Therefore, the cooling system must be thoughtful and efficient, that is, have a radiator that can cool the electronic components well. If a low temperature has been registered while monitoring the heating temperature, then a less powerful cooling system can be used.
Current stabilizer up to 10A
The stabilization current can be increased to 10 amperes if a transistor marked KT825A and a resistance with a value of 12 ohms are added to the circuit. This distribution of electronic components is used by radio amateurs who do not have an LM338 or LM350. The circuit with a current strength of 3A is assembled on the basis of the KT818 transistor. Load amperes in any of the circuits are calculated identically.
If the radio amateur has a great desire to make a driver, but the necessary power supply is not available, then you can use alternative options.
You can use the option of series or parallel connection of resistors.
If the LEDs require a current equal to one ampere, then in the calculation we get a resistance equal to 1.25 Ohm. You will not be able to choose a resistor with such a value, because they are not produced, so you need to take the first near one, with a slightly higher resistance.
Suggest to a familiar radio amateur to change the power supply that is suitable for the parameters, to the radio component or electronic circuit he needs. To power the assembled circuit, connect a Krona battery or similar in terms of parameters to 9V. If there is no Krona, connect 6 batteries of any size at 1.5 V in series and connect them to the circuit.
We strongly advise you not to use the LM317 beyond its limits. Electronic components made in China have a low margin of safety. Of course, there is protection against short circuit or overheating, but it works successfully, not in all critical modes and situations. In such situations, in addition to the LM317, other electronic components may burn out, and this is not at all desirable.
Main parameters LM317: Input voltage up to 40V, load up to 1.5A; maximum operating temperature +125°С, short circuit protection.
The circuit of a linear integrated stabilizer with an adjustable output voltage LM317 was developed by the author of the first monolithic three-output stabilizers R. Widlar almost 50 years ago. The microcircuit turned out to be so successful that it is currently produced without changes by all major manufacturers of electronic components and is used in many devices in various switching options.
general information
The circuitry of the device provides higher rates of parameter instability, in comparison with stabilizers for a fixed voltage, and has almost all types of protection used for integrated circuits: output current limitation, shutdown in case of overheating and exceeding the limit operating parameters.
This requires a minimum number of external components for the LM317, the circuit uses built-in stabilization and protection.
The device is available in three versions -LM117/217/317, differing in the maximum permissible operating temperature:
- LM117: -55 to 150°C;
- LM217: -25 to 150°C;
- LM317: 0 to 125°C.
All types of stabilizers are produced in standard TO-3 cases, various modifications of TO-220, for surface mounting - D2PAK, SO-8. For low power devices, TO-92 is used.
The pinout for all three-pin products is the same, which makes it easy to replace them. Depending on the case used, additional designations are introduced into the marking:
- K - TO-3 (LM317K);
- T - TO-220;
- P - ISOWATT220 (plastic case);
- D2T-D2PAK;
- LZ - TO-92;
- LM-SOIC8.
All standard sizes are used for LM317, LM117 is available only in TO-3 case, LM217 - in TO-3, D2PAK and TO-220. LM317LZ microcircuits in TO-92 packages are distinguished by reduced values of maximum power and output current, up to 100 mA, with similar other properties. Sometimes the manufacturer uses its own marking, for example, LM317HV from Texas Instruments - high-voltage regulators in the range of 1.2-60 V, while the pinouts of the cases coincide with products from other companies. Unlike other microcircuits, the abbreviation LM (LM) is used by all manufacturers. Explanation of other possible designations is given in the technical description of a particular device.
Basic electrical parametersLM117/217/317
The characteristics of the regulators are determined by the difference between the input (Ui) and output voltage (Uo) 5 volts, load current 1.5 amperes and maximum power 20 watts:
- Voltage instability - 0.01%;
- Reference voltage (UREF) - 1.25 V;
- Minimum load current - 3.5 mA;
- Maximum output current - 2.2 A, with a difference in input and output voltages of not more than 15 V;
- Maximum power dissipation is limited by internal circuitry;
- Suppression of input voltage ripple - 80 dB.
It is important to note! At the maximum possible value Uin - Uout \u003d 40 volts, the permissible load current is reduced to 0.4 amperes. The maximum power dissipation is limited by the internal protection circuit, for the TO-220 and TO-3 cases - approximately from 15 to 20 watts.
Variable Stabilizer Applications
When designing electronic devices containing voltage stabilizers, it is more preferable to use a voltage regulator on the LM317, especially for critical equipment components. The use of such solutions requires an additional installation of two resistors, but provides better power parameters than traditional microcircuits with fixed stabilization voltages, they have more flexibility for different applications.
The output voltage is calculated by the formula:
UOUT = UREF (1+ R2/R1) + IADJ where:
- VREF = 1.25V, control output current;
- IADJ is very small - about 100 µA and determines the voltage setting error, in most cases it is not taken into account.
The input capacitor (ceramic or tantalum 1 μF) is installed at a significant distance from the microcircuit of the power supply filter capacitance - more than 50 mm, the output capacitor is used to reduce the effect of transients at high frequencies, for many applications it is optional. The switching circuit uses only one adjustment element - a variable resistor, in practice a multi-turn resistor is used or is replaced by a constant of the desired value. The control method allows you to implement a programmable source for several voltages, switched by any available method: a relay, a transistor, etc. Ripple suppression can be improved by shunting the control output of a 5-15 microfarad capacitor.
Diodes of type 1N4002 are installed in the presence of an output filter with large capacitors, an output voltage of more than 25 volts and a shunt capacitance of more than 10 microfarads. The LM317 microcircuit is rarely used in extreme operating conditions, the average load current for many solutions does not exceed 1.5 A. Installation of the device on a radiator is necessary in any case, with an output current of more than 1 ampere, it is advisable to use a TO-3 or TO-220 case with a metal contact platform LM317T.
For your information. You can increase the load capacity of the voltage stabilizer by using a powerful transistor as a regulating element for the output current.
The load current of the device is determined by the parameters VT1, any n-p-n transistor with a collector current of 5-10 A is suitable: TIP120/132/140, BD911, KT819, etc. Parallel connection of two or three pieces is possible. As VT2, any medium-power silicon of the corresponding structure is used: BD138/140, KT814/816.
The features of such circuits should be taken into account: the allowable difference between the input and output voltages is formed from the voltage drops across the transistor, about 2 volts, and the microcircuit, for which the minimum value is 3 volts. For stable operation of the device, at least 8-10 volts is recommended.
The properties of the LM317 series microcircuits make it possible to stabilize the load current with high accuracy over a wide range.
Fixing the current is provided by connecting only one resistor, the value of which is calculated by the formula:
I \u003d UREF / R + IADJ \u003d 1.25 / R, where UREF \u003d 1.25 V (resistance R in ohms).
The circuit can be used to charge batteries with a stable current, power LEDs, for which it is important that the current is constant when the temperature changes. Also, the current stabilizer on the LM317 can be supplemented with transistors, as in the case of voltage stabilization.
The domestic industry produces functional analogues of the LM317 with similar parameters - KR142EN12A / B microcircuits with load currents of 1 and 1.5 amperes.
An output current of up to 5 amps is provided by the LM338 stabilizer with similar other characteristics, which allows you to use all the advantages of an integrated device without external transistors. A complete analogue of the LM317 in all respects, except for polarity, is the LM337 negative voltage regulator; bipolar power supplies are easily built on the basis of these two microcircuits.
Video
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.
The LM317 adjustable voltage regulator is available in TO-220, TO-220FP, TO-3, D 2 PAK monolithic packages. The microcircuit is designed for an output current of 1.5 A, with an adjustable output voltage in the range from 1.2 to 37 V. The nominal output voltage is selected using a resistive divider.
Key Features of LM317
- Maximum input voltage 40V
- Output voltage range 1.2 to 37V
- Output current 1.5 A
- Load instability 0.1%
- current limit
- Thermal shutdown
- Operating temperature 0 to 125 o C
- Storage temperature -65 to 150 o C
Analog LM317
The domestic analogue of the LM317 is the KP142EH12A chip.
Pin configuration
The scheme of the regulated power supply on the LM317 will look like this:
The power of the transformer is 40-50 W, the voltage of the secondary winding is 20-25 volts. Diode bridge 2-3 A, 50 volt capacitors. C4 - tantalum, if this is not the case, you can use a 25 microfarad electrolyte. The variable resistor R2 allows you to adjust the output voltage from 1.3 volts, the upper limit of the output voltage will depend on the voltage of the secondary winding of the transformer. At the input of the LM317 stabilizer, there should be no more than 40 volts, the maximum output voltage will be 3 volts less than at the input. Diodes VD1 and VD2 serve to protect the LM317 in some situations.
If a fixed voltage power supply is required, then the variable resistor R2 must be replaced with a constant one, the value of which can be calculated using the LM317 calculator or using the formula from the LM317 datasheet.
On the LM317 chip, you can assemble a current stabilizer, the value and power of the resistor R1 is calculated using the LM317 calculator. This circuit is used as a power source for high-power LEDs.
Charger on LM317 (diagram from datasheet)
This charger circuit is designed for 6 volt batteries, but by selecting R2 you can set the desired output voltage for other batteries. With a rating of R3 equal to 1 Om, the charging current will be limited to 0.6 A.