The LM317 adjustable three-terminal current regulator provides a load of 100 mA. The output voltage range is from 1.2 to 37 V. The device is very easy to use and requires only a couple of external resistors to provide the output voltage. Plus, the performance instability is better than similar models with a fixed output voltage supply.
Description
LM317 is a current and voltage regulator that functions even when the ADJ control pin is disconnected. During normal operation, the device does not need to be connected to additional capacitors. An exception is the situation when the device is located at a considerable distance from the primary filtering power supply. In this case, you will need to install an input shunt capacitor.
Output analog allows you to improve the performance of the LM317 current stabilizer. As a result, the intensity of transient processes and the value of the ripple smoothing coefficient increase. Such an optimal indicator is difficult to achieve in other three-terminal analogues.
The purpose of the device in question is not onlyreplacement of stabilizers with a fixed output rate, but also for a wide range of applications. For example, the LM317 current regulator can be used in high voltage power supply circuits. In this case, the individual system of the device affects the difference between the input and output voltage. The operation of the device in this mode can continue indefinitely until the difference between the two indicators (input and output voltage) exceeds the maximum allowable point.
Features
It is worth noting that the LM317 current stabilizer is convenient for creating simple adjustable pulse devices. They can be used as a precision regulator by connecting a fixed resistor between the two outputs.
Creation of secondary power sources operating with non-durable short circuits became possible due to the optimization of the voltage indicator at the control output of the system. The program keeps it at the input within 1.2 volts, which is very small for most loads. The LM317 current and voltage stabilizer is manufactured in a standard TO-92 transistor core, operating temperatures range from -25 to +125 degrees Celsius.
Features
The device in question is excellent for designing simple regulated units and power supplies. In this case, the parameters can be adjusted and specified in the load plan.
The adjustable current stabilizer on LM317 has the following specifications:
- Output voltage range - from 1, 2 to 37 volts.
- Load current to the maximum - 1.5 A.
- There is protection against a possible short circuit.
- Provided circuit protection fuses to prevent overheating.
- Output voltage error is less than 0.1%.
- Integrated circuit housing - type TO-220, TO-3 or D2PAK.
Circuit current stabilizer on LM317
The most frequently considered device is used in LED power supplies. The following is a simple circuit in which a resistor and a microcircuit are involved.
A power supply voltage is supplied at the input, and the main contact is connected to the output analogue with a resistor. Next, aggregation occurs with the anode of the LED. The most popular LM317 current regulator circuit described above uses the following formula: R=1/25/I. Here I is the output current of the device, its range varies between 0.01-1.5 A. The resistor resistance is allowed in sizes of 0.8-120 Ohm. The power dissipated by the resistor is calculated by the formula: R=IxR (2).
Information received is rounded up. Fixed resistors are produced with a small spread of the final resistance. This affects the receipt of calculated indicators. To solve this problem, an additional stabilizing resistor of the required power is connected to the circuit.
Pros and cons
As practice shows, the power of the resistor atoperation, it is better to increase the dispersion area by 30%, and in the low convection compartment - by 50%. In addition to a number of advantages, the LM317 LED current stabilizer has several disadvantages. Among them:
- Small efficiency.
- The need to remove heat from the system.
- Current stabilization over 20% of limit value.
The use of switching regulators will help to avoid problems in the operation of the device.
It is worth noting that if you need to connect a powerful LED element with a power of 700 milliamps, you will need to calculate the values using the formula: R=1, 25/0, 7=1.78 Ohm. The dissipated power will accordingly be 0.88 watts.
Connection
The calculation of the LM317 current stabilizer is based on several connection methods. Below are the main schemes:
- If you use a powerful Q1 type transistor, you can get a current of 100 mA at the output without a microassembly heatsink. This is quite enough to control the transistor. As a safety net against excessive charge, protective diodes D1 and D2 are used, and a parallel electrolytic capacitor performs the function of reducing extraneous noise. When using transistor Q1, the maximum output power of the device will be 125W.
- In another circuit, current limiting and stable operation of the LED are provided. A special driver allows you to power elements with power from 0.2 watts to 25 volts.
- The next design uses a step-down transformervoltage from a variable network from 220 W to 25 W. With the help of a diode bridge, the alternating voltage is transformed into a constant indicator. At the same time, all interruptions are smoothed out by a capacitor of type C1, which ensures that the voltage regulator maintains stable operation.
- The following connection scheme is considered one of the simplest. The voltage comes from the secondary winding of the transformer at 24 volts, is rectified when passing through the filter, and a constant indicator of 80 volts is obtained at the output. This avoids exceeding the maximum voltage supply threshold.
It is worth noting that a simple charger can also be assembled based on the microcircuit of the device in question. You get a standard linear stabilizer with an adjustable output voltage indicator. The microassembly of the device can function in a similar role.
Analogues
The powerful stabilizer on the LM317 has a number of analogues in the domestic and foreign markets. The most famous of them are the following brands:
- Domestic modifications of KR142 EH12 and KR115 EH1.
- Model GL317.
- SG31 and SG317 variations.
- UC317T.
- ECG1900.
- SP900.
- LM31MDT.
Reviews
As evidenced by user feedback, the stabilizer in question does a good job of its functions. Especially when it comes to aggregation with LED elements, voltage up to 50 volts. Simplifies the maintenance and operation of the deviceadjustments and connections in different schemes. There is a complaint about this product in the sense that the range of output and supply voltages for it is limited by the maximum standards.
Finally
The LM317 integrated regulator is ideal for designing simple power supplies, including electronics units and assemblies equipped with various output parameters. These can be devices with a given current and voltage, or with adjustable specified characteristics. To facilitate the calculation, the instructions provide a special stabilizer calculator that allows you to select the desired scheme and determine the possibility of adaptation.
