The LM317 adjustable three-pin current regulator provides a 100 mA load. The output voltage range is from 1.2 to 37 V. The device is very convenient to use and requires only a pair of external resistors that provide output voltage. Plus, instability in terms of performance has better parameters than similar models with a fixed output voltage.
Description
The LM317 is a current and voltage stabilizer 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, the installation of an input shunt capacitor will be required.
The output analogue improves the performance of the current stabilizer LM317. As a result, the intensity of transients and the value of the smoothing coefficient of pulsations increase. Such an optimal indicator is difficult to achieve in other three-lead analogues.
The purpose of this device is not only to replace stabilizers with a fixed output indicator, but also for a wide range of applications. For example, the LM317 current stabilizer can be used in high voltage power 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 permissible 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 stabilizer by connecting a constant resistor between two outputs.
The creation of secondary power sources operating during short-circuiting was made possible by optimizing the voltage index at the control terminal of the system. The program keeps it at the input within 1.2 volts, which is very small for most loads. The current and voltage stabilizer LM317 is manufactured in a standard transistor core TO-92, the operating temperature mode is from -25 to +125 degrees Celsius.
Specifications
The device in question is great for designing simple, adjustable units and power supplies. In this case, the parameters can be adjusted and specified in terms of load.
The adjustable current regulator on the LM317 has the following technical specifications:
- The output voltage range is from 1.2 to 37 volts.
- The maximum load current is 1.5 A.
- There is protection against a possible short circuit.
- Fuses for overheating are provided.
- The voltage error at the output is not more than 0.1%.
- Integrated circuit case - type TO-220, TO-3 or D2PAK.
Current stabilizer circuit on the LM317
The most often considered device is used in LED power supplies. The following is the simplest circuit in which a resistor and a microcircuit are involved.
The voltage of the power source is supplied at the input, and the main contact is connected to the output analog using a resistor. Next, there is aggregation with the anode of the LED. In the most popular current regulator circuit LM317, the description of which is given above, the following formula is used: R = 1/25 / I. Here I is the output current of the device, its range varies from 0, 01-1.5 A. Resistor resistance is allowed in the sizes of 0, 8-120 Ohms. The power dissipated by the resistor is calculated by the formula: R = IxR (2).
The information received is rounded up. Fixed resistors are available with a small variation in the final resistance. This affects the receipt of calculated indicators. To resolve this problem, an additional stabilizing resistor of the required power is connected to the circuit.
Pros and cons
As practice shows, it is better to increase the resistor power during operation by the dispersion area by 30%, and in the low convection compartment - by 50%. In addition to a number of advantages, the current stabilizer of the LM317 LED has several disadvantages. Among them:
- Low coefficient of performance.
- The need to remove heat from the system.
- Current stabilization over 20% of the limit value.
The use of pulse stabilizers 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 capacity of 700 milliamps, you will need to calculate the values according to the formula: R = 1, 25/0, 7 = 1.78 Ohms. Power dissipation will be respectively 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 transistor of type Q1, you can get a current of 100 mA at the output without a micro-assembly radiator. This is enough to control the transistor. Protective diodes D1 and D2 are used as security against excessive charge, 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 125 watts.
- In another circuit, current limitation 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.
- In another design, a voltage reduction transformer from a variable network from 220 W to 25 W is used. Using a diode bridge, the alternating voltage is transformed into a constant indicator. In this case, all interruptions are smoothed out due to the C1 type capacitor, which ensures the stability of the voltage regulator.
- 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 threshold.
It is worth noting that a simple charger can also be assembled on the basis of the microcircuit of the device in question. You will get a standard linear stabilizer with an adjustable output voltage indicator. In a similar role, the microassembly of the device can function.
Analogs
The powerful stabilizer on the LM317 has a number of analogues in the domestic and foreign market. The most famous of them are the following brands:
- Domestic modifications of 142 12 and 115 1.
- Model GL317.
- Variations of SG31 and SG317.
- UC317T.
- ECG1900.
- SP900.
- LM31MDT.
Reviews
According to 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 device the ability to adjust and connect it in different schemes. There is a gripe with this product in the sense that the range of output and supply voltages for it is limited by limit standards.
In conclusion
The LM317 integral regulating regulator is ideally suited for the design of simple power supplies, including units and components for electronic equipment, 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 choose the right scheme and determine the possibility of adaptation.