Adjustable current stabilizer LM317

The adjustable three-output current regulator LM317 provides a load of 100 mA. 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 providing output voltage. Plus, the performance instability has better parameters than similar models with a fixed output voltage.

Description

LM317 is a current and voltage stabilizer, which functions even when the ADJ control terminal 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 filter supply. In this case, an input shunt capacitor is required.

The output analog allows to improve the current stabilizer LM317. As a result, the intensity of transient processes and the value of the smoothing coefficient of pulsations increase. This optimal indicator is difficult to achieve in other three-lead analogs.

The purpose of the device in question is not only to replace stabilizers with a fixed output index, but also for a wide range of applications. For example, the LM317 current stabilizer can be used in high-voltage circuits. In this case, the individual device system affects the difference between the input and output voltages. Operation of the device in this mode can continue indefinitely, until the difference between the two indicators (input and output voltage) does not exceed the maximum permissible point.

Features

It should be noted that the current stabilizer LM317 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 supply sources, working with short-duration short-circuits, was made possible by optimizing the voltage index at the control output of the system. The program keeps it at the input within 1.2 volts, which for most loads is very small. The current and voltage stabilizer LM317 is manufactured in the standard transistor core of TO-92, the operating temperature range is -25 to +125 degrees Celsius.

Characteristics

The device in question is perfectly suited for the design of simple adjustable blocks and power supplies. The parameters can be adjustable and set in the load plan.

The adjustable current regulator on the LM317 has the following technical characteristics:

• The output voltage range is from 1.2 to 37 volts.
• Load current to a maximum of 1.5 A.
• There is protection against a possible short circuit.
• The circuit fuses are provided against overheating.
• The error of the output voltage is not more than 0.1%.
• The case of an integrated microcircuit - type ТО-220, ТО-3 or D2PAK.

The circuit of the current stabilizer on LM317

The device most commonly used is used in the power supplies of the LEDs. The simplest circuit in which the resistor and the microcircuit is involved is presented below.

The input voltage is supplied by the power supply, and the main contact is connected to the output analog with a resistor. Next, aggregation occurs with the anode of the LED. In the most popular circuit of the current stabilizer 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 is in the range 0, 01-1.5 A. Resistance of the resistor is allowed in sizes 0, 8-120 Ohm. The power dissipated by the resistor is calculated by the formula: R = IxR (2).

The information received is rounded up. Constant resistors are produced with a small spread of 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.

Advantages and disadvantages

As practice shows, the power of the resistor during operation is better to increase by dissipation area by 30%, and in the compartment of low convection - by 50%. In addition to a number of advantages, the LM317 LED current regulator has several disadvantages. Among them:

• A small coefficient of efficiency.
• The need to remove heat from the system.
• Stabilization of current is more than 20% of the limit value.

To avoid problems in the use of the instrument will help the use of impulse stabilizers.

It should be noted that if you need to connect a powerful LED element with a capacity of 700 milliamperes, you will need to calculate the values according to the formula: R = 1, 25/0, 7 = 1.78 Ohm. The power dissipation is, respectively, 0, 88 watts.

Connectivity

The calculation of the current stabilizer LM317 is based on several methods of connection. Below are the main schemes:

1. If you use a powerful transistor type Q1, you can get a current of 100 mA without the micro-assembly radiator. This is enough to control the transistor. Protective diodes D1 and D2 are used as a safeguard against excessive charge, and a parallel electrolytic capacitor performs a function to reduce extraneous noise. When using transistor Q1, the maximum output power of the device is 125 W.
2. In another scheme, the current supply is limited and the LED is stable. A special driver allows you to power elements from 0, 2 watts to 25 volts.
3. In the next design, a transformer is used to reduce the voltage from a variable network from 220 W to 25 W. With the aid of the diode bridge, the alternating voltage is transformed into a constant index. In this case, all faults are mitigated due to a capacitor of the C1 type, which ensures the stable operation of the voltage regulator.
4. The following connection scheme is considered one of the simplest. Voltage comes from the secondary winding of the transformer at 24 volts, rectified when passing through the filter, and the output produces a constant value of 80 volts. This avoids exceeding the maximum voltage threshold.

It is worth noting that a simple charger can also be assembled on the basis of the chip of the device in question. We get a standard linear regulator with a regulated output voltage. A 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 EN12 and KR115 EH1.
• Model GL317.
• Variations of SG31 and SG317.
• UC317T.
• ECG1900.
• SP900.
• LM31MDT.

Reviews

As evidenced by user feedback, the stabilizer under consideration does a good job of its functions. Especially if it concerns aggregation with LED elements, voltage up to 50 volts. Simplifies the maintenance and operation of the device, the possibility of its adjustment and connection in different schemes. There is a problem with this product in the sense that the range of output and supply voltages for it is limited to the maximum standards.

In conclusion

The LM317 adjustable integral regulator is ideally suited for the design of simple power supplies, including units and assemblies for electronic equipment, equipped with different output parameters. This can be devices with a specified current and voltage or with adjustable specified characteristics. To facilitate calculation, the instruction provides a special stabilizer calculator, which allows you to select the desired circuit and determine the possibility of adaptation.