What Is a LM317K Voltage Regulator?

What Is LM317K？
- The LM317K is an adjustable three-terminal voltage regulator.
- It provides a stable output voltage between 1.25V and 37V with a maximum current of 1.5A.
- It is widely used in power supply circuits, battery chargers, and other electronic applications that require adjustable voltage regulation.
- The LM317K offers protection features such as thermal overload and short-circuit protection.
- The output voltage of The LM317K is easily set using a simple resistive divider, allowing flexibility in various applications without the need to stock multiple fixed regulators.
Pinout of LM317K
Adjust (Adj): This pin is used to adjust the output voltage. It connects to the lower part of the resistive divider that helps set the regulated output voltage.
Output (Out): This pin provides the regulated output voltage, which can be adjusted between 1.2V and 37V based on the external resistor configuration.
Input (In): This is where the unregulated input voltage is applied. The LM317K regulates this input voltage to provide a stable, adjustable output.
Test Circuit of LM317K
The LM317K is an adjustable positive voltage regulator whose output voltage can be set using two external resistors. Its basic operating principle is to control the input voltage, keeping the output voltage stable within the desired range. A typical test circuit includes a power source, the LM317K regulator, a resistive voltage divider to adjust the output voltage, and the load.
In the circuit, the input voltage is supplied to the LM317K's input pin (In), allowing current to flow into the regulator. The LM317K uses its internal control circuitry to regulate the voltage at the output pin (Out), and this output voltage can be adjusted by the two resistors connected between the adjust pin (Adj) and the output pin.
The adjust pin monitors the output voltage and makes necessary internal adjustments to maintain stability. The current flowing through the resistor network creates a voltage drop based on Ohm's law, setting the regulator's output voltage. The regulated output is then delivered to the load, ensuring consistent voltage supply.
Specification of LM317K
Input Voltage (Max): 40V
Output Voltage Range: 1.2V ~ 37V
Output Current: 1.5A
Dropout Voltage: 3V ~ 3.5V
Load Regulation: 0.1%
Line Regulation: 0.01%/V
Operating Temperature: 0°C ~ 125°C
Reference Voltage: 1.25V
PSRR: 66dB (100Hz)
Current - Quiescent (Iq): 100µA
Package Types: TO-220, TO-3, ISOWATT220, D2PAK
Features of LM317K
Output Voltage Range: 1.2 to 37V
Output Current in Excess of 1.5A
0.1% Line And Load Regulation
Floating Operation For High Voltage
Complete Series of Protections : Current Limiting, Thermal Shutdown and SOA Control
Package of LM317K
LM317K is available in a variety of packages, mainly including TO-220, TO-3, ISOWATT220 and D2PAK.
The TO-220 package usually has a large heatsink area for high power applications, has good thermal conduction properties, can effectively dissipate heat and maintain the stability of the device, and is widely used in applications that require a large power output, such as in power management and industrial equipment.
The TO-3 package is a metal package, which can directly contact with the heat sink, helping to reduce the operating temperature, more suitable for high power circuits, such as audio amplifiers and power supply modules.
The ISOWATT220 package, on the other hand, is an insulated package that effectively isolates the electrical parts from the external environment to avoid potential electrical interference, making it suitable for applications that require electrical isolation and heat dissipation.
The D2PAK package has a large bottom surface, suitable for surface mount technology, can provide better heat dissipation performance,and at the same time, can be effective in miniaturization design to save space.
Where to Use LM317K?
The LM317K is a practical adjustable voltage regulator suitable for a variety of applications. In DIY electronics projects, such as homemade power supplies, the LM317K can provide stable voltage for various electronic components. Additionally, it is widely used in audio equipment to deliver clear and stable power to amplifiers and other audio circuits. It's also well-suited for automotive electronic systems, providing voltage support for sensors and control units. In laboratory equipment, household appliances, and communication devices, the LM317K is capable of supplying the necessary power, helping us achieve various functions.
How to Use LM317K?
First, gather the necessary components, including the LM317K chip, two resistors (R1 and R2) to set the output voltage, as well as the input power supply and load.
Next, connect the positive terminal of the input power supply to the input pin (In) of the LM317K, and connect the negative terminal to ground.
Then, connect resistor R1 between the output pin (Out) and the adjustment pin (Adj) of the LM317K, and connect resistor R2 between the adjustment pin and ground. Based on the desired output voltage, you can set the output voltage by adjusting the values of R1 and R2.
Finally, connect the load to the output pin of the LM317K, turn on the power supply, and you will obtain a stable output voltage.
FAQs
How does the LM317K work?
The LM317K works by adjusting its output voltage through two external resistors (R1 and R2) connected to the adjustment (Adj) pin. It can regulate output voltage in the range of 1.2V to 37V.
How do I set the output voltage of LM317K?
The output voltage is set using two external resistors (R1 and R2) connected between the output pin (Out) and the adjustment pin (Adj), and between the adjustment pin and ground, respectively.