What is an LM117 Linear Voltage Regulator : Features and Working

Due to unpredictable loads or based conditions of the local power grid, the voltage levels of the power supply received at the load end or consumer end fluctuate. These voltage fluctuations could shorten the lifespan of the consumer’s electrical and electronic products or harm the loads. Therefore, it is necessary to protect loads from over and under voltages or to supply a constant voltage to the loads to preserve system voltage stability. Voltage regulators are used for voltage regulation because it is necessary to maintain constant voltage or keep a system’s voltage level within acceptable bounds under a variety of load scenarios. For linear voltage regulation, an occasionally adjustable LM317 voltage regulator is used wherein the non-standard voltage is intended.

What is the Voltage Regulator?

Voltage regulators are electrical or electronic devices that are used to regulate the voltage in a power supply system. Voltage regulators come in a variety of designs, including fixed and variable voltage regulators. Again, these are classified into a wide variety of sorts, including electronic voltage regulators, electromechanical voltage regulators, automatic voltage regulators, linear voltage regulators, switching regulators, LM317 voltage regulators, hybrid regulators, SCR regulators, and others.

LM317 Voltage Regulator

Robert C. Dobkin and Robert J. Widlar created a class of positive-linear-voltage regulators for voltage regulation in 1970 while they were employed with National Semiconductor. It is a three-terminal adjustable voltage regulator that is simple to use because the LM317 voltage regulator circuit just needs two external resistors to control the output voltage. It mostly serves local and on-card regulatory purposes. The LM317 regulator can be used as a precision current regulator if a fixed resistor is connected between the output and adjustment.

The input pin, output pin, and adjustment pin are the three terminals. A common arrangement of the LM317 voltage regulator circuit diagram, including the decoupling capacitors, is depicted in the figure below. This LM317 circuit has a 1A output and a 30V range of adjustment, and it can offer variable DC power. A resistive voltage divider, a passive linear circuit used to generate an output voltage that is a portion of its input voltage, is created by connecting a low-side resistor and a high-side resistor in series.
Decoupling capacitors are used to decouple electrical circuit components from one another or to stop this from happening. The decoupling capacitors in the circuit are utilized for addressing the input noise and output transients to prevent the effect of noise created by some circuit parts over the remaining circuit elements. The circuit uses a heat sink to prevent overheating of the components from increased power dissipation.

There are some special features of the LM317 regulator and a few are as follows.

It is capable of providing an excess current of 1.5A, hence it is conceptually considered an operational amplifier with an output voltage ranging from 1.2V to 37V.
The LM317 voltage regulator circuit internally consists of thermal overload protection and short circuit current limiting constant with temperature.
It is available in two packages as 3-Lead Transistor Package and surface mount D2PAK-3.
Stocking many fixed voltages can be eliminated.

Due to its capacity to produce excess output current, the LM317 regulator is conceptually regarded as an operational amplifier. The non-inverting input of the amplifier is set using an internal bandgap reference voltage, and the adjustment pin serves as the amplifier’s inverting input. This produces a stable reference voltage of 1.25V.
A resistive voltage divider between the output and ground can be used to continually change the output pin voltage to a set value, converting the operational amplifier to a non-inverting amplifier.
To maintain a consistent output voltage regardless of variations in source power, a bandgap reference voltage is employed. A temperature-independent reference voltage is another name for it, and integrated circuits routinely employ it.
The output voltage (ideally) of the LM317 voltage regulator circuit
Vout = Vref (1+ (RL/RH))
An error term is added because some quiescent current flows from the adjustment pin of the device.
Vout = Vref (1+(RL/RH)) + IQR
The LM317 voltage regulator circuit schematic is made to have a quiescent current less than or equal to 100 micro Ampere to produce a more stable output. Thus, the inaccuracy can be disregarded in all real-world scenarios.
The setup of the LM317 regulator will control the current to a load if the load is used in place of the low-side resistor of the divider in the LM317 voltage regulator circuit diagram. As a result, the LM317 circuit in question can be thought of as a current regulator circuit.

The output current is the voltage drop of reference voltage across the resistance RH and is given as
Output current in the ideal case is
Iout = Vref/RH
Considering the quiescent current, the output current is given as
Iout = (Vref/RH) + IQ
The LM317 and LM337 linear voltage regulators are often employed in DC-DC converter applications. Naturally, linear regulators supply as much current as they use. The power generated as a result of this current’s multiplication by the voltage difference between the input and output will be lost as heat and dissipated.
Because of this, heat must be taken into account during important design, which results in inefficiency. The power that is wasted will rise as the voltage differential widens, and occasionally this wasted power will exceed the amount that was given.
We must accept this trade-off even though it is negligible since linear voltage regulators with a few extra components are a straightforward approach to attaining stable voltage. The switching voltage regulators are an alternative to conventional linear regulators because they are typically more efficient, but their design calls for more components, which takes up more room.
I hope that this article provides a concise overview of the LM317 voltage regulator circuit’s operation. You can also get in touch with us by leaving comments or questions in the space below if you have any questions about voltage regulators and their uses.