There are different LM-series ICs which are made by National Semiconductor. In LM series ICs, the term ‘LM’ stands for linear monolithic, which means the analog components were incorporated into a single Si (silicon). The LM series ICs mainly include; Op-Amps, differential comparators, current mode amplifiers, audio amplifiers, instrumentation amplifiers, voltage regulators, voltage-to-frequency converters, current sources, temperature sensors, etc. This article provides brief information on one of the voltage regulator ICs like; the LM317 voltage regulator, pin configuration, specifications & its applications.
What is the LM317 Voltage Regulator?
The LM317 IC is a three-terminal and adjustable positive voltage regulator that supplies above 1.5A of current over a voltage range from 1.25V to 37V. This type of voltage regulator is very simple to use & needs two external resistors only to set the o/p voltage. In addition, this IC also uses thermal shutdown, safe area compensation & internal current limiting to make it full overload protection. For the output voltage adjustment, simply two external resistors are necessary. This IC has improved line regulation standards & load regulation. The LM317 IC can also be used as a precision current regulator by simply placing a constant resistor in between its output & adjustment terminal.
LM317 working principle is; that it supports different levels of output voltage for a stable applied input voltage supply. To control the output voltage level based on the circuit requirements, a variable resistor is simply connected at its Adj (Adjustment) terminal so that LM317 IC can reduce the voltage supply from 12V to different lower levels.
Pin Configuration:
The pin configuration of the LM317 voltage regulator is shown below. This voltage regulator IC includes three pins which are discussed below.
LM317 IC Pin Configuration
- Pin1 (Adj): This Adj pin is used to adjust the o/p voltage.
- Pin2 (Vout): This output voltage pin obtains the regulated o/p voltage which is set by the adjust pin.
- Pin3 (Vin): This i/p voltage pin which has to be adjusted can be given to this pin.
Features & Specifications:
The features and specifications of the LM317 voltage regulator include the following.
- LM317 is an adjustable positive voltage regulator.
- This regulator has three terminals.
- Its output voltage ranges from 1.25V to 37V.
- Its output current is 1.5A.
- It is available in SOT223, TO263 & TO-220 packages.
- Its max i/p to o/p voltage difference is 40 volts.
- Once the voltage difference is 15V then max o/p current will be 2.2Amps.
- Its operating junction temperature ranges from -55 to 125°C.
- It has thermal overload protection internally.
- It has floating operations mainly for high-voltage applications.
- This IC eliminates stocking several fixed voltages.
- These ICs are halogen-free, Pb-free, and BFR-free.
Equivalent and Alternative ICs
The equivalent LM317 ICs are; LT1086, PB137, LM1117 (SMD), LM337, etc. An alternative LM317 ICs are; LM7806, LM7805, LM7809, LM7812, LM7912, XC6206P332MR, LM7905, LM117V33, etc.
Adjustable LM317 Voltage Regulator Circuit
In any power supply unit of electronic equipment, an adjustable DC power supply is a primary part. Here we are designing a simple and adjustable power supply circuit with an LM317 voltage regulator IC. The circuit diagram of the adjustable lm317 voltage regulator is shown below.
The required components to make this voltage regulator circuit include; a step-down transformer, LM317 voltage regulator, 3A 50v bridge rectifier diode, 1N4002 diodes, 100 ohms resistors, 10k Potentiometer, 220uF,100uF & 10uF electrolytic capacitors, 0.33uF ceramic capacitor, breadboard, and connecting wires.
Adjustable LM317 Voltage Regulator Circuit
Working
The transformer in this circuit is used to step down the voltage from 220V AC to 24V AC. The rectifier is used to change the sinusoidal AC input to a unidirectional DC pulsating voltage which is not constant & includes ripples. A 1000uf capacitive filter in the circuit filters out most of the ripples from the bridge rectifier’s output.
An LM317 voltage regulator IC is used to change the o/p voltage from 1.25V to 37V. Here the o/p voltage mainly depends on the voltage divider circuit that can be formed with 12kohm & 220ohm resistors. A 10kohm potentiometer is utilized for adjusting the voltage at the adj terminal of the voltage regulator IC.
In this circuit, two 1N4007 diodes are connected simply in the reverse direction. If a wrong high voltage supply is provided to the voltage regulator IC, then it gets damaged. So these two diodes will guard the voltage regulator from harm by simply providing an alternate lane to the maximum current. At last, a 470uf capacitor in the circuit is parallel connected to make the o/p more constant.
Working
The working of this circuit is; that whenever a 230V of input voltage is provided at the primary winding of this transformer then it steps down to 28V 3A by maintaining 50Hz frequency. After that, this voltage signal goes through a bridge rectifier that changes the signal from AC to rippling DC. After that, the rectified voltage is fed into the input of LM317 IC and its output operating voltage ranges from 1.2V to 37V DC with up to 1.5A of maximum load current.
The two diodes like; D1 & D2 within the circuit are used to guard the voltage regulator from excess current flow throughout it if any voltage source is connected across the regulator’s output terminals. Here, the range of output voltage can be controlled by simply connecting a potentiometer to the regulator’s ADJ pin. After that, the DC signal is supplied through a 100μF smoothing capacitor before being supplied to the output. This is a variable voltage power supply circuit that provides above 32V at an output current of 1.5A.
The LM317 is a linear voltage regulator, so a heat sink must be used. The voltage drop across this IC is 2.5 volt which causes more heat so it can damage the regulator IC. Thus to guard the voltage regulator IC, you have to utilize a proper heat sink & cooling solution.
This voltage regulator circuit is used in power banks, motor speed controllers, power supply modules in lab, battery charger circuits, waveform or signal generators, home utilities, and electronic appliances.
Advantages
The advantages of the LM317 voltage regulator include the following.
- It has an overheated shutdown function.
- It is capable of short-circuit protection.
- It needs two external resistors only for adjustment of output.
- It is not expensive.
- It is reliable to utilize within commercial applications.
- It has less standby current.
- It needs low external components.
- It has a simple design, less noise, and occupies less space.
- It has a small form factor.
- The main benefit of this IC over an SMPS is its less noise, so it is ideal to use within audio projects wherever less noise is preferred.
The disadvantages of the LM317 voltage regulator include the following.
- LM317 voltage regulator generated a lot of heat, so heat sinks are necessary for high-current-based applications.
- In addition when the dissimilarity between the i/p and o/p voltage is high, then a sufficient size heat sink must be used.
- Its higher input voltage is limited to about 40V only.
- Its o/p current is also restricted to 1.5A.
Applications
The applications of the LM317 voltage regulator include the following.
- LM317 voltage regulator is used in a wide range of applications like; battery chargers, constant regulators, microprocessor supplies, Ethernet switches, automatic LED lightning, femto base stations, IP phones, hydraulic valves, motor controllers, power quality monitoring, power bank solutions, embedded systems and many more.
- This voltage regulator helps in making a programming o/p regulator (or) by simply connecting a fixed resistor in between the pins of adjustment & output, so this regulator is used as a precision current regulator.
- This IC is used in power bank solutions, motor controllers, battery chargers, ethernet switches, hydraulic valves, etc.
- This voltage regulator is applicable in washing machines, refrigerators, waveform generators, motor controllers, PLCs, power quality meters, fingerprints, automotive LED lighting, constant current regulators, private branch exchange, ethernet switches, microprocessor supplies, battery chargers, etc.
- These voltage regulators are used frequently in DC-DC converter applications.
- This IC can be used as a linear voltage regulator commonly in DC circuits.
- These are used in positive voltage regulation, solar power supply, variable power supply, etc.
- These are applicable in microcontroller-based applications, reverse polarity circuits, and current limiting circuits, used in PCs, desktops, DVDs, portable instruments & other consumer electronic devices.
Please refer to this link for the LM317 Voltage Regulator Datasheet.
Thus, this is an overview of the LM317 voltage regulator IC, pin configuration, features, specifications, circuit, working, and applications. This is a three-terminal voltage regulator IC, with 1.5A of high output current. This IC has many features like thermal protection, safe operating area protection & current limiting. If we detach the adjustable terminal of this IC, then it will be useful even in overload protection. Here is a question for you, what is a 7805 voltage regulator IC?