LM1117 Linear Voltage Regulator

For our day to day need, we use various types of electrical, electronic and mechanical devices. The functioning of these devices, as well as their power requirements, is different. Due to various reasons, sometimes the power supplied to these devices can fluctuate. For such reasons, regulators like LM1117 are used. Among these, some can tolerate the fluctuations in power whereas some may get damaged. To prevent the damage caused to the devices due to an unstable power supply, we need a device that can provide a stable output voltage even when the input voltage changes. Voltage regulators came as an answer to this necessity.

What is LM1117?

LM1117 is a series of Low dropout linear voltage regulators. These have a dropout value of 1.2V at 800mA of load current. Here the low dropout means that this device can regulate the voltage even when the input voltage is closer to the output voltage.

These IC are also available as an adjustable version where one can set the output voltage from 12.5 V to 13.6V just by using two external resistors.

Circuit Diagram

The circuit of LM1117 can be understood by looking at the basic circuit of a low dropout linear voltage regulator. It consists of a Differential amplifier, a FET and resistors. In this series Zener diodes of cutoff voltage, VZ is used.

LM1117 circuit diagram
LM1117 circuit diagram

The reference voltage applied to the Differential amplifier is also equal to VZ. To keep the regulator in working condition input should be greater than the sum of output voltage and dropout value.

It is of two types. Adjustable form, in which the output voltage of the regulator can be adjusted, with the help of two external resistors. Fixed voltage form, in which the output voltage of the regulator is the fixed value. The fixed voltage form of LM1117 is available in the range of 1.8V, 2.5V, 3.3V and 5V.

In the circuit, capacitors are used to filter out the noise in the signal. Capacitors are used both at the input end and output end. The value of these capacitors can be chosen as per requirement but usually, the capacitor at the input terminal has a higher value than the capacitor at the output terminal. 10UF is the minimum value of the capacitor used at the output terminal.

The source of the FET circuit is controlled by the input voltage. Differential amplifier controls the gate of the FET circuit. When the input voltage becomes less than the sum of output voltage and dropout value, the differential amplifier makes the FET gate value zero. At this condition, FET behaves as a simple resistive circuit and the input value is equal to the output value.

LM1117 Pin Configuration

These are available as different packages by various manufacturers. Mostly these are available as DCY Package 4-pin SOT, KTT Package 3-pin TO-263, NDE Package 3-pin TO-220, NDP Package 3-pin TO-252, NGN Package 8-pin WSON.

There are three main pins on an LM1117 Package- the input pin, the output pin, the ground pin. In all the above packages pin 1 is used as a ground pin when used in fixed voltage mode and as an adjustable pin when used in adjustable mode.


Pin 3 in all the packages except WSON is used as input voltage pin of the regulator VIN. Whereas in WSON package pins 2,3,4 are used as input pins of the regulator. Pin 2 and TAB of all the packages except WSON are used as output voltage pin of the regulator VOUT.

Whereas in WSON pins 5,6,7, TAB and in package SOT-223 pins 2,4 are used as output pins of the regulator. When using WSON package pin 2,3,4 should be connected together and pins 5,6,7 must be connected together.

LM1117 Specifications

The specifications of the LM1117 are as follows

  • It can operate in the temperature range of 00C to 120oC.
    Maximum input voltage is 20V.
  • Power dissipation is internally limited.
  • These IC’s have current limiting and thermal protection circuits.
  • Electrostatic discharge of LM1117 is±2000V.
  • They are available with a minimum dropout voltage of 1.1V.
  • Minimum load current for adjustable LM1117 operating at 250c with 15V input voltage is 1.7mA. And when operating at a temperature in the range 00 to 1250c is 5mA.
  • Thermal regulation at 250c is minimum of 0.01/%W.
  • To protect the regulator from heat an external diode is attached between input and output pins.
  • These have a line regulation of 0.1%max.
  • Load regulation provided by LM1117 is 0.2%max.
  • These have moisture sensitivity of level 3.
  • For this IC the storage temperature is in the range of -650c to 1500c.

Applications of LM1117

The applications of this IC are as follows

  • LM1117 are very useful for switching DC-DC converters where they act as post regulators.
  • These are well known for applications requiring high-efficiency linear regulations.
  • These are also used in battery chargers.
  • Due to their compact design, they opt for voltage regulation in portable instruments.
  • Active SCSI Termination regulator.
  • It is a versatile and high-performance regulator.
  • Available in different temperature ranges.
  • The output voltage adjustable feature makes them a high choice for applications requiring different types of voltages.
  • Used as regulator for Arduino microprocessors.
  • These are also used as disk-drives.
  • LM1117 opt for laptops and notebook computers.

Alternative Voltage Regulators of LM1117 Series

LM1117 are available as LM1117ABC-X, where A represents the mode .i.e. either Halogen free mode or Pb mode. B represents package type either S =SOT-223,RS=SOT-89,F=TO-252. C represents MLCC applicability if C then applicable. X represents output voltage.

Some of the other voltage regulators similar to LM1117 are Infineon TLE4266GHTMA1, AMS1117 available in both fixed and adjustable ranges.

LM1117 are used in the circuits where even the slightest difference in the output voltage cannot be tolerated. These are very much opted for applications in portable devices due to their compact size. Connections of LM1117 are also simple.

LM1117 dissipate the extra voltage in the form of heat. So to prevent them from damage caused due to high temperatures, capacitors are used in the circuit. Further electrical characteristics can be found in LM1117 datasheet. Based on which of its characteristics have you chosen LM1117 for your application?


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