Get to Know the LM1117 Linear Voltage Regulator

Ⅰ. What is a voltage regulator?

Ⅱ. Overview of LM1117 linear voltage regulator

Ⅲ. Pin configuration of LM1117

Ⅳ. Features of LM1117 linear voltage regulator

Ⅴ. How does LM1117 linear voltage regulator work?

Ⅵ. How to use LM1117 linear voltage regulator?

Ⅶ. What are the advantages and disadvantages of LM1117 linear voltage regulator?

Ⅷ. What is the difference between LM1117 and LM317?

Ⅸ. Applications of LM1117 linear voltage regulator

A voltage regulator is a power supply device that can automatically adjust the output voltage, which can stabilize the power voltage that fluctuates greatly or does not meet the requirements of electrical equipment within the set range, ensuring that various circuits or electrical equipment can work normally at the rated working voltage. In this article, we will introduce the LM1117 linear voltage regulator.

A voltage regulator is an electronic component or circuit used to maintain the power supply voltage at a stable value. It mainly consists of voltage regulating circuit, control circuit and servo motor. The control circuit will sample, compare, amplify and drive the servo motor to rotate, adjusting the coil turns ratio of the voltage regulator. In this way, it can automatically adapt to changes in input voltage or load and keep the output voltage stable.

Voltage regulators are often used to keep the power supply voltage of electronic devices stable to ensure they can operate properly. It can be divided into linear regulator and switching regulator.

The LM1117 serves as a versatile voltage regulator, offering both fixed and adjustable voltage outputs. It maintains a constant voltage differential of 1.2V, even under a load current of 800mA. With a pinout identical to National Semiconductor's widely used LM317, the LM1117 provides ease of integration. In its adjustable voltage variant, the LM1117 allows users to set the output voltage within the range of 1.25V to 13.8V using only two external resistors.

In addition to this, it provides current limiting and thermal protection. The circuit includes a Zener-adjusted bandgap reference voltage to ensure that the output voltage is accurate to within ±1%. For the output, it is recommended to use a tantalum capacitor of at least 10uF to improve transient response and stability.

Replacements and equivalents:

• LM317

• LM7805

• LM7812

• LM7905

• LM117V33

As shown in the figure, LM1117 has three pins, namely input, output and ground. The input terminal (VIN) accepts high voltage input, the output terminal (VOUT) outputs a bucked low voltage, and the ground (GND) is the reference potential.

• Provides five fixed voltages: 1.8V, 2.5V, 2.85V, 3.3V and 5V.

• Multiple packages: The LM1117 series is available in TO-263, TO-220, LLP, SOT-223 and TO-252 D-PAK packages.

• Overheating protection: It has overheating protection feature to protect electronic devices from overheating.

• Current limiting and thermal protection: It provides current limiting and thermal protection features to ensure stable operation of electronic devices.

• High efficiency: It has the characteristics of high efficiency and can achieve a voltage drop of 1.2V when the load current is 800mA.

• Low quiescent current: It possesses low quiescent current features, contributing to a notable reduction in overall power consumption.

The working principle of the LM1117 voltage stabilizing circuit is based on the principle of a three-terminal voltage regulator. It consists of an input terminal, an output terminal and a ground terminal. The input terminal accepts the voltage from the power supply, and the output terminal outputs a stable voltage. In a voltage stabilizing circuit, in order to remove noise and clutter in the power supply, the input voltage passes through a capacitor filter. Next, the voltage goes to a reference voltage circuit in the regulator chip. This circuit will stabilize the voltage at a fixed value. An error amplifier then compares the reference voltage to the output voltage and amplifies the error signal. Finally, the error signal is passed through a power amplifier to control the output voltage to keep the output voltage stable.

The LM1117 proves to be an uncomplicated component for application. When employing the IC with a fixed voltage regulator, utilize the Vin pin for powering and the Vout pin for obtaining a regulated output. In such instances, the Adj/Ground pin serves solely as a ground connection. To mitigate noise, introducing a capacitor on the output side is advisable. The circuit diagram of a fixed output regulator is given below.

In this circuit, capacitors are connected to the input and output and they perform the function of filtering noise from the output voltage signal. A capacitor of at least 10uF is usually used on the output, but the value of the input capacitor is usually higher than the output capacitor. The output capacitor is responsible for providing stable voltage and improving transient response.

For an adjustable regulator, we need two external resistors to determine the output voltage of the regulator. The reference circuit diagram is shown below. Among them, resistors R1 and R2 are the key components for regulating the output voltage. If further improvement of ripple suppression is required, we can add capacitor CAdj. Additionally, we need two capacitors to filter input and output noise.

The formula for calculating the regulator output voltage is given below. We choose the values of R1 and R2 based on the output voltage required for the project. It should be noted that the value of R1 should be less than 1k. If we want to change the voltage in real time, we can use a variable resistor on R2.

Vout = 1.25 (1 + R2 / R1)

The LM1117 is commonly employed in battery charging circuits due to its capability to function as either a fixed voltage or variable voltage regulator. Additionally, it can be configured to deliver negative voltage if needed.

1. Advantages of LM1117

(1) Overheating protection function: It can automatically detect chip overheating and adjust it.

(2) Good stability: It has a built-in reference voltage source and can be adjusted according to different load conditions.

(3) High efficiency: It has extremely low quiescent current and high accuracy of output voltage.

2. Disadvantages of LM1117

(1) It cannot achieve high voltage reduction to negative voltage output.

(2) It cannot achieve high efficiency comparable to switching regulator devices.

First, the LM1117 is a low dropout linear regulator suitable for applications with a lower input voltage range (typically 1.8V to 15V). In contrast, the LM317 is an adjustable linear regulator with a wider input voltage range (typically 3V to 40V). Between the two, the LM317 has a wider output voltage range, typically 1.2V to 37V.

Secondly, the LM1117 and LM317 differ in their pinout. LM1117 has three pins, namely input (VIN), output (VOUT) and ground (GND). The LM317 has five pins, including input (VIN), output (VOUT), ground (GND), adjustment pin (ADJ) and current limit pin (LOCK).

• Communication equipment: LM1117 can effectively provide stable power supply for wireless communication equipment, network equipment and other communication systems, allowing them to maintain normal operation under various harsh power conditions.

• Embedded systems: It is frequently employed to ensure a consistent power source for microcontrollers, sensors, and various other devices.

• Consumer electronics: Due to its compact package and reliable performance, LM1117 is widely used in various consumer electronics, such as tablets, smartphones, digital cameras, etc.

• Industrial automation: It can be used to provide the stable power required for various sensors and actuators.

• Instruments and measuring equipment: The LM1117 finds extensive use across various instruments and measuring devices, playing a crucial role in guaranteeing both the precision of measurements and the reliability of equipment.

• Automotive electronics: It can be used to provide power for various electronic devices, such as in-car entertainment systems, navigation systems, etc.

• Electronic equipment power management: LM1117 is widely used in electronic equipment to provide stable voltage output for other components to ensure that they operate normally within the appropriate voltage range.

Frequently Asked Questions

1. What is the LM1117?

The LM1117 is a low dropout voltage regulator IC that provides a stable output voltage from a higher input voltage. It is commonly used to regulate the voltage in electronic circuits.

2. What is the input voltage of LM1117?

The LM1117 is available in an adjustable version, which can set the output voltage from 1.25 V to 13.8 V with only two external resistors. In addition, the device is available in five fixed voltages, 1.8 V, 2.5 V, 3.3 V, and 5 V. The LM1117 offers current limiting and thermal shutdown.

3. What is the function of LM1117?

The LM1117 is a low dropout voltage regulator with a dropout of 1.2 V at 800 mA of load current. The LM1117 is available in an adjustable version, which can set the output voltage from 1.25 V to 13.8 V with only two external resistors.

4. How to use LM1117?

To set up, attach one capacitor from the output pin of the LM1117 to the ground pin of the LM1117. Next, do the same going from the input pin to the ground pin. These capacitors are polarized. Ensure the positive leg of the capacitor is in the input/output and the negative leg is connected to ground.

5. What is the difference between LM1117 and LM317?

The main difference is dropout voltage. It is 1.2V for the lm1117 and about 3V for the LM317, so it depends upon the supply voltage that powers the regulator as to which one you can use. The LM1117 would require a minimum of 4.5V supply voltage (allowing operation from a standard 5V supply).