The LM1117 is a low-dropout linear voltage regulator used to turn a higher DC input voltage into a stable lower output voltage. It is commonly used in circuits that need 3.3V, 5V, 2.5V, 1.8V, or a custom adjustable voltage. The article explains these points clearly, from pinout and fixed or adjustable versions to application circuits, capacitor stability, comparisons with other regulators, and practical selection tips.

Catalog

LM1117 Pinout and Package Types

LM1117 Fixed and Adjustable Output Versions

The LM1117-1.8

How the LM1117 Works Internally

The image shows the functional diagram of the LM1117 linear voltage regulator. It helps explain how the regulator keeps the output voltage stable while also protecting the device from unsafe operating conditions.

Inside the LM1117, the regulator compares the output voltage with an internal reference voltage. If the output voltage drops because the load current increases, the internal control circuit adjusts the pass transistor so more current can flow to the output. If the output voltage becomes too high, the control circuit reduces the drive to the pass transistor. This feedback action keeps the output voltage close to its rated value.

The diagram also shows two important protection blocks: current limit and thermal limit. The current limit helps protect the regulator when the load draws too much current or when a short circuit happens at the output. The thermal limit helps shut down or reduce operation when the chip becomes too hot. These protections make the LM1117 safer to use, but they do not replace proper circuit design.

For fixed-output versions, the ground pin sets the reference point for the output voltage. For the adjustable version, the ADJ pin works with external resistors to set the required output voltage. This is why the LM1117 can be used either as a simple fixed-voltage regulator or as a custom adjustable regulator.

Key Features of LM1117

LM1117 Technical Specifications

LM1117 Adjustable Regulator Circuit

This circuit shows the LM1117-ADJ used as an adjustable voltage regulator. The output voltage is set by resistors R1 and R2, based on the formula shown in the diagram. The input capacitor helps smooth the incoming supply, while the output capacitor keeps the regulated voltage stable. The optional CADJ capacitor can improve ripple rejection, which helps reduce output noise. This design is useful when the circuit needs a custom voltage instead of a fixed 3.3V or 5V output.

LM1117 Load Regulation Circuit

This circuit shows how the LM1117 can reduce voltage error caused by wiring, PCB trace resistance, or load distance. The regulator adjusts the output based on the voltage reaching the load, not only the voltage at the regulator pin. This helps keep the load voltage more accurate when current flows through resistance in the path. It is useful for circuits where the load is farther from the regulator or where voltage drop may affect performance.

LM1117 5V to 3.3V Regulator Circuit

This circuit shows a fixed LM1117-3.3V regulator converting a 5V input into a stable 3.3V output. The input and output capacitors help filter noise and support stable operation. The LED and resistor act as a power indicator for the 5V input line. This type of circuit is commonly used to power 3.3V microcontrollers, sensors, communication modules, and digital logic devices.

Capacitor Selection for LM1117 Stability

Capacitor selection is important because the LM1117 needs proper input and output capacitors to keep the output voltage stable. The input capacitor helps reduce noise and voltage dips from the supply source, especially when the regulator is placed far from the main power input. The output capacitor is more critical because it affects regulator stability, ripple control, and load response.

A wrong capacitor value or unsuitable ESR can cause output oscillation, voltage ripple, startup problems, or random circuit resets. In a typical LM1117 circuit, the capacitors should be placed close to the regulator pins, with short PCB traces and a good ground path. This reduces unwanted resistance and inductance in the layout. For best results, always follow the datasheet recommendations for capacitor value, capacitor type, and ESR range, especially when using ceramic, tantalum, or electrolytic capacitors.

LM1117 vs Other Voltage Regulators

The LM1117 is often compared with AMS1117, 7805 regulators, modern LDOs, and buck converters because all of them can provide a regulated DC output. However, they are not the same in real circuit design. Some are better for simple low-noise regulation, while others are better for higher efficiency, lower heat, or battery-powered devices.

LM1117 vs AMS1117

The LM1117 and AMS1117 are very similar because both are 1117-style low-dropout linear voltage regulators. They are commonly used for 3.3V and 5V power rails in microcontroller boards, sensor modules, and small embedded circuits. Their basic circuit connection is also similar because both usually need input and output capacitors for stable operation.

The main difference is source and specification control. LM1117 is a regulator family from major manufacturers such as Texas Instruments, while AMS1117 is commonly produced by different suppliers. Because of this, AMS1117 parts may vary more in output accuracy, dropout voltage, thermal behavior, and capacitor requirements. In simple circuits, both may work as replacements, but in a reliable product design, the exact datasheet of the chosen part should always be checked.

LM1117 vs 7805 Voltage Regulator

The LM1117 and 7805 are both linear voltage regulators. This means they control voltage by dropping the extra input voltage, and the unused power becomes heat. They are both simple to use, but they are not equally suitable for low-voltage designs.

The 7805 is mainly a fixed 5V regulator and usually needs a higher input voltage to maintain a stable 5V output. The LM1117 has a lower dropout voltage, so it can regulate with a smaller difference between input and output. This makes the LM1117 more suitable for circuits such as 5V to 3.3V conversion. The 7805 is still useful in older or basic 5V power supply circuits where the input voltage is high enough and heat dissipation is properly handled.

LM1117 vs Modern LDO Regulators

The LM1117 is simple, affordable, and easy to find, but many newer LDO regulators offer better performance for modern electronics. Modern LDOs often have lower dropout voltage, lower quiescent current, improved transient response, smaller packages, and better support for ceramic capacitors.

This difference matters in battery-powered and compact devices. The LM1117 can still work well in simple circuits where power loss is acceptable and the load current is moderate. Modern LDOs are usually better when the design needs longer battery life, less heat, smaller board space, or stable operation with small ceramic capacitors. For new product designs, a modern LDO is often a better choice unless the LM1117 already fits the electrical and thermal requirements.

LM1117 vs Buck Converter

The LM1117 and a buck converter can both reduce a higher DC voltage to a lower DC voltage, but they work in very different ways. The LM1117 is a linear regulator, so it is simple and produces a clean output with low noise. Its main weakness is heat, because the voltage difference between input and output is wasted as power.

A buck converter is a switching regulator. It is more efficient because it transfers energy using switching components instead of simply burning off the extra voltage as heat. This makes a buck converter better for large voltage drops, higher load current, and battery-powered systems. For example, using the LM1117 to convert 12V to 3.3V can create too much heat, while a buck converter can do the same job with much less power loss.

How to Choose the Right LM1117 Version

Choose the Correct Output Voltage

Start by checking the voltage needed by your circuit. Use LM1117-3.3 for 3.3V microcontrollers, sensors, wireless modules, and logic circuits. Use LM1117-5.0 when the circuit needs a regulated 5V supply. If your circuit needs a less common voltage, such as 1.8V or 2.5V, choose the matching fixed version. A fixed-output LM1117 is easier to use because it does not need external resistors to set the voltage.

Use the Adjustable Version for Custom Voltages

Choose LM1117-ADJ when your circuit needs an output voltage that is not available in the fixed versions. The adjustable version uses two external resistors to set the output voltage. This gives more design flexibility, but it also needs careful resistor selection and layout. It is useful for custom analog circuits, test supplies, or special logic voltage rails.

Check the Input Voltage Headroom

The input voltage must be higher than the output voltage by at least the required dropout voltage. For example, a 3.3V LM1117 usually needs around 4.5V or higher input for stable operation under heavier load. If the input voltage is too low, the output may drop below the rated voltage. Always check the lowest possible input voltage, not only the normal input voltage.

Estimate the Load Current

The LM1117 can supply up to about 800 mA, but this does not mean every circuit can safely use the full current. The actual safe current depends on input voltage, output voltage, package type, PCB copper area, and temperature. For small loads such as sensors, logic ICs, and microcontrollers, the LM1117 is usually practical. For high-current modules, motors, LEDs, or wireless devices with large current peaks, check the power and heat carefully.

Check Heat Dissipation

Heat is one of the most important limits when choosing an LM1117 version. The regulator turns the voltage difference into heat, so a large input-to-output voltage drop can make the device very hot. For example, converting 12V to 3.3V is usually not a good use of the LM1117 at medium or high current. If the circuit needs to drop a large voltage or supply higher current, a buck converter is usually a better choice.

Select the Right Package

Choose the package based on board space and heat dissipation needs. SOT-223 is common for compact PCB designs, but it needs enough copper area to spread heat. TO-220 is easier to cool and can be used with a heatsink. TO-252 and TO-263 are suitable for surface-mount designs that need better thermal performance. The package should match both the mechanical layout and the expected power dissipation.

Follow the Capacitor Requirements

The LM1117 needs proper input and output capacitors for stable operation. The output capacitor is especially important because the wrong value or ESR can cause oscillation, ripple, or startup problems. Choose capacitor values based on the datasheet and place them close to the regulator pins. Do not place the capacitors far away from the device, because long traces can reduce stability.

Check the Manufacturer Datasheet

Not all 1117 regulators have exactly the same performance. Dropout voltage, tolerance, package pinout, thermal resistance, and capacitor requirements can differ by manufacturer. Before finalizing the design, check the datasheet for the exact LM1117 part number you are using. This is especially important when replacing LM1117 with AMS1117 or another compatible-looking regulator.

Match the LM1117 to the Application

The LM1117 is a good choice for simple power rails, prototype boards, microcontroller circuits, sensor supplies, and local post-regulation after a switching regulator. It is less suitable for battery-powered products, high-efficiency systems, large voltage drops, or compact devices with limited heat dissipation. Choose the LM1117 only when its voltage, current, thermal, and stability requirements fit the real operating conditions of the circuit.

LM1117 Linear Voltage Regulator Uses

• 3.3V microcontroller power supply - The LM1117-3.3 is commonly used to power microcontrollers that need a stable 3.3V rail.

• Sensor module power regulation - It can provide a clean voltage for low-power sensors used in embedded and IoT circuits.

• 5V to 3.3V conversion - The LM1117 is often used when a 5V supply must be stepped down to 3.3V for logic devices.

• Prototype and breadboard circuits - It is useful in simple test circuits because it needs only a few external components.

• Arduino and development boards - Many development boards use 1117-style regulators to create local 3.3V or 5V power rails.

• Logic IC power supply - It can power digital logic circuits that require fixed low-voltage operation.

• Post-regulation after a buck converter - The LM1117 can clean up the output of a switching regulator when lower noise is needed.

• Small analog circuits - It can supply stable voltage for basic analog sections, reference circuits, and signal-conditioning stages.

• Communication modules - It can power low-to-moderate current modules such as Bluetooth, RF, or simple serial communication circuits.

• Battery-powered circuits with light loads - It may be used in simple battery circuits, but only when the voltage drop, current, and heat are within safe limits.

• Fixed local power rails on PCBs - It is useful for creating a local regulated supply near a specific IC or circuit section.

• Adjustable voltage test circuits - The LM1117-ADJ version can be used when a custom output voltage is needed for testing or special circuit requirements.

Mechanical Dimension

Conclusion

The LM1117 linear voltage regulator remains a practical choice for simple, low-cost, and moderate-current power supply circuits. It is especially useful when converting 5V to 3.3V, powering small embedded circuits, or creating a clean local voltage rail near a sensitive IC. Its fixed-output versions are easy to use, while the adjustable version gives more flexibility for custom voltage designs. Texas Instruments is one of the well-known manufacturers associated with the LM1117 regulator family.