The AMS1117 is a common linear voltage regulator used to change a higher DC voltage into stable 3.3V or 5V output. It is simple, low-cost, and useful in small circuits, but heat, dropout voltage, capacitors, pinout, and PCB layout affect its performance. This article provides information about AMS1117 pinout, circuit design, applications, problems, and practical limits.
What Is the AMS1117 Voltage Regulator?
The AMS1117 is a three-terminal low-dropout linear voltage regulator used to convert a higher DC voltage into a stable lower DC voltage. It is used in 3.3V and 5V power rails for microcontrollers, sensor modules, development boards, and small embedded circuits.
Unlike a switching regulator, the AMS1117 does not convert power with high efficiency. It regulates voltage by dropping the extra voltage as heat. This makes it simple, low-cost, and easy to use, but it also means the device can become hot when the input voltage is much higher than the output voltage.
AMS1117 Pinout and Package Types
AMS1117 SOT-223 Pin Configuration
| Pin | Name | Function |
|---|---|---|
| Pin 1 | GND / ADJ | Ground for fixed versions or adjust pin for adjustable version |
| Pin 2 | VOUT | Regulated voltage output |
| Pin 3 | VIN | Input voltage |
| Tab | VOUT | Connected internally to output |
The SOT-223 AMS1117 is one of the most common versions used on development boards and small modules. The metal tab is connected to VOUT, not ground. This is required when designing a PCB or checking for shorts.
Fixed Version vs Adjustable Version
• AMS1117-3.3: fixed 3.3V output
• AMS1117-5.0: fixed 5V output
• AMS1117-ADJ: adjustable output using two external resistors
• Fixed versions use the first pin as GND
• Adjustable versions use the first pin as ADJ
Technical Specifications of AMS1117
| Feature | Specification | Notes |
|---|---|---|
| Max Output Current | 1A | Requires adequate heat sinking. |
| Max Input Voltage | 15V | Absolute maximum rating. |
| Dropout Voltage | 1.1V (Typ) | At 1A load. Input must be > (Vout + 1.1V). |
| Line Regulation | 0.20% | Max deviation. |
| Load Regulation | 0.40% | Max deviation. |
| Package | SOT-223 | Most common. Also available in TO-252. |
How the AMS1117 Works in a Circuit?
The AMS1117 works by maintaining a stable output voltage even when the input voltage or load current changes within its operating limits. For example, an AMS1117-3.3 can take a 5V input and provide a regulated 3.3V output for a microcontroller or sensor circuit.
Because it is a linear regulator, the unused voltage is not converted into extra current. Instead, the voltage difference between input and output is dissipated as heat. This is why AMS1117 circuits are simple but not very efficient when the input voltage is much higher than the output voltage.
For stable operation, the AMS1117 needs proper input and output capacitors. Without the correct capacitors, the output may oscillate, ripple, or become unstable when the load changes quickly.
Common AMS1117 Applications
Arduino-Compatible Boards
The AMS1117 is used on Arduino-compatible boards to convert a higher input voltage into a stable logic-level voltage, such as 5V or 3.3V. It is chosen because of its simple design and low component count.
ESP8266 / ESP32 Modules
Many ESP8266 and ESP32 development boards use the AMS1117 to provide a stable 3.3V supply rail for wireless communication modules.
Sensor Modules
The AMS1117 is often used in sensor modules because it provides simple and low-cost voltage regulation for moderate current loads.
USB-Powered Circuits
In USB-powered devices, the AMS1117 can convert the 5V USB input into a stable 3.3V output for low-voltage electronics.
Small Control Boards
Small control boards commonly use the AMS1117 because it is easy to integrate into compact PCB layouts and requires few external components.
LED Indicator Circuits
The AMS1117 can provide a stable low-voltage rail for LED indicator circuits and low-current lighting sections.
Battery Circuits
The AMS1117 may be used in some battery-powered circuits where simple voltage regulation is required.
AMS1117 5V to 3.3V Circuit Example
A common AMS1117 application is converting a 5V USB or adapter input into a 3.3V supply for low-power digital circuits. This setup is often used for microcontrollers, sensors, logic modules, and small development boards.
In the circuit, the 5V input connects to VIN, the 3.3V output is taken from VOUT, and the ground pin is shared by the input source and load. An input capacitor is placed between VIN and GND, while an output capacitor is placed between VOUT and GND. These capacitors should be placed close to the AMS1117 pins to reduce noise and improve stability.
Basic Connection Tips
| Connection | Where It Goes |
|---|---|
| VIN | 5V input |
| GND | Common ground |
| VOUT | 3.3V output |
| Input capacitor | Between VIN and GND |
| Output capacitor | Between VOUT and GND |
For example, a 5V USB input can power a 3.3V sensor board at about 150mA through an AMS1117-3.3. This is usually acceptable if the PCB has enough copper area for heat spreading and the 5V input remains stable under load.
This circuit should be checked more carefully when powering wireless modules, motors, relay boards, or other loads with current spikes. If the input voltage drops too low, the AMS1117 may fall out of regulation. If the load current is too high, the regulator may overheat. These issues are covered in the next design section.
AMS1117 Design Considerations
AMS1117 Stability and Capacitor Design
AMS1117 circuits often fail because of three design issues: unstable capacitors, insufficient input voltage headroom, and excessive heat. These problems are more common than the regulator itself failing, so the surrounding circuit should always be checked before replacing the IC.
Recommended Capacitor Setup
The AMS1117 needs proper input and output capacitors to stay stable during load changes. Poor capacitor selection or long PCB traces may cause output oscillation, startup failure, excessive ripple, or unstable voltage.
| Capacitor Location | Common Value | Main Purpose |
|---|---|---|
| Input Capacitor | 10µF typical | Reduces input noise and improves transient response |
| Output Capacitor | 10µF–22µF typical | Maintains regulator stability and smooths VOUT |
| Small Ceramic Capacitor | 0.1µF optional | Filters high-frequency noise |
AMS1117 Voltage Headroom and Dropout
AMS1117 is a linear regulator, so VIN must stay higher than VOUT by a sufficient margin. This voltage difference is called dropout voltage.
VDROP = VIN − VOUT
Many AMS1117 devices need about 1.1V to 1.3V of headroom near higher load current. For example, AMS1117-3.3 usually works from a 5V input, but problems may occur if the 5V rail drops because of USB cable loss, weak adapters, or current spikes.
AMS1117 Heat Dissipation and Thermal Control
AMS1117 converts excess voltage into heat. The larger the difference between VIN and VOUT, and the higher the load current, the hotter the regulator becomes.
Power loss can be estimated as:
P=Vin− Vout x Iload
| Example | Calculation | Result | Practical Meaning |
|---|---|---|---|
| 5V → 3.3V at 100mA | (5 − 3.3) × 0.1 | 0.17W | Manageable |
| 5V → 3.3V at 300mA | (5 − 3.3) × 0.3 | 0.51W | Warm during operation |
| 9V → 3.3V at 300mA | (9 − 3.3) × 0.3 | 1.71W | Likely too hot without cooling |
| 12V → 3.3V at 500mA | (12 − 3.3) × 0.5 | 4.35W | Not practical for AMS1117 |
This is why AMS1117 is suitable for small voltage drops, such as 5V to 3.3V, but not for high-drop, high-current conversion. For 12V to 3.3V or heavy loads, a buck converter is usually a better choice.
AMS1117 Adjustable Output Voltage Configuration
The AMS1117-ADJ version uses two external resistors to set the output voltage. It is useful when a fixed 1.8V, 2.5V, 3.3V, or 5V version is unavailable.
Vout=Vref x (1+R2/R1) +IADJ x R2
In quick design estimates, the IADJ term is often small enough to ignore.
| Target Output | Example R1 | Example R2 | Notes |
|---|---|---|---|
| 2.5V | 240Ω | 240Ω | Simple balanced setup |
| 3.3V | 240Ω | 390Ω | Common custom output |
| 5V | 240Ω | 720Ω | Requires higher VIN |
AMS1117 vs LM1117, 7805, Buck Converter, and Modern LDOs
| Option | Best Use | Advantages | Limitations |
|---|---|---|---|
| AMS1117 | Low-cost 3.3V or 5V regulation | Simple, cheap, common | Gets hot with high voltage drop |
| LM1117 | Similar LDO applications | Often comparable in function | Must check pinout and specs |
| 7805 | 5V regulation from higher voltage | Rugged and known | Higher dropout, larger package |
| Buck converter | High-efficiency voltage step-down | Better for high current and large voltage drops | More parts and switching noise |
| Modern low-IQ LDO | Battery-powered circuits | Lower standby current, better dropout options | May cost more |
Common AMS1117 Problems and Troubleshooting
| Problem | Possible Cause | What to Check |
|---|---|---|
| Output voltage is too low | Input voltage below dropout requirement | Measure VIN under load |
| Regulator gets very hot | Excessive power dissipation | Calculate power loss |
| No output voltage | Wrong pinout, bad solder joint, damaged IC | Check VIN, VOUT, and GND |
| Output is unstable | Wrong capacitor value, ESR, or placement | Check output capacitor |
| ESP32 or module resets | Current spikes or weak 3.3V rail | Test with a stronger supply |
| Output drops when load connects | Load current too high | Measure load current |
| Regulator shuts down | Thermal protection activated | Reduce input voltage or load |
| Board works without load but fails in use | Poor layout or insufficient current capacity | Test under real operating load |
Conclusion
The AMS1117 works well for simple 5V to 3.3V or 5V regulation when the load current is moderate, and heat is controlled. Its stable operation depends on correct pin connections, enough input voltage, proper capacitors, short PCB traces, and good thermal design. It is not best for large voltage drops, high-current loads, or battery circuits where efficiency matters. A buck converter or modern LDO is better for those conditions.
Frequently Asked Questions [FAQ]
Q1. Why does the AMS1117 get hot during use?
The AMS1117 gets hot because it drops extra voltage as heat. Higher input voltage and higher load current create more heat, so thermal design is important.
Q2. Can the AMS1117 really supply 1A?
Yes, but only with enough heat dissipation. In small boards, the current is lower because the regulator may overheat before reaching 1A.
Q3. Why is AMS1117 commonly used for 5V to 3.3V conversion?
Because 5V gives enough voltage headroom for a stable 3.3V output. It is simple, low-cost, and useful for microcontrollers, sensors, and small modules.
Q4. Can ceramic capacitors be used with AMS1117?
Yes, but the datasheet should be checked. Some AMS1117 versions may need a suitable output capacitor ESR range for stable operation.
Q5. Why do ESP8266 or ESP32 boards reset with AMS1117?
Wi-Fi modules draw sudden current spikes. If the supply, capacitors, or PCB traces are weak, the 3.3V rail may dip and reset the module.
