ATM - How to Choose a MOSFET | DigiKey

Selecting the right MOSFET can make or break a power-switching design, whether you're driving LEDs, motors, or other loads from a microcontroller. This video walks through the essential steps of choosing a MOSFET, focusing on the practical parameters that determine reliability, efficiency, and performance in real-world circuits. We begin with a quick refresher on what a MOSFET is: an electronic switch that uses a small control signal to handle larger voltages and currents. If you already have a basic understanding of MOSFET operation but need guidance on selecting one for your project, this video is designed for you. 1. MOSFET Types and Use Cases Many Makers, engineers, and hobbyists rely on N-channel MOSFETs for low-side switching, placing the MOSFET between the load and ground. They typically offer lower on-resistance and better efficiency compared to P-channel MOSFETs, making them a common go-to for controlling DC loads. 2. Voltage Ratings: VDS & VGS We explain how to evaluate two critical voltage specifications: • Drain-Source Voltage (VDS): Choose a MOSFET rated comfortably above your supply voltage. A good rule of thumb is selecting a device with at least 1.5× to 2× the expected load voltage. This extra margin protects against ringing, spikes, and other transient events that can damage the device. • Gate-Source Voltage (VGS): Ensure the MOSFET can safely tolerate the voltage you’re using to turn it on. While many MOSFETs have a very low threshold voltage, they may also have a maximum VGS rating (for example, ±8V or ±12V). Exceeding this limit can overstress or destroy the gate. Always check that your microcontroller or driver stays within the allowable range. 3. Current Rating & RDS(on) The current a MOSFET must carry is just as important as the voltage it must withstand. • Drain Current (ID): Look for the continuous drain current value and ensure it exceeds the expected load current. As with voltage, some margin is recommended to reduce thermal stress. • RDS(on): This is the resistance across the MOSFET when it is fully on. Lower RDS(on) results in less heat, lower power loss, and higher efficiency. For high-current or battery-powered designs, a low RDS(on) can make a substantial difference in performance. 4. Switching Speed Considerations If your design uses PWM such as in dimming, motor control, or DC-DC converters, switching speed becomes a major factor. • Gate Charge (Qg): MOSFETs with lower gate charge switch faster and are easier for microcontrollers or gate drivers to control. Faster switching means less heat and better efficiency in high-frequency applications. 5. Putting It All Together The video walks through a practical example to show the selection process in context: controlling a load with a typical microcontroller, evaluating the required headroom on voltage and current, verifying that the gate drive is within limits, and checking RDS(on) to maintain efficient operation. While the example uses a 12-volt LED strip and a 5-volt microcontroller, the methodology applies to nearly any MOSFET-based power-switching application. By understanding how each datasheet parameter affects performance, you can confidently choose a MOSFET for motor control, lighting, power converters, and more.