Understanding FET Part Numbers: Decoding Features and Choosing the Right FET for Your Circuit

FETs (Field Effect Transistors) come in countless part numbers, and for beginners, they can look like random strings of letters and digits. However, each model name contains hints about the manufacturer, voltage rating, gate drive level, and other key characteristics. In this post, we’ll explore how to decode common FET part numbers and how to use that information to select the right FET for your circuit.

 

 

1. IRF vs IRL: Identifying Gate Drive Levels

A good example is the difference between IRF and IRL series FETs from International Rectifier (now Infineon).

  • IRF series: Standard MOSFETs that typically require 10V or more to fully turn on the gate.
  • IRL series: Logic-level MOSFETs that can be driven directly by 5V or even 3.3V microcontrollers like Arduino or Raspberry Pi.

Choosing an IRL model ensures better switching performance in low-voltage digital systems.

 

 

2. What You Can Tell from the Part Number (Without a Datasheet)

  • Numbers: Often relate to voltage or current capacity. Ex: IRF540N ≈ 100V, 33A.
  • Suffix “N”: Usually indicates an N-channel enhancement-mode FET.
  • Suffix “P”: Indicates a P-channel version, useful in high-side switching.

While a datasheet is always essential, decoding part numbers gives you a quick overview when planning or prototyping.

An infographic illustrating how to decode FET part numbers by identifying manufacturer prefixes, series (e.g., IRF vs IRL), voltage and current hints in the digits, and suffixes like N or P to guide circuit selection.

3. Manufacturer-Specific Naming Patterns

Manufacturer Example Part Notes
IR / Infineon IRF540N, IRLZ44N Widely used for general-purpose high-current switching
STMicroelectronics STP55NF06 Voltage and current often reflected in the name
ON Semiconductor FQP30N06L FQP = ex-Fairchild series, often low-cost and popular
Vishay SIR800DP SMD-focused, high-speed switching devices

 

 

4. What to Double-Check in the Datasheet

The part number is only a hint. Before finalizing any component, you should verify these specs in the datasheet:

  • VGS(th) (Threshold Voltage): Must be compatible with your controller logic voltage.
  • RDS(on): Lower is better for efficiency and heat reduction.
  • Qg (Gate Charge): Affects how fast the MOSFET can switch.
  • Package Type: TO-220 vs SMD matters for thermal dissipation and mounting.

 

 

5. Conclusion

FET part numbers aren’t just labels — they carry real, actionable information. With a bit of practice, you can use naming patterns to anticipate specs, make smarter choices early in your design, and streamline your BOM decisions. And of course, always verify with the datasheet before committing to production.