Mosfet Guide - Basics
This guide goes over what a mosfet is, the different types, and why you need one.
For a comparison of mosfet functions, check out our Mosfet Guide - Functions article, which will help decide which to choose for your airsoft gun or M-Trigger.
Mosfet Basics
A MOSFET (Metal Oxide Semiconductor Field Effect Transistor) is a general electronic device that is widely used for switches in various electronics, not just airsoft. When specifically discussing airsoft uses, mosfets are used for diverting the electrical current away from the trigger contacts.
The trigger in AEG’s works by simply touching two metal contacts together when you pull the trigger. This closes the electrical circuit and allows the current from the battery to flow through the wires to the motor. When using high powered batteries such as 11.1 volt LiPo batteries, the electrical current is great enough to cause arcing between the trigger contacts. This arcing will appear like burn marks, and eventually lead to the failure of the trigger.
When installed into the wiring of an airsoft gun, the mosfet redirects the current from the battery to go straight to the motor without going through the trigger contacts first. Mosfets use an additional wire called a signal or trigger wire that lets the mosfet know when the trigger is pressed. This signal wire is only used to tell the mosfet when to fire. Only a very small amount of current goes through, thus saving your trigger from arcing damage.
By adding a mosfet, the reliability of you AEG goes up along with performance. The lower electrical resistance of the mosfet circuit can lead to small performance gains in both trigger response (semi auto speed) and full auto rate of fire.
Mosfet Types
There are several types of mosfets:
Just plain mosfets (Nukefet)
Plug and play mosfets (Burst Wizard)
Programmable mosfets/fire control units (Merf, Warfet)
Drop-in triggerboard replacements (Gate Titan and Aster, BTC Spectre and Chimera, etc.)
Most airsoft mosfets also come with additional functions or features. Strictly speaking, a mosfet is only a specific part of the whole circuit board that redirects the electrical current. Any other functions or features are controlled by additional electronics or programming, not by the mosfet. However, the airsoft community still generally refers to any circuit board with mosfet functions as just a “mosfet.”
Just Plain Mosfets
These mosfets are simple enough that it is not uncommon for airsofters to just build their own. Mosfets like these have one job: protecting the trigger contacts. These are budget friendly ($15-$30), small, and work great if you don’t want any customizable controls for your AEG.
Plug-and-Play Mosfets
Be careful with these. Remember that a mosfet’s main purpose is to protect the trigger contacts. Plug-and-play mosfets are advertised as just being plugged in between the existing AEG wiring and your battery. Without doing any rewiring, nothing has changed! All of the battery’s current is still going through the trigger contacts like before. Plug-and-play mosfets usually come with features like burst fire. If all you are looking for is to add burst fire to your gun, then these will do it, but do not expect them to protect your trigger contacts without doing some rewiring first. Some plug and play mosfets also have the option for hardwiring, which is recommended for trigger protection.
Programmable Mosfets/Fire Control Units
Some of the more popular mosfets grant you the ability to add customizable functions to your AEG. Gate is the most popular manufacturer of programmable mosfets. These mosfets can be programmed by entering programming mode, counting trigger pulls, and following along with the manual. The Gate Warfet has a programming card that makes it much easier to program and doesn’t involve trigger pulls. The programmable functions control how the electrical current is delivered to your gearbox. These are good choices for airsofters who want more function out of their AEG’s, and are almost a necessity for higher end builds that need some electronic control for optimal performance. The cost is slightly higher ($35-$80), but let you tune your gun exactly how you want it. For more info on the different functions and models of mosfets, check out Part 2.
Drop-in Trigger Board Replacements
The most sought-after (and most expensive) mosfets are the drop-in trigger boards. The BTC Specter and Chimera, the Gate Titan and Aster, Jefftron, and others are some examples. These mosfets directly replace the moving trigger contacts with sensors (either microswitches or optical sensors). If you want to change how the trigger feels to your finger, these are the only ones that will do that. Trigger feel is usually much lighter and shorter compared to traditional trigger contacts. Functionally, they have several features that are not offered in other mosfets. The improved trigger feel, ability to change setting via bluetooth, and cycle completion are the biggest reasons for choosing a drop-in vs. regular mosfet. The downsides are the cost ($100-$150) and compatibility issues. If you have unique guns that do not use a typical V2 (M4) or V3 (AK) gearbox, these will not fit at all. You also need to buy one of these for each gun you want it for, whereas other Gate mosfets can be switched around to whichever gun you want to use. Most airsofters who want to build the best gun they can choose to use drop-in mosfets.
Do I need a mosfet?
If you want to get the most out of your AEG, then YES! Besides cost and labor, there are no downsides to using a mosfet. You will get better performance and more reliability no matter which you choose and no matter what battery you are using.
If you are using an 11.1 lipo battery, then it is almost mandatory so you do not burn out your trigger contacts. Using an 11.1 temporarily is not going to be catastrophic, however prolonged use (6-12 months) is not recommended.
Mosfets are becoming more and more popular in the airsoft community. Some manufacturers (Krytac, G&G) are putting mosfets in their guns straight from the factory. The success of the Gate Titan (and the BTC mosfets before it) have made mosfets become the standard for upgraded guns and is leading to more options on the market.