Why MOSFETs

Metal-oxide semiconductor field-effect transistors, or MOSFETs for short, are transistors designed to switch large currents based on gate voltage. Unlike regular BJT transistors, MOSFETs do not require current flow through the gate and are instead switched on the voltage applied to the gate. MOSFETs are also extremely efficient, making them suitable for switching of the large currents involved in an AEG. Typical MOSFETs have 3 pins: Source, Drain, and Gate, abbreviated "S", "D", and "G" respectively. When a positive charge is allowed to accumulate at the Gate pin, the MOSFET allows current to flow between the Drain and Source pins. Conversely, if the charge at the Gate pin is discharged, the MOSFET becomes an extremely large resistor, preventing current flow between Drain and Source. In this way, the MOSFET acts as a solid state switch, turning current on and off based on voltage at the gate.

Using MOSFETs in an AEG isolates the contact switches from the main conduction path, allowing current to flow directly to the motor without encountering the added resistance of the contacts. Additionally, with the primary current isolated, the trigger and selector plate contacts are not subject to the detriments of arcing due to the inductive load presented by the motor. This effectively eliminates the prospect of burned or melted contacts when very high currents are used.

The numerous benefits of incorporating MOSFETs into AEG fire control have long been explored by the Japanese airsoft community, such as this excellent article at "Gun Engineer". Building upon their experiences, we explore the installation of a MOSFET on our test platform G3 SG1 and document any gains which result.