MOSFET (Metal Oxide Semiconductor FET)
A semiconductor switch that turns on and off with the voltage applied to its gate terminal and carries the current in the power stage. It is preferred in 12–24 V DC drivers, because in conduction it behaves like a small resistor instead of a fixed voltage drop and can typically be switched without trouble up to the order of 10–100 kHz.
A MOSFET consists of two terminals that carry the current (drain–source) and an insulated gate that controls them. Since the gate is insulated it draws no continuous current; it only asks for a pulse of current to charge and discharge the gate capacitance at the turn-on and turn-off moments. For this reason its static consumption is low while the drive circuit has to have high current capability.
In low-voltage DC drivers the advantage of the MOSFET is this: while conducting, a voltage of I × RDS(on) is dropped across it. For 15 A and 10 mΩ this is only 0.15 V. At the same current a bipolar transistor or a diode drops 0.4–0.7 V; in a 12 V system that means 3–6 percent of the power going into heat.
In AXI's DC driver family (ST42, KS250, PT500) direction and current control run through a power stage built with switches of this type. When selecting a driver you are concerned not with the MOSFET model itself but with the continuous and peak current values given by the manufacturer: 15 A continuous / 45 A peak for the KS250, 30 A continuous / 40 A maximum for the PT500.
The context in which this term is used: DC motor and driver fault diagnosis matrix