Electric OU: MOSFETs…How Do They Work — basic review
Gate current, gate voltage, linear operation region of the IRFPG50 mosfet. The gate current required to turn the mosfet on is shown to be extremely small and operating only during the turn-on and turn-off, not during the ON or OFF periods themselves. This is because the FIELD EFFECT TRANSISTOR operates by the electric field of the gate charge…. and this charge is small and requires only a tiny current to establish and leaks away only slowly if no path to the negative rail is provided. The gate voltage required to operate the mosfet gate is shown — the voltage is of course proportional to the charge on the gate and is how we control the charge on the gate. Linear operation is illustrated by keeping the gate voltage between 3.3 and 3.8 volts, showing the 12 volt bulb connected as a high-side load being regulated throughout its full brightness range, by varying the gate voltage by less than half a volt. The MOSFET is being used as an amplifier, not a switch. And, like all amplifiers, if it is fed an input signal that is 180 degrees out of phase with its output… it will oscillate. When I see the bulb come on, I reduce the voltage to the gate. When I see the bulb go out I increase the voltage on the gate. Lather rise repeat…. this a fundamental illustration of a feedback oscillation.