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What is the biasing rule for the MOSFET to be used as a switch?
In the saturation or linear region, the transistor will be biased so that the maximum amount of gate voltage is applied to the device which results in the channel resistance RDS(on being as small as possible with maximum drain current flowing through the MOSFET switch.
What is pinch off point in MOSFET?
This phenomenon is known as “pinch-off” and the point where the inversion layer thickness is reduced to zero is called the “pinch-off point.” Pinch-off occurs because, at VSAT, the effective potential between the gate and substrate at the source end of the channel (Veff = VGS) is greater than the potential between the …
Can a MOSFET be switched off in a high side circuit?
While the MOSFET is off in a high side circuit the Source voltage will be virtually zero volts so the Gate could switch the MOSFET on, but once it is on, the Source voltage will be almost the same as the Drain voltage due to the very low resistance of the conducting MOSFET.
What happens when the voltage of the MOSFET is zero?
When the input voltage, (VIN) to the gate of the transistor is zero, the MOSFET conducts virtually no current and the output voltage (VOUT) is equal to the supply voltage VDD. So the MOSFET is “OFF” operating within its “cut-off” region.
What happens when the MOSFET is switched off in an opto coupler?
Circuits that are turned on for long periods require different techniques. When the output transistor of the opto-coupler is switched on, its collector terminal and the MOSFET gate voltage is pulled down to 0V; The MOSFET is switched off and with the Drain voltage at Vcc (12V), the capacitor C1 charges via the diode D1 to almost Vcc (12V).
Why is the opto-isolator important in a MOSFET switch?
The opto-isolator (IC1) and its two resistors R1 and R2 are not absolutely essential to the operation of the MOSFET but are highly desirable because the complete circuit makes a very useful self contained switch, suitable for interfacing many low voltage, low current electronics projects to higher voltage/current peripherals.