MOSFET comes under FET family, there are two types of MOSFET those are
Depletion Mode MOSFET and enhancement mode MOSFET.
Depletion Mode MOSFET like a normally like a closed switch, in this depletion mode MOSFET current can flow when low voltage applied, when negative voltage applied current flow stops and open the switch.
ENHANCEMENT MOSFETToday Electronics world uses the Enhancement Mosfet mostly, so lets talk about the enhancement mode mosfet. Enhancement mode MOSFET is like a variable resistor.
MOSFET Metal Oxide Field Effect Transistor, the Field Effect suggests that it works by voltage. Bipolar Junction Transistor ( BJT) works by current.
MOSFET IS ALL ABOUT VOLTAGESWhen voltages applied between gate to source the current can flow between drain to source. see the picture below.
MOSFET WORKS AS A VARIABLE RESISTOR
Below the picture: 1
0v voltage applied to Gate and the resistance of Drain to Source is in high, see the Ohm meter and Volt meter below.
Below the picture: 2
5v voltage applied to gate and the resistance of Drain to Source is decreasing see the Ohm meter and volt meter below.
Below the picture: 3
19v voltage applied to gate and the resistance Drain to Source is very low in resistance, almost no resistance. see the ohm meter and volt meter below.
For N Channel MOSFET’s Gate voltage:the Gate voltage is higher than the input voltage. Say if we apply 19v on the laptop’s N channel MOSFET at VIN Mosfet or 1st MOSFET the Drain pin has 19v and the Source pin outputs the 19v , to get the proper 19v output on the source pin the Gate pin voltage should be higher than the 19v, usually it will be around 24v at the Gate pin.
For P Channel MOSFET the gate voltage is less or negative than the input voltage, say if 19v applied on the P Channel MOSFET’s Source pin has 19v and the drain outputs the 19v, to get the proper 19v output on the Drain the gate voltage should be low or negative than the input voltage. it will be around 6 to 7 voltage on the the Gate.
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