Difference Between MOSFET & BJT | MOSFET Basics | How does a MOSFET work?

hey guys mosfets are very special transistors that are widely used in our electronics design mosfet is a metal oxide semiconductor field defect transistor this time we'll look into basics of mosfets and also we'll see how it is different from bgt so let's start [Music] there are two type of mosfets enhancement mode mosfet and depletion mode mosfets we mostly use enhancement mode mosfets in our design and now videos will cover only enhanced mid mode mosfets just like bjts mosfet can be used as amplifiers or switches in a circuit but before that we should know the basic difference between bgt and mosfet we know there are pnp and npn type bjts which we have seen in many of our previous videos with analogies and these are the schematic symbols just like that we have p channel and angel mosfets in this category the beach iron mosfet is analogous to pnp transistors and n channel mosfet is analogous to npn transistors these are the symbols actually both mosfets and bjts come in the same package so it is very hard to tell the difference between them without knowing the part number bjts have three terminals which are base collector and emitter to turn on obesity we provide a signal to the base turn it on and current starts flowing to the collector and emitter and mosfets have gate drain and source in mosfets we provide a signal to the gate and current starts flowing to the drain and source bjt is a current control device mosfet is a voltage control device that means the amount of voltage provided at the gate of the mosfet enters the amount of current flowing to the drain to source it is like a driving force to turn on the mosfet bht is a negative temperature coefficient device that means when the junction temperature of the bjt increases its electrical resistance decreases but mosfet is a positive temperature coefficient device that means when the junction temperature of the mosfet increases the resistance that is rds on of the mosfet increases input resistance of the bjt is very low but input resistance of the mosfet is high well bjt is a current driven device and its input resistance is very less so it needs microamperes to milliamps current at the input depending on the current flowing through the collector and emitter mosfet is voltage control device and its input resistance is very high so it restricts the high current at the input so input current is very less say in pico amperes of the mosfets to turn it on as bjt is a needed temperature coefficient device so when it saturates it dissipates less heat but the mosfet is positive temperature coefficient device so when temperature increases its resistance also increases as its resistance increases participation across it also increases which results in an increase of more temperature so when it saturates it dissipates more heat switching speed of the bjd is very low but the mosfet switching speed is very high and last but not least the bjt is an unidirectional device that means if we take an npn bjt the current can flow through collector to emitter and for pnp transistor it flows from emitter to collector only but mosfet is a bi-directional device current can flow from both direction that is from day into source or from source to drain in both n channel and p channel mosfet well it's quite difficult to understand and do it in actual circuit i forgot to tell you about this body dart of a power mosfet if you consider the n channel mosfet it needs a gate threshold voltage to turn on when the mosfet is connected in the circuit and we provide a voltage signal between gate and source the mosfet turns on so current start flowing to the drain to source and as soon as we remove this voltage signal the mosfet turns off the mosfet gate needs sufficient amount of gate voltage if the signal is not high enough the mosfet doesn't turn on we just discussed that mosfet is a voltage control device so the mosfet resistance depends on the gate source voltage that is vgs if there is no vgs then the mosfet resistance is very high when it acts as an open switch as soon as we provide vgs this resistance decreases gradually until this mosfet fully turns on we are considering this resistance between drain and source of the mosfet so we call it as rds and when the mosfet turns on this rds value becomes constant which we refer as rds on for p channel mosfet we either need to give negative vgs at the gate or we can connect the gate of the mosfet to the ground to turn it on and it works the same way as that of an n channel mosfet mosfets are widely used in many applications till now we have seen in our videos like all types of dc-dc converters battery management system and constant current controllers also mosfet can be used in automotive abs application pass trading led lighting motor drivers or voltage protection and many more for starters this is sufficient in the next video we'll see different parameters of a mosfet till then stay tuned i hope you got something from this if you haven't you can watch the video again still if you don't you can ask your doubts in the comment box below hit the like button if you like this video subscribe to my channel and finally thanks for watching

Channel: Foolish Engineer

Views: 40,072

Keywords: foolish engineer, electronics, voltage, current, electronics basics, power electronics, arduino, transistor, battery charger, BJT, NPN BJT, Transistor as a switch, Low side switch, NPN BJT as a low side switch, PNP BJT, Bipolar Junction Transistors, BJT basics, BJT working, PNP BJT workig, overvoltage protection, BJT as a protection, MOSFET, MOSFET working, MOSFET switch, MOSFET transistor, BJT vs MOSFET, Difference between MOSFET & BJT

Id: nwmqYoBBVbQ

Length: 7min 13sec (433 seconds)

Published: Thu Jan 06 2022