MOSFET | Power MOSFET | Structure of MOSFET | Working of MOSFET | Characteristics of MOSFET |
-:Power MOSFET:-
A metal oxide semiconductor effect transistor (MOSFET) is a unipolar device and its operation depends on the flows of majority carriers. It has three terminals called drain(D) Source(S) and Gate(G). It is a bond is controllable device and it acts as a fact acting switch. It has very high input impedance and has a positive temperature coefficient of resistance.
Type of MOSFET- MOSFET are of following four types -
Structure of MOSFET-The n channel enhancement power MOSFET is more generally used because of higher mobility of electrons the basic structure and device symbol of an n-channel power MOSFET are shown in figure it has three terminal the drain, the source and the gate.
Working of MOSFET-The working of a MOSFET depends upon the MOS capacitor. The MOS capacitor is the main part of MOSFET. The semiconductor surface at the oxide layer which is located between source and drain terminals full stop it can be inverted from p type to n type by applying positive or negative gate voltage.
When a positive supply is given to the gate with respect to the source an electric field is established in SiO2 layer below the gate. This induces negative charge in the substrate below SiO2 layer. This forms an n-channel between the n + and n- reasons. This induced channel shown in figure. This channel provides a path for the flow of electrons from the source to drainfull stop the current can flow from drain to source. If the gate supply is made more positive, the n channel becomes deep and therefore more current flows from the drain to source. The n-channel enhanced by the increase of gate to source voltage and hence the name n-channel enhancement MOSFET.
the p channel operation is same accepted the voltage qualities are opposite to those of n-channel.
Characteristics of MOSFET-The static characteristic of power MOSFET are not described briefly the basic circuit diagram of n channel P-MOSFET. Is shown in figure. Where voltage and current are indicated. The source terminal S is taken as common terminal as usual between input and output of a MOSFET.
Transfer characteristics-The characteristics shows the the variation of drain current ID as function of of gate source voltage VGS .The device is in the year off state when thershold voltage is below VGST. The magnitude of VGST is of the order of 2 to 3 V.
Output characteristics-It indicates the variation of drain current ID as function of drain source voltage VDS, with Vas as parameter. For low values of VDS the value of resistance
RDS= VDS/ID
load line intersect the output characteristics at A and B are full on and off condition respectively. Power MOSFET operates as a switch either at A or B.
Switching characteristics-The switching characteristics of a power MOSFET are influenced by the internal capacitance of the device and the internal impedance of the gate drive circuit. At turn on there is initial delay tdn
And input capacitance charge to gate threshold voltage VGS.
tdn =turn on delay time
tr=rise time during which gate voltage rises to VGSP . During tr, iD rises from zero to full on current
ton=tdn + tr.
tdf=turn off delay time is the time during which input capacitance discharge from overdrive gate voltage V1 to VGSP .
tf =fall time is time during
A metal oxide semiconductor effect transistor (MOSFET) is a unipolar device and its operation depends on the flows of majority carriers. It has three terminals called drain(D) Source(S) and Gate(G). It is a bond is controllable device and it acts as a fact acting switch. It has very high input impedance and has a positive temperature coefficient of resistance.
Type of MOSFET- MOSFET are of following four types -
- N channel enhancement MOSFET
- P channel enhancement MOSFET
- N channel depletion MOSFET
- P channel depletion MOSFET
Structure of MOSFET-The n channel enhancement power MOSFET is more generally used because of higher mobility of electrons the basic structure and device symbol of an n-channel power MOSFET are shown in figure it has three terminal the drain, the source and the gate.
Working of MOSFET-The working of a MOSFET depends upon the MOS capacitor. The MOS capacitor is the main part of MOSFET. The semiconductor surface at the oxide layer which is located between source and drain terminals full stop it can be inverted from p type to n type by applying positive or negative gate voltage.
When a positive supply is given to the gate with respect to the source an electric field is established in SiO2 layer below the gate. This induces negative charge in the substrate below SiO2 layer. This forms an n-channel between the n + and n- reasons. This induced channel shown in figure. This channel provides a path for the flow of electrons from the source to drainfull stop the current can flow from drain to source. If the gate supply is made more positive, the n channel becomes deep and therefore more current flows from the drain to source. The n-channel enhanced by the increase of gate to source voltage and hence the name n-channel enhancement MOSFET.
the p channel operation is same accepted the voltage qualities are opposite to those of n-channel.
Characteristics of MOSFET-The static characteristic of power MOSFET are not described briefly the basic circuit diagram of n channel P-MOSFET. Is shown in figure. Where voltage and current are indicated. The source terminal S is taken as common terminal as usual between input and output of a MOSFET.
Transfer characteristics-The characteristics shows the the variation of drain current ID as function of of gate source voltage VGS .The device is in the year off state when thershold voltage is below VGST. The magnitude of VGST is of the order of 2 to 3 V.
Output characteristics-It indicates the variation of drain current ID as function of drain source voltage VDS, with Vas as parameter. For low values of VDS the value of resistance
RDS= VDS/ID
load line intersect the output characteristics at A and B are full on and off condition respectively. Power MOSFET operates as a switch either at A or B.
Switching characteristics-The switching characteristics of a power MOSFET are influenced by the internal capacitance of the device and the internal impedance of the gate drive circuit. At turn on there is initial delay tdn
And input capacitance charge to gate threshold voltage VGS.
tdn =turn on delay time
tr=rise time during which gate voltage rises to VGSP . During tr, iD rises from zero to full on current
ton=tdn + tr.
tdf=turn off delay time is the time during which input capacitance discharge from overdrive gate voltage V1 to VGSP .
tf =fall time is time during
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