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Homework Help: Any Professional can write equations for IRF510 MOSFET for Id=30mA;Vo=5;Vdd=9?

  1. Jan 12, 2012 #1
    guys i had spend more times on how to determine the drain current exactly using
    the prefer equations , but I failed i think the problem comes from extracting the correct
    Kp (constant of mosfet)
    any one can put here in details how to calculating + writing the procedures&equations
    step by step; please help me find Kp to determine the current i would like
    please please ..............etc
    extremely; DATASHEET did not including Kp;Ids(on); only they mentioned Rd(on)
    WHY;;;;;;;;;;;;;;;;;;;;;;;;;;???????????????????????????????????????????????????//
     
    Last edited: Jan 12, 2012
  2. jcsd
  3. Jan 12, 2012 #2
    ok here my tries :=
    IRF510 Datasheet including this INFO:
    gfs = 1.3 @ 3.4 A and sometimes in other datasheet 1.3@4 A. & VgsOFF=4V
    i do not know what if that gfs is same as Kp or gm ;
    i assume it is gm ; thus:
    as Id = Kn (Vgs - VgsOFF)^2 .............................. (1)
    also
    gm = 2 root (Id * Kn) then ---> Kn = (gm)^2 / (4 * Id)
    apply this equation yiald: Kn = (1.3)^2 / (4* 3.4) = 124.5 mA/V^2

    the required ( given ) parameters are : design MOSFET with Id=10mA with output = 5V
    Vdd=9 V ; with using the voltage-divider ... here i want not to includes Rs ( resistor at
    source ) .
    as Vdd= Vds + Id*Rd
    thus Rd= (Vdd - Vds)/ Id = (9-5)/10mA = 400 ohms
    at this point all things correct right? theoretically YES yes yes
    then as Vgg = Vgs
    Vgg = Vdd * (R2/R1+R2) = Vgs
    multiply both denominator and divisor by R1/R1 gives :

    Vgs = Vdd * Rbb/ R1----------------------- (2)

    for MOSFET :
    for Id-= 10mA ; assume R1= 10K then
    using Equation (1) yiald: Vgs = root(Id/Kn)+VgsOFF = Root(10/124)+4V=4.28 V
    Assume R1 =10K
    using Equations (2) and solve for Rbb yealds: Rbb = (4.28/9V) * 10K = 4759.9 ohms

    and as 1/Rbb = 1/R1 + 1/R2 -----> thus R2 = 1 / ( 1/Rbb - 1/R1) = 1/(1/4759.9 - 1/10K)
    thus R2 = 9083 =~ 9K ohms

    THE RESULTs :
    Id = 10mA
    Vgs = 4.28 > VgsOFF (i,e MOSFET is ON )
    Id = 10mA @ V0 =5v for Vdd = 9 V

    The DISASTERs :
    when apply the design on LT-Spice it is not success WHY WHY WHY ....

    PLEASE ANYONE GIVE ME AN ANSWERS

    YOU HAVE TO LOOK THAT I FORETHOUGHT ( DELIBERATE) NOT TO INCLUDE RS IN MY DESIGN FOR ANALYSIS PURPOSES
    SO PLEASE CALCULATE WITHOUT RS
     
    Last edited: Jan 12, 2012
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