MOSFET for controling DC motor direction

Discussion in 'Homework Help' started by AD633, Jun 25, 2013.

  1. AD633

    Thread Starter Member

    Jun 22, 2013
    96
    1
    The N channel in Figure MOSFEF operate under ON-OFF to put the DC motor to rotate in either direction, as polarity of the voltage applied to it.

    Assuming that each gate can apply one of the following voltage values​​: VK> VT or 0 V, determine the combinations of 4 voltages (VA, VB, VC and VD) that must be applied to the gates of each transistor so as to put the engine running in each senses.


    So when we have VGS>VT, this will make a current flow through IDS right?

    So i suppose if we want the motor to rotate in one direction we wiil have to apply Va>VT ,Vb=0,Vc=0, Vd>VT and for the motor to rotate in a different direction we will have to apply Va>VT,Vb=0,Vc>VT and Vd=0,right?

    What is the function of the diode conected between the Drain and the Source of the MOSFET?

    Thanks
     
    Last edited: Jun 25, 2013
  2. Ramussons

    Active Member

    May 3, 2013
    557
    92
    The motor operates when the opposite pairs of MOSFETs conduct.

    rotate in one direçtion we wiil have to apply Va>VT ,Vb=0,Vc=0, Vd>VT OK

    rotate in a different direction Va>VT,Vb=0,Vc>VT and Vd=0 Wrong

    rotate in a different direction Va=0,Vb>VT,Vc>VT and Vd=0 Right

    The diode conected between the Drain and the Source of the MOSFET is a Protection against Reverse Polarity that could damage the device.

    Ramesh
     
  3. t_n_k

    AAC Fanatic!

    Mar 6, 2009
    5,448
    782
    That is the integral body diode inherent in the MOSFET technology fabrication. It comes with the device whether you want (or need) it or not.
     
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