Operation of MOSFET

Discussion in 'The Projects Forum' started by vivek20055, Nov 5, 2012.

  1. vivek20055

    Thread Starter Member

    Nov 4, 2012
    88
    0
    Hello,


    I like to know exactly the operation of BJT transistor in the circuit. Actually we can give directly pulse to MOSFET for switching purpose. what is the need of using BJT infront of MOSFET and giving the collector current to gate driver which drives the MOSFET.


    Thanks & regards,
    Vivek Alaparthi.
     
  2. vivek20055

    Thread Starter Member

    Nov 4, 2012
    88
    0
    Hello,

    Can I replace BJT with AND gate in the circuit? Can anyone help me in understanding the operation of circuit?





    Thanks & regards,
    Vivek Alaparthi
     
  3. maxthestork

    New Member

    Oct 13, 2011
    13
    1
    Hi Vivek,

    You need to check the gate to source threshold Vgs for the MOSFET. Sometimes this is higher than what is available from the switching signal.
     
  4. Jony130

    AAC Fanatic!

    Feb 17, 2009
    3,957
    1,097
    Are you sure that this diagram is correct ? You don't forgot about capacitor connect between Vg1 and gnd and also VG2 and GND?
    This circuit look like a external synchronous self oscillator ZVS converter.
    As long as voltage at point Vg1 don't go below V1 * R5/(R5+R8) = 2.44V the MOSFET will be OFF. So we can force this by switching ON the BJT or circuit can do it
    "himself" via D3 or D2 if the BJT is OFF.
     
  5. vivek20055

    Thread Starter Member

    Nov 4, 2012
    88
    0
    Hello Jony130,

    Thank you for your reply.

    This is exactly the ZVS converter as you said. Can I replace the BJT by AND gate for fast switching. If yes , how can I give inputs to the AND gate . I have only one pulse with 5v available in my circuit.


    Thanks & regards,
    Vivek Alaparthi
     
  6. Jony130

    AAC Fanatic!

    Feb 17, 2009
    3,957
    1,097
    Why you want to replace the BJT with AND gate?
     
  7. vivek20055

    Thread Starter Member

    Nov 4, 2012
    88
    0
    Hello Jony,

    I have been thinking of the connection to the gate drive and the possibility of shutting the device off.
    Instead of the BJT used now I tried to remove the two NPN transistors and use a AND gate (74V2T08) for the inputs. The and gate and the resistor after the diode should then both be connected to 5V instead of 12V.



    Thanks & regards,
    Vivek Alaparthi
     
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