Electronic load, need some help

Discussion in 'The Projects Forum' started by hejiang666666, Jul 28, 2013.

  1. hejiang666666

    Thread Starter New Member

    Jun 10, 2013
    9
    0
    Dear all

    I have already built an electronic load circuit, unfortunately, the voltage source V1 cannot supply any voltage to the Mosfet. Only the gate of Mosfet has voltage about 10V. So anyone can give me suggestions ? Many thanks

    P.S. the op-amp I use is op37, and the voltage source itself is good.
     
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  2. Ramussons

    Active Member

    May 3, 2013
    557
    92
    Your OpAmp power supply V5 is wrong - change the polarity.

    Ramesh
     
  3. hejiang666666

    Thread Starter New Member

    Jun 10, 2013
    9
    0
    Thanks, but do you mean both +12V to the op-amp? But there is an output from op37 already. I think the problem is on the mosfet.
     
  4. LDC3

    Active Member

    Apr 27, 2013
    920
    160
    I'm a little confused.
    What does a pulse from V3 do to the output of the op-amp?
     
  5. hejiang666666

    Thread Starter New Member

    Jun 10, 2013
    9
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    The pulse is only used personally to check the ability to keep stable, a constant voltage is used practically. sorry for the confusion.:D
     
  6. LDC3

    Active Member

    Apr 27, 2013
    920
    160
    Your question is unclear (to me). What do you want to know?
    A second power supply?
    Why there is no voltage across R6?
     
  7. crutschow

    Expert

    Mar 14, 2008
    13,056
    3,245
    Post your simulation results. My simulation of your circuit works properly.

    Note that if you apply a -5V input with a +5V MOSFET supply the circuit will be saturated (maximum current) and the loop will not be controlling the current.


    Edit: Since the value of V5 is defined as a negative voltage, your power connections are correct as you show.
     
  8. tubeguy

    Well-Known Member

    Nov 3, 2012
    1,157
    197
    Try running the pulse/control signal from R4 to the + input instead of the - input of the op-amp.
     
  9. crutschow

    Expert

    Mar 14, 2008
    13,056
    3,245
    Either way will work. The only difference is the different input signal polarity.
     
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  10. Ramussons

    Active Member

    May 3, 2013
    557
    92

    Oh, I get it. V5 is -12V :D

    Ramesh
     
  11. hejiang666666

    Thread Starter New Member

    Jun 10, 2013
    9
    0
    Hi, this is the simulation, the blue line is voltage at gate, and the green one is at source of mosfet.
    another pic is the practical measurements, green is input, yellow is voltage at gate. The source and drain is zero
     
  12. hejiang666666

    Thread Starter New Member

    Jun 10, 2013
    9
    0
    I tried that, but the voltage at gate is negative, and no voltage at source.BUT, the drain can be supplied by 5V source. It is interesting~~
     
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