kcl problem!!??!!

Discussion in 'General Electronics Chat' started by saghar19, Dec 9, 2012.

  1. saghar19

    Thread Starter Member

    Jul 16, 2012
    In this circuit kcl is not confirmed?!why?What is wrong?
  2. Jony130

    AAC Fanatic!

    Feb 17, 2009
    The answer is very simple your op-amp pspice model incorrectly model the power-supply current. But this is nothing new because almost all op-amp models are macromodels.
  3. WBahn


    Mar 31, 2012
    I ran into this same thing after working for about a year as an IC designer. Because all of our circuit sims were at the transistor level, we never saw this quirk in the models for opamps and such. Then one day I was designing a system-level schematic and needed to know the total supply current (because I had to keep total power supply draw under 900uA) and was totally dismayed when it was coming up to be something like 90A ! After checking the circuit stem to stern I determined that the opamp supply currents were just totally out of whack. I called the manufacturer (TI, I think, but it might have been National) and discovered that they only put effort into modelling the behavior at the I/O pins and that the supply currents are whatever they turn out to be. That was nearly twenty years ago. Recently, someone was showing me some sims they were doing with LTSpice and it actually appeared that the couple of TI models they were using were doing a reasonable job of modelling the power supply behavior as well. I had hoped that, since battery-powered designs are so common these days, that the component models were making an effort to do so.