Early voltage problems.

Discussion in 'General Electronics Chat' started by Nik, Aug 23, 2010.

  1. Nik

    Thread Starter Well-Known Member

    May 20, 2006
    55
    3
    I'm trying to model a 6n139 split-darlington opto-coupler in Spice. I've collected hFE data on the Q1 (~45) and Q2 (~100) of my tube of 25 chips, but I've run into a problem with the Early voltage of Q2.

    I set base currents at 5~~100 uA using an LM334 and 15 resistor chain, used a 3V~~12V switched PSU for Vcc.

    When you plot iCollector against Vcc for different values of iBase, the tangents are supposed to converge, albeit waaay off to the left.

    Well, mine don't. At 10 uA (μA), Early voltage is ~200. At 20 uA ~160, 50 uA ~100, 70 uA ~85 and 100 uA ~65. I've tried ignoring the 3 & 4.5V data-points, but the tangents still don't converge...
    :confused:
    Any ideas where I've gone wrong ??
    (I'm a hobbyist, not a student.)
     
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