[sdiy] LT1228 Lm13600 crap

[harrybissell]

I simulated the 13600 and 13700 with discrete transistors, and also
compared it to the National Semi macromodels.  This is where I got the
figures for the Hfe of the buffer transistors.

I think the LM13600 and NE5517 differ only in the intermediate current
mirror.  OTOH I'm not sure. Maybe I should cut one ???   :^P

H^) harry

ASSI wrote:

> On Sonntag, 22. Mai 2005 03:56, René Schmitz wrote:
> > I would guess the reason for this difference is that there is current
> > stolen from going to the diffamp, which is used for the variable bias
> > in the output stage.
>
> Considering that it's a Wilson mirror, the only way to "steal" current
> would be an incorrectly sized transistor so that the base currents
> don't cancel. On the other hand, the results from Ian might indicate
> that the DUT generally showed bad matching. The Wilson mirror needs
> considerably more voltage headroom to work correctly. Low bias voltages
> or high common mode input is one of the applications where the CA3080
> can't be replaced.
>
> On Sonntag, 22. Mai 2005 04:07, harrybissell wrote:
> > The NE5517 has a different arrangement of bias for the buffer... It
> > might act differently
>
> I've heard that before, but the data sheets are inconclusive on that
> point. The circuit in the LM13700 data sheet does not match the
> description in the same data sheet and I personally think that the
> arrangement is quite close (if not outright identical) to that shown in
> the NE5517 data sheet (which is copy&paste in most other respects). Do
> you have any (better) information on the buffer biasing?
>
> On Sonntag, 22. Mai 2005 17:18, Ian Fritz wrote:
> > Worth having a close look at.  Is the data sheet on line?
>
> The Philips Datasheet is on their website, document number 939-750-10796
> (the partnumber search might be easier, but I'm not sure if it turns up
> an inactive part that the NE5517 now is).
>
> > Looking at the 13700 vs the 13600
> > schematics, it appears that they just erased Q3!  Do you think the
> > current theft could be eliminated by tying the buffer input to the
> > negative rail?  I'm not sure how simplified these schematics are.
>
> As I said above, the LM13600/LM13700 schematics should certainly be
> taken with a grain of salt.
>
> Achim.
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