In any case, The idea is that the gain of the device increases
with current, and increases with voltage. Ideally we want the
gain to be constant, which would make it distortionless. So
when we examine the voltage/current load line of a linear
amplifier, we see that for a resistive load the voltage across
the device decreases as the current increases, and so by
choosing the load line carefully, we have an opportunity to
cancel some nonlinearity in the gain device. This technique
appears to be most popular with triodes.
I got curious about how LU behaves in cascode and reread Pa's Cascode Article
The LU model I'm using, models the triode region pretty well.
Sim looks like what I traced, only difference was slightly higher Vgs needed to get sim look like scope.
I drew lines where Pa recommended LU operating area in cascode. He explains in article well. See, you don't let it get to that pentode area.
I'll build the cascode module and trace curves for sanity check.... eventually... I wish it were in a TO-220 package.
Thanks lhquam for links to Pa's explainations of Zen v9/F4. You got my wheels turning on triode in cascode. Learning a bit more.
My fav amp these days is this cascode module with coil as current source, will start a thread about it someday.
Can you post your Lu1014D Spice model? I am using the one from Lovoltech, but I suspect that it isn't good at the 1.5A region of operation. The transconductance values I see in simulations are high, like 40S. I do not have parts to measure. Do you have parts and can measure transconductance?
Here's the spice model. That one from Lovoltech didn't work for me either.
...
ZM: Can you measure the AC voltages across the output MOSFET drain sense resistors R131 and R129? Test at something like 1 Watt, 1kHz, or lower frequency that you multimeter can accurately measure.
Run a Vgs-Id curve on the LU1014 at 3.7v Vds. That is how it will behave cascoded in your LUDEF as long as Vds remains at 3.7v.
Run a Vgs-Id curve on the LU1014 at 3.7v Vds. That is how it will behave cascoded in your LUDEF as long as Vds remains at 3.7v.
Hi ZM,
Would it be ok with you if I made my own layout of just the LuDEF output stage so I can try with different input stages? This will be open source for DIYA (will not be used for any commercial stuff) and all Gerber files will be posted back to this thread for all to use.
Thanks,
X
Here is what I get using the LU1014 model from Cinco. (RsM1 is 10^-6R, ie. shorted).