[Ktechlab-devel] Buggy circuit for diagnostics

[Alan Grimes]

Link wrote:
> Please find attached a circuit to debug. This circuit is a
> voltage-controlled voltage source/voltage follower intended to source
> and sink more current than the op-amp allows (in real-life). The voltage
> across and current through the load work fine, however, the current and
> voltage between the op-amp output and the transistor bases is extremely
> buggy. The op-amp output is extremely erratic; sometimes it oscillates
> between -500 and +500V and -50/+50A, and at other times it works almost
> as expected but bumps into the gigavolt range at the sine peaks.

> All I can say is "happy bughunting". :)

Now that's a useful circuit!!!

And here I thought BJT was the one that worked. =(

There's also a glitch in the chart recorder (oscilloscope). Put a
voltage probe on the glitchy part and then as you crank the voltage up
it changes from being + and - to being + or minus only in phase with the
signal.

It looks like putting a 30 pf capacitor from after the 10k resistor to
the inverting line of the opamp will fix the glitch too.

It still shouldn't be drawing 60 mA of DC through that resistor, even
with the capacitor in place. This can be slugged off by putting a 2meg
direct feedback resistor in...

Still, the only glitch that should appear is when it tries to compensate
for the transistor switching...

Opamp consists of no code, it is a pure abstract model.

The transistors are modeled in several classes including Nonlinear,
ECBJT, and BJT. The current version is known broken -- please fix! =P

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