Darkfenriz,
Not really. The only reason there are two diodes and not one is to compensate for the diode voltage drop - in saturation collector potential is the same as base - no matter what diode type is used, as long as both diodes are the same - even LED would work (but of course one wants as little capacitance as possible)
In switching applications there might be a third diode allowing the source to draw the current from the transistor base to speed up transitions (anode connected to the base, cathode to the source).
What I was really interested in were opinions on how lilkely not protecting against saturation may lead to a catastrofic event.
BTW one could replace one of the diodes with resistor - advantage is that clamp level can be adjusted.
Not really. The only reason there are two diodes and not one is to compensate for the diode voltage drop - in saturation collector potential is the same as base - no matter what diode type is used, as long as both diodes are the same - even LED would work (but of course one wants as little capacitance as possible)
In switching applications there might be a third diode allowing the source to draw the current from the transistor base to speed up transitions (anode connected to the base, cathode to the source).
What I was really interested in were opinions on how lilkely not protecting against saturation may lead to a catastrofic event.
BTW one could replace one of the diodes with resistor - advantage is that clamp level can be adjusted.
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Very interesting topic.
I repeated Przemeks simulation and had similar results.
I compared various versions of the anf ccs I found in different amps and a very simple one that responses best to transient but when I replaced the simple (Zener) one with the anf in an amp simulation the anf seemed to perform better. I doubt a transient test reveals all about the ccs. Any ideas for further simulation?
Thanks
Lee
I repeated Przemeks simulation and had similar results.
I compared various versions of the anf ccs I found in different amps and a very simple one that responses best to transient but when I replaced the simple (Zener) one with the anf in an amp simulation the anf seemed to perform better. I doubt a transient test reveals all about the ccs. Any ideas for further simulation?
Thanks
Lee
try a cap from collector of Q4 to -90V supply rail.
Maybe the same cap on all of them.
Try adding a LED in lieu of the Zener.
Try adding a cascode to each.
The cascode is only effective if the base currents of the cascode transistor and the active transistor are swamped by that through the ref string that these base currents go to/come from.
Maybe the same cap on all of them.
Try adding a LED in lieu of the Zener.
Try adding a cascode to each.
The cascode is only effective if the base currents of the cascode transistor and the active transistor are swamped by that through the ref string that these base currents go to/come from.
Thank you, Andrew!
Adding a cap with 22nF as you proposed fixed the overshoot completely while maintaining the improved performance of the ANF CCS. Evaluation of performance was done by THD comparison in the amplifier simulation only.
Attached a plot of the three current sources compared.
GREEN is the Zener CCS
BLUE is the undamped ANF CCS
RED is the dampened ANF CCS
Adding a cap with 22nF as you proposed fixed the overshoot completely while maintaining the improved performance of the ANF CCS. Evaluation of performance was done by THD comparison in the amplifier simulation only.
Attached a plot of the three current sources compared.
GREEN is the Zener CCS
BLUE is the undamped ANF CCS
RED is the dampened ANF CCS
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