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Re: mr. pimm's baterry biased ccs q's

Posted by Gary P on November 16, 2004 at 20:42:35:
Hi,
Some answers...
"First, mr. Gary uses 3.3V battery cells in the table in his article on his web page. I have 3.6V cells - and because of that I would need to adjust slightly the circuit. Would it be enough to use the same circuit as he made it and adjust it with the pot as in the sch or should I change some values?"
The difference between 3.3 volts and 3.6 volts is only 9%. Less difference than you will find in the turn-on voltage of different batches of mosfets. You might want to increase the value of R1 5% or so to hit the current you want.
"Second, he has metioned that he uses 2,3 or 4 cells- I asume that he use them in series with eachother. So if I would decide to use 2 cells I would need 4 battery cells for the whole circuit, right?"
Yes, to do a 2 cell version would use 4 total per CCS. Performance is better with the 4 cell version though.
"Third, and most important of all, what is the voltage drop across that ccs?"
The CCS doesn't really have a set voltage drop. It does have a minimum voltage that has to be met or it won't work properly. The CCS also has a maximum voltage that if exceeded will cause the smoke in the parts to escape, causing the CCS to not work properly once again .
Minimum voltage (hard clipping) is around 10 volts. Best to keep the minimum voltage at during signal peak conditions to 20 volts or higher. Good rule of thumb for maximum signal voltage is to have the same voltage across the CCS as the triode. In line stages where the signal is small you can run less voltage across the CCS.
The voltage across the CCS in a circuit is controled by the triode's characterstics. The grid bias and plate current will determine what the plate voltage will be at the chosen operating point. The remainder of B+ will be on the CCS.

Hope this helps.
Gary