Technical CCS Questions

K&K Audio / Lundahl Transformers

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The schematic above, from Bas's website, illustrates a constant current source built around two depletion-mode MOSFETS, model DN2540. I'm interested in better understanding how this circuit works, not how to get one working, so for the questions below assume we can not take any measurements of the system.
1) How do we calculate the value of R in terms of desired current output?
2) The DN2540 datasheet claims that it can handle up to 400mA at 10V, 100mA at 100V, and 50mA at 400V. What will that voltage be across? (Say, can this circuit be used in the cathode of a differential 300B amp stage (100mA at 85V to ground) but not in the B+ (100mA at 400V to ground), or do we not care about what potential we're sitting at relative to earth ground?)
3) How do we calculate the power dissipated by *each* DN2540?
4) How do we calculate the voltage drop across the entire CCS?

DN2540 Datasheet (Open in New Window)

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Topic - Technical CCS Questions - Aaron Boyer 03:15:08 12/30/03 (5)

Confused about the whole idea - Tre' 18:36:52 12/30/03 (1)

Re: Confused about the whole idea - KevinC 07:06:27 12/31/03 (0)

Re: Technical CCS Questions - KevinC 05:33:02 12/30/03 (2)

Re: Technical CCS Questions - Aaron Boyer 17:41:45 12/30/03 (0)

Re: Technical CCS Questions - Kuei Yang Wang 06:57:43 12/30/03 (0)

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