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Tube DIY Asylum Do It Yourself (DIY) paradise for tube and SET project builders. |
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Tube DIY Asylum Do It Yourself (DIY) paradise for tube and SET project builders. |
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In Reply to: "CCS driving a resistor"... posted by Lew on August 12, 2012 at 13:41:21:
The CCS (constant current source) can be, as in this example, a two-transistor cascode. (The zener is 6.2v, the most stable and least noisy) It takes its current through a (high stability) fixed resistor. Fixed current through a fixed resistor = fixed voltage. This acts as a voltage reference for the gate of a suitable MOSFET. The source of the MOSFET is also at that reference voltage because of the extremely low gate-source impedance. The current for G2 is taken from the source via the drain. The variability of G2 current has nothing to do with the CCS current.Incidentally, the regulator shown includes a slow-srart, to ramp up the G2 voltage (the 1.5Meg and 2uF capacitor). This helps to ensure tnat the fixed bias reaches its required level well before the pentodes start taking current.
Edits: 08/12/12
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Follow Ups
- RE: "CCS driving a resistor"... - Ray Moth 16:49:01 08/12/12 (1)
- A belated thanks... - Lew 10:51:28 08/14/12 (0)
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