• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

How's about a Depletion Mode / Enhancement Mode CCCS

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Show us your curves!

This might be useful for the DN2450. Top curve is -1.5V, and the curves go progressively more negative at 0.1V per curve.
 

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Ex-Moderator
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Because you can use it in the same way that you use pentode curves to determine the required resistance for a particular current.

Vertical axis: Ids
Horizontal axis: Vds

Suppose that you wanted to pass 9mA. Looking at that current, you find that the second curve down is pretty well 9mA, and it achieves this with Vgs = -1.6V. If you put a resistor in the source circuit of 1.6/0.009 = 178R, and connect the gate to the bottom of that resistor, you have created a 9mA two-terminal CCS.

Additionally, the curves show the minimum voltage required across the device (Vds) for it to achieve a constant (high) output resistance.
 
9mA achieved with -1,6v.. so where does that put you on the graph..i.e. where is the operating point?


Additionally, the curves show the minimum voltage required across the device (Vds) for it to achieve a constant (high) output resistance.

Where is resistance on the chart? :) I mean..how does one see that? Left of the dotted line?
 

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Resistance

Resistance is inversely proportional to the slope of the curves. A perfectly horizontal curve has slope = 0, and implies infinite resistance. For best CCS operation, you want to avoid operating where the curve deviates from horizontal, so at higher currents, you need a higher Vds to stay on the horizontal part.
 
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Joined 2003
Operating point

Your operating point is somewhere along the 1.6V line. If you were using the CCS in the cathode circuit of a valve, and the grid was grounded, then the cathode might be at 8V, so that would place the operating point at 8V less the 1.6V drop across the source resistor = 6.4V, which is well to the right of the curved region.
 
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