Help CCS for 1.33mA

[merlin el mago]

I used DN2540 for higher currents, I guess can't use it for this low current so I'm looking for schematic to make a CCS for 1.33mA.

Any suggestion will welcome.

TIA
Felipe

 

[Sheldon]

Select, or Parallel a couple of these: http://ww1.microchip.com/downloads/en/DeviceDoc/LND150 C041114.pdf

 

[merlin el mago]

Thank you Sheldon, could you post schematic or link to schematic?

 

[artosalo]

LND150 is for sure better for low currents. However, you could try this:

 

[merlin el mago]

Thanks Artosalo, I will try beause I have on hand DN2540.

What about a cascode with two bipolar transistors?

file:///C:/Users/fcv/Downloads/diyAudio-CCS-beta3.pdf

 

[Sheldon]

Thank you Sheldon, could you post schematic or link to schematic?

The schematic is on the data sheet I linked (Id vs Rsource). You can see that the temp coefficient is stable about 0.6ma current. So parallel two FETs with a common source resistor. Source resistor value will be 1/2 of that for a single FET. Resistor value would be about 500R. Start with a trimmer, then replace with a fixed value if you like.

 

[merlin el mago]

I only see a test circuit.

 

[merlin el mago]

Ohhh I see on the typical perfomance curves.

 

[Sheldon]

See my edit.

 

[merlin el mago]

Like attached pic?

 

[Sheldon]

Yes, although it can't hurt to add 1k or so gate stoppers.

 

[artosalo]

Why to put two elements in parallel ?
That halves the dynamic impedance of the CCS.

 

[Sheldon]

Yes, as I said in my original reply, one can select parts with high enough Idss, so that one will suffice. Depends on the power handling limits of the part, whether or not parallel devices are required. Merlin didn't specify voltage and I'll leave it up to him to do the analysis. Can always cascade too if you need higher dynamic impedance. Parallel parts in the top half, single part on the bottom. Trade-offs, as always.

 

[merlin el mago]

It's to substitute the 100K plate load resistor of 7N7, attached schematic.

 

[artosalo]

Felipe, can you show the circuit where CCS will be used ?

 

[merlin el mago]

Crossed posts.

 

[artosalo]

With 7N7 you can use much higher anode current than 1.3 mA.
Practically up to 10 mA, so you can manage with DN2540 very well.

 

[Sheldon]

Or, to have the current source self adjust as the tube ages, and to complicate matters just for fun, a gyrator would be even better. An example in the final stage of this phono amp:
http://www.diyaudio.com/forums/tubes-valves/169428-unholy-alliance-phono-amp-3.html#post2372139

 

[merlin el mago]

@artosalo
The attached schematic isn't my design, how to be improved?

@Sheldon
Interesting stuff. How can do it fo my headphone amp?

Many thanks guys.

 

[merlin el mago]

With 7N7 you can use much higher anode current than 1.3 mA.
Practically up to 10 mA, so you can manage with DN2540 very well.

So It will be better the standard CCS cascode DN2540, If I'm right I remember the best CCS for 7n7 can be 8mA?