[SOLVED] Building current source with variable load and input voltage

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tictac

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Hi
I want to build a current source with vairable load from 1mA to 10mA.
I have one resistive element at the output that must be have a constant current with changing the resistance of it and the applied voltage.

1 volts < Vin <100 volts
1mA <output current <10 mA


I want to have a fix current with changing in V11 and R7. Is it possible ? whats the wrong of my circuit. It works for current below 1mA.

Regards

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I put the JFET in the circuit for testing and finally I replace it with higher Vds .
 

R7 is too large. 10mA x 10K ohm is 100V. The supply is only 30V. R7 is probably not needed at all. Also, is the polarity of V10 correct? It looks the same as V9 but should be the opposite. Also, 10mA time the 1K ohm load might be too much voltage for the 12V supplies.
 
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    tictac

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R7 is for example.
it can be 1k and with maximun current such a 10mA .
V10 polarity is correct and the value of it is -12 volts
Why R7 does not need? It is the load and I think it must be there. I want to change the value of v11 from 1volts to 100 volts and the load current does not change.
What can I do? Also I want to have a fix current with variable load.
Regards
 

The BF245B has a worst-case current of only 6mA @ Vgs=0V. You need a FET with a higher current rating. Try a high voltage logic-level type N-MOSFET instead. Also change R6 to 500 ohms so you will have enough voltage to drive the MOSFET with a 10mA current (@5V, V12 input).

If you want V11 to go to 100V then the transistor will need a rating of over 100V. The BF245B is rated only to a max of 30V.
 
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    tictac

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Finally it works.
I use IRF840. Its last updated from current source that worked
 

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