Lower a Current Signal

[lambchops511]

Suppose I have a current signal coming through a variable resistor .. i.e. the variable resistor is attached to a voltage source and my output is the other end of the variable resistor.

The current signal is on the order of magnitude of 1mA ... how would I scale it down to an order of magnitude of 1uA?

Thanks.

 

[goldsmith]

Dear lambchops511
Hi
Why you don't use a simple current source ? ( my mean is a hartley current source , it is ideal for low currents and its precision is ok! )
Bets Wishes
Goldsmith

 

[lambchops511]

hi goldsmith

thank you for your reply. what do you mean by "hartley current source"? google did not turn up anything except for the "hartley oscillatory"

Do you mean replace my variable resistor and voltage supply w. this current source? I can not replace this -- this is an external component handed off to me.

Many thanks.

 

[keith1200rs]

I suspect he meant a Howland Current Source.

Keith

 

[varunkant2k]

First I need to know the use of reducing current and its application. Because , you can not use 1mA is different than you want to reduce 1mA to 1uA.
Current source need to be terminated in ideal resistance, to sense it. Terminate in a very high resistance. Since Voltage source and variable resistors are varying to make Current signal constant, the voltage across RLoad will be constant. you can use capacitor across Rload to make voltage constant.

 

[goldsmith]

Dear Friends
Hi
Sorry . it's name is very old , and i don't know it's todays name .
It is here: . it's precision is very high.
Best Wishes
Goldsmith

 

[varunkant2k]

This is just the positive feedback latch, it just increase the current gain with beta square times. Zener to protect VBE. I am eager to know if it should be used or if then for what application ?

 

[erikl]

The current signal is on the order of magnitude of 1mA ... how would I scale it down to an order of magnitude of 1uA?

Can't you use the standard method?

 

[goldsmith]

Dear varunkant2k
Hi
No in fact it is a ultra constant current source . if you use a series transistor with the zener and load. and it can provide very accurate current .you can see that in some specific instrumentation applications.
But i tested it. and many circuit can be based on that.
Regards
Goldsmith

---------- Post added 04-01-12 at 00:01 ---------- Previous post was 03-01-12 at 23:58 ----------

Dear erikl
Hi
I think , your circuit is temperature dependent . my mean is that , if the temp become change , according to the tolerance of resistors , the current will change , because , this current is very low. but i think it is possible to use 0 percent tolerance resistors but it will be expensive .
Best Regards
Goldsmith