Volts to Current problem

[Magnus Danielson]

> Dear All,
> 
> 	I have a question. If I want to control
> a current from a voltage how woudl I do it?
> A the moment the circuit I have has two resistors
> controlling the PW of an OSC (8038) if I want
> to change the width I have to decrease one and 
> increase the other. How do I do this with a a single
> CV?. My theory was two opamps (one inverting the
> signal and one not) driving (via a small resistor)
> the two I/P pins on the 8038 therefore controlling
> the current into these... Is this a Bad way? Is there
> a Much neater way?
> 	Could I find a voltage controlled resistor?
> could a FET be used and if so how?

Maybe you should use an OTA, which is a kind of op-amp but with current
output. This device has a third input which allows you to adjust the
transconductans (voltage to current gain). Popular OTAs is CA3080 and LM13600.

Read more on LM13600 on
http://www.national.com/pf/LM/LM13600.html

Useing an OTA I would consider a neat way (assumeing that I have understood
your needs).

An alternative would be to use up a simple transitor in a current output
configuration. This cursuit is normally 4 resistors.. here you would replace
one of the resistors with your device... however, this solution only pulls
current one way and has also some other limitations... but never the less could
be considered.

Magnus