Voltage - current converter

[samuel82]

Hi, Im working on the design of a Voltage controlled oscillator for a synth. I need a voltage-current converter circuit that will convert a voltage range of about 1V-2.5V linearly to about 1mA-10mA.

Any suggestions? Ive been playing around with a circuit involving an opamp, a couple of resistors and 2 transistors, but i cant seem to get the current output to change linearly with the voltage input.

Thanks a lot.

Sam

 

[nettron1000]

Use the opamp in the non-inverting configuration. This will improve stability and output to input linearity.
A bjt transistor is a current gain device, use the non-inverting opamp to drive the transistor via a base resistor.

If you are not too concerned about voltage gain, connect the opamp for unity gain (1).