Best way to build a voltage controlled current source

[FvM]

Achievable output impedance and maximum output voltage are different limitations of a real current source.

As already stated in several posts, the output voltage of an active current source will be always limited by the supply voltage. High voltage OPs or discrete transistor amplifier circuits can be used to increase the output voltage of your current source. In some cases, an output transformer may be a solution for a pure AC current source.

The howland current source's output impedance is particularly restricted by resistor matching errors, generally the OP gain restricts the achievable output impedance of active current sources and the gain-bandwitdh product the output impedance at high frequencies.

If you calculate the output impedance, you'll notice that the shunt resistor value is also a factor of output impedance. Implementing a large current ratio with respective low shunt resistance gives a lower output impedance than a smaller range with respective higher shunt value.

So the first point would be to derive a realistic specification.ö

 

[Anandi Basu]

The specification cannot be changed. I need to design with that spec.

Isnt every circuit limited by the current supply?

If I use transformers in the output stage, where can I simulate the effect?

 

[crutschow]

Your spec is impossible to meet. What is the maximum output voltage you need? As noted you can't deliver 100mA AC into a 100kΩ load as that requires 14,000 peak volts. You don't seem to understand the basics of Ohm's Law. So if you can't come up with reasonable specs, then we are all just spinning our wheels.

You said you have seen commercial devices that do what you want. Who makes them and what is the peak voltage and current?

 

[Anandi Basu]

I have come back with better specs

50mA over a load variable from 10 ohm to 1k ohm.

100Hz to 100kHz

I have come up with this circuit. Its supposed to give me (60/0.5k ) 120mA but its giving much lesser/

Whats wrong?

the voltage is taken before the 1.5k resistor on the last op amp