Voltage to Current Converter

[pedroamg]

Hello All,

This is my first thread in this forum, which I follow for a while.

I need to make a voltage to current converter with the following characteristics:
-Input Voltage: 0-5V
-Output current: 0-30mA @18V.

The Load is tied to ground, so I can't use the simple voltage to current converters.

I have available the following voltages: +5V,+12V,-12V and +18V.

Please suggest the possible circuit. Thanks in advance.;-)

Regards

 

[chuckey]

The obviuos circuit would have a PNP out put transistor, connected emitter to +18V via a low value resistor (say 1 ohm), collector as current output with the 0V line the other current output. the base of the transistor would have a resistor to the output of an Op-amp. The disadvantage would be that you cannot quite achieve +18V output voltage, rather more like 17.6V.
The junction of the emitter/1 ohms goes to the negative input via a high value resistor,say 100K. The input would go via a 100K X .03/5 = 600 ohms. If your input does not like this current then you will need a unity gain buffer stage before it.
Frank

 

[pedroamg]

The obviuos circuit would have a PNP out put transistor, connected emitter to +18V via a low value resistor (say 1 ohm), collector as current output with the 0V line the other current output. the base of the transistor would have a resistor to the output of an Op-amp. The disadvantage would be that you cannot quite achieve +18V output voltage, rather more like 17.6V.
The junction of the emitter/1 ohms goes to the negative input via a high value resistor,say 100K. The input would go via a 100K X .03/5 = 600 ohms. If your input does not like this current then you will need a unity gain buffer stage before it.
Frank

Thank you for your answer.
The circuit you tell me definetly puts an output of 30mA, but in the simulator it doesn't reacts to the input of 0-5V. Can you tell me why?
I put an image of what I have simulated.

Regards