A simple circuit for a 20 to 320 Ohms output

[gallo]

I'm looking for a simple circuit to convert a linear voltage or an MCU digital output to a 20-320 ohms output. Can any one tell me how to build such a converter ( I don't want to use digital potentiometer)? Thank you.

 

[melone]

How much current does this "resistor" have to pass? Is the voltage constant (will the high side of the "resistor" be connected to a power supply or will it be a series element)? What type of application is this for?

 

[buzzp]

Do you have fixed number of resistances that you need? You could possible mux them if there were not to many. You simply select an address and it connects the corresponding circuit hooked to the mux.Buzzp

 

[gallo]

The "resistor" have to pass only few miliAmps and would be a "floatting resistor (serial). It has to replace an old resistive sensor. The required precision is about 2% that means 6 Ohms or 50 steps. Thank you for your idea Buzzp but in my case muxing resistances would take to much area.

 

[buzzp]

Is this a temperature sensor? It may be possible to match the change in resistance with the temps you need. 50 steps is a lot and I am not sure what to tell you from here without hogging real estate or using too many components. Is there a reason a digital pot wouldn't work? That seems to be the way to go if real estate is an issue or maybe its cost. Sorry I couldn't have been more help.

 

[melone]

Or you can try using a transistor and vary the Gate / Base voltage.

 

[gallo]

Thank you everybody for your help, I think I found my solution with a variable voltage applied to the gate of a transistor.

 

[fansel]

What about a digital potentiometer ? ( Xicor, Catalyst )

There's no value around what you look for, but with a fixed resistor, it might be possible to cover the range.

Fabienne