Welcome to our site!

Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

  • Welcome to our site! Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

voltage to current converter

Status
Not open for further replies.

dardar86

New Member
Hi,

I need to create a circuit to convert 0-10 V to 4-20ma, using a 741 op amp.

I need to use this op amp because I already have it and a power supply.

If anybody could show me a circuit using a 741 op amp to achieve the above I would be greatly appreciative!!

Regards,

DarDar86
 

ericgibbs

Well-Known Member
Most Helpful Member

Hero999

Banned
Here you go, you'll need a band gap reference for the -1.2V, see the LM113.

Or course, you could recalculate the resistor values to suit a different voltage and trim it.
 

Attachments

  • 0 to 10V to 4 to 2.PNG
    0 to 10V to 4 to 2.PNG
    794 bytes · Views: 1,196
Last edited:

ericgibbs

Well-Known Member
Most Helpful Member
Here you go, you'll need a band gap reference for the -1.2V, see the LM113.

Or course, you could recalculate the resistor values to suit a different voltage and trim it.

hi hero,
As the Vout of the OPA is always > +0.5V the -15V supply is not required, it would reduce the circuit cost.
 

Hero999

Banned
I thought the input is supposed to be able to go down to 0V?

It's a 741 which needs a dual supply and a negative voltage is already required to get -1.2V

No doubt there's another way of doing this with a single supply amplifier so no negative supply is required.
 

ericgibbs

Well-Known Member
Most Helpful Member
hi hero,
Look at this variant of your posted circuit.
 

Attachments

  • V2Cconv2..asc
    1.6 KB · Views: 456

Hero999

Banned
hi hero,
Look at this variant of your posted circuit.

The problem with that is the current will vary between 0 to 20mA as the voltage is varied between 0 to 10V.

The original poster wanted 0 to 10V to be converted to 4mA to 20mA, hence the negative voltage to get 4mA when the input voltage is 0V.

It's important that the current never drops to zero because that's treated as an error on a current loop transmission system.

https://en.wikipedia.org/wiki/Current_loop#Process-control_use
 
Last edited:

ericgibbs

Well-Known Member
Most Helpful Member
The problem with that is the current will vary between 0 to 20mA as the voltage is varied between 0 to 10V.

The original poster wanted 0 to 10V to be converted to 4mA to 20mA, hence the negative voltage to get 4mA when the input voltage is 0V.

It's important that the current never drops to zero because that's treated as an error on a current loop transmission system.


hi,
Thats a small change to make the circuit 4mA to 20mA.

Thanks for the link, but I have used 4-20mA for quite a time.;)
 

Attachments

  • V2Cconv3...asc
    1.6 KB · Views: 185

Hero999

Banned
That's a better way of doing it.

You'll need a regulated 15V supply to power the circuit, I know you know this, it's for the original posters benefit.
 
Status
Not open for further replies.

Latest threads

Top