How design a isolated current loop 0/4..20mA??

[gauchosuizo]

isolated current loop

hi guys

I'm looking for a current loop 0/4..20mA. I've a PIC with a PWM output and I want to need this to control the current loop. My idea is the following:
With a Filter (LPF) I can convert the PWM into a DC Voltage and with them I can drive a VCO. The generated Signal from VCO will be connected to a transformator. On the secondary side of this I get a voltage, wich I can rectifier and need as a current output. What do you think about this?

If you have an other Idea, it's welcome. Maybe has anyone a circuit? other a link?

Thank you very much and aloha

Pablo

 

[Mr_Programmer]

isolated current loop dac

I've seen a lot of application notes from Analog Devices concerning current loops. Just as a option for you to look for.

 

[gauchosuizo]

hi Mr_Programmer

thank you for your answer. I will check the homepage from AD.

Aloha Pablo

 

[koky]

see dac8512 data sheet, there are an example, you can change 8512 with dac

 

[gauchosuizo]

hi

I've checked the page from AD and I've found nothing. I don't know where you saw it. Please if you have some link about this, I will be very happy.
You must see: the current loop must be not expensive and as simply as possible.

Thanks

Pablo

 

[Mr_Programmer]

Pablo,

I'm sorry, I was wrong. I saw app notes in a Burr Brown Application book, but TI bought Burr Brown not AD. Again, I'm sorry.
I make a search at TI web site for "current loop" and got 500+ hits.

Under the first 25 hits is the following:
https://focus.ti.com/lit/an/sboa025/sboa025.pdf

In this app note you can also see the internals of a XTR1xx, I hope this will help you.

Regards...

 

[gauchosuizo]

hi Mr_Programmer

I know this application note and the IC line XTR... My problem is, that the current loop must be isolated. Now how can I isolate the current loop? With a transformator or maybe with optocouplers?
You see my problem?

Thanks and regards from Switzerland.

Pablo

 

[papyaki]

Hi,

Here are some links :

h**p://www.bb-europe.com/bb-euro/literature/curentlp.pdf

h**p://www.discovercircuits.com/C/cur-loop.htm

* = t

 

[Mr_Programmer]

@Pablo:
Well ... I see...

I found this circuit, it works with optocouplers:
**broken link removed**

Regards from Germany

 

[koky]

see at pag 17

 

[gauchosuizo]

hi guys

thanks for your answers.
@koky
I've checked the circuit. It's not what I'm looking for, you know? I don't want to need to much components on the isolated side. Therefor I thought at a transformator to isolate the current loop.

@Mr_Programmer
thanks again for your answer. I know this design. First I want to try with a transformator.

@papyaki
Thanks for the links. I will see it.

Regards and aloha

Pablo