4-20ma output

geneshults

Hello to all
I have a project going on that requires me to control a I/P transducer.
It is being powered by a 24 vdc supply. I want to be able to control this device via the BS2.
I know I can use the PWM function of the BS2, but interfacing it with the BS2 and and the devices 24 vdc is making me uneasy. Don't want to damage the BS2. Has any one else done some thing like this? And if so what parts and pieces did you use.
Thanks
Gene

Tomato

A transistor will fork fine (check datasheet to make sure that all electrical characteristics are adequate, ie, V_cb max should be more than ~19V (the diff between the stamp's output voltage and the 24V supply. Increase that value by 50%, or even double it, just to be safe). Or you could use a mosfet since the insulated gate allows you a wider range of voltages to play with (again, check datasheet). Tie grounds together

If you're still worried about collector-base (drain-gate) breakdown, a simple phototransistor optocoupler will probably work fine. That way, all your stamp has to do is drive a LED! And also, you don't need to tie the phototransistor's ground to the stamp's ground (just make sure it has the reight specs forhandling your 24V supply, load current, etc).

hope it hleps!
Tomato

bennettdan

geneshultz

Here is a nice isolated PWM to 4-20ma circuit that can be zeroed in.
http://archive.electronicdesign.com/files/29/4950/figure_01.gif
And here is the article explaining about it.
http://electronicdesign.com/article/analog-and-mixed-signal/simple-current-loop-transmitter-converts-pwm-to-4-.aspx

Hope this helps you out.

geneshults

Thanks Will give it a try....