Amplify Current

[Markom]

Hi All!

I am new to this site but have heard good things so here goes!!

I have a 0-5volts out of a DAQ that can only give a maximum of 5mA drive current. I need this to control a burst firing module that needs 4-20mA to control it.

My question is then how would I do this? I presume it is current amplification I need to do..but how!?? I have a second 24volt supply that I can use if needed.

Thank you for your time and if you need any more info please let me know!!

 

[smanches]

Wouldn't a simple 2n2222 handle this? I'm asking others, as my BJT knowledge is limited.

 

[crutschow]

What voltage output does the current input need?

How do you want to map the 0-5V to 4-20ma, for example, 0V = 4ma, 5V = 20ma?

 

[Markom]

Hi Carl,

Thank you for your reply!

The current input also needs 5 volts, I forgot to mention that the burst firing module has a 5volt supply which I can use to create the current if necessary.

Yes the mapping would be 0V = 4mA, 5v = 20mA. Although if necessary I could change the lower limit to create current.

 

[crutschow]

The easiest is to use something like this from TI or this from AD.

a circuit using a dual op amp.

 

[Markom]

Hi Carl,

Thank you for your advice!

I will check these items and see what I can get here!

 

[Markom]

Hi Again!

So I checked out the Texas Instruments XTR111, this definately looks like what I need.

I have been looking through the spec pages and its mostly over my head, I was wondering what extra components I will have to add to make it work in my project?

I will be using a 0-5v output from an NI made USB 6008 to create the input signal and I can use either a 24 volt supply or a 5volt supply as Vsp for the converter, as I said before I need 4-20mA at the other side to control a burst firing module!

I have looked at the different arrangements in the spec sheets but I am lost as to what arrangment I use!

Any help is appreciated!

 

[crutschow]

After further looking at the TI devices I think the XTR110 might be better for you. It comes in a DIP package and has built-in resistors to generate the 4-20mA you need. Look at Figure 1 in the XTR110 data sheet. The table shows the connections required (second row from bottom) for a 0-5V input range and a 4-20ma output (slightly different connections from that shown in the schematic). The only added components needed are the decoupling capacitor and the output PMOSFET.

 

[Markom]

Hi Carl,

Thank you for your recomendations, I have decided on the XTR110 as you said, and a 1 microfarad decoupling capacitor, the mosfet I hope I got right, I am going to use IR1204 MOSFET, I hope this will do the job?

Also with regards the connections to ground, what ground should I use? would it be the ground of the DAQ device for the input and then the ground of the 24v power supply for the rest?

Thanks again!

Mark