# 4-20mA source

Discussion in 'General Electronics Chat' started by Ganapati, Aug 2, 2006.

1. ### Ganapati Thread Starter New Member

Aug 2, 2006
2
0
Anybody can help me by giving an idea on how to make a 4 to 20mA variable current source. The current can be varied using a potentiometer. The output current should be ir-respective of the load resistance.

- Ganapati

2. ### hgmjr Moderator

Jan 28, 2005
9,030
214
What power supply voltage do you intend to use to power this current source circuit? 5V, 12V, of something else?

hgmjr

3. ### hgmjr Moderator

Jan 28, 2005
9,030
214
One simple way to accomplish a 4-20 ma variable current source is to design it based on a current mirror.

I have included a link to a section on the "current mirror" circuit that is located in the AAC tutorials.

It is referred to as a current mirror since the current that you source or sink into the input transistor is duplicated at the collector of the output transistor.

The resistor labeled Rbias is the point at which you would connect you potentiometer. Rload represents the load to which you intend to connect your current generator.

hgmjr

4. ### Gorgon Senior Member

Aug 14, 2005
113
0
Hi,
If you use this converter chip from BB http://pdf1.alldatasheet.co.kr/datasheet-pdf/view/56889/BURR-BROWN/XTR110.html - the XTR110, you may make it easy.

Since the chip has got ref. voltage outputs you only need a pot to make an adjustable 4-20mA output. You say that you want any load resistance, that is depending on the supply voltage. You will need more voltage to generate 20mA in a 1k resistor than a 100 ohm resistor. With a max supply voltage (<40V) you can use loads of more than 1k5. This is way more than the normal measurement load resistors in the hundred of ohms range. Remember to use a high power transistor with a cooling fin, if you use a high supply voltage and 20mA for some time on a low load resistor.

TOK