Jump to content
Electronics-Lab.com Community

Current-dropping current source! I don't get it! Please help!


vicious5id

Recommended Posts

Greets everyone,

I am not sure if this is the right place to post this in the forum, but I have a problem with a circuit that I designed at the implementation stage.



^ That's the circuit that I have designed. The purpose of it is to behave as a current source that supplies a range of current from 0 to 120 mA, to a 20 Ohm load (R11 in schematic). I have simulated the circuit within software known as SIMetrix and it works as I want it to under high temperatures, long periods of operation and if the 20 Ohm load alters in value. However once I built the circuit and tried it out I was surprised.

When I begin to rotate the pot, and stop it at a point where I need it say 52.2 mA (?!), the current will immediately begin to drop by 0.1 mA. Over time it will keep on dropping (over time = ~10 mins) but the 0.1 mA reduction gets very slow. I thought that it's becuase my resistors or something else was getting hot, however if I cooled the transistor more current began to flow!

I really don't want the current to drift by 0.1 mA at all! I want the current to stay exactly where I set it regardless of how much temperature changes. Also the current I set should stay constant for +/- 10 Ohms in the load. So if I were to set the current I want output to 80 mA it should stay constant over a 10, 20 and 30 Ohm load.

Well anyway I think this post is getting long enough and I don't want to start mixing my objectives and confusing everybody!

I really appreciate any help you guys have to offer.

v5 0ut.

Link to comment
Share on other sites


Oh damn I forgot I posted something similar to this already in this forum, sorry, any moderator want to chuck this topic back into my old one?

Hmm, OK, how would I go about regulating VIN+? I thought about using a diode, or a Zener diode, in like a shunt configuration, or would it be better for me to build/buy a regulator?

Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

Loading...
×
  • Create New...