Jump to content
Electronics-Lab.com Community

Current Sink for LEDs


Recommended Posts

Hi everybody!

I want to design a project with some LEDs, something like a signboard and I need to use a current sink, which can drive up to approximately 500-600mA. I have thought of using a NPN transistor (for example 2N2222),  but I do not know what the exact circuit should look like. I have simply connected the E to the negative supply (ground), the C to the negative lead of the LED (of course the + of the LED is connected through a resistor to the positive supply) and the B to ground, but it doesn`t work at all!

Can anybody help me? Perhaps is there another solution, apart from using a transistor? (an IC maybe?)

Link to comment
Share on other sites



Hi Nick,

Why not use the LM317 or LM350?



Well... I haven`t understand what you mean Ante... :-[ I`m sorry...

How can the LM317 be used as a current sink?

Actually I mean something like the following circuit (except that instead of 1 I want to use more LEDs), where the ON or OFF state of the LED can be changed by the voltage applied at the base of the transistor.

But I obviously make a mistake because it simply doesn`t work at all!

post-15243-14279143088667_thumb.jpg

Link to comment
Share on other sites


OK Nick, I did misunderstand your question!


It`s ok! Perhaps I didn`t express myself very clearly and I should have posted that picture too!

Well I simply triggered it by connecting it to the ground or to the positive supply (later at my real circuit this will be connected to the output port of a PIC, but I guess it is the same thing!)

I don`t know, I may have made a mistake... I will check it once more!
Link to comment
Share on other sites

Thanks a lot Zeppelin! That resistor must be my mistake (I had thought of it, but couldn`t find the proper value). The guide is very helpful on that too!


With a 5V supply you can't drive that many LEDs, tops 3, I guess-you need a higher supply voltage.


I know that, I intend to use only two LEDs on series and organize all of them on doubles!
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...