constant current sources

[walters]

How does a Constant current source works?

Does the Transitor have to Re-Bias itself it self adjusts with different LOADS?

How does it self adjust because of the different emitter voltage drops it puts out the same current how?

 

[pebe]

How does a Constant current source works?

Does the Transitor have to Re-Bias itself it self adjusts with different LOADS?

How does it self adjust because of the different emitter voltage drops it puts out the same current how?

You're still trolling, then?

 

[walters]

Why u say that?

 

[checkmate]

The current mirror circuits are not always readily identifiable by a novice. We normally remember the common configurations. The basis on how it works is not usually explained in words, but computed using maths.

Try computing it yourself. You'll learn more than simply asking for answers. Remember the final aim is to compute Ic/Iref, and to prove that it is approximately 1 for large beta. The following are some points in which you should take note.

1. Transistor Law Ic=betaxIb
2. If Q1 and Q2 are matched transistors, Ib1=Ib2

 

[walters]

Thanks checkmate for the PDF file that helps out alot

but what is the concept how does a constant current source work and a current mirror and whats the difference between them?

 

[checkmate]

Just do the maths and as long as you can prove that Ic/Iref is approximately 1, that would imply that R sets the reference (ie constant) current Iref, and that would be "mirrored" by Ic. Since Iref is constant, Ic will also remain constant, regardless of load Rc.

 

[walters]

So when i hook up a LOAD to the output of a constant current source or a current mirror by changing the Load resistance the current stays the same how ?

Does the Constant current source use feedback to self adjust it self?

I know its sets a FIX voltage at the Base of the transitor does it "compare" the base voltage with the emitter voltage drop? to self adjust

 

[checkmate]

So when i hook up a LOAD to the output of a constant current source or a current mirror by changing the Load resistance the current stays the same how ?

Because, the MATHS says so. If you can prove that Iref=Ic (approximately), then this equation is independent of Rc, the load!

Does the Constant current source use feedback to self adjust it self?

From the circuit, you can see that Q2 adjusts its Vce to maintain a fixed Ic when Rc varies.

I know its sets a FIX voltage at the Base of the transitor does it "compare" the base voltage with the emitter voltage drop? to self adjust

Don't know what you are talking about.

 

[kausu999]

pls give a simple description about constant current sources and constant voltage sources?

 

[ronsimpson]

**broken link removed**

 

[audioguru]

Whew!
For a minute I thought Walters came back after being away for more than 6 years.