what does a dependent power supply look like?!

Thread Starter

PG1995

Joined Apr 15, 2011
832
Hi :)

I was wondering what a dependent power supply, either voltage or current, looks like. I have seen a 'general' power supply in the lab (see link #2). Actually I was looking at the example problem 1.7 in the given link #1. It has a dependent current which is rated 0.2I. When I is 5A, the current supply by the dependent source is 1A. But how does it sense that the current supplied by the "independent" source on the left is 5A. There should be some way; I don't think it works using telepathic means!;)

Please help me. Thanks a lot.

1: example problem from the book:
http://img716.imageshack.us/img716/2527/dependentsupply.jpg

2: the power supply I've seen in the lab:
http://img696.imageshack.us/img696/8841/powersupplyg.jpg
 

Wendy

Joined Mar 24, 2008
23,415
Hi :)

I was wondering what a dependent power supply, either voltage or current, looks like. I have seen a 'general' power supply in the lab (see link #2). Actually I was looking at the example problem 1.7 in the given link #1. It has a dependent current which is rated 0.2I. When I is 5A, the current supply by the dependent source is 1A. But how does it sense that the current supplied by the "independent" source on the left is 5A. There should be some way; I don't think it works using telepathic means!;)

Please help me. Thanks a lot.

1: example problem from the book:
http://img716.imageshack.us/img716/2527/dependentsupply.jpg

2: the power supply I've seen in the lab:
http://img696.imageshack.us/img696/8841/powersupplyg.jpg
I have never heard of a dependent power supply. I am in doubt that such exists.

Your first link refers to an independent power supply. Is this what you are talking about?

BTW, judging from the links this should have been in the homework forum.

****************************

OK, I see what you were referring to.

We should observe that the 20-V voltage source and the 0.2I dependent current source are supplying power to the rest of the network, while the two passive elements are absorbing power.
I have to agree, that is clear as mud. I am willing to bet the text book used the phrase earlier to explain a concept in the authors mind, look for the key words in the chapter in front of that test. It isn't part of the standard terminology. The only thing I can think of is a current source or sink, that or a power supply set for providing a constant current source or sink. My leaning is toward the former.

What is the name of the text book, and revision?
 
Last edited:

Adjuster

Joined Dec 26, 2010
2,148
These are mathematical abstractions, used as part of exercises in circuit theory. In practice, devices like transistors and FETs can approximate to them, as can amplifiers made using such devices. A real controlled source always requires some sensing element to detect the controlling voltage or current, but this is not necessary for a theoretical analysis problem.

Computer simulation models for frequently employ controlled sources, but again these are mathematical simplifications of processes occurring e.g. in transistors.

Some types of power supply can be constructed to develop an output related to an external reference, but these are not common lab items.
 
Last edited:

Thread Starter

PG1995

Joined Apr 15, 2011
832
Thanks, Bill, Adjuster. Adjuster, you reply was very helpful. I like to understand things from 'physical' world point of view. So, is it safe to assume that in real 'physical' world no such 'dependent' device exists as shown in the link? It's just mathematical abstraction. Please let me know. Thanks.
 

ErnieM

Joined Apr 24, 2011
8,377
Yep, dependent sources are complete mathematical abstractions, excepting of course if you look hard enough you could probably buy something that does the same function off EBay.
 

Thread Starter

PG1995

Joined Apr 15, 2011
832
Yep, dependent sources are complete mathematical abstractions, excepting of course if you look hard enough you could probably buy something that does the same function off EBay.
Hi Ernie

Would you please use your googling skills to find such something for me? I'm just curious!:)
 

Thread Starter

PG1995

Joined Apr 15, 2011
832
These are mathematical abstractions, used as part of exercises in circuit theory. In practice, devices like transistors and FETs can approximate to them, as can amplifiers made using such devices. A real controlled source always requires some sensing element to detect
I was thinking that how a transistor could would imitate the behavior of a dependent power supply. Could you please tell of some simple circuit which uses such a configuration where a transistor is acting like a dependent source? Thanks.
 

jegues

Joined Sep 13, 2010
733
I was thinking that how a transistor could would imitate the behavior of a dependent power supply. Could you please tell of some simple circuit which uses such a configuration where a transistor is acting like a dependent source? Thanks.
A BJT will act like a current controlled current source when in its active mode, with Ib as the controlling current, and Ic as the controlled current.
 

Thread Starter

PG1995

Joined Apr 15, 2011
832
Hi, again, :)

I was reading this thread again and I think I need your help. I tried to find it myself without any success. I wanted to see a simple circuit which implements a transistor (preferably BJT) to emulate mathematical dependent current source. I understand it's not considered good to post in somewhat old thread but starting a new thread wasn't a good idea either. Thank you.
 
Top