# how we can get dc current??? help...

Discussion in 'Homework Help' started by adn07, Sep 25, 2007.

Sep 25, 2007
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we all know from where we got a dc voltage ...but what about dc current
plz if you know a semple way tell me...

2. ### JoeJester AAC Fanatic!

Apr 26, 2005
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Sep 25, 2007
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thanx joe ....but the page you gave, dosent answare my qoustion ....

4. ### beenthere Retired Moderator

Apr 20, 2004
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In the same way that a DC voltage is always positive or negative, a DC current never changes polarity.

5. ### thingmaker3 Retired Moderator

May 16, 2005
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The DC current is created by the DC voltage whenever the circuit is completed. The DC current will always be directly proportional to the DC voltage and inversely proportional to the circuit series resistance.

Sep 25, 2007
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frindes thingmaker and beenthere.....what your are saying is absloutly right
mybe my qustion is not clear and i m sorry for that ...
i mean as a source !!!! we all know that we can get a dc voltage source from battries ....so how we can establish a dc current source as well ....thats what i meant ...
thanx for your response ...thanx alot..

7. ### Eduard Munteanu Active Member

Sep 1, 2007
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Transistors can be used to make current sources. Google up 'transistor current source' or look in Art of Electronics (by Horowitz & Hill) if you have it.

8. ### thingmaker3 Retired Moderator

May 16, 2005
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Voltage regulators can also be set up as constant current sources. Most voltage regulator datasheets contain an example of this.

9. ### beenthere Retired Moderator

Apr 20, 2004
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Any DC voltage can be a source of DC current. As soon as AC voltage is rectified, it becomes DC, and thus a DC current source.

10. ### Eduard Munteanu Active Member

Sep 1, 2007
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That's not even close to a current source as in Norton's theorem's sense. I think that's what he was interested in, that is, constant current no matter what the load is (within its compliance limits, of course).

Sep 25, 2007
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May 16, 2005
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13. ### cumesoftware Senior Member

Apr 27, 2007
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Look at this equation: AC current + Bridge or center-tap rectifier + Capacitor = DC current.

But if you are looking for an ideal current source, I will let you know that doesn't exist. The closest thing is a HV DC supply with a current limiter.

14. ### Eduard Munteanu Active Member

Sep 1, 2007
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The mains is an AC voltage source, not a current source.

And there's no ideal voltage source either, although voltage sources exist in nature.