What is the Difference Between a Voltage & Current Sourc

Dear Members

Somehow i have always been confused about the voltgae and current source's existance in isolation. How can a current source supply the current if there is no voltage. Whats the basic idea of them and what for they are used in practical life except some analysis in the classroom.

Your thoughts and opnions Pls.

Ess ESS

Re: What is the Difference Between a Voltage & Current S

A current source does not necessarily mean that the volatge across it is zero. It just means that the current supplied by the source will remain constant and will not change with load impedence (in the ideal case). For example if a circuit consists of a current source of 5 amps with a load resistance of 5 ohms in series then the voltage across the current source is 25 volts. If the resistance was changed to 10 ohms the current source would still provide 5 amps but the voltage across it is now 50 volts.
Similarly with a voltage source, voltage across it remains constant but the current thru it can change.

Difference between voltage and current sources:

https://answers.google.com/answers/threadview?id=393999

What are
1)ideal voltage source
2)non-ideal voltage source
3)ideal current source
4)non-ideal current source?
---------------------------------
And how do they affect a circuit?

Re: What is the Difference Between a Voltage & Current S

Voltage Source -> Infinite internal Resistance
Current Source -> Zero internal Resistance

Re: What is the Difference Between a Voltage & Current S

Spauls,

Is it not opposite way around?
I have always that costant current source has very high internal impedance.......

Re: What is the Difference Between a Voltage & Current S

one more thing
if the current source short circuit is senseless
the voltage source open circuit is senseless too

Re: What is the Difference Between a Voltage & Current S

The main difference between an ideal source and a practical one is internal resistance as those guys above have pointed out.
An ideal voltage source outputs a fixed voltage regardless of load. However, real voltage sources have non-zero internal resistance that would drop some of the output voltage.
An ideal current source outputs a fixed current regardless of load. However, real current sources have non-infinite internal resistance, and therefore output current is actually load dependent.

I think most of us are familiar with voltage sources, but not current source. I like to think of a current source as a current-limited voltage source. If you use a resistive load, they will simply turn into a voltage source, since Ohm's law cannot be violated. Therefore, current sources are not normally used in resistive loads. The concept of current source should by right adjust the output voltage to maintain a constant current, but that is not usually done in practice.

However, when the loads used are diodes, FET/Transistors or inductive coils, which when switched on, theoretically provide unrestricted current flow, which would naturally drive the current source into current limiting mode whereby current output is maximum. They are often used in power amps and laser diode systems, where output parameters such as sound, torque or laser power is dependent on current rather than voltage.

Re: What is the Difference Between a Voltage & Current S

spauls:

Voltage Source -> Infinite internal Resistance
Current Source -> Zero internal Resistance

Click to expand...

IanP:

Spauls,

Is it not opposite way around?
I have always that costant current source has very high internal impedance.......

Click to expand...

i think spauls is correct,,,i almost confuse too....after some tot...i remember tht v use to draw the source~voltage as an open circuit and connected to the load....

current source is 0 resistance so tht it would not hav voltage drop on it....

and 1 more thing.....remeber 1 of my lecturer said b4,,,there is no pure current source exist...all is built wth voltage source....

¾λ²

Other ways to look at it:
An ideal voltage source outputs the specified voltage no matter how much current the load draws.
An ideal voltage source outputs whatever current is necessary to maintain the specified voltage.
An ideal current source outputs the specified current no matter how much voltage is across the load.
An ideal current source outputs whatever voltage is necessary to maintain the specified current.

Real-world sources have limits, of course.

Re: What is the Difference Between a Voltage & Current S

sp said:

spauls:

Voltage Source -> Infinite internal Resistance
Current Source -> Zero internal Resistance

Click to expand...

IanP:

Spauls,

Is it not opposite way around?
I have always that costant current source has very high internal impedance.......

Click to expand...

i think spauls is correct,,,i almost confuse too....after some tot...i remember tht v use to draw the source~voltage as an open circuit and connected to the load....

current source is 0 resistance so tht it would not hav voltage drop on it....

and 1 more thing.....remeber 1 of my lecturer said b4,,,there is no pure current source exist...all is built wth voltage source....

¾λ²

Click to expand...

I think Ianp's comment is correct. Ideal voltage has Zero Internal resistance.

Re: What is the Difference Between a Voltage & Current S

Ianp's comment is correect indeed. The non-ideal current source is modeled with a resistance in parallel to the source while the non-ideal voltage source is modeled with a resistance in series with the source. When the sources become ideal the resistance should be infinite for the current source, so that all the current flows out from the source and not through the resistance. For an ideal voltage source the (output) resistance should be zero so that the voltage on the terminals of the source equals the nominal voltage of the source and there is no voltage drop on the resistance.

It's interest discussion. I agree IanP. I think we can think a voltage source as ideal voltage followed a small resisoter.

Re: What is the Difference Between a Voltage & Current S

Explenations on this topic you can find in any encyclopedia (see picture below) and please do not treat topics like this as a poll.
We can agree or disagree on several things but not on current/voltage sources.
Best regards,
IanP

Re: What is the Difference Between a Voltage & Current S

voltage source produces voltage and if you use this voltage his current may change but his voltage don't change .
current source produces current and if you use this current his voltage may change but his current don't change.