Questions about current source and voltage

[BeefBowl]

hey guys, do ideal current sources have polarity? When I measure the voltage of a current source, it gave me a negative voltage. What does it mean? Also, can we use KVL in a loop containing a current source without converting it to equivalent voltage source?

 

[gneill]

hey guys, do ideal current sources have polarity? When I measure the voltage of a current source, it gave me a negative voltage. What does it mean? Also, can we use KVL in a loop containing a current source without converting it to equivalent voltage source?

Ideal current sources have a polarity of sorts -- they produce a unidirectional current of fixed magnitude. They will also, however, produce any voltage whatsoever that is required to enforce that current magnitude and direction, regardless of the voltage polarity. It's not a good idea to have an ideal current source unconnected to a load of some sort

You can write KVL equations for circuits with a current source, but you'll have to introduce a new variable to represent the voltage across the current source, and the current source is going to cause you to add another constraint equation for the mesh currents (of course, since you're introducing a new variable, you'll need another simultaneous equation anyways...).

 

[NascentOxygen]

hey guys, do ideal current sources have polarity? When I measure the voltage of a current source, it gave me a negative voltage. What does it mean?

Imagine connecting a current source to a rechargeable battery. It will either charge the battery, or discharge it, depending on the connection. Reverse the connecting leads, and it will do the opposite. The voltage you measure across the terminals of the current source will be the voltage of the battery. Or if reversed, the reversed voltage.

The same will happen if you connect a current source to a charged capacitor. The initial polarity (of the voltage across the terminals of the current source) will be determined by the initial polarity of the capacitor. Eventually the polarity will reverse if the current flow is in a direction so as to discharge the capacitor (as it then charges it up with the opposite polarity).

 

[BeefBowl]

Thanks everyone!

 

[DeeNos]

Yes, ideal current sources do have polarity. However, unlike voltage sources where the polarity determines the direction of current flow, the polarity of an ideal current source does not affect the direction of current flow. It simply indicates the direction of the current flowing out of the source.

A negative voltage measurement from a current source means that the current is flowing in the opposite direction of the assumed polarity. This does not necessarily indicate an error, as current sources can have negative voltages depending on the circuit configuration.

KVL (Kirchhoff's Voltage Law) can be used in a loop containing a current source without converting it to an equivalent voltage source. This is because KVL is a fundamental law that states the sum of voltages in a closed loop must equal zero, regardless of the type of source present. However, it is important to note that the polarity of the current source must be taken into account when applying KVL.