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:
https://img716.imageshack.us/img716/2527/dependentsupply.jpg
2: the power supply I've seen in the lab:
**broken link removed**
Hi,
Some very good questions. It's not obvious sometimes when you first look at these dependent sources (that's really what they are called), but if you look close at the circuit in the first link, you will see one of the connecting lines (usually taken to be perfect wires) labeled with "I=5A". Then if you look at the dependent source you will see it is labeled "0.2I" which really means "0.2*I" (ie 0.2 times I). Now we know where I is located (it's in the line labeled "I=5A" or sometimes just "I", so we take I and multiply it by 0.2 and that's how we get the current of the dependent source. In this case I=5 so that means the dependent source has 0.2*5 which equals 1 amp flowing through it.
The reason this seems strange is probably because there is no indication what the 0.2I source is 'sensing', but it is implied by the "0.2I" part. Sometimes there are lines drawn and an arrow to show current direction of the sense leads too, but many times there are no lines drawn for the sensing part of the dependent source, just a label. It means that the dependent source is sort of 'measuring' that other place in the circuit and using that to determine its own current or voltage.
Another example: Say we see "6*Ix" next to a dependent current source. We would then look for where "Ix" is in the circuit and that's what we would use to calculate the current from the dependent current source. If we found Ix was equal to 1 amp then the dependent current would be 6 times that.
Another: Say we see "8*Vx" next to a dependent current source. We would then look for where "Vx" is in the circuit and use that to find the unknown current.
Another: Say we see "8*Vx" next to a dependent voltage source. We would then look for where "Vx" is in the circuit and use that to find the unknown voltage of the dependent voltage source.
So we have several types of dependent sources:
Voltage controlled voltage source,
Current controlled voltage source,
Voltage controlled current source, and
Current controlled current source.
In real life others have mentioned the kinds of real power supplies available. Also in real life however the dependent current and voltage sources are used as part of sub circuits to show how some real life circuit would work. For example, a real life op amp can be made using a dependent voltage or current source, and this kind of sub circuit would have many qualities similar to a real life op amp.