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For example this circuit, A current source is something with would alter the voltage across it to meet a certain current.

But where is there a voltage source to do this or even have a voltage at Vx. How is this circuit functioning without even having a voltage supply?

I have looked here : Is current source also a voltage source?

To try to understand the difference between what a current source is and a voltage source but nothing helped answer this question.

Could in this case the current source act as a voltage supply?

Thanks

These are idealized elements. Neither voltage sources nor current sources exist in reality. Reality has generators and galvanic cells etc.

You can model a galvanic cell as either

• a voltage source with an internal resistance in series




• a current source with an internal resistance in parallel

Of course you can always add more things to your model, but these two options are the minimum. If you drop the internal resistance connected the right way, you aren't talking about real world things any more but you are talking about your modeling.

And that's what these circuit lessons and practice is about. Learn to understand the modeling. So you can build and understand models for real world elements.

I think you can now easily understand what to do with R2, and what the current source and R1 can be transformed into afterwards.

An Ideal current source will produce whatever voltage is necessary to permit it to deliver its specified current.

An ideal voltage source will deliver whatever current the rest of the circuit requires when it is delivering its specified voltage.

Real current and voltage sources will have limits on the voltage (for a current source) or current (for a voltage source) that they can deliver.

A current source does have to have a voltage source. But, because a current source is designed to supply a fixed amount of current, we can ignore its inner workings and just focus on its purpose: to be a current source.

If you think about it, we treat sources as ideal a lot, and it works out just fine. If we couldn't do that, a voltage source in a circuit would have to include all the components that allows it to output that particular voltage. And if it were plugged into the wall, it would have to include a circuit that went all the way back through transformers and many miles of wire to the electricity source...

The case you expose is an idealized element. So it is a model that you use to do calculations with other models.

Could in this case the current source act as a voltage supply?

If you look at a regulator based on a current mode DC-DC converter, you verify that it actually has two control loops:

1. The "inner" loop regulates the output current as requested by the outer loop.


2. The outer loop, in turn, "asks" the current needed so the output matches the desired voltage.

So effectively the whole regulator can be thought as a controlled current source, supplying the current needed such that the output voltage is the desired one.

A constant current (CC) source has its own DC source or one needs to be supplied.

You can buy a DC-DC CC regulator or an AC powered CC power supply.

An AC powered CC power supply will have an AC-DC power supply input and DC-DC CC regulator output.

Here is a very basic DC-DC step down (buck) CC regulator driving some LEDs.

The current flows through the R_set resistor. The chip measures the voltage across R_set to monitor the current flow.

If the current is insufficient, the internal PWM signal will increase the duty cycle of the SW (switching) input, increasing the current flow in to SW. And vice versa.

When the duty cycle is at its maximum (maximum rated current) the CC source essentially becomes a voltage source.

It's a load related thing. When the CC reaches maximum voltage or current, it is then a voltage source.

Example if the forward voltage of these LEDs being driven is greater than the input voltage the maximum voltage is reached.

If the load is a resistive load that could draw more current than the CC source can provide, the maximum current is reached.