If a circuit only has a current source and no voltage source where does the voltage come from to supply the circuit?

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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










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  • Think of a solar cell, current is generated from incoming light, there is no voltage source.
    – sstobbe
    2 hours ago






  • 1




    You said it yourself: "A current source is something with would alter the voltage across it to meet a certain current". That's it -- the current is constant, forced by the current source, and the voltage just has to rise enough to satisfy that.
    – TimWescott
    1 hour ago






  • 1




    Also, how can a Voltage Source possibly create any currents? After all, it has to produce voltage alone and nothing else! (Wrong, "voltage source" actually means constant voltage with variable current.)
    – wbeaty
    1 hour ago















up vote
2
down vote

favorite












enter image description here



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










share|improve this question







New contributor




fred is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.



















  • Think of a solar cell, current is generated from incoming light, there is no voltage source.
    – sstobbe
    2 hours ago






  • 1




    You said it yourself: "A current source is something with would alter the voltage across it to meet a certain current". That's it -- the current is constant, forced by the current source, and the voltage just has to rise enough to satisfy that.
    – TimWescott
    1 hour ago






  • 1




    Also, how can a Voltage Source possibly create any currents? After all, it has to produce voltage alone and nothing else! (Wrong, "voltage source" actually means constant voltage with variable current.)
    – wbeaty
    1 hour ago













up vote
2
down vote

favorite









up vote
2
down vote

favorite











enter image description here



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










share|improve this question







New contributor




fred is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.











enter image description here



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







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share|improve this question







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  • Think of a solar cell, current is generated from incoming light, there is no voltage source.
    – sstobbe
    2 hours ago






  • 1




    You said it yourself: "A current source is something with would alter the voltage across it to meet a certain current". That's it -- the current is constant, forced by the current source, and the voltage just has to rise enough to satisfy that.
    – TimWescott
    1 hour ago






  • 1




    Also, how can a Voltage Source possibly create any currents? After all, it has to produce voltage alone and nothing else! (Wrong, "voltage source" actually means constant voltage with variable current.)
    – wbeaty
    1 hour ago

















  • Think of a solar cell, current is generated from incoming light, there is no voltage source.
    – sstobbe
    2 hours ago






  • 1




    You said it yourself: "A current source is something with would alter the voltage across it to meet a certain current". That's it -- the current is constant, forced by the current source, and the voltage just has to rise enough to satisfy that.
    – TimWescott
    1 hour ago






  • 1




    Also, how can a Voltage Source possibly create any currents? After all, it has to produce voltage alone and nothing else! (Wrong, "voltage source" actually means constant voltage with variable current.)
    – wbeaty
    1 hour ago
















Think of a solar cell, current is generated from incoming light, there is no voltage source.
– sstobbe
2 hours ago




Think of a solar cell, current is generated from incoming light, there is no voltage source.
– sstobbe
2 hours ago




1




1




You said it yourself: "A current source is something with would alter the voltage across it to meet a certain current". That's it -- the current is constant, forced by the current source, and the voltage just has to rise enough to satisfy that.
– TimWescott
1 hour ago




You said it yourself: "A current source is something with would alter the voltage across it to meet a certain current". That's it -- the current is constant, forced by the current source, and the voltage just has to rise enough to satisfy that.
– TimWescott
1 hour ago




1




1




Also, how can a Voltage Source possibly create any currents? After all, it has to produce voltage alone and nothing else! (Wrong, "voltage source" actually means constant voltage with variable current.)
– wbeaty
1 hour ago





Also, how can a Voltage Source possibly create any currents? After all, it has to produce voltage alone and nothing else! (Wrong, "voltage source" actually means constant voltage with variable current.)
– wbeaty
1 hour ago











5 Answers
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up vote
3
down vote













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.






share|improve this answer



























    up vote
    1
    down vote













    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.






    share|improve this answer



























      up vote
      0
      down vote













      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...






      share|improve this answer





























        up vote
        0
        down vote













        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.






        share|improve this answer








        New contributor




        Pitagoras is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
        Check out our Code of Conduct.
























          up vote
          0
          down vote













          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.



          enter image description here



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



          enter image description here



          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.






          share|improve this answer






















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            5 Answers
            5






            active

            oldest

            votes








            5 Answers
            5






            active

            oldest

            votes









            active

            oldest

            votes






            active

            oldest

            votes








            up vote
            3
            down vote













            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.






            share|improve this answer
























              up vote
              3
              down vote













              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.






              share|improve this answer






















                up vote
                3
                down vote










                up vote
                3
                down vote









                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.






                share|improve this answer












                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.







                share|improve this answer












                share|improve this answer



                share|improve this answer










                answered 2 hours ago









                Janka

                7,4771818




                7,4771818






















                    up vote
                    1
                    down vote













                    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.






                    share|improve this answer
























                      up vote
                      1
                      down vote













                      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.






                      share|improve this answer






















                        up vote
                        1
                        down vote










                        up vote
                        1
                        down vote









                        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.






                        share|improve this answer












                        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.







                        share|improve this answer












                        share|improve this answer



                        share|improve this answer










                        answered 1 hour ago









                        Peter Bennett

                        35.3k12762




                        35.3k12762




















                            up vote
                            0
                            down vote













                            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...






                            share|improve this answer


























                              up vote
                              0
                              down vote













                              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...






                              share|improve this answer
























                                up vote
                                0
                                down vote










                                up vote
                                0
                                down vote









                                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...






                                share|improve this answer














                                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...







                                share|improve this answer














                                share|improve this answer



                                share|improve this answer








                                edited 1 hour ago

























                                answered 2 hours ago









                                Annie

                                3688




                                3688




















                                    up vote
                                    0
                                    down vote













                                    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.






                                    share|improve this answer








                                    New contributor




                                    Pitagoras is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
                                    Check out our Code of Conduct.





















                                      up vote
                                      0
                                      down vote













                                      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.






                                      share|improve this answer








                                      New contributor




                                      Pitagoras is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
                                      Check out our Code of Conduct.



















                                        up vote
                                        0
                                        down vote










                                        up vote
                                        0
                                        down vote









                                        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.






                                        share|improve this answer








                                        New contributor




                                        Pitagoras is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
                                        Check out our Code of Conduct.









                                        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.







                                        share|improve this answer








                                        New contributor




                                        Pitagoras is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
                                        Check out our Code of Conduct.









                                        share|improve this answer



                                        share|improve this answer






                                        New contributor




                                        Pitagoras is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
                                        Check out our Code of Conduct.









                                        answered 1 hour ago









                                        Pitagoras

                                        964




                                        964




                                        New contributor




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                                        New contributor





                                        Pitagoras is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
                                        Check out our Code of Conduct.






                                        Pitagoras is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
                                        Check out our Code of Conduct.




















                                            up vote
                                            0
                                            down vote













                                            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.



                                            enter image description here



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



                                            enter image description here



                                            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.






                                            share|improve this answer


























                                              up vote
                                              0
                                              down vote













                                              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.



                                              enter image description here



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



                                              enter image description here



                                              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.






                                              share|improve this answer
























                                                up vote
                                                0
                                                down vote










                                                up vote
                                                0
                                                down vote









                                                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.



                                                enter image description here



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



                                                enter image description here



                                                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.






                                                share|improve this answer














                                                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.



                                                enter image description here



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



                                                enter image description here



                                                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.







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                                                Misunderstood

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