What is Current source: Definition and 136 Discussions

A current source is an electronic circuit that delivers or absorbs an electric current which is independent of the voltage across it.
A current source is the dual of a voltage source. The term current sink is sometimes used for sources fed from a negative voltage supply. Figure 1 shows the schematic symbol for an ideal current source driving a resistive load. There are two types. An independent current source (or sink) delivers a constant current. A dependent current source delivers a current which is proportional to some other voltage or current in the circuit.

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  1. K

    Issues with Voltage Controlled Current Source

    Good afternoon PhysicsForums! I have a design for a voltage controlled current source. I've included the circuit diagram. The basics of the design is that I have an AC voltage and a DC Voltage summed then passed through a 1MOhm resistor to give me a current on the order of 1 microAmp. This of...
  2. S

    Constant Current Source Simulation Question

    I found this constant current source circuit over at instructables.com. This circuit calls for 2N5088BU for Q1 and FQP50N06L for M1, but I replaced those parts with 2N2222 for Q1 and PHT6NQ10T for M1 because that's what I have on hand for simulation. I calculated R2 = 0.5/0.125 = 4 ohms, but in...
  3. Y

    Measuring current output from a floating current source

    Hi - I am by no means an EE, so please be aware I may have some fundamental flaws in my knowlege. I have a battery powered isoluation unit that takes some voltage in and provides either a voltage or current source output. I am giving it 1V as an input and according to the conversion ratio...
  4. M

    Help understanding current source

    Homework Statement This is a really basic problem, just a closed circuit with a current source and a resistor. We are meant to give the voltage and the current across the resistor in terms of the current from the source and the resistance of the resistor. (From the diagram, express Vr...
  5. D

    What is the Voltage Compliance Range of a Current Source?

    Thank you for any help that you can offer. Did I answer all of the questions correctly and thoroughly? Can you please find any errors, and point them out to me so that I can fix them? Homework Statement Show that : VB = 1.6V VE = 1.0V IE = 1.0 mA IL = 1.0 mA What is the voltage...
  6. gfd43tg

    Op-Amp Current Gain with current source

    Homework Statement Problem #6 on the attachment Homework Equations The Attempt at a Solution I am stuck because if I do KCL at the node above the current source, It seems like all of the current should go back into Rs and none from the current source goes up to Rf
  7. S

    0-1A Bidirectional Current Source

    I'm trying to design a bidirectional current source for the purpose of measuring very small (0.0001 Ohm) resistances. I've come across this circuit: I can see that the transistors are there to 'boost' the current but I don't understand the purpose of the 1K resistors and the capacitor. I...
  8. Jarvis323

    Engineering Solving a simle circuit with a voltage and current source

    Attached is the model. Find Vx and Vy. The Attempt at a Solution The total resistance is 10 ohms, and the circuit elements are all in series. So 2 Amps of current is flowing in the direction of the arrow in the diagram across all elements, Vtotalsrc = (to the voltage from the current...
  9. B

    Finding voltage across current source

    Homework Statement Homework Equations The Attempt at a Solution
  10. X

    Voltage dependent Current source

    Homework Statement Find Vout at t=0.782s (I already found Vout at t=0 s. It is 0 V.) Homework Equations V=IRThe Attempt at a Solution First I found Vs = 9*sin(14*0.782)=-8.989817V (with t in radians) Since Rpi is in parallel with the Vs, its voltage Vpi also equals to -8.98917 V. Since the...
  11. J

    When to transform the current source to voltage source?

    Homework Statement Homework Equations The Attempt at a Solution First, I found all the impedance values. (starting from the left) Z1 = 1 / (j * 16E5 * 15E-9) = -j41.67 Z2 = 80 Z3 = 30 Z4 = j * 16E5 * 60E-6 = j96 I then combined Z1 and Z2. Z1 || Z2 = (-j41.67 * 80) /...
  12. D

    Superposition with a dependent current source

    Homework Statement I uploaded the assignment it is problem 2 Homework Equations The Attempt at a Solution I really just want confirmation that my work is ok, and the command for a dependent current source in PSpice. The things that I found that are dependent, are very confusing...
  13. mishima

    Mesh analysis, 2 meshes 1 known current source

    Homework Statement Find i1 in the following figure, given: Vs=10V, I=1A, R1=5, R2=2, R3=4 Homework Equations KVL The Attempt at a Solution Applying KVL to mesh 1: Vs-i1R1-(i1-i2)R3=0 and i2=I=1A So, i1=(Vs+i2R3)/(R1+R3)=(10+1*4)/(5+4)=14/9=1.56 A But book gives answer as...
  14. C

    Find the Thevenin resistance for network with dependent current source

    Homework Statement http://imageshack.us/a/img15/7218/sg2prob11.jpg Find the Thevenin resistance for the network(Sorry for the bad drawing, but that is a point like point / node A on the bottom where it's going out too and likely part of the load too, with a wire connected to the circuit, I'll...
  15. C

    Superpostioning of an inpendent voltage and current source with depend

    Homework Statement 3 branches, Indpendents are a 15 Volt source (left most branch) in series with a 2 ohm resistor (current that flows from left to right though this resistor is 'i delta'), Middle branch contains a 5 ohm resistor in series with a current controlled voltage source (3 ohms * i...
  16. H

    Creating a 1mA AC Current Source with Noninverting Op-Amp Configuration

    Homework Statement Design a circuit based on the noninverting op-amp configuration that functions as a 1mA ac current source. Homework Equations Gain = Vout/Vin = 1 + R2/R1 The Attempt at a Solution I really don't know how to start.
  17. C

    Dependent current source, find Vo

    Homework Statement http://imageshack.us/a/img26/4592/homeworkprintprob.jpg Find the voltage V0 in the network.Homework Equations V = IR Voltage Division: (Voltage across series resistor) = [(resistance) / total series resistance)](total input V) Current Division (for 2 parallel resistors)...
  18. W

    Precise constant current source for NTC

    Hello, everyone, I have to design a constant current source for NTC, to have a more precise measurement. The NTC resistance used range is 1kΩ~13kΩ. I have tried several circuits, but the problem is the the current is not precise enough even in simulation. 1uA difference All the...
  19. NukeEngineer

    Ideal current source parallel connected with ideal Voltage Source and vice versa

    Homework Statement Homework Equations Anyone Know why If an ideal voltage source and an ideal current source are connected in parallel, then the combination has exactly the same properties as a voltage source alone? and If an ideal voltage source and an ideal current source are...
  20. B

    Resistor and Current Source in Parallel with Short Circuit?

    This circuit is really confusing me. I'm trying to find i using KVL and KCL. What's throwing me off is the short circuit effectively created by the inductor. I know that the whole circuit can't be short circuited because there is a current source that is preventing all of i from going through...
  21. E

    Non-ideal voltage and current source

    1. What is the difference between non-ideal voltage and non-ideal current source ( not in terms of circuit diagram like ideal voltage source plus series resistance )? 2. And how to decide that which source is used where and when ? ( because output of both is not constant)
  22. Z

    Mesh Current Analysis w/ Controlled Current Source

    Solve i_x when a=2. (See attached picture) This is my attempt (mesh current analysis): I made i1 be the lower left loop current. I made i2 be the lower right loop current. I made i3 be the upper loop current. Mesh1: i1 = 2ix Mesh2: -10 + 3(i2-i3) + 20i2 = 0 Mesh3: -5 + 3(i3 -...
  23. T

    Electronics - Determine voltage across current source

    Homework Statement Determine the voltage across the 2A current source Homework Equations kirchhoff voltage law (kvl) kirchhoff current law (kcl) ohm's law The Attempt at a Solution I'm new to the concept of a current source. I'm not sure how there can be voltage drop across the...
  24. I

    Engineering Circuits analysis with independent current source

    Homework Statement https://www.edx.org/static/content-mit-6002x/images/circuits/H1P2.79e52b492b94.png Homework Equations It's been a while since I've done KCL/KVL, could be that I'm being just being stupid. I'm trying to find v1, i4, and the power in all the circuit elements...
  25. N

    The amount of power supplied/received by the dependent current source

    Homework Statement http://imgur.com/jsIWS Homework Equations Ʃ V_{n} = 0 Ʃ I_{n} = 0 v = ir The Attempt at a Solution I combined the two 2Ω resistors into a single 4 Ω resistor because they're in series. Then I tried to use KCL but I got 2 unknowns in one equation. 0.2A + \frac{Vi}{4} = I
  26. K

    How to measure noise from a current source

    I'm asked to get the noise signal from the constant current source I built with a 741 Op-Amp. I know I have to read it from the scope, but how do I go about the connections to the scope, and what other procedures must I follow to read the noise contribution? Pls refer to the figure provided in...
  27. K

    Engineering Thevenin equivalent circuit with dependent current source

    Homework Statement Find the thevenin equivalent circuit of the circuit to the left of the terminals AB. Circuit diagram is attacted below. Homework Equations The Attempt at a Solution I know that the thevenin resistance is 1kohm. I also know that the thevenin voltage is the voltage across...
  28. M

    Rlc circuit with ac current source

    Homework Statement An AC current source, 1 ∠0° A, with angular frequency 1 rad/s is to be applied to the input terminals of the circuit. Circuit is RLC, the current source is in parallel with a 1F capacitor which is in parallel with a 1H inductor which is in series with a 1Ω resistor. I...
  29. W

    Voltage and current source in superposition theorem

    why we take current source as a open and voltage source as a short in superposition theorem. is this is because of its internal resistance or any other reason exist?
  30. F

    Transistor as Current Source. Forward Active?

    Homework Statement Why does a transistor with a constant V_{B} (e.g. V_{B}=1V) only need V_{C} \approx 0.3V to act as a current source; If V_{C} < V_{B} doesn't that mean the transistor is not in forward active mode and thus not a mode we want to work in. Homework Equations The...
  31. _maxim_

    High precision, good accuracy Current Source Schematic

    I am looking for a schematic diagram of a compact, temperature compensated, stabilized, high precision (accuracy within 0.5% or less) current source. The target current should be easily set to 100/150 mA, no matter if discrete or integrated solutions must be used. This project will be...
  32. R

    A device connected to a current source and then resistor

    Forgive the title, I was unsure of how to briefly describe the problem. Attached are diagrams. Homework Statement The device shown in Figure P2.5 can be modeled as a current source in parallel with a resistance. When this device is connected to a 5[mA] current source, so that...
  33. L

    Efficient BJT Constant Current Source for Precise Current Regulation

    I need a constant current source ckt which can source current in the range of 0.1 to 1mA, with +/-1% tolerance, with Vcc 3.3v Any ideas? I found this - http://www.ecircuitcenter.com/Circuits_Audio_Amp/BJT%20Current_Source/BJT_Current_Source.htm But no info on tolerance. What happens to Io...
  34. A

    Engineering Help! Stuck on Dependent Current Source Problem

    I am stuck with this problem,the dependent current source is creating a big problem for me, please help. I have attached the problem.
  35. O

    Find the Electric power of the Current source

    in the picture you can see the electrical network. in blue is the Current of each side of the electrical network. (did it with loop equations) i asked to find the Electric power of E and the Electric power of the Current source. so for E i found it and i got pe=11.4w. i also know what...
  36. M

    Power over current source and resistor in series

    Problem description: The problem is Kotitehtävä 7 in the attachement. The idea is to calculate the output power (both P and Q) of the current source. Attempt: I know the current through the current source (obviously) and want to calculate the voltage over it to get the power. I have...
  37. F

    Current source and capacitor in parallel

    I don't know if this is the right place to post this question, but here goes. Whilst solving a circuit in class from a homework assignment, we arrived at a situation where a capacitor was in parallel with just a single independent DC current source. The question is, would current flow...
  38. M

    Confusion on Independent Current Source and Independent Voltage Source

    Homework Statement Given the this circuit calculate the voltage through the 3amp source? attached is a jpeg of the circuit. I wasn't able to get a good score on this one question quiz since this boggled me. Is true if I put current source that it will dictate the current of the battery...
  39. B

    Transistor as a current source

    Hello, So this thread is about using transistor as a current source. I understood the concept and all. But the main point of this thread is to finally seal my knowledge of transistor in saturation mode. We did an lab exercise about current sources, by biasing transistor with voltage divider...
  40. I

    Voltage drop over dependent current source?

    I have a circuit with 3 meshes for which I have to find the mesh currents, and I have. However, I just thought that there might be a voltage drop over the dependent current source in the circuit, which would change the mesh current equations. The CCCS is shared by two meshes. When I did the...
  41. D

    Find the Current Through a Resistor with a Constant Current Source

    Homework Statement Hey everyone. I might be overthinking this one, but I thought I'd post it. (sorry for the crappy MS Paint sketch!) I need to find the current through R3 Homework Equations V=IR \SigmaV=0 (around a closed loop) \SigmaI=0 (going into a junction) The Attempt...
  42. B

    Questions about current source and voltage

    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?
  43. PainterGuy

    Parallel resistance Rs in current source

    Hi :smile: I have always thought of a current source as a very, very high voltage supply with a very, very large resistor, Rs, in series (I mean this large resistor would make series connection with the load resistor, RL). The larger the series resistor the less effect the change in load...
  44. M

    Electric Circuits: Current Source & EMF

    I've been going through some materials, and I was reading about electric circuits. From what I read I figured that the electric current is dictated by the current source, and it's preserved(in the respectable branches) by the emf. Is that right? Or my feeling that I'm way off is true :)
  45. C

    Find (practical) current source constants, I and R

    Homework Statement A practical current source has a current of 22 A. Loading the source with 50 \Omega results in terminal voltage of 390.3 V. Obtain the source constants, I and R.Homework Equations V=I\times RThe Attempt at a Solution In my clumsy picture below, shouldn't I_{load} be replaced...
  46. G

    Current source = Total current?

    If a circuit schematic contains a current source, is it safe to assume I(total) is that value?
  47. PainterGuy

    Current source, voltage source

    Hello everyone,:wink: I am having difficulty understand the concept of current source and what it really is. I have written down below what I think of current source. Some things I said will be wrong and there could be possibility that some are not wrong!:tongue: Now you help me out please...
  48. A

    Why Is Internal Resistance Shown Differently in Voltage and Current Sources?

    why the internal resistance of energy source or cell is shown in series for voltage source and in parallel for current source? thanks.
  49. J

    How Do You Calculate Current and Power in a Circuit with a Dependent Source?

    Homework Statement In the circuit above, use R1 = 4Ω, R2 = 3Ω, V0 = 10V, and k = 1/5 Find the value of ix Find the power delivered by the dependent source 2. The attempt at a solution So what I assumed was that Ix+kIa=Ia so k=1/5 so Ix=(4/5)Ia then the equation for Ix would be Ix +...
  50. J

    Current Source with two settings

    Hey all, I am trying to create a type of current source to switch between 10 mA and 1.4 A at some frequency. I have an idea to use a BJT transistor as a variable resistor in a LM317 (or whatever the high current version is) but am not sure how to do it. Any suggestions? This circuit is to...
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