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. E

    Why Does a Current Source Have Internal Resistance in Parallel?

    hello.. this is my first post..forgive me if my question is wrong.. Why does a current source is modeled in such a way that it has its internal resistance in parallel ? Why can't it have its internal resistance in series ? The question may seem awkward , but please answer me.. thanks in advance..
  2. N

    Thevenin Eq. with controlled current source

    Hi! So, I've got this problem, and it's doing my head in a bit; http://yfrog.com/mtthevcsj I'm not entirely sure where to begin with this one. I've tried a few things, and hit dead ends pretty quickly on all of them; trying to find vx, Voc, Isc, node analysis by treating terminal 'a' to...
  3. L

    What is the Optimal Current Source for Extremely Low Current Applications?

    an application I'm working on requires 1.35 yoctoamps with a tolerance of + or - 0.10yoctoamps. Any current-source reccomendations?
  4. C

    How do I make a current source?

    I have an AC generator hooked up to a non-constant torque. The rate of change of flux through the wire loops will vary, thus the voltage will vary. However, I want to draw a constant current from this generator. How do I make a circuit that can limit a current regardless of voltage? Say I...
  5. G

    Help with programming a Keithley 220 Current Source in C++

    Hello guys, I want to program a Keithley 220 Current Source using C++. (C++ is m only option). (My task is to find out the V-I relation of a certain sample for which I want to program the current source). I am having problems getting the device into remote operation mode. I try to...
  6. R

    Current source in series with resistor

    1. In the case of a current source in series with a resisitor, can this be transformed to just a current source with 0 resistance, or is the resistance infinity in the Norton equivalent? Homework Equations The Attempt at a Solution My teacher told us this in class but i can't...
  7. S

    How Do Independent Current Sources Work Without a Potential Drop?

    I still can't visualise them. They deliver the same current all the time, however there is no potential drop across them. Is it just a theoretical device that doesn't exit? I am sure current sources do not add new charge into the circuit, but rather move charges around but this requires a...
  8. M

    How Do You Solve a Circuit with a Voltage Dependent Current Source?

    Voltage dependent current source? Please help Homework Statement Attached the problem. Homework Equations ?? The Attempt at a Solution Tried to Use KCL, not sure what else to do.
  9. F

    Setting Up a Current Source: Parallel Resistances

    To set up a current source why do we need to place the resistances in parallel rather than than placing them in series.
  10. F

    Current Controlled Current Source Help Maybe other things?

    Hey, So I'm making a really cool RGB LED project, and I need four of the RGB's to be in series. Now, as I understand this it's impossible since all three share an Anode. The LED's are going to be controlled via MAX6966, it's a PWM constant current source for the LEDs. I'm treating this...
  11. L

    Solving a Simple Circuit involving Current Source by the Loop Current Method

    Homework Statement For the resistor network in the picture, use loop currents to find the current through the 4Ω resistor and the change in voltage E across the current source. Circuit Attached Below . Homework Equations Kirchoffs Laws Loop Current Method V=IR The Attempt at a Solution...
  12. I

    Constant current source using an op amp

    I'm currently in the process of building a constant current source using an op amp. Circuit diagram: http://upload.wikimedia.org/wikipedia/en/9/97/Op-amp_current_source_with_pass_transistor.png I'm using a voltage reference instead of a zener diode. Currently the load resistance is 0...
  13. D

    Self-biasing JFET current source

    Homework Statement For the self-biasing JFET current source in Figure (http://sound.westhost.com/ab-f5-2.gif), what prevents this circuit from reaching the characteristic curve (showing ID vs. VDS) where VGS equals zero? The answer has to do with the self-biasing aspect of this circuit...
  14. P

    How to build a constant current source using vacuum tubes

    I need to discharge a lot of current into an inductive load from a large capacitive bank. Ideally the current waveform would be as close to a flat-top as possible. Typically this seems to be done either by switching many caps in sequence using SCRs into a filter network to remove ripple or by...
  15. C

    PSPICE Voltage Controlled Current Source Question

    1. My Attempt I need to convert the book problem of a circuit with a voltage controlled current source with one in PSPICE. I am attaching a picture which shows my attempt. I think I have it wrong but it might be right. So if someone with knowledge in EE and PSPICE could help me it would be...
  16. K

    Can Known Electric and Magnetic Fields be Used to Derive Current Sources?

    Hi, Lets say the electric and magnetic fields in an closed surface (2-D) are known. Is it possible to derive electric/magnetic currents that can create these fields? We can assume that the closed surface is homogenous with constant permittivity and permeability. Is this a well known...
  17. D

    Voltage Controlled Constant Current Source

    My project is to make a Voltage-Controlled Constant Current Source. I have found two solutions… This is first one http://electronicdesign.com/Articles/Index.cfm?AD=1&ArticleID=9018 Problem is last sentence: For the circuit shown, a maximum current of 20 mA is feasible for a maximum load...
  18. B

    Calculating the effective impedance of a current source

    I'd like to calculate the gain of a common emitter transistor circuit I'm looking at that has a a constant current source as the emitter load. Now I know the gain is going to be -gm(Re||RL) but how do I calculate what the effective resistance of the current source is? The current source I'm...
  19. L

    : 50mA-500mA constant Dc current source

    URGENT: 50mA-500mA constant Dc current source Hi everyone, I am trying to design a 50mA-500mA constant current source for my project. I found the following link. But I think it would give slightly less than the required or designed value...
  20. M

    Engineering RC circuit with dc current source

    Homework Statement Solve for the current in each branch of the following circuit as a function of time & derive and expression for the time dependence of teh emf of the constant current source in the circuit below. Homework Equations Zc = Xc = 1/(wC) = t/(2pi*C) The Attempt at a...
  21. A

    Porential across current source

    Homework Statement Title says it all. Question is attached. Homework Equations Simple KCLs, KVLs etc The Attempt at a Solution What I don't get is that isn't I_{R_{4}} = \frac{R_{3}}{R_{3}+R_{4}} * I1
  22. T

    KVL with a current source in loop

    I'm trying to solve for a number of different currents in a circuit, and I'm wondering how to do KVL with a current source in a loop? The current source is actually part of two loops, so is it possible to just name the current source 'V' during KVL and add (or subtract) the two resulting...
  23. G

    Voltage controlled dependent current source

    I had a question. When you have a circuit with a independent current source and a voltage dependent current source. And the dependent current source is dependent on the Voltage drop across the independent current source. How do I solve for this voltage drop when the currents are in parallel...
  24. D

    Voltage Controlled Current Source

    guys, i need some help... i'm looking for a voltage-controlled current source... i found this: http://electronicdesign.com/Articles/ArticleID/9018/9018.html" but when i try it for a maximum current of 500mA (using LM324N for the opamp and 2N2222 for the transistor), it doesn't work...
  25. W

    Circuit with Dependent Current Source

    Homework Statement I'm not sure how to solve this question, the method you're supposed to use is nodal analysis. Homework Equations The Attempt at a Solution I tried to use KCL at node A, so I have (12-Va)/8 - 3Va =0 Once I solved Va, the current is 3*Va. However, I'm not...
  26. J

    AC Current Source from a function generator

    First of all, i do not know if this is the ideal forum. If not, mods, please move it. Second of all, I know the title is redudant but whatever. Anyway, I am doing some experimental work that requires us to be able to controll the current, but we want to have it be a sine wave. We had been...
  27. V

    General SEcond Order Circuit: 2 Res. - 2 Inductors - Current Source

    Homework Statement Obtain i_1 and i_2 for t > 0 in the circuit below. http://img258.imageshack.us/img258/7765/problem60as1.jpg Homework Equations V_L\,=\,\frac{di_L}{dt} The Attempt at a Solution To get initial conditions, I made a second circuit diagram for t < 0...
  28. F

    Engineering Circuit with capacitor, current source, voltagr source and a switch

    Homework Statement the switch in the circuit is closed at t=0 for a very long time. find the current across the 2 ohm resistor before the switch is closed. find the current across the 5 ohm resistor before the switch is closed. find the current across the 2 ohm resistor RIGHT at...
  29. V

    Engineering CIRCUIT ANALYSIS: 2 resistors, Indep. Current Source, V.C.C.S - find v0

    Homework Statement Find v_0 in the circuit below and the power dissipated by the controlled source. http://img291.imageshack.us/img291/5479/chapter2problem22wy5.jpg Homework Equations KCL v\,=\,i\,RThe Attempt at a Solution KCL: i\,=\,2\,v_0\,+\,10\,A v_o\,=\,i\,R...
  30. V

    CIRCUITS: Three resistors, two Indep. Voltage sources, one Indep. Current source

    Find I in the circuit using the superposition principle: My work so far: I\,=\,I_1\,+\,I_2\,+\,I_3 This reduces down to: 16\,V\,=\,I_1\,(8\Omega) I_1\,=\,\frac{16\,V}{8\Omega}\,=\,2\,A This reduces down to: I_2\,=\,-\frac{12\,V}{8\Omega}\,=\,-\frac{3}{2}...
  31. V

    CIRCUIT ANALYSIS: Use superposition - 2 Current source, 1 Voltage source, 4 resistors

    Using superposition, find v_0 in the following circuit. My work so far: v_1\,=\,2\,i_2\,+\,v_{0\,1} v_1\,=\,4\,i_1 v_{0\,1}\,=\,3\,i_3 v_{0\,1}\,=\,6\,i_4 KCL @ v1: 1\,A\,=\,i_1\,+\,i_2 i_2\,=\,i_3\,+\,i_4 Using these six equations, with 6 variables...
  32. V

    Engineering EECS: Find i_0 in a circuit with 4 resistors and 1 indep. current source

    (a) Using nodal analysis, determine i_0 in the circuit. (b) Now use linearity to find i_0. Work so far: i_0\,=\,\frac{v_1\,-\,0}{6\,\ohm}\,=\,\frac{v_1}{6\,\ohm} KCL@v_1: \frac{v_1\,-\,0}{3\,\ohm}\,+\,\frac{v_1\,-\,0}{6\,\ohm}\,+\,\frac{v_1\,-\,v_2}{2\,\ohm}\,=\,0 KCL@v_2...
  33. E

    Node method analysis with dependent current source annoying me

    I've been trying to solve the exercise 4 below,but with no avail.I've worked through the equations,which I think that are okay, but I'm not sure because the result doesn't match with the one that is provided.Could you help me and check if those equations are okay?Also,how do I work with...
  34. M

    JFET Current Source: Understanding & Calculations

    Hello, I'm trying to brush up on my analog electronics a bit. I've been studying "The Art of Electronics". In chapter 4 they show a jfet current source. It consists of two nfets. The source of the top one is connected to the drain of the bottom one. Both have their gates connected to...
  35. I

    AC Generators: Voltage or Current Source?

    hey I'm wondering whether an ac generator would be classified as a voltage source or current source, or neither (if that's possible)? I'm asking you guys since i have nooooo idea how i would go about determining this. Thanks!
  36. S

    Are Voltage Sources and Current Sources Interchangeable in Transistor Circuits?

    I have learned that transistors are current source. a) I want to know what is the difference between current source and voltage source? b) Can't voltage source also be a current source? c) When we use a current source and when a voltage source Thanking you in advance. :rofl:
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