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Voltage and Current sources

Discussion in 'Electronic Design' started by [email protected], Jan 15, 2009.

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  1. Guest

    Hi,

    Is anyone here familiar with any circuit's for voltage and/or current
    sources programmatically controllable? Voltage ranges max or fixed of
    around 500-750VDC with a power rating from 5W to 200W. Regulation and
    repeatability of about 1% would be needed.

    My initial approach was to use motorized potentiometer with a fixed
    voltage source with feedback as this seems relatively straight
    forward. This is not the approach I want to take for various reasons.

    I've looked at some of the basic current source circuits but all tend
    to be low power and low current. I believe it is possible to design a
    larger version by using higher capacity components and/or paralleling
    or serializing several smaller circuits.

    Any suggestions?
     
  2. Guest

    Sounds like a job for a string of power FETS. What is the load? Ie
    if its a arc, or something similar, there are more details we need to
    know.

    Steve
     
  3. Guest

    Essentially it is just resistive but of course a little capacitive and
    inductive. The power needs to be applied continuously. Actually in one
    case it would need to supply power to a transformer for voltage
    translation into a highly inductive load.

    In this case something like PWM would not work or at least I believe
    it would not be a good option because of certain complicating
    factors.

    I need to emulate a *real* voltage/current source as closely as
    possible that can supply continuous current to the load. By continuous
    current I mean as if the supply was ideal.

    The supplies will mainly power passive components but some power may
    need to siphoned off to power some integrated circuitry.

    A similar application which a variable source is needed is in
    computing IV characteristic curves. This is almost what I am doing but
    not quite. In my case the device is actually being used in real time
    and not being sampled at discrete voltage or current points. Here
    using something like PWM to control the current or voltage might
    introduce artifacts in the operation of the devices. This is not to
    say that one might still be able to use PWM and regulate the output.

    What it all boils down to is that I need a simple programmable voltage
    and, separately, current source that while operating at it's
    programmed state acts closely, as close as any basic power source, to
    an ideal source.
     
  4. Guest

    Could you also explain to me the reasons, for my own enlightenment,
    why "arc loads" are different from any standard load?
     
  5. MooseFET

    MooseFET Guest

    Do you need one or are you going into production?

    A programmable power supply can be bought.
     
  6. neon

    neon

    1,325
    0
    Oct 21, 2006
    You first have to understand a current source inpedance and voltage source inpedance. define that for me I will help. Finaly there is no absolute current sources or voltage sources.
     
  7. Guest

    yes, but I need a circuit so I can use it in my for my own
    application. It most likely won't go into production but that isn't
    the point.

    I could use a triac to cut down the power but I'd need separate filter
    caps for each "sub-supply". It would also have very low regulation and
    high inrush currents when in low power mode.

    AFAIK there are many ways to do "it" but I can't seem to find a way to
    do it decently. Maybe some switched mode power design would work?
     
  8. Jon Kirwan

    Jon Kirwan Guest

    You want a general purpose semiconductor pin driver for test
    equipment?

    Jon
     
  9. Fred_Bartoli

    Fred_Bartoli Guest

    Hey, that's an idea: a pin drivers for power toobs...
     
  10. Jon Kirwan

    Jon Kirwan Guest

    4CX1000A? hehe. (I think I still have one or two in a box,
    somewhere.)

    Jon
     
  11. Guest

    No, it was only to compare the requirements for something that is
    easily conceivable without me having to explain all the details of
    what I'm trying to do. i.e., if I had a somewhat simple circuit that
    solved the problem I mentioned about the IV characteristics then it
    would also solve my real problem except for the caveat I mentioned.

    All I need is a voltage controlled voltage source and a voltage
    controlled current source for the voltage range.

    e.g., http://www.daycounter.com/Circuits/Voltage-Servo/Voltage-Servo.phtml

    Those circuits may or may not work for my application. I suppose I
    have to do some experimentation. Unfortunately I haven't seen many
    mosfets with a very large DS breakdown(about 1k).

    I was hoping for a bit more circuits to look at besides using a fet in
    linear mode. I guess I should try it out though as it does seem the
    simplest I have found. Ultimately I need to use feedback so I can set
    the voltage digitally. Maybe I can do that with a simple
    microprocessor feedback loop but maybe there is some package that can
    take care of all that for me? i.e., buffer's the fet input for drive
    and has an input for selecting output voltage to be proportional to
    supply voltage?
     
  12. Jon Kirwan

    Jon Kirwan Guest

    Winfield Hill and Paul Horowitz are authors of a book called "The Art
    of Electronics." If you look in the 2nd edition (I think that's 1989,
    or so), there is a nice section on "Special-Purpose Power Supply
    Circuits," starting on page 368 in chapter 6. First thing talked
    about is high voltage regulators and in figure 6.48 they talk about
    regulating the ground return as one example in the ballpark of the
    voltage you are looking at. Another is optoisolation, examples shown
    in figure 6.50. Some of the basic ideas are in there, but a complete
    circuit for your needs probably isn't.

    Jon
     
  13. JeffM

    JeffM Guest

    It sounds like you are making the classic mistake
    (read: time=money) of building (a one-of) something you can buy.

    If this is a short term need, it's even crazier.
    Buying a programmable power supply (perhaps used)
    then reselling it when your need has passed
    would likely be essentially zero cost.
     
  14. Guest

    I'll take a look at it. I have designed a simple feedback loop using
    opamps that compares the voltage scaled down with a reference voltage
    and attempts to match it by using feedback and a mosfet. I'll have to
    play around with it some more and look at more examples to see if it's
    a good idea. The difficult part is controlling the high side mosfet of
    several hundred volts from a low side driver. I'll have to dust off
    AOE and read it. Wasn't a new edition suppose to come out shortly?
     
  15. Guest

    Let me decide that. It's my time and money so I should be the one who
    makes that choice.
    Trust me that a programmable supply, which I assume you mean some
    thing like a large bulky bench supply and not some IC, is out of the
    question. It totally defeats the purpose of what I'm trying to do.
    This is a side project with part learning and part utility. If it
    performs extremely well then it could be marketed so I don't want to
    limit it's capabilities just to save a few bucks and hours in the
    short term.

    Now if there are small modules/IC's that do exactly that then it
    definitely would be something to look into. In fact this would be
    preferred rather than implementing it discretely assuming it isn't too
    costly.
     
  16. neon

    neon

    1,325
    0
    Oct 21, 2006
    If you want to learn about voltage-current sources the easy thing is look up lm317 regulators. Basicaly is a 1.2v regulator that can be designed to do both.
     
  17. JosephKK

    JosephKK Guest

    I think if it were me i would start with a 24 to 36 V feed that into a
    two transistor inverter then to a transformer followed by a voltage
    multiplier; finally a skimming regulator and current limiter. Best
    efficiency, all reasonable parts, add fast shutdown for load faults
    and all that is good.
     
  18. Actually, we do have several examples of exactly what Jon is
    talking about. A voltage-controlled voltage-source, VCVS, is
    simple enough: Use an amplifier. Voltage-controlled current
    sources, or VCCS, as spice calls them, or transconductance
    amps, come in several forms. The Howland circuit (AoE 2nd
    pg 182) is often mentioned in textbooks. It's not one of my
    favorites, but just yesterday I came across one in Keithley's
    642 electrometer, where it does a great job of adding an input
    offset voltage to a discrete MOSFET follower opamp stage.

    I'm more fond of circuits like AoE fig 4.11, page 181, where an
    intrinsically high-impedance device configuration (BJT collector
    or MOSFET drain) is used for the output. These are easy to
    setup in a bipolar form, if needed.

    You can find many different forms of these circuits discussed
    in detail on s.e.d in the Google archives, if you look.
    http://groups.google.com/advanced_search

    I'm especially fond of a circuit that I developed in collaboration
    with Tony Williams, an old s.e.d. regular, R.I.P., such as here,
    http://groups.google.com/group/sci.electronics.design/msg/50c27d2be1a63489

    You can download my RIS-496 programmable CS circuit, see,
    ftp://ftp.rowland.org/pub/hill/RIS-496-1.pdf
    This circuit has been discussed several times on s.e.d, like
    http://groups.google.com/group/sci.electronics.design/
    browse_frm/thread/3ea0f2abab62703a/37b18ceb992e5b69

    I recently upgraded the circuit to use power MOSFETs instead
    of Darlington transistors (they have serious second-breakdown
    problems, severely limiting their high-voltage power capability).
    The new circuit is called an AMP-671, and its output features
    a pair of opamp-controlled MOSFET current sources. These
    circuits can have a voltage-control stage added, so they're a
    programmed current source until a voltage limit is reached.

    Win
     
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