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LC circuit

Discussion in 'Electronic Basics' started by Ken, Mar 3, 2006.

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  1. Ken

    Ken Guest


    I am looking for a method to keep an oscillation going in a tank circuit (
    inductor parallel to a capacitor). Therefore I would just like inject into
    the circuit the power loss created by the natural resistance everyone so
    cycle or a percentage of the peak value..
    Yes I tried google and nothing comes close to what I m lookign for.

  2. Ken

    Ken Guest

    Liek I said, I tried Google= nothing
    I am NOT lookign for theory on it. I want a schematic.

  3. Ken

    Ken Guest

  4. Ken

    Ken Guest

    yes that is exactly it.
    I have been trying to find a solution to this a over a week now. You have
    any ideas?
  5. John Larkin

    John Larkin Guest

    Google "lc oscillator"

  6. This sort of oscillator is often referred as a negative resistance
    oscillator, because once the negative resistance gets higher than the
    loss resistance, oscillations ensue.

    Here is an LC meter that uses a comparator to produce the negative
    resistance to keep an arbitrary LC tank oscillating.
  7. John  Larkin

    John Larkin Guest

    You must be using a different Google than the one I use.

  8. As I understand your problem (correct my errors) you want to cause an
    LC tank to oscillate. But you don't want it to be driven into
    oscillation, continuously, but given a blast of energy only when the
    oscillation has damped down to some minimum amplitude. I don't
    understand if the blast is to be a single pulse, of a negative
    resistance that feeds energy in, slowly, till the amplitude gets to a
    second, larger amplitude. Then there is some other feature about
    operating only when the supply voltage is larger than some value.
  9. I would think in terms of adding a high input impedance buffer to the
    tank, so you can use that output for both the positive feedback that
    generates the negative resistance, and also feeds the rectifier, so
    you can use that to measure the amplitude, without loading down the
    tank. Then you need a comparator, with hysteresis (some positive
    feedback), to make the drive versus coast decision, based on the
    rectified and filtered tank amplitude signal. A second comparator and
    some sort of voltage reference would be used to shut the drive down
    when the supply voltage is too low. You might use a CMOS analog
    switch to turn the negative resistance drive on and off, based on
    these two control signals. This might all be distilled down to a few
    transistors, but doing it with nice, clean functional blocks, first,
    will probably get you a working unit, sooner.
  10. Brian

    Brian Guest

    When VComp's output goes low, does that turn the simple switch off. If not,
    that is your problem. Have you checked to make sure that VSen1 is turning
    on, when capacitor C3 has the positive charge on it? If VSen1 does turn on,
    does VComp turn off, when VSen1 turns on? The only thing that can discharge
    C3, is the input of VSen1. If VSen1 has a CMOS input, that current could be
    very small. Also, have you tried using another VSen1 device (in case the one
    you are using is bad)?

  11. Ken

    Ken Guest

    I would think in terms of adding a high input impedance buffer to the

    ... Sorry , I am not sure what you mean by that. I know you are talking about
    a voltage follower with unity gain , but what for.

    I have added a second cirduit to the site:

  12. A follower would be one example of what I am thinking about. Any non
    inverting amplifier configuration with a high input impedance might
    work. But you could try a follower if you have no particular need for
    more gain. You put energy into the tank, but you use the copy of its
    voltage from the follower for any need to have information about what
    is going on in the tank (phase feedback for the driver, or amplitude
    Add the follower between the resonant circuit and the diodes.
  13. Ken

    Ken Guest

    Actually its an oscillator-resonator,
    cannot accomplish that with semiconductors
  14. Ken

    Ken Guest

    WOW this is a great program ,
    thankyou for your time. You circuit is for sure better then mine.
    How does LT spice compare with Pspice or Orcad 10.5 , any idea ??
    I am going to take a day to see how your circuit woks completely, but from
    the simulation , its not giving me a nice wave.
    I posted the output at this site:

  15. Ken

    Ken Guest

    Sorry After zooming in , .. it IS a sin wave. sorry again.
  16. Your first circuit was nearly there!. Needs a discharge path across C3.
    Probably more important is that the circuit has a perfectly stable state in
    the non oscillating condition that you noted.
    A sim needs the comparitor "+" input holding at 0V until the circuit has
    stabilised. Releasing it will then give the 'kickstart' to force the circuit
    into it's oscillating mode.
    Difficult to make a 'good' circuit given the small number of components and
    how they all notice each other. Really a couple of monostables and a
    flip-flop wouldn't go amiss.
    Below is similar but working circuit in the "LTspice" format. Includes a bit
    of hysteresis for the comparitor, a transistor for the 'switch' and a CR to
    give a rough LC energising pulse. Should though be buildable for real.
    Side note; Tuned circuit Q factor can be measured simply as counting the
    number of cycles to the point where the voltage has dropped to 4.3% of the
    initial voltage. [ InitialV / (e^pi) ]

    Version 4
    SHEET 1 880 680
    WIRE -576 -48 -576 -128
    WIRE -576 64 -576 32
    WIRE -576 96 -576 64
    WIRE -576 208 -576 176
    WIRE -496 64 -576 64
    WIRE -496 112 -496 64
    WIRE -496 208 -496 176
    WIRE -400 160 -400 96
    WIRE -400 176 -400 160
    WIRE -400 272 -400 256
    WIRE -368 64 -496 64
    WIRE -368 96 -400 96
    WIRE -336 -128 -576 -128
    WIRE -336 48 -336 -128
    WIRE -336 160 -400 160
    WIRE -256 -128 -336 -128
    WIRE -256 -48 -256 -128
    WIRE -256 80 -304 80
    WIRE -256 80 -256 32
    WIRE -256 160 -272 160
    WIRE -256 160 -256 80
    WIRE -176 272 -400 272
    WIRE -176 320 -176 272
    WIRE -176 512 -176 400
    WIRE -160 -128 -256 -128
    WIRE -160 -112 -160 -128
    WIRE -160 0 -160 -32
    WIRE -112 272 -176 272
    WIRE -112 336 -112 272
    WIRE -112 512 -112 400
    WIRE -96 80 -256 80
    WIRE -80 272 -112 272
    WIRE -16 -128 -160 -128
    WIRE -16 -48 -16 -128
    WIRE -16 80 -32 80
    WIRE -16 80 -16 16
    WIRE 32 -128 -16 -128
    WIRE 32 -64 32 -128
    WIRE 32 80 -16 80
    WIRE 32 80 32 16
    WIRE 48 272 -16 272
    WIRE 48 352 48 272
    WIRE 48 512 48 416
    WIRE 64 80 32 80
    WIRE 128 -128 32 -128
    WIRE 128 32 128 -128
    WIRE 128 272 48 272
    WIRE 128 272 128 128
    WIRE 128 288 128 272
    WIRE 128 400 128 368
    WIRE 128 512 128 480
    FLAG -160 0 0
    FLAG 128 512 0
    FLAG 48 512 0
    FLAG -112 512 0
    FLAG -176 512 0
    FLAG -576 208 0
    FLAG -336 112 0
    FLAG -496 208 0
    SYMBOL voltage -160 -128 R0
    WINDOW 123 0 0 Left 0
    WINDOW 39 0 0 Left 0
    SYMATTR InstName V1
    SYMATTR Value 10
    SYMBOL pnp 64 128 M180
    SYMATTR InstName Q1
    SYMATTR Value 2N2907
    SYMBOL ind 112 384 R0
    SYMATTR InstName L1
    SYMATTR Value 461m
    SYMBOL cap 32 352 R0
    SYMATTR InstName C1
    SYMATTR Value 15.27µ
    SYMBOL res 16 -80 R0
    SYMATTR InstName R1
    SYMATTR Value 100k
    SYMBOL cap -32 64 R90
    WINDOW 0 0 32 VBottom 0
    WINDOW 3 32 32 VTop 0
    SYMATTR InstName C2
    SYMATTR Value 1µ
    SYMBOL diode -16 256 R90
    WINDOW 0 0 32 VBottom 0
    WINDOW 3 32 32 VTop 0
    SYMATTR InstName D1
    SYMATTR Value 1N4148
    SYMBOL cap -128 336 R0
    SYMATTR InstName C3
    SYMATTR Value 1µ
    SYMBOL res 112 272 R0
    SYMATTR InstName R3
    SYMATTR Value 1
    SYMBOL res -192 304 R0
    WINDOW 3 28 84 Left 0
    SYMATTR InstName R2
    SYMATTR Value 1meg
    SYMBOL Opamps\\1pole -336 80 R0
    SYMATTR InstName U1
    SYMATTR Value2 Avol=1Meg GBW=1Meg Slew=1Meg
    SYMBOL res -592 -64 R0
    SYMATTR InstName R4
    SYMATTR Value 47k
    SYMBOL res -592 80 R0
    SYMATTR InstName R5
    SYMATTR Value 22000
    SYMBOL cap -272 144 R90
    WINDOW 0 0 32 VBottom 0
    WINDOW 3 32 32 VTop 0
    SYMATTR InstName C5
    SYMATTR Value 10n
    SYMBOL res -384 272 R180
    WINDOW 0 -20 48 Left 0
    WINDOW 3 -35 28 Left 0
    SYMATTR InstName R8
    SYMATTR Value 1meg
    SYMBOL diode 0 16 R180
    WINDOW 0 24 72 Left 0
    WINDOW 3 24 0 Left 0
    SYMATTR InstName D2
    SYMATTR Value 1N4148
    SYMBOL cap -512 112 R0
    WINDOW 0 23 8 Left 0
    WINDOW 3 25 50 Left 0
    SYMATTR InstName C4
    SYMATTR Value 10µ
    SYMBOL res -272 -64 R0
    SYMATTR InstName R6
    SYMATTR Value 2k2
    TEXT -584 288 Left 0 !.tran 10
    TEXT -480 48 Left 0 !,ic v(n002)=0
    TEXT -560 48 Left 0 ;("Pot")
    TEXT -440 -8 Left 0 ;(Comparitor LM393)
    TEXT 64 480 Left 0 ;60Hz
  17. Sjouke Burry

    Sjouke Burry Guest

    You have just described an oscilator.... -)-)-)
    try googling for that!!!
  18. Guest

    John, like probably you,I get 612,000 hits on "lc oscillator using

    The very first hit of the 612,000 is:

    Considering that even this first link contains schematics for the
    Armstrong, Hatlesy, Colpitts, Electron Coupled and other common
    oscillators. Evidently you know how to use Google, but Ken doesn't, or
    else he want's someone to hold his hand an spoon feed him very basic

    ....And to Ken, "we ain't you mamma"! :-(

    Harry C
  19. Ken

    Ken Guest

    HI Bob,
    Good question:
    One of the thing I am trying to do well.
    I can only explain well using an analogy.
    You get on a swing set, you generate enough energy so that you start swing
    (oscillating) everutime you reach a peak value, you give yourself (or a
    friend..) a small push to keep going the same amplitude.BUT if you keep
    giving the same push everytime with the same strenght you did the first one,
    you will reach a point where you will no longer get to go any higher, or
    simply break and fall. In an oscillating mechanical system when you reach
    that point, the machine simply over heat or break down. This is what I want
    to do electrically.

  20. Bob Myers

    Bob Myers Guest

    I sure hope you can...vacuum tubes are getting
    harder to come by...:)

    What exactly do you mean by an "oscillator-resonator"?
    I looked over your schematic, and followed the
    thread so far - but unless you really, really need to
    have something that lets an LC tank "ring" all on its
    on, and only kicks it again when the amplitude drops
    down to some given point, this seems like an awful
    lot of trouble to go to for a sine wave - you can do
    THAT with a single transistor. What is it you're really
    trying to do here?

    Bob M.
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