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LC circuit

K

Ken

Jan 1, 1970
0
Hi,

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.

thanks
Ken
 
K

Ken

Jan 1, 1970
0
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.

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

John Larkin

Jan 1, 1970
0
Hi,

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.

thanks
Ken

Google "lc oscillator"

John
 
J

John Popelish

Jan 1, 1970
0
Ken said:
Hi,

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.

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.

http://my.integritynet.com.au/purdic/lc-meter-project.htm#circuit-osc
 
J

John Larkin

Jan 1, 1970
0
Liek I said, I tried Google= nothing
I am NOT lookign for theory on it. I want a schematic.

Ken

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

John
 
J

John Popelish

Jan 1, 1970
0
Ken said:
Looks good, thanks
here is a link with my circuit so far and my problem:
http://www3.sympatico.ca/lerameur/

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.
 
J

John Popelish

Jan 1, 1970
0
Ken said:
yes that is exactly it.
I have been trying to find a solution to this a over a week now. You have
any ideas?
K
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.
 
B

Brian

Jan 1, 1970
0
Ken said:
Looks good, thanks
here is a link with my circuit so far and my problem:
http://www3.sympatico.ca/lerameur/

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)?

Brian
 
K

Ken

Jan 1, 1970
0
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,


... 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:
http://www3.sympatico.ca/lerameur/

Ken
 
J

John Popelish

Jan 1, 1970
0
Ken said:
.. 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.

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
measurement).
I have added a second circuit to the site:
http://www3.sympatico.ca/lerameur/

Add the follower between the resonant circuit and the diodes.
 
K

Ken

Jan 1, 1970
0
You have just described an oscilator.... -)-)-)
try googling for that!!!

Actually its an oscillator-resonator,
cannot accomplish that with semiconductors
 
K

Ken

Jan 1, 1970
0
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) ]
john


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:
http://www3.sympatico.ca/lerameur/

ken
 
K

Ken

Jan 1, 1970
0
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:
http://www3.sympatico.ca/lerameur/

Sorry After zooming in , .. it IS a sin wave. sorry again.
 
J

John Jardine.

Jan 1, 1970
0
Ken said:
.. 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:
http://www3.sympatico.ca/lerameur/

Ken

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) ]
john

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
 
S

Sjouke Burry

Jan 1, 1970
0
Ken said:
Hi,

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.

thanks
Ken
You have just described an oscilator.... -)-)-)
try googling for that!!!
 
John, like probably you,I get 612,000 hits on "lc oscillator using
Google.

The very first hit of the 612,000 is:

http://www.electronixandmore.com/articles/oscillators.html

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
information.

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

Harry C
 
K

Ken

Jan 1, 1970
0
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.

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.

K
 
B

Bob Myers

Jan 1, 1970
0
Ken said:
Actually its an oscillator-resonator,
cannot accomplish that with semiconductors

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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