ffrige Posted March 2, 2004 Report Share Posted March 2, 2004 Hi. I ran into the problem of subtracting two impedances. I thought I could solve it simply by putting the first in series with the negation of the second (using a negative impedance converter), but something is not working. Is it really possible, for example, to put a resistance in series with its negative equivalent and then read zero across the two with a simple ohmmeter? Or is the circuit more complicated? Thanks! Quote Link to comment Share on other sites More sharing options...
MP Posted March 2, 2004 Report Share Posted March 2, 2004 It is a little more complicated than that and the cure is dependent upon the characteristics of your circuit.It is a well discussed topic and I am not an expert on it. Using the search words, "compensate negative impedance", I find 83 pages of articles on google.com . Many are pdf files with schematics. I would start there.MP Quote Link to comment Share on other sites More sharing options...
Ldanielrosa Posted March 3, 2004 Report Share Posted March 3, 2004 Yes to the last one. The circuit is more complicated. The term "negative resistance" is used to describe the behavior (oops, most of the folks here are in Europe, so that's behaviour) of the device as the voltage (or current) varies within the range so described. Instead of voltage and current increasing or decreasing together (linearly or otherwise), and increase in one is the cause or result of a decrease in the other. Quote Link to comment Share on other sites More sharing options...
Silkarian Posted November 2, 2005 Report Share Posted November 2, 2005 Does anyone know why if the frequency of the impedance converter input voltage is increased thephase shift will vary? Quote Link to comment Share on other sites More sharing options...
prateeksikka Posted November 2, 2005 Report Share Posted November 2, 2005 hi ffrige!as far as i know there is no negative impedance!u can only make it capacitive or inductive by conjugates of corresponding complex values.how did u acheive this negation of impedance? Quote Link to comment Share on other sites More sharing options...
Guest Alun Posted November 2, 2005 Report Share Posted November 2, 2005 A neggitive impedance reduces its resistance as the current increases instead of remaining constant, this means that if the current is increased the voltage across it won't increase proportionally as ohms law normally states and in some cases can cause destruction of the componants.Examples of negitive impedances are:Electrical arcs this includes discharge lamps (neon, flourescent, sodium ect.).Transistors, eg. output stages of class AB amplifiers.Negitive coefficient thermistors.Diacs.Zener diodes.Diodes.LEDs.The first two have the desructive properites I described before the current is limited with a ballast inductor or resistor with discharge lamps and purly with resistors in amplifier output stages. Results from experiment I've conducted indicate you can (despite what some people say) power LEDs from a constant voltage source but it has to be exactly the right voltage for the forward current you require and this is totally differant for each LED even if they have the same make/model. Quote Link to comment Share on other sites More sharing options...
V8meathead Posted November 3, 2005 Report Share Posted November 3, 2005 There are also negative resistance Op-Amp circuits. Voltage increases inversely(?) I believe with current. I believe it looks like a negative slope. If you are really interested. I will take the time to verify it for you, just ask. Quote Link to comment Share on other sites More sharing options...
prateeksikka Posted November 5, 2005 Report Share Posted November 5, 2005 hi all!A device can never be purely negative resistance.Even a tunnel diode has a negative resistance but that too in a definite voltage range.But there is no negative resistance of say -4 ohms as such. ;D Quote Link to comment Share on other sites More sharing options...
V8meathead Posted November 6, 2005 Report Share Posted November 6, 2005 http://www.maxim-ic.com/appnotes.cfm/appnote_number/815/ln/enWhat's your take on this? ??? Quote Link to comment Share on other sites More sharing options...
prateeksikka Posted November 12, 2005 Report Share Posted November 12, 2005 hi there!this also says the same as i said in my last post .u commercially cant get a negative resistance of say -10 ohms .only some devices exhibit such results and that too under some conditions. Quote Link to comment Share on other sites More sharing options...
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