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Conductance Negative

 

Dear all, I am trying to simulate a circuit with negative conductance using transistors and passive components. Does anyone have a circuit for this?
Best regards.
Sebastian?
 

Can be done easily with a behavioral current source. The equation can be defined by:
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I = V(Vi,Vo)/R
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Where Vi and Vo are the voltages across the current source.
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Example netlist with a sweep:
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B1 Vi Vo I = V(Vi,Vo)/V(Vr)
V1 Vi 0 5
Rmeas 0 Vo 1m
V2 Vr 0 1
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On Fri, Mar 28, 2025 at 11:53 AM, <sebastian.herrera@...> wrote:
Dear all, I am trying to simulate a circuit with negative conductance using transistors and passive components. Does anyone have a circuit for this?
Use the educational examples, oscillators, Colpits and remove the resonating inductor leaving the active device and passive feedback?
elements in place. Do a scattering parameter operation and note the modulus of S11 is > unity over the range of potential frequency
of operation. This yields negative conductance. Note there is a nice peak in negative G value in the 1-10 MHz range and extends out to ~ 40 MHz.?
 

On Sat, Mar 29, 2025 at 05:41 PM, alan victor wrote:
Use the educational examples, oscillators, Colpits and remove the resonating inductor leaving the active device and passive feedback?
elements in place. ...
I might be wrong, but I think alan is referring to one of the example schematics that installs on your computer's disk when you install LTspice.
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...\examples\Educational\Colpitts.asc
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Andy
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Yes Andy. Exactly.?
 

I think I have the circuit you need. It is circa-1965 and uses 3-4 bipolar transistors, a zener diode, and a handful of resistors. All components are "garden variety" with nothing special. It works to a few MHz. It IS a 2-terminal device and can be used much like a tunnel diode. Voltages are a lot higher than a tunnel diode: peak voltage is around 2V, valley voltage is around 5V and peak current is a few 10s of mA; all of these values are settable as part of the circuit design. ?I have it ONLY as a PDF but it is simple enough to create in LTspice. I will put it, appropriately named, in the group image/picture directory and post a message with a link. This should be done within a few hours of this message time.
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Jim Wagner
Oregon Research Electronics
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On 03/28/2025 11:44 AM PDT sebastian.herrera via groups.io <sebastian.herrera@...> wrote:

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?
Dear all, I am trying to simulate a circuit with negative conductance using transistors and passive components. Does anyone have a circuit for this?
Best regards.
Sebastian?

 

A negative resistance circuit with brief description has been uploaded to: /g/LTspice/album?id=301539
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Have fun
Jim
 

Along a similar line, this circuit placed in LTspice, provides negative conductance.?
Generate a single DC source sweep on applied V and monitor source current.?
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https://hackaday.com/2019/05/08/fun-with-negative-resistance-jellybean-transistors/#more-356020
 

The circuit referenced in this note does have the advantage of using only NPN transistors and no zener. ?However, the I/V curve is less well defined and you have less control over the peak/valley voltages and currents. Otherwise, part count is similar.
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On "my" circuit, since zeners close to 5.5V are almost ideal and have very sharp knees, using one of those puts the peak voltage close to 5.5V; that may be a bit high for many applications. This circuit is very close to piecewise-linear so it is relatively easy to analyze with some precision. ?Some of the behavior DOES depend pretty strongly on the beta of Q1, however; for many transistors, beta can vary over a rather wide range.
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Jim
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On 03/29/2025 10:09 PM PDT alan victor via groups.io <avictor73@...> wrote:

?
?
Along a similar line, this circuit placed in LTspice, provides negative conductance.?
Generate a single DC source sweep on applied V and monitor source current.?
?
https://hackaday.com/2019/05/08/fun-with-negative-resistance-jellybean-transistors/#more-356020

 

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On 28/03/2025 19:44, sebastian.herrera via groups.io wrote:
I am trying to simulate a circuit with negative conductance using transistors and passive components. Does anyone have a circuit for this?
A constant power load is an example of a circuit with negative resistance. A common example of a constant power load is a switch-mode converter. Quite a few SMPS designers don't appreciate this.

Try this introduction:

--
Regards,
Tony

 

Hi,
?
i have been interested in bipolar NDR devices similar to the Lambda-Diode and did some basic simulations which i can share later, if there is interest.?
I can also recommend the publications by Chua, where he identifies dozens of these circuits:

Negative resistance devices

Negative resistance devices: Part II

Bipolar - JFET - MOSFET negative resistance devices

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For now, try this link:
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Best,
Nils
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I tried to simulate a negative resistance using btdeboi's netlist, but I can't complete the schematic.
Can you help me complete it ?
See Negative Conductance.asc
 

On Mon, Mar 31, 2025 at 03:26 AM, jacfev wrote:
I tried to simulate a negative resistance using btdeboi's netlist, but I can't complete the schematic.
Can you help me complete it ?
See Negative Conductance.asc
Compared to the netlist in btdeboi's?message, there is one omission in your schematic.? Change the formula of the B-source B1, from this:
I = V(Vi,Vo)/R
to this:
I = V(Vi,Vo)/V(Vr)
That's all I can tell you because it is missing a SPICE simulation command (.OP or .DC or .AC or .TRAN?) and I don't know where/why it works.? I guess you need to work that out.
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If you sweep the voltage source V1 (.DC V1 ...), the current through B1 and Rmeas linearly decreases as V(Vi) increases.
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Andy
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On Sat, Mar 29, 2025 at 09:38 PM, Jim Wagner wrote:
I think I have the circuit you need. It is circa-1965 and uses 3-4 bipolar transistors, a zener diode, and a handful of resistors. ...
Jim,
?
Your schematic in the photo you uploaded shows two NPN transistors, but the description that accompanies it mentions "2N3904/6" which implies that one of them is a PNP.? I have not tried (nor studied the circuit in detail), but I wondered if Q2 is supposed to operate in reverse breakdown mode so it is an NPN, or if it was supposed to be a PNP.
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Did you draw that schematic, or was it originally drawn with two NPNs, and is one of them wrong?
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Andy
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So, sorry - that drawing has been bad for lots of years! ?Q2 should be PNP! ?I will correct it. Don't want bad stuff out there. Should I remove the incorrect post?
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Jim

On 03/31/2025 5:56 AM PDT Andy I via groups.io <ai.egrps+io@...> wrote:
?
?
On Sat, Mar 29, 2025 at 09:38 PM, Jim Wagner wrote:
I think I have the circuit you need. It is circa-1965 and uses 3-4 bipolar transistors, a zener diode, and a handful of resistors. ...
Jim,
?
Your schematic in the photo you uploaded shows two NPN transistors, but the description that accompanies it mentions "2N3904/6" which implies that one of them is a PNP.? I have not tried (nor studied the circuit in detail), but I wondered if Q2 is supposed to operate in reverse breakdown mode so it is an NPN, or if it was supposed to be a PNP.
?
Did you draw that schematic, or was it originally drawn with two NPNs, and is one of them wrong?
?
Andy
?

 

A new file has been uploaded: ? ? ? ? ? ? ? ? ? ? ?Negative_Resistance_Ckt.asc.zip ? ? ? ? ??? This is a generic (architectural) schematic with no component values but it IS an LTspice file. Pick a zener (typically around 5V), an NPN transistor (I use 2N3904), a PNP transistor (I use 2N3906), ?I use a few KOhm for R1, R2, R3, R4. ?I use a few hundred ohms for R5. R4 should not be so large that Q1 saturates at peak current. Avoid reverse base-emitter breakdown of Q1 at maximum input voltage.
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Jim Wagner
Oregon Research Electronics
 

Hello everyone,

First of all, I appreciate your comments, suggestions, and circuits. I am reading the papers and will simulate what you suggested. I work in a laboratory where we are characterizing some biological samples, and they exhibit Memristor-like behavior or something similar.

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