Summer Fun Circuit - Negative Resistance oscillator circuits

[Born2BeWired]

Looking for a simplest and cheapest electronics circuits you can build and tinker this summer? It could not get any simpler than the following circuit.

A NPN transistor with C-E connected the wrong way may exhibit a Negative Differential Resistance NDR. NDR  is a region in the collector to emitter I-V curve where increasing current results in decreasing voltage (-dV/dI = -R). This is a well known phenomenon, but still is something you won?t see  in datasheets and textbooks.

NDR allows you to build several useful circuits with just a few components. Like a sawtooth generator which you can build with just 3 parts.

A complete sawtooth generator working prototype


Not all NPN transistor will exhibit this phenomenon. I made a quick test with several of my TO-92s NPN and found out the 2222 variety (2N2222A, PN2222A, MPS2222A, etc)  seems to give the largest NDR range. So I decided to make a more detailed characterization of this device and came up with the following results:

Transistor Type: KSP2222A
Ambient Temp: 32C  RH: 78%
Instruments used: TEK TDS784 1GHz DSO, Keithley 2430 SourceMeter

Current   Vce
(uA)       Volts
1   8.95
10   8.84
20   8.55
30   8.21
31   8.17
32   8.12
34   7.98
36   7.09
38   6.97
40   6.85
42   6.42
44   5.58
46   5.29
48   5.25
50   5.29
60   5.46

Current   Vce
(mA)      (Volts)
0.1   9.09
0.2   8.42
0.3   8.24
0.4   8.08
0.5   7.98
0.6   7.91
0.7   7.85
0.8   7.8
0.9   7.77
1   7.74
2   7.57
3   7.45
4   7.35
5   7.25
6   7.15
7   7.07
8   6.88
9   6.79
10   6.66
11   6.54
12   6.43
13   6.35
14   6.28
15   6.17
16   6.04
17   5.94
18   5.92
19   5.91
20   5.9
30   5.84
40   5.82
50   5.84


What I found very interesting with the 2222 data is the revelation of two negative differential resistance occurring on two current regions. One shows up in the 10uA to 50uA range, and the other, much wider valley, occurring on 100uA to 40mA range. I am expecting NDR occuring in the mA region, but this is the first I have seen it occurring in the 10uA region.

The uA region turned out to be useful in generating noise, the 2222 device under test generated a hefty one as the sourcemeter pumped out a constant 42-46uA current through the device. The test setup is shown in the following photo.



Connecting a 10K resistor and a 100nF capacitor resulted in a very simplistic sawtooth generator circuit. This circuit will work with supply voltage >9VDC, and generates sawtooth frequencies in proportion with the supply voltage. A simple VCO!. Driving the base with a rectangular wave gets you a pulse keyed output.

NDR Sawtooth generator circuit


Actual waveform generated by the above ckt


NDR sawtooth with pulse gating input


Actual waveform of gated NDR sawtooth generator




It is possible to generate sine and other waveforms with a few more components. More from the following links:

http://jlnlabs.online.fr/cnr/negosc.htm
http://www.intalek.com/Index/Projects/Research/Negistor.htm
http://www.vk2zay.net/article.php/157

Enjoy!

[paranz]

i got 120mV peak to peak sawtooth output using multisim with TTL 1khz freq

its 400mV peak to peak at 100 hz 

galing ng multisim 

['yus]

hindi ko na naman napagana yung NDR Sawtooth generator circuit  sa simulation.. 
mukhang magiging "busy" na naman ako bukas sa work.. hehe

@Born2BeWired
napagana mo ba sya sa simulation? sa multisim ba yan?

[mArKhAo]

panu po pag mathematical approach?  

[paranz]

hindi ko na naman napagana yung NDR Sawtooth generator circuit  sa simulation.. 
mukhang magiging "busy" na naman ako bukas sa work.. hehe

@Born2BeWired
napagana mo ba sya sa simulation? sa multisim ba yan?

hehe actual lab equipments gamit nya, not multisim.

Im surprised my multisim simulation worked 

panu po pag mathematical approach? 

walang math, its pure empirical, trial and error design 

[beginner wan]

nice post si born2bewired. galing nung circuit, simple lang pero ang galing...hehehe...

OT:sir julznc, diesel generator ka na din ah.. congrats..

['yus]

hehe actual lab equipments gamit nya, not multisim.

i'm referring dun sa naka-post na schematic.. 

OT:sir julznc, diesel generator ka na din ah.. congrats..

sumusunod na ako sa yapak ni sir paranz.. "paranz the ________".. hehe

[Born2BeWired]

@julznc, Orcad schematic, di ako gumagamit ng simulation. Congratz din sa gold star mo!

I would have challenged everyone to try the circuit with simulation to see if simulation software can model this unusual circuit, but sir paranz beaten me to it .

And I was really surprised it did. I disdain analog simulation software because of several bad experience I had with their use.  Maybe it is time for me to take a second look. 

sir paranz, pacopy ng multisim

[rdpzycho]

marami workarounds with simulation. pero hindi laging tama yung models nila, mostly kailangan pang palitan ng malapit sa real world models. for simple circuits mas nadadalian pa rin ako ng actual test.

ideal world kasi sila, Bistable Multivibrator won't normally run on a simulator kasi walang difference sa components on both sides. kailangan pa lagyang ng trigger or lagyan ng difference.

yung mga the best na simulator mahirap kumuha ng "free" version. medyo masaya na ako sa OrCad PSice.

[paranz]

@julznc, Orcad schematic, di ako gumagamit ng simulation. Congratz din sa gold star mo!

I would have challenged everyone to try the circuit with simulation to see if simulation software can model this unusual circuit, but sir paranz beaten me to it .

And I was really surprised it did. I disdain analog simulation software because of several bad experience I had with their use.  Maybe it is time for me to take a second look. 

sir paranz, pacopy ng multisim

sa emule po marami doon madownload from version 5 to 10 

[mArKhAo]

di ko mapalabas sa simulation

[paranz]

 

[mArKhAo]

bakit po ganun?

yun din po mismo ung ginawa q, with function gen.

['yus]

nag-overtime ako sa work para lang dito.. hehe
my own circuit:
Q1 = BCX56
C1 = 220nF
R1 = 10kohm
V1 = 10V


result:
frequency = 387Hz sawtooth (voltage dependent)
5.72V pk-to-pk, 7.80V peak

[paranz]

i love that scope! 

[mArKhAo]

 

bakit sa akin ayaw. 

['yus]

i love that scope! 

sir paranz, turuan mo pa ako ng ibang techniques sa "art of spamming" gaya nito!
basic pa lang kasi ang alam ko..

[paranz]

sir paranz, turuan mo pa ako ng ibang techniques sa "art of spamming" gaya nito!
basic pa lang kasi ang alam ko..

you already reached 1k posts, therefore, you have mastered it already hehe 

['yus]

back to topic:
@Born2BeWired
na-try mo na yung sine wave generator? yung gaya nito:

http://jlnlabs.online.fr/cnr/negosc.htm

[mArKhAo]

d q mapagana sa simulation