PN Junctions, Zener and Avalanche Breakdown

Discussion in 'General Electronics Chat' started by cbecket13, Nov 25, 2014.

  1. cbecket13

    Thread Starter Member

    Nov 15, 2014
    106
    3
    I am experimenting with reverse biased Zener and Avalanche breakdown and noise generation. I also have just started testing a handful of junk box transistors as well as some new assortments.

    I'm using a pretty simple setup;

    Reverse biased Transistor pn junction test.JPG
    I'm not using any amplification. It works fairly well on a breadboard. I've tested dozens, at least, of devices and separated and labelled the ones I find interesting. I find the onset of the breakdown noise and look for a sensitive "sweet spot" just past the knee.

    I leave it running quite often over night with various pn devices and bias voltages. Then I run the results through Audacity software, check the spectrograms and the waveform and the frequency spectrum.

    I have been noting in the waveform some extremely high (relatively) fast spikes, sometimes to clipping.

    These spikes seem to be randomly occurring, clustered or isolated, day or night etc. They are definitely discreet, fast events caused by something. Could it be cosmic rays, muons, gamma radiation, etc. Or are they just some kind of artifact of the apparatus?
     
  2. MrChips

    Moderator

    Oct 2, 2009
    12,442
    3,361
  3. WBahn

    Moderator

    Mar 31, 2012
    17,747
    4,796
  4. Alec_t

    AAC Fanatic!

    Sep 17, 2013
    5,800
    1,103
    You might also want to monitor the output of your power supply.
     
  5. cbecket13

    Thread Starter Member

    Nov 15, 2014
    106
    3
    Ideas for a good circuit to do this?
     
  6. Alec_t

    AAC Fanatic!

    Sep 17, 2013
    5,800
    1,103
    Whatever you're using to monitor the breakdown noise should do; just taking its input from the +ve rail.
     
  7. cbecket13

    Thread Starter Member

    Nov 15, 2014
    106
    3
    Here's two hours of the waveform for the effect rendered by Audacity software. The full file is 9 hours. shot_flicker_x_noise.jpg The small ripples in the main sections are the breakdown noise of the junction just barely past the knee. They look very "noise-like" when zoomed in but they are not amplified in hardware or software here.

    But my question was about the tall spikes within the breakdown noise. It's highly intermittent, just a few, if any, per hour. Would that frequency of occurrence be compatible with shot noise or 1/f noise.
     
  8. Alec_t

    AAC Fanatic!

    Sep 17, 2013
    5,800
    1,103
    Have you monitored the power supply rail to see if that is the source of the spikes?
     
  9. cbecket13

    Thread Starter Member

    Nov 15, 2014
    106
    3
    Should I use the ground on the sound card with the ground on the power supply. I assume you mean run it through a capacitor so should my reference be the power supply ground, the sound card ground or both ? Same circuit as above, but with the transistor removed and that post grounded?
     
  10. Brownout

    Well-Known Member

    Jan 10, 2012
    2,375
    998
    g
    That can happen when an appliance, say a refrigerator, turns on or off.
     
  11. Alec_t

    AAC Fanatic!

    Sep 17, 2013
    5,800
    1,103
    Yes.
    Yes. Post #1 circuit with everything except C1 removed. Power +ve rail > C1 > sound card input.
     
  12. atferrari

    AAC Fanatic!

    Jan 6, 2004
    2,648
    764
    Any chance to say their duration?
     
  13. cbecket13

    Thread Starter Member

    Nov 15, 2014
    106
    3
    I will, but I've got to wait till I get home in a couple hours to post it.
     
  14. cbecket13

    Thread Starter Member

    Nov 15, 2014
    106
    3
    I attached an image. The time scale is at the top. It looks like the spike itself is something like 0.0002 second
    with a precursor of about 0.001 second. A hysteresis period of about 0.003 second follows. spike_duration.jpg
     
  15. cbecket13

    Thread Starter Member

    Nov 15, 2014
    106
    3
    Here's what I came up with for a power supply monitoring circuit, again run into my sound card. I'm running it now and no spikes yet, but I'm going to run it for > 9 hrs. Power_Supply_Noise.png
     
  16. ian field

    Distinguished Member

    Oct 27, 2012
    4,415
    784
    There are numerous examples in hobby magazines that use a series pair of PP3 type 9V batteries. The current limiting resistor is usually pretty high.
     
  17. cbecket13

    Thread Starter Member

    Nov 15, 2014
    106
    3
    Here's what I got from the capacitor only circuit. They seem to persist, though the rate seems reduced. I supposed that indicts the power supply or the mains. Capacitor_Only.jpg
     
  18. Alec_t

    AAC Fanatic!

    Sep 17, 2013
    5,800
    1,103
    Yes, looks like interference on the power supply rail. Or it could be interference getting through from the PC to the sound card; or even a sound card fault.
     
  19. cbecket13

    Thread Starter Member

    Nov 15, 2014
    106
    3
    This use of the sound card for data acquisition is probably not ideal. Unfortunately, it remains the lowest cost option. Buying batteries for an application like this is a wallet buster. And I absolutely have to have at least +18V (+-9) or more variable down to 2V or so, or even lower. The power supply is nothing special. "Bog-standard" as they might say in the UK.
    power_supply.jpg
     
  20. cbecket13

    Thread Starter Member

    Nov 15, 2014
    106
    3
    Maybe the circuit should have been:
    Power_Supply_Noise.jpg
    I'll try that a while.
     
Loading...