Author Topic: Why zener diode is glowing?  (Read 5808 times)

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Offline Kedar264

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Why zener diode is glowing?
« on: March 08, 2015, 07:03:26 am »
When I reverse biased 12 v zener diode  it glows red , on the background  blue light is of power supply ,does this effect same as LED?
See this video
http://youtu.be/BgQRbyeZBHo
 

Online blueskull

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Re: Why zener diode is glowing?
« Reply #1 on: March 08, 2015, 07:13:05 am »
Every thing glows if you fry it with enough voltage.

Watch the video carefully, and you will see that the glowing decays slowly after power is off. This suggests it is glowing because high internal temperature.
 

Offline amyk

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Re: Why zener diode is glowing?
« Reply #2 on: March 08, 2015, 07:13:45 am »
Because it's getting hot enough to glow. How much reverse current are you putting through it?
 

Offline T3sl4co1l

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Re: Why zener diode is glowing?
« Reply #3 on: March 08, 2015, 07:22:54 am »
Never seen that before.

Silicon has been known to emit light under avalanche (reverse bias) conditions.  For example, a 2N3055 emitter-base junction emits a green-yellow sort of light, very faint (it's barely visible indoors at 1A!).

Possible you've got a strange substitute, like a stack of LEDs. Though it should be a lot brighter if that were the case, and it wouldn't conduct in the "forward" direction.

Testing a 1N5242B right now, I don't see anything.

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Offline bktemp

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Re: Why zener diode is glowing?
« Reply #4 on: March 08, 2015, 07:44:59 am »
Never seen that before.

Silicon has been known to emit light under avalanche (reverse bias) conditions.  For example, a 2N3055 emitter-base junction emits a green-yellow sort of light, very faint (it's barely visible indoors at 1A!).
It is quite inefficent, but depending in on the size of the junction I can see the light at a few 10mA using small TO18 and need around 100mA for large TO3 transistors. It is not bright but you can see it indoors without much lighting.

I have seen pictures of glowing zener diodes several times, but was not able to see it myself. It is quite rare. Maybe some sort of impurities in the silicon are needed to generate light.
The diode in the video does not look like heating up: The light is almost instantly there, no time for heating up. The slow decay maybe a charged cap slowly decreasing the current thru the diode. Since most image sensors are sensitive to near IR, hot glowing objects typically have a white or at least not so intense color than in the video.
 

Online Psi

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Re: Why zener diode is glowing?
« Reply #5 on: March 08, 2015, 08:05:57 am »
Ive seen something like this before

Mate: Damn it, why is it not working, the led is on.
Me: Dude: that's not an led, that's a signal diode on fire.
Greek letter 'Psi' (not Pounds per Square Inch)
 

Offline Kedar264

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Re: Why zener diode is glowing?
« Reply #6 on: March 08, 2015, 08:40:46 am »
Watch carefully ,when power supply is turned off ( blue light goes off) and zener diode intensity also  ,after doing this the diode is working Good and its not fried.
 

Offline Kedar264

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Re: Why zener diode is glowing?
« Reply #7 on: March 08, 2015, 08:47:36 am »
I used zener diode for battery cutoff circuit so I connected it to base of transistor with 47k resistor
 

Offline Refrigerator

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Re: Why zener diode is glowing?
« Reply #8 on: March 08, 2015, 09:24:46 am »
The silicon is getting hot, and because it's just squeezed in between the leads and there's no bondwire it just continues to glow.
Most diodes have a little bondwire going from one lead to the silicon die, the production a little more reliable that way, yet it will blow if too much current is passed that way.
What you have there is effectively an incandescent bulb.
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Offline dannyf

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Re: Why zener diode is glowing?
« Reply #9 on: March 08, 2015, 12:17:40 pm »
p-n junctions are known to behave like leds. 2n3055 for example - you can find pictures of them on the web.
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