# zener and avalanche diodes-change in characteristics with temperature

Discussion in 'General Electronics Chat' started by legend killer, Dec 31, 2013.

1. ### legend killerMember

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Hello everyone
I am trying to understand the effect of temperature on the reverse characteristics of zener and avalanche diodes.
Uptil now i've learned that the reverse current increases with temperature for both zener and avalanche diodes. I want to understand the effect of temperature on the breakdown voltage of zener and avalanche diodes.
Does zener diode have negative temperature coefficient and avslanche have positive temp coefficient, If is it so, does that mean that breakdown voltage of zene
r diode decreases with temperature and vice-versa for avalanche diodes?

2. ### audioguruWell-Known MemberMost Helpful Member

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I buy and use zener diodes, I do not make them so I do not bother if they zener or if they avalanche.
If you look at the datasheet for a family of zener diodes you will see that a 5.6V one has close to zero temperature coefficient.
A smaller voltage zener diode has a negative and a higher voltage has a positive temperature coefficient.
A zener diode that is about 7V has the best voltage regulation.

I found this graph but it did not agree with datasheets so I fixed it so that 5.6V has a zero temperature coefficient.

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3. ### legend killerMember

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Hi audioguru
Actually i wanted to understand how the reverse breakdown voltage changes with temperature. As you said, it doesnt matter whether they are zener or avalanche when we use it. But just for the sake of theoretical knowledge, what is the difference.
I had two diagrams showin the difference. Although the curves are shown far apart, its just for illustrative purpose. Do u think the graph is correct. I am not sure about the authenticity of the graph

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5. ### audioguruWell-Known MemberMost Helpful Member

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I do not know what you want to know and I do not know why.

6. ### crutschowWell-Known MemberMost Helpful Member

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From Wikipedia:

The Zener effect is a type of electrical breakdown in a reverse biased p-n diode in which the electric field enables tunneling of electrons from the valence to the conduction band of a semiconductor, leading to a large number of free minority carriers, which suddenly increase the reverse current,

The avalanche breakdown is due to minority carriers accelerated enough to create ionization in the crystal lattice, producing more carriers which in turn create more ionization.

Thus the Zener effect is due to tunneling of electrons and the avalanche effect is due to ionization of the carriers due to the high voltage gradient across the junction.

So temperature apparently makes it easy for electrons to tunnel across the junction but more difficult to avalanche. Further elaboration of this would likely require some quantum mechanical equations which are beyond my pay scale.

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7. ### legend killerMember

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Thanks crutschow for your valuable input.
Let me try to explain again what i want to know. There are two types of diodes-Avalanache and zener. I just want to know that does avalanche diodes have positive temperature coefficient and zeners have negative temperature coefficient?

8. ### crutschowWell-Known MemberMost Helpful Member

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Yes they do. Just don't ask me why.

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9. ### audioguruWell-Known MemberMost Helpful Member

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They are both called "a zener diode.

10. ### RatchitWell-Known Member

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LK,

"I am trying to understand the effect of temperature on the reverse characteristics of zener and avalanche diodes.
Uptil now i've learned that the reverse current increases with temperature for both zener and avalanche diodes."

No, it doesn't, you learned wrong. The reverse current through any diode depends on the breakdown voltage and the load it is trying to regulate. Even without any change in temperature, the reverse current of the diode will vary depending on the load impedance. Perhaps you mean the temperature dependence of the Zener breakdown voltage.

"I want to understand the effect of temperature on the breakdown voltage of zener and avalanche diodes."

OK.

"Does zener diode have negative temperature coefficient and avslanche have positive temp coefficient,

For what, the breakdown voltage? If so, then yes.

"If is it so, does that mean that breakdown voltage of zene
r diode decreases with temperature and vice-versa for avalanche diodes?

Yes, it does.

"Actually i wanted to understand how the reverse breakdown voltage changes with temperature. As you said, it doesnt matter whether they are zener or avalanche when we use it. But just for the sake of theoretical knowledge, what is the difference.
I had two diagrams showin the difference. Although the curves are shown far apart, its just for illustrative purpose. Do u think the graph is correct. I am not sure about the authenticity of the graph"

They both look good to me.

Ratch

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11. ### audioguruWell-Known MemberMost Helpful Member

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In my post #2 I showed a graph I found that shows that a low voltage zener diode has a negative temp coefficient, a 5.6V zener diode has zero coefficient and a higher voltage zener diode has a positive coefficient. But before I found the graph I saw the results printed in text on a datasheet of a family of zener diodes.

12. ### nsaspookWell-Known Member

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It's mainly the doping levels needed to create the correct width depletion zone for the diode working voltage and the manner of reverse bias carrier generation
from the junction e-field effects at that voltage.
This document has the detailed process reasons of why.

Pages 5,6&30

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13. ### legend killerMember

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Thank you all for the replies.