1
\$\begingroup\$

Regarding the PN junction diode, is the following information correct?:

enter image description here

How come the reverse breakdown voltage increases with temperature according to the above graph? Am I interpreting the plots wrong?: At 75C the break down is more close to the origin which means to me at higher temperature the breakdown happens at a lower reverse voltage. But the above info says the Vr increases with the temperature. Isn't |Vr| at 75C smaller than |Vr| at 25C?

\$\endgroup\$
3
  • \$\begingroup\$ Not according to this: electronics.stackexchange.com/questions/181995/… \$\endgroup\$
    – CapnJJ
    Jun 5, 2018 at 0:56
  • 2
    \$\begingroup\$ From the graph, it appears that reverse breakdown voltage decreases as you move horizontally from the 25C curve to the 75C curve. So, maybe you have it backwards? Either that or I am the one who is confused. \$\endgroup\$
    – user57037
    Jun 5, 2018 at 6:43
  • \$\begingroup\$ Correct, the caption and plot are contradictory. \$\endgroup\$ Jul 24, 2022 at 22:15

3 Answers 3

1
\$\begingroup\$

Forward Vf are NTC (negative temperature coefficient), and Vzt or Vr are PTC but your thresholds are not to scale. |Vr|>>Vf

Current levels and slopes (ESR) depend on the junction power capacity.

enter image description here

\$\endgroup\$
5
  • \$\begingroup\$ My problem is whether the info on the top of the graph in my question is contradicting the graph. My question is about interpreting that particular graphs. The info says Vr increases with temperature rise but it seems that in the graph |Vr| decreases with temperature. \$\endgroup\$
    – GNZ
    Jun 5, 2018 at 1:35
  • \$\begingroup\$ I just realized I put my hand sketched graph wrong and your graph looks inaccurate too. \$\endgroup\$ Jun 5, 2018 at 2:05
  • \$\begingroup\$ Many often mean |magnitude| then show actual polarized values in a graph. Watch out for this confusion. For example Vr is often a positive value since we define it as reverse. Same result for Zener Voltages as positive. \$\endgroup\$ Jun 5, 2018 at 2:13
  • \$\begingroup\$ As an example for example, if Vr moves to -3V from -6V when the temperature increases; do we say that Vr decreased or increased with temperature? Mathematically -3V > -6V but |-3V| < |-6V|. I don't know which one is correct to say in this context. This also creates confusion when it comes to positive/negative temperature coefficient in reverse region. \$\endgroup\$
    – GNZ
    Jun 5, 2018 at 2:43
  • \$\begingroup\$ Logically when we say reversed voltage threshold we think it as a positive number but in actual values both thresholds shift towards +ve voltage with temperature. The same "inverted" logic applies to increasing a "load" means decreasing R because we are implying increasing current. So the meaning always must have a context or reference in this case Vr means reverse voltage threshold. But for overall %,drift, it would never double in voltage 3 to 6V . Did you see my calculations for 20mV/'C for Vr? but the relative shift = -20mV/'C for Vr = 10x the Vf shift = -2.0mV/'C \$\endgroup\$ Jun 5, 2018 at 3:38
0
\$\begingroup\$

Breakdown voltage does not always increase with temperature (PTC - Positive Temperature Coefficient), and neither is it always decreasing with temperature (NTC - Negative Temperature Coefficient). It depends on what type of breakdown it is. If it is the Avalanche effect causing breakdown, then the breakdown voltage will be PTC. If it is the Zener effect, then the breakdown voltage is NTC. You can read why here.

However, the graph in the picture can be considered correct. If temperature increases, then the reverse breakdown voltage increases from eg. -10V to -9V, that means it increases with temperature on the graph.

\$\endgroup\$
2
  • \$\begingroup\$ Oh so you they call the move from -10V to -9V an increase? I thought they would look at the absolute values. I would call that a decrease. \$\endgroup\$
    – GNZ
    Jun 5, 2018 at 12:35
  • \$\begingroup\$ I can't say for sure if that's what they mean. TBH, I think they just didn't draw it correctly... The arrows on the axis seem to indicate that they're using \$V_R = -V_F\$, which is inconsistent with their explanation. I just wanted to point out that it can be considered correct if you use that convention. \$\endgroup\$
    – Sven B
    Jun 5, 2018 at 12:39
-2
\$\begingroup\$

What we call "zener" diodes are not all zener...the low voltage ones are avalanche diodes. Avalanche diodes have a positive temperature coefficient, while zener diodes have a negative one.

https://circuitglobe.com/difference-between-avalanche-and-zener-breakdown.html

\$\endgroup\$
3
  • \$\begingroup\$ Just as an aside, if you pick a 5.6V Zener/Avalanche diode, both effects occur and nearly cancel out the temperature coefficient, so that's the value to go for for a more temperature-stable reference. \$\endgroup\$
    – John D
    Jun 5, 2018 at 14:56
  • 2
    \$\begingroup\$ It's the other way around; low voltage==Zener, it takes higher voltage to sustain avalanche. \$\endgroup\$
    – Whit3rd
    Jun 6, 2019 at 21:33
  • 1
    \$\begingroup\$ en.wikipedia.org/wiki/Zener_diode voltage below approx 5.6 V is zener. Above that voltage avalanche effect dominates. \$\endgroup\$
    – Aditya P
    Aug 23, 2019 at 19:00

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.