[SOLVED] high voltage zener operation

[Zak28]

...Is it actually capable of delivering 250 watts?

No infact I unfortunately didnt specify the wattage being 25w another words the current is negligible but power is infact 25w

 

[Nik_2213]

"or doesn't it work like that?" It doesn't. Your recommended HV R pair plus a wary Zener rating should have no problem.

Um, is this circuit watching the output of a Cockroft-Walton diode multiplier, by any chance ??
https://en.wikipedia.org/wiki/Cockcroft–Walton_generator

 

[KlausST]

Hi,

Then you can calculate the max possible overall current,
Then determine the useful current which is the same in R and in the zener,
Then you can calculate the power dissipation of R and the zener.

And you will find out that the current is low, the value of R is high and the power dissipation in the zener is negible.

Klaus

 

[Zak28]

...the value of R is high and the power dissipation in the zener is negible...

Why bother limiting current if zener can fully handle it, the 1N2810B for instance can handle more power than the source can deliver.

...output of a Cockroft-Walton diode multiplier, by any chance ??...

No, it is strictly a hypothetical scenario which might materialize in a topology I will put together in the near future, althought with less voltage but still considerably high hence the exaggerated 50kv potential. The object of this question is to understand whether a zener cares any for the potential which breaks it down so as to permit it to regulate it at its defined voltage, which is why I repeatedly reiterated diodes power & temperature would NOT be exceeded.

...In wonder what's the purpose of the circuit, what's the HV source's available current and power?

Source is hypothetical 50kv @ 25w

 

[Audioguru]

No infact I unfortunately didnt specify the wattage being 25w another words the current is negligible but power is infact 25w

A Zener diode has a spec'd current that might be 5mA. It does not work with "negligible current". The resistor will heat with 50kV x 5mA= 250W plus the load current times 50kV.

 

[asdf44]

Ok the bottom line is that a 25W 50kv source can only deliver 500uA of current. Knocked down to 12V via any linear means that’s 0.006W.

Why are you doing this? If you need 12V get it from somewhere else.

 

[KlausST]

Hi,

Why bother limiting current if zener can fully handle it, the 1N2810B for instance can handle more power than the source can deliver.

It's useless to talk about specified zener current when your supply is not able to generate it.
It seems you refuse to calculate with your own specified values to get realistic circuit values and part values.

Then it's useless to further discuss.

Klaus

 

[Zak28]

Hi,


It's useless to talk about specified zener current when your supply is not able to generate it.
It seems you refuse to calculate with your own specified values to get realistic circuit values and part values.

Then it's useless to further discuss.

Klaus

You missed the object of the topic. I know microamps arent enough to get the zener to go into reverse breakdown, the object is wether the zener can survive high voltage and still operate in reverse breakdown.

 

[KlausST]

Hi,

You missed the object of the topic. I know microamps arent enough to get the zener to go into reverse breakdown, the object is wether the zener can survive high voltage and still operate in reverse breakdown.

The answers are already given:
* the zener doesn't know about the high voltage, it just sees the current. And the current is determined by the supplies capabilities and/or the resistor. Depending on which one is smaller.
* the zener datasheet tells you which voltage you can expect at this current.

Klaus

 

[FvM]

You missed the object of the topic. I know microamps arent enough to get the zener to go into reverse breakdown, the object is wether the zener can survive high voltage and still operate in reverse breakdown.

Zener diode voltage is linked to current by an I/V characteristic. To determine the maximum voltage that can be driven into a zener diode, you need to know the current capability of the source. For DC (steady state) current, the question has been answered in part by the "25 W" specification. A complete answer would also specify the voltage short short circuit current and the dynamic behavior.

 

[Zak28]

...the zener doesn't know about the high voltage, it just sees the current...

I suspected the same since nothing is mentioned about overvoltage hazards in datasheets for zeners pertinent to reverse breakdown operation. I really appreciate that you verified this.

 

[KlausST]

Hi,

since post#2 we tried to explain this.

BTW: The datasheet gives the V/I curve. Thats all you need to know. I is the input.

Klaus

 

[FvM]

The datasheet gives the V/I curve. Thats all you need to know.

Plus pulse absorption capability for dynamic behavior, e.g. withstanding to ESD events.