# Zerner at reverse biased

Discussion in 'Electronic Projects Design/Ideas/Reviews' started by ESDR, Jun 14, 2016.

1. ### ESDRNew Member

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Helllo,
If we have zener diode at reverse biased of rating 5V and connected to 12V the output will be 7V what will be the maximum current that can flow through it?

2. ### specWell-Known MemberMost Helpful Member

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Hi ESDR

Apologies. Thanks to AG for pointing out the gross error on this original post, which will be rewritten to answer your question about a Zener diode (not LED).

(1) With semiconductor devices, Zener diodes included, the maximum junction temperature is the fundamental limit and must not be exceeded or the device performance may be degraded or the device may be destroyed. For most silicon devices the maximum junction temperature is 150 deg C or 170 deg C depending on manufacturer and specific device.

(2) Also, the maximum voltage and current must not be exceeded or the semiconductor structure may be damaged.

(3) There is a thermal resistance between the junction and the case, so you can calculate the maximum possible dissipation the device can handle if you know what the ambient temperature is. The industry standard ambient temperature used on most data sheets is 25 deg C. But what counts is the ambient temperature that the case of the device is actually in, and also if there is a free flow of air around the device. For example in many equipment the ambient temperature can typically be 50 deg C or higher.

(4) Taking a specific Zener diode, the NZY series Zener diodes made by NXP (Phillips)
Data sheet
http://www.mouser.com/ds/2/302/NZX_SER-841470.pdf

spec

PS: if you are just want to generate 7V from 12V there are much better ways.

Last edited: Jun 14, 2016
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3. ### ESDRNew Member

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Hello,
i was just thinking that zener diode is used as voltage stabilizer.
and if we bias in reverse order the volatge will be 7V but how much load can carries current from it?

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5. ### ericgibbsWell-Known MemberMost Helpful Member

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hi E,
It would be better to tell us, what load current you want from the 7v.?
E

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6. ### ESDRNew Member

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ok, i want 1Am or even more.
and what will be the max current the diode can withstand

7. ### AnalogKidWell-Known Member

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It depends on the part number of the diode you are using. What is it? The data sheet for the part will tell you its maximum power dissipation limit, and Watt's Law will tell you the maximum current.

Most zener diodes are limited by the amount of power the device package can dissipate. For example, if you are using a 1/2 W zener diode rated for 5.1 V, then the max current through the diode must be kept to less than 98 mA. And note that at that current the diode is very hot, close to burning up. As a starting point for decent reliability, never run a diode at more than 50% of its rated power dissipation. If you want 1 A through a 5 V diode, that is a peak power dissipation of 5 W. So go on the internet and search for a 5 V, 10 W zener diode that is available in your country.

As with your other posts, this is a very basic concept in electronics, one that you already should know if you are trying to design a circuit at this power level.

ak

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9. ### audioguruWell-Known MemberMost Helpful Member

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I do not know why Spec talked about a reverse biased LED.

A zener diode is a shunt voltage regulator when it is reverse biased. If you connect a 5V zener diode to a 12V power supply then both will blow up because nothing is limiting the massive current. A zener diode usually has a resistor feeding it and the resistor limits the current.

The huge 5.1V zener diode is rated at maximum allowed heating of 10W if it is cooled properly so its maximum allowed current is 10W/5.1V= 1.96A. Since it is a shunt regulator then it is throwing away a lot of the power from the power supply even when it has no load. Usually we use a series voltage regulator for high load currents. A zener diode is used inside some series voltage regulator ICs. The current in the zener diode is tiny and the transistors in the IC pass the high load current.

10. ### ESDRNew Member

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ok, zener diode is used in circuit and than current is amplified.
what is current to voltage and voltage to current working and application?

11. ### specWell-Known MemberMost Helpful Member

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Sorry everybody- just ignore my post #2. I will delete or modify it. That's what you get for not reading the OPs post thoroughly.

spec

Last edited: Jun 14, 2016
12. ### ericgibbsWell-Known MemberMost Helpful Member

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hi spec,
As I tell others and myself, avoid standing too close to the microwave oven when heating a ready meal.
E

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13. ### ESDRNew Member

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i know resistance voltage divider only in DC.

14. ### specWell-Known MemberMost Helpful Member

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OK will do. I will get my post #2 sorted first

spec

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15. ### audioguruWell-Known MemberMost Helpful Member

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Does cooked gonads cause loss of memory?

16. ### ESDRNew Member

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audioguru
hello,
you said you work for Philips how you learn so much electronics?

17. ### ericgibbsWell-Known MemberMost Helpful Member

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hi 'AG'

E

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Very true.

19. ### DerStrom8Super ModeratorMost Helpful Member

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Hello all,

Just so you know, ESDR has been banned as this name is an alias for someone who has been banned many times in the past. Feel free to keep discussing for future readers, but there is no need to address the OP any further.

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