Author Topic: Zener's burning out  (Read 3256 times)

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Offline lordvader88Topic starter

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Zener's burning out
« on: July 19, 2019, 03:09:37 pm »
I was using a 5V1 1/4W (surely it's not 1/8W?) in a linear PSU I made, and it would pass up to 20mA sometimes, maybe even 30mA. LTSpice said it would barely pass 1mA, and that was at 120Hz peaks.

So I tried a 2v0 and 3v0, and they burned out too, during a test of about 15V at 300mA of the PSU. So now I have a 1/2W 5V1, if thtis burns out, I'll try a TL431.


The schematic used a 1/2W zener, and I guess it will get pretty hot. 1W zeners and expensive


I guess there's no question here, I'll try and see if 1/2W zener survives.
« Last Edit: July 19, 2019, 03:20:34 pm by lordvader88 »
 

Online Vgkid

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Re: Zener's burning out
« Reply #1 on: July 19, 2019, 03:46:47 pm »
Schematic, what value   of current limiting resistor are you using?
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Offline james_s

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Re: Zener's burning out
« Reply #2 on: July 19, 2019, 04:14:13 pm »
Without posting the schematic, how can you expect anyone to help you?
 

Offline MagicSmoker

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Re: Zener's burning out
« Reply #3 on: July 19, 2019, 04:44:08 pm »
Well, 20mA through a 5.1V zener works out to around 0.1W of Pd, so if a 0.25W zener is failing then either the current measurement is in error or the zener isn't actually capable of dissipating even 0.1W... If you bought said zener from some shady ebay seller for really cheap then no prizes for guessing which cause is more likely.

That said, post a schematic and/or LTSpice .asc file if you actually want some help.


 

Offline tggzzz

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Re: Zener's burning out
« Reply #4 on: July 19, 2019, 05:23:03 pm »
Without posting the schematic, how can you expect anyone to help you?

I refer you to a thread started by the OP yesterday - which was locked 4 hours later.

https://www.eevblog.com/forum/chat/is-science-allowed-on-eevblog-if-it-contradicts-the-offical-version/msg2554770/#msg2554770

Currently he's at 911(!) posts. I wonder whether he will reach 1000.
There are lies, damned lies, statistics - and ADC/DAC specs.
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Offline Gyro

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Re: Zener's burning out
« Reply #5 on: July 19, 2019, 06:04:12 pm »
Currently he's at 911(!) posts. I wonder whether he will reach 1000.

...but he has been thanked a whole 33 times! (Two of them were from Treez though  ;D)
« Last Edit: July 19, 2019, 06:14:06 pm by Gyro »
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Online ebastler

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Re: Zener's burning out
« Reply #6 on: July 19, 2019, 07:08:46 pm »
I refer you to a thread started by the OP yesterday - which was locked 4 hours later.
https://www.eevblog.com/forum/chat/is-science-allowed-on-eevblog-if-it-contradicts-the-offical-version/msg2554770/#msg2554770
Currently he's at 911(!) posts. I wonder whether he will reach 1000.

Ahh, now I see! This mysteriously burning Zener must be the proof of the Science-which-cannot-be-named about which the OP mumbled in yesterday's thread...  :P
 

Offline james_s

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Re: Zener's burning out
« Reply #7 on: July 19, 2019, 10:40:45 pm »
Without posting the schematic, how can you expect anyone to help you?

I refer you to a thread started by the OP yesterday - which was locked 4 hours later.

https://www.eevblog.com/forum/chat/is-science-allowed-on-eevblog-if-it-contradicts-the-offical-version/msg2554770/#msg2554770

Currently he's at 911(!) posts. I wonder whether he will reach 1000.

Hm I'm reminded a bit of the strange emails I started getting from a former friend. Later I found out he had gotten into methamphetamine.
 

Offline OwO

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Re: Zener's burning out
« Reply #8 on: July 20, 2019, 05:50:24 am »
I was using a 5V1 1/4W (surely it's not 1/8W?) in a linear PSU I made, and it would pass up to 20mA sometimes, maybe even 30mA. LTSpice said it would barely pass 1mA, and that was at 120Hz peaks.
Ok, maybe the first step should be to figure out why the circuit is behaving differently from simulation.

So I tried a 2v0 and 3v0, and they burned out too, during a test of about 15V at 300mA of the PSU. So now I have a 1/2W 5V1, if thtis burns out, I'll try a TL431.
Huh what? That's a bit of a non-sequiteur; zener passing more current than it should => I should replace it with a lower voltage zener! If that burns out too => a TL431 should work better?

The schematic used a 1/2W zener, and I guess it will get pretty hot. 1W zeners and expensive

5.1V * 30mA = 0.153W, so I'm not sure how the original zener burned out, but you should probably double check your measurements and make sure you are using the correct probing techniques.

I guess there's no question here, I'll try and see if 1/2W zener survives.
If a 1/4W zener "burned out", it's probably dissipating way more than the datasheet absolute maximum rated power, so it's likely not in spec for a 1/2W zener either. I would suggest getting the simulation not matching reality sorted first.
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Offline lordvader88Topic starter

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Re: Zener's burning out
« Reply #9 on: July 20, 2019, 06:47:30 am »
Schematic, what value   of current limiting resistor are you using?
It's on page 11/12
http://www.introni.it/pdf/Farnell%20-%20L%20series%20Bench%20Power%20Supplies

The 470 ohm resistor passes around 32mA

Z4, the 5V1 is what burns out. One time, P1 also burnt out. It normally is locked around 1mA, I admit IDK how the feedback loop toasted it.
« Last Edit: July 20, 2019, 06:52:09 am by lordvader88 »
 

Offline mikerj

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Re: Zener's burning out
« Reply #10 on: July 20, 2019, 10:20:54 am »
Schematic, what value   of current limiting resistor are you using?
It's on page 11/12
http://www.introni.it/pdf/Farnell%20-%20L%20series%20Bench%20Power%20Supplies

The 470 ohm resistor passes around 32mA

Z4, the 5V1 is what burns out. One time, P1 also burnt out. It normally is locked around 1mA, I admit IDK how the feedback loop toasted it.

Where are you pulling these numbers from?  Given your recent thread I can take a pretty good guess...

Z4 is a 1N823 6.2V Zener to start with, and the current through the 470 ohm resistor is set by Z3, a 5.1v zener on the other side of the current mirror: 5.1/470 ~ 10mA.  This is the maximum that should be passing through Z4, since some of the current will be going into P101/P102.
 

Offline bd139

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Re: Zener's burning out
« Reply #11 on: July 20, 2019, 10:34:04 am »
I see the problem here:

1. Circuit copied verbatim without understanding it.
2. Circuit something from the middle ages to start with (Farnell power supplies usually are - decent supplies however).
3. Cargo cult developing.

Solution:

1. Go back to basics and understand the problem.
2. Get art of electronics and the learning the art of electronics book (both are on library genesis if you're a cheap arse)
3. Work through the whole damn thing until after lab 11.
4. Consider oneself hit with the clue stick.

Short cut as I know it'll be taken:

1. Get an LM723 in and use a circuit off the datasheet.
2. Build the supply around that and an external pass transistor.
3. Admit that it's a cargo cult.

Some advice: building a bench power supply is much much harder than it looks. Even all the semi sexy looking designs on here and a lot of commercial units are full of stupid flaws. Overshoot, spontanous oscillation, failure prone (try charging a car battery up with that Farnell supply and then the line power fails!), all sorts. Even an LM317 can oscillate like hell if you happen to have a couple of metres of test leads hanging off it.
« Last Edit: July 20, 2019, 10:37:09 am by bd139 »
 

Offline thinkfat

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Re: Zener's burning out
« Reply #12 on: July 20, 2019, 10:57:24 am »
LM723 is actually not such a bad choice. You can make quite decent power supplies with it if you combine it with some power transistors.

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Offline bd139

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Re: Zener's burning out
« Reply #13 on: July 20, 2019, 11:05:23 am »
Yeah it's a VERY nice IC despite being 50 years old this year. It's still going strong.
 

Offline tggzzz

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Re: Zener's burning out
« Reply #14 on: July 20, 2019, 12:07:02 pm »
Snipped a reasonable analysis of PEBCAK...

2. Get art of electronics and the learning the art of electronics book (both are on library genesis if you're a cheap arse)

First time I have bumbled into this:
Quote
Sorry, this page is not available through Virgin Media
Virgin Media has received an order from the High Court requiring us to prevent access to this site. For more information about the order and your rights, please click the relevant link below.

Suppose I'll have to investigate how to avoid that, presuming they aren't using deep packet inspection.
There are lies, damned lies, statistics - and ADC/DAC specs.
Glider pilot's aphorism: "there is no substitute for span". Retort: "There is a substitute: skill+imagination. But you can buy span".
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Offline xavier60

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Re: Zener's burning out
« Reply #15 on: July 20, 2019, 12:07:10 pm »
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Offline bd139

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Re: Zener's burning out
« Reply #16 on: July 20, 2019, 12:08:46 pm »
Snipped a reasonable analysis of PEBCAK...

2. Get art of electronics and the learning the art of electronics book (both are on library genesis if you're a cheap arse)

First time I have bumbled into this:
Quote
Sorry, this page is not available through Virgin Media
Virgin Media has received an order from the High Court requiring us to prevent access to this site. For more information about the order and your rights, please click the relevant link below.

Suppose I'll have to investigate how to avoid that, presuming they aren't using deep packet inspection.

http://libgen.unblockall.org/

I suggest you move to Zen or Andrews and Arnold if you can. No blocking.

Edit: of course, the best option...



I only keep the electronic copies as well as they are easier to read on the toilet thinking throne :D
« Last Edit: July 20, 2019, 12:14:02 pm by bd139 »
 

Offline tggzzz

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Re: Zener's burning out
« Reply #17 on: July 20, 2019, 12:20:15 pm »
Snipped a reasonable analysis of PEBCAK...

2. Get art of electronics and the learning the art of electronics book (both are on library genesis if you're a cheap arse)

First time I have bumbled into this:
Quote
Sorry, this page is not available through Virgin Media
Virgin Media has received an order from the High Court requiring us to prevent access to this site. For more information about the order and your rights, please click the relevant link below.

Suppose I'll have to investigate how to avoid that, presuming they aren't using deep packet inspection.

http://libgen.unblockall.org/

I suggest you move to Zen or Andrews and Arnold if you can. No blocking.

Same problem, and I can't reasonably. I'm on VogonMuddia cable, and the ADSL broadband checkers indicate "up to 17Mb/s estimated 6Mb/s". That's consistent with what my neighbour used to get.

Quote
Edit: of course, the best option...



I only keep the electronic copies as well as they are easier to read on the toilet :D

Well, you wouldn't want someone to be, um, confused on the toilet.

I have paper TAoE 1, plus both formats of TAoE 3. Continuing to (very selectively) read usenet is highly beneficial sometimes!
There are lies, damned lies, statistics - and ADC/DAC specs.
Glider pilot's aphorism: "there is no substitute for span". Retort: "There is a substitute: skill+imagination. But you can buy span".
Having fun doing more, with less
 

Offline bd139

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Re: Zener's burning out
« Reply #18 on: July 20, 2019, 12:23:28 pm »
Yes I've got 1st edition (black one) on the shelf above that as well. I prefer that one if I'm honest unless I need some detailed information.
 

Offline tggzzz

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Re: Zener's burning out
« Reply #19 on: July 20, 2019, 12:50:21 pm »
Yes I've got 1st edition (black one) on the shelf above that as well. I prefer that one if I'm honest unless I need some detailed information.

Yes, it is swings and roundabouts. I'm keeping both :)
There are lies, damned lies, statistics - and ADC/DAC specs.
Glider pilot's aphorism: "there is no substitute for span". Retort: "There is a substitute: skill+imagination. But you can buy span".
Having fun doing more, with less
 

Offline james_s

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Re: Zener's burning out
« Reply #20 on: July 20, 2019, 06:29:49 pm »
Some advice: building a bench power supply is much much harder than it looks. Even all the semi sexy looking designs on here and a lot of commercial units are full of stupid flaws. Overshoot, spontanous oscillation, failure prone (try charging a car battery up with that Farnell supply and then the line power fails!), all sorts. Even an LM317 can oscillate like hell if you happen to have a couple of metres of test leads hanging off it.


This is one of the things I like about it though. A power supply is simple in concept but you can really dive deep into the details and learn a tremendous amount if you want to. It doesn't have to be complicated, when I was about 12 I built a simple fixed 12V power supply using three 7812 regulators in parallel (yeah, I know that's bad practice but it worked) and I used that thing heavily for around 15 years. A basic zener referenced voltage regulator with a pass transistor can teach you all kinds of basic concepts and in the end you get something useful, it's hard to have too many power supplies. These days I use a commercially made bench PSU but when I was starting out I couldn't afford something like that and I'm glad I was building my own because it taught me a lot.
 


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