Fast zener diode substitute

Sat Feb 06, 2010 11:57 pm   

I decided to built this:

http://notes.ump.edu.my/fkee/e-Magazine/Elektor%202004/Articles/E/e04b020.pdf

It keeps the battery a little bit active, preventing sulphation by
loading the battery with a hefty current (40 A) for a short interval
(50 μs) approximately every two minutes.

But they used a fast zener diode (BZT03 27V) across the FET for
protection, as rather large voltage spikes can occur when the FET
switches off.

I can not find this diode where I am, so can you suggest a substitute? I
guess I can not just put regular 27V zener diode here?


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Sun Feb 07, 2010 12:10 am   

"Yvan" <killefitz_at_invalid.invalid> wrote in message
news:hkkok2$fo4$1_at_news.eternal-september.org...

Have a look at the data sheet for the TL431 adjustable zener, you put a
potential divider (2 resistors or a trimpot) across it with the tap/wiper to
the control input to adjust the zener voltage, if you need it to be
particularly fast just put a few tens of pF capacitance in parallel with the
top leg of the divider.

HTH.

Sun Feb 07, 2010 12:46 am   

Nedavno ian field napisa:



I am electronics newbie, this sound complicated :-(


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Sun Feb 07, 2010 12:51 am   

"Yvan" <killefitz_at_invalid.invalid> wrote in message
news:hkkrgn$hlo$1_at_news.eternal-september.org...

Not at all, search and download the data sheet - it has application examples
for you to follow, to speed it up you only need add a small disc-ceramic
capacitor from cathode to control pin.

Sun Feb 07, 2010 7:18 am   

"ian field" <gangprobing.alien_at_ntlworld.com> schrieb im Newsbeitrag
news:iombn.346312$gm2.109775_at_newsfe18.ams2...

ban

Sun Feb 07, 2010 9:05 am   

Nedavno ian field napisa:



I've been suggested in another NG to just use any 3-5W 27V zener diode.
What do you think?


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Sun Feb 07, 2010 6:07 pm   

"Ban" <bansuri_at_web.de> wrote in message
news:hklidv$t4g$1_at_news.eternal-september.org...

Pretty much the same as would happen to a BZT03, the test current for the
27V part is 25mA, the TL431 can handle 100mA as long as the dissipation
isn't exceeded.

Sun Feb 07, 2010 6:17 pm   

"Yvan" <killefitz_at_invalid.invalid> wrote in message
news:hkloo9$n61$2_at_news.eternal-september.org...

The best thing to do is study the data sheet;

http://www.ieeta.pt/~alex/docs/DataSheets/BZT03.pdf

It mentions that these zeners are suitable for transient suppressors, that
might be connected to the idea that these are fast zeners, you could search
under transient suppressors and select a substitute from the results.

Sun Feb 07, 2010 8:38 pm   

"ian field" <gangprobing.alien_at_ntlworld.com> schrieb im Newsbeitrag
news:ZIBbn.19222$zD4.9142_at_newsfe19.ams2...

The same datasheet states a non repetitive current of 7.9A in transient
suppression, maybe we dont need that much for the application, but certainly
a long lead will give some inductive kick when driven with 40A.

ciao Ban

Sun Feb 07, 2010 9:07 pm   

"Yvan" <killefitz_at_invalid.invalid> wrote in message
news:hkkok2$fo4$1_at_news.eternal-september.org...


BTW: thanks for the URL - backspacing it found some pretty interesting
magazines & e-books.

There's an ftp at that address too - I'll download it and see what I get.

Sun Feb 07, 2010 11:44 pm   

Nedavno ian field napisa:



Yeah, I noticed that too :-)


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Mon Feb 08, 2010 12:58 am   

"Yvan" <killefitz_at_invalid.invalid> wrote in message
news:hkloo9$n61$2_at_news.eternal-september.org...

This search might be a good starting point;

http://www.google.co.uk/search?sourceid=navclient&ie=UTF-8&rlz=1T4GZAZ_en-GBGB333GB333&q=p6ke

Mon Feb 08, 2010 4:58 pm   

Nedavno ian field napisa:




I am electronics newbie, are you suggesting that I can just use 27V P6KE
in place of BZT03 without modifications?

There are uni-polar and bi-polar P6KE, which one should I use?


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Mon Feb 08, 2010 6:39 pm   

"Yvan" <killefitz_at_invalid.invalid> wrote in message
news:hkp8pr$gpu$2_at_news.eternal-september.org...

I was suggesting you use that search as a starting point, download the data
sheets and compare the spec with the type you want to replace.

It wouldn't matter if you used a bidirectional part since the MOSFET has a
body diode that would be in parallel with the zener.

I've had a cursory glance at the schematic you plan to build, and I'm a
little sceptical about "battery revitalisers" that take pulsed current
without incorporating a float charger to replenish the energy taken - if
left and forgotten it will eventually discharge the battery and cause
sulphation.

It is also possible to do the same job with a much simpler circuit.

If you start with a simple current limiting PSU as a float charger, you can
add a zero-crossing detector to the rectifier section and use the narrow
pulses to switch the MOSFET which then takes pulses of current from the
battery as in the Elektor project.

Years ago I had a project to do exactly that, published in Television &
Consumer Electronics, but that was sold as a NiCd reviver.

Mon Feb 08, 2010 9:36 pm   

Nedavno ian field napisa:



Since I do not know what values to compare, that does not help a lot
My knowledge in electronics is limited to finding schematics on the
Internet, drawing a board in eagle, and soldering components to it.




This circuit is not a battery revitaliser as I understand it this is
sort of sulphation preventer. I am also building battery revitaliser:

http://home.comcast.net/~ddenhardt201263/desulfator/n_channel_schem.gif



As I wrote I have (very) limited knowledge in electronics, so unless you
give me a link to the schematics, this does not help. I have a lot to
learn, but very little time for that, unfortunately.


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