Zeners in Series

On Sat, 9 Nov 2019 21:42:38 -0000 (UTC), Cursitor Doom
<curd@notformail.com> wrote:

Whilst mere hobbyists like myself can easily get away with making up a
desired zener value from putting two smaller value ones in series to add
together their rated voltages, can such a dodge be employed by
professional designers without losing face? I mean, in the case where
there is no commercially available zener with precisely the desired
breakdown voltage? Would a pro designer be open to ridicule and risking
his rep by pulling such a stunt?

Zeners around 5 V have nearly zero temperature coefficient, those
above have a positive TC and those below a negative TC. Thus making a
10 V zener from two 5 V zeners would have zero TC. Using less than 4 V
and over 6 V in series may also reduce the TC. Alternative put some
forward biased diode(s) (TC -2.2 mV/K) in series to compensate for the
positive TC of more than 5 V zeners.

 

On Saturday, November 9, 2019 at 6:49:32 PM UTC-5, Phil Allison wrote:

alan.ye...@gmail.com wrote:
-------------------------------------



But, is it really good practice to use only a stack of zeners?
Should there not be a hi impedance bleeder path in parallel to
each of the diode(s) stack so they all start to conduct and zener
properly.
Phil I'm surprised you did not mention this.


** Surely you jest ?

Might as well fit bleeders in parallel with cells in a battery.

Make the bastards share the damn current ....



... Phil

Suppose one of the zeners in the stack has very low leakage. So low that the others in the stack don't turn on. The bleeder resistors would then allow the other diodes to turn on and eventually the bad actor would turn on too. Once the series string of diodes turns on they can 'share the same damn current'.
Bleeders among the cells in a battery would be counter productive wasting the energy with no beneficial purpose.

 

[Tim Williams]

I made these current-limiting switches:
https://www.seventransistorlabs.com/Images/SwitchingCurrentLimitUnits.jpg
https://www.seventransistorlabs.com/Images/SwitchingCurrentLimitUnits2.jpg
The row of three SMDJ15CA in series gobbles up a surge of 600W and begs for
more. I can mash the "fire" button as fast as I can, and it simply thermal
limits, no damage. I can actually see skin oils evaporate from the top of
the diodes, following a surge -- they get nice and toasty internally, but
still well before failure. (Reliability, who knows -- the thermal cycling
is likely a factor, but this isn't a million-cycle product either.)

It's also got a ground-return connection, so if you want to use it as a
current-limiting buck converter instead, you can save a lot of power
dissipation and operate at higher duty cycle. Otherwise, it works as a
two-terminal, bidirectional current-regulating diode, gobbling the excess
power internally.

Tim

--
Seven Transistor Labs, LLC
Electrical Engineering Consultation and Design
Website: https://www.seventransistorlabs.com/

"Tom Gardner" <spamjunk@blueyonder.co.uk> wrote in message
news:SaHxF.69412$om6.5287@fx27.am4...

On 09/11/19 21:42, Cursitor Doom wrote:
Whilst mere hobbyists like myself can easily get away with making up a
desired zener value from putting two smaller value ones in series to add
together their rated voltages, can such a dodge be employed by
professional designers without losing face? I mean, in the case where
there is no commercially available zener with precisely the desired
breakdown voltage? Would a pro designer be open to ridicule and risking
his rep by pulling such a stunt?

My question would be "what is the problem to which you think
that is a good solution?".

Only then I would consider whether that is an adequate
thing to do.

If nothing else, you should assure yourself that the
voltage will be sufficiently accurate and stable as
temperature and current vary.

 

[Bill Sloman]

On Monday, November 11, 2019 at 12:39:47 AM UTC+11, alan.ye...@gmail.com wrote:

On Saturday, November 9, 2019 at 6:49:32 PM UTC-5, Phil Allison wrote:
alan.ye...@gmail.com wrote:
-------------------------------------



But, is it really good practice to use only a stack of zeners?
Should there not be a hi impedance bleeder path in parallel to
each of the diode(s) stack so they all start to conduct and zener
properly.
Phil I'm surprised you did not mention this.


** Surely you jest ?

Might as well fit bleeders in parallel with cells in a battery.

Make the bastards share the damn current ....

Suppose one of the zeners in the stack has very low leakage. So low that the others in the stack don't turn on. The bleeder resistors would then allow the other diodes to turn on and eventually the bad actor would turn on too. Once the series string of diodes turns on they can 'share the same damn current'.

Zener current increases rapidly with voltage around the rated breakdown voltage.

Look at the data sheets.

In so far as zener diodes have a "leakage current", it has to measured at voltages well below the voltage at which is designed to operate.

If one zener in a string has a lower "leakage current" than the others in a nominally identical string it will have a slightly higher operating voltage at whatever current you chose to run the string at.

The only way that the other diodes in the stack "wouldn't turn on" would be if the offending diode had blown open circuit. Bleeder resistor wouldn't be a good way to solve that problem.

> Bleeders among the cells in a battery would be counter productive wasting the energy with no beneficial purpose.

Equally true of a zener diode string.

--
Bill Sloman, Sydney

 

[Tim Williams]

<alan.yeager.2013@gmail.com> wrote in message
news:44553b93-c61c-4150-8396-e7262d9644db@googlegroups.com...

But, is it really good practice to use only a stack of zeners? Should
there not be a hi impedance bleeder path in parallel to each of the
diode(s) stack so they all start to conduct and zener properly. Phil I'm
surprised you did not mention this.

Yes, it is. In fact, many TVSs in higher ratings (>=48V maybe?) are stacked
die construction!

The absence of a safe breakdown mechanism is precisely what causes leakage
problems for some devices. You're literally using the best possible device
to stack in series. ;-)

The opposite sutation is of a bit more concern: TVSs in parallel. But there
too, they are pretty good. The only downside is, at modest currents (where
quiescent power dissipation is the most likely failure mode, i.e., a given
part just eventually overheats), parallel diodes will tend not to share
current. And that's only down to mismatch in breakdown voltage.

Avalanche breakdown has a positive tempco, so it's not a current-hogging
issue like it is for paralleled transistors or (forward biased) diodes. And
at high peak currents, internal resistance dominates, so the sharing under
surge is okay.

Tim

--
Seven Transistor Labs, LLC
Electrical Engineering Consultation and Design
Website: https://www.seventransistorlabs.com/

 

On Sun, 10 Nov 2019 10:18:59 -0000 (UTC), Cursitor Doom
<curd@notformail.com> wrote:

On Sat, 09 Nov 2019 18:38:31 -0800, jlarkin wrote:

I even -gasp- sometimes use only half of a dual diode!

But ridicule? Reputation? Who would know?

Everyone here, now you've admitted to still using dual diodes!
:-D

Oh, the shame!

BAV23S, dual series, 250V, 4 cents

BAV99, dual series, 70V, 1.4 cents

The BAV23S is great in C-W high voltage boosted flyback supplies. I'd
post an example but people would whine.



--

John Larkin Highland Technology, Inc

lunatic fringe electronics

 

[Tom Del Rosso]

Cursitor Doom wrote:

On Sat, 09 Nov 2019 19:43:40 -0500, Tom Del Rosso wrote:

Cursitor Doom wrote:
Whilst mere hobbyists like myself can easily get away with making
up a desired zener value from putting two smaller value ones in
series to add together their rated voltages, can such a dodge be
employed by professional designers without losing face? I mean, in
the case where there is no commercially available zener with
precisely the desired breakdown voltage? Would a pro designer be
open to ridicule and risking his rep by pulling such a stunt?

Win and others here have noted that zeners above 7V produce much more
noise.

You were in this thread too.

Indeed I was. ISTR I started it. But this is a completely different
matter!

But isn't the anser the same? Obviously it is done routinely.

 

On Sun, 10 Nov 2019 07:59:28 -0600, "Tim Williams"
<tiwill@seventransistorlabs.com> wrote:

alan.yeager.2013@gmail.com> wrote in message
news:44553b93-c61c-4150-8396-e7262d9644db@googlegroups.com...

But, is it really good practice to use only a stack of zeners? Should
there not be a hi impedance bleeder path in parallel to each of the
diode(s) stack so they all start to conduct and zener properly. Phil I'm
surprised you did not mention this.


Yes, it is. In fact, many TVSs in higher ratings (>=48V maybe?) are stacked
die construction!

The absence of a safe breakdown mechanism is precisely what causes leakage
problems for some devices. You're literally using the best possible device
to stack in series. ;-)

The opposite sutation is of a bit more concern: TVSs in parallel. But there
too, they are pretty good. The only downside is, at modest currents (where
quiescent power dissipation is the most likely failure mode, i.e., a given
part just eventually overheats), parallel diodes will tend not to share
current. And that's only down to mismatch in breakdown voltage.

Avalanche breakdown has a positive tempco, so it's not a current-hogging
issue like it is for paralleled transistors or (forward biased) diodes. And
at high peak currents, internal resistance dominates, so the sharing under
surge is okay.

Tim

Some big diode packages are multiple paralleled diodes. Diodes get
ohmic, and have positive TCs, at high current, so it works out.




--

John Larkin Highland Technology, Inc

lunatic fringe electronics

 

[Cursitor Doom]

On Sun, 10 Nov 2019 07:28:49 -0800, jlarkin wrote:

Oh, the shame!

BAV23S, dual series, 250V, 4 cents

BAV99, dual series, 70V, 1.4 cents

The BAV23S is great in C-W high voltage boosted flyback supplies. I'd
post an example but people would whine.

ISTR you already did a few months ago; one of your 'Dremmelboard' [TM]
prototypes. I hope you take proper precautions with the dust!



--
This message may be freely reproduced without limit or charge only via
the Usenet protocol. Reproduction in whole or part through other
protocols, whether for profit or not, is conditional upon a charge of
GBP10.00 per reproduction. Publication in this manner via non-Usenet
protocols constitutes acceptance of this condition.

 

[Phil Allison]

alan.ye...@gmail.com wrote:

--------------------------

** Surely you jest ?


Suppose one of the zeners in the stack has very low leakage.
So low that the others in the stack don't turn on.

** Crikey - he wasn't jesting.

Maybe he struggles with the concept of current.



...... Phil

 

[Robert Baer]

Cursitor Doom wrote:

On Sat, 09 Nov 2019 18:38:31 -0800, jlarkin wrote:

I even -gasp- sometimes use only half of a dual diode!

But ridicule? Reputation? Who would know?

Everyone here, now you've admitted to still using dual diodes!
:-D



Get out the swords, let's duel!

 

On Sun, 10 Nov 2019 14:34:38 -0800, Robert Baer
<robertbaer@localnet.com> wrote:

Cursitor Doom wrote:
On Sat, 09 Nov 2019 18:38:31 -0800, jlarkin wrote:

I even -gasp- sometimes use only half of a dual diode!

But ridicule? Reputation? Who would know?

Everyone here, now you've admitted to still using dual diodes!
:-D



Get out the swords, let's duel!

Here's my programmable power supply for an extreme-UV (13 nm)
photodiode. It has a dual diode AND zeners in series.

https://www.dropbox.com/s/9e2ojyx0beflcaq/ESM_PD_Supply.jpg?raw=1


Try to surrender with dignity.



--

John Larkin Highland Technology, Inc

lunatic fringe electronics

 

On Sun, 10 Nov 2019 18:55:13 -0500, "Tom Del Rosso"
<fizzbintuesday@that-google-mail-domain.com> wrote:

jlarkin@highlandsniptechnology.com wrote:

Here's my programmable power supply for an extreme-UV (13 nm)
photodiode. It has a dual diode AND zeners in series.

https://www.dropbox.com/s/9e2ojyx0beflcaq/ESM_PD_Supply.jpg?raw=1

Why the wacky transformer connection?

It's a stock, cheap ISDN transformer. The AC is stolen from another
circuit, an isolated dc-dc converter.

Is Q3 really supposed to short the output or is that a stray dot at that
junction?

Stray dot? The mosfet gate drive net name is a hint. The powerup
default is zero volts.



--

John Larkin Highland Technology, Inc

lunatic fringe electronics

 

[Tom Del Rosso]

jlarkin@highlandsniptechnology.com wrote:

Here's my programmable power supply for an extreme-UV (13 nm)
photodiode. It has a dual diode AND zeners in series.

https://www.dropbox.com/s/9e2ojyx0beflcaq/ESM_PD_Supply.jpg?raw=1

Why the wacky transformer connection?

Is Q3 really supposed to short the output or is that a stray dot at that
junction?

 

[George Herold]

On Sunday, November 10, 2019 at 6:17:06 PM UTC-5, jla...@highlandsniptechnology.com wrote:

On Sun, 10 Nov 2019 14:34:38 -0800, Robert Baer
robertbaer@localnet.com> wrote:

Cursitor Doom wrote:
On Sat, 09 Nov 2019 18:38:31 -0800, jlarkin wrote:

I even -gasp- sometimes use only half of a dual diode!

But ridicule? Reputation? Who would know?

Everyone here, now you've admitted to still using dual diodes!
:-D



Get out the swords, let's duel!

Here's my programmable power supply for an extreme-UV (13 nm)
photodiode. It has a dual diode AND zeners in series.

https://www.dropbox.com/s/9e2ojyx0beflcaq/ESM_PD_Supply.jpg?raw=1

Oh that's fun and just my 'speed'. Thanks.
George H.

Try to surrender with dignity.



--

John Larkin Highland Technology, Inc

lunatic fringe electronics

 

[Robert Baer]

jlarkin@highlandsniptechnology.com wrote:

On Sun, 10 Nov 2019 14:34:38 -0800, Robert Baer
robertbaer@localnet.com> wrote:

Cursitor Doom wrote:
On Sat, 09 Nov 2019 18:38:31 -0800, jlarkin wrote:

I even -gasp- sometimes use only half of a dual diode!

But ridicule? Reputation? Who would know?

Everyone here, now you've admitted to still using dual diodes!
:-D



Get out the swords, let's duel!

Here's my programmable power supply for an extreme-UV (13 nm)
photodiode. It has a dual diode AND zeners in series.

https://www.dropbox.com/s/9e2ojyx0beflcaq/ESM_PD_Supply.jpg?raw=1


Try to surrender with dignity.

Shouldn't C73, C77 be rated at least 500V? More like 1000V for safety?
At least C64 is protected by R88 (pop).
And....those BAV23S seem to be rated at a paltry 200V which will
surely fry shorted.
FURthermore, will that transformer withstand AC line voltage?

Gurr.

 

On Mon, 11 Nov 2019 21:37:34 -0800, Robert Baer
<robertbaer@localnet.com> wrote:

jlarkin@highlandsniptechnology.com wrote:
On Sun, 10 Nov 2019 14:34:38 -0800, Robert Baer
robertbaer@localnet.com> wrote:

Cursitor Doom wrote:
On Sat, 09 Nov 2019 18:38:31 -0800, jlarkin wrote:

I even -gasp- sometimes use only half of a dual diode!

But ridicule? Reputation? Who would know?

Everyone here, now you've admitted to still using dual diodes!
:-D



Get out the swords, let's duel!

Here's my programmable power supply for an extreme-UV (13 nm)
photodiode. It has a dual diode AND zeners in series.

https://www.dropbox.com/s/9e2ojyx0beflcaq/ESM_PD_Supply.jpg?raw=1


Try to surrender with dignity.



Shouldn't C73, C77 be rated at least 500V? More like 1000V for safety?
At least C64 is protected by R88 (pop).
And....those BAV23S seem to be rated at a paltry 200V which will
surely fry shorted.
FURthermore, will that transformer withstand AC line voltage?

Gurr.

The voltage at TP15 is about +120.

The input AC is high frequency, swiped from the main DC-DC converter
circuit. Here's the whole sheet:

https://www.dropbox.com/s/cs1lhp7gslfs3e0/ESM_power.pdf?dl=0

We've sold about 3500 of these with roughly zero failures.



--

John Larkin Highland Technology, Inc

lunatic fringe electronics

 

[Lasse Langwadt Christense]

tirsdag den 12. november 2019 kl. 06.37.40 UTC+1 skrev Robert Baer:

jlarkin@highlandsniptechnology.com wrote:
On Sun, 10 Nov 2019 14:34:38 -0800, Robert Baer
robertbaer@localnet.com> wrote:

Cursitor Doom wrote:
On Sat, 09 Nov 2019 18:38:31 -0800, jlarkin wrote:

I even -gasp- sometimes use only half of a dual diode!

But ridicule? Reputation? Who would know?

Everyone here, now you've admitted to still using dual diodes!
:-D



Get out the swords, let's duel!

Here's my programmable power supply for an extreme-UV (13 nm)
photodiode. It has a dual diode AND zeners in series.

https://www.dropbox.com/s/9e2ojyx0beflcaq/ESM_PD_Supply.jpg?raw=1


Try to surrender with dignity.



Shouldn't C73, C77 be rated at least 500V? More like 1000V for safety?
At least C64 is protected by R88 (pop).
And....those BAV23S seem to be rated at a paltry 200V which will
surely fry shorted.

for a 75V supply?

FURthermore, will that transformer withstand AC line voltage?

Gurr.

AC line voltage?

 

[Winfield Hill]

jlarkin@highlandsniptechnology.com wrote...

Here's my programmable power supply for an extreme-UV (13 nm)
photodiode. It has a dual diode AND zeners in series.

https://www.dropbox.com/s/9e2ojyx0beflcaq/ESM_PD_Supply.jpg?raw=1

Try to surrender with dignity.

The voltage at TP15 is about +120.

The input AC is high frequency, swiped from the main
DC-DC converter circuit. Here's the whole sheet:

https://www.dropbox.com/s/cs1lhp7gslfs3e0/ESM_power.pdf?dl=0

We've sold about 3500 of these with roughly zero failures.

Interesting. But I couldn't find any information about
the T932 on your website.


--
Thanks,
- Win

 

[Robert Baer]

Lasse Langwadt Christensen wrote:

tirsdag den 12. november 2019 kl. 06.37.40 UTC+1 skrev Robert Baer:
jlarkin@highlandsniptechnology.com wrote:
On Sun, 10 Nov 2019 14:34:38 -0800, Robert Baer
robertbaer@localnet.com> wrote:

Cursitor Doom wrote:
On Sat, 09 Nov 2019 18:38:31 -0800, jlarkin wrote:

I even -gasp- sometimes use only half of a dual diode!

But ridicule? Reputation? Who would know?

Everyone here, now you've admitted to still using dual diodes!
:-D



Get out the swords, let's duel!

Here's my programmable power supply for an extreme-UV (13 nm)
photodiode. It has a dual diode AND zeners in series.

https://www.dropbox.com/s/9e2ojyx0beflcaq/ESM_PD_Supply.jpg?raw=1


Try to surrender with dignity.



Shouldn't C73, C77 be rated at least 500V? More like 1000V for safety?
At least C64 is protected by R88 (pop).
And....those BAV23S seem to be rated at a paltry 200V which will
surely fry shorted.

for a 75V supply?

FURthermore, will that transformer withstand AC line voltage?

Gurr.

AC line voltage?

Schematic DOES say AC..