Zeners in series

[Steve Kraus]

Just wanted to be sure of this. If you connect two zeners in series with
the same polarity the effect is the same as having one zener of the sum of
the two voltages, right?

 

[Michael A. Terrell]

Steve Kraus wrote:

Just wanted to be sure of this. If you connect two zeners in series with
the same polarity the effect is the same as having one zener of the sum of
the two voltages, right?

Yes, as long as you don't exceed the curent either diode is rated
for. If you do, that diode will overheat and short.


--
Politicians should only get paid if the budget is balanced, and there is
enough left over to pay them.

 

[N_Cook]

Steve Kraus <screen@SPAMBLOCKfilmteknik.com> wrote in message
news:TsGdnTFrO6H_ylfRnZ2dnUVZ_qGdnZ2d@earthlink.com...

Just wanted to be sure of this. If you connect two zeners in series with
the same polarity the effect is the same as having one zener of the sum of
the two voltages, right?

While at it 2 diacs in series , assuming 2x 8V ones , would give 8V ?
What if high ohm balancing R across each, too high to turn on the associated
device?

 

[Arfa Daily]

"Steve Kraus" <screen@SPAMBLOCKfilmteknik.com> wrote in message
news:TsGdnTFrO6H_ylfRnZ2dnUVZ_qGdnZ2d@earthlink.com...

Just wanted to be sure of this. If you connect two zeners in series with
the same polarity the effect is the same as having one zener of the sum of
the two voltages, right?

Basically, yes. I do it all the time. Doesn't usually work out *quite*
right, but close enough as not to normally matter.

Arfa

 

[N_Cook]

Arfa Daily <arfa.daily@ntlworld.com> wrote in message
newsnvyo.19007$7p5.3310@newsfe22.ams2...

"Steve Kraus" <screen@SPAMBLOCKfilmteknik.com> wrote in message
news:TsGdnTFrO6H_ylfRnZ2dnUVZ_qGdnZ2d@earthlink.com...
Just wanted to be sure of this. If you connect two zeners in series
with
the same polarity the effect is the same as having one zener of the sum
of
the two voltages, right?

Basically, yes. I do it all the time. Doesn't usually work out *quite*
right, but close enough as not to normally matter.

Arfa

And to adjust for the odd 1/4 or 1/2 a volt more, add a normal diode or 2 in
the chain

 

[Arfa Daily]

"N_Cook" <diverse@tcp.co.uk> wrote in message
news:iae09e$gh0$1@news.eternal-september.org...

Arfa Daily <arfa.daily@ntlworld.com> wrote in message
newsnvyo.19007$7p5.3310@newsfe22.ams2...


"Steve Kraus" <screen@SPAMBLOCKfilmteknik.com> wrote in message
news:TsGdnTFrO6H_ylfRnZ2dnUVZ_qGdnZ2d@earthlink.com...
Just wanted to be sure of this. If you connect two zeners in series
with
the same polarity the effect is the same as having one zener of the sum
of
the two voltages, right?

Basically, yes. I do it all the time. Doesn't usually work out *quite*
right, but close enough as not to normally matter.

Arfa


And to adjust for the odd 1/4 or 1/2 a volt more, add a normal diode or 2
in
the chain

Quite

Arfa

 

[David Nebenzahl]

On 10/28/2010 10:10 PM Steve Kraus spake thus:

Just wanted to be sure of this. If you connect two zeners in series with
the same polarity the effect is the same as having one zener of the sum of
the two voltages, right?

Done all the time (2 or more diodes in series). You can even take
intermediate voltages from taps in a series string of zeners.


--
The fashion in killing has an insouciant, flirty style this spring,
with the flaunting of well-defined muscle, wrapped in flags.

- Comment from an article on Antiwar.com (http://antiwar.com)

 

[Art Todesco]

On 10/29/2010 1:42 PM, David Nebenzahl wrote:

On 10/28/2010 10:10 PM Steve Kraus spake thus:

Just wanted to be sure of this. If you connect two zeners in
series with the same polarity the effect is the same as having one
zener of the sum of the two voltages, right?

Done all the time (2 or more diodes in series). You can even take
intermediate voltages from taps in a series string of zeners.

Just one more thing to add. In general the forward drop is a "don't

care", however, in some applications, it might enter into the
equation, so you have to double that.

 

[David Nebenzahl]

On 10/29/2010 11:21 AM Art Todesco spake thus:

On 10/29/2010 1:42 PM, David Nebenzahl wrote:

On 10/28/2010 10:10 PM Steve Kraus spake thus:

Just wanted to be sure of this. If you connect two zeners in
series with the same polarity the effect is the same as having
one zener of the sum of the two voltages, right?

Done all the time (2 or more diodes in series). You can even take
intermediate voltages from taps in a series string of zeners.

Just one more thing to add. In general the forward drop is a "don't
care", however, in some applications, it might enter into the
equation, so you have to double that.

It's still the usual 0.7 V per junction, right?

--
The fashion in killing has an insouciant, flirty style this spring,
with the flaunting of well-defined muscle, wrapped in flags.

- Comment from an article on Antiwar.com (http://antiwar.com)

 

[who where]

On Fri, 29 Oct 2010 10:42:09 -0700, David Nebenzahl
<nobody@but.us.chickens> wrote:

On 10/28/2010 10:10 PM Steve Kraus spake thus:

Just wanted to be sure of this. If you connect two zeners in series with
the same polarity the effect is the same as having one zener of the sum of
the two voltages, right?

Done all the time (2 or more diodes in series). You can even take
intermediate voltages from taps in a series string of zeners.

and you can tweak the overall tempco by selection of the elements to
combine.

 

[Damon Hill]

who where <noone@home.net> wrote in
news:6ulmc61qmkng6t480ijqddbqm3i5ct7h0r@4ax.com:

On Fri, 29 Oct 2010 10:42:09 -0700, David Nebenzahl
nobody@but.us.chickens> wrote:

On 10/28/2010 10:10 PM Steve Kraus spake thus:

Just wanted to be sure of this. If you connect two zeners in series
with the same polarity the effect is the same as having one zener of
the sum of the two voltages, right?

Done all the time (2 or more diodes in series). You can even take
intermediate voltages from taps in a series string of zeners.

and you can tweak the overall tempco by selection of the elements to
combine.

Don't forward-biased silicon diodes have a tempco reverse that of
a zener diode? If I want a temperature-compensated 40VDC, I could
combine a 39 volt zener and a diode or two and get very close to
40 volts with minimum drift.

--Damon

 

[isw]

In article <Xns9E23EA8D25BB7damon161attbicom@127.0.0.1>,
Damon Hill <damon1SIX1@comcast.netnet> wrote:

who where <noone@home.net> wrote in
news:6ulmc61qmkng6t480ijqddbqm3i5ct7h0r@4ax.com:

On Fri, 29 Oct 2010 10:42:09 -0700, David Nebenzahl
nobody@but.us.chickens> wrote:

On 10/28/2010 10:10 PM Steve Kraus spake thus:

Just wanted to be sure of this. If you connect two zeners in series
with the same polarity the effect is the same as having one zener of
the sum of the two voltages, right?

Done all the time (2 or more diodes in series). You can even take
intermediate voltages from taps in a series string of zeners.

and you can tweak the overall tempco by selection of the elements to
combine.


Don't forward-biased silicon diodes have a tempco reverse that of
a zener diode? If I want a temperature-compensated 40VDC, I could
combine a 39 volt zener and a diode or two and get very close to
40 volts with minimum drift.

There's a natural "turnover point" at something about 5.6 volts for
reverse-biased diode junctions. For breakovers below that voltage, the
Zener effect predominates, and the devices exhibit a negative tempco.
Above it, the avalanche effect becomes predominant, with a positive
tempco. Right around 5.6 volts, the tempco can be very near to zero. You
can make composite devices with very low tempco for voltages well above
5.6 devices by putting one (or more) of each type in series.

So if you wanted, say, a 40volt stable reference, you'd probably get
best performance by putting (say) a 36 volt device and a 4 volt device
in series -- or maybe 37 volts and 3 volts; check the tempco curves. And
be sure to thermally connect the two devices together.

Isaac

 

[Damon Hill]

isw <isw@witzend.com> wrote in
news:isw-F4887F.00161102112010@[216.168.3.50]:

In article <Xns9E23EA8D25BB7damon161attbicom@127.0.0.1>,
Damon Hill <damon1SIX1@comcast.netnet> wrote:

Don't forward-biased silicon diodes have a tempco reverse that of
a zener diode? If I want a temperature-compensated 40VDC, I could
combine a 39 volt zener and a diode or two and get very close to
40 volts with minimum drift.

There's a natural "turnover point" at something about 5.6 volts for
reverse-biased diode junctions. For breakovers below that voltage, the
Zener effect predominates, and the devices exhibit a negative tempco.
Above it, the avalanche effect becomes predominant, with a positive
tempco. Right around 5.6 volts, the tempco can be very near to zero.
You can make composite devices with very low tempco for voltages well
above 5.6 devices by putting one (or more) of each type in series.

So if you wanted, say, a 40volt stable reference, you'd probably get
best performance by putting (say) a 36 volt device and a 4 volt device
in series -- or maybe 37 volts and 3 volts; check the tempco curves.
And be sure to thermally connect the two devices together.

Aha! I'd wondered why that trick wasn't used more often in an
integrated package. Thanks for the explanation.

--Damon

 

[isw]

In article <Xns9E246B89E13D6damon161attbicom@127.0.0.1>,
Damon Hill <damon1SIX1@comcast.netnet> wrote:

isw <isw@witzend.com> wrote in
news:isw-F4887F.00161102112010@[216.168.3.50]:

In article <Xns9E23EA8D25BB7damon161attbicom@127.0.0.1>,
Damon Hill <damon1SIX1@comcast.netnet> wrote:

Don't forward-biased silicon diodes have a tempco reverse that of
a zener diode? If I want a temperature-compensated 40VDC, I could
combine a 39 volt zener and a diode or two and get very close to
40 volts with minimum drift.

There's a natural "turnover point" at something about 5.6 volts for
reverse-biased diode junctions. For breakovers below that voltage, the
Zener effect predominates, and the devices exhibit a negative tempco.
Above it, the avalanche effect becomes predominant, with a positive
tempco. Right around 5.6 volts, the tempco can be very near to zero.
You can make composite devices with very low tempco for voltages well
above 5.6 devices by putting one (or more) of each type in series.

So if you wanted, say, a 40volt stable reference, you'd probably get
best performance by putting (say) a 36 volt device and a 4 volt device
in series -- or maybe 37 volts and 3 volts; check the tempco curves.
And be sure to thermally connect the two devices together.

Aha! I'd wondered why that trick wasn't used more often in an
integrated package. Thanks for the explanation.

While we're talking about stable references, the way to get a
low-voltage one (2 volts, say), is to thermally tie together 20 volt and
22 volt devices and take the difference between them as the reference.
The two devices (Which should be from the same manufacturer, etc.) will
drift together, leaving a constant difference.

Or, you could just use an LM-10...

Isaac

 

[Clyde]

On 02/11/2010 06:03, Damon Hill wrote:

who where<noone@home.net> wrote in
news:6ulmc61qmkng6t480ijqddbqm3i5ct7h0r@4ax.com:

On Fri, 29 Oct 2010 10:42:09 -0700, David Nebenzahl
nobody@but.us.chickens> wrote:

On 10/28/2010 10:10 PM Steve Kraus spake thus:

Just wanted to be sure of this. If you connect two zeners in series
with the same polarity the effect is the same as having one zener of
the sum of the two voltages, right?

Done all the time (2 or more diodes in series). You can even take
intermediate voltages from taps in a series string of zeners.

and you can tweak the overall tempco by selection of the elements to
combine.


Don't forward-biased silicon diodes have a tempco reverse that of
a zener diode? If I want a temperature-compensated 40VDC, I could
combine a 39 volt zener and a diode or two and get very close to
40 volts with minimum drift.

--Damon

I did this in a VCR switch mode power supply which had failed. I was
repairing on the cheap using parts I had laying around. Couldn't find a
zener of the right voltage so I put 2 in series to get as close as
possible. Worked fine.