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Sci.Electronics.Basics -> Alternative voltage reference?

There are 13 messages in this thread.
You are currently looking at messages 1 to 13.


Author: MRW
Date: 14:28 23-07-07

Hi! I would like to know if there are other means to setup a voltage
reference. I came up with this circuit:
http://bayimg.com/iAeflAAbg

The purpose is to have a voltage divider (via a potentiometer) where
the output swings from 2.5 to 2V. One way I came up with is by using an
opamp voltage follower. Is there another way to design a voltage source
without using an opamp?

Thank you again everybody!


--


Author: Jonathan Kirwan
Date: 14:43 23-07-07


On 23 Jul 2007 18:28:07 GMT, "MRW" <mr.whatever@gmail.com> wrote:

>Hi! I would like to know if there are other means to setup a voltage
>reference. I came up with this circuit:
>http://bayimg.com/iAeflAAbg
>
>The purpose is to have a voltage divider (via a potentiometer) where
>the output swings from 2.5 to 2V. One way I came up with is by using an
>opamp voltage follower. Is there another way to design a voltage source
>without using an opamp?

What's the voltage reference for? (I'm guessing here, but in the
schematic do you mean that R11 and R20 are to simulate your
potentiometer and that you already have a 2.5V supply for V2? Do you
already have 5V and 2.5V supplies already present?)

Jon
Author: MRW
Date: 14:59 23-07-07

Jonathan Kirwan wrote:

> On 23 Jul 2007 18:28:07 GMT, "MRW" <mr.whatever@gmail.com> wrote:
>
> > Hi! I would like to know if there are other means to setup a voltage
> > reference. I came up with this circuit:
> > http://bayimg.com/iAeflAAbg
> >
> > The purpose is to have a voltage divider (via a potentiometer) where
> > the output swings from 2.5 to 2V. One way I came up with is by
> > using an opamp voltage follower. Is there another way to design a
> > voltage source without using an opamp?
>
> What's the voltage reference for? (I'm guessing here, but in the
> schematic do you mean that R11 and R20 are to simulate your
> potentiometer and that you already have a 2.5V supply for V2? Do you
> already have 5V and 2.5V supplies already present?)
>
> Jon

Hi Jon, Sorry for not being clear. R11 and R20 are used to simulate my
potentiometer. I already have a 2.5V source and a 5V source. The
section highlighted in green is the part that I was referencing.

Thanks!


--


Author: Jonathan Kirwan
Date: 16:48 23-07-07

On 23 Jul 2007 18:59:29 GMT, "MRW" <mr.whatever@gmail.com> wrote:

>Jonathan Kirwan wrote:
>
>> On 23 Jul 2007 18:28:07 GMT, "MRW" <mr.whatever@gmail.com>
wrote:
>>
>> > Hi! I would like to know if there are other means to setup a voltage
>> > reference. I came up with this circuit:
>> > http://bayimg.com/iAeflAAbg
>> >
>> > The purpose is to have a voltage divider (via a potentiometer) where
>> > the output swings from 2.5 to 2V. One way I came up with is by
>> > using an opamp voltage follower. Is there another way to design a
>> > voltage source without using an opamp?
>>
>> What's the voltage reference for? (I'm guessing here, but in the
>> schematic do you mean that R11 and R20 are to simulate your
>> potentiometer and that you already have a 2.5V supply for V2? Do you
>> already have 5V and 2.5V supplies already present?)
>>
>> Jon
>
>Hi Jon, Sorry for not being clear. R11 and R20 are used to simulate my
>potentiometer. I already have a 2.5V source and a 5V source. The
>section highlighted in green is the part that I was referencing.

What's the voltage reference for?

Jon
Author: John Popelish
Date: 18:39 23-07-07

MRW wrote:
> Hi! I would like to know if there are other means to setup a voltage
> reference. I came up with this circuit:
> http://bayimg.com/iAeflAAbg
>
> The purpose is to have a voltage divider (via a potentiometer) where
> the output swings from 2.5 to 2V. One way I came up with is by using an
> opamp voltage follower. Is there another way to design a voltage source
> without using an opamp?

There are series references (essentially 3 terminal voltage
regulators) and shunt references (essentially integrated
zener diodes) that can be programmed with 2 or 3 resistors
to produce clean, stable voltage references, for low current
loads.

For example:
http://www.national.com/ds/LM/LM4041.pdf
http://www.national.com/ds/LM/LM4121.pdf
Author: Mike
Date: 13:06 24-07-07

On 23 Jul 2007 18:28:07 GMT, "MRW" <mr.whatever@gmail.com> wrote:

>Hi! I would like to know if there are other means to setup a voltage
>reference. I came up with this circuit:
>http://bayimg.com/iAeflAAbg
>
>The purpose is to have a voltage divider (via a potentiometer) where
>the output swings from 2.5 to 2V. One way I came up with is by using an
>opamp voltage follower. Is there another way to design a voltage source
>without using an opamp?
>
>Thank you again everybody!

How about something like this?
It provides a low Z output drive and only a 100uA load on the 2.5v ref in.

|-----------
| +5 |
2.50v ------- | |
| | |\| |
| ---|-\ |
.-. | >----------- 2.00 - 2.50v
| |<----------|+/
5k | | |/| LT1078 etc
'-' |
| ===
| GND
.-.
| |
20k | |
'-'
|
|
===
GND
created by Andy´s ASCII-Circuit v1.24.140803 Beta www.tech-chat.de
view with fixed width font.


Mike



When truth is absent politics will fill the gap.
Author: MRW
Date: 22:12 24-07-07

On Jul 24, 1:06 pm, Mike <nomtrxs...@comcast.net> wrote:
> On 23 Jul 2007 18:28:07 GMT, "MRW" <mr.whate...@gmail.com> wrote:
>
> >Hi! I would like to know if there are other means to setup a voltage
> >reference. I came up with this circuit:
> >http://bayimg.com/iAeflAAbg
>
> >The purpose is to have a voltage divider (via a potentiometer) where
> >the output swings from 2.5 to 2V. One way I came up with is by using an
> >opamp voltage follower. Is there another way to design a voltage source
> >without using an opamp?
>
> >Thank you again everybody!
>
> How about something like this?
> It provides a low Z output drive and only a 100uA load on the 2.5v ref in.
>
> |-----------
> | +5 |
> 2.50v ------- | |
> | | |\| |
> | ---|-\ |
> .-. | >----------- 2.00 - 2.50v
> | |<----------|+/
> 5k | | |/| LT1078 etc
> '-' |
> | =3D=3D=3D
> | GND
> .-.
> | |
> 20k | |
> '-'
> |
> |
> =3D=3D=3D
> GND
> created by Andy=B4s ASCII-Circuit v1.24.140803 Betawww.tech-chat.de
> view with fixed width font.
>
> Mike
>
> When truth is absent politics will fill the gap.

Thanks, Mike! This looks like a better setup than the one with my
opamp circuit.
Author: MRW
Date: 22:12 24-07-07

On Jul 23, 6:39 pm, John Popelish <jpopel...@rica.net> wrote:
> MRW wrote:
> > Hi! I would like to know if there are other means to setup a voltage
> > reference. I came up with this circuit:
> >http://bayimg.com/iAeflAAbg
>
> > The purpose is to have a voltage divider (via a potentiometer) where
> > the output swings from 2.5 to 2V. One way I came up with is by using an
> > opamp voltage follower. Is there another way to design a voltage source
> > without using an opamp?
>
> There are series references (essentially 3 terminal voltage
> regulators) and shunt references (essentially integrated
> zener diodes) that can be programmed with 2 or 3 resistors
> to produce clean, stable voltage references, for low current
> loads.
>
> For
example:http://www.national.com/ds/LM/LM4041.pdfhttp://www.national.com/ds/LM/LM4121.pdf

Thanks again, John!
Author: MRW
Date: 22:15 24-07-07

On Jul 23, 4:48 pm, Jonathan Kirwan <jkir...@easystreet.com> wrote:
> On 23 Jul 2007 18:59:29 GMT, "MRW" <mr.whate...@gmail.com> wrote:
>
>
>
> >Jonathan Kirwan wrote:
>
> >> On 23 Jul 2007 18:28:07 GMT, "MRW" <mr.whate...@gmail.com>
wrote:
>
> >> > Hi! I would like to know if there are other means to setup a voltage
> >> > reference. I came up with this circuit:
> >> >http://bayimg.com/iAeflAAbg
>
> >> > The purpose is to have a voltage divider (via a potentiometer) where
> >> > the output swings from 2.5 to 2V. One way I came up with is by
> >> > using an opamp voltage follower. Is there another way to design a
> >> > voltage source without using an opamp?
>
> >> What's the voltage reference for? (I'm guessing here, but in the
> >> schematic do you mean that R11 and R20 are to simulate your
> >> potentiometer and that you already have a 2.5V supply for V2? Do you
> >> already have 5V and 2.5V supplies already present?)
>
> >> Jon
>
> >Hi Jon, Sorry for not being clear. R11 and R20 are used to simulate my
> >potentiometer. I already have a 2.5V source and a 5V source. The
> >section highlighted in green is the part that I was referencing.
>
> What's the voltage reference for?
>
> Jon

Nothing special really. I had some old notes that I was reviewing and
one of the exercise questions that was on it was to come up with this
type of circuit. Simple really, but I guess it's good practice for the
fall semester.
Author: David L. Jones
Date: 23:04 24-07-07

On Jul 24, 4:28 am, "MRW" <mr.whate...@gmail.com> wrote:
> Hi! I would like to know if there are other means to setup a voltage
> reference. I came up with this circuit:http://bayimg.com/iAeflAAbg
>
> The purpose is to have a voltage divider (via a potentiometer) where
> the output swings from 2.5 to 2V. One way I came up with is by using an
> opamp voltage follower. Is there another way to design a voltage source
> without using an opamp?
>
> Thank you again everybody!
>
> --

You could use an LM317 with a suitable value pot in series with one of
the voltage setting resistors, calculated to give you the adjustment
range you want.

Dave.
Author: Jonathan Kirwan
Date: 02:45 25-07-07

On Wed, 25 Jul 2007 02:15:32 -0000, MRW <mr.whatever@gmail.com> wrote:

>On Jul 23, 4:48 pm, Jonathan Kirwan <jkir...@easystreet.com> wrote:
>> On 23 Jul 2007 18:59:29 GMT, "MRW" <mr.whate...@gmail.com>
wrote:
>>
>>
>>
>> >Jonathan Kirwan wrote:
>>
>> >> On 23 Jul 2007 18:28:07 GMT, "MRW"
<mr.whate...@gmail.com> wrote:
>>
>> >> > Hi! I would like to know if there are other means to setup a
voltage
>> >> > reference. I came up with this circuit:
>> >> >http://bayimg.com/iAeflAAbg
>>
>> >> > The purpose is to have a voltage divider (via a potentiometer)
where
>> >> > the output swings from 2.5 to 2V. One way I came up with is by
>> >> > using an opamp voltage follower. Is there another way to design a
>> >> > voltage source without using an opamp?
>>
>> >> What's the voltage reference for? (I'm guessing here, but in the
>> >> schematic do you mean that R11 and R20 are to simulate your
>> >> potentiometer and that you already have a 2.5V supply for V2? Do you
>> >> already have 5V and 2.5V supplies already present?)
>>
>> >> Jon
>>
>> >Hi Jon, Sorry for not being clear. R11 and R20 are used to simulate my
>> >potentiometer. I already have a 2.5V source and a 5V source. The
>> >section highlighted in green is the part that I was referencing.
>>
>> What's the voltage reference for?
>>
>> Jon
>
>Nothing special really. I had some old notes that I was reviewing and
>one of the exercise questions that was on it was to come up with this
>type of circuit. Simple really, but I guess it's good practice for the
>fall semester.

Hehe. Well, since it doesn't really need to go anywhere and it is
about practice, there are a number of options:

>: +5V
>: |
>: |
>: \
>: / R1
>: \ 1.5k
>: /
>: |
>: ,-----+
>: | |
>: | \
>: | / R2
>: | \ 910
>: | /
>: | |
>: Q1 e>| |
>: 2N3906 |---+
>: c/| |
>: | |
>: | |
>: gnd |
>: \
>: R3 /
>: 1k \ <----------- Vout
>: pot /
>: |
>: |
>: \
>: / R4
>: \ 2.7k
>: /
>: |
>: |
>: gnd

Note that there is no use of the 2.5V supply, here. And it is NOT a
precision reference and it would be simply horrible over temperature
changes -- only good for some +/-10C -- as drift per temperature
changes are in the area of something on the order of 5mV/K or more.

Another option would be:

>: +5 +5
>: | |
>: | |
>: \ R1 \ R2
>: / 680 / 680
>: \ \
>: | |
>: | |
>: Q1 e>| |<e Q2
>: 2N3906 |---+---| 2N3906
>: c/| | |\c
>: | | |
>: | | |
>: +-----' |
>: | R3 \
>: | 1k / <------ Vout
>: | pot \
>: R5 \ |
>: 5.6k / |
>: \ R4 \
>: | 2.7k /
>: | \
>: gnd |
>: |
>: gnd

Again, no precision. But better temperature drift -- on the order of
1mV/K.

I picked something like 700uA as the desired current through the 1k
pot. This was to generate about 0.7V, top to bottom of the sweep of
the pot, which means you can at least trap your 0.5V in there with a
little extra so you don't have to nail it precisely. In other words,
your 1k pot shown will sweep a little wider range than 0.5V. And
there is nothing precision about any of these, nor temperature
stabilized. The 2.7k*700uA produces about 1.9V, a pedestal upon which
the 0.7V range of the pot rests. So roughly speaking, we're talking
about a sweep from 1.9 to 2.6 volts. Of course, you can tweek things
a little with R5 in the 2nd circuit and R2 with the first, so that you
get it centered okay.

For precision sweep and temperature stability, a different topology
would probably be used. Of course, you can keep the opamp and use the
pot as part of a series resistive divider that feeds the (+) input of
the opamp and use it as a unity gain follower.

Jon
Author: MRW
Date: 15:57 25-07-07

Jonathan Kirwan wrote:

> On Wed, 25 Jul 2007 02:15:32 -0000, MRW <mr.whatever@gmail.com> wrote:
>
> >On Jul 23, 4:48 pm, Jonathan Kirwan <jkir...@easystreet.com> wrote:
> >> On 23 Jul 2007 18:59:29 GMT, "MRW" <mr.whate...@gmail.com>
wrote:
> > >
> > >
> > >
> >> >Jonathan Kirwan wrote:
> > >
> >> >> On 23 Jul 2007 18:28:07 GMT, "MRW"
<mr.whate...@gmail.com>
> wrote:
> > >
> >> >> > Hi! I would like to know if there are other means to setup a
> voltage >> >> > reference. I came up with this circuit:
> >> >> >http://bayimg.com/iAeflAAbg
> > >
> >> >> > The purpose is to have a voltage divider (via a
> potentiometer) where >> >> > the output swings from 2.5 to 2V. One
> way I came up with is by >> >> > using an opamp voltage follower. Is
> there another way to design a >> >> > voltage source without using
an
> opamp?
> > >
> >> >> What's the voltage reference for? (I'm guessing here, but in
> the >> >> schematic do you mean that R11 and R20 are to simulate your
> >> >> potentiometer and that you already have a 2.5V supply for V2?
> Do you >> >> already have 5V and 2.5V supplies already present?)
> > >
> >> >> Jon
> > >
> >> >Hi Jon, Sorry for not being clear. R11 and R20 are used to
> simulate my >> >potentiometer. I already have a 2.5V source and a 5V
> source. The >> >section highlighted in green is the part that I was
> referencing.
> > >
> >> What's the voltage reference for?
> > >
> >> Jon
> >
> > Nothing special really. I had some old notes that I was reviewing
> > and one of the exercise questions that was on it was to come up
> > with this type of circuit. Simple really, but I guess it's good
> > practice for the fall semester.
>
> Hehe. Well, since it doesn't really need to go anywhere and it is
> about practice, there are a number of options:
>
> > : +5V
> > : |
> > : |
> > : \
> > : / R1
> > : \ 1.5k
> > : /
> > : |
> > : ,-----+
> > : | |
> > : | \
> > : | / R2
> > : | \ 910
> > : | /
> > : | |
> > : Q1 e>| |
> > : 2N3906 |---+
> > : c/| |
> > : | |
> > : | |
> > : gnd |
> > : \
> > : R3 /
> > : 1k \ <----------- Vout
> > : pot /
> > : |
> > : |
> > : \
> > : / R4
> > : \ 2.7k
> > : /
> > : |
> > : |
> > : gnd
>
> Note that there is no use of the 2.5V supply, here. And it is NOT a
> precision reference and it would be simply horrible over temperature
> changes -- only good for some +/-10C -- as drift per temperature
> changes are in the area of something on the order of 5mV/K or more.
>
> Another option would be:
>
> > : +5 +5
> > : | |
> > : | |
> > : \ R1 \ R2
> > : / 680 / 680
> > : \ \
> > : | |
> > : | |
> > : Q1 e>| |<e Q2
> > : 2N3906 |---+---| 2N3906
> > : c/| | |\c
> > : | | |
> > : | | |
> > : +-----' |
> > : | R3 \
> > : | 1k / <------ Vout
> > : | pot \
> > : R5 \ |
> > : 5.6k / |
> > : \ R4 \
> > : | 2.7k /
> > : | \
> > : gnd |
> > : |
> > : gnd
>
> Again, no precision. But better temperature drift -- on the order of
> 1mV/K.
>
> I picked something like 700uA as the desired current through the 1k
> pot. This was to generate about 0.7V, top to bottom of the sweep of
> the pot, which means you can at least trap your 0.5V in there with a
> little extra so you don't have to nail it precisely. In other words,
> your 1k pot shown will sweep a little wider range than 0.5V. And
> there is nothing precision about any of these, nor temperature
> stabilized. The 2.7k*700uA produces about 1.9V, a pedestal upon which
> the 0.7V range of the pot rests. So roughly speaking, we're talking
> about a sweep from 1.9 to 2.6 volts. Of course, you can tweek things
> a little with R5 in the 2nd circuit and R2 with the first, so that you
> get it centered okay.
>
> For precision sweep and temperature stability, a different topology
> would probably be used. Of course, you can keep the opamp and use the
> pot as part of a series resistive divider that feeds the (+) input of
> the opamp and use it as a unity gain follower.
>
> Jon

Neat. Thanks, Jon! Practice makes perfect, and I need a lot of that. A
year ago, I was not very comfortable with opamps. But thanks to what
I've picked up here, I'm getting used to them a little better.

--


Author: Manoj
Date: 02:57 26-07-07

On Jul 26, 12:57 am, "MRW" <mr.whate...@gmail.com> wrote:
> Jonathan Kirwan wrote:
> > On Wed, 25 Jul 2007 02:15:32 -0000, MRW <mr.whate...@gmail.com> wrote:
>
> > >On Jul 23, 4:48 pm, Jonathan Kirwan <jkir...@easystreet.com> wrote:
> > >> On 23 Jul 2007 18:59:29 GMT, "MRW"
<mr.whate...@gmail.com> wrote:
>
> > >> >Jonathan Kirwan wrote:
>
> > >> >> On 23 Jul 2007 18:28:07 GMT, "MRW"
<mr.whate...@gmail.com>
> > wrote:
>
> > >> >> > Hi! I would like to know if there are other means to
setup a
> > voltage >> >> > reference. I came up with this circuit:
> > >> >> >http://bayimg.com/iAeflAAbg
>
> > >> >> > The purpose is to have a voltage divider (via a
> > potentiometer) where >> >> > the output swings from 2.5 to 2V.
One
> > way I came up with is by >> >> > using an opamp voltage
follower. Is
> > there another way to design a >> >> > voltage source without
using an
> > opamp?
>
> > >> >> What's the voltage reference for? (I'm guessing here, but
in
> > the >> >> schematic do you mean that R11 and R20 are to simulate
your
> > >> >> potentiometer and that you already have a 2.5V supply for
V2?
> > Do you >> >> already have 5V and 2.5V supplies already present?)
>
> > >> >> Jon
>
> > >> >Hi Jon, Sorry for not being clear. R11 and R20 are used to
> > simulate my >> >potentiometer. I already have a 2.5V source and a 5V
> > source. The >> >section highlighted in green is the part that I was
> > referencing.
>
> > >> What's the voltage reference for?
>
> > >> Jon
>
> > > Nothing special really. I had some old notes that I was reviewing
> > > and one of the exercise questions that was on it was to come up
> > > with this type of circuit. Simple really, but I guess it's good
> > > practice for the fall semester.
>
> > Hehe. Well, since it doesn't really need to go anywhere and it is
> > about practice, there are a number of options:
>
> > > : +5V
> > > : |
> > > : |
> > > : \
> > > : / R1
> > > : \ 1.5k
> > > : /
> > > : |
> > > : ,-----+
> > > : | |
> > > : | \
> > > : | / R2
> > > : | \ 910
> > > : | /
> > > : | |
> > > : Q1 e>| |
> > > : 2N3906 |---+
> > > : c/| |
> > > : | |
> > > : | |
> > > : gnd |
> > > : \
> > > : R3 /
> > > : 1k \ <----------- Vout
> > > : pot /
> > > : |
> > > : |
> > > : \
> > > : / R4
> > > : \ 2.7k
> > > : /
> > > : |
> > > : |
> > > : gnd
>
> > Note that there is no use of the 2.5V supply, here. And it is NOT a
> > precision reference and it would be simply horrible over temperature
> > changes -- only good for some +/-10C -- as drift per temperature
> > changes are in the area of something on the order of 5mV/K or more.
>
> > Another option would be:
>
> > > : +5 +5
> > > : | |
> > > : | |
> > > : \ R1 \ R2
> > > : / 680 / 680
> > > : \ \
> > > : | |
> > > : | |
> > > : Q1 e>| |<e Q2
> > > : 2N3906 |---+---| 2N3906
> > > : c/| | |\c
> > > : | | |
> > > : | | |
> > > : +-----' |
> > > : | R3 \
> > > : | 1k / <------ Vout
> > > : | pot \
> > > : R5 \ |
> > > : 5.6k / |
> > > : \ R4 \
> > > : | 2.7k /
> > > : | \
> > > : gnd |
> > > : |
> > > : gnd
>
> > Again, no precision. But better temperature drift -- on the order of
> > 1mV/K.
>
> > I picked something like 700uA as the desired current through the 1k
> > pot. This was to generate about 0.7V, top to bottom of the sweep of
> > the pot, which means you can at least trap your 0.5V in there with a
> > little extra so you don't have to nail it precisely. In other words,
> > your 1k pot shown will sweep a little wider range than 0.5V. And
> > there is nothing precision about any of these, nor temperature
> > stabilized. The 2.7k*700uA produces about 1.9V, a pedestal upon which
> > the 0.7V range of the pot rests. So roughly speaking, we're talking
> > about a sweep from 1.9 to 2.6 volts. Of course, you can tweek things
> > a little with R5 in the 2nd circuit and R2 with the first, so that you
> > get it centered okay.
>
> > For precision sweep and temperature stability, a different topology
> > would probably be used. Of course, you can keep the opamp and use the
> > pot as part of a series resistive divider that feeds the (+) input of
> > the opamp and use it as a unity gain follower.
>
> > Jon
>
> Neat. Thanks, Jon! Practice makes perfect, and I need a lot of that. A
> year ago, I was not very comfortable with opamps. But thanks to what
> I've picked up here, I'm getting used to them a little better.
>
> --- Hide quoted text -
>
> - Show quoted text -

Welll i would like to say that there is difference between regulators
and reference circuits. i refer to using LM317, its a adjustable
regulator and not a reference circuits.
But i would add that its better than references made using only
resistors. they are no reference circuits at all. First write down
what u mean by a reference circuit. Just a voltage output is not the
requirements of a reference circuit. It should first be specified like
whats the stability that would be required, whats teh temperatrue co-
efficient, what should be change in output voltage if the supply
voltage changes etc etc.

If you wish to have a fixed reference circuit, u can try LM336 adn
things like that.

well, i would like to reference circuits with just resistors are
useless in real life.
LM317 is good if u want some current to be fed to circuits. its not a
reference but a regulator.

I hope i didnot offend anyone with my comments

with regards

manoj
1


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