Current Sources

[Jim Thompson]

On Mon, 04 Sep 2017 13:31:05 -0400, DJ Delorie <dj@delorie.com> wrote:

Just to add to the noise...

A voltage source is like keeping your foot in the same spot on the gas
pedal, and letting the car go whatever speed it goes.

A current source is like cruise control, where the car does what it
needs to do to go the same speed, regardless of terrain.

Except when the side G-force sensors say "NO!" BTDT, circa 1968,
driving up and down 101 and 280, scaring the hell out of my boss by
sitting in the driver's seat Yoga style and letting my fingers do the
driving ;-)

...Jim Thompson
--
| James E.Thompson | mens |
| Analog Innovations | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| STV, Queen Creek, AZ 85142 Skype: skypeanalog | |
| Voice480)460-2350 Fax: Available upon request | Brass Rat |
| E-mail Icon at http://www.analog-innovations.com | 1962 |

I'm looking for work... see my website.

Thinking outside the box...producing elegant & economic solutions.

 

[John Larkin]

On Mon, 04 Sep 2017 13:31:05 -0400, DJ Delorie <dj@delorie.com> wrote:

Just to add to the noise...

A voltage source is like keeping your foot in the same spot on the gas
pedal, and letting the car go whatever speed it goes.

A current source is like cruise control, where the car does what it
needs to do to go the same speed, regardless of terrain.

Or maybe the exact opposite.


--

John Larkin Highland Technology, Inc

lunatic fringe electronics

 

[default]

On Sun, 3 Sep 2017 22:26:49 -0400, M Philbrook
<jamie_ka1lpa@charter.net> wrote:

In article <oohbkq$k0v$12@dont-email.me>, cbx@noreply.com says...

On Sun, 03 Sep 2017 12:30:12 -0400, M Philbrook wrote:

[....]

I'm sure you're only trying to help, but this leaves me no more better
informed. I just want a simple way of visualising a current source. For
example, using analogs like a lake, waterfall, a river, a dam and such
like.

ok.

If you were standing next to a small river and you placed a floatable
object in it to measure the speed of movement, you can think of this as
voltage.

Now, get your hip boots on because we're going to explore this river
now, taking with us a 4 x 4 sheet of plywood.

Now slowly start to put that sheet of plywood in the river vertically
as you hold it. you'll notice now you have pressure that is a measure of
the surface area times the water speed (Voltage). This pressure is
current and the source of the current is the speed x volume.

Now lets assume you have put the board in as far as it can go and the
remaining water in the river is left to move on, this would be the
voltage reserve for larger currents if needed and to get larger currents
with this voltage (speed), you need more surface area to block the
water which will create more push, hence a wider board.

Lets take this from a pipe view.

You are standing infront of a drainage pipe, a large one but only 25%
of it has water coming out and it is at a slow pace. Place that board on
it and see how much pressure it produces..

Now do that with a garden hose, even if you crank up the valve for a
nice tall tail of water(voltage), you can stop it with your hands, that
is low current but the nice tall water stream can be looked at as
voltage and may sting a little.

I like this because if high pressure exhausting water (Voltage/Speed)
will feel like you got hit with a few needles. The same will happen with
a HV arc on your skin, like a static arc. That is HV but low current/
Not enough mass to cause problems..

So a current source is something that is moving (voltage) and the volume
of movement (current). So Speed x Volume..

Years ago I use to teach boy scouts simple programming and basic
electronics. They understood that fine.

Have fun..
Btw,
Pay no mind to Bill Slow-Man.. He's one of those that puts lipstick on
a pig. or was he putting it on him? Who knows.

Jamie

I thought your first explanation nailed it...

The second analogy is a good one to describe power.

 

[George Herold]

On Sunday, September 3, 2017 at 5:31:07 PM UTC-4, John Larkin wrote:

On Sun, 3 Sep 2017 15:32:26 -0000 (UTC), Chris <cbx@noreply.com
wrote:

Hi

Finding it real tough trying to visualise a current source. I have no
probs with voltage sources which seem very logical, but for some reason I
can't get my head around current sources. How should I try to see them?
Any guidance would be much appreciated; thanks.

Imagine two metallic spheres. Standing on one of them is a small demon
who, once a second, grabs an electron from near her feet and hurls it
at the other sphere, as hard as it takes to hit and stick. She is a
current source, 1.6e-19 amps.

The voltage between the spheres gradually increases, as one gets
depleted of electrons and the other gets too many. She has to pitch
harder and harder as time goes on, to get electrons to go where there
are too many already. The numbers are fun.

I always found current sources harder to imagine than voltage sources.
Batteries for the voltage source. But you can't buy stand alone current
sources. Some beta decay source inside a metal sphere is not a bad example.

(I mostly think of current sources, as how I make the electronics..
which seem to all go back to a voltage and a resistor...
hmm I guess we could argue about jfet current sources.)

George H.

She looks like this:

https://www.dropbox.com/s/yl3kqe9mp4jhvxp/Elmo.jpg?raw=1

Good arm.




--

John Larkin Highland Technology, Inc

lunatic fringe electronics

 

[John Larkin]

On Tue, 5 Sep 2017 07:09:23 -0700 (PDT), George Herold
<gherold@teachspin.com> wrote:

On Sunday, September 3, 2017 at 5:31:07 PM UTC-4, John Larkin wrote:
On Sun, 3 Sep 2017 15:32:26 -0000 (UTC), Chris <cbx@noreply.com
wrote:

Hi

Finding it real tough trying to visualise a current source. I have no
probs with voltage sources which seem very logical, but for some reason I
can't get my head around current sources. How should I try to see them?
Any guidance would be much appreciated; thanks.

Imagine two metallic spheres. Standing on one of them is a small demon
who, once a second, grabs an electron from near her feet and hurls it
at the other sphere, as hard as it takes to hit and stick. She is a
current source, 1.6e-19 amps.

The voltage between the spheres gradually increases, as one gets
depleted of electrons and the other gets too many. She has to pitch
harder and harder as time goes on, to get electrons to go where there
are too many already. The numbers are fun.

I always found current sources harder to imagine than voltage sources.
Batteries for the voltage source. But you can't buy stand alone current
sources. Some beta decay source inside a metal sphere is not a bad example.

Beta batteries are cool, but it's hard to use a 400KV nanoampere power
source. It has been done.

I know of no simple-physics sources (like, for example, an illuminated
photodiode, makes photons into electrons) that are as good as an
electronic cc circuit.

(I mostly think of current sources, as how I make the electronics..
which seem to all go back to a voltage and a resistor...
hmm I guess we could argue about jfet current sources.)

Another interesting gadget is the pumped single-electron transistor.
Every clock pulse, it lets through exactly one electron.


--

John Larkin Highland Technology, Inc

lunatic fringe electronics

 

[George Herold]

On Tuesday, September 5, 2017 at 12:04:29 PM UTC-4, John Larkin wrote:

On Tue, 5 Sep 2017 07:09:23 -0700 (PDT), George Herold
gherold@teachspin.com> wrote:

On Sunday, September 3, 2017 at 5:31:07 PM UTC-4, John Larkin wrote:
On Sun, 3 Sep 2017 15:32:26 -0000 (UTC), Chris <cbx@noreply.com
wrote:

Hi

Finding it real tough trying to visualise a current source. I have no
probs with voltage sources which seem very logical, but for some reason I
can't get my head around current sources. How should I try to see them?
Any guidance would be much appreciated; thanks.

Imagine two metallic spheres. Standing on one of them is a small demon
who, once a second, grabs an electron from near her feet and hurls it
at the other sphere, as hard as it takes to hit and stick. She is a
current source, 1.6e-19 amps.

The voltage between the spheres gradually increases, as one gets
depleted of electrons and the other gets too many. She has to pitch
harder and harder as time goes on, to get electrons to go where there
are too many already. The numbers are fun.

I always found current sources harder to imagine than voltage sources.
Batteries for the voltage source. But you can't buy stand alone current
sources. Some beta decay source inside a metal sphere is not a bad example.

Beta batteries are cool, but it's hard to use a 400KV nanoampere power
source. It has been done.

Huh, I didn't know there was such a device.
https://en.wikipedia.org/wiki/Betavoltaic_device

Sounds like it didn't have 400 kV of compliance, but blasted the beta's
into a PN junction and collected the ionized electrons.

George h.

I know of no simple-physics sources (like, for example, an illuminated
photodiode, makes photons into electrons) that are as good as an
electronic cc circuit.


(I mostly think of current sources, as how I make the electronics..
which seem to all go back to a voltage and a resistor...
hmm I guess we could argue about jfet current sources.)

Another interesting gadget is the pumped single-electron transistor.
Every clock pulse, it lets through exactly one electron.


--

John Larkin Highland Technology, Inc

lunatic fringe electronics

 

[John Smith]

"Chris" <cbx@noreply.com> wrote in message
newsoh7aa$k0v$9@dont-email.me...

Hi

Finding it real tough trying to visualise a current source. I have no
probs with voltage sources which seem very logical, but for some reason I
can't get my head around current sources. How should I try to see them?
Any guidance would be much appreciated; thanks.

Is this because you can buy voltage sources in the shops but not current
sources?

You know that a voltage source does its best to change the current so as to
keep the voltage constant.

Any real voltage source has a very low but finite internal resistance.
Within limits it can produce whatever current you want and the voltage
doesn't change very much, but the current can only go up to some limit and
then it will fail. If you put 8 AA cells in series you can have a curent of
1 mA or 100mA and still measure 12V. You can make the load resisrance go
lower and lower and still measure 12 V but you'll measure 0V if you try to
start the car.

Do you know that a current source does its best to change the voltage so as
to keep the current constant?

Any real current source has a very high but finite internal resistance.
Within limits it can produce whatever voltage you want and the current
doesn't change very much, but the voltage can only go up to some limit and
then it will fail. So a 1mA current source, unless it's designed to do so,
won't likely be able to produce the 100,000 volts needed to sustain 1mA
through 100M ohms and will produce 0mA instead, but if it's connected to 1K
ohms then it probably won't find it hard to produce the necessary 1 volt.
And if it's connected to 2K ohms then it will likely be happy to produce the
necessary 2V.

 

[whit3rd]

On Tuesday, September 5, 2017 at 7:03:41 PM UTC-7, John Smith wrote:

"Chris" <cbx@noreply.com> wrote in message
newsoh7aa$k0v$9@dont-email.me...

Finding it real tough trying to visualise a current source.

Is this because you can buy voltage sources in the shops but not current
sources?

Probably not: the collector of a transistor is such a current source, and
they're CHEAP, sell by the millions. The reason you can't buy "a current source"
is that they're so easy to build. Well, until you get to the megavolts-of-compliance
current sources, they're easy.

 

[Phil Hobbs]

On 09/05/2017 10:04 PM, John Smith wrote:

"Chris" <cbx@noreply.com> wrote in message
newsoh7aa$k0v$9@dont-email.me...
Hi

Finding it real tough trying to visualise a current source. I have no
probs with voltage sources which seem very logical, but for some reason I
can't get my head around current sources. How should I try to see them?
Any guidance would be much appreciated; thanks.

Is this because you can buy voltage sources in the shops but not current
sources?

You can buy current sources too, if you don't mind adding one resistor
to an LM7805.

Cheers

Phil Hobbs


--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics

160 North State Road #203
Briarcliff Manor NY 10510

hobbs at electrooptical dot net
http://electrooptical.net

 

[John Larkin]

On Wed, 6 Sep 2017 00:40:09 -0400, Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:

On 09/05/2017 10:04 PM, John Smith wrote:
"Chris" <cbx@noreply.com> wrote in message
newsoh7aa$k0v$9@dont-email.me...
Hi

Finding it real tough trying to visualise a current source. I have no
probs with voltage sources which seem very logical, but for some reason I
can't get my head around current sources. How should I try to see them?
Any guidance would be much appreciated; thanks.

Is this because you can buy voltage sources in the shops but not current
sources?

You can buy current sources too, if you don't mind adding one resistor
to an LM7805.

Cheers

Phil Hobbs

There are 2-terminal current-limiting things available, typically used
as LED regulators. I'm guessing that they are depletion fets inside.



--

John Larkin Highland Technology, Inc

lunatic fringe electronics

 

[Jim Thompson]

On Wed, 6 Sep 2017 00:40:09 -0400, Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:

On 09/05/2017 10:04 PM, John Smith wrote:
"Chris" <cbx@noreply.com> wrote in message
newsoh7aa$k0v$9@dont-email.me...
Hi

Finding it real tough trying to visualise a current source. I have no
probs with voltage sources which seem very logical, but for some reason I
can't get my head around current sources. How should I try to see them?
Any guidance would be much appreciated; thanks.

Is this because you can buy voltage sources in the shops but not current
sources?

You can buy current sources too, if you don't mind adding one resistor
to an LM7805.

Cheers

Phil Hobbs

If you don't mind about a 7V drop. I think you meant those regulators
that use an LM317-style chip architecture?

...Jim Thompson
--
| James E.Thompson | mens |
| Analog Innovations | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| STV, Queen Creek, AZ 85142 Skype: skypeanalog | |
| Voice480)460-2350 Fax: Available upon request | Brass Rat |
| E-mail Icon at http://www.analog-innovations.com | 1962 |

I'm looking for work... see my website.

Thinking outside the box...producing elegant & economic solutions.

 

[Phil Hobbs]

On 09/06/2017 02:35 PM, Jim Thompson wrote:

On Wed, 6 Sep 2017 00:40:09 -0400, Phil Hobbs
pcdhSpamMeSenseless@electrooptical.net> wrote:

On 09/05/2017 10:04 PM, John Smith wrote:
"Chris" <cbx@noreply.com> wrote in message
newsoh7aa$k0v$9@dont-email.me...
Hi

Finding it real tough trying to visualise a current source. I have no
probs with voltage sources which seem very logical, but for some reason I
can't get my head around current sources. How should I try to see them?
Any guidance would be much appreciated; thanks.

Is this because you can buy voltage sources in the shops but not current
sources?

You can buy current sources too, if you don't mind adding one resistor
to an LM7805.

Cheers

Phil Hobbs

If you don't mind about a 7V drop. I think you meant those regulators
that use an LM317-style chip architecture?

...Jim Thompson

You can do that too. The OP was apparently asking a rhetorical question.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics

160 North State Road #203
Briarcliff Manor NY 10510

hobbs at electrooptical dot net
http://electrooptical.net

 

[George Herold]

On Tuesday, September 5, 2017 at 11:41:51 PM UTC-4, Phil Hobbs wrote:

On 09/05/2017 10:04 PM, John Smith wrote:
"Chris" <cbx@noreply.com> wrote in message
newsoh7aa$k0v$9@dont-email.me...
Hi

Finding it real tough trying to visualise a current source. I have no
probs with voltage sources which seem very logical, but for some reason I
can't get my head around current sources. How should I try to see them?
Any guidance would be much appreciated; thanks.

Is this because you can buy voltage sources in the shops but not current
sources?

You can buy current sources too, if you don't mind adding one resistor
to an LM7805.

Sure but you have to wrap a voltage source around it.

It would be cool to have a stand alone current source*.
I guess more so when I was younger and didn't have an
intuitive feel for a current source.

George H.
*OK a battery operated lm7805/ lm317 current source, but
that is somehow not the same.

Cheers

Phil Hobbs


--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics

160 North State Road #203
Briarcliff Manor NY 10510

hobbs at electrooptical dot net
http://electrooptical.net

 

[Phil Hobbs]

On 09/06/2017 03:16 PM, George Herold wrote:

On Tuesday, September 5, 2017 at 11:41:51 PM UTC-4, Phil Hobbs wrote:
On 09/05/2017 10:04 PM, John Smith wrote:
"Chris" <cbx@noreply.com> wrote in message
newsoh7aa$k0v$9@dont-email.me...
Hi

Finding it real tough trying to visualise a current source. I have no
probs with voltage sources which seem very logical, but for some reason I
can't get my head around current sources. How should I try to see them?
Any guidance would be much appreciated; thanks.

Is this because you can buy voltage sources in the shops but not current
sources?

You can buy current sources too, if you don't mind adding one resistor
to an LM7805.

Sure but you have to wrap a voltage source around it.

Tape it to a battery.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics

160 North State Road #203
Briarcliff Manor NY 10510

hobbs at electrooptical dot net
http://electrooptical.net

 

[John Larkin]

On Wed, 6 Sep 2017 16:03:36 -0400, Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:

On 09/06/2017 03:16 PM, George Herold wrote:
On Tuesday, September 5, 2017 at 11:41:51 PM UTC-4, Phil Hobbs wrote:
On 09/05/2017 10:04 PM, John Smith wrote:
"Chris" <cbx@noreply.com> wrote in message
newsoh7aa$k0v$9@dont-email.me...
Hi

Finding it real tough trying to visualise a current source. I have no
probs with voltage sources which seem very logical, but for some reason I
can't get my head around current sources. How should I try to see them?
Any guidance would be much appreciated; thanks.

Is this because you can buy voltage sources in the shops but not current
sources?

You can buy current sources too, if you don't mind adding one resistor
to an LM7805.

Sure but you have to wrap a voltage source around it.

Tape it to a battery.

Cheers

Phil Hobbs

I once (for a school project) built a 2-terminal negative 1K resistor,
battery powered. It executed all of the standard circuits, with a
negative R value plugged into the equations: voltage dividers, RCs,
LC's with negative Qs, all that. It was fun. My prof seemed
unimpressed.


--

John Larkin Highland Technology, Inc
picosecond timing precision measurement

jlarkin att highlandtechnology dott com
http://www.highlandtechnology.com

 

[Jasen Betts]

On 2017-09-06, George Herold <gherold@teachspin.com> wrote:

On Tuesday, September 5, 2017 at 11:41:51 PM UTC-4, Phil Hobbs wrote:
On 09/05/2017 10:04 PM, John Smith wrote:
"Chris" <cbx@noreply.com> wrote in message
newsoh7aa$k0v$9@dont-email.me...
Hi

Finding it real tough trying to visualise a current source. I have no
probs with voltage sources which seem very logical, but for some reason I
can't get my head around current sources. How should I try to see them?
Any guidance would be much appreciated; thanks.

Is this because you can buy voltage sources in the shops but not current
sources?

You can buy current sources too, if you don't mind adding one resistor
to an LM7805.

Sure but you have to wrap a voltage source around it.

It would be cool to have a stand alone current source.

You mean like an arc welder, a generator, a current transformer,
even a capacitive dropper makes a reasonable approximation of a
current soruce.

OTOH:

A CR2032 cell is sufficiently current-source like to make it useful for
testing LEDs

--
This email has not been checked by half-arsed antivirus software

--
This email has not been checked by half-arsed antivirus software

 

[whit3rd]

On Wednesday, September 6, 2017 at 12:16:26 PM UTC-7, George Herold wrote:

It would be cool to have a stand alone current source*.
I guess more so when I was younger and didn't have an
intuitive feel for a current source.

Simplest thing is a current regulator diode (jFET with G-S short);
compliance circa 200V, power supply not included.
<

A small van de Graaff generator, battery powered, is just a little
too... complicated to be an 'ideal component'. Imagination
doesn't grasp the intrinsic simplicity when confronted with whirs and
zaps.

 

[whit3rd]

On Wednesday, September 6, 2017 at 3:58:59 PM UTC-7, whit3rd wrote:

On Wednesday, September 6, 2017 at 12:16:26 PM UTC-7, George Herold wrote:

It would be cool to have a stand alone current source*.

Simplest thing is a current regulator diode (jFET with G-S short);
.... compliance circa 100V, power supply not included.

Forgot the link:
<http://www.mouser.com/ds/2/68/1n5283-5314-43522.pdf>

 

[George Herold]

On Wednesday, September 6, 2017 at 6:01:27 PM UTC-4, Jasen Betts wrote:

On 2017-09-06, George Herold <gherold@teachspin.com> wrote:
On Tuesday, September 5, 2017 at 11:41:51 PM UTC-4, Phil Hobbs wrote:
On 09/05/2017 10:04 PM, John Smith wrote:
"Chris" <cbx@noreply.com> wrote in message
newsoh7aa$k0v$9@dont-email.me...
Hi

Finding it real tough trying to visualise a current source. I have no
probs with voltage sources which seem very logical, but for some reason I
can't get my head around current sources. How should I try to see them?
Any guidance would be much appreciated; thanks.

Is this because you can buy voltage sources in the shops but not current
sources?

You can buy current sources too, if you don't mind adding one resistor
to an LM7805.

Sure but you have to wrap a voltage source around it.

It would be cool to have a stand alone current source.

You mean like an arc welder, a generator, a current transformer,
even a capacitive dropper makes a reasonable approximation of a
current soruce.

Sure or just a high voltage and a big resistor. But I meant a current
source that was like a battery. A two terminal thing, that spits
out ~1mA (or anything) at 1 kV of compliance. You'd keep it
short circuited with a kilo ohm or so, so it wouldn't kill you.

It's really just a pipe dream.

George H.

OTOH:

A CR2032 cell is sufficiently current-source like to make it useful for
testing LEDs

--
This email has not been checked by half-arsed antivirus software

--
This email has not been checked by half-arsed antivirus software

 

[John Larkin]

On Thu, 7 Sep 2017 07:37:13 -0700 (PDT), George Herold
<gherold@teachspin.com> wrote:

On Wednesday, September 6, 2017 at 6:01:27 PM UTC-4, Jasen Betts wrote:
On 2017-09-06, George Herold <gherold@teachspin.com> wrote:
On Tuesday, September 5, 2017 at 11:41:51 PM UTC-4, Phil Hobbs wrote:
On 09/05/2017 10:04 PM, John Smith wrote:
"Chris" <cbx@noreply.com> wrote in message
newsoh7aa$k0v$9@dont-email.me...
Hi

Finding it real tough trying to visualise a current source. I have no
probs with voltage sources which seem very logical, but for some reason I
can't get my head around current sources. How should I try to see them?
Any guidance would be much appreciated; thanks.

Is this because you can buy voltage sources in the shops but not current
sources?

You can buy current sources too, if you don't mind adding one resistor
to an LM7805.

Sure but you have to wrap a voltage source around it.

It would be cool to have a stand alone current source.

You mean like an arc welder, a generator, a current transformer,
even a capacitive dropper makes a reasonable approximation of a
current soruce.

Sure or just a high voltage and a big resistor. But I meant a current
source that was like a battery. A two terminal thing, that spits
out ~1mA (or anything) at 1 kV of compliance. You'd keep it
short circuited with a kilo ohm or so, so it wouldn't kill you.

It's really just a pipe dream.

George H.

1 mA wouldn't kill you, or even shock you. But a just-right bad skin
contact could dissipate 1 watt, which might make a small burn.


--

John Larkin Highland Technology, Inc

lunatic fringe electronics