Current Sources

[George Herold]

On Thursday, September 7, 2017 at 11:52:21 AM UTC-4, John Larkin wrote:

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.

OK, Still if I had such a current source it would be best to keep it
shorted. That's where it's dissipating the least energy. Like keeping
a battery as an open circuit.

George h.

--

John Larkin Highland Technology, Inc

lunatic fringe electronics

 

[rickman]

George Herold wrote on 9/6/2017 3:16 PM:

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.

That's not true. You simply need a power source with enough voltage to
power the circuit and enough current to supply the load. It can be neither
a voltage nor a current source.

--

Rick C

Viewed the eclipse at Wintercrest Farms,
on the centerline of totality since 1998

 

[rickman]

George Herold wrote on 9/7/2017 10:37 AM:

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.

Instead of short circuiting with resistance, it would be better to short it
with a... short. The short is the current source's equivalent of an open
circuit for a voltage source. No resistance equals no power.

> It's really just a pipe dream.

I bet it just requires more thought from the right perspective. A chemical
battery works because of the work function of various elements and
compounds. This work function equates to a voltage independent of whether
current flows. What would produce a current that depletes if the current
doesn't flow? I will say I doubt something as simple and compact as a
battery will be found. I think someone pointed out that radioactive decay
is like that but hard to turn into a battery. What else?

--

Rick C

Viewed the eclipse at Wintercrest Farms,
on the centerline of totality since 1998

 

[George Herold]

On Friday, September 8, 2017 at 2:41:06 PM UTC-4, rickman wrote:

George Herold wrote on 9/6/2017 3:16 PM:
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.

That's not true. You simply need a power source with enough voltage to
power the circuit and enough current to supply the load. It can be neither
a voltage nor a current source.

Aren't all power sources best approximated as voltage sources?
I don't know that much about power generation.

George H.

--

Rick C

Viewed the eclipse at Wintercrest Farms,
on the centerline of totality since 1998

 

[George Herold]

On Friday, September 8, 2017 at 3:26:58 PM UTC-4, rickman wrote:

George Herold wrote on 9/7/2017 10:37 AM:
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.

Instead of short circuiting with resistance, it would be better to short it
with a... short. The short is the current source's equivalent of an open
circuit for a voltage source. No resistance equals no power.

It's really just a pipe dream.

I bet it just requires more thought from the right perspective. A chemical
battery works because of the work function of various elements and
compounds. This work function equates to a voltage independent of whether
current flows. What would produce a current that depletes if the current
doesn't flow? I will say I doubt something as simple and compact as a
battery will be found. I think someone pointed out that radioactive decay
is like that but hard to turn into a battery. What else?

Well as someone else said a photodiode with a bunch of light shinning on it.
But the compliance stinks. I guess you could stack up a hundred or so.

George H.

--

Rick C

Viewed the eclipse at Wintercrest Farms,
on the centerline of totality since 1998

 

[Ralph Mowery]

In article <8b827b99-b7ac-44a6-a72f-6cd7566a7e08@googlegroups.com>,
gherold@teachspin.com says...

Aren't all power sources best approximated as voltage sources?
I don't know that much about power generation.

I would not say all, as most of the old nicad batteries were charged
with a constan current source.

Many of the most often power sources are mainly a voltage source. The
power coming into your house is mainly a voltage source. It will most
often have 120 volts plus or minus about 5 volts depending on many
things. The Batteries are mostly voltage sources. The put out a
relative constant voltage as long as they can provide enough current to
the load.

Outside of charging some batteries and maybe a welder I can not think of
any common use of a constant courrent source most ordnary people would
come in contact with.

 

[rickman]

George Herold wrote on 9/8/2017 3:49 PM:

On Friday, September 8, 2017 at 2:41:06 PM UTC-4, rickman wrote:
George Herold wrote on 9/6/2017 3:16 PM:
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.

That's not true. You simply need a power source with enough voltage to
power the circuit and enough current to supply the load. It can be neither
a voltage nor a current source.

Aren't all power sources best approximated as voltage sources?

Not sure what "best approximated" means. Batteries are pretty much voltage
sources as the output impedance is pretty low. But a transformer with a
bridge diode can look a lot like a current source if the winding resistance
is high. This is often done deliberately in car battery chargers (or were
anyway) so they didn't run too much current into a dead battery and would
survive a short without any fancy electronics. Now days they mostly use
some electronics so they don't enable the full power until they see the
battery voltage on the output. If your battery is totally down one of these
chargers might not turn on. I've got a small 15 volt wall wart that I use
to trickle charge a car battery. It looks exactly like a current source to
the battery because it is always current limited to something less than half
an amp.


> I don't know that much about power generation.

Ok...

--

Rick C

Viewed the eclipse at Wintercrest Farms,
on the centerline of totality since 1998

 

[Jim Thompson]

On Fri, 8 Sep 2017 16:09:17 -0400, Ralph Mowery
<rmowery28146@earthlink.net> wrote:

[snip]

Outside of charging some batteries and maybe a welder I can not think of
any common use of a constant courrent source most ordinary people would
come in contact with.

Those of us in the I/C design business use them extensively as bias
methods that are stable over temperature and process corners (or track
ratiometrically ;-)

...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.

 

[Ralph Mowery]

In article <gnu5rchrcl3uei9e435caql20cjnn876rq@4ax.com>, To-Email-Use-
The-Envelope-Icon@On-My-Web-Site.com says...

On Fri, 8 Sep 2017 16:09:17 -0400, Ralph Mowery
rmowery28146@earthlink.net> wrote:

[snip]

Outside of charging some batteries and maybe a welder I can not think of
any common use of a constant courrent source most ordinary people would
come in contact with.



Those of us in the I/C design business use them extensively as bias
methods that are stable over temperature and process corners (or track
ratiometrically ;-)

...Jim Thompson

I am sure the constant current sources are used in many places, but
unless you are really into electronics and design, not too many people
will see the current sources. Most will see constant voltage or almost
constant voltage in many things.

 

[rickman]

Ralph Mowery wrote on 9/8/2017 6:09 PM:

In article <gnu5rchrcl3uei9e435caql20cjnn876rq@4ax.com>, To-Email-Use-
The-Envelope-Icon@On-My-Web-Site.com says...

On Fri, 8 Sep 2017 16:09:17 -0400, Ralph Mowery
rmowery28146@earthlink.net> wrote:

[snip]

Outside of charging some batteries and maybe a welder I can not think of
any common use of a constant courrent source most ordinary people would
come in contact with.



Those of us in the I/C design business use them extensively as bias
methods that are stable over temperature and process corners (or track
ratiometrically ;-)

...Jim Thompson

I am sure the constant current sources are used in many places, but
unless you are really into electronics and design, not too many people
will see the current sources. Most will see constant voltage or almost
constant voltage in many things.

I'm not sure who else would even know what that means. I don't get your
point.

Another example of a current source would be some DACs. They aren't true
current sources, but can only be used if you treat them as such with a
current to voltage buffer.

--

Rick C

Viewed the eclipse at Wintercrest Farms,
on the centerline of totality since 1998

 

[Cursitor Doom]

On Tue, 05 Sep 2017 09:04:18 -0700, John Larkin wrote:

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

My carpeting seems to manage it every winter, though.

--
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.

 

[Cursitor Doom]

On Fri, 08 Sep 2017 16:09:17 -0400, Ralph Mowery wrote:

Outside of charging some batteries and maybe a welder I can not think of
any common use of a constant courrent source most ordnary people would
come in contact with.

Laser psu.



--
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.

 

[George Herold]

On Friday, September 8, 2017 at 4:09:22 PM UTC-4, Ralph Mowery wrote:

In article <8b827b99-b7ac-44a6-a72f-6cd7566a7e08@googlegroups.com>,
gherold@teachspin.com says...


Aren't all power sources best approximated as voltage sources?
I don't know that much about power generation.



I would not say all, as most of the old nicad batteries were charged
with a constan current source.

Many of the most often power sources are mainly a voltage source. The
power coming into your house is mainly a voltage source. It will most
often have 120 volts plus or minus about 5 volts depending on many
things. The Batteries are mostly voltage sources. The put out a
relative constant voltage as long as they can provide enough current to
the load.

Outside of charging some batteries and maybe a welder I can not think of
any common use of a constant courrent source most ordnary people would
come in contact with.

I use a lot of current sources, running magnetic field coils,
controlling heater power (resistor or TEC)
Biasing all sorts of diodes accurately.

George H.

 

[John Larkin]

On Sun, 10 Sep 2017 18:05:07 -0700 (PDT), George Herold
<gherold@teachspin.com> wrote:

On Friday, September 8, 2017 at 4:09:22 PM UTC-4, Ralph Mowery wrote:
In article <8b827b99-b7ac-44a6-a72f-6cd7566a7e08@googlegroups.com>,
gherold@teachspin.com says...


Aren't all power sources best approximated as voltage sources?
I don't know that much about power generation.



I would not say all, as most of the old nicad batteries were charged
with a constan current source.

Many of the most often power sources are mainly a voltage source. The
power coming into your house is mainly a voltage source. It will most
often have 120 volts plus or minus about 5 volts depending on many
things. The Batteries are mostly voltage sources. The put out a
relative constant voltage as long as they can provide enough current to
the load.

Outside of charging some batteries and maybe a welder I can not think of
any common use of a constant courrent source most ordnary people would
come in contact with.

I use a lot of current sources, running magnetic field coils,
controlling heater power (resistor or TEC)
Biasing all sorts of diodes accurately.

George H.

I have a zillion current source scribbles. This one is fun, and lights
up too!

https://www.dropbox.com/s/d4ntmq7fdzah69a/LED_Isrc_data.JPG?raw=1

The LED forward drop can just about cancel the transistor's Vbe
temperature coefficient.

This is really goofy:

https://www.dropbox.com/s/ufiq2bmnlsshkjy/LED_Current_Sink.JPG?raw=1

The current sink is the opamp's supply rail.


--

John Larkin Highland Technology, Inc

lunatic fringe electronics

 

[George Herold]

On Tuesday, September 12, 2017 at 12:17:34 AM UTC-4, John Larkin wrote:

On Sun, 10 Sep 2017 18:05:07 -0700 (PDT), George Herold
gherold@teachspin.com> wrote:

On Friday, September 8, 2017 at 4:09:22 PM UTC-4, Ralph Mowery wrote:
In article <8b827b99-b7ac-44a6-a72f-6cd7566a7e08@googlegroups.com>,
gherold@teachspin.com says...


Aren't all power sources best approximated as voltage sources?
I don't know that much about power generation.



I would not say all, as most of the old nicad batteries were charged
with a constan current source.

Many of the most often power sources are mainly a voltage source. The
power coming into your house is mainly a voltage source. It will most
often have 120 volts plus or minus about 5 volts depending on many
things. The Batteries are mostly voltage sources. The put out a
relative constant voltage as long as they can provide enough current to
the load.

Outside of charging some batteries and maybe a welder I can not think of
any common use of a constant courrent source most ordnary people would
come in contact with.

I use a lot of current sources, running magnetic field coils,
controlling heater power (resistor or TEC)
Biasing all sorts of diodes accurately.

George H.

I have a zillion current source scribbles. This one is fun, and lights
up too!

https://www.dropbox.com/s/d4ntmq7fdzah69a/LED_Isrc_data.JPG?raw=1

The LED forward drop can just about cancel the transistor's Vbe
temperature coefficient.

This is really goofy:

https://www.dropbox.com/s/ufiq2bmnlsshkjy/LED_Current_Sink.JPG?raw=1

The current sink is the opamp's supply rail.

I do enjoy your creative use of the opamp power rail(s).
We mostly forget it's there, 'cause it gets stuck down at the bottom
of the schematic with a cluster of bypass caps.

George H.

--

John Larkin Highland Technology, Inc

lunatic fringe electronics

 

"Chris" <c...@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;

In either union electrician's school or HVAC school, I think I remember hearing this equivalent:
Air in a balloon is VOLTAGE. Poke a hole in the balloon - that airstream is CURRENT.

 

[amdx]

On 9/3/2017 12:43 PM, rickman wrote:

Ralph Mowery wrote on 9/3/2017 1:23 PM:
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.

That may be hard to do.


A constant current source would be a variable voltage source with a
resistor in series with it.   When the load resistance changes, then the
voltage will go up or down dependin if you need more or less current.

Maybe a bycycle rider going up and down hills.  He peddles with a
constand pressure on the peddles.  As he goes up a hill, the
transmission shifts gears and he will have to speed up his peddle
pushing to get up the hill.

Another may be a pully and rope system.  Say a man can only pull with
force of 10 pounds.  you put a box on the ground an a pully in a tree.
he pulls it up .  The box then weighs 20 pounds and you add more pullies
so he can still pull the box up.  To get it up in the same ammout of
time , he will have to pull fster.

I highly recommend you never try teaching.

I don't quite have it, but if you think about a regulated current source
it may get you there.

How about, a regulated current source is a water source with limit on
how much water (current) can flow. No matter how hard you try only X
amount of water (current) will flow.
However, if your (voltage) water source (height of water) is not high
enough the (current) water flow could be less if you squeeze the hose
(more resistance).
Best I got for now.
Mikek

 

[rickman]

amdx wrote on 9/23/2017 7:01 PM:

I don't quite have it, but if you think about a regulated current source
it may get you there.

How about, a regulated current source is a water source with limit on how
much water (current) can flow. No matter how hard you try only X amount of
water (current) will flow.
However, if your (voltage) water source (height of water) is not high
enough the (current) water flow could be less if you squeeze the hose (more
resistance).

There are pumps that create pressure but do not force any given volume.
Centrifugal comes to mind. The fluid is spun by an impeller and centrifugal
force creates pressure at the periphery. But it does not require the fluid
to flow at any given rate or at all.

Other pumps force a flow rate regardless of back pressure such as the oil
pump in your car or a piston pump. In each case there is a volume of fluid
that is being squeezed like toothpaste in a tube so that the fluid will
create a great force to get out.

The former is like a voltage source, the latter is like a current source.

I'm not sure these analogies help to understand the workings of a current
source.

--

Rick C

Viewed the eclipse at Wintercrest Farms,
on the centerline of totality since 1998

 

[Chris]

On Sun, 03 Sep 2017 13:23:41 -0400, Ralph Mowery wrote:

A constant current source would be a variable voltage source with a
resistor in series with it. When the load resistance changes, then the
voltage will go up or down dependin if you need more or less current.

This seems perfectly clear to me now. I'm hoping no one will find fault
with it. Are we all agreed?

 

[rickman]

Chris wrote on 9/24/2017 5:46 AM:

On Sun, 03 Sep 2017 13:23:41 -0400, Ralph Mowery wrote:


A constant current source would be a variable voltage source with a
resistor in series with it. When the load resistance changes, then the
voltage will go up or down dependin if you need more or less current.

This seems perfectly clear to me now. I'm hoping no one will find fault
with it. Are we all agreed?

If you understand it why does anyone else need to like it?

In the real world a current source is approximated by a high voltage and a
high value series resistor. No need to adjust the voltage. As long as the
resistance of the load is significantly smaller than the series resistance
it will be very close to a constant current supply.

--

Rick C

Viewed the eclipse at Wintercrest Farms,
on the centerline of totality since 1998