Current Sources

On Sun, 24 Sep 2017 09:46:45 -0000 (UTC), Chris <cbx@noreply.com>
wrote:

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?
Click to expand...

Or maybe a voltage source with a series resistor such that,
irrespective of the load, the drop across the series resistor is
constant?

...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 | |
| Voice:(480)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.
 
On Sun, 24 Sep 2017 10:11:12 -0700, Jim Thompson wrote:

Or maybe a voltage source with a series resistor such that, irrespective
of the load, the drop across the series resistor is constant?
Click to expand...

Sorry, now I'm back to square one again. :(
Are we to take it, then, that Ralph's definition is incorrect in some way?
 
On Sun, 24 Sep 2017 20:30:39 -0000 (UTC), Chris <cbx@noreply.com>
wrote:

On Sun, 24 Sep 2017 10:11:12 -0700, Jim Thompson wrote:

Or maybe a voltage source with a series resistor such that, irrespective
of the load, the drop across the series resistor is constant?

Sorry, now I'm back to square one again. :(
Are we to take it, then, that Ralph's definition is incorrect in some way?
Click to expand...

No. I was just offering another way of looking at it.

...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 | |
| Voice:(480)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.
 
On Sun, 24 Sep 2017 09:46:45 -0000 (UTC), Chris <cbx@noreply.com>
wrote:

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?
Click to expand...

This is a bootstrap current source:

https://www.dropbox.com/s/lznbrhc5gfc7xe8/Ramp.JPG?raw=1

The idea is to keep a constant voltage across the left-most 1K
resistor, so it dumps a constant 5 mA current into the 39 pF cap. That
makes a linear voltage ramp.




--

John Larkin Highland Technology, Inc

lunatic fringe electronics
 
On Sun, 24 Sep 2017 14:51:11 -0700, John Larkin
<jjlarkin@highlandtechnology.com> wrote:

On Sun, 24 Sep 2017 09:46:45 -0000 (UTC), Chris <cbx@noreply.com
wrote:

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?

This is a bootstrap current source:

https://www.dropbox.com/s/lznbrhc5gfc7xe8/Ramp.JPG?raw=1

The idea is to keep a constant voltage across the left-most 1K
resistor, so it dumps a constant 5 mA current into the 39 pF cap. That
makes a linear voltage ramp.
Click to expand...

Maybe a Howland current source circuit schematic (a variation on your
scheme) would aid the OP in his understanding.

...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 | |
| Voice:(480)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.
 
Jim Thompson wrote on 9/24/2017 10:01 PM:
On Sun, 24 Sep 2017 14:51:11 -0700, John Larkin
jjlarkin@highlandtechnology.com> wrote:

On Sun, 24 Sep 2017 09:46:45 -0000 (UTC), Chris <cbx@noreply.com
wrote:

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?

This is a bootstrap current source:

https://www.dropbox.com/s/lznbrhc5gfc7xe8/Ramp.JPG?raw=1

The idea is to keep a constant voltage across the left-most 1K
resistor, so it dumps a constant 5 mA current into the 39 pF cap. That
makes a linear voltage ramp.

Maybe a Howland current source circuit schematic (a variation on your
scheme) would aid the OP in his understanding.
Click to expand...

Yes, these circuits are exactly what a person who doesn't understand a
current source would need to help them. NOT! lol

--

Rick C

Viewed the eclipse at Wintercrest Farms,
on the centerline of totality since 1998
 
Chris wrote on 9/24/2017 4:30 PM:
On Sun, 24 Sep 2017 10:11:12 -0700, Jim Thompson wrote:

Or maybe a voltage source with a series resistor such that, irrespective
of the load, the drop across the series resistor is constant?

Sorry, now I'm back to square one again. :(
Are we to take it, then, that Ralph's definition is incorrect in some way?
Click to expand...

It's not incorrect if you understand it. A current source is just that, a
source the supplies enough potential to drive a given current though a load
regardless of resistance. You can think of this as a variable voltage
source and a smaller resistor or you can think of it as a very large fixed
voltage source and a very large resistor. Both do the same thing.

How about we turn this around and ask you how you see a current source? For
that matter, why don't you explain to us what a voltage source is?

--

Rick C

Viewed the eclipse at Wintercrest Farms,
on the centerline of totality since 1998
 
On Sunday, September 24, 2017 at 5:51:20 PM UTC-4, John Larkin wrote:
On Sun, 24 Sep 2017 09:46:45 -0000 (UTC), Chris <cbx@noreply.com
wrote:

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?

This is a bootstrap current source:

https://www.dropbox.com/s/lznbrhc5gfc7xe8/Ramp.JPG?raw=1

The idea is to keep a constant voltage across the left-most 1K
resistor, so it dumps a constant 5 mA current into the 39 pF cap. That
makes a linear voltage ramp.
Click to expand...
Right, I do that with a 5V reference (REF02 or similar) I'm guessing
that it (REF02) would be slow compared to the LM4040...
also has headroom issues.

George H.
--

John Larkin Highland Technology, Inc

lunatic fringe electronics
Click to expand...
 
On Sun, 24 Sep 2017 14:51:11 -0700, John Larkin wrote:

This is a bootstrap current source:

https://www.dropbox.com/s/lznbrhc5gfc7xe8/Ramp.JPG?raw=1

The idea is to keep a constant voltage across the left-most 1K resistor,
so it dumps a constant 5 mA current into the 39 pF cap. That makes a
linear voltage ramp.
Click to expand...

What sort of application did you design this for?



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This message may be freely reproduced without limit or charge only via
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protocols constitutes acceptance of this condition.
 
On Tue, 26 Sep 2017 17:49:35 -0000 (UTC), Cursitor Doom
<curd@notformail.com> wrote:

On Sun, 24 Sep 2017 14:51:11 -0700, John Larkin wrote:

This is a bootstrap current source:

https://www.dropbox.com/s/lznbrhc5gfc7xe8/Ramp.JPG?raw=1

The idea is to keep a constant voltage across the left-most 1K resistor,
so it dumps a constant 5 mA current into the 39 pF cap. That makes a
linear voltage ramp.

What sort of application did you design this for?
Click to expand...

Picosecond-resolution delay generators and time stampers. Both need
fast linear ramps.




--

John Larkin Highland Technology, Inc
picosecond timing precision measurement

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