Switch mode current sink topology?...

I

Ian

Guest
This feels like it should be simple, but my google-fu and electronics-fu are
failing today.

I need a switch-mode current /sink/, something that looks like this:

Vin o-------
|
---
| L |
| o |
| a |
| d |
---
|
v Ireg
|
-------
| |
| ??? |
-------
|
Gnd o-------

Vin is +24V, Ireg variable up to ~1A (assumed possible with somewhere below
24V across the load). Load is resistive.

For reasons, the load must be connected to Vin, not Gnd (there are several
loads, each requiring separate control, with a common +ve that\'s non-negotiable)

Any pointers to a suitable topology / part?

(I could probably work out the combination of FET, inductor and diode that works,
but worry that wiring it \"upside-down\" may cause stability problems if I just use
a standard buck controller...)

--
Ian

\"Tamahome!!!\" - \"Miaka!!!\"
 
torsdag den 9. december 2021 kl. 12.48.49 UTC+1 skrev Ian:
This feels like it should be simple, but my google-fu and electronics-fu are
failing today.

I need a switch-mode current /sink/, something that looks like this:

Vin o-------
|
---
| L |
| o |
| a |
| d |
---
|
v Ireg
|
-------
| |
| ??? |
-------
|
Gnd o-------

Vin is +24V, Ireg variable up to ~1A (assumed possible with somewhere below
24V across the load). Load is resistive.

For reasons, the load must be connected to Vin, not Gnd (there are several
loads, each requiring separate control, with a common +ve that\'s non-negotiable)

Any pointers to a suitable topology / part?

(I could probably work out the combination of FET, inductor and diode that works,
but worry that wiring it \"upside-down\" may cause stability problems if I just use
a standard buck controller...)
Click to expand...

look at LED drivers, quite few of those that are constant current \"upside down\" buck
 
On 2021-12-09, Lasse Langwadt Christensen <langwadt@fonz.dk> wrote:
torsdag den 9. december 2021 kl. 12.48.49 UTC+1 skrev Ian:

I need a switch-mode current /sink/, something that looks like this:


look at LED drivers, quite few of those that are constant current \"upside down\" buck
Click to expand...

Great call, thanks. Sounds like that could be just what I need.


--
Ian

\"Tamahome!!!\" - \"Miaka!!!\"
 
On 2021-12-09, Ian <${send-direct-email-to-news1021-at-jusme-dot-com-if-you-must}@jusme.com> wrote:
On 2021-12-09, Lasse Langwadt Christensen <langwadt@fonz.dk> wrote:
torsdag den 9. december 2021 kl. 12.48.49 UTC+1 skrev Ian:

I need a switch-mode current /sink/, something that looks like this:


look at LED drivers, quite few of those that are constant current \"upside down\" buck

Great call, thanks. Sounds like that could be just what I need.
Click to expand...

This might do, if it wasn\'t made from enriched unobtainium:

https://uk.farnell.com/microchip/hv9911ng-g/led-driver-40-to-85deg-c/dp/3580669?ost=hv9911

(\"Back order today stock arriving week commencing 03/02/23\")

But it\'s a starting point, and the datasheet has the topology I was looking for.

--
Ian

\"Tamahome!!!\" - \"Miaka!!!\"
 
torsdag den 9. december 2021 kl. 13.48.44 UTC+1 skrev Ian:
On 2021-12-09, Ian <${send-direct-email-to-news1021-at-jusme-dot-com-if-you-must}@jusme.com> wrote:
On 2021-12-09, Lasse Langwadt Christensen <lang...@fonz.dk> wrote:
torsdag den 9. december 2021 kl. 12.48.49 UTC+1 skrev Ian:

I need a switch-mode current /sink/, something that looks like this:


look at LED drivers, quite few of those that are constant current \"upside down\" buck

Great call, thanks. Sounds like that could be just what I need.

This might do, if it wasn\'t made from enriched unobtainium:

https://uk.farnell.com/microchip/hv9911ng-g/led-driver-40-to-85deg-c/dp/3580669?ost=hv9911

(\"Back order today stock arriving week commencing 03/02/23\")

But it\'s a starting point, and the datasheet has the topology I was looking for.
Click to expand...

https://www.aliexpress.com/item/32820709549.html
 
On Thu, 9 Dec 2021 12:48:37 -0000 (UTC), Ian
<${send-direct-email-to-news1021-at-jusme-dot-com-if-you-must}@jusme.com>
wrote:

On 2021-12-09, Ian <${send-direct-email-to-news1021-at-jusme-dot-com-if-you-must}@jusme.com> wrote:
On 2021-12-09, Lasse Langwadt Christensen <langwadt@fonz.dk> wrote:
torsdag den 9. december 2021 kl. 12.48.49 UTC+1 skrev Ian:

I need a switch-mode current /sink/, something that looks like this:


look at LED drivers, quite few of those that are constant current \"upside down\" buck

Great call, thanks. Sounds like that could be just what I need.


This might do, if it wasn\'t made from enriched unobtainium:

https://uk.farnell.com/microchip/hv9911ng-g/led-driver-40-to-85deg-c/dp/3580669?ost=hv9911

(\"Back order today stock arriving week commencing 03/02/23\")

But it\'s a starting point, and the datasheet has the topology I was looking for.
Click to expand...

A buck-boost is difficult to turn into a constant current regulator
without added control features (as with all flybacks) - hence the
addition of HV7800 in the led driver application diagram.

RL
 
Ian wrote:
Ian wrote:
Lasse Langwadt Christensen wrote:
Ian wrote:

I need a switch-mode current /sink/, something that looks like this:


look at LED drivers, quite few of those that are constant current \"upside down\" buck

Great call, thanks. Sounds like that could be just what I need.


This might do, if it wasn\'t made from enriched unobtainium:

https://uk.farnell.com/microchip/hv9911ng-g/led-driver-40-to-85deg-c/dp/3580669?ost=hv9911

(\"Back order today stock arriving week commencing 03/02/23\")

But it\'s a starting point, and the datasheet has the topology I was looking for.
Click to expand...

There\'s some stock available at mouser:

https://www.mouser.com/c/?q=hv9911

Danke,

--
Don, KB7RPU, https://www.qsl.net/kb7rpu
There was a young lady named Bright Whose speed was far faster than light;
She set out one day In a relative way And returned on the previous night.
 
09.12.21 12:48, Ian wrote:
This feels like it should be simple, but my google-fu and electronics-fu are
failing today.

I need a switch-mode current /sink/, something that looks like this:

Vin o-------
|
---
| L |
| o |
| a |
| d |
---
|
v Ireg
|
-------
| |
| ??? |
-------
|
Gnd o-------

Vin is +24V, Ireg variable up to ~1A (assumed possible with somewhere below
24V across the load). Load is resistive.

For reasons, the load must be connected to Vin, not Gnd (there are several
loads, each requiring separate control, with a common +ve that\'s non-negotiable)

Any pointers to a suitable topology / part?

(I could probably work out the combination of FET, inductor and diode that works,
but worry that wiring it \"upside-down\" may cause stability problems if I just use
a standard buck controller...)

A buck converter just set for lower output voltage than your high side. Synchronous half bridge. Current sense in the return path
Click to expand...

--
Klaus
 
On Thursday, December 9, 2021 at 4:48:44 AM UTC-8, Ian wrote:
On 2021-12-09, Ian <${send-direct-email-to-news1021-at-jusme-dot-com-if-you-must}@jusme.com> wrote:
On 2021-12-09, Lasse Langwadt Christensen <lang...@fonz.dk> wrote:
torsdag den 9. december 2021 kl. 12.48.49 UTC+1 skrev Ian:

I need a switch-mode current /sink/, something that looks like this:


look at LED drivers, quite few of those that are constant current \"upside down\" buck

Great call, thanks. Sounds like that could be just what I need.

This might do, if it wasn\'t made from enriched unobtainium:

https://uk.farnell.com/microchip/hv9911ng-g/led-driver-40-to-85deg-c/dp/3580669?ost=hv9911

(\"Back order today stock arriving week commencing 03/02/23\")

But it\'s a starting point, and the datasheet has the topology I was looking for.
--
Ian

\"Tamahome!!!\" - \"Miaka!!!\"
Click to expand...

Vin of 24V. What is Vload?
 
On 09/12/2021 11:48, Ian wrote:
This feels like it should be simple, but my google-fu and electronics-fu are
failing today.

I need a switch-mode current /sink/, something that looks like this:

Vin o-------
|
---
| L |
| o |
| a |
| d |
---
|
v Ireg
|
-------
| |
| ??? |
-------
|
Gnd o-------

Vin is +24V, Ireg variable up to ~1A (assumed possible with somewhere below
24V across the load). Load is resistive.

For reasons, the load must be connected to Vin, not Gnd (there are several
loads, each requiring separate control, with a common +ve that\'s non-negotiable)

Any pointers to a suitable topology / part?

(I could probably work out the combination of FET, inductor and diode that works,
but worry that wiring it \"upside-down\" may cause stability problems if I just use
a standard buck controller...)
Click to expand...

Can\'t resist a challenge! Here is an untried discrete hysteretic buck
sink. Q1-3-4 are the switcher, Iload is set by Q1vbe and R10. To get
lower load currents Q2 pulls current thru R9 to cheat the feedback. At
some values tempco of Q2 may approximately cancel tempco Q1?

www.dropbox.com/s/6ekvkgopqtrbrfv/20211209_BuckSink_SED_Ian.pdf?raw=1

piglet
 
On Thursday, December 9, 2021 at 10:34:16 AM UTC-8, erichp...@hotmail.com wrote:
On 09/12/2021 11:48, Ian wrote:
This feels like it should be simple, but my google-fu and electronics-fu are
failing today.

I need a switch-mode current /sink/, something that looks like this:

Vin o-------
|
---
| L |
| o |
| a |
| d |
---
|
v Ireg
|
-------
| |
| ??? |
-------
|
Gnd o-------

Vin is +24V, Ireg variable up to ~1A (assumed possible with somewhere below
24V across the load). Load is resistive.

For reasons, the load must be connected to Vin, not Gnd (there are several
loads, each requiring separate control, with a common +ve that\'s non-negotiable)

Any pointers to a suitable topology / part?

(I could probably work out the combination of FET, inductor and diode that works,
but worry that wiring it \"upside-down\" may cause stability problems if I just use
a standard buck controller...)

Can\'t resist a challenge! Here is an untried discrete hysteretic buck
sink. Q1-3-4 are the switcher, Iload is set by Q1vbe and R10. To get
lower load currents Q2 pulls current thru R9 to cheat the feedback. At
some values tempco of Q2 may approximately cancel tempco Q1?

www.dropbox.com/s/6ekvkgopqtrbrfv/20211209_BuckSink_SED_Ian.pdf?raw=1

piglet
Click to expand...

I would use a shunt regulator, but pending Vload answer from the OP.
 
torsdag den 9. december 2021 kl. 19.39.24 UTC+1 skrev Ed Lee:
On Thursday, December 9, 2021 at 10:34:16 AM UTC-8, erichp...@hotmail.com wrote:
On 09/12/2021 11:48, Ian wrote:
This feels like it should be simple, but my google-fu and electronics-fu are
failing today.

I need a switch-mode current /sink/, something that looks like this:

Vin o-------
|
---
| L |
| o |
| a |
| d |
---
|
v Ireg
|
-------
| |
| ??? |
-------
|
Gnd o-------

Vin is +24V, Ireg variable up to ~1A (assumed possible with somewhere below
24V across the load). Load is resistive.

For reasons, the load must be connected to Vin, not Gnd (there are several
loads, each requiring separate control, with a common +ve that\'s non-negotiable)

Any pointers to a suitable topology / part?

(I could probably work out the combination of FET, inductor and diode that works,
but worry that wiring it \"upside-down\" may cause stability problems if I just use
a standard buck controller...)

Can\'t resist a challenge! Here is an untried discrete hysteretic buck
sink. Q1-3-4 are the switcher, Iload is set by Q1vbe and R10. To get
lower load currents Q2 pulls current thru R9 to cheat the feedback. At
some values tempco of Q2 may approximately cancel tempco Q1?

www.dropbox.com/s/6ekvkgopqtrbrfv/20211209_BuckSink_SED_Ian.pdf?raw=1

piglet
I would use a shunt regulator, but pending Vload answer from the OP.
Click to expand...

it is a shunt regulator, it is just a switching rather than linear
 
On Thursday, December 9, 2021 at 10:42:57 AM UTC-8, lang...@fonz.dk wrote:
torsdag den 9. december 2021 kl. 19.39.24 UTC+1 skrev Ed Lee:
On Thursday, December 9, 2021 at 10:34:16 AM UTC-8, erichp...@hotmail.com wrote:
On 09/12/2021 11:48, Ian wrote:
This feels like it should be simple, but my google-fu and electronics-fu are
failing today.

I need a switch-mode current /sink/, something that looks like this:

Vin o-------
|
---
| L |
| o |
| a |
| d |
---
|
v Ireg
|
-------
| |
| ??? |
-------
|
Gnd o-------

Vin is +24V, Ireg variable up to ~1A (assumed possible with somewhere below
24V across the load). Load is resistive.

For reasons, the load must be connected to Vin, not Gnd (there are several
loads, each requiring separate control, with a common +ve that\'s non-negotiable)

Any pointers to a suitable topology / part?

(I could probably work out the combination of FET, inductor and diode that works,
but worry that wiring it \"upside-down\" may cause stability problems if I just use
a standard buck controller...)

Can\'t resist a challenge! Here is an untried discrete hysteretic buck
sink. Q1-3-4 are the switcher, Iload is set by Q1vbe and R10. To get
lower load currents Q2 pulls current thru R9 to cheat the feedback. At
some values tempco of Q2 may approximately cancel tempco Q1?

www.dropbox.com/s/6ekvkgopqtrbrfv/20211209_BuckSink_SED_Ian.pdf?raw=1

piglet
I would use a shunt regulator, but pending Vload answer from the OP.
it is a shunt regulator, it is just a switching rather than linear
Click to expand...

Yes, we need more info from OP. Is Vin stable? If not, what range. Is Vload resistive and/or stable. etc.
 
torsdag den 9. december 2021 kl. 19.46.57 UTC+1 skrev Ed Lee:
On Thursday, December 9, 2021 at 10:42:57 AM UTC-8, lang...@fonz.dk wrote:
torsdag den 9. december 2021 kl. 19.39.24 UTC+1 skrev Ed Lee:
On Thursday, December 9, 2021 at 10:34:16 AM UTC-8, erichp...@hotmail.com wrote:
On 09/12/2021 11:48, Ian wrote:
This feels like it should be simple, but my google-fu and electronics-fu are
failing today.

I need a switch-mode current /sink/, something that looks like this:

Vin o-------
|
---
| L |
| o |
| a |
| d |
---
|
v Ireg
|
-------
| |
| ??? |
-------
|
Gnd o-------

Vin is +24V, Ireg variable up to ~1A (assumed possible with somewhere below
24V across the load). Load is resistive.

For reasons, the load must be connected to Vin, not Gnd (there are several
loads, each requiring separate control, with a common +ve that\'s non-negotiable)

Any pointers to a suitable topology / part?

(I could probably work out the combination of FET, inductor and diode that works,
but worry that wiring it \"upside-down\" may cause stability problems if I just use
a standard buck controller...)

Can\'t resist a challenge! Here is an untried discrete hysteretic buck
sink. Q1-3-4 are the switcher, Iload is set by Q1vbe and R10. To get
lower load currents Q2 pulls current thru R9 to cheat the feedback. At
some values tempco of Q2 may approximately cancel tempco Q1?

www.dropbox.com/s/6ekvkgopqtrbrfv/20211209_BuckSink_SED_Ian.pdf?raw=1

piglet
I would use a shunt regulator, but pending Vload answer from the OP.
it is a shunt regulator, it is just a switching rather than linear
Yes, we need more info from OP. Is Vin stable? If not, what range. Is Vload resistive and/or stable. etc.\"
Click to expand...

\" Vin is +24V, Ireg variable up to ~1A (assumed possible with somewhere below 24V across the load). Load is resistive.\"
 
On 09/12/2021 18:42, Lasse Langwadt Christensen wrote:
torsdag den 9. december 2021 kl. 19.39.24 UTC+1 skrev Ed Lee:
On Thursday, December 9, 2021 at 10:34:16 AM UTC-8, erichp...@hotmail.com wrote:
On 09/12/2021 11:48, Ian wrote:
This feels like it should be simple, but my google-fu and electronics-fu are
failing today.

I need a switch-mode current /sink/, something that looks like this:

Vin o-------
|
---
| L |
| o |
| a |
| d |
---
|
v Ireg
|
-------
| |
| ??? |
-------
|
Gnd o-------

Vin is +24V, Ireg variable up to ~1A (assumed possible with somewhere below
24V across the load). Load is resistive.

For reasons, the load must be connected to Vin, not Gnd (there are several
loads, each requiring separate control, with a common +ve that\'s non-negotiable)

Any pointers to a suitable topology / part?

(I could probably work out the combination of FET, inductor and diode that works,
but worry that wiring it \"upside-down\" may cause stability problems if I just use
a standard buck controller...)

Can\'t resist a challenge! Here is an untried discrete hysteretic buck
sink. Q1-3-4 are the switcher, Iload is set by Q1vbe and R10. To get
lower load currents Q2 pulls current thru R9 to cheat the feedback. At
some values tempco of Q2 may approximately cancel tempco Q1?

www.dropbox.com/s/6ekvkgopqtrbrfv/20211209_BuckSink_SED_Ian.pdf?raw=1

piglet
I would use a shunt regulator, but pending Vload answer from the OP.

it is a shunt regulator, it is just a switching rather than linear
Click to expand...

Not shunt - it is a series pass switching, buck topology.

piglet
 
On 2021-12-09, piglet <erichpwagner@hotmail.com> wrote:
On 09/12/2021 11:48, Ian wrote:
This feels like it should be simple, but my google-fu and electronics-fu are
failing today.

I need a switch-mode current /sink/, something that looks like this:

Vin o-------
|
---
| L |
| o |
| a |
| d |
---
|
v Ireg
|
-------
| |
| ??? |
-------
|
Gnd o-------

Vin is +24V, Ireg variable up to ~1A (assumed possible with somewhere below
24V across the load). Load is resistive.

For reasons, the load must be connected to Vin, not Gnd (there are several
loads, each requiring separate control, with a common +ve that\'s non-negotiable)

Any pointers to a suitable topology / part?

(I could probably work out the combination of FET, inductor and diode that works,
but worry that wiring it \"upside-down\" may cause stability problems if I just use
a standard buck controller...)


Can\'t resist a challenge! Here is an untried discrete hysteretic buck
sink. Q1-3-4 are the switcher, Iload is set by Q1vbe and R10. To get
lower load currents Q2 pulls current thru R9 to cheat the feedback. At
some values tempco of Q2 may approximately cancel tempco Q1?

www.dropbox.com/s/6ekvkgopqtrbrfv/20211209_BuckSink_SED_Ian.pdf?raw=1

piglet
Click to expand...

Interesting, thanks for the input, appreciated!


--
Ian

\"Tamahome!!!\" - \"Miaka!!!\"
 
On 2021-12-09, Ed Lee <edward.ming.lee@gmail.com> wrote:
On Thursday, December 9, 2021 at 10:34:16 AM UTC-8, erichp...@hotmail.com wrote:
On 09/12/2021 11:48, Ian wrote:
This feels like it should be simple, but my google-fu and electronics-fu are
failing today.

I need a switch-mode current /sink/, something that looks like this:

Vin o-------
|
---
| L |
| o |
| a |
| d |
---
|
v Ireg
|
-------
| |
| ??? |
-------
|
Gnd o-------

Vin is +24V, Ireg variable up to ~1A (assumed possible with somewhere below
24V across the load). Load is resistive.

For reasons, the load must be connected to Vin, not Gnd (there are several
loads, each requiring separate control, with a common +ve that\'s non-negotiable)

Any pointers to a suitable topology / part?

(I could probably work out the combination of FET, inductor and diode that works,
but worry that wiring it \"upside-down\" may cause stability problems if I just use
a standard buck controller...)

Can\'t resist a challenge! Here is an untried discrete hysteretic buck
sink. Q1-3-4 are the switcher, Iload is set by Q1vbe and R10. To get
lower load currents Q2 pulls current thru R9 to cheat the feedback. At
some values tempco of Q2 may approximately cancel tempco Q1?

www.dropbox.com/s/6ekvkgopqtrbrfv/20211209_BuckSink_SED_Ian.pdf?raw=1

piglet

I would use a shunt regulator, but pending Vload answer from the OP.
Click to expand...

Vload will be between ~10 and ~20V for the intersting range of Ireg.

Vin isn\'t regulated.

--
Ian

\"Tamahome!!!\" - \"Miaka!!!\"
 
On 2021-12-09, Klaus Kragelund <klauskvik@hotmail.com> wrote:
09.12.21 12:48, Ian wrote:
This feels like it should be simple, but my google-fu and electronics-fu are
failing today.

I need a switch-mode current /sink/, something that looks like this:

Vin o-------
|
---
| L |
| o |
| a |
| d |
---
|
v Ireg
|
-------
| |
| ??? |
-------
|
Gnd o-------

Vin is +24V, Ireg variable up to ~1A (assumed possible with somewhere below
24V across the load). Load is resistive.

For reasons, the load must be connected to Vin, not Gnd (there are several
loads, each requiring separate control, with a common +ve that\'s non-negotiable)

Any pointers to a suitable topology / part?

(I could probably work out the combination of FET, inductor and diode that works,
but worry that wiring it \"upside-down\" may cause stability problems if I just use
a standard buck controller...)


A buck converter just set for lower output voltage than your high side. Synchronous half bridge. Current sense in the return path
Click to expand...

If that works I could use standard parts/design. Breadboard time...


--
Ian

\"Tamahome!!!\" - \"Miaka!!!\"
 
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