Switch mode current sink topology?

Question

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...)

Lasse Langwadt Christensen · Accepted Answer

torsdag den 9. december 2021 kl. 12.48.49 UTC+1 skrev Ian:look at LED drivers, quite few of those that are constant current "upside down" buck

Ian <$ · Answer

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

Ian <$ · Answer

This might do, if it wasn't made from enriched unobtainium:("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.

Lasse Langwadt Christensen · Answer

torsdag den 9. december 2021 kl. 13.48.44 UTC+1 skrev Ian:

legg · Answer

On Thu, 9 Dec 2021 12:48:37 -0000 (UTC), Ianwrote: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

Don · Answer

There's some stock available at mouser:    Danke,

Klaus Kragelund · Answer

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

Ed Lee · Answer

Vin of 24V.  What is Vload?

piglet · Answer

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?

formatting link

piglet

Ed Lee · Answer

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

Lasse Langwadt Christensen · Answer

torsdag den 9. december 2021 kl. 19.39.24 UTC+1 skrev Ed Lee:it is a shunt regulator, it is just a switching rather than linear

Switch mode current sink topology?

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