Buck with simple output overload protection?

[cupoftea]

Hi,
The attached is a 24v to 15v, 3A Buck. (Jpeg and LTspice)
It has the shown output current clamp for overload
or short circuit output.
We will just use cheapo MCPXXXX 5V opamps (R2R in and out) for this purpose.
Eg MCP6002
Why do all the semico's not offer this simple , cheap solution
for this widespread requirement, of rough overcurrent
protection?

MCP6002

https://ww1.microchip.com/downloads/aemDocuments/documents/MSLD/ProductDocuments/DataSheets/MCP6001-1R-1U-2-4-1-MHz-Low-Power-Op-Amp-DS20001733L.pdf

 

[KlausST]

Hi,

why? Because:
* often there is a cycle by cycle current limit
* it is slow in reaction time (compared to cycle by cycle)
* many whouldn´t call this solution as "simple"
* it causes rather nasty hickup than true "current clamp"
.. and this may cause a high capacitive load to never power up

(I did no simulation, just what I expect by the view of the schematic)

Klaus

 

[cupoftea]

Thanks, i think i should apologise for "snowing" the issue with the schem that shows all manner of other bells and whistles...but for this qu, i am just referring to the bit in the oval dotted line. It works fine and does the job, but isnt a recomended solution anywhwere......and ayk, current monitor ic's wont work with a shorted rail...but what you see above will...because the opamp is powered by a separate 5v rail.
So why nobody does this?

 

[KlausST]

Hi,

It works fine and does the job, but isnt a recomended solution anywhwere......and ayk, current monitor ic's wont work with a shorted rail...but what you see above will...because the opamp is powered by a separate 5v rail.

There are current sense monitors with separate power supply. So, nothing special here.
As far as I can see the switcher IC provides cycle by cycle current limit.

Tbh: I don´t see the benefit.

Klaus

 

[D.A.(Tony)Stewart]

The schema uses 33 times faster slew rate which is wasted with the 10us RC filter but then the MCP is limited to 6mA vs 50 mA, which is not a huge obstacle.



Maybe it was designed by a graduate with < 5 yrs experience and not cost-reduced in China (or someone with > 30yr experience) in your examples.