Purpose of 0.5 ohm resistor between input and output on -ve rail of SPS?

[synoptica]

Hi all,

I'm building up a proof-of-concept circuit using several small switching buck converters like these: https://www.aliexpress.com/store/product/Li-lion-Lithium-Battery-Charger-Module-5V-32V-to-0-8V-30V-5A-LED-Driver-Step/1818738_32829346770.html

On the negative rail, there is a 0.5 ohm resistor that separates the input from the output.  Is this most likely a current shunt, or something else?

I'd like to make a simple PCB to house all the components, but this would be easier with a common negative rail.

Any input appreciated!

[brabus]

Yep it is a current shunt. The whole idea behind it is that the battery ground and the supplied circuit ground will remain separate.

Measuring the charging current with a low-side resistor is therefore easy and practical (you just measure its voltage referenced to ground).

[synoptica]

Cool.  I didn't realise that 2-sided PCBs were barely more expensive ones so shouldn't be the problem I thought it would be anyway - but good to know I had the right idea anyway - thanks!

[Zero999]

Yes, having the current sense resistor on the negative side is extremely common, because quite often op-amps and comparators work with both inputs at the negative rail, but not at the positive rail. Linked below is an LED driver kit, which uses the LM393 comparator and has the sense resistor on the negative side of the LED chain, because the LM393 won't work with its inputs at the positive rail.

https://www.velleman.eu/downloads/0/illustrated/illustrated_assembly_manual_k8071_rev1.pdf