ASK: Parallel Buck converter ( for 5 string leds ) with same positive output together.

Thread Starter

Hitmanvxx

Joined May 16, 2019
4
Hello everyone,
I have a question that sound stupid but im got stucked on.

In the parallel buck converter config ( imagine 3 LM2596 module ), with same DC supply. Can i stick all of positive output or must separate each pos-neg output for each converter ?.

If stick together, we will got all postive output + all anode of ledstrings. Then each neagative output of each converter will connect to each ledstring cathode. ( Total 4 wire for 3 strings . positive / neagative 1/ negative 2/ negative 3). May it work ?
 

Alec_t

Joined Sep 17, 2013
10,372
It's difficult to understand your question in the absence of a schematic, and to suggest a solution without knowledge of the converter and LED specifications.
 

Thread Starter

Hitmanvxx

Joined May 16, 2019
4
It's difficult to understand your question in the absence of a schematic, and to suggest a solution without knowledge of the converter and LED specifications.
Sorry bro, its my fault. In this case, i didnt have schematic because its just my thinking to build my own led driver with 5 led strings.

I plan to use 5 separate buck converter to drive them ( constant current mode IC) ( low side switch, so the inductor will be connect to led cathode) . Then i sudden realize that may i can use just 1 positive wire ouput for all of 5 led strings instead of 1 pair for each.
 

crutschow

Joined Mar 14, 2008
23,361
Bro, you can't put the LED strings in parallel if they are being driven by a constant-current supply.
One string will tend to hog more current than the other.
So use one current source per string.
 

ci139

Joined Jul 11, 2016
720
in principle - say if your inductor value is 33µH then you use 1:5 or 1:10 of that to filter it for parallel SMPS-es ...
... also you need to tie out (separate) the inputs by diode inductor and cap from master supply
so add 3.3 or 6.6 µH from each to master OUTP what gets a filter cap 5x to 10x of that the SMPS have
. . . at the bad day the oscillations may occur it might take extra measures to prevent such if their cause is clear

the better choice is to def 380mV higher outputs and use Schottky + inductor from each outp to the master one ← decreases the possibility of possible oscillations a lot

if your load has an extremely varying nature ↑ the above may be not applicable/stable ! ↑
 
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