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Topic: LM2576-5.0 problem ... (Read 8 times) previous topic - next topic


While more copper is good, the layout is still poor.
That schematic is telling you to implement a star ground with pin 3, the anode of D1 and the negative leads of Cin and Cout.
You have them in a chained arrangement. What you need to do is arrange these components to join together at only one point to prevent any inductance in the ground return path.
That is the first step towards getting it right.


May 03, 2011, 10:56 am Last Edit: May 03, 2011, 12:04 pm by WanaGo Reason: 1
While not exactly the same chip, it basically is - I am using the LM2596

I have created a test board, which I ended up routing wrong, actually had a component in the wrong spot, however have reworked the circuit as a trial and got it working well, so have adjusted the design and will get the next revision printed.

Here is the Top and Bottom prints of my circuit. I have had very little input from other people, so any critique is welcome before I get it printed.
NOTE: The company I get my boards printed cannot print Plated Through Holes (ie Via's), so I have to manually do them with a resistor leg soldered each side. It is a downside, however at around $10 - $15 for a single ($5 - $10 US) 80mm x 80mm board, its perfect for prototyping.

Anyway, this may be of some use to you.
Red is top layer, Blue is bottom layer. Done in Altium Designer.

As mentioned, feel free to critique. I have never built a switcher before, other than the 1st attempt.


May 03, 2011, 11:17 am Last Edit: May 03, 2011, 12:09 pm by simkard Reason: 1
Thanks WanaGo !

So i made some changes reflecting what you have told to me.
By the way, i wanted to thank you for your help because i couldn't determine that the ground should be done as a star.

I think you will be proud of me now  :smiley-mr-green: ... errr ... i hope !  :smiley-eek-blue:

Have a look :

EDIT (2 things) :
1st : Fritzing is alcoolic so do not bother why the holes are quite full of copper
2nd : i had to let space between the diode and the LM2576 because i have to put a heat sink so i evaluated the good space as is on this PCB.

I finally found how to increase track width (by asking on Fritzing forum ...) so now the tracks around the LM2576 and the +5V / +12V / GND of my board are 80 mils !!! yeehaaaa !


I think you will be proud of me now

Yes I am proud of your attitude to learning, keep it up.

Unfortunately I don't think you have got the idea about star grounding. The arrangement is that all the grounds go to the one point. So let's say the star point is the ground on D1. The LM2596 should go straight to D1 no where else. Likewise the track from C2 should go directly to D1, no where else. The track from C2 should go to D1, no where else. So if you follow the paths that the ground current can take it goes from each component to that point, no where else. Any current path to the star point never has the current from two or more components flowing through it.
The star point can be anywhere, not just D1, maybe best on the LM2596 or some other point not on a component, but the principle is the same, short tracks, wide tracks, star ground.

OK on the gap between the LM2596 and the other components being due to the heatsink. Can you not turn the heatsink over and reduce that distance? It really will make it more stable. Physics is a cruel master. :)


May 03, 2011, 06:31 pm Last Edit: May 03, 2011, 06:40 pm by simkard Reason: 1
Me again !!!!

And now teacher ? am i in the right direction ? is it good this time.
I understood the STAR POINT way of thinking.
I think this time is the good one  :smiley-mr-green:

Please tell if i've done great job  ]:D :

EDIT : I modified the location of the LM2576 in order to place the heat sink in the right place. Now it will fit perfectly.
So if you confirm that this will work, YEEEHAA !! let's make the PCB now !

Thanks !

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