Author Topic: My Very first fully custom PCB looking for Schematic Input and maybe any errors.  (Read 4779 times)

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Offline Buriedcode

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Again it is hard to say what is going on with a schematic of your entire power supply, and the part numbers of all the parts (I meant the inductor, the diode and the caps, although the caps just need a capacitance and voltage rating).  TI's webench is very handy, but layout and part selection can still make or break a circuit.   So, a photo of the board, and a schematic of what you've got - not what you intend to have.

As for filtering, I would first get the switching power supply working, so it can provide adequate current and regulation for your given input voltage range.  Then you can play about with the output cap value, or possibly add a post regulator LC filter if needed.
 

Offline SirAlucardTopic starter

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Again it is hard to say what is going on with a schematic of your entire power supply, and the part numbers of all the parts (I meant the inductor, the diode and the caps, although the caps just need a capacitance and voltage rating).  TI's webench is very handy, but layout and part selection can still make or break a circuit.   So, a photo of the board, and a schematic of what you've got - not what you intend to have.

As for filtering, I would first get the switching power supply working, so it can provide adequate current and regulation for your given input voltage range.  Then you can play about with the output cap value, or possibly add a post regulator LC filter if needed.

I hadn't shared a photo of the board yet cause I was in the mists of redoing it. However here it is.

* swbot.pdf (159.86 kB - downloaded 102 times.)
* swtop.pdf (470.17 kB - downloaded 71 times.)

Also for the Schematic, it is the same as a couple posts back, however for Q1 and Q2 They've been replaced with a MMBT4401, however now I think I'm second guessing it.

* schematic5262020.pdf (89.67 kB - downloaded 79 times.)
« Last Edit: May 29, 2020, 04:25:55 pm by SirAlucard »
 

Offline NivagSwerdna

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Within the power supply sections it might be worth using copper fill regions for the high current paths.  You can normally do this by overlaying the region on top of the routed tracks.  For example on the botton right hand side a filled region to pin 8 and the C and L would be easy.  You might find this affects your rotation too... e.g. maybe pin 8 is too far away in its current orientation.
I don't use those parts.... but be careful with L and C selection.... if necessary just follow the datasheet.
 

Offline sokoloff

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But I am still curious about the parts used.  There are many inductors about, ranging from ratings from mA to tens of Amps, form nano henrys right up to 500mH, something I used to regularly see in the beginners forum is people using small axial "filter" inductors for power switchers - ones that look like resistors.  This is why I asked for a photo of the whole test set up, the components, and/or the part numbers used.
Atm my final parts haven't been chosen, I'm looking at a 68uH inductors to go onto the 12v and 5v rails, I'm mostly following TI's power supply designer WEBENCH atm, it suggests 68uF Electrolytic on the output but is that really enough? I've already got 220uF that I was going to reuse. Also What's the best way to figure out filtering? As I'm noticing my 12v rail is being effected by the 5v switching. That also may be because I'm not using the correct inductors atm.
No one’s worried about the level of polish or the final parts selection.
You’ve got a lot of people willing to help you get to the second revision of your board.
You made a first version and assembled it. Share photos of that with pride and you’ll get much better level of help from people who can look at what’s actually going on rather than make guesses semi-blindly.

Pics, please. It’ll make things go so much more smoothly and efficiently for those trying to help and for you to get better advice for your second board spin.
 

Offline NivagSwerdna

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No one’s worried about the level of polish or the final parts selection.
Hm... reusing a 220uF electrolytic that was lying around might not work.... depends on ESR.... check the specs.  In my experience TI Webbench doesn't always get it right... or that's my theory anyway. (i.e. better to have a bit more headroom L wise)
 

Offline SirAlucardTopic starter

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No one’s worried about the level of polish or the final parts selection.
Hm... reusing a 220uF electrolytic that was lying around might not work.... depends on ESR.... check the specs.  In my experience TI Webbench doesn't always get it right... or that's my theory anyway. (i.e. better to have a bit more headroom L wise)

It wasn't a 220 that was laying around, it was the 220 that was purchased for the v1 of the board, that's what I meant by reusing it.
 

Offline n1ist

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Switchers are very sensitive to layout, especially if you want to avoid EMI issues.  If you look at the data sheet, they have a suggested layout.  Note the high-current paths are short and done with pours. 
 


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