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Old 7th May 2017, 12:58 AM   #1
Bibio is offline Bibio  Scotland
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Default 0V, GND schemes

i have been messing with different schemes for 0V, GND or what you would like to call it.

below is some designs i have implemented to see what others think would be the correct or not way of doing things.

first up is a full point to point: test_a
Test_a.jpg

same as test_a but with a half 0V,GND plane: test_b
Test_b.jpg

different layout of point to point: test_c
Test_c.jpg

same as test_c but with half 0V,GND plane: test_d
Test_d.jpg

full 0V,GND: test_e
Test_e.jpg

same as test_e but with 0V,GND Tbar underneath going to middle of board: test_f
Test_f.jpg

Last edited by Bibio; 7th May 2017 at 01:02 AM.
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Old 7th May 2017, 01:41 AM   #2
rayma is offline rayma  United States
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Quote:
Originally Posted by Bibio View Post
below is some designs i have implemented to see what others think would be
the correct or not way of doing things.
It will help if you post the schematic also.
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Old 7th May 2017, 01:59 PM   #3
Bibio is offline Bibio  Scotland
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here is the schematic

sch.jpg
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Old 7th May 2017, 03:28 PM   #4
rayma is offline rayma  United States
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Quote:
Originally Posted by Bibio View Post
here is the schematic.
Of these layouts, I'd probably prefer version D.
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Old 7th May 2017, 04:30 PM   #5
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I start with the current loops. These should be small, not overlap or use the same traces.
Do some sims if you are not sure what the currents look like.

Modify the schematic to fix the loops and any important connections like feedback or ground.

Now all you have to do is copy the schematic to layout.
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File Type: png sch2.png (529.0 KB, 233 views)
File Type: png sch1.png (482.7 KB, 224 views)
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Old 7th May 2017, 11:49 PM   #6
Bibio is offline Bibio  Scotland
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thanks for the comments so far :-)

@Mark, whats the reason for taking the 0V,GND from the smoothing caps instead of the rectifiers?
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Old 8th May 2017, 03:09 AM   #7
PRR is offline PRR  United States
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> whats the reason for taking the 0V,GND from the smoothing caps instead of the rectifiers?

Rectifier current is BIG spikes. Like standing near the highway when a convoy of gravel trucks is going past. Or a 100Hz jack-hammer.

Smoothing cap voltage is (should be) smoother.

Treat the rectifier lines like garbage. Don't let them bleed toward your audio. Generally they should be short, direct, and not conjoined with the "good DC".

Also plagiarize. You are not the first to design such a thing. Study/steal the work of others.
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Old 8th May 2017, 07:27 AM   #8
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Bibio, you can't think of the whole ground trace as being 0V.

My choices are based on analysis of the circuit. You have used LM317/LM337 regulators. The datasheet tells me that the maximum output current (Io) is 1.5A. I did some simulations and I see that the full wave current into C1 from the rectifiers is about 8 to 10 times higher than Io. This is the red current loop in the schematic. I need to prevent this really nasty looking current from interacting with any other parts of the circuit. To accomplish this, I run parallel traces from the AC input to the rectifier and then to the pins of C1. Even better if you can layout the return traces overlapping on the underside of the board.

The regulator adj input connects to a voltage divider (R1 and V1). Where you connect V1 becomes the reference voltage for the regulator. The regulator output will be a fixed voltage above this "0V". If the "0V" fluctuates because of current passing through it, the output will also do the same.
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Old 8th May 2017, 01:25 PM   #9
Bibio is offline Bibio  Scotland
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Quote:
Originally Posted by Mark Whitney View Post
Bibio, you can't think of the whole ground trace as being 0V.

My choices are based on analysis of the circuit. You have used LM317/LM337 regulators. The datasheet tells me that the maximum output current (Io) is 1.5A. I did some simulations and I see that the full wave current into C1 from the rectifiers is about 8 to 10 times higher than Io. This is the red current loop in the schematic. I need to prevent this really nasty looking current from interacting with any other parts of the circuit. To accomplish this, I run parallel traces from the AC input to the rectifier and then to the pins of C1. Even better if you can layout the return traces overlapping on the underside of the board.

**The regulator adj input connects to a voltage divider (R1 and V1). Where you connect V1 becomes the reference voltage for the regulator. The regulator output will be a fixed voltage above this "0V". If the "0V" fluctuates because of current passing through it, the output will also do the same.**
** your bang on the money there Mark.

yes i'm getting a small tick of voltage fluctuation but i put that down to measuring with a DMM. ''i really need a scope''

so what i'm best to do is move things around and get the input caps in the middle of the board, take the +- from the recs to the corresponding +- of the input caps and then create the 0V from there.

my reasoning was the 0V is return so no smoothing needed but i now know i'm wrong.

mad idea warning.. lol
if one were to place small lets say 0.1uF ceramic caps in place of the traces (or a break in the traces to place cap in as a bridge) from each of the rec +- before the input caps would this not smooth the pulses better?
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Old 8th May 2017, 03:36 PM   #10
Bibio is offline Bibio  Scotland
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better?

Test_h.jpg
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