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Old 2nd February 2011, 10:53 PM   #1
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Question Dual layer PCB with second layer being only ground

After my PCB design for class D failed miserably, i noticed that it would have probably worked good if the ground plane i tried to do (and ended up being nothing but trouble) would have been a dedicated ground plane. And i'm thinking to do just that - leaving the PCB design as-is, just using thicker traces and a dedicated ground plane on the top layer. The design is all thru-hole btw. I can do SMD but since i have all the parts and they have tested working on a stripboard (and not working properly on my current PCB), and just got a little PCB drill which is really handy, i thought it'd be fun to do thru-hole. Improvising vias with a piece of wire going from wherever needed to the ground plane won't be too hard, and it sure is gonna look funky with all that copper on top.

Has anyone done this type of board before and has useful insight about it? If not, i'll probably make it anyway to see what gives.
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Old 2nd February 2011, 11:22 PM   #2
savu is offline savu  Romania
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Hello,

Ground planes are mandatory for class D amps. IR has some application notes on IRS2092 describing the importance of ground planes and how they must be designed on different stages of a class D amp.
Attached you will find an example.

regards,
savu
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Last edited by savu; 2nd February 2011 at 11:25 PM.
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Old 3rd February 2011, 01:18 AM   #3
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I've done loads of boards of all kinds. A board that doesn't work as-is is unlikely to spring to life just because you pour a ground plane over one side. Sort out the return paths on the board, keeping them as short as possible, and keeping (powerful) switching signal returns away from and definitely not crossing less powerful analog returns before you pour the ground plane. Ground planes can make you lazy in your layout if you are incautious.

w
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Old 3rd February 2011, 10:07 AM   #4
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Quote:
Originally Posted by savu View Post
Ground planes are mandatory for class D amps.
My stripboard worked perfectly without one, the waveforms were very nice. And it was wired in a really really really ugly way. I think my problems come from making the traces too thin.

I'm curious about one thing - where are the output transistors in the layout you posted? I don't see them.
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Old 3rd February 2011, 10:12 AM   #5
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It is a single die dual transistor IRFI4019h

http://www.irf.com/product-info/data...4019h-117p.pdf

regards,
savu
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Old 3rd February 2011, 11:29 AM   #6
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Default always ask Where is the current flowing?

when sticking to just 2 layers you should consider added power bus bars and jumpers as options that can improve electrical performance

especially with mixed signal, switching circuits the circuit connection's parasitics and mutual coupling are major determinants of the product performance

if you're not going for at least 4-layer PCB then you need to abandon the idea that you can get all of your connections on the 2-layers at the same time as controling the coupling and parasitics
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Old 3rd February 2011, 02:23 PM   #7
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Since i'm making them myself i can only do 2 layer. Anyway, one learns by building stuff that doesn't work, so i'll give it another go, same layout mostly, only thicker traces and dedicated ground plane. We'll see how much difference it makes.
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Old 3rd February 2011, 07:29 PM   #8
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Last bit of FeCl3 + cold = it took FOREVER to etch. It's about done now, i'll be drilling it and populating it to see what happens. I'm thinking of building a heater thingy with a little motor to shake the container. This should get stuff done in a reasonable amount of time.
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Old 3rd February 2011, 07:41 PM   #9
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Quote:
Originally Posted by savu View Post
Hello,

Ground planes are mandatory for class D amps. IR has some application notes on IRS2092 describing the importance of ground planes and how they must be designed on different stages of a class D amp.

regards,
savu
My PCB worked fine without a ground plane.
I kept things as close as possible to the 2092.
Loads of careful decoupling.
Plenty of decoupling around the 12vregulator.
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Old 4th February 2011, 11:25 AM   #10
Eva is offline Eva  Spain
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A class D amplifier may appear to work fine but still suffer from self disturbance at high output currents and extreme duty cycles.

Decoupling becomes useless when only a few cm of PCB tracks are added between the capacitors and the load. A ground plane reduces PCB track inductance considerably and allows for longer PCB tracks (and makes decoupling more efficient even when distances are short). On low voltage supplies, I use local decoupling with high value (1uF) SMD capacitors to ensure that the resulting LRCRLRCR..LRCR string is reasonably damped (or resonates at frequencies too low to cause trouble, (the Cs are the SMD caps, the Ls come from PCB tracks joining them, and the R comes both from caps and PCB tracks).
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Last edited by Eva; 4th February 2011 at 11:29 AM.
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