Good pcb design

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Hi

How about if I put powerplane for GND.
Will this work any better??
Yellow is tracks from before.

D.jpg
 
Hi Luka!

My opinion about your design:
The power plane is for high-frequency currents. Because current can change fastest on lowest impedance, the high frequency currents are flowing in the smallest loops. If there is a ground plane, all ground looped currents are flowing below the tracks in the ground plane. I think in your design you should to minimize the tracks and loops where the current should to change rapidly. Otherwise the current can't change fast enough (MOSFET drivers), and they accumulate too much energy. The MOSFETs can be used in avalanche for snubbing that energy. But if I were you, I place the two FETs beside to each other, or turn them opposite.
This circuit must work with light load, or without load. You will not see any problem on the scope if the gate driving circuitry will be correct. But when the MOSFETs' body diode will be reverse-recovered by the another FET, the supply will be loaded with dirac-like current spikes. These spikes may induce some volts of ringing on the C placed next to Q1 and the L of the supply cable. You should also consider the max. dV/dt of C for this purpose. And for feeding the square-like current of the loaded Half-Bridge, there should be placed some electrolytic capacitors for the ripple current. These snubber and buffer capacitors should be placed close to the Half-Bridge's suplly. Opposite placing of the MOSFETs is a good support for this. And this placing has the shortest connection for S(Q1) and D(Q2).

Good Luck! :cool:
 
Hi

It is more and more clear to me that there is no quick fix, ah well someday I have to try to make good PCB, with smd that is.

I will leave mosfets as they are, just more close each other. Using smd's will force me/ will force myself to use 2nd layer as ground. Most of the elements will be smd (IR woun't be), that will be on top layer, so I will have bottom as ground, splitted into two. These two will be connected together at speaker/supply connector which is bellow inductor and output cap, next to S of fet. This will seperate digital(power) GND from signal.

What do you think guys, if this planes are 0.5mm from each other and connected with 2mm wide line? Will this be ok, or... well you tell me, I don't really know how to do that, just by looking pictures from others.
 
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Gyula said:
If there is a ground plane, all ground looped currents are flowing below the tracks in the ground plane.

That is exactly why it usually a bad idea to use multiple split ground planes or run lots of traces through the ground plane.

luka said:
It is more and more clear to me that there is no quick fix, ah well someday I have to try to make good PCB, with smd that is.

What do you think guys, if this planes are 0.5mm from each other and connected with 2mm wide line? Will this be ok, or... well you tell me, I don't really know how to do that, just by looking pictures from others.

You're right that there's no quick fix. A redesign would definitely be in order, when you get the time :)

I would suggest using one soild ground plane if possible. If you keep the power grounds close together and the signal grounds away from the high current paths they shouldn't interfere too much. Again, it's hard to say because it really is layout dependent.
 
Hi

Probably some time will go by when I'll have PCB ready to show.
Mean while, I have found this

http://www.diyaudio.com/forums/showthread.php?s=&threadid=58476&perpage=10&pagenumber=11



analogspiceman said:
A couple more noise reduction tips:

A switching transistor's ungrounded heatsink can radiate e-field noise into the small signal circuitry. Ground the heatsink to the output power ground, i.e. the center point between the output stage bypass capacitors (the 470uF electrolytics). This will mend your heatsink's EMI spraying ways and convert it into an EMI sink as well (Faraday shield).

By the way, the ground for all of the small signal audio circuitry should not be connected to this center point at all. That ground should only be connected to the power circuitry at one point, the final output filter capacitor ground (C25, 470nF, in your case).

The output power ground (capacitor center point) should also be the point where you tie in the grounds from your output stage power supplies. The loop area formed between the totem pole mosfets and their bypass capacitor should be squeezed down to the absolute minimum. Place these components as close together as possible, but as or more importantly, run the traces that form this loop right next to or on top of each other so that enclosed loop area is as close to zero as possible. This means that these trace will probably not run in the shortest straight lines between points.

click here for more tips about working with driver ICs.

Regards -- analogspiceman
 
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luka said:
If I use 0805 for driver to gates, will they be ok? Also what about smd cap size, which one to use? Or will I have to buy them before to see size?

And what smd transistors to use for 2n5401 and 2n3904, or they are available in smd package?

The package size of the gate resistors depends on a few things: the required power dissipation, the space available, and how comfortable you are soldering SMDs ;)

A 1206 size package for a resistor should be fine in terms of dissipation and it will allow you to comfortably run a trace between its pads. The 1206 package is very easy to handle and solder by hand. The 0805 package is also easy to handle and solder by hand once you get used to working with SMDs. Package sizes for caps depends on the capacitance and voltage ratings. Either package will be fine.

The 3904 is available in a SOT23 package. It goes by MMBT3904 rather than 2N3904.
 
BWRX said:


The package size of the gate resistors depends on a few things: the required power dissipation, the space available, and how comfortable you are soldering SMDs ;)

A 1206 size package for a resistor should be fine in terms of dissipation and it will allow you to comfortably run a trace between its pads. The 1206 package is very easy to handle and solder by hand. The 0805 package is also easy to handle and solder by hand once you get used to working with SMDs. Package sizes for caps depends on the capacitance and voltage ratings. Either package will be fine.

The 3904 is available in a SOT23 package. It goes by MMBT3904 rather than 2N3904.

yep

:) :) :) :)
 
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