strange ripple noise in DC power supplies ? - Page 2 - diyAudio
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Old 27th May 2012, 08:43 AM   #11
skibum is offline skibum  France
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Join Date: Dec 2009
Quote:
Originally Posted by AndrewT View Post
The charging circuit, from transformer through the rectifier to the smoothing caps, must not share any common wire or wiring with the load circuit that receives the smoothed DC supply.
These two separate circuits must be grounded at ONE POINT.
That fixed it! I was taking my "ground" to different components from different locations off of the ground wire. I changed it so all the grounds come from a central point (star grounding?) and problem is now gone.

OK, I have a question and I bet it is a can of worms... (ask 10 people and 5 will answer one way, 3 the other and 2 something totally different). If I lay this out on a board am I better to:

1) Have a ground plane

2) Set up a "star" grounding layout?

I realize one way done properly will always be better than the other done improperly, but for my setup of two independent single tap transformers with 2 independent DC power supplies sharing the same ground which way would you lean?


Thanks!
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Old 27th May 2012, 09:51 AM   #12
Pafi is offline Pafi  Hungary
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If there were only 2 power supplies in your circuit, then grounding was not an issue at all. But there must be some other circuits which can be disturbed by gnd noise. You should design the whole system, not the PSU alone!

1) or 2) ? These general rules/strategies are misleading. A designer always have to know that there are noise sources, and transfer paths to the useful signal (s). You have to analise and eliminate/reduce them below the acceptable level. First you have to identify the noise sources (in this case one of them is the charging current of the puffer capacitor) and entry points to the signal path (which is unknown by us, since we dont know what do you want to supply).

1) The star point grounding can be almost perfect or absolutely terrible depending on the details.

2) The grounding plane ensures some degree of noiselessness without considering any details, but to make it perfect attention is needed also.

3) You missed the chain style grounding. If the signal path is straightforward, and you can apply separate PSUs to every stage, then you have the chance to avoid every ground loop problems entirely! Be careful, the whole system have to be free from ground loops!

4) You can forget GND noise problems if you use differential signal paths.
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Old 27th May 2012, 01:29 PM   #13
DF96 is online now DF96  England
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Don't follow a pattern. Instead, think about where the currents go. Treat each ground connection as a resistor, however short and thick the connection. Keep circulating currents circulating well away from the ground point or busbar, then run a ground conductor from a quiet point (such as a capacitor terminal) to the ground.
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