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Old 19th January 2013, 12:36 AM   #11
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Quote:
Originally Posted by Fusion916 View Post
Yes there are no pulses with no load, and increase in amplitude with load.

Is there anyway to diminish or eliminate these charge pulses?
You simply have not provided enough information. How much capacitance is between the rectifier and the regulator? How much load current? Ripple voltage max and min values, before regulator? Schematic?
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Old 19th January 2013, 09:00 AM   #12
Elvee is offline Elvee  Belgium
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The pulses have a fundamental of 60Hz, which means it cannot the capacitor path causing troubles, it is either the path of one of the diodes in the bridge, or induction from the AC input wires.
Can you post a pic of your set-up?
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Old 19th January 2013, 01:19 PM   #13
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I missed the 60 hz aspect. Sorry. Now we do need a photo of the setup.
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Old 19th January 2013, 01:49 PM   #14
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Quote:
Originally Posted by Fusion916 View Post
Yes there are no pulses with no load, and increase in amplitude with load.

Is there anyway to diminish or eliminate these charge pulses?
As said before, these come from charging current through the wiring.
Did you try to change the scope ground lead connection? You may be picking it up that way, fasely thinking it is on the supply.
Connect the scope directly across the last supply cap: tip to the cap voltage, gnd lead directly at the cap neg terminal. Close as possible. Don't include any nominal ground wiring in your measurement.
If it is clean, good job.
If not, let us know.

jan
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Old 19th January 2013, 01:51 PM   #15
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Quote:
Originally Posted by Elvee View Post
The pulses have a fundamental of 60Hz, which means it cannot the capacitor path causing troubles, it is either the path of one of the diodes in the bridge, or induction from the AC input wires.
Can you post a pic of your set-up?
The charging pulses charge the cap and then return through the ground wiring. That's what we're seeing here.

jan
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Old 19th January 2013, 03:30 PM   #16
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Quote:
Originally Posted by jan.didden View Post
The charging pulses charge the cap and then return through the ground wiring. That's what we're seeing here.

jan
If it was the case, their frequency would be 120Hz, not 60.
The fact they are symetrical gives another clue: it cannot originate from one diode, because the waveform would be asymetrical.
This leaves one possibility: induction from the AC input.
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Old 19th January 2013, 03:44 PM   #17
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So does it then have to be layout and wire dress, i.e enclosed loop areas making antennas? Or could it still be scope-probe-related, only?
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Old 19th January 2013, 04:41 PM   #18
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Quote:
Originally Posted by Elvee View Post
If it was the case, their frequency would be 120Hz, not 60.
The fact they are symetrical gives another clue: it cannot originate from one diode, because the waveform would be asymetrical.
This leaves one possibility: induction from the AC input.
Of course it isn't one diode! One up, one down, per chance?
Do you realise that this is going on in ALL power supplies, and that it is a matter of where you chose your grounding, also for measurement, that determines whether you 'see' it or not?

jan
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Old 19th January 2013, 07:15 PM   #19
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Quote:
Originally Posted by jan.didden View Post
Of course it isn't one diode! One up, one down, per chance?
Do you realise that this is going on in ALL power supplies, and that it is a matter of where you chose your grounding, also for measurement, that determines whether you 'see' it or not?

jan
Do you realize that there is only one single loop in the supply circuit where this type of signal can be observed?
I let you guess which one
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Old 20th January 2013, 01:42 AM   #20
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Hmm, ok forget the regulated power supply for a second, I am getting these waveforms at the output of the rectifier diodes with just loading the output rectifiers and caps alone.

I'm starting to think perhaps the diodes I am using are the suspect?

I have 15000ufx8 at the output of the rectifier diodes and I am using 4 of these Digi-Key Part Search for full wave rectification.

With just adding a load at the rectifier output to draw about 400mA I am getting the waveforms pictured at the OP.

So lets forget stability issues or whatever. Diode, cap, or layout issue?
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