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Spikes in Power Supply

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I never measured my 0 - 35 Volt, 0 - 8 Amps, linear Power supply Before, So I just did.
I am Impressed:
Less than 1 mV with no load.
Same with a car tail light bulb as a load. (about 2.5 Amp load)

It is a Home Made Supply, Built it over 25 Years Ago.
MC1466L Regulator Technology
 
18 replies and we still do not have a schematic. I think the power supply was purchased and is either welded together or it is cast in concrete so it cannot be opened to see what is inside.
Started getting replies yesterday evening. Power supply is at my office. Can send circuit today only. Yes , it is a power supply board purchased from outside.
 
First, find where the noise is coming from.
My first thought is that it does not come from a linear regulator.
Could be coming down the mains wiring from who knows what, who knows where.

It look like some of the crud which comes out of the control system for my CNC milling machine.

JimB
Useful information. I will do some more checking keeping this in mind and revert.
 
I have no doubt you will see a 10 x reduction on noise with the method I outlined.
You can get maybe a 100x improvement on noise by using a good cap near supply in series with 50 Ohm coax soldered within 1cm of source and a 50 Ohm terminator at scope in x1 mode.

You can use a shorted loop as an antenna to find the noise source, usually switching power supply or a brush type motor. etc, either conducted via ground or radiated..
 
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I am attaching noise across a 12V battery, across 1ft wire, when holding the same wire with hand, when probe pin shorted with probe ground.
From this can we conclude that this is a radiated noise? How can it be eliminated/ reduced?
 

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It appears to be noise measurement error from radiated noise. THe probe loop must be very small and if you want to try good coax shorted to ground with 50 Ohm termination, then you can improve measurement methods as I outlined before..
 
It appears to be noise measurement error from radiated noise. THe probe loop must be very small and if you want to try good coax shorted to ground with 50 Ohm termination, then you can improve measurement methods as I outlined before..
Ok. There may be errors in the noise level measured. What could be the source for such radiated noise. What could be the implication of such noise pick ups.
 
As I said before, impossible to tell your situation. But using a shorted ground clip to probe tip use this loop as antenna to locate source. if you can
Such as SMPS, motor brush arc etc. Conducted noise on cables becomes a radiating noise source like antenna.
 
As I said before, impossible to tell your situation. But using a shorted ground clip to probe tip use this loop as antenna to locate source. if you can
Such as SMPS, motor brush arc etc. Conducted noise on cables becomes a radiating noise source like antenna.
Ok. Thank you for the guidance. I will try to do that.
 
Personally I believe you're wasting your time, that kind of noise it perfectly acceptable.

Although, generally you should measure using 20Mhz bandwidth limitting on your scope. Also, with noise that low, your test setup needs to be spot on, so I'm not even convinced the noise is even there in the first place!
 
It is a common mode noise error showing up on a differential measurement from poor ground loop in probe.

With clip removed and no ground wire just using the pin and barrel of the probe, right at the PSU output terminals or test pins with a small cap., you should see acceptable quiet results.

Sometimes two probes are needed when the common mode noise is very high, or high quality coax with 50 Ohm load. ( AC coupled). Other times the twin probe method needs both probe cables twisted together for very fast rise time noise pulses.

Every Engineer should learn how to make textbook-like good-looking waveforms of low impedance signals with a scope.
 
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