Spikes in Power Supply

premkumar9 · Apr 13, 2015

Hello,
I am attaching the photograph of noise coming on my 12V supply line.How can I eliminate such noise?

Colin · Apr 13, 2015

Is the power supply connected to a project?

MikeMl · Apr 13, 2015

If it is a SMPS, live with it, or take the damn thing out and shoot it with a gun.

MCU88 · Apr 13, 2015

MikeMl said:
If it is a SMPS, live with it, or take the damn thing out and shoot it with a gun.

I have an lifetime ban on AAC for sticking up for you. I won't lose any sleep though

premkumar9 · Apr 13, 2015

MikeMl said:
If it is a SMPS, live with it, or take the damn thing out and shoot it with a gun.

Not SMPS. Series regulator supply.

premkumar9 · Apr 13, 2015

Colin said:
Is the power supply connected to a project?

Without load and with load, the change is marginal only.

audioguru · Apr 13, 2015

A linear regulated supply will make the output noise if it uses a lousy old 741 opamp in its circuit. Please post the schematic.

MikeMl · Apr 13, 2015

premkumar9 said:
Not SMPS. Series regulator supply.

Post the circuit. Likely missing capacitors or bad capacitor.

Nigel Goodwin · Apr 13, 2015

Looking at the scope settings it's only 20mV p-p anyway

premkumar9 · Apr 13, 2015

Nigel Goodwin said:
Looking at the scope settings it's only 20mV p-p anyway

Do you mean that that much level is acceptable for a series regulator? Is there no way to eliminate that?

crutschow · Apr 13, 2015

premkumar9 said:
Do you mean that that much level is acceptable for a series regulator? Is there no way to eliminate that?

Two choices are to modify/fix the circuit (if you have its schematic) or add an LC filter on the output.

Edit: That noise looks like it's coming from a switcher, not a linear supply.

MCU88 · Apr 13, 2015

premkumar9 said:
Do you mean that that much level is acceptable for a series regulator? Is there no way to eliminate that?

5mV peak-to-peak is a spec quote from many half decent lab power supplies. Trying 100nF capacitors on the rails. Try an LC line filter.

premkumar9 · Apr 13, 2015

Theoretically what could be the reason for such spikes? Where do they originate from?

Nigel Goodwin · Apr 13, 2015

premkumar9 said:
Do you mean that that much level is acceptable for a series regulator? Is there no way to eliminate that?

I would imagine it's perfectly acceptable, I'm also confused as to why you were scoping it in the first place?

MikeMl · Apr 13, 2015

What kind of regulator?

Tony Stewart · Apr 13, 2015

Voltage spikes are a simple result of Ohm's Law. Current Spike * ESR of Cap.

To improve this impedance ratio consider adding a series ferrite bead and lower ESR cap to ground measured in milliohms from spec.

But 10mV peak is fairly good. If you need much lower then specify or cascade more RLC or RC filtering, but series R affects load regulation by load impedance ratio as well.

JimB · Apr 13, 2015

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

MikeMl · Apr 13, 2015

I ask: when you recorded the noise, where was the scope probe ground clip?

audioguru · Apr 13, 2015

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.

Tony Stewart · Apr 13, 2015

I presume you can get a flat line on the closest ground pin.

If not then remove gnd clip and probe tip and use probe barrel and pin between 2 pins or wires added for low noise probing.

If still you have noise ingress, make an antenna with probe gnd grounded to tip and locate the signal or make one.

Spikes in Power Supply

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