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Measuring power supply ripple with Siglent 1202X-E
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tautech:

--- Quote from: nctnico on September 02, 2023, 07:07:21 pm ---
--- Quote from: tautech on September 02, 2023, 07:04:36 pm ---
--- Quote from: dophuc on September 02, 2023, 06:56:32 pm ---You can use an isolation transformer to power the PSU, which ensures the PSU is not grounded. And that's how I do it when testing PSU ripple/noise

--- End quote ---
Any decent PSU output should be isolated from mains Gnd.

--- End quote ---
Define isolated... You'll still have capacitance towards ground and neutral has a reference to ground as well. Together with the X and Y caps, you have all kinds of ground paths together with capacitive coupling to the surroundings.

--- End quote ---
Most of that should be on the primary side = isolated from outputs.
BillyO:
Even if some of this noise is common mode it's still noise being produced by the power supply and in many cases, like where the powered equipment if ground referenced or will be connected to ground referenced equipment, it becomes a factor.  It will even affect circuitry it is attached to through currents created by radiated energy.  I see no reason to ignore it by filtering it out.  :-//
nctnico:

--- Quote from: tautech on September 02, 2023, 07:19:55 pm ---
--- Quote from: nctnico on September 02, 2023, 07:07:21 pm ---
--- Quote from: tautech on September 02, 2023, 07:04:36 pm ---
--- Quote from: dophuc on September 02, 2023, 06:56:32 pm ---You can use an isolation transformer to power the PSU, which ensures the PSU is not grounded. And that's how I do it when testing PSU ripple/noise

--- End quote ---
Any decent PSU output should be isolated from mains Gnd.

--- End quote ---
Define isolated... You'll still have capacitance towards ground and neutral has a reference to ground as well. Together with the X and Y caps, you have all kinds of ground paths together with capacitive coupling to the surroundings.

--- End quote ---
Most of that should be on the primary side = isolated from outputs.

--- End quote ---
It isn't. Especially for switching power supplies / AC-DC converter modules. Due to parasitic capacitances in the transformer these will push HF current into the secondary side. The X and Y caps can short some of this current back to the primary side but without extra filtering (a common mode choke + some capacitors for example), this HF current will flow anywhere where there is a path of low resistance.
Fungus:

--- Quote from: MarioBros69 on August 31, 2023, 09:51:55 pm ---With 20 Mhz it removes some noise but I still can't see the ripple and the strangest thing is that with the source off it shows almost the same

With this oscilloscope and the default probe, should I be able to see it?

--- End quote ---

You won't see any ripple unless the PSU is under load. More load=more ripple.
MarioBros69:

--- Quote from: BillyO on September 02, 2023, 07:29:08 pm ---Even if some of this noise is common mode it's still noise being produced by the power supply and in many cases, like where the powered equipment if ground referenced or will be connected to ground referenced equipment, it becomes a factor.  It will even affect circuitry it is attached to through currents created by radiated energy.  I see no reason to ignore it by filtering it out.  :-//

--- End quote ---

Thank you very much for all your posts, they have helped me a lot to understand how difficult it is to measure the ripple of a power supply.

And it leads me to the next reflection, does it make sense to buy an expensive oscilloscope if you are in a noisy environment?
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