Ripple voltage measurement of SMPS

[hioyo]

As per my knowledge for ripple measurement, we need to use a tip and barrel probe because it has less loop area and the oscilloscope bandwidth
should be set to 20Mhz to avoid unwanted external noise pick-up. Please correct me if I am wrong.

I am going through the below article about ripple voltage measurement.

How to Measure Ripple and Transient in Power Supplies | CUI Inc

Two of the most common specifications when evaluating a power supply are ripple and transient. While they may seem like simple measurements, there are two important aspects that should be kept in mind to obtain the correct data. The first is the measurement technique when utilizing...

www.cui.com

In paragraph 2nd of the Proper Measurement Techniques Using an Oscilloscope Probe,it says that " The loop created by the probe's
return path causes an inductance which can amplify internal noise and pick up external noise"

I have 2 questions regarding this,

1)May I know how the loop inductance amplifies the internal noise?

2)For external noise pick up the loop acts as an antenna and picks up the noise. Please correct me If I am wrong.

 

[KlausST]

Hi,

1) I´d say "amplify" is a bit misleading. I´d say it´s rather some kind of "resonance" that can increase the signal amplitude at certain frequencies.

2) generally yes. In my eyes there may be a second loop. The Ground loop. Especially when scope inputs are connected to earth ... and usually an SMPF also includes a capacitor from Earth to secondary. This is a bigger loop, often rather low impedance for high frequencies ... and is prone to add the switching noise of the SMPS to the measurement signal.

Klaus

 

[danadakk]

Some ref material on probing :

https://download.tek.com/document/ABCs%20of%20Probes%2060W-6053-15.pdf

Regards, Dana.