Author Topic: Output capacitor ripple  (Read 745 times)

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Offline Ohm_MyTopic starter

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Output capacitor ripple
« on: February 09, 2020, 02:25:14 am »
I'm a young player here, as Dave says, and fall into traps on occasion.

I've been viewing some of Dave's older videos about measuring PS ripple and noise. I have a commercial generic step-down voltage regulator (5v) and have been trying to measure the ripple with my scope just for my satisfaction.

In several other videos I see that it is "best practice", I guess, to take the measurement across the output capacitor. This is easier said than done as I am dealing with a 0805 package sized cap. I think Dave would use the "bee's dick" size standard. I'm also using the little springy thing for the ground on my probe as to avoid minimizing any stray signals.

Given the size of the capacitor and trying to position the probe correctly on the cap while making scope adjustments would make even an ordained priest swear. My question is can I make the measurement across the actual voltage output and ground solder pad locations? What is the advantage of measuring directly off the cap itself?

I appreciate any comments.
 

Online langwadt

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Re: Output capacitor ripple
« Reply #1 on: February 09, 2020, 03:46:24 am »
the output is what matters
 

Offline Cubdriver

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Re: Output capacitor ripple
« Reply #2 on: February 09, 2020, 09:08:49 am »
Yes, you can take the measurement across the output.

-Pat
If it jams, force it.  If it breaks, you needed a new one anyway...
 

Online Siwastaja

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Re: Output capacitor ripple
« Reply #3 on: February 09, 2020, 11:21:54 am »
Yes, the idea with the small spring clip thing is to avoid creating a long wire loop with the oscillosscope's ground alligator clip. Output connector itself is what matters, that's what you use anyway, so you can measure there.

The suggestion of measuring over an output capacitor makes sense when you measure a power supply of an integrated product, so that there is no output connector, the supply output being connected directly to the rest of the circuitry on PCB. Then, the output capacitor is a logical place to get the most accurate ripple figure of that power supply part.
 
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