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Oscilloscope help

tsteele93

tsteele93

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Ok, I got my scope and I understand the basics of what I am seeing on the screen. But I'm trying to figure out how to check the current ripple of a driver.

I tried hooking the scope across the 1ohm resistor on my test load but I wasn't seeing any ripple. Was I doing it right? Maybe I just didn't have the sensitivity set high enough?

I'm also trying to see the voltage/current at startup to see if it is spiking and I'm not sure how to trigger my TDS210 scope to show me the first few milliseconds of startup.

Any scope people out there that can give me some quick lessons?

:thanks:
 





Cyparagon

Cyparagon

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To see ripple, change the input coupling to AC and turn the sensitivity up.

To see the first few milliseconds, you need "single-shot" mode. That will be in the trigger menu.
 
tsteele93

tsteele93

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Cyparagon said:
To see ripple, change the input coupling to AC and turn the sensitivity up.

To see the first few milliseconds, you need "single-shot" mode. That will be in the trigger menu.
Click to expand...

Thanks, I knew that I needed to trigger it somehow - but being new to oscilloscopes (or at least I havent used one in 20+ years) I was thinking "external trigger" or something like that. Overlooking the obvious. I'll look at the trigger menu and adjust my voltage. :)
 
Bionic-Badger

Bionic-Badger

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If you have a digital oscilloscope, hit the "Auto" button first. Usually it gets things right, or at least gets you in range.
 
Cyparagon

Cyparagon

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Most experts will tell you the auto-button is all-but-useless except for the simplest of waveforms.

In this case, it does nothing at all for one-shot. Even for something as simple as ripple, it's still useless without first changing to AC coupling.

Trust me when I say it is in your best interest to learn how to use the scaling properly.:yh:
 
Sigurthr

Sigurthr

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What type of ripple are you probing for?

The only voltage changes across a resistor are ones which relate to current changes through the resistor. Are you trying to check for current ripple or voltage ripple? This would be good for current ripple, but you are not probing correctly for voltage ripple. You need very high sensitivity for current ripple because you'll be looking ar very small variances in voltage across one ohm.
 
Bionic-Badger

Bionic-Badger

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Well you don't rely on the auto to give you exactly what you're looking for, but rather the starting point to home in on the area of interest. I find the auto works pretty well at finding a good trigger point for a repeating signal. After that you scale down and offset until you get to the area of interest.
 
Sigurthr

Sigurthr

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@ Cyparagon, haha my bad, I missed one word there while reading. Never hurts to ask and make sure though, right?
 
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