Strange behavior from voltage regulator

Other Hardware General Electronics
1

I have a strange little thing happening with a voltage regulator. It is a extra deluxe Chinese buck converter which I have used multiple times and it works ok for powering an Arduino.
The thing is I get some strange distortion when I measure it with the scope. Even stranger (for me at least) is that the distortion happens after I have added cables to the out ports.
When I measure at the screw terminal it looks fine:

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It when I measure at the added cables it is distorted:
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I have tried different cables but get the same result.
Very peculiar in my eyes. Some kind of resonant frequency issue perhaps? I am guessing wildly here :slight_smile:

2

Do you suppose the extra wires could act as antennas and pick up all kinds of magnetic signals from your lights, etc?

Paul

3

Especially if the wire being measured is the red one that looks like an antenna.

4

Easy enough to check if the scope is AC powered and has a line sync option.

5

That sound like a good idea to check, thanks! I’ll have a look if my scope has that.

6

Didn’t find any line sync option on the scope. Any ideas of how to mitigate an unwanted “antenna function”? :slight_smile: Would a ferrite ring help maybe?

7

Is the output cap OK? I think it has a bit bulged top. Do you have other module to compare the behavior?

8

Yep, the output cap is ok :+1:t2: If I measure at the start of the cable everything is fine but when I measure at the end of it the distortion appears. This leads me to think that the antenna idea is pretty possible.

9

Hi,
Is the gnd clip of your scope connected to the other gnd terminal where you are measuring?

Do you have a load on the regulator?
Don't forget that regulator is a SMPS so will have noise on it already.
Depending on the quality Chinesium it was made from, the performance may suffer.

scopecon1111

Tom... :smiley: :+1: :coffee: :australia:

10

Yes I can see no ground clip in the picture here, but the previous measurement with no output wires you can see the scope-probe ground clip is connected to the input ground as it needs to be.

My vote is a spurious reading due to not connecting the ground clip. This makes the entire setup into a large loop antenna.

11

Sorry, bad picture due to my inability to hold the probe and take a photo at the same time :slight_smile: The ground is connected to the black cable you see here:

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That is what is so confusing but also makes me think that the “antenna idea” might be on to something.
The only difference I make between the readings is moving from the screw terminal where the black cable is attached to the end of the cable, approximately 15cm.

12

HI,

Move the gnd to the other terminal of the pair you are measuring, not a length of wire.

Tom... :smiley: :+1: :coffee: :australia:

13

Problem kind of solved. I shortened the outgoing lead and Voila:

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14

I wouldn't call that 'connected'. It's basically floating in space, in general proximity of where it should be connected. Just lying two loose pins next to each other is NOT a good way of making a contact...

No, you put a crocodile clamp onto the GND lead allowing for a better contact and hence a better measurement...

15

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