Electronics > Beginners

Full bridge rectifier shows wrong curve on scope

<< < (7/8) > >>

Jwillis:

--- Quote from: mikerj on January 06, 2020, 10:47:46 am ---
--- Quote from: Jwillis on January 06, 2020, 01:26:26 am ---I did the same experiment and mine does the same thing. It's like the small voltage from the generator doesn't go below zero.So it's not a true AC sine wave.Simplest solution is use a low voltage transformer to test your rectifier.

--- End quote ---

That's a pretty terrible signal generator if the output can not swing below ground.  Easiest method would be to add a capacitor in series with the sig gen output to remove the DC offset.

--- End quote ---

It's an Atten ATF20B .It was all I could afford . Still not sure of many of the functions and how to use it. I'll figure it out eventually.

petert:

--- Quote from: Ysjoelfir on January 07, 2020, 02:02:49 pm ---Just a shot in the blue: To isolate the grounds of your sig gen and scope... you didn't happen to use a multi-outlet extension cord, isolated the ground of that, and plugged both devices into the same extension? That would make both devices basically isolated from mains earth/ground, but the grounds of the scope would still be connected to the ground of the signal generator.

--- End quote ---
Well, that's embarrassing. It turns out you were guessing right! I didn't think of the "multi-socket shorting independent of house earth". But I could have sworn I tried all possible combinations (isolating the scope plug, isolating the signal gen plug, isolating the plug of the multi-outlet extension cord / multi-outlet power strip), so it should have worked anyways.

Maybe I had the right isolation (by "chance"), but the signal didn't look clean enough for some other reason and that threw me off course...
But it's good I made the mistake to be aware of my misconception about the multi-outlet power strip.

Thanks! Better knowing why you are a fool than staying wrong while clueless haha (sorry about the professor).

I was a bit nervous about testing the power plugs with the multi-meter, but I suppose I could have done continuity testing between the scope bnc and signal generator bnc plugs (the outer shells), safely.

Doing that indeed confirmed the (now obvious) direct connection between the earth plugs in the multi-outlet power strip (and therefore the scope and signal gen). I somehow assumed that the connection would just be made in the house wiring, later (and therefore not occur if the main's earth is not connected). But since the multi-outlet strip gets connected to the wall outlet by a single power plug, it should have been obvious that this could not be the case (and all individual sockets earth must be joined together). Oops.

I'll post a "success scope" image and a summary of the essential points, in case someone else stumbles upon this again.

Thanks again everyone for your patience.

Mr. Scram:
I actually typed that question and solution a couple of days ago, then deleted it because you mentioned you isolated the signal generator after that. Should have gone with my hunch.

Vovk_Z:

--- Quote from: StillTrying on January 05, 2020, 11:28:16 pm ---It looks like the bottom-right diode is in the wrong row ?

--- End quote ---
+1. It's an answer.

petert:
For reference, a related two part video, which talks about full bridge rectifiers and "Oscilloscope Earthing / Isolation Challenges":

Navigation

[0] Message Index

[#] Next page

[*] Previous page

There was an error while thanking
Thanking...
Go to full version
Powered by SMFPacks Advanced Attachments Uploader Mod