Power supply and oscilloscope problem - diyAudio
Go Back   Home > Forums > Design & Build > Equipment & Tools

Equipment & Tools From test equipment to hand tools

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 27th November 2012, 01:20 PM   #1
diyAudio Member
 
Join Date: Jul 2012
Location: Gatineau
Default Power supply and oscilloscope problem

I have a power supply with an AC output (0-22V, 4A). I want to use this output to simulate the secondary of a power transformer, not having to worry about circuit protection for now.

I wanted to use my oscilloscope (a Tektronix analog scope) to look at the effect of load variation from my regulation circuit.

I have the following problem: when I connect the tip of the oscillloscope probe, then the common, the voltage of the power supply drops significantly (as can be seen on the power supply display) and after 5 seconds the circuit breaker of the unit goes off. I made several test, I even succeeded at blowing the 2 amp fuse of the unit.

After some tests, I also noticed that using the DC output has the same effect. I switched probes, same results. I also verified with a multimeter (battery powered) there is no voltage drop between the oscilloscope and the unit grounds.

When I use my PC oscilloscope, this does not happen.

Does anybody have an idea of what could be wrong here? I never had any problem with the scope before.
  Reply With Quote
Old 27th November 2012, 03:09 PM   #2
DUG is offline DUG  Canada
diyAudio Member
 
Join Date: Jan 2003
Location: mississauga ontario canada
Here is my guess:

The analog scope ground is connected to the AC safety ground and your power supply is the equivalent of a btl output. You are actually shorting one of the outputs to ground.

Solution(s):

If your scope has two inputs then connect the two probes to the two AC feeds and use the A-B function to view the difference.

OR build a differential to SE opamp cct that divides by 10

Always watch out for smoke.
Attached Images
File Type: jpg diff-amp.jpg (12.4 KB, 85 views)
__________________
Doug We are all learning...we can all help
"You can't stop the signal, Mal. Everything goes somewhere..."
  Reply With Quote
Old 27th November 2012, 04:09 PM   #3
diyAudio Member
 
Join Date: Jul 2012
Location: Gatineau
Do you mean that one of the AC outputs is directly connected to the ground? Could reversing the outputs fix the problem?

I could check to see which output has zero voltage with ground.

And thanks for the smoke warning
  Reply With Quote
Old 27th November 2012, 04:19 PM   #4
DUG is offline DUG  Canada
diyAudio Member
 
Join Date: Jan 2003
Location: mississauga ontario canada
maybe

just a guess...I'm not there
__________________
Doug We are all learning...we can all help
"You can't stop the signal, Mal. Everything goes somewhere..."
  Reply With Quote
Old 27th November 2012, 04:28 PM   #5
diyAudio Member
 
Join Date: Jul 2012
Location: Gatineau
Ok, I'll just try that. Thanks for the info, it never came to my mind that one of the output could be gronded.
  Reply With Quote
Old 27th November 2012, 10:43 PM   #6
DF96 is offline DF96  England
diyAudio Member
 
Join Date: May 2007
Unless told the contrary you should always assume that a power supply output, whether AC or DC, has a ground reference. In some cases this may be absent or switchable.
  Reply With Quote
Old 28th November 2012, 12:41 PM   #7
diyAudio Member
 
Join Date: Jul 2012
Location: Gatineau
Thaks guys for your replies.
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
LeCroy 9354AM oscilloscope power supply Craig405 Parts 3 19th December 2011 07:34 AM
power supply problem denmobfast Power Supplies 2 11th August 2011 12:30 PM
Power Supply problem Landoctor Chip Amps 3 8th September 2007 07:50 PM
Power supply problem argonrepublic Parts 0 23rd January 2006 05:35 AM
Power supply problem (or something) ir Chip Amps 4 23rd August 2003 08:44 AM


New To Site? Need Help?

All times are GMT. The time now is 11:41 PM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright 1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2