Scope tricks for detecting rectifier/choke switching - diyAudio
Go Back   Home > Forums > Amplifiers > Tubes / Valves

Tubes / Valves All about our sweet vacuum tubes :) Threads about Musical Instrument Amps of all kinds should be in the Instruments & Amps forum

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 20th June 2008, 03:00 PM   #1
diyAudio Member
 
zigzagflux's Avatar
 
Join Date: Oct 2006
Location: Charlotte, NC
Default Scope tricks for detecting rectifier/choke switching

Was wondering if anyone has some ideas on how to best detect both rectifier switching artifacts, as well as choke ringing when commissioning your power supplies.

Was going through Morgan Jones 3rd ed, and he has some pictures of examples of choke ringing, which were helpful to an extent. It's easy to look at the transformer secodary and see if there is any ringing, which I've been successful snubbing with R-C. Detecting subtle aberrations in the choke voltage or rectifier switch-off is a lot more difficult.

Problem is I have a hard time (20Mhz analog scope) getting a good zoomed in view of the waveform to see rectifier switching, and choke ringing. I've played with the trigger level and timebase to get it as close as possible, but just can't seem to get as close as I could with my (now sold) TDS210 digital scope. When I get close enough, I lose the trigger.

I am up a creek without a paddle?
  Reply With Quote
Old 20th June 2008, 05:21 PM   #2
oshifis is offline oshifis  Hungary
diyAudio Member
 
Join Date: Mar 2004
Location: Budapest, Hungary
These signals occur in sync with the line frequency. Use line triggering, set 1 ms/div, pull the 10x button and find the ringing with the horizontal pos.
  Reply With Quote
Old 20th June 2008, 11:10 PM   #3
diyAudio Member
 
nigelwright7557's Avatar
 
Join Date: Apr 2008
Location: Carlisle, England
Default Re: Scope tricks for detecting rectifier/choke switching

Quote:
Originally posted by zigzagflux
Was wondering if anyone has some ideas on how to best detect both rectifier switching artifacts, as well as choke ringing when commissioning your power supplies.

Was going through Morgan Jones 3rd ed, and he has some pictures of examples of choke ringing, which were helpful to an extent. It's easy to look at the transformer secodary and see if there is any ringing, which I've been successful snubbing with R-C. Detecting subtle aberrations in the choke voltage or rectifier switch-off is a lot more difficult.

Problem is I have a hard time (20Mhz analog scope) getting a good zoomed in view of the waveform to see rectifier switching, and choke ringing. I've played with the trigger level and timebase to get it as close as possible, but just can't seem to get as close as I could with my (now sold) TDS210 digital scope. When I get close enough, I lose the trigger.

I am up a creek without a paddle?

My scope is very similar to yours and the switching pulses occurr every 20ms (half wave).
I killed them with a 100nf across the transformer winding.
The switching pulses could be heard through my tweeters.
__________________
PCBCAD50 software. http://www.murtonpikesystems.co.uk
  Reply With Quote
Old 21st June 2008, 02:18 AM   #4
diyAudio Member
 
zigzagflux's Avatar
 
Join Date: Oct 2006
Location: Charlotte, NC
I guess I'm not stating my goal clearly enough. Since I don't want to break any copyright laws, I won't scan and attach a copy of page 316 of Morgan Jones' 3rd edition. The bottom graph (Figure 5.16) is really what I'm trying to capture.

I want to play around with C's or RC's to get that little transient eliminated. I am reasonably skilled with my o-scope, and I understand the above suggestions, but I'm just not able to get the same type of resolution.

Maybe it's just the scope. I am considering splurging for a color 4-channel Tek, but need to wait a few months yet.

Note also his success story between Figures 5.17 and 5.20. I don't see a whole lot of difference between the voltages: it's the current that really shows the improvement. I don't see a good way to capture the current without an active probe. Would subtracting channels 1-2 across a resistor really work well enough? Got to break solder connections to get that.
  Reply With Quote
Old 21st June 2008, 02:49 AM   #5
SY is offline SY  United States
diyAudio Moderator
 
SY's Avatar
 
Join Date: Oct 2002
Location: Chicagoland
Blog Entries: 1
You've put your finger on it- he was using a current probe. You might be able to rig something up for measurement, but it won't be trivial to do it safely since both sides of a resistor would be floating on the B+ rails.
__________________
You might be screaming "No, no, no" and all they hear is "Who wants cake?" Let me tell you something: They all do. They all want cake.- Wilford Brimley
  Reply With Quote
Old 21st June 2008, 03:26 AM   #6
diyAudio Member
 
Join Date: Mar 2007
Location: Canandaigua, NY USA
It's not hard to make a usable current probe, if you can break the connection. Just a few turns of wire on a small toroid, terminate it with a low value resistor, and run the conductor to be probed through the hole.
__________________
I may be barking up the wrong tree, but at least I'm barking!
  Reply With Quote
Old 24th June 2008, 07:14 PM   #7
diyAudio Member
 
zigzagflux's Avatar
 
Join Date: Oct 2006
Location: Charlotte, NC
How about something like this?

http://www.aemc.com/products/pdf/1200.67.pdf

Only reason I picked it was the low mA measurement ability; the 2 kHz bandwidth isn't very desirable, especially since I'm looking for switching transients.

Other option would be the Fluke 80i-110s, which is good for 100 kHz, but only reads (on a practical level) to 10-50 mA. Might be a little noisy this low in its measurement range.

http://assets.fluke.com/datasheets/80i-110s-Spexs.pdf

What would be a good bandwidth to shoot for to detect and correct rectifier switching transients in the current waveforms? I can get some very high bandwidths with Tektronix probes, but those are in excess of $2000.
  Reply With Quote
Old 24th June 2008, 08:36 PM   #8
diyAudio Member
 
nigelwright7557's Avatar
 
Join Date: Apr 2008
Location: Carlisle, England
Quote:
Originally posted by zigzagflux
How about something like this?

http://www.aemc.com/products/pdf/1200.67.pdf

Only reason I picked it was the low mA measurement ability; the 2 kHz bandwidth isn't very desirable, especially since I'm looking for switching transients.

Other option would be the Fluke 80i-110s, which is good for 100 kHz, but only reads (on a practical level) to 10-50 mA. Might be a little noisy this low in its measurement range.

http://assets.fluke.com/datasheets/80i-110s-Spexs.pdf

What would be a good bandwidth to shoot for to detect and correct rectifier switching transients in the current waveforms? I can get some very high bandwidths with Tektronix probes, but those are in excess of $2000.
I have a 20MHz scope and that captures rectifier switching very well.

I built my own digital scope many years ago using a PIC with a memory chip. It could either capture 8 channels simultaneously or a couple of analog channels simultaneously.
Once it was triggered and captured the memory full of data it was uplaoded via the serial port to a PC program that displayed teh results.
It reall ywasnt tha thard.
__________________
PCBCAD50 software. http://www.murtonpikesystems.co.uk
  Reply With Quote
Old 10th July 2008, 01:53 PM   #9
diyAudio Member
 
zigzagflux's Avatar
 
Join Date: Oct 2006
Location: Charlotte, NC
Default Some progress

Okay, bought the scope and current probe, started to poke around. This is fun (and a little dangerous). Pictures attached.

I have a capture of the transient in the current. Just as MJ and SY noted, the transient is absent from the voltage, yet most noticeable on the current. I would like to eliminate this transient.

There doesn't seem to be much ringing, though that may have to do with the bandwidth of the current probe (-3dB at 100 kHz).

Slugging what remains has proven a little tricky, but I'll keep you posted as to the results.

http://www.just4sheep.com/RevRec.pdf
  Reply With Quote
Old 10th July 2008, 05:27 PM   #10
diyAudio Member
 
zigzagflux's Avatar
 
Join Date: Oct 2006
Location: Charlotte, NC
There's some nice progress. Tried out caps from 0.1 to 0.47 uF directly across the PT secondary. Values from 0.22 to 0.47 resolved the transient, but the larger the cap got, the more grunting I could hear out of the transformer.

Reduced the cap to 0.22 uF, which seemed to be the minimum needed to clear up the transient. Then, I proceeded to place resistors in series to ease up on the PT, while still clearing up the transient. 100 ohms worked, but you could still see a slight hump. 50 ohms was about the right value. Switching the snubber in and out, you can't hear any audible difference in transformer noise. Time to get some carbon comps on order.

Pictures attached showing the improvement. Just to be redundant, I would point out that at no point (snubber, no snubber) was a change in the voltage detected. It was only by watching the current that I could see any progress. Hope this results in a nice clean supply at the end of the day.

http://www.just4sheep.com/site/images/fixed.pdf
  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
How can we see, on a scope, the switching noises of an any amps output stage ? gaetan8888 Solid State 6 19th March 2009 12:17 PM
Rectifier switching / choke ringing noise zigzagflux Tubes / Valves 13 12th October 2007 04:18 PM
Great deal on Digital scope. Is this enough scope? hifimaker Pass Labs 1 1st May 2007 09:59 PM
digitally detecting zero cross on 120v Myren Solid State 0 14th January 2004 08:25 AM
Help with detecting/reducing ocilation on a gainclone PaulHilgeman Chip Amps 1 29th January 2003 07:46 AM


New To Site? Need Help?

All times are GMT. The time now is 09:13 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