push-pull smps funny observation - Page 3 - diyAudio
Go Back   Home > Forums > Amplifiers > Power Supplies

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 7th April 2008, 10:46 PM   #21
zilog is offline zilog  Sweden
diyAudio Member
 
Join Date: Oct 2005
I have now rebuilt the smps prototype using epoxy glued EE cores from the scrapheap, the result is NO MORE FUNNY BEHAVIOUR!!! Guess simple 3F3 material should work nice since the EE cores are at least 20 years old

The waveforms now keep relation between primary and secondary voltage. Efficiency for the veroboarded version is 82% at 1.29A/93V @ 14.5V input, and 85% eff given 9.9V input. I, havent dared to take any prolonged measurements using higher power levels as mosfets are expensive, and I am a coward when sober..

The current setup:
ee1.jpg
ee2.jpg
  Reply With Quote
Old 7th April 2008, 11:37 PM   #22
diyAudio Member
 
Join Date: May 2007
Nice. Do the waveshapes look better?
Do yourself a favor and when you wind the final version get a bobbin so you can wind carefully. Come back and I'll show you how to optimize the xfmr.

So those are beer stains on your schematic?
  Reply With Quote
Old 7th April 2008, 11:42 PM   #23
zilog is offline zilog  Sweden
diyAudio Member
 
Join Date: Oct 2005
Quote:
Originally posted by switchmodepower
Nice. Do the waveshapes look better?
Do yourself a favor and when you wind the final version get a bobbin so you can wind carefully. Come back and I'll show you how to optimize the xfmr.
I will, I skipped the bobbin because it didnt fit the prototype

The waveforms have about the same amount of ringing, but the corresponcence between primary/secondary add up. I guess I have less leakage inductance as the lossless clamping-capacitors are way cooler than before.

Do you have any opinion regarding lossless clamping compared to simple RC clamps? I mean, are the lossless kinds more prone to ringing even when used on a real PCB? I have observed that if I go too low on capacitor ESR (I currently use 100uF/30mOhm electrolyte), things go really bad, high frequency ringing and very low efficiency etc, but it might just be the veroboard that cant keep up with the fast edges that X7R caps cause. I would prefer to use ceramic caps if I could as the ESR of electrolytes is an additional source of heat.
  Reply With Quote
Old 14th April 2008, 08:40 AM   #24
Eva is offline Eva  Spain
diyAudio Member
 
Eva's Avatar
 
Join Date: Oct 2003
Location: Near the sea
Send a message via MSN to Eva
This is quite a difficult project. You will have trouble balancing the magnetic flux in the main transformer, resetting the current transformers (which may result in an erratic current reading) and operating at low duty cycles where current waveform synthesizing becomes more difficult due to turn-on spikes. You may consider a plain shunt at the drains instead, and peak current control.

Layout symmetry is critical for flux balancing, including resistance and leakage inductance of transformer windings. Toroids are easier because you can do bifilar winding.
__________________
I use to feel like the small child in The Emperor's New Clothes tale
  Reply With Quote
Old 12th December 2012, 01:16 AM   #25
diyAudio Member
 
Join Date: Sep 2012
Hi, I'm working in a push-pull SMPS to convert 12V to +-24V using the SG3525 PWM controler and two IRFZ44.

The transformer is made around a scrap toroid from a old audio car amplifier with 6+6 turns in the primary and 12+12 turns around the secundary.

When there's no load in secundary, the Vgs is a perfect square wave with almost 50% of Duty Cycle.
Vgs.JPG
When I apply some load, the Vgs looks like this:
Vgswithload.JPG
BUT when I modify the Duty Cycle, the Vgs looks very bad to me. Also is visible some resonance. (in facts,I'm using a 10ohm+2.2nF snubber).
Lessthan50%.JPG
Lessthan50%2.JPG
How can I solve this problem?

Best regards,
Anthony
  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
12V push pull SMPS Archimedes Power Supplies 151 11th August 2008 10:39 AM


New To Site? Need Help?

All times are GMT. The time now is 10:20 AM.


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