Go Back   Home > Forums > Design & Build > Parts

Parts Where to get, and how to make the best bits. PCB's, caps, transformers, etc.

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 22nd September 2002, 09:50 PM   #1
diyAudio Member
 
Join Date: Sep 2002
Location: Nebraska
Default SMPS Elliott Project 89--Winding Xformers

My question is this: when winding the center tapped primary on the transformer, and say I was going to have 8 total turns, would I wind 4 all the way around the torroid and another 4 all the way around, or just 8 all the way around once?

The link to the page is:
http://sound.westhost.com/project89.htm

But it doesnt answer this particular question and I can see his example transformer well enough ...perhaps someone else has some coil winding experience.

Thanks,

A.H.
  Reply With Quote
Old 22nd September 2002, 10:05 PM   #2
diyAudio Member
 
Holger Barske's Avatar
 
Join Date: Jan 2001
Location: Ruhrgebiet
Should not make too much difference.
But, as you want to keep the wire as short as possible on that big currents, I woul suggest to put all 8 windings as close as possible, means: 4 windings, center tap, next four windings.
You don't need to cover the whole core with wire.
  Reply With Quote
Old 23rd September 2002, 12:38 PM   #3
diyAudio Member
 
Circlotron's Avatar
 
Join Date: Jun 2002
Location: Melbourne, Australia
Sorry to be contradictory HBarske, but it would in fact be better if the two halves of the primary were wound bifilar, i.e. the two wires wound side by side at the same time. This will reduce the drain voltage overshoot as each fet turns off because the opposite winding will clamp the voltage more effectively. Spreading the winding around the full circumference of the core will be beneficial for cooling if nothing else. There is also something to do with proximity effect where the magnetic field pushes the current over to one side of the wire; this is minimised by spreading out the turns. Don't really understand that part but I have heard others talk about it.

Where the page says "then the secondary over it in the *opposite* direction, to maximise inter-winding coupling.", this is pure nonsense. Wind it the same direction as the primary.

That example of a commercially made transformer in the picture - wow! talk about rough! Someone should be hanging their head in shame!

GP.
  Reply With Quote
Old 23rd September 2002, 01:43 PM   #4
diyAudio Member
 
Peter Daniel's Avatar
 
Join Date: Jul 2002
Location: Toronto, Canada
Send a message via AIM to Peter Daniel
According to the article, the primaries should be wired like this, using whole lenght of the core.
Attached Images
File Type: jpg to1.jpg (5.5 KB, 410 views)
__________________
www.audiosector.com
“Do something really well. See how much time it takes. It might be a product, a work of art, who knows? Then give it away cheaply, just because you feel that it should not cost so much, even if it took a lot of time and expensive materials to make it.” - JC
  Reply With Quote
Old 23rd September 2002, 02:01 PM   #5
diyAudio Member
 
jackinnj's Avatar
 
Join Date: Apr 2002
Location: Llanddewi Brefi, NJ
Default remember to note the polarity of the windings

1) the SG3525 isn't exactly the lowest noise PWM switcher on the planet. I suppose that this doesn't matter since the amp is used in an automobile with high ambient noise.

2) you can simplify the design by driving the switching transistors with a diode, even an 1n4148, and tie the gates to ground through a 220 ohm resistor -- this will make sure they are truly off when they are supposed to be off.

3) the SG3525 has the option of "soft-start". I don't know why the author didn't use it.

4) it's a good idea to use a variable resistor, or a resistor pair to set Rt -- I have found that the switching frequency can be audible with the SG3525 -- more a problem in robotics than in this application, but good to know.

5) If you are using a "no-name" torroid, before you wind the transformer, you should "characterize" the torroidal core. You do this with an LCR meter -- find the inductance with 10 turns of wire (you can use #28 wire!). The inductance index is then:<p>
A(L) = 10,000 * L (uH) / N^2
The required impedance of the inductor is inversely related to frequency and load. Characterizing the torroid will at the minimum, prevent you from using a completely inappropriate core.

6) 3300uF is bit "overkill" for a power supply operating at 35kHz when you consider that you have millivolts of swithing noise and ambient noise -- make sure, however, to use low ESR caps designed for switching supplies --

7) I suppose that the resistor from VRef to the non-inverting input is some form of current limitation. Usually a resistive divider is used to adjust the non-inverting input.

9) Some RFI protection (in the name of some ferrites or a choke capable of handling 3 Amps) on the output would be nice. The switching transients merely glance at the filter capacitors, wave adieu and say "a bientot" before they are on their merry way down to the amplifier. Oh, and while you're at it, put some ferrites on the battery line also -- switching transients will go anywhichway.

8) mount the entire power supply in a salvaged PC power supply case. No kidding. Things can and do go wrong with switching power supplies (although I don't know if it exists, there should an addendum to Murphy's law which would describe the rate of catastrophic failure as exponentially related to the load current.)
  Reply With Quote
Old 23rd September 2002, 02:02 PM   #6
diyAudio Member
 
Holger Barske's Avatar
 
Join Date: Jan 2001
Location: Ruhrgebiet
Ok, guys. I'm convinced.
---
Holger
  Reply With Quote
Old 23rd September 2002, 02:15 PM   #7
diyAudio Member
 
jackinnj's Avatar
 
Join Date: Apr 2002
Location: Llanddewi Brefi, NJ
Default advice from the folks at Linear Tech

From Application Note 73:
Attached Images
File Type: gif switch.gif (91.4 KB, 397 views)
  Reply With Quote
Old 24th September 2002, 06:42 AM   #8
diyAudio Member
 
Join Date: Mar 2002
Location: Torrance, CA
That's pretty funny!
__________________
== John ==
  Reply With Quote
Old 15th November 2013, 06:04 PM   #9
diyAudio Member
 
Join Date: Oct 2011
Quote:
Originally Posted by ghettorigged View Post
My question is this: when winding the center tapped primary on the transformer, and say I was going to have 8 total turns, would I wind 4 all the way around the torroid and another 4 all the way around, or just 8 all the way around once?

The link to the page is:
Switchmode Power Supply For Car Audio

But it doesnt answer this particular question and I can see his example transformer well enough ...perhaps someone else has some coil winding experience.

Thanks,

A.H.
Do it this way, wind 4 turns on half of the core, centre tap, and wind the other 4 turns on the remaining half. These will be your primary turns. Wind the secondaries on top of the primary turns in a similar fashion.
  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
Quick question about winding your own toroids for SMPS MikeHunt79 Power Supplies 1 15th January 2008 07:01 AM
Toroidal core for Elliott Project 89 Flemming J P Car Audio 7 7th June 2007 05:43 PM
smps transformer winding zilog Power Supplies 3 22nd December 2005 08:21 AM
SMPS xformers Mr Teal Parts 0 8th November 2004 04:47 AM
DAC, project 85 of Rod Elliott tschrama Digital Source 22 25th January 2002 12:27 AM


New To Site? Need Help?

All times are GMT. The time now is 10:39 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