transformer winding question - 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 20th January 2006, 10:56 AM   #1
diyAudio Member
 
gearheadgene's Avatar
 
Join Date: Jul 2005
Location: CT
Default transformer winding question

I'm working on a smps design but have some questions

The supply needs to generate:
+40V
-40V
+5V
+3.3V
low voltage supply (5V) for PWM

The +/-40V will supply an audio amp with around 450Watts, the rest of the power is shared by the +5 and 3.3V windings.

Supply is going to be full-bridge type, zero volt switching.

Question 1:
I think it's more important to regulate the +/-40 supply. There's going to be 2 windings for this. Does it make sense to have the feedback circuit to the pwm measure across the +/-40, checking for 80V or is it better to measure just + or - 40V to ground?

Question 2:
Cross regulation isn't very clear to me. But, does it make sense to have 2 smps: one for the +/-40V and another for the low voltage stuff?

Question 3:
Assuming I wind all the voltages on a single core. I think that it would go something like (from inner to outer):
primary, pwm 5V, +40, -40, +5, +3.3
How hard is it to fit, and what are the consequences of this many windings on a single core?

Question 4:
I'm pretty sure a bobbin will be used for this. Also, in order to meet safety requirments, either safety margins need to be used with another barrier from primary to secondary, or I could use triple insulated wire. Any thoughts there? Is that stuff expensive? Easier to work with than margins? I think only one layer needs to be wound with it, yes? Although if the primary is triple insulated, I suppose the 5V pwm voltage winding needs to be also (given the stack I listed) so that all the remaining windings can be normal magnet wire. Is that correct?
  Reply With Quote
Old 20th January 2006, 11:21 AM   #2
diyAudio Member
 
Ouroboros's Avatar
 
Join Date: Dec 2003
Location: Nottingham UK
For a 450W supply, one solution is to produce +/-40V from a two-transistor forward converter, with the low-voltage supplies produced from dc-dc buck regulators off the 40V output.

The dynamic loading on the +/- 40V outputs will see a large current swing (unless you're feeding a class-A amp) so it's not wise to try to get all the outputs from the main stage: you'll find serious cross-regulation problems.
  Reply With Quote
Old 20th January 2006, 12:46 PM   #3
diyAudio Member
 
jackinnj's Avatar
 
Join Date: Apr 2002
Location: Llanddewi Brefi, NJ
First, you can use a sitching chip/regulator capable of bipolar measurement -- the LT1683 -- but it is SSOP20 and about $9.00 at Digikey. i think it is rather overkill.

you must use mylar tape between the windings --

you could use push-pull -- the transformer doesn't retain energy --you want it passing the energy through to the load -- take a look at this PDF by National Semiconductor -- they walk you through the mathematics of the transformer:
http://www.national.com/appinfo/powe...001i-new-4.pdf

i've linked a lot of SMPS articles on my this page of my website:
http://www.tech-diy.com/smps.htm
  Reply With Quote
Old 20th January 2006, 02:22 PM   #4
diyAudio Member
 
gearheadgene's Avatar
 
Join Date: Jul 2005
Location: CT
Quote:
Originally posted by Ouroboros
For a 450W supply, one solution is to produce +/-40V from a two-transistor forward converter, with the low-voltage supplies produced from dc-dc buck regulators off the 40V output.

The dynamic loading on the +/- 40V outputs will see a large current swing (unless you're feeding a class-A amp) so it's not wise to try to get all the outputs from the main stage: you'll find serious cross-regulation problems.

Yeah, I agree with you - cross reg stuff - which partly prompted this thread. BTW, amplifier is Class-D type, 6 or possibly eight channels worth.

This option of another follow on stage came to mind a while ago, but I completely forgot about it - until now. I suppose I could live with the efficiency loss, but need to think about that. All the digital logic will be running, let's say, around 30 watts - the total isn't yet clear, but am working to nail that down. My supply is going to be PFC'd, so efficiency total may not be all that wonderful -> .9 * .9 = 0.81. Then add another switcher for the low voltage stuff, another factor of 0.9, maybe 72% total efficiency there - hmm. At least the heat gets distributed around
  Reply With Quote
Old 20th January 2006, 03:12 PM   #5
diyAudio Member
 
Ouroboros's Avatar
 
Join Date: Dec 2003
Location: Nottingham UK
It's a similar situation to one I have here at work on a 250W PSU I designed for a large voice alarm / fire alarm panel. That has an L4981 PFC stage, followed by the 2-transistor forward convertor isolating stge producing the main 46V dc output (to some Class-D audio amps), with 24V dc and 3.3V dc buck regulators to feed the electronics of the system, together with two separate switch-mode battery chargers feeding a pair of 24V 26A-hr backup battery packs, all supplied by dc-dc buck stages from the 46V.

You'll find that the PFC stage will give very high efficiency. It provides me with 400V dc from the normal UK 230V mains. Fortunately I don't have to be able to work from 115V mains. It will, but the efficiency drops when the PFC has to provide 400V dc from 115V supplies.

ST Micro provide ggod app notes for the L4981 chip.
  Reply With Quote
Old 20th January 2006, 06:32 PM   #6
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
First, I would probably use a small flyback for the +5V and +3.3V outputs, probably a self-oscillating one (simple, reliable and inherently overload-proof), since these small windings would cause a lot of trouble if they had to be placed in the main transformer and output inductor. Also, even when putting your best efforts on it, cross-regulation wouldn't probably be good enough to avoid undervoltage and overvoltage conditions to the logic chips, so post-regulation would be required. Furthermore, having a separate small flyback for +5V and +3.3V allows to implement standby and shutdown features in a quite easy way by just turning-off the main converter.

I would wind the main transformer this way: half primary | bifilar secondaries | half primary, with the primary halves connected in series. Output inductor should be also bifilar (one for both outputs), and one or more stacked iron-powder cores may be well suited for that. Doing it this way, you can even sense only one of the +40V outputs, or you can sense both in series as you mention, it will be quite stable anyway provided good coupling and matching between both 40V outputs.

Triple insulated wire seems to be expensive and very hard to find, I have not been able to find any practical source for it in small quantities yet. But its main drawback is size: it's much thicker than standard wire, so I would regard it as only practical for small turn counts in low-voltage outputs.

To wind such a power transformer, I would probably employ something like a ETD39 core (first guess of required size) with a vertical bobbin, leaving 5mm margin between the windings and the edge of the coil in the side of the pins and 2.5mm in the opposite side. Pins from the primaries and secondaries should be in opposite sides of the coil former and the three usual layers of mylar tape should be placed between primary and secondary winding layers. You may stack two sets of bifilar secondaries connected in paralell if required.

p.s. I would enjoy designing and building such a PSU if anybody were willing to pay for it
  Reply With Quote
Old 21st January 2006, 02:04 AM   #7
diyAudio Member
 
gearheadgene's Avatar
 
Join Date: Jul 2005
Location: CT
Hi Eva!

Quote:
Originally posted by Eva
First, I would probably use a small flyback for the +5V and +3.3V outputs, probably a self-oscillating one (simple, reliable and inherently overload-proof)
Where would you connect the primary of this? To the PFC? To the +40V? It should work well off the +40 supply, I think , and won't need to meet safety. Also, I'm not familiar with any self-oscillating circuits. Can you point me at a data sheet?

I need a little help on the bifilar windings, since I don't know how to set that up.

Can you point me to a good source for the bobbins, cores, and clips? Not sure where to get them.

Oh, you didn't mention where to put the low voltage winding for the pwm? Any thoughts?
  Reply With Quote
Old 21st January 2006, 02:16 AM   #8
diyAudio Member
 
jackinnj's Avatar
 
Join Date: Apr 2002
Location: Llanddewi Brefi, NJ
Quote:
Originally posted by gearheadgene

I need a little help on the bifilar windings, since I don't know how to set that up.

Can you point me to a good source for the bobbins, cores, and clips? Not sure where to get them.

Oh, you didn't mention where to put the low voltage winding for the pwm? Any thoughts?
someone will have nightmares -- but I have done bifilar windings this way -- get the approximate length of wire you need, fold in half, attach one end to a drill chuck, the other to a fixed point and wind it slowly -- works !!!!

good source of cores and bobbins -- ham radio guys use Amidon -- but even more use computer power supply transformers -- you take the main transformer off the PCB, wrap in aluminum foil, bake in a 400 degree oven for 45 minutes and gently pry apart making sure not to crack the core or bobbin -- this works beautifully and will give you a core capable of 300 watts -- you can stack two or more cores for more juice.
  Reply With Quote
Old 21st January 2006, 08:32 PM   #9
DaBit is offline DaBit  Netherlands
diyAudio Member
 
Join Date: Aug 2005
Send a message via ICQ to DaBit
Quote:
Originally posted by Eva

p.s. I would enjoy designing and building such a PSU if anybody were willing to pay for it
Excuse me for polluting the topic, but you seem to be unreachable outside the forum.

We (my company) might have a project coming up which demands a reliable, extended temperature range power supply. Guesstimate is around 250W, 230VAC only, 2-3 DC output voltages of which one will be +5VDC for the digital stuff. Must comply to a shitload of regulations, and can probably not be bought due to mechanical issues.

My first offline SMPS ever (85-265VAC in, 16-32VDC in, builtin UPS, 48VDC+5VDC out) which I had to design and build because nobody else could do it at that moment (in the land of the blind, one-eye is king) works well and is awaiting certification, but I am still far, far away from becoming a seasoned SMPS designer. Now, I know what is going to happen next: you did it once, you can do it again. But personally I would prefer to outsource that part to someone with more experience.

Would you be willing to pick up that part of the design or provide some consultancy if it crosses my path? I do understand that your labour and prototypes must be paid for
  Reply With Quote
Old 21st January 2006, 10:35 PM   #10
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
You've got mail.
  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
DIY Transformer Winding GlidingDutchman Parts 14 13th February 2012 06:00 AM
Transformer Winding microsim444 Power Supplies 4 3rd February 2009 09:58 PM
Transformer primary winding question gary h Power Supplies 4 21st December 2008 06:21 PM
Transformer winding Tahmid Power Supplies 104 8th July 2008 07:56 AM
Winding 1:100 Transformer for ESL ??? kristijan-k Planars & Exotics 0 26th March 2002 11:04 AM


New To Site? Need Help?

All times are GMT. The time now is 09:36 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