toroid for car amp smps

[subwo1]

Originally posted by B.I.G
my only problem is that the core is getting hot(about 62C celsius ) when the amp is running at low volumes and getting colder(55C celsius) when i increase the volume .

This type of problem is one reason I avoid push-pull even for 12v powered SMPS circuits. Unless active monitoring and compensation of the duty cycle is performed, the transformer always experiences at least some net flux creep. There are at least two reasons why. The first is that the current * time product applied to the windings is different in each direction due to different pulse widths at the MOSFET gates, and maybe worse, that the on-resistances of the MOSFETs are not the same. The other is that those drive currents are applied to the core slightly differently since both windings cannot occupy the same physical location.

When the load on the transformer secondary is increased the reset current through the primary windings increases when they fly low. The result is that the core flux resets faster, getting closer to zero magnetism before the dead time period expires.

Well, that way is how I understand things, anyway. If the problem is not critical in your application, the answer would be to make sure the core has enough ventilation. Otherwise, you could reduce the duty cycle at low power output which would increase the flyback current through the primaries, as well as providing more dead time for the core to demagnetize. But then the output choke becomes more important and a feedback circuit becomes necessary.

[jackinnj]

Originally posted by subwo1


Well, that way is how I understand things, anyway. If the problem is not critical in your application, the answer would be to make sure the core has enough ventilation.

Agreed:

1) Use a bigger core
2) Use a pulse-by-pulse current mode controller

[Eva]

Even simpler :

Increase turn counts and/or add something like 10% dead time

Also check for symmetry the pulses generated by the controller IC. I've found some SG3525 units from SGS-Thomson to produce asymetric pulses

EMI feedback into the IC signal paths may also cause asymetric pulses

[jackinnj]

or do a better job of winding the turns -- you could use a small computer fan to cool the core --

i really think that this discussion gets very complex for a bulletin board -- sanjay at National Semi has done a really good job of explaining the route to optimization -- again search "magnetics" on their website . With a core you pull out of a hamfest grab-bag it's difficult, but not impossible, to get really good results -- but you have to characterize aspects of the core so that you can apply the design equations.

[soundbag]

I think the best advice anybody could give on smps is to push aside one"s linear attitude or knowhow aside for the moment and master the ferrite and is principles.

Honestly, that is what I am doing for the main time and that is what Eva and the smps guru did.

BWG, pls conquer the ferrite and you will be surpriced.

soundbag.
_________________
"DONT TRUST ANYMAN,
MEASURE EVERYTHING"

[jackinnj]

This seems to be new on National Semi's "Power Bench" website, a reading list for prospective SMPS designers:

http://www.national.com/appinfo/powe...68,319,00.html

btw, I have been adding links to resources I find helpful at:
www.tech-diy.com/smps.htm

jack

[robin2d]

Hi,
I red your many thread replly. really you are very knowledgeable person.
I want to build a SMPS from this thread
Making car amplifier SMPS with tl494 + DC Protection

But problem that i did not find any toroid in my city. i found a ETD 39 transformer . Can you tell me how to winding a ETD transformer?
i want to use for 34 vols output transformer for this SMPS.

Let me know how meny AWG wire i have to use?
How many turn i have to use for primary and secondary?

I did not send mail directly to u, sorry for write to u from this thread
regards
Robin

[robin2d]

I am sorry that my last reply (Post #247 ) was for 'Eva'. sorry again for my mistake. I was forgeted to mention her name.

But any one can help me pls.


Regards
Robin

[gearheaddruid]

Robin, I have done a lot with the ETD series of cores. First make sure you have an UNGAPPED core! Hold the two halves together and look at a light source through the joint of the middle legs. You should not see any light. There are also different ferrites available in the same core shape. The H7C ferrite is the one you want for smps.

Eight turns center tapped for the primary and 12 or thirteen turns center tapped for the secondary. For the primary, I would use the equivalent of #10 wire and for the secondary, #12. There should be plenty of window space for the wire on the bobbin. I would recommend using a Litz type wire or at least several smaller wires in parallel for the windings.

Aside to Eva, A woman who speaks smps, ...... I Love you Best regards, Steve

[DT]

Hi to all,

i am building my first smps from project 89. I wound my transformer(just primary), and have a question.
My ferite core(permeability is 2000) is 29mm inner diameter, 45mm outer diameter and 8mm height and width. I wound my primary with double solid cooper wire (2mm diam. each). Maybe anyone can look at my work and coment if i do this right?

What power rating can i expect from this transformer?

primary winding

thanks