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Old 4th July 2005, 01:46 PM   #1
Todor is offline Todor  Bulgaria
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Default SMPS noises with TL494

Hello, I am making a +-40V car amp PS with the 494 and as I can say i experience some problems with making it work normally.
First of all if someone could tell me what noises should be heard from the PS when not loaded? Should the sound be smooth and regular because i can say i hear some "misbehaviors" around the center frequncy. Also i have a very big startup peak of about 10-15A in the 14V. I also doubt about the toroid i am using.It is around 40x25x10 with M 2000. I dont know if it is suitable for the job. I cannot adjust the frequncy somehow cus when i load it it makes awful sounds and the Amper meter jumps where it is not supposed to go for that load. The FETs are IRFP150N.
I would be gratefull If someone could add anything to my problem and if unsufficient i could bring some more info about this project. thank you all!
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Old 4th July 2005, 02:02 PM   #2
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Default We need more information

Hi:You will need to provide a lot more information if you want any help.First of all what is your switching frequency,are you using push pull configuration?,how did you determine the proper number of turns for your core?...

If you can post a schematic of your design it would help towards getting the ball rolling. RC
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Old 4th July 2005, 02:23 PM   #3
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You don't want to run a switching power supply "unloaded" -- the value of the inductors are inversely related to the load!

Send me an email privately and I will send you the article on how to mod an ATX supply -- it describes the theory well and uses the TL494. The author wrote it for a ham radio magazine -- in their applications the current demand will run from a few hundred MA to tens of amps -- and they need very quiet performance.
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Old 4th July 2005, 02:47 PM   #4
djQUAN is offline djQUAN  Philippines
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in a normal SMPS there should be no sound. is the sound that you hear more like a whistle? if so, the cores or the windings are vibrating which is not a good thing. have you seen the input/output waveforms of the transformer?
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Old 4th July 2005, 02:56 PM   #5
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Default My Guess

If I had to guess I would have to say that his switching frequency is set too low..the lower harmonics of the square wave will be very audible!!..I do suspect he may have other design issues.
Bob C.
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Old 4th July 2005, 07:47 PM   #6
Todor is offline Todor  Bulgaria
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What should be the value of magnetic permeability of the ferrite core? Noone mentiones this, because here in my country ferrite toroidal cores are not widespread I can even say they are hard to find, so i haven't got much choice.
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Old 4th July 2005, 08:25 PM   #7
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Default Need more info

If you want help you need to supply information.A schematic can overcome the language barrier.I asked you a few questions in an earlier post but you have not responded to them.
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Old 4th July 2005, 10:04 PM   #8
Todor is offline Todor  Bulgaria
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maybe i have to give up with this and just repeat someone other's design which at least is known to be working.The problem is that i want to use 494 and the schemes i found with it somehow didn't like them. Some of them were without voltage regulation, something i need. I am now searching for sg3525 or 24 for they are more often used. I haven't got any luck of finding it so far! It may sound weird but when some electronic component is not made in your country it's sometimes hard to find it as the only way is import.
Anyway if i have any further experience with the PS i would post here
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Old 5th July 2005, 08:49 PM   #9
Eva is offline Eva  Spain
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You are trying to do too much design and development in a single step.

Audible noises in regulated SMPS are almost always due to instability in the regulation loop. Anyway, you should gain experience with unregulated circuits first.
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Old 5th July 2005, 09:11 PM   #10
Todor is offline Todor  Bulgaria
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Thanks for the advice about the unregulated PS Eva, I will try it.
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