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Old 19th March 2001, 11:57 AM   #1
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Does anybody have any good links for schematics or projects
for a car amp or more specificly a dc dc converter ?
The amp part is the easy part but I would like to find info on how to make a high frequency converter and the transformers involved with that. The problem is that you shouldnt use a normal transformer because it is way too big. A high frequency transformer at 30 - 50 Khz is very small. So it is easy to boost up the 12V power supply of the car to say +/- 35V.
Any ideas would be great.
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Old 19th March 2001, 02:54 PM   #2
blmn is offline blmn  Brazil
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There is an article about the matter - in fact, itīs a project - in Audio Amateur Amplifier Projects book, at Old Colony Lab.

Itīs a car audio power amp. using smps (+/- 45VDC).

I have additional information about this kind of amp, books of SMPS design etc. I will make a little research and tell you something more.

Regards

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Old 19th March 2001, 05:28 PM   #3
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The correct name of this book is:

Audio Amateur Power Amp Projects - ISBN 1-882580-08-7

Regards
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Old 19th March 2001, 11:10 PM   #4
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Thank you very much for the information blmn.
I hope I find something on the subject.
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Old 20th March 2001, 01:00 AM   #5
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Let me explain a little more what I know about SMPS for car audio power amps. I've already done some designs;

- you can use push-pull topologies until 1.2Kw input power. Many car power amps use this topology (some in a unregulated mode, many in a fully regulated mode);

- the frequencies you told are the usual ones, a good range for the most common ferrite material with low losses;

- the design and construction of the transformer are critical, you can use toroidal ferrite types from Magnetics. They sent to me a complete set of catalogs with no questions. Very good people there;

I recommend the following books about SMPS and high frequency transformers:
Switchmode Power Supply Handbook - Keith Billings - ISBN 0-07-005330-8
Switching Power Supply Design - Abraham I. Pressman - ISBN
0-07-052236-7
Designing magnetic Components for High Frequency DC-DC Converters - ISBN 1-883107-00-8

- the most common PWM ics used are SG3525 and TL494. They drive power mosfets like IRFZ44 or MTP50N06 (Motorola);

- the rectifiers are usually ultra-fast types like the MUR series from Motorola;

- since the currents and frequencies are high, the PCB design is critical too. Short and VERY large cooper areas are necessary;

- the efficiency is usually 85% or more, but the heat generation on the primary side of the circuit must be considered. Input filtering is very important. The capacitors at the input must be high temperature types with low ESR;

- ground loop is a big problem in car audio design. I used optical coupling from primary to secondary side of the SMPS.

I started my projects with the Audio Amateur project that I told you (just the SMPS) to learn how this type of power supply works on pratice. After that, I was growing the power until aprox. 600W eff. at the output under 4 ohms load in bridged mode (2x300W at 2ohms)using the same topology (push-pull with optical coupling). The toroid in this case was a 40mm diameter one with 13mm height!! I reached 2x375W eff. but with no good stability (not enough mains power in my house to make more tests. I'm thinking on buying a big battery to continue my tests. HI!!!).

But 2 ohms or less are very hard loads to deal with and
8 ohms loads for high power need output filter capacitors
with "not easy to put into little boxes" sizes. I think 4 ohms is the best deal.

There is another DIY car audio power amp from Elektor Electronics, but, if I remember, it's a full bridge SMPS, much more complex than necessary for amateur purposes, in my opinion.

Regards
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Old 20th March 2001, 12:49 PM   #6
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I know a few basic things about smps but its very hard for me to design a transformer for them. The sg 3525 was used in the elektor magazine design but I dont have that mag any more. I can remember also that the transformer there was very complex. In the car amplifiers I see of commercial type I see small toroid type transformers.
Anyway thanks again for the tips about the books.
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Old 21st March 2001, 05:09 PM   #7
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I just ran into this and remembered your post.

http://valveaudio.tripod.com/

[Edited by vdi_nenna on 03-21-2001 at 12:19 PM]
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Old 6th July 2007, 07:20 PM   #8
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Default CAR AUDIO SMPS

Hello projects builders

Take a look in this SMPS that I built. Itīs project with DBL494 PWM controller, 1,5 in. toroidal, IGBT output transistors, +52V/-52V output. This is 115VAC model, but I have other for car audio with same characteristics and +63V/-63V output and zener regulated by opto 4N25.
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Old 6th July 2007, 07:22 PM   #9
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Default CAR AUDIO SMPS

Here is other picture:
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File Type: jpg mps7.jpg (44.0 KB, 521 views)
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Old 6th July 2007, 07:27 PM   #10
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Default CAR AUDIO SMPS

I will post here the pics of the CAR SMPS. Itīs a big powerfull. SG3524 PWM, 2 inches toroidal, push-pull, 12 FQP50N06 mosfets.

Waiting to tomorow.
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