Car amplifier with dc dc converter ?

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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.
 
Promitheus,

There is an article about the matter - in fact, it´s a project - in Audio Amateur Amplifier Projects book, at Old Colony Lab.

It´s 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
 
Promitheus,

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
 
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.
 
CAR AUDIO SMPS

Hello projects builders

Take a look in this SMPS that I built. It´s 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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Mr. Netlist

Hello Mr. Netlist

About the design, no all. (excuse my bad english). I use Rod Elliott instructions in SG3525 SMPS and various mixed designs. I like it so much. In output I use since IRFP264, IRFP450/460 and SGW15N60(IGBT). I don´t have the complete schematic, it´s in my mind only. But I can post something for you. OK?

REgards
 
blmn said:
Promitheus,

There is an article about the matter - in fact, it´s a project - in Audio Amateur Amplifier Projects book, at Old Colony Lab.

It´s 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


PROMETHEUS:

I built the amp you referred to in the Audio Amateur of 04/89 & 01/90. I also did the voltage-mode SMPS (SG3525). Worked well, but there was output noise when I plugged in the MCT271 Optocoupler. When I removed it (run wide-open unregulated), the noise disappeared. I realized that I needed a (+/-) mutually-coupled output inductor for true regulation. Regulated, it ran +/- 33V & +/- 10V (for front end). Unregulated, it ran +/- 47V & +/-
13V. Its output was rated for 220W, max., and its switching freq was 26kHz.

Since the original Old Colony board did not include space for a mutually-coupled inductor, I contacted the author (Mr. Vikan)about this. He introduced me to his un-published SG1846-controlled current-mode switcher. Its output capacity was 290W, and it switching frequency ran at 40kHz.

That was 15 years ago, and I've long since parted it out for other projects. Also, I've moved out of the car audio world (family now), but still consult with firends on their setups.

What I liked about both supplies was that they sensed both the (+) snd (-) output voltages for true symmetric regulation. This has been a bone of contention in the DIY forum, but I am happy with sensing both (+) and (-) voltages.

Here are a few pics of the voltage-mode DC-DC I made from a new board from Old Colony before they cleared them out a few years ago.

Steve
 

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