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Old 25th June 2002, 10:01 PM   #1
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Exclamation 12V in switchmode power supplies

One of the major problems with my big system is coming up with the money for it. In order to help with the funds, I need to start producing high quality modular 150W/channel car amps in fairly large quantity. To do this, I must have a design for a SMPS with +/-45V out capable of at least 250W. Has anyone built ESP project89? PCB layout for it anyone? I noticed he does not have PCBs for this project for sale. Are there any other switchers I could make or maybe even complete units or kits for sale?
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Old 25th June 2002, 11:09 PM   #2
e96mlo is offline e96mlo  Sweden
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Since you probably will have to draw the PCB's for the car amps yourself then why don't you draw a PCB for the PSU aswell? Then you will have total control over component placement, copper thickness, looks etc.

/Marcus
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Old 25th June 2002, 11:14 PM   #3
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The amps use a very stable design and is easy to design a pattern for. I'm worried it might blow up if I try to design my own pattern for the PSU. SMPS's are picky about such things aren't they? They're pretty high-tech.
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Old 25th June 2002, 11:22 PM   #4
e96mlo is offline e96mlo  Sweden
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If you are going to produce them then you will either have to buy someones design or make one yourself.

It won't blow up. Not more than the amp board. It's the same thing; high current - wider traces, high voltage - wider spacings. Since it is somewhat higher frequencies involved you will have to think twice about decoupling and noise reduction. But it is NOT an impossible task even for the DIYer.

I say go for it!

/Marcus
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Old 25th June 2002, 11:54 PM   #5
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All Right! But it's gonna be hard as hell to compete with commercial manufacturers' prices. I'll have to SELL each channel for around $100. And I'll have to make the cases (with cooling fins and good device mounting surfaces) myself from bent aluminum plate. Not easy to do, but they should look really nice.
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Old 26th June 2002, 12:39 AM   #6
e96mlo is offline e96mlo  Sweden
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Can't you use ready made alu profiles that you just cut? There are quite a variety to choose from. Some should fit your demands.
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Old 26th June 2002, 06:09 AM   #7
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Unlikely, I have a fairly specific design in mind to keep the modules as compact as possible and so they can be connected to form a unit almost undecernable from a single amp. I'm using TO-3 output devices, and they must be completely hidden because of their live cases. I need a cross section something like this. There will be a 92 cm fan at one end, and a panel with input, volume, gain, Xover controls and power connections on the other. There will be holes in the sides for air from the fan that goes inside the amp to escape from. The - power terminal will be part of the case, and the + will be a strip inside the area where the top of the TO-3's come out which will come out the end to be accessed. This strip will only be in the dominant units, the slave units will be connected via lateral cables within that corresponding area. There will be a plug at each end to connect dominant units at the the amp's input level (after the preamp, so that only adjustment of the controlls on the end unit will be valid. Because of this, each preamp will need to be capable of driving lots of units). There will be a plug on the side to connect slave units. The speaker outputs will be on the sides. The units will be connected end to end by long bolts (or threaded rods with nuts) and side by side with metal plates that screw on. It looks like this might require welding on the fins, but I don't have a TIG welder, nor do I have access to one, but I will when school starts. Are there any aluminum extrusions that look like what I need? I think not. It's OK because I need to keep cost down anyway.
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Old 28th June 2002, 01:39 AM   #8
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Make sure that current-mode control is utilized or the output FETs will fail due to core saturation. This does not happen immediately but slowly over time by not subjecting the core to equal and opposite Volt-second products or a DC current. This is the trickiest part of switchers especially with dynamic power demands such as audio. Also keep in mind the skin depth at whatever frequency you are running. It may be necessary to use parallel smaller guage wire for the windings in order to minimize the copper losses. Good Luck!!!

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Old 28th June 2002, 02:40 AM   #9
blmn is offline blmn  Brazil
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Look for my old replies about smps or car amps. There are some references about SMPS power supplies there, inclunding a complete project, in Audio Amateur, for a car amp using +/- 45 VDC SMPS.

Beanz,

Using current-mode control in SMPS power suplies in this kind of SMPS using MOSFETS is not necessary to avoid flux imbalances, and, if I remember well, the design is more complex. You can see some information about the matter in "Switching Mode Power Supply Design", second edition, chapter 2.25, by Abraham I. Pressman - ISBN 0-07-052236-7. Actually, I have some designs using push-pull SMPS running since 1997 with no problems. Your tips about skin effects are very usefull and I just add the design and construction of the power transformer (where the perfect simmetry is necessary) have to be very well made.

Regards
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Old 28th June 2002, 03:00 AM   #10
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Without current-mode, there is no way to prevent flux imbalance and there is no way to prevent it from happening without it. At least use a DC blocking capacitor to avoid DC currents from flowing through the primary. The Pressman book is also highly recommended by myself. I own a copy of the second edition. Also the "Switching Power Supply Handbook, 2nd ed" by Keith Billings is also highly recommended. Also for reference, "The Inductor and Transformer Design Handbook" by Col. Wm McLymann. However, for a true beginner, the first two books cover transformer and inductor design fundamentals and basics rather well.

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