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Old 22nd December 2004, 08:35 PM   #1
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Default Switching 12V power supply PCB

I want to build this project:

http://sound.westhost.com/project89.htm

but PCBs aren't avaliable.

Has anybody made this project and has a good, working PCB layout?

Thanks!
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Old 24th December 2004, 03:30 PM   #2
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Location: Great White North, eh?
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I don't know yet, my transformers and MOSFETs aren't here yet.

I have a board layout done, but I haven't etched it yet. When I have results, I'll post 'em up.

Note:

I have a lot of respect for Rod and his designs. Chances are that I will submit my artwork for the boards to him, which he may choose to modify or use as-is to possibly produce boards for this design. If he does so, then I will not post artwork.

Personally, though I don't think that he will choose to make a board available for this SMPS. There is far too much that can go wrong in construction, and if it does, I don't think that he wants to have any responsibility for the failure of the SMPS. I could be wrong, though.

I've got a bunch of Rod's boards, sitting on my desk right now, and the design and layout are top notch. I'm going to try to do my own PCB for a couple of these designs, too.
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Old 24th December 2004, 03:55 PM   #3
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Default Re: Switching 12V power supply PCB

Quote:
Originally posted by soundNERD
I want to build this project:

http://sound.westhost.com/project89.htm

but PCBs aren't avaliable.

Has anybody made this project and has a good, working PCB layout?

Thanks!
National Semi, On Semi, Infineon (and probably TI and Maxim) have board outlines on their websites -- for their chips -- these have been "vetted" so you have a modicum of insurance that they are going to work --

take an outline off the chip manufacturer's website, download the ExpressPCB freeware and have boards made for some tens of dollars.

I believe that Infineon has a board outline for one of their highpower switcher development kits. Check their site.
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Old 30th December 2004, 03:17 PM   #4
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I have this that may be interseting for you.
The upc494 is a very common chip used for pwm power supply in car amplifiers.
This power supply drive a very powerfull power amp (500w)

Pat Allen
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Old 16th January 2005, 08:47 AM   #5
Kenshin is offline Kenshin  China
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Default Re: Switching 12V power supply PCB

soundNERD:

There's some problem with the schematic: push-pull topology in SMPS is vulnerable of transformer core saturation .

The MOSFET and the switching transformer has very low resistance, so a slight unsymmetry on duty cycle or on resistance could cause large DC current passing through the transformer and saturate it. Then high current will flow and.....

It's a classical problem in SMPS papers, and somebody even used DSP (!) to control the bridge to overcome it.

Perhaps using other topology like half bridge (with a big capacitor series with the transformer primary ) or use some current-mode PWM controller to control the bridge and ensure the current symmetry will be safer.

Another simple choice is : use a charge pump made by capacitors, diods and a half bridge switch(something that's used in class D) to boost the voltage up. We used it on our robot to get 24V from 12V and it's reliable.

Use more capacitors and diods can get a higher voltage,but the output voltage is fixed to several times of the input voltage and can't be adjusted continuously.
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Old 16th January 2005, 01:31 PM   #6
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that schematic is a commercial power amp, its been used since many years in many car amps and i never saw one of those with problems you related. This almost same exact schematic is used also in the higher series of Alpine car audio amp, they were still using the upc494 int the mid 90's. Its an OLD schematic, shown just as a guide.
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Old 16th January 2005, 10:37 PM   #7
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Thanks to everybody!

I checked out those websites, though couldn't find anything. At Infineon's site, I found a SMPS supply, but it's a 120VAC step down power supply.

Just wondering, SupraGuy, have you made any more progress on the PCB?
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Old 17th January 2005, 08:03 AM   #8
ssanmor is offline ssanmor  Spain
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Hello all.
Glad to see that there is still some interest in the Project 89 at ESP. I am the writer of that article, with the unvaluable help of Rod.

A long time ago I started with that design, that has proven to be very reliable. I have developed an improved design for a car SMPS, and plan to sell the finished boards in a short time, as long as some other stuff that I think can be interesting for audio entusiasts, like Class-D amplifiers and also off-line SMPS for them.
You are invited to have a look at:

www.coldamp.com

The webpage has only minimal information by the moment, as it is on construction, but please be patient, it will be filled with lots of info soon.

Best regards,
Sergio
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Old 11th March 2005, 06:41 AM   #9
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Hey i brought an alpine amp that has a pwm powersuply in it similar to this one

i brought it pretty cheap and found it was broken and never took it back cause it was that cheap i opened it up and the powerfets had been major cooked

they are irfz44 about a 50amp fet that switches ground just like in the diagram

with the transformer what kind of load should it put on the fets
cause mine is putting mega load on the fets and practically a short on the fets

sorry to rabble on a bit

what kind of resistance should be on the 12v side of the transformer

sorry for my stupid question.. im only 16
thanks
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Old 11th March 2005, 07:25 AM   #10
ssanmor is offline ssanmor  Spain
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Not a stupid question, congratulations if you are only 16 and are involved in these things, then the only thing I can say is: well done, keep working on it!

You wont be able to measure the load that the transformer puts on the fets, as with a multimeter you only see DC, and the primary of the transformer is almost a shortcircuit from the fets to +12V.
The load the transformer puts in the fets effectively at the working frequency depends on the load of the power supply, that is, the current the amp is demanding. To put it simple, if the amp is demanding 1A rms, the primary current will be that multiplied by the turns ratio of the transformer (for example, about 3 if the supply is +/-36V).

If your mosfets have exploded there are some simple possibilities:

a) There is a shortcircuit in the secondary: try to disconnec the amplifier from the power supply (if there are coils you can simply desolder both of them), and see if there is shortcircuit. Sometimes the capacitors fail to shortcircuit, what cause huge primary currents and even fet destruction.
b) There is a problem in the driving of the mosfets, that cause its spurious destruction, although not likely in a commercial product.
c) A problem in the input supply (like someone has connected polarity backwards or 220V or whatever).

Hope this helps diagnose your problem.

Best regards,

Sergio
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