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Old 14th February 2012, 06:20 PM   #1
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Default linear psu for intel d945gsejt

Hi everybody, I've recently bought a intel d945gsejt in order to build a pc dedicated to music.
It will run voyage mpd on a CF via IDE port and a onkyo se200 is on the way to my home.

The real difficulty is the powersupply, because I would like to have it linear and in the same case of the pc.
The mobo power consumption is really low and voyage is really light, furthermore the mobo needs only the P4 connector.

It would be really cool to find something as easy as this: http://piyanas.com/showroom/componen...ON-BDP-1-3.jpg

A psu that connects directly to the transformer and to the mobo.


My goal is to build up something cheap (under 100 possibly) and easy.

What do you suggest guys?
If not possible or effective enough, consider that the mobo as a 12V jack for external psu.
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Old 15th February 2012, 08:52 AM   #2
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Default It is basically a problem

Hi there

I welcome your effort to do linear power supply, but I'd like to point out a few potential issues you may come across.

First of all, if you feed 12V to the board, then beware that there will be several SMPS circuits on the moterhboard (and I am saying this only to make you aware that there is no getting around SMPS on an Intel box like this - they will be on the motherboard regardless of what you do). The CPU probably likes about 1V, and even if it just takes 10W, that means 10A - i.e a lot of current. Normal PC's take up to about 100A, an insane amount of current, in practice you cannot do it at all linearly, the dynamic rate change needed to accommodate various power states of the CPU is likely 2000A/s. For most normal moterhboards you need a bunch of input voltages as well in which case you can get nice Pico converters that simply plug into the big hungry sockets (but they are SMPS). The good thing about the Pico converters is that you can ge them in quite forgiving voltage ranges (for the input) so you shouldn't need good regulation and so on + you can get them in high voltages - all good points if you want to build a linear supply.

Having said that, if all you need is 12V to feed the board, the board takes about 1-2 amps etc. then a linear option is not at all impossible. Using standard techniques you should be able to build one for about $50. Think of it as a power amp supply.

I would say, have fun, go for it, and make sure that you consider some sort of noise blocking between supply and board + between wall and supply (the latter is easy with input filters - you can likely salvage something from old equipment or buy something new).

Petter
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Old 15th February 2012, 11:52 AM   #3
marce is offline marce  United Kingdom
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Most of the noise in digital circuits is self generated and not from the SMPS.
Also instantaneous switching currents can be up to 50A, for a very very small amount of time.
The best way of minimisimng the noise of digital PCB's is done during the layout, with the evaluation of the PDS (power deliver system) optimising decoupling and optimising switching and switching rise times within the devices. Not somthing you can do later as any extra decoupling will not realy work as the caps have to be on the board with low inductance connections.
If the front end SMPS is well designed swapping for a linear wont make much difference, if any, at the end of the day if you have clean DC going in its DC.
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Old 15th February 2012, 02:54 PM   #4
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So it seems that only an alix board consuming 4watts, more or less, can have a linear power supply.

Do you think that somthing like this: M2-ATX-HV Automotive DC-DC Power Supply, 140 W would be better?

Maybe, just a hypothesis, powering the P4 directly would be better than using an external psu, so that I can avoid the intel DC converter.
Following this idea, what smps ready to use, would you suggest?
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Old 15th February 2012, 03:23 PM   #5
marce is offline marce  United Kingdom
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Any good reputable SMPS will do the job, we have recently moved from battery, linear main supply to battery, SMPS for vechicle communications (MIL) for 3 reasons, power consumption, heat and the linear was failing on EMC cs101 (conducted suseptability).
And when we looked at both varients with a 13GHz scope and the EMC spectrum, there was no difference.
That said it does need to be a good SMPS, there are lots of bad layouts out there, I spent monday with linears SMPS application engineer going through my layouts in very fine detail, and he was saying that there are a lot of bad designs that do give SMPS a bad name, if done right they are excellent, but unlike linear they are not as forgiving to bad layout, wrong choice of components.
Where there is on board core voltages etc depending on the required power we use either a little SMPS (3V3 IO supplies etc where there is going to be lots of ports switching noise any way) and where possible LDO's for core voltages, xtals etc.
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Old 15th February 2012, 03:41 PM   #6
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Ok, but what's the solution you would suggest?
I don't have enough knowledge about electronic stuff to judge the quality of the layouts or else.
For example I read that seasonic open frame psus should be good, right?

What I'm searching for is a board that accepts AC input and gives out the right DC output for the P4 connector. This would be really cool!

Last edited by acvtre; 15th February 2012 at 03:44 PM.
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Old 16th February 2012, 11:42 AM   #7
marce is offline marce  United Kingdom
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I dont use other peoples we design our own, sorry. but I will ask around and get reccomendartions.
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Old 17th February 2012, 02:15 PM   #8
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I've checked the intel manual and found out that the P4 and the jack for the external psu apss through the same DC converter.
The maximum possible consumption is about 19W, but I wont use an internal hdd and I'll overclock the cpu, since I use voyage. This means that the power consumption will be much lower.

A friend of mine uses a 12V 5A stabilized psu and it's not even warm, with a similar mobo.
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Old 18th February 2012, 04:39 AM   #9
i2k92 is offline i2k92  Indonesia
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Currently I uses Pico PSU + external 12V DC brick to power my E350 board. I was about to order a 12V toroid to build a linear PSU to replace the DC brick but I read this thread an found out that there some technical issues in using linear PSU on computer.

If my understanding is correct there is no point of using linear PSU and it is more important to pick a quality SMPS.

I agree that not all SMPS are equal. A friend tested some SMPS to be used for Charlize TA2020 amp, at the end he ended up with a SMPS pulled out of decommissioned Hitachi Data Storage server (the most expensive from the bunch that he tested). Andthat charlize sounds awesome.

What do you guys think about this (got a positive marks from Tripath guys, can be customized to 12V) :
Connexelectronic

Otherwise, I'll snag one of those Hitachi PSU.
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Old 18th February 2012, 09:29 AM   #10
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Quote:
Originally Posted by i2k92 View Post
Currently I uses Pico PSU + external 12V DC brick to power my E350 board. I was about to order a 12V toroid to build a linear PSU to replace the DC brick but I read this thread an found out that there some technical issues in using linear PSU on computer.

If my understanding is correct there is no point of using linear PSU and it is more important to pick a quality SMPS.

I agree that not all SMPS are equal. A friend tested some SMPS to be used for Charlize TA2020 amp, at the end he ended up with a SMPS pulled out of decommissioned Hitachi Data Storage server (the most expensive from the bunch that he tested). Andthat charlize sounds awesome.

What do you guys think about this (got a positive marks from Tripath guys, can be customized to 12V) :
Connexelectronic

Otherwise, I'll snag one of those Hitachi PSU.
There is also people using linear psu with the same mobo I'm going to use and have no problem. Furthermore, they have compared a good psu, like seasonic x460, with a simple linear and said that the difference is really big and it doesn't gets even warm.
Where's the truth? Consider that the power consumption should be near to 10W, in my case.

Last edited by acvtre; 18th February 2012 at 09:32 AM.
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