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kp93300 26th December 2012 10:59 PM

Linear power supply for pc
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I made this linear power supply based on LM 338 with pretracking regulator and the regulated output is 11.8 V. I use a 10 V zener to reg the output.
The trans is 13.5 V ac out and at least 400W capability and is source from an old medical laser printer.
I made it to power an atom based pc which utilize a 60 W smps.

The reg power supply will not power on the pc .

What are the special requirements to use a linear power supply for pc use ??

pointers are most welcomed.


MarianB 27th December 2012 07:22 AM

Althoug linear PSU's are less complex and have less noise than switching ones, still they require a much bigger power transformer and filter caps, also the power devices have to cope with much more dissipation si heatsinks have to be much larger too, in other words they cost much more and occupy way more space in the case, and this is only to be verry short.

metalsculptor 27th December 2012 11:18 AM

The PC needs a PWR good signal before it will boot, so it will sit there waiting for this signal.
Old computers used linear or phase controlled power supplies

AndrewT 27th December 2012 11:52 AM


Originally Posted by kp93300 (
I made this linear power supply based on LM 338 with pretracking regulator and the regulated output is 11.8 V. I use a 10 V zener to reg the output.
The trans is 13.5 V ac out

13.5Vac, with pre-tracking regulator and series regulator !!!!!
What is the output of the transformer at the smoothing capacitors?

You may find that the regulator drops out when demand goes a little bit higher than just ticking over.

MarianB 27th December 2012 01:10 PM

Linear PSU's have one major drawback, for verry good stabilised outputs you have to take into account the minimum possible mains voltage and at that level the psu still has to deliver the needed power, that means higher voltage outputs for the transformer, high current capability and ofcourse much power lost on the series regulator, at hig mains level the PSU will experiance the lowest efficiency and the most power lost on the regulator, all that means you will end up with one big PSU ( real big sometimes ) and much more money spent on it, so that is why swithcers are prefered.

d a o 27th December 2012 03:42 PM


Linear Power Supply for Audio Computers

high price

kp93300 28th December 2012 02:35 AM

Thanks all.
The commends are all valid.
I start this exercise for experimentation. I just want to hear for myself whether there is any difference in sound quality from my atom based min atx sound system.
I realise that with the pretracking reg , the Vout do not have enough headroom . I think it requires about 5 to 6 V differnce between the input and output.
I remove the pretracking reg and manage to power the pc for 2 minutes before it went into shutdown because of overheated Lm338 !



marce 28th December 2012 10:47 AM

The problem of using a linear PSU is thay any noise is gonna be in the audible range, a well designed SMPS would be better, and contary to belief is not the only source of noise in a PC, the logic switching creates a lot of the noise.

qusp 28th December 2012 12:56 PM

that coreaudio place is a joke, so much ********

qusp 28th December 2012 01:18 PM

haha itemaudio offers a cryo treatment for my Mac mini for 60GBP lol

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