Logisys 575W

[Toasty]

Re: Logisys 575W

KJ: >>Seriously, didn't somebody somewhere calculate that a PSU with four Diodes instead of a Bridge Rectifier is limited to about 290 watts on the input side?<<

PH: >>WoW, I have NEVER seen a PSU use fucking diodes as a rectifier<<

Please explain. I do not understand why these "negative" comments about using diodes. What do you suppose is in all of those units pictured above? The one shown that you speak of is a 3 amp 400 volt unit.

I have used the individual, cylindrically cased, plastic diodes rated up to 8 amps @ 600 volts. Why do you say "limited to about 290 watts on the input side" ?

Toast

[370forlife]

Re: Logisys 575W

Its just most cheaper manufacturers use lower power diodes that can't actually deliver the required watts for the full output of the psu.

But ya, you could use higher power diodes in place of a rectifier as long as they can deliver the amps.

[Toasty]

Re: Logisys 575W

Understood. Hence your use of my quote.

However, both of the quoted comments (and those are not the only ones on the forums) would lead others to believe that individual diodes are a sub-standard method for the rectification process, which makes no sense at all.

Four diodes are arranged as a bridge rectifier. In this application they are arranged in a full-wave bridge design.

Diodes are a type of rectifier. There are other types.

A MOSFET bridge rectifier circuit I recently saw:
http://www.edn.com/article/CA6447287.html

Toast

[KeriJane]

Re: Logisys 575W

Hi Toasty!

Oh, it's not that four diodes can't be used as a Bridge Rectifier. Of course they can! That's what's inside one anyway.

It's just that when four Diodes are used in a PSU instead of a Bridge Rectifier it is usually because they are four REALLY CHEAP Diodes like the 3a ones mentioned. Or sometimes even smaller ones.

It's all about cost. If four larger single Diodes (like the 8a ones you mention) were cheaper than a decent Bridge Rectifier I'm sure we would find some in use somewhere. Bridge Rectifiers aren't exactly expensive so anything capable of any kind of power generally uses one.

One problem with separate Diodes is heat dissipation. Unlike a Bridge Rectifier there is no practical way to attach a heatsink to the little round Diodes so as to increase the capacity by dissipating more heat. Bridge Rectifiers usually have a nice hole for a bolt and flat, smooth surfaces that can readily transfer heat to something else.

Hence, the general rule of thumb: "4 Diodes in the Primary = Less than 300w AND extremely likely to have other corners cut."

Have Fun!

Keri

[Toasty]

Re: Logisys 575W

I'll agree to a point. None of the PSU's I have worked on have the one-piece bridge mounted to anything. Some have it "gooped" to the side wall of the unit, but I suspect that's more for noise/vibration dampening than anything. From what I have seen, the quantity of goop precludes any decent heat dissipation and, IMO, blocks it.

It may be a rule of thumb, but we don't know the ratings of the diodes in this supply.

Toast

[Per Hansson]

Re: Logisys 575W

That is exactly what I meant too Keri, i.e. that if diodes where used instead of a bridge rectifier then the beancounters went so all out that I'm suprised it will even be able to deliver 100w of DC without issues
It just to me seems like an extreme way of reducing the costs on these already utterly pathetic Deer based designs
(Btw, the bridge rectifier I linked was just one I found on Wikipedia, not at all related to a SMPSU, just to show what I meant...)

[KeriJane]

Re: Logisys 575W

Say......

Wasn't the Bridge Rectifier one of the very first INTEGRATED CIRCUITS commonly available?
Born around 1950, the lowly Bridge Rectifier has the following advantages over discreet components:

Fewer external connections to make (4 instead of 8)

Better heat dissipation and provision for heat-sinking

Smaller "footprint" on the circuit board

The disadvantage:

3a/1000v 5408 diode= 8¢ each (qty 1000)
3a/1000v bridge rectifier = 70¢ each (qty 1000)

Ah Hah! No wonder the Four Diode Treatment is so popular. (with accountants) Wait a second.... it's an "FDT"!


Bridge Rectifier: The mark of a company willing to spend a few more cents for a better component.

Avoid the FDT
Keri

[ratdude747]

Re: Logisys 575W

Hehe I remember seeing Logisys pushing PSUs in acrylic cases with blue backlighting a few years back.

I wonder if when the PSUs finally melted down if they would melt right through the case ?

I guess the resulting plastic blob would be a nice piece of modern art.

at fry's i saw a clear one, showing off the f**ku caps

does it get any more obvious?

[370forlife]

Re: Logisys 575W

Scariest part is he is now using this logisys as a power supply in a pentium dual core machine with a 9800gt.

He can't figure out why it shuts off at high load. At least this psu knows its own limits and shuts itself off unlike other cheap psu's that are way overrated.

[zandrax]

Re: Logisys 575W

He can't figure out why it shuts off at high load.

Tell him he'll know the answer when he'll smell fried silicon.

Zandrax

[370forlife]

Re: Logisys 575W

Tell him he'll know the answer when he'll smell fried silicon.

Zandrax

I'm bringing my old 500w Rosewill stallion this sunday to the lan party and going to throw it in there. Maybe that will show him that logisys can't even measure up to a cheap ATNG rosewill.

[ratdude747]

Re: Logisys 575W

rosewill=deer =piece of S***

[370forlife]

Re: Logisys 575W

rosewill=deer =piece of S***

This one is a ATNG built.

[etnietering]

Re: Logisys 575W

can somebody delete this post? i posted twice accidentally, and I can't figure out how to delete it. thanks

[etnietering]

Re: Logisys 575W

In what I'm sure all of you will deem a giant waste of premium capacitors, I have recapped my Logisys "480W" junker. The replacements went as such:

3.3V line
1x 2200uF @ 10v BH and 1x 470uF @ 16v BH -> 2x 2700uF @ 6.3v Panny FC

5v line
1x 2200uF @ 10v BH and 1x 470uF @ 16v BH -> 2x 1500uF @ 10v Panny FM

12v line
1x 1000uF @16v BH and 1x 470uF @ 16v BH -> 2x 1200uF @ 16v Panny FM

5vsb line
2x 470uF @ 16v BH -> 2x 680uF @ 16v Panny FM

-5v and -12v (each)
1x 470uF @ 16v BH -> 1x 680uF @ 16v Panny FM

Here's a before shot - notice the wimpyness of the BH caps:


And here's the after shot - ooooooooo Panasonic T vents they're HUGE compared to the ones they replaced:


If you remember from the previous pictures I posted, this unit's input filter consists of a fuse. In case you don't, here's another picture (and you can see the nice burn mark from when the current inrush limiter exploded):


Well I ordered some parts to make a better one:


Y caps are:
2x 1000pF 250vac Panny ECK Class X1/Y2

X cap is:
1x 0.33uF 275vac Panny ECQ Class X2

Inductors are:
2x 39uH 4.3A Coilcraft PCH (You can get free samples of pretty much everything on their site)

Bleeder resistor (it didn't have one of these before!):
1x 470K 0.25W something (I got a zillion of them on ebay)

We also added 2 green LEDs, so now instead of just looking cheap, it looks cheap AND tacky but it still works, and now I'll actually trust it to be a backup PSU for me, should I ever need it. I still plan on replacing the diodes with a real bridge rectifier, and the input caps with something other than fuhjyjyjyjyjyjyjyuuuuuuuu (still need to order more parts for that)

[370forlife]

Re: Logisys 575W

Nice. With some good input caps and a real bridge rectifier with a heatsink on it, it will actually be pretty nice.

[370forlife]

Re: Logisys 575W

This one is a ATNG built.

Ohh ya, it actually is a deer, but actually a nicely built deer if it weren't for the caps.

[etnietering]

Re: Logisys 575W

Yeah, I'm going to replace the fuhjyyyyyu's with panasonic TS-ED, 820uF @ 200v. I don't remember the capacitance of the ones in there now (and it's ALL THE WAY downstairs....) but they're probably 470uF
and I'm junking the 4 diodes, and putting in a bridge rectifier rated 8A @ 1000v I think, and going to do something to heat sink it (probably cut up an aluminum pop can again )

[370forlife]

Re: Logisys 575W

If you have an old computer case, just cut a chunk of aluminum out of that and put some fins in it.

[etnietering]

Re: Logisys 575W

good thinking! I'll have to check to see if I have any aluminum ones, they might all be steel