Found a brand new Comp USA PSU

[larrymoencurly]

Re: Found a brand new Comp USA PSU

Yes, This design looks particularly old. The 5vsb transistor not being attached to the heatsink is a good indicator that this was originally an AT design that was adapted to ATX.

I had an ATX that may have originally been an AT design because its 5Vsb was on a separate circuit board. PC Power & Cooling featured it in a magazine ad to show how bad a PSU could be.

Here's a Leadman identical to Pentium4's CompUSA unit, right down to the April 13, 2001 production date, only the +3.3V has a choke in its output, and the heatsinks are different.

[Pentium4]

Re: Found a brand new Comp USA PSU

Not yet! I just got it that day

[everell]

Re: Found a brand new Comp USA PSU

Absolutely it is It needs your 5VSB mod!!!

So...................did you put the 5vsb mod on your Antec?

[Pentium4]

Re: Found a brand new Comp USA PSU

Absolutely it is It needs your 5VSB mod!!!

[everell]

Re: Found a brand new Comp USA PSU

Regardless of efficiency here is why 2 transistor 5VSB sucks, this one had the critical cap fail. It killed an Intel 775 motherboard

Is that an Antec power supply?

[Pentium4]

Re: Found a brand new Comp USA PSU

Regardless of efficiency here is why 2 transistor 5VSB sucks, this one had the critical cap fail. It killed an Intel 775 motherboard

[Behemot]

Re: Found a brand new Comp USA PSU

If they are present… It clearly has *some* impact if the THD is such problem, right?

[tom66]

Re: Found a brand new Comp USA PSU

There is basically zero energy beyond a few kilohertz. It's all shunted to ground by the Y- and X-caps anyway.

[Behemot]

Re: Found a brand new Comp USA PSU

Masuring the current may not be that easy if the drain is realized by harmonics spikes with base at say several tens of kHz and than many more ending somewhere in MHz range.

[tom66]

Re: Found a brand new Comp USA PSU

I'm not sure what you mean. Measuring power factor is easy. Simply measure current using a high speed ADC, use a DSP to compute RMS current and multiply by RMS voltage (in the same way) which gives you reactive power in VA. Then measure power by integrating voltage and current, and divide the two to get PF.

If you use a cheap meter you're going to get poor results but that's how some of the equipment that the company I work at makes, does it.

[Behemot]

Re: Found a brand new Comp USA PSU

My meter shows that but I won't put my hand into fire for the accuracy. Especially when we are talking about harmonic distortion, not phase shifting.

[tom66]

Re: Found a brand new Comp USA PSU

A good power meter can measure down to 0.01 PF. Actual power factor of a standby circuit is typically 0.3 to 0.5PF.

[Behemot]

Re: Found a brand new Comp USA PSU

Sure but still there are loses.

There is also possibility of very inaccurate measurement of drawed power because of low power factor (usually <0,1), but much more ppl than me have the same results so statistically…

[tom66]

Re: Found a brand new Comp USA PSU

Rectifier draws only power as required by standby circuit and losses are very low at the 10's of mA drawn by the standby circuit. The X capacitor draws reactive power, which is not included in real power calculations. The bulk capacitor has negligible leakage current. 99% goes to standby power circuit.

[Behemot]

Re: Found a brand new Comp USA PSU

Input filtering is not active? Rectifier, PFC and capacitor is not active? Only inactive thing in there are switching transistors, everything else works. These days almost only Champion Micro's PFC+PWM combo chips are used and PFC part of them is active, just the PWM not.

[tom66]

Re: Found a brand new Comp USA PSU

What do you mean whole primary side? The only thing active would be bleed resistors and small leakage currents.

[Behemot]

Re: Found a brand new Comp USA PSU

I am talking about +5 V SB, my own load tests. I have never seen 80 % efficiency on that. Remember that you have the whole primary side to feed even if just the +5 V SB rail is operating.

Will have another 80 PLUS Platinum PSU in next days reviewed and later some 80 PLUS Gold ones in next weeks (Fortron Aurum should arrive). Anyone wanna bet on crossing the 80% barrier?

[tom66]

Re: Found a brand new Comp USA PSU

Do you have any real numbers or you are just making it out? I have never achieved even 80 % with 80+ Platinum Power Supplies with the best PWM combo chips, best result with Fractal Design Newton R3 600 W was 73,9 % on overload.

Two transistor usualy barely achieves 65 %. It burns insane power, mostly on the rectifying diode which, if not enough sized and/or superfast used, is sometimes capable of baking itself and everything around. They don't usually even count with 60+ % long-term output on these things so if that happenes, it won't survive that for long.

I'm talking about the 5VSB, not the main switcher; for the 5VSB 80% efficiency is possible due to the single switch, lower losses and small transformer. Bigger output powers do not lend themselves to flyback designs, you may be confusing it with a two-transistor NPN bipolar design (half bridge I think?) which does have poor efficiency.

You have to remember with those tests involving the 5VSB in an integrated design is the 5VSB transformer often powers the TL494 or similar chip on a separate rail plus other control logic. As I said it's possible to make them efficient, but more costly than a good TNY- single chip design.

[Pentium4]

Re: Found a brand new Comp USA PSU

I believe on one of JG's reviews, an el cheapo he reviewed was something crazy like 59% efficiency in stand by with a 2 transistor design, maybe even lower

Edit: Found it, look at that, it was 41% at some point! http://www.jonnyguru.com/modules.php...tory3&reid=324

[Behemot]

Re: Found a brand new Comp USA PSU

5VSB transistor usually dissipates no more than 1W with 5V, 3A load. Two-transistor 5VSB is actually pretty efficient, around 75% to 80% (which is good for a small, low cost flyback.) And it's possible to make it without the killer cap, but you may as well use a controller IC because all of the tweaks will likely cost more than a cheap TNY-type switcher.

Do you have any real numbers or you are just making it out? I have never achieved even 80 % with 80+ Platinum Power Supplies with the best PWM combo chips, best result with Fractal Design Newton R3 600 W was 73,9 % on overload.

Two transistor usualy barely achieves 65 %. It burns insane power, mostly on the rectifying diode which, if not enough sized and/or superfast used, is sometimes capable of baking itself and everything around. They don't usually even count with 60+ % long-term output on these things so if that happenes, it won't survive that for long.