Cheap PSU: Piece of junk or semi-decent?

[Behemot]

Re: Cheap PSU: Piece of junk or semi-decent?

This crappy PSU doesn't have any PI coil in the output

I can see one from here on +3,3 V

If you remember that Eurocase of mine, it actually had two coils on +3,3 V. I think that's the reason why this rail stayed in spec almost under all circuimstances. Other rails were so-so, barely in spec even with 50 % higher total capacitance

[goodpsusearch]

Re: Cheap PSU: Piece of junk or semi-decent?

1,2 (+5V) · 1000uF · 10V · 105C · ASIA
3 (+5VSB) · 470· 16V· 105C · ASIA
4 (-12V) · 470· 16V· 105C · ASIA
5,6 (+12V) · 1000uF · 16V· 105C · ChengX
7,8 (+3.3V) · 1000uF · 10V · 105C · ASIA

12 (+5VSB) · 1000uF · 16V· 105C · ChengX
13 (+5VSB) · 47uF · 50V · ChengX

1,2 (+5V) · 2200uF
3 (+5VSB) · 1000uF
4 (-12V) · 470· 16V · don't change the value of that cap
5,6 (+12V) · 2200uF · 16V
7,8 (+3.3V) · 2200uF

12 (+5VSB) · 1000uF · don't change the value of that cap

[momaka]

Re: Cheap PSU: Piece of junk or semi-decent?

^ what goodpsusearch said. Those are good values to use. The Panasonic FJ may actually work due to lack of PI coils and small output inductors. Also make sure to change #14, 15, and 16. Use same or higher voltage and same capacitance values. #13 looks like a filter cap for the auxiliary rail that powers the PWM controller. Not necessary to replace unless it plays part in the 5VSB regulation. On older Deer/L&C units, I know it doesn't, but not sure about this one. Probably doesn't so you can leave it alone.

I can see one from here on +3,3 V

You must have the ability to see ghosts too then because I don't see any PI coils either .

[TELVM]

Re: Cheap PSU: Piece of junk or semi-decent?

Thanks!

Hmmm ... I'm wondering about adding PI coils to a PCB that lacks parking slots for them ... ...

If I understand it correctly,


to add a PI coil for say caps no. 1 & 2, I should cut the direct trace from 1+ to 2+, then bridge 1+ and 2+ with the PI coil. Right?

[Behemot]

Re: Cheap PSU: Piece of junk or semi-decent?

Well it's not typical, but still SOME output filter in there. See the big toroid coil? I bet it sits on +3,3 V.

[c_hegge]

Re: Cheap PSU: Piece of junk or semi-decent?

to add a PI coil for say caps no. 1 & 2, I should cut the direct trace from 1+ to 2+, then bridge 1+ and 2+ with the PI coil. Right?

Yes. Exactly

[TELVM]

Re: Cheap PSU: Piece of junk or semi-decent?

Yes. Exactly

Thanks C_hegge . Piece of cake then .

[momaka]

Re: Cheap PSU: Piece of junk or semi-decent?

Well it's not typical, but still SOME output filter in there. See the big toroid coil? I bet it sits on +3,3 V.

Which torroid are you referring to? There are 3, but they are all required for proper operation of the PSU. 1 is for the common mode choke for the 12V, 5V, and -12V rails, 1 is for the 3.3V rail, and the last small one between the 2 heat sinks is used for deriving the 3.3V rail from the 5V rail output pins on the transformer (the mag amp circuit).

The PI coils/bobbins, on the other hand, are not required but they can improve the ripple and noise filtering quite a bit.

Piece of cake then

I think I foresee more ghetto PSU modding here

[Behemot]

Re: Cheap PSU: Piece of junk or semi-decent?

1 is for the 3.3V rail

This. There are PSU without this one When it's present, it greatly improves ripple. So I personally take it as part of the filtration.

[momaka]

Re: Cheap PSU: Piece of junk or semi-decent?

This. There are PSU without this one

The PSUs that don't have it use a totally different design to get their 3.3V rail. On such PSUs, there will also be no mag amp torroid - that's because there is no mag amp circuit. Most PSUs that don't have the 3.3V rail torroid use linear regulation to get the 3.3V rail and most of these designs will actually have even cleaner 3.3V rail with much less noise.
So just because there is a torroid for the 3.3V rail doesn't mean the PSU will have cleaner output on the 3.3V rail.

[Behemot]

Re: Cheap PSU: Piece of junk or semi-decent?

I gess you are out of picture. I thoguh we are talking about cheap chineese craps here. So how the hell got things like „a totally different desing to get their 3.3V rail“ here? You are way of price region we are in.

[goodpsusearch]

Re: Cheap PSU: Piece of junk or semi-decent?

No, he is right. If I get it correct he talks about using a mosfet to get 3.3V. Many cheap psus use that solution because they save some cents not having to use some parts and the result is cleaner 3.3V, but lower in A.

[Behemot]

Re: Cheap PSU: Piece of junk or semi-decent?

I have never seen it in my life yet and only once here on pictures. Also getting it from +5 V is pure insanity, efficency is terrible. Better to get it from +12 V.

More common is to get +5 V SB using refference from some higher voltage from small transformer.

[Th3_uN1Qu3]

Re: Cheap PSU: Piece of junk or semi-decent?

I have never seen it in my life yet and only once here on pictures. Also getting it from +5 V is pure insanity, efficency is terrible. Better to get it from +12 V.

The MOSFET is used a linear regulator - efficiency would be even worse if they would take it from 12v. Why do you think that even the lowest end units use 40A parts there? They'd cheap out on those if they could. Highest i've seen so far was rated 80A.

More common is to get +5 V SB using refference from some higher voltage from small transformer.

That's how any regulated SMPS works.

[tom66]

Re: Cheap PSU: Piece of junk or semi-decent?

Most of the time it is actually magamp regulated, not linear regulated. But it almost always uses the same transformer tap.

I think maybe 10A would be the maximum practical from a linear regulated 3.3V, a low end motherboard would probably be OK with that (it usually only provides RAM and chipset power; both of which are usually linear regulated on the motherboard again... so almost all of the power is thrown away.)

[Behemot]

Re: Cheap PSU: Piece of junk or semi-decent?

That's how any regulated SMPS works.

I mean refference like, for example, http://pdf1.alldatasheet.com/datashe...ICS/LM123.html. The refference component, not using comparator against refference voltage

[Wester547]

Re: Cheap PSU: Piece of junk or semi-decent?

I think maybe 10A would be the maximum practical from a linear regulated 3.3V, a low end motherboard would probably be OK with that (it usually only provides RAM and chipset power; both of which are usually linear regulated on the motherboard again... so almost all of the power is thrown away.)

Do you mean the amount that would be practically used by the +3.3V rail or literally the practical maximum DC-DC converted +3.3V (or linear regulated) would be good for? Some would contest that more than 15A is not drawn. You'd probably be right though if you consider the DC-DC converters on a motherboard and how many ICs essentially use even lower voltages than +3.3V because of that.

The MOSFET is used a linear regulator - efficiency would be even worse if they would take it from 12v. Why do you think that even the lowest end units use 40A parts there? They'd cheap out on those if they could. Highest i've seen so far was rated 80A.

Do you mean DC-DC conversion/linear regulation is less effective than the traditional 2-toroidal coil setup and schotty barrier rectifiers? I always thought a secondary circuit made up of MOSFETs (for DC-DC conversion, considering the limitations of group-regulated power supplies) instead of diode packages would be more effective (synchronous rectification in place of diodes).

[momaka]

Re: Cheap PSU: Piece of junk or semi-decent?

Well, I know we're going off-topic, so I'll try to keep this post to a minimum...

I think maybe 10A would be the maximum practical from a linear regulated 3.3V

I thought so too, but then I noticed a lot of the older 200-250W HiPro PSUs from OEM PCs use that and they are rated usually 14A or more. Those, however, do have a separate transformer tap for the 3.3V rail. I never measured it but I'm guessing it's probably just a bit higher than 3.5V.

Do you mean DC-DC conversion/linear regulation is less effective than the traditional 2-toroidal coil setup and schotty barrier rectifiers?

There's 2 ways to do DC-DC conversion in a PSU. One is with 2 MOSFETs in a synchronous buck DC-DC circuit, the other is with a single MOSFET in a linear regulated circuit. The linear is very inefficient but very simple to build. Buck is extremely efficient but complex and requires a buck PWM controller.
Synchronous rectification is a totally different animal, so I won't discuss it here. And yes, it's very efficient too.

[TELVM]

Re: Cheap PSU: Piece of junk or semi-decent?

... we're going off-topic, so I'll try to keep this post to a minimum...

Please feel free, it's very interesting and educative stuff .

[goodpsusearch]

Re: Cheap PSU: Piece of junk or semi-decent?

Please feel free, it's very interesting and educative stuff .

Quoted for truth. Thanks momaka!!