PS4 PSU capacitors overheating?

[flolic]

I have this PS4 power supply that I am working on. Console suffered lightning strike and PSU was dead. After replacing whole bunch of components it now turns on and works ok, tested without load and under full load (17.5A on 12V output). But the two 1000pF capacitors connected in series across drain and source of the PFC mosfet gets to 110-120C when PSU is under any load, even an 1A. I guess that's not ok?

[srb1954]

Are you sure that the replacement capacitors are suitable for the circuit conditions?

The tan colour of the replacement capacitors probably means that they utilise the more lossy class II ceramic dielectric (X7R and similar types), and would consequently generate more heat from the capacitor ESR and dielectric losses.

Class I dielectrics, COG and NP0 types, may be preferred in circuits like this for their lower losses. Class I dielectrics are generally a light grey colour.

 

[flolic]

Those capacitors are original ones. I tried to replace them with capacitors from another good PSU of the same type, but behaviour is the same.
There is discoloration on the other side of the PCB that shows that overheating is not a new thing, and I don't know if there is some design flow or something is really wrong with it.

[wraper]

Those capacitors are original ones. I tried to replace them with capacitors from another good PSU of the same type, but behaviour is the same.
that shows that overheating is not a new thing, and I don't know if there is some design flow or something is really wrong with it.

Picture obviously is from a different place or maybe even different PCB. So it makes no sense.

[flolic]

What do you mean?

[wraper]

OK, it's the same PCB. On the photo it looked like it's corner of PCB while in fact it was just a recess which made it look like this.

[wraper]

As of heating, I think it's the same on every PSU of this model. Capacitors do heat and there is quite high current through these. The only way to reduce temperature without redesigning PFC is to use capacitors with lower ESR so they heat less or larger size so they dissipate heat better.

[flolic]

Thank you. I guess I'll just leave it as it is because I don't have better capacitors.
I will check capacitors temperature on other PSUs, I have few of other type but quite similar.

[MathWizard]

Well IDK how to calculate a good choice for such a thing, but what about those green Mylar flim caps, that are usually rated in the hundreds of volts. They are often large bodied through hole type. Assuming lead inductance won't matter at typical switching freq. like 100kHz, could you just solder a couple of them on the pads ?

https://www.google.com/search?q=green+mylar+film+capacitor&tbm=isch&client=firefox-b-d&hl=en&sa=X&ved=2ahUKEwiRosPj27T-AhWCF2IAHQ30CkgQBXoECAEQQw&biw=2331&bih=1190

[fzabkar]

What do those capacitors actually do? Normal APFC circuits don't have them. In fact the application circuit in the datasheet doesn't have any, either.

https://www.onsemi.com/download/data-sheet/pdf/ncp1612-d.pdf

[bobbydazzler]

Are you sure it's not Q5 heating up the board, the heatsink is soldered in close there too?  MLCC's have almost 0 esr I don't see how they'd heat up under load. 

[ingalopez]

Those capacitors are for snubbing, and /or educe EMI. It is a lousy design, it is no strange they overheat. Appropiate snubber designs utilize a diode and resitor combination to divert the loses to the resistor. Just tolerate it, as long the thing don´t explode!. After all, they survived the destruction event...

[MathWizard]

The Corsair 750W computer PSU's I've worked on, don't have any type of extra RC snubber network around the PFC boost FET's. After the main's input rectifier, they have a highly rated, huge sized, like 1cm*1cm*2cm ,1uF cap, that meets the inductor, before the FETs, and that's it.

[flolic]

Are you sure it's not Q5 heating up the board, the heatsink is soldered in close there too?  MLCC's have almost 0 esr I don't see how they'd heat up under load.

Q5 is of course heating up, but that's to be expected. But the "problem" is in capacitors.
I checked few other PSUs and they all heats us, some more, some less. But on all of them capacitors are over 90C. To be honest, inside console temperatures should be lower because there is big fan pushing air through PSU, but PSU is after CPU cooler that gets quite hot.
To conclude, everything seems to be normal. I don't like it, but that's how it is...