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Old 10-21-2020, 05:25 PM   #28
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Default Re: 4700uF 6.3v and 3300uF 16v in a 10mm Diameter

Originally Posted by pc7fan View Post
reducing to 3300u low-Z caps shouldn't be an issue whatsoever, plus that may reduce the risk of oscillations and will roughly match in ripple current ratings.
For PSUs, reducing capacitance while also reducing the ESR actually increases the risk of oscillation... but in most cases (it does vary a bit with designs) you have to get silly with the ESR reduction to cause that. Off top of my head, only Sirtec -made PSUs will start to oscillate badly if you use lower ESR caps than what they had (and in some cases, some of their designs oscillate at low and high loads by default.)
But by far and large, reducing capacitance (drastically - as in half or less) is much worse and more likely to cause oscillations than anything else.

On the other hand, increasing the ESR simply decreases ripple filtering. Again, you have to go silly with increasing the ESR to cause oscillations... and as long as you use the same capacity caps as the originals, there won't be a chance for the ESR to be so high as to cause oscillation. So because of that, you could technically use GP caps in any PSU. Of course, they may not last long and the ripple output may be higher... but again, it depends on the PSU design.

Originally Posted by pc7fan View Post
SMG is a fine choice, but remember that estimated lifetime doubles each 10 degrees Celcius less. KMG then should technically have double the lifetime than SMG at 4000 hours at 85C, if other factors are the same. KMG is the high-temperature variant of SMG.
So it comes down to application, really.

SME does indeed have higher rated ripple current, though, as mockingbird pointed out. Thus, at 120 Hz rectified DC applications (such as the output of line-connected transformers), it should technically be able to take more abuse than KMG.

On the other hand, in applications where you don't really expect a lot of ripple current but just need a GP filter (such as 3.3V, 5V, and 12V rail on the PCI slots, USB connectors, and Firewire I/O on motherboards), KMG may be a better choice than SMG, simply due to the higher temperature rating. This is why on the Xbox 360, Hann-Star used KMG (or Nichicon VZ) for the 16V, 100 uF caps instead of 85C series. Those Xbox 360 consoles can get pretty toasty inside. That said, I have not seen any of those KMG or VZ small caps fail inside them. So I think KMG is an OK series.

BTW, KMG and SMG are the successors (and lead-free versions, if I'm not mistaken) of KME and SME series, respectively.

Last edited by momaka; 10-21-2020 at 05:32 PM..
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