Re: Suggestion: Macron MPT-xxx and MPT-xxx2
Posted: June 22nd, 2013, 1:08 pm
It depends on what the feedback loop is tuned to and it depends on what other methods the PSU uses to suppress ripple. You could probably get away with anything as high as 75-85 ohms rated capacitors ESR wise. True, having lower ESR capacitors does mean an ultimately lower ripple voltage.LongRunner wrote:I think these PSUs do require low ESR caps.
Well, it can't, because lower ESR capacitors keep the ripple voltage lower anyway. But in order to do that, they have to work even harder.PCBONEZ's explanation (half ESR = twice the ripple current) assumed that the ripple voltage remains the same
PCBONEZ did say that one 3300uF capacitor would overheat where two 1500uF capacitors in parallel were designed to work. I could understand why.If you replace (say) [b]one cap out of eight in parallel in a VRM with one of lower ESR, you will indeed get more ripple current through that individual cap, because they are at the same voltage and lower resistance across the same voltage does indeed mean more current, but if you replace all of the caps with lower ESR units the ripple voltage will drop, and the current through the group will (hypothetically) remain the same. (In practice it's not that simple, but I'm sure it's closer to the truth than what PCBONEZ said.)