RE: insuring the stability of power delivery
Comments on Brian's Input
Adding cable to the mix: The closed loop output impedance of the PSE
plus the maximum cable impedance (R and L) must be lower than the
closed loop input impedance of the PD plus the maximum cable impedance
(L and R)=> Since we do not know the cable length to insure system
stability, the closed loop output impedance of the PSE plus the cable
impedance must be less than the PD's closed loop input impedance.
Notice that I have said "closed loop" impedance. This means that the
feedback loops of the PSE power supply and PD DC/DC converter plus the
load of the PD are included in the calculations. Not an easy task for
an open standard.
[rkaram] this is either too simple or a mess. my guess is that in Front of the
DC/DC we have some Choke and ceramic caps, these are meant for emi control.
so looking into the PD the AC impedance can be inductive or capacitive based
on where the choke's resonance is (as its parasitic capacitance and the caps on
each side come into play with the inductance) so if we are after some really low
Z at very low frequencies, then we would need a huge cap at the pd input?
of course now to make this more fun, if what Yair mentioned (negative Z)
looking into the DC there goes another twist now...
a lot to munch on...
roger