Schottky seems to have much lower values of forward voltage drop and
breakdown voltage then fast recovery diode. What is their difference
other then this? I'm confused with which one I should choose as
bootstrap diode for a MOSFET bridge driver. Thanks for helping.
Schottky diodes are essentially half junctions, made of
metal and P type semiconductor, instead of a PN junction.
As you say, this allows then to conduct forward current with
about half the normal voltage drop (half the wasted power)
than full, PN junctions. And also, as you say, they have
low reverse voltage ratings (and high reverse leakage
current. And the reverse leakage goes up very fast as
temperature rises. Though they generally have high reverse
biased capacitance than similarly current rated PN diodes,
and it is a very nonlinear capacitance, with respect to
reverse voltage, there is no real reverse recovery time that
PN junctions have.
Reverse recovery refers to the fact that PN junctions, when
forward biased, fill each side of the junction with minority
carrier charges (i.e. the N side has holes injected into it,
and the P side has electrons injected into it). And if the
forward bias is changed to reverse bias, suddenly, most of
those minority carriers have to get sucked out of the
semiconductor, back across the junction, before the junction
can develop an insulating, charge depleted layer that
withstands reverse voltage. So, during this clean up
process (the reverse recovery time), the diode looks pretty
much like a short across the reverse bias. And the end of
this process can result in a nasty snap from high reverse
current to low current, and that snap can generate lots of
high frequency energy. Schottky diodes are more graceful as
they swing to reverse blocking, with only the changing
junction capacitance carrying a little reverse current.
So, if you want higher efficiency during forward conduction,
cleaner, faster switching to reverse blocking and can live
with the low reverse voltage rating, the higher reverse bias
leakage current (especially at high temperature), and the
probably higher price for the Schottky device, then the
Schottky is probably the best choice.