POWER OVER ETHERNET Diode/ Rectifier
Bridge Rectifier
First and for all, there are either one or two
bridge rectifiers. The current through the
rectifiers is very low (<300mA) and the voltage
environment is also low. The standard bridge for
this application will be the B1S~B6S which has an
industry standard pin pitch of 2.5mm. Bruckewell
further does have the advantage of the MBL06S bridge
rectifiers, Low forward voltage drop, high power
efficiency.
Since two bridges are used, the space saving could
be important (e. g. in PoE webcams). There is no
significant thermal or current stress in this
application so the MBS bridge is the right choice.
TVS Diode
On the input, in general also a 58V TVS is used.
Whenever a cable is plugged and unplugged it is wise
to use a TVS rectifier. Select a part with 58V
minimum stand-off voltage such as the P4SMAJ58 with
400W peak pulse power. A transient voltage
protection diode is ideal when the protection needed
is against ESD (IEC61000-4-2) and EFT
(IEC61000-4-5). Most PoE applications are indoors
and as such Lightning protection only needs to be up
to level 2 in IEC61000-4-5. A 400W TVS like the
P4SMAJ series can easily handle this also because
the lightning pulse waveforms should be short (8/20
– 1.2/50).
Only in extreme cases would a company have to use an
600W/1500W TVS if there are long outside lines.
Schottky Rectifier
A fly back converter tends to be used in a lot of
applications. In most cases, the output voltages
tend to be low and as such Schottky rectifiers are
the preferred choice. One can use a number of
industry standard Schottky rectifiers such as the
SS14, SS24 and SS34 depending on the current you
need to provide at 5V or 3.3V. Since PoE webcams
application, the space saving could be important.
Bruckewell further does havbe the SD14, SD24, SD34
that SOD-123 small package.
