> 1. Mouser shows several DO-35 zener diodes that are apparently able to
> dissipate 5W. Is this really (safely) possible?
>=20

Yes, but this is below a certain temperature (25 - 75 degrees Celsius, see =
the=20
datasheet). Above that temperature the power derates linearily with the=20
temperature. The datasheets have diagrams showing this. Also, the longer th=
e=20
lead length, the lower the maximum power dissipation.

If the maximum temperature before derating is 25 degrees Celsius and you ar=
e=20
designing a device for an ambient temperature between 0 - 50 degrees Celsiu=
s,=20
adding the temperature rise of the zener itself, then there is not much of=
=20
those 5W left! In some cases (e.g. intrinsic safety barriers and safety=20
circuits) you also need to stay withing 2/3 of the nominal values which giv=
es=20
you even less to work with.

/Ruben

=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D
Ruben J=F6nsson
AB Liros Electronic
Box 9124, 200 39 Malm=F6, Sweden
TEL INT +46 40142078
FAX INT +46 40947388
ruben@pp.sbbs.se
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D

--=20
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