(C) ZENE RCLIPPERS: (Standard Tolerance *1 O% and *5%).
Special clipper diodes with opposing Zener junctions built
into the device are available by using the following nomen-
clature:
Device INominal
Description ~“oltage 1
!
Motorola
Example: IM20ZZSI0
Zener
Diode
zs10
~SurLtic
Clipper
Tolerance for each of
the two Zener voltages
(not amatching require- J
Motorola guarantees the zener voltage when measured at 90
seconds while maintaining the lead temperature (TL) at 30°C +l°C,
3/8” from the diode body.
The zener impedance is derived from the60cycle acvo~$age,,:$
which results when anac current having anrmsvalue equal$~LIOYO
of the dc zener current (1ZT or IZK) is superimposed on lz~;~r ‘F*K.
*l\:t\.i.$l}y,
.<.,,>,:’,*,,.,,
,,,!;, ‘1,.;,$
NoTE5–su R’G=cuRRENT{ir)NON-REPET:W$%F4$?:::
?li\t,,+~ii-’
The rating listed in the electrical characteQ&t~+~~*~e is maxi-
mum peak, non-repetitive, reverwsurge curr~F~,~$~2 square wave
or equivalent sine wave pulse of l/12QfgePQ~~&duration super-
imposed on the test current, IZT, per J~@~~&.~lstration, however,
actual device capability isasdescribed~p F$$ures4 and 5.
,*.Xy*,,,..~~})~:?
,,.!,: ‘S:i
‘.\;,,,
t#$$&<$,;$.>,
Since the actual voltage available from agiven :W,$.$!,O@e is
temperature dependent, it is nacessary to detarmin~~u@$!~ tem-
perature under any set of operating conditions in @.d’@~@*~alculate
.~~“1:>
its value. The following procedure is recomm~~,d,:~+,
t~.:..?,,~.,.\.\:*,
,,>l.~,.,.,.- ,:{
6LA is the lead-to-ambi~~j~~ermal resistance (“clw) and
PD is the power di::~~%~~?’’’The value for oLA will vary
and depends on th$,&,~y;c&+hou nting method. eLA is 9an-
erally 30-400C/W~?@$~~ ~k various clips and tie points in
common usa an~.f~w,.p>~tad circuit board wirin9.
..!.,%,,.s.\.:a.t,,
‘\~’.+.\‘.~~
‘!.,.,
The tempera@~&of the lead can also be measured usin9 athermo-
couple placed~~~~%~$ead as close as possible to the tie point. The
1! thermal ~~’’~~%ticted to the tia point is normally iarge enough
so that+~t>yt~$:fl~~t significantly respond to heat surges generated in
the diob,q;as arasult of pulsed operation once steady-state condi-
tio~$ are “&hi evad. Using the maasured value of TL, the junction
.-
temperature and may be found from Figure 2for atrain of
power pulses (L =3/8 inch) or from Figure 3for dc power.
ATJL =eJL PD
For worst-case design, using expected limits of Iz, limits of PD
and the extremas of TJ(ATJ) may be astimatad. Changes in voltage,
VZ, can then ba found from:
AV =OVZATJ
evz, the zener voltage temperature coefficient, is found from
Figures 6 and 7.
Under high power-pulse operation, the zener voltage will vary
with time and may also be affected significantly by tha zaner resist-
ance. For best regulation, keep current excursions as low as possible.
Data of Figure 2should not ba used to compute surga capability.
Surge limitations are given in Figure 4. They are lower than would
be expected by considering only junction temperature, as currant
crowding effects cause temperatures to be extremely high in small
spots resulting in device degradation should the limits of Figure 4
be exceeded.
I