1N4740A ON Semiconductor, 1N4740A Datasheet - Page 6

• Manufacturer Part Number: 1N4740A
• Manufacturer: ON Semiconductor

Specifications of 1N4740A

• Lead Free Status / Rohs Status: Not Compliant

diode is temperature dependent, it is necessary to determine
junction temperature under any set of operating conditions
in order to calculate its value. The following procedure is
recommended:
is the power dissipation. The value for
depends on the device mounting method.
to 40 C/W for the various clips and tie points in common use
and for printed circuit board wiring.
thermocouple placed on the lead as close as possible to the
tie point. The thermal mass connected to the tie point is
normally large enough so that it will not significantly
respond to heat surges generated in the diode as a result of
pulsed operation once steady-state conditions are achieved.
Using the measured value of T
may be determined by:
LA
Since the actual voltage available from a given zener
Lead Temperature, T
The temperature of the lead can also be measured using a
is the lead-to-ambient thermal resistance ( C/W) and P
T
T
L
J
L
=
, should be determined from:
= T
LA
L
P
+ T
D
L
+ T
, the junction temperature
JL
A
.
.
LA
LA
is generally 30
will vary and
APPLICATION NOTE
1N4728A Series
http://onsemi.com
D
6
temperature and may be found as follows:
conditions. For worst-case design, using expected limits of
I
estimated. Changes in voltage, V
from:
from Figure 2.
vary with time and may also be affected significantly by the
zener resistance. For best regulation, keep current
excursions as low as possible.
than would be expected by considering only junction
temperature, as current crowding effects cause temperatures
to be extremely high in small spots, resulting in device
degradation should the limits of Figure 5 be exceeded.
Z
VZ
, limits of P
Under high power-pulse operation, the zener voltage will
Surge limitations are given in Figure 5. They are lower
JL
T
, the zener voltage temperature coefficient, is found
JL
may be determined from Figure 3 for dc power
is the increase in junction temperature above the lead
D
and the extremes of T
T
V =
JL
=
VZ
JL
P
T
D
J
.
.
Z
, can then be found
J
( T
J
) may be