EPR-00011 - 70 W Adapter 22-Jan-01
Page 40 of 46
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- Input and Output Diodes:
For the power diodes the maximum junction temperature is generally 150
o
C.
Depending on the required product life expectancy and the maximum lead
temperature of the PC board material chosen, the actual allowed maximum
junction temperature (T
J
) may be significantly less. Also the junction temperature
(T
J
) will be significantly higher than the tab temperature (T
C
) and must be
computed from the measured tab temperature and the estimated power
dissipation in the device using the thermal impedance junction to case (θ
JC)
of the
device given in its data sheet.
- Magnetic Components:
If the transformer and the other magnetic components use 130
o
C magnet wire in
their construction, then the maximum hot spot temperature is limited to 105
o
C.
Higher operating temperatures are possible with higher temperature rated wire.
Generally, however, the ferrite core temperatures should be limited to near 100
o
C
to maintain the saturation flux density.
13.5 Conclusion:
Careful design and rigorous testing are required to ensure that a design will perform
adequately under high load and high temperature conditions.
