cupoftea
Advanced Member level 5
Hi,
Been doing thermal testing on the secondary diode of a 20V, 0.8A (non interleave wound) Flyback SMPS (90-265VAC).
This TO220 diode is not heatsunk, but stands with the back of its body about 1mm
away from the earthed metal enclosure wall.
There are no cooling fans in the enclosure.
The enclosure is all metal.
The external ambient was 21degC.
VAC input was 265VAC.
Three different TO220 diodes were tested and compared....
BYVF32-200 (plastic tab TO220, 3 pin)
BYW80-200 (Metal tab TO220, 2 pin)
STTH1502 (plastic tab TO220, 2 pin)
All three diodes had a thermocouple glued to the front of their plastic body.
However, the metal tabbed one also had a thermocouple superglued to its metal tab, and the temperature of this was quickly taken by quickly turning off the power (as the Picologger would have broken otherwise)
Results:
The BYVF32-200 ran coolest at 70degC
The STTH1502 was next coolest at 74degC
The metal tabbed BYW80-200 was hottest at 80degC. (Its metal tab was only a degree less at 79degC).
It seemed a surprise that the metal tabbed one was hottest.
Also, would you say it is unusual that the metal tab temperature was so close to the temperature recorded
at the front on the plastic body of the same metal tabbed diode?
(All diodes were a few degrees hotter at 265VAC compared to 90VAC input)
Been doing thermal testing on the secondary diode of a 20V, 0.8A (non interleave wound) Flyback SMPS (90-265VAC).
This TO220 diode is not heatsunk, but stands with the back of its body about 1mm
away from the earthed metal enclosure wall.
There are no cooling fans in the enclosure.
The enclosure is all metal.
The external ambient was 21degC.
VAC input was 265VAC.
Three different TO220 diodes were tested and compared....
BYVF32-200 (plastic tab TO220, 3 pin)
BYW80-200 (Metal tab TO220, 2 pin)
STTH1502 (plastic tab TO220, 2 pin)
All three diodes had a thermocouple glued to the front of their plastic body.
However, the metal tabbed one also had a thermocouple superglued to its metal tab, and the temperature of this was quickly taken by quickly turning off the power (as the Picologger would have broken otherwise)
Results:
The BYVF32-200 ran coolest at 70degC
The STTH1502 was next coolest at 74degC
The metal tabbed BYW80-200 was hottest at 80degC. (Its metal tab was only a degree less at 79degC).
It seemed a surprise that the metal tabbed one was hottest.
Also, would you say it is unusual that the metal tab temperature was so close to the temperature recorded
at the front on the plastic body of the same metal tabbed diode?
(All diodes were a few degrees hotter at 265VAC compared to 90VAC input)