Fig.5 Junction temperature vs. estimated loss (60 V/20 A)
8
7
YG805C06R Forward side
YG805C06R Flyback side
YG865C06R Forward side
YG865C06R Flyback side
New device:
YG865C06R
Conventional device:
YG805C06R
3
2
1
0
20
40
60
80
100
120
140
160
180
Table 2 Ambient temperature when beginning thermal
runaway at LCD-TV 24 V output power supply
Condition : installation cooling fin (30°C /W)
Estimated loss
W
O
(W)
6
5
4
Model number
23-inch LCD-TV
power supply
(+24 Vout /3.5 A)
Forward
Flyback
Approx.
84°C
Approx.
108°C
30-inch LCD-TV
power supply
(+24 Vout /5.0 A)
Forward
Approx.
72°C
Approx.
97°C
Flyback
Approx.
77°C
Approx.
100°C
Conventional device : Approx.
YG805C06R
74°C
New device :
YG865C06R
Approx.
98°C
Junction temperature
T
j
(°C)
Fig.6 Thermal runaway data (TS868C04R, TS808C04R)
45
40
1
DC
2
New device: TS868C04R
30
25
20
15
10
5
0
0
50
100
150
Ambient temperature
T
a
(°C)
200
DC
Conventional device:
TS808C04R
generated in the case of a 24 V power supply
(V
dc
= 380 V,
I
= 5 A) for a liquid crystal display (LCD)
TV.
Figure 5
shows the relationship between junction
temperature (T
j
) and estimated loss (W
o
) for a 60 V/
20 A product. For the sake of comparison, a conven-
tional SBD is also shown. In the region of low
T
j
, the
conventional product has less loss, but because IR has
a large effect on loss at high temperatures, the low
I
R
device achieves less loss than the conventional device
at high temperatures, and at
T
j
= 150°C, the low
I
R
product achieves approximately 76 % less loss than the
conventional product, and its application to higher
efficiency power supplies is anticipated.
Reverse voltage
V
R
(V)
35
increases, and
I
R
becomes more noticeable as it
increases at higher temperatures. As a result, a
vicious cycle ensues in which the increase in
I
R
leads to
an increase in loss, which generates heat in the
element, leading to an increase in
I
R
, etc. In some
cases, this phenomenon ultimately leads to thermal
damage (thermal runaway) of the element.
Figure 6
shows thermal runaway data of the ambient tempera-
ture vs. reverse voltage for a 40 V/30 A product. For
the sake of comparison, a conventional SBD is also
shown. Compared to the conventional product, it can
be seen that the allowable operating temperature
range has been expanded due to the lower
I
R
.
Table 2
shows the estimate thermal runaway temperatures for
a 60 V/ 20 A product in 24 V output power supplies
(V
dc
= 380 V,
I
= 3.5 A or 5 A) for 23-inch and 30-inch
LCD TVs, which approximate actually installation
conditions. Compared to the conventional product, the
thermal runaway ambient temperature is estimated to
be 32 % higher (98°C) at the forward side and 28 %
higher at the flyback side (108°C) in the case of the 23-
inch LCD, and 34 % higher (97°C) at the forward side
and 29 % higher at the flyback side (100°C) in the case
of the 30-inch LCD. With a high maximum allowable
operating temperature, these new devices are well
suited for high temperature applications.
6. Conclusion
An overview of the low
I
R
-SBD and its application
to secondary source rectification applications in switch-
ing power supplies have been presented.
In response to the anticipated future requests for
power supplies that are smaller in size, generate less
loss and have higher efficiency, Fuji Electric intends to
further improve SBD characteristics and to develop a
product line of small package products. Fuji will
continue to make additional improvements in order to
develop high quality products and enrich this product
series.
5. Consideration of the Thermal Runaway Tem-
perature
The temperature of an element rises as its loss
60
Vol. 51 No. 2
FUJI ELECTRIC REVIEW