Dutycycle:δ = 0.6
(δIF/dt)ON= 200 A/µs
(dIF/dt)OFF=500 A/µs
Tj=125°C
f = 30 kHz
In these conditions the reverse recovery
characteristics of the diodes are given in fig.7 :
The losses of the table fig.8 are calculatedby
using relationsgiven in part2.
In this type of application,the TURBOSWITCH ”A”
is obviouslythe betterchoice.
Example2 : In this example, the diode is used
as a rectifierdiode with the following conditions:
IF=12A
(dIF/dt)ON= (dIF/dt)OFF= 100 A/µs
Vaa= 350V
Tj =125°C
δ=0.8
f = 20 kHz
The estimatedlosses are summarized in the table
fig.9
In thisapplication,we haveto takeinto accountthe
leakage inductance and the fact that a very soft
diode is requiredto limit the overvoltage.The total
losses are 10% lower with the STTB1206D,
therefore the TURBOSWITCH ”B” is the best
choice.
IV. CONCLUSION
This note shows how to calculate the different
losses due to the diodes in basic power switching
circuits. These calculations can be doneby using
the parameters given in the datasheet of the
TURBOSWITCH ”A” and theTURBOSWITCH ”B”.
In most of cases, it is easy to choosebetween the
”A” typeand the ”B” type.
The ”A” type is very efficient in freewheel diode
applications with high frequencies (f > 10 kHz).
The ”B” type is better when conductionlosses are
predominant like in the case of the power factor
corrector circuit in discontinuous mode (low
(diF/dt)OFF), or for applications where very high
soft recovery behaviour is required (commutation
with seriesinductances,for example).
TYPE IRM S
STTA1206D 16 A 0.42
STTB1206D 30 A 0.90
Fig.7 : Reverse recovery characteristics of
STTA1206D and STTB1206D with the conditions
of the example 1
TYPE Con-
duction
losses
Switch
ON
losses
Switch
OFF
losses
Tran-
sistor
losses
Total
losses
STTA1206D 9 W 0.1 W 0.43 W 9.5 W 19 W
STTB1206D 7.8 W 0.07 W 3.2 W 29.8 W 40.9 W
Fig.8 : Comparison between STTB1206D and
STTA1206Din afreewheel diode function
TYPE Conduc-
tion
losses
Switch
ON
losses
Switch
OFF
losses
Total
losses
STTA1206D 14.4 W negligible 0.2 W 14.6 W
STTB1206D 12.4 W negligible 1 W 13.4 W
Fig.9 : Comparison between STTA1206D an
STTB1206Din arectifier function
APPLICATION NOTE
4/5