7
Motorola Bipolar Power Transistor Device Data
POWER DERATING FACTOR
Figure 19. Forward Bias Power Derating
There are two limitations on the power handling ability of
a transistor: average junction temperature and second
breakdown. Safe operating area curves indicate IC–VCE
limits of the transistor that must be observed for reliable
operation; i.e., the transistor must not be subjected to
greater dissipation than the curves indicate. The data of
Figure 19 is based on TC = 25°C; TJ(pk) is variable
depending on power level. Second breakdown pulse limits
are valid for duty cycles to 10% but must be derated when
TC > 25°C. Second breakdown limitations do not derate the
same as thermal limitations. Allowable current at the
voltages shown on Figure 16 may be found at any case
temperature by using the appropriate curve on Figure 18.
TJ(pk) may be calculated from the data in Figures 21 and
22. At any case temperatures, thermal limitations will
reduce the power that can be handled to values less than
the limitations imposed by second breakdown. For induc-
tive loads, high voltage and current must be sustained
simultaneously during turn–off with the base–to–emitter
junction reverse biased. The safe level is specified as a
reverse–biased safe operating area (Figure 17). This rating
is verified under clamped conditions so that the device is
never subjected to an avalanche mode.
TC, CASE TEMPERATURE (
°
C)
1.0
0.8
0.6
0.4
0.2
016014012010080604020
SECOND
BREAKDOWN
DERATING
THERMAL
DERATING
TYPICAL STATIC CHARACTERISTICS
Figure 20. Dynamic Saturation
Voltage Measurements Figure 21. Inductive Switching Measurements
TYPICAL SWITCHING CHARACTERISTICS
(IB1 = IB2 FOR ALL CURVES)
TIME
10
4
0820 6
8
6
2
4
9
7
5
3
1
1 3 5 7
VCE
0 V
IB
90% IB
1
µ
s
3
µ
s
dyn 1
µ
s
dyn 3
µ
s
IB
IC
Vclamp
tsi
tc
tfi
90% IC
10% IC
90% IB1
10% Vclamp
TIME