MJE18004D2
10 Motorola Bipolar Power Transistor Device Data
TYPICAL CHARACTERISTICS
POWER DERATING FACTOR
Figure 30. 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 28 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 28 may be found at any case
temperature by using the appropriate curve on Figure 30.
TJ(pk) may be calculated from the data in Figure 31. 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 inductive
loads, high voltage and current must be sustained simulta-
neously during turn–off with the base–to–emitter junction
reverse biased. The safe level is specified as a reverse–
biased safe operating area (Figure 29). 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
Figure 31. Typical Thermal Response (ZθJC(t)) for MJE18004D2
TYPICAL THERMAL RESPONSE
1
0.01 100.10.01 t, TIME (ms)
0.1
1 100 1000
r(t), TRANSIENT THERMAL RESISTANCE
(NORMALIZED)
R
θ
JC(t) = r(t) R
θ
JC
R
θ
JC = 2.5
°
C/W MAX
D CURVES APPLY FOR POWER
PULSE TRAIN SHOWN
READ TIME AT t1
TJ(pk) – TC = P(pk) R
θ
JC(t)
P(pk)
t1t2
DUTY CYCLE, D = t1/t2
0.05
SINGLE PULSE
0.5
0.2
0.1
0.02