MMBTA70LT1 Datasheet, PDF (5/8 Pages) Motorola, Inc – General Purpose Transistor

1.0
0.7
0.5
D = 0.5
MMBTA70LT1
0.3
0.2
0.2
0.1
0.1
0.07
0.05
0.05
0.02
0.03
0.02
0.01
SINGLE PULSE
0.01
0.01 0.02 0.05 0.1 0.2 0.5 1.0 2.0
FIGURE 19
DUTY CYCLE, D = t1/t2
P(pk)
D CURVES APPLY FOR POWER
PULSE TRAIN SHOWN
t1
READ TIME AT t1 (SEE AN–569)
t2
Z_θJA(t) = r(t) • R_θJA
TJ(pk) – TA = P(pk) Z_θJA(t)
5.0 10 20 50 100 200
t, TIME (ms)
500 1.0 k 2.0 k 5.0 k 10 k 20 k 50 k 100 k
Figure 17. Thermal Response
104
VCC = 30 V
103
102
ICEO
101
ICBO
AND
100
ICEX @ VBE(off) = 3.0 V
10–1
10–2
–4 –2
00
0 + 20 + 40 + 60 + 80 + 100 + 120 + 140 + 160
TJ, JUNCTION TEMPERATURE (°C)
Figure 18. Typical Collector Leakage Current
DESIGN NOTE: USE OF THERMAL RESPONSE DATA
A train of periodical power pulses can be represented by the model
as shown in Figure 19. Using the model and the device thermal
response the normalized effective transient thermal resistance of
Figure 17 was calculated for various duty cycles.
To find Z_θJA(t), multiply the value obtained from Figure 17 by the
steady state value R_θJA.
Example:
Dissipating 2.0 watts peak under the following conditions:
t1 = 1.0 ms, t2 = 5.0 ms (D = 0.2)
Using Figure 17 at a pulse width of 1.0 ms and D = 0.2, the reading of
r(t) is 0.22.
The peak rise in junction temperature is therefore
∆T = r(t) x P(pk) x R_θJA = 0.22 x 2.0 x 200 = 88°C.
For more information, see AN–569.
Motorola Small–Signal Transistors, FETs and Diodes Device Data
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