MMBTA70LT1G Datasheet, PDF (6/7 Pages) ON Semiconductor – General Purpose Transistor

MMBTA70LT1G
1.0
0.7
0.5
D = 0.5
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
P_(pk)
Figure 18.
t₁
t₂
DUTY CYCLE, D = t₁/t₂
D CURVES APPLY FOR POWER
PULSE TRAIN SHOWN
READ TIME AT t₁ (SEE AN−569)
Z_qJA(t) = r(t) • R_qJA
T_J(pk) − T_A = P_(pk) Z_qJA(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
DESIGN NOTE: USE OF THERMAL RESPONSE DATA
V_CC = 30 V
10³
I_CEO
10²
A train of periodical power pulses can be represented by the
model as shown in Figure 18. Using the model and the device
thermal response the normalized effective transient thermal
resistance of Figure 17 was calculated for various duty cycles.
10¹
I_CBO
AND
To find Z_qJA(t), multiply the value obtained from Figure 17
by the steady state value R_qJA.
10⁰
I_CEX @ V_BE(off) = 3.0 V
Example:
Dissipating 2.0 watts peak under the following conditions:
10^-1
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
10^-2
reading of r(t) is 0.22.
- 4 - 2 0 + 20 + 40 + 60 + 80 + 100 + 120 + 140 + 160 _{The peak rise in junction temperature is therefore}
00
T_J, JUNCTION TEMPERATURE (°C)
DT = r(t) x P_(pk) x R_qJA = 0.22 x 2.0 x 200 = 88°C.
Figure 19. Typical Collector Leakage Current ^{For more information, see AN−569.}
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