BCW30LT1G, SBCW30LT1G
www.onsemi.com
6
Figure 17. Thermal Response
t, TIME (ms)
1.0
0.01
r(t) TRANSIENT THERMAL RESISTANCE
(NORMALIZED)
0.01
0.02
0.03
0.05
0.07
0.1
0.2
0.3
0.5
0.7
0.02 0.05 0.1 0.2 0.5 1.0 2.0 5.0 10 20 50 100 200 500 1.0k 2.0k 5.0k 10k 20k
50k
100k
D = 0.5
0.2
0.1
0.05
0.02
0.01
SINGLE PULSE
DUTY CYCLE, D = t
1
/t
2
D CURVES APPLY FOR POWER
PULSE TRAIN SHOWN
READ TIME AT t
1
(SEE AN-569)
Z
q
JA(t)
= r(t) • R
q
JA
T
J(pk)
- T
A
= P
(pk)
Z
q
JA(t)
t
1
t
2
P
(pk)
FIGURE 19
T
J
, JUNCTION TEMPERATURE (°C)
10
4
-4
0
I
C
, COLLECTOR CURRENT (nA)
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
q
JA(t)
, multiply the value obtained from Figure 17 by the
steady state value R
q
JA
.
Example:
The BCW29LT1 is dissipating 2.0 watts peak under the following
conditions:
t
1
= 1.0 ms, t
2
= 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
DT = r(t) x P
(pk)
x R
q
JA
= 0.22 x 2.0 x 200 = 88°C.
For more information, see AN−569.
10
-2
10
-1
10
0
10
1
10
2
10
3
-2
0
0 + 20 + 40 + 60 + 80 + 100 + 120 + 140 + 160
V
CC
= 30 V
I
CEO
I
CBO
AND
I
CEX
@ V
BE(off)
= 3.0 V
