BCW72LT1G, SBCW72LT1G
www.onsemi.com
6
Figure 19. 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 19A
Figure 19A.
T
J
, JUNCTION TEMPERATURE (°C)
10
4
-4
0
I
C
, COLLECTOR CURRENT (nA)
Figure 20.
V
CE
, COLLECTOR-EMITTER VOLTAGE (VOLTS)
400
2.0
I
C
, COLLECTOR CURRENT (mA)
DESIGN NOTE: USE OF THERMAL RESPONSE DATA
A train of periodical power pulses can be represented by the model
as shown in Figure 19A. Using the model and the device thermal
response the normalized effective transient thermal resistance of
Figure 19 was calculated for various duty cycles.
To find Z
q
JA(t)
, multiply the value obtained from Figure 19 by the
steady state value R
q
JA
.
Example:
The MPS3904 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 19 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.
The safe operating area curves indicate I
C
−V
CE
limits of the
transistor that must be observed for reliable operation. Collector load
lines for specific circuits must fall below the limits indicated by the
applicable curve.
The data of Figure 20 is based upon T
J(pk)
= 150°C; T
C
or T
A
is
variable depending upon conditions. Pulse curves are valid for duty
cycles to 10% provided T
J(pk)
≤ 150°C. T
J(pk)
may be calculated from
the data in Figure 19. At high case or ambient temperatures, thermal
limitations will reduce the power that can be handled to values less
than the limitations imposed by second breakdown.
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 Vdc
I
CEO
I
CBO
AND
I
CEX
@ V
BE(off)
= 3.0 Vdc
T
A
= 25°C
CURRENT LIMIT
THERMAL LIMIT
SECOND BREAKDOWN LIMIT
1.0 ms
10 ms
T
C
= 25°C
1.0 s
dc
dc
4.0
6.0
10
20
40
60
100
200
4.0 6.0 8.0 10 20
40
T
J
= 150°C
100 ms
