Communication Concepts 2N5194 User Manual
Page 5
2N5194, 2N5195
http://onsemi.com
5
Figure 12. Thermal Response
t, TIME OR PULSE WIDTH (ms)
1.0
0.01
0.01
0.7
0.5
0.3
0.2
0.1
0.07
0.05
0.03
0.02
0.02 0.03
r(t)
, EFFECTIVE
TRANSIENT
THERMAL
RESIST
ANCE
(NORMALIZED)
0.05
0.1
0.2 0.3
0.5
1.0
2.0 3.0
5.0
10
20
30
50
100
200 300
1000
500
q
JC(max)
= 3.12°C/W
D = 0.5
0.2
0.05
0.02
0.01
SINGLE PULSE
0.1
DESIGN NOTE: USE OF TRANSIENT THERMAL RESISTANCE DATA
t
P
P
P
P
P
t
1
1/f
DUTY CYCLE, D = t
1
f =
t1
tP
PEAK PULSE POWER = P
P
Figure 13.
A train of periodical power pulses can be represented by
the model shown in Figure 13. Using the model and the
device thermal response, the normalized effective transient
thermal resistance of Figure 12 was calculated for various
duty cycles.
To find
q
JC
(t), multiply the value obtained from Figure 12
by the steady state value
q
JC
.
Example:
The 2N5193 is dissipating 50 watts under the following
conditions: t
1
= 0.1 ms, t
p
= 0.5 ms. (D = 0.2).
Using Figure 12, at a pulse width of 0.1 ms and D = 0.2,
the reading of r(t
1
, D) is 0.27.
The peak rise in junction temperature is therefore:
D
T = r(t) x P
P
x
q
JC
= 0.27 x 50 x 3.12 = 42.2
_
C