Download Two Devices on a Common Heat Sink

Survey
yes no Was this document useful for you?
   Thank you for your participation!

* Your assessment is very important for improving the work of artificial intelligence, which forms the content of this project

page
1
page
2
page
3
page
4
page
5
page
6
page
7
page
8
page
9
page
10
page
11
page
12
Document related concepts
no text concepts found
Transcript 
Two Devices on a Common Heat Sink
• Thermal Model
ECE 442 Power Electronics
1
T  P (R
JC ,1
 R )  (P  P )R  T
T  P (R
JC ,2
 R )  (P  P )R  T
J ,1
J ,2
D ,1
D ,2
CS ,1
CS ,2
D ,1
D ,1
ECE 442 Power Electronics
D ,2
D ,2
SA
SA
A
A
2
The heat sink Thermal Resistance
T  T  P (R
R 
P P
JC ,1
T  T  P (R
R 
P P
JC ,2
J ,1
A
D ,1
R )
CS ,1
SA
D ,1
J ,2
A
D ,2
D ,2
R )
CS ,2
SA
D ,1
ECE 442 Power Electronics
D ,2
3
If the two devices are identical

1 T  T
R  
R R 
2 P

J
A
SA
JC
CS
D
The heat sink needs to have half of the thermal
resistance required for one device alone.
If the devices are not identical, the required thermal
resistance is the smaller of the two previously computed
values.
ECE 442 Power Electronics
4
Example
• Specify a heat sink for two identical power
devices with a maximum junction
temperature of 150C to operate in an
ambient temperature of 50C. The power
dissipation in each device is 20W and the
junction-to-case thermal resistance is
1.5C/W. The thermal resistance of the
mica insulators is 0.5C/W.
ECE 442 Power Electronics
5

1 T  T
R  
R R 
2 P

J
A
SA
JC
CS
D
1 150  50

R 
 1.5  0.5  1.5C / W

2  20
SA
One device would require RSA = 3.0C/W
ECE 442 Power Electronics
6
Check the Junction Temperature
Device #1
T  P (R
J ,1
D ,1
JC ,1
 R )  (P  P )R  T
CS ,1
D ,1
D ,2
SA
T  20(1.5  0.5)  (20  20)1.5  50
J ,1
T  150C
J ,1
ECE 442 Power Electronics
7
A
For N devices with Common Heat Sink
For the nth device
T
J ,n
 P (R
D ,n
 R )  R  P T
N
JC ,n
CS ,n
T  T  P (R
R 
P
J ,n
SA
A
D ,n
SA n 1
JC ,n
D ,n
A
R )
CS ,n
N
n 1
D ,n
ECE 442 Power Electronics
8
For n Identical Devices

1 T  T
R  
R R 
n P

J
A
SA
JC
CS
D
ECE 442 Power Electronics
9
Example
• Repeat the previous example if there are
three identical devices that dissipate 10W
each.
ECE 442 Power Electronics
10

1 T  T
R  
R R 
n P

J
A
SA
JC
CS
D
1 150  50

R 
 1.5  0.5

3  10
R  2.67C / W
SA
SA
ECE 442 Power Electronics
11
Check the Junction Temperature
Device #1
T  P (R  R )  (P  P  P )R  T
J ,1
D ,1
C ,1
CS ,1
D ,1
D ,2
D ,3
SA
A
T  10(1.5  0.5)  (10  10  10)(2.67)  50
J ,1
T  150.1C / W
J ,1
ECE 442 Power Electronics
12
Related documents