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8/8/2019 Thermal Re Sis Trance and Colling System
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What is Power? What is Junction Temperature? What is Thermal Resistance? .Electrical Parameters vs Thermal ParametersThermal SpecificationsHeatsinksDC Thermal Calculations
Dissipation and ThermalResistance
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h a t i s P o w e r ? What is Junction Temperature? What is Thermal Resistance? .Electrical Parameters vs Thermal ParametersThermal SpecificationsHeatsinksDC Thermal Calculations
Dissipation and ThermalResistance
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What is Power?
Work is the result of a power appliedfor a given amount of time
W ork = Pow er * Tim e
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What is Power?Electrically, power is a product of a
voltage and a current :
For example, a battery that can deliver 10Aat 12V can supply 120W of power:
Pow e r = Voltag e * C u rren t
P = V * I
P = 1 2 V * 1 0 A = 1 2 0 W
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If a battery can provide 120W of power, the batteryload must consume 120W of power
Some of the power put into the battery load is
absorbed and dissipated as heatFrom Ohms Law (V=IR), the power dissipated as
heat in a load is given by:
What is Power?
1 2 0 WS u p p lie d
1 2 0 WC o n su m e d
= * = ( )* =P V I IR I I2R
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,If a b a tte ry can p rovid e 1 2 0 W of p ow e r th e b attery loa d m u st con su m e 1 2 0 W of p ow er
Some of the power put into the battery load is
absorbed and dissipated as heat
( = ),From Ohm s Law V IR the power dissipated as:heat in a load is given by
What is Power?
120WSupplied
120WConsumed
= * = ( )* =P V I IR I2
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Electrical Power
=P VI=P I
2R
The important things you mustremember here:
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W h a t is Po w e r? h a t i s J u n c t i o n T e m p e r a t u r e ? What is Thermal Resistance?
.Electrical Parameters vs ThermalParametersThermal Specifications
Heatsinks
DC Thermal Calculations
Dissipation and ThermalResistance
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Junction Temperature
Junction temperature is the temperature of the silicon die in an integrated circuit
C Board
S i l i
co
n
d i
e
JunctionTemperature
L e a
d
f r a m e
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This is not the same as the (case or)package temperature or the (ambient or)air temperature
C Board
S i l i
co
n
d i
e
JunctionTemperature
CaseTemperature
AmbientTemperature
L e a
d
f r a m e
&Ambient Case Temperature
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, ,Junction Case and AmbientTemperatures
, (First the system is off no power is being)dissipated , ,The ambient package case and silicon die
junction temperatures are in thermal equilibrium
Tambient = Tcase = Tjunction
C Board
L
e a
d
f r a m e
S i l i
co
n
d i
e
JunctionTemperature
CaseTemperature
AmbientTemperature
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,Next the system is turned onThe silicon die heats up due to the absorbed power being dissipated as heat
Tambient = Tcase < Tjunction
C Board
L
e a
d
f r a m e
S i l i
co
n
d i
e
JunctionTemperature
CaseTemperature
AmbientTemperature
, ,Junction Case and AmbientTemperatures
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Some of the heat is transferred to the package( )case ,The case heats up but not as much as the silicon
die
Tambient < Tcase < Tjunction
C Board
L
e a
d
f r a m e
S i l i
co
n
d i
e
JunctionTemperature
CaseTemperature
AmbientTemperature
, ,Junction Case and AmbientTemperatures
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( ),From the package case some of the heat is transferred to the ambient air ,The air heats up but not as much as the case
T ,ambientoriginal < Tambient < Tcase < Tjunction
C Board
L
e a
d
f r a m e
S i l i
co
n
d i
e
JunctionTemperature
CaseTemperature
AmbientTemperature
, ,Junction Case and AmbientTemperatures
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, :Therefore under almost all conditionsT ,ambientoriginal < Tambient < Tcase