For locations, phone, fax, E-Mail see back cover
9
Hi-Rel
Grade
MGDM-150 Low Input Series
Gaia Converter FC02-009.08/06 Revision N
©
4
10- Thermal Characteristics
Characteristics
Conditions
Limit or typical
Performances
Operating ambient temperature range
at full load
Ambient temperature *
Minimum
Maximum
- 40°C
see section below
Baseplate temperature
Base plate temperature
Minimum
Maximum
- 40°C
+ 105°C
Storage temperature range
Non functionning
Minimum
Maximum
- 55°C
+ 125°C
Thermal resistance
Baseplate to ambient
Rth(b-a) free air
Typical
8°C/W
Note * : The upper temperature range depends on configuration, the user must assure a max. baseplate temperature of + 105°C.
The MGDM-150 low input series maximum baseplate
temperature at full load must not exceed 105°C. Heat can
be removed from the baseplate via three basic
mechanisms :
• Radiation transfert : radiation is counting for less
than 5% of total heat transfert in majority of case, for
this reason the presence of radient cooling is used as
a safety margin and is not considered.
• Conduction transfert : in most of the applications,
heat will be conducted from the baseplate into an
attached heatsink or heat conducting member; heat is
conducted thruthe interface.
• Convection transfert : convecting heat transfer
into air refers to still air or forced air cooling.
In majority of the applications, heat will be removed from
the baseplate either with :
• heatsink,
• forced air cooling,
• both heatsink and forced air cooling.
To calculate a maximum admissible ambient temperature
the following method can be used.
Knowing the maximum baseplate temparature Tbase =
105°C of the module, the power used Pout and the
efficienc
y h:
• determine the power dissipated by the module Pdiss
that should be evacuated :
Pdiss = Pout(1/h
h
h
h
h
- 1)
(A)
• determine the maximum ambient temperature :
Ta = 105°C - Rth(b-a) x Pdiss
(B)
where Rth(b-a) is the thermal resistance from the
baseplate to ambient.
This thermal Rth(b-a) resistance is the summ of :
• the thermal resistance of baseplate to heatsink
(Rth(b-h)). The interface between baseplate and
heatsink can be nothing or a conducting member, a
thermal compound, a thermal pad.... The value of
Rth(b-h) can range from 0.4°C/W for no interface down
to 0.1°C/W for a thermal conductive member inter-
face.
• the thermal resistance of heatsink to ambient air
(Rth(h-a)), which is depending of air flow and given
by heatsink supplier.
Fischer Elektronic and Thermalloy are heasink manufacturers. «Silpad» © is a registered trademark of Berquist.
Note* : Silpad performance are for Silpad 400 with pressure conditions of 50 Psi. Surface of MGDS-150 series is 5,5 inch2.
The table hereafter gives some example of thermal resistance for different heat transfert configurations.
Heat transfert
Thermal resistance heatsink to air Rth(h-a)
Thermal resistance baseplate to
heatsink
Global
resistance
Free air cooling
only
No Heatsink baseplate only :
8°C/W
No need of thermal pad
8°C/W
Heatsink Thermalloy 6516B :
4,4°C/W
Berquist Silpad* :
0,14°C/W
4,54°C/W
Heatsink Fischer Elektronik SK DC 5159SA :
3,8°C/W
Berquist Silpad* :
0,14°C/W
3,94°C/W
Forced air cooling
200 LFM
No Heatsink baseplate only :
4,5°C/W
No need of thermal pad
4,5°C/W
Heatsink Thermalloy 6516B :
3°C/W
Berquist Silpad* :
0,14°C/W
3,14°C/W
Heatsink Fischer Elektronik SK DC 5159SA :
2,5°C/W
Berquist Silpad* :
0,14°C/W
2,64°C/W
Forced air cooling
400 LFM
No Heatsink baseplate only :
3,2°C/W
No need of thermal pad
3,2°C/W
Heatsink Thermalloy 6516B :
1,75°C/W
Berquist Silpad* :
0,14°C/W
1,89°C/W
Heatsink Fischer Elektronik SK DC 5159SA :
1,7°C/W
Berquist Silpad* :
0,14°C/W
1,84°C/W
Forced air cooling
1000 LFM
No Heatsink baseplate only :
1,7°C/W
No need of thermal pad
1,7°C/W
Heatsink Fischer Elektronik SK DC 5159SA :
0,9°C/W
Berquist Silpad* :
0,14°C/W
1,04°C/W
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