For locations, phone, fax, E-Mail see back cover
9
Hi-Rel
Grade
MGDM-75 Series
Gaia Converter FC03-032.12/13 Revision L
©
4
10- Thermal Characteristics
Characteristics Conditions Limit or typical Performances
Operating ambient temperature range
at full load Ambient temperature * Minimum
Maximum
- 40°C
see 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 11°C/W
Note * : The upper temperature range depends on configuration, the user must ensure a max. baseplate temperature of + 105°C.
The following discussion will help designer to determine
the thermal characteristics and the operating temperature.
The MGDM-75 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 thru the 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
efficiency η :
• determine the power dissipated by the module Pdiss
that should be evacuated :
Pdiss = Pout(1/ηη
ηη
η - 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.
The table hereafter gives some example of thermal resistance for different heat transfert configurations.
Radian and Thermaflo are heasink manufacturers. «Silpad» © is a registered trademark of Bergquist.
Note* : Silpad performance are for Silpad 400 with pressure conditions of 50 Psi. Surface of MGDS-75 series is 3,3 inch2.
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 : 11°C/W No need of thermal pad 11°C/W
Heatsink Thermaflo 4245OOBOOOO : 7,64°C/W Bergquist Silpad* : 0,21°C/W 7,85°C/W
Heatsink Thermaflo 4248OOBOOOO : 3,5°C/W Bergquist Silpad* : 0,21°C/W 3,71°C/W
Forced air cooling
200 LFM
No Heatsink baseplate only : 6,9°C/W No need of thermal pad 6,9°C/W
Heatsink Radian HS1568EX : 3,5°C/W Bergquist Silpad* : 0,21°C/W 3,71°C/W
Heatsink Thermaflo 4248OOBOOOO : 2,8°C/W Bergquist Silpad* : 0,21°C/W 3,01°C/W
Forced air cooling
400 LFM
No Heatsink baseplate only : 4,8°C/W No need of thermal pad 4,8°C/W
Heatsink Radian HS1568EX : 2°C/W Bergquist Silpad* : 0,21°C/W 2,21°C/W
Heatsink Thermaflo 4248OOBOOOO : 1,8°C/W Bergquist Silpad* : 0,21°C/W 2,01°C/W
Forced air cooling
1000 LFM
No Heatsink baseplate only : 2,8°C/W No need of thermal pad 2,8°C/W
Heatsink Thermaflo 4248OOBOOOO : 1°C/W Bergquist Silpad* : 0,21°C/W 1,21°C/W