Vicor VIPAC 28 Vdc MIL-COTS - Manual (Page 20)

19 v i c o r p o w e r . c o m
Selecting Heat Sinks
VIPAC Power Systems are rated for operation in ambient
temperatures up to 65˚C with a maximum chassis temperature of
95˚C. Operation within these limits is essential for long life and
users should select an appropriate thermal management system.
The thermal performance of a particular VIPAC chassis
configuration can be approximated from the thermal resistance
of the chassis, ambient operating temperature and total power
dissipation, using a few simple formulas shown below.
Thermal Resistance: Refer to pg 20
Ambient Temperature: User specified, not to exceed 65˚C
Power Dissipation: Calculated as: (Pout/Efficiency) –Pout
Example:
Verify a 400 W, 28 Vdc output VIPAC does not exceed 95˚C
chassis temperature (Tc).
• MVP-B chassis configuration with 1" transverse heat
sink is selected and 200 LFM airflow is provided.
• Thermal resistance ( θ) of 0.47˚C/W is obtained from
the chart on pg 20.
• Ambient operating temperature (TA) specified by the
user is 40˚C.
• VIPAC Power System efficiency ( η) is 80% overall.
Formula:
Tc = (( – Pout ) x θ) + T
A
= (( – 400) x 0.47) + 40
= 87˚C
Conclusion:
This VIPAC will operate in the conditions specified and
not exceed maximum chassis temperature.
Comment:
Efficiency of a particularVIPAC will depend on the
specific output voltages and operating load conditions.
In general the efficiency ofVIPACs with outputs of
5 Vdc or less is approximately 70% and those with
outputs greater than 5 Vdc is 80%. A more accurate
calculation can be derived by summing dissipation of
each DC-DC converter module used in the VIPAC and
the front-end section of theVIPAC (using 95% efficiency
for the front end).
VIPAC Power System Dissipation
Pdiss =
- Pout (n)
1 – n
0.95
Remote Sense
A remote sense feature is provided on outputs configured
with Mini or Maxi sized DC-DC converters. The output
sense connections must be terminated either locally or re-
motely and may not be left open. The sense lines for
VIPACs configured with a single paralleled output must
be terminated to the same point. VIPACs provided with
the optional LugMate connectors are configured for local
sensing via removable jumpers installed at the factory.
The jumpers will need to be removed if access to the
secondary control function is made via mating connector
P/N 16385 and connections will need to be established
for local or remote sensing.
Wire Routing
Avoid routing wires over VIPAC Power System.
Do not bundle Input and Output leads together.
Parallel Outputs
The VIPAC can be configured with parallel modules for
increased power or redundancy. When used for increased
power, short the SC pin to –Sense on one module. This
configures the module as a Booster. The user must
properly connect the output and sense terminals (See
above). At no time operate a paralleled output with a load
applied only to one module! (See Output Connection
Options, pages 10 – 12)
400
0.8
Pout
η
A
PPLICATION
T
IPS
Pout (n)
η(n)
Σ