Data Sheet
QBK020A Series Power Modules; DC-DC Converters
36 – 55 Vdc Input; 12Vdc Output; 20A Output Current
March 27, 2008
The use of Figures 14 - 15 are shown in the following
example:
Thermal Considerations
The power modules operate in a variety of thermal
environments and sufficient cooling should be provided
to help ensure reliable operation.
Example
What is the minimum airflow necessary for a
QBK020A0B operating at VI = 48 V, an output current of
8A, and a maximum ambient temperature of 70 °C in
transverse orientation.
Thermal considerations include ambient temperature,
airflow, module power dissipation, and the need for
increased reliability. A reduction in the operating
temperature of the module will result in an increase in
reliability. The thermal data presented here is based on
physical measurements taken in a wind tunnel.
Solution:
Given: VI = 48V, Io = 8A, TA = 70 °C
Determine required airflow (V) (Use Figure 14):
V = 1.0 m/sec. ( 200 ft./min.) or greater.
Heat-dissipating components are mounted on the top
side of the module. Heat is removed by conduction,
convection and radiation to the surrounding environment.
Proper cooling can be verified by measuring the thermal
reference temperature (TH). Peak temperature (TH)
occurs at the position indicated in Figure 13. For reliable
operation this temperature should not exceed the listed
temperature threshold.
24.0
20.0
16.0
12.0
TH
1.0 m/s (200 ft./min.)
8.0
2.0 m/s (400 ft./min.)
4.0
3.0 m/s (600 ft./min.)
0.0
15
25
35
45
55 65
75
85
95
LOCAL AMBIENT TEMPERATURE, TA (°C)
23.6
(.93)
Figure 14. Output Current Derating for the
QBK020A0B in the Transverse Orientation; Airflow
Direction from Vin(+) to Vin(-); Vin = 48V.
24.0
20.0
16.0
15.7
(.62)
Figure 13. Location of the thermal reference
temperature TH.
12.0
1.0 m/s (200 ft./min.)
8.0
2.0 m/s (400 ft./min.)
The output power of the module should not exceed the
rated power for the module as listed in the Ordering
Information table.
4.0
3.0 m/s (600 ft./min.)
0.0
Although the maximum TH temperature of the power
modules is 110 °C - 115 °C, you can limit this
temperature to a lower value for extremely high
reliability.
15
25
35
45
55
65
75
85
95
LOCAL AMBIENT TEMPERATURE, TA (°C)
Figure 15. Output Current Derating for the
QBK020A0B (Vo = 12V) in the Transverse
Orientation with baseplate; Airflow Direction from
Vin(+) to Vin(–); Vin = 48V.
Heat Transfer via Convection
Increased airflow over the module enhances the heat
transfer via convection. The thermal derating figures
(14-16) show the maximum output current that can be
delivered by each module in the respective orientation
without exceeding the maximum TH temperature versus
local ambient temperature (TA) for air flows of 1 m/s (200
ft./min), 2 m/s (400 ft./min) and 3 m/s (600 ft./min).
LINEAGE POWER
11
LINEAGEPOWER [ LINEAGE POWER CORPORATION ]
