Q36SR12019_08092012

9

THERMAL CONSIDERATIONS

Thermal management is an important part of the system

design. To ensure proper, reliable operation, sufficient

cooling of the power module is needed over the entire

temperature range of the module. Convection cooling is

usually the dominant mode of heat transfer.

Hence, the choice of equipment to characterize the

thermal performance of the power module is a wind

tunnel.

Thermal Testing Setup

Delta’s DC/DC power modules are characterized in

heated vertical wind tunnels that simulate the thermal

environments

encountered

in

most

electronics

equipment. This type of equipment commonly uses

vertically mounted circuit cards in cabinet racks in which

the power modules are mounted.

The

following

figure

shows

the

wind

tunnel

characterization setup. The power module is mounted

on a test PWB and is vertically positioned within the

wind tunnel. The space between the neighboring PWB

and the top of the power module is constantly kept at

6.35mm (0.25’’).

AIR F LOW

MODULE

PWB

AIR VELOCITY

AND AMBIENT

TEMPERATURE

SURED BELOW

THE MODULE

FANCING PWB

Note: Wind Tunnel Test Setup Figure Dimensions are in millimeters and (Inches)

Figure 18: Wind tunnel test setup

Thermal Derating

Heat can be removed by increasing airflow over the

module. To enhance system reliability, the power

module should always be operated below the maximum

operating temperature. If the temperature exceeds the

maximum module temperature, reliability of the unit may

be affected.

THERMAL CURVES

(LONGITUDINAL ORIENTATION)

HOT SPOT

AIRFLOW

NTC RESISTOR

Figure 19: * Hot spot & NTC resistor temperature measured

points

0

40

80

120

160

200

240

25

30

35

40

45

50

55

60

65

70

75

80

85

Output Power(W)

Ambient Temperature (℃)

Q36SR12019(Standard) Output Power vs. Ambient Temperature and Air Velocity

@Vin = 24V (Longitudinal Orientation)

Natural

Convection

100LFM

200LFM

300LFM

400LFM

500LFM

Figure 20: Output power vs. Ambient temperature @Vin=24V

(Longitudinal orientation，Airflow direction from Vin+ to Vout+,

without heat spreader)