AF-M datasheet(13/20 Pages) GE

13 / 20 page

Lineage Power

Data Sheet

April 2008

36 Vdc to 75 Vdc Input; Dual Outputs; 25 W

DW025 Dual Output-Series Power Modules: dc-dc Converters;

Thermal Considerations (continued)

Basic Thermal Performance

The DW025-Series Dual Output Power Modules have a

separate power stage for each of the outputs. This

means that the maximum operating temperature can

be predicted quite closely by treating each output indi-

vidually and then summing the results. Figures 16

through 21 are used to predict the safe operating con-

dition for many different operating and environmental

conditions.

The method used to determine the maximum ambient

temperature at a given air velocity is a four-step pro-

cess.

1. Find the power dissipated for output 1 by using the

appropriate chart (Figures 16 through 19) for a par-

ticular output condition (IO1).

2. Repeat step 1 for output 2 using Figures 16 through

19.

3. Find the total power dissipated by summing the

power dissipated on each of the outputs:

(PDOUT1 + PDOUT2) = PDtotal

4. Use the total power dissipated with Figure 20 to

determine the maximum ambient temperature at dif-

ferent air velocities.

For example, the DW025AF-M power module operating

at full load on both outputs with 54 V input has a power

dissipation of 3.6 W (from Figure 17) plus 3.1 W (from

Figure 16) for a total of 6.7 W. Using Figure 20, it can

be determined that the maximum ambient temperature

at natural convection that the DW025AF-M can operate

at is approximately 56 °C.

Keep in mind that these are approximations of the tem-

peratures and airﬂows required to keep the case tem-

perature below its maximum rating. The maximum case

temperature at the point shown in Figure 15 must be

kept at 100 °C or less.

Air Velocity

The air velocity required to maintain a desired maxi-

mum case temperature for a given power dissipation

and ambient temperature can be calculated using

Figure 21 and the following equation:

θCA =

where

θCA is the thermal resistance from case-to-ambi-

ent air (°C/W), TC, max is the desired maximum case

temperature (°C), TA is the ambient inlet temperature

(°C), and PDtotal is the total power dissipated from the

module (W).

For example, to maintain a maximum case temperature

of 85 °C with an ambient inlet temperature of 55 °C and

a power dissipation of 6.7 W, the thermal resistance is:

θCA ≤

= 4.5 °C/W

This corresponds to an air velocity greater than

0.46 ms–1 (90 fpm) in Figure 21.

TC max

–

PDtotal

--------------------------------

85 °C

55 °C

–

6.7 W

------------------------------------

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