DC/DC Converter

URF1D_QB Series

2014.12.09-A/1

Page 6 of 8

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5. Thermal design

The maximum operating temperature of base- plate TB is 100 ℃,aslong asthe user's thermal system keeps TB <100 ℃, the converter

can deliver its full rated power. A power derating curve can be calculated for any heatsink that is attached to the base-plate of the

converter. It is only necessary to determine the thermal resistance, Rth(B-A), of the chosen heatsink between the base-plate and the

ambient air for a given airflow rate. This information is usually available from the heatsink vendor. The following formula can the be used to

determine the maximum power the converter can dissipate for a given thermal condition if its base-plate is to be no higher than 100 ºC.

）

（

℃

A

-

B

A

max

th

100

R

T

P

diss

−

=

The maximum load operating power of power supply module at a certain ambient temperature can be calculated by the power

dissipation, Formula is as follows:

)

1

1

(

max

max

−

=

η

diss

P

Po

Therefore, customers can according to the actual application to choose the right heatsink.

6. Application of Trim and calculation of Trim resistance

0V

Trim

+Vot

0V

Trim

+Vot

Trim up

Trim down

Applied circuits of Trim (Part in broken line is the interior of models)

Calculation formula of Trim resistance:

up:

a=

Vref

Vo’-Vref

R=

T

R-a

2

down:

a=

Vref

Vo’-Vref

R=

T

R-a

1

voltage.

table 1

Vo

Parameter

24(VDC)

R1(KΩ)24.87

R2(KΩ)2.87

R3(KΩ)20

Vref(V)

2.5

7. The product does not support in parallel and hot-plug use