RDF50 Series

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DC-DC Converter

Example (Without Heatsink)

To determine the minimum airflow necessary for a RDF5072S12 operating at an input voltage of 72 V, an output current of 4.20 A, and a maximum

ambient temperature of 40°C:

Determine Power dissipation (Pd):

Pd = Pi-Po = Po(1-

η)/η,

Pd =12 V× 4.2 A×(1-0.87)/0.87=7.53Watts

Where Pi = Input power, Po = Output Power and

η=Efficiency

Determine airflow from airflow derating graph using data points for Pd=7.53 W and Ta = 40 °C

Minimum airflow= 200 ft./min.

To check that the maximum case temp of 100 °C is not exceeded:

Maximum temperature rise is

ΔT = Pd × Rca=7.53x5.4 = 40.67°C.

Maximum case temperature is

Tc=Ta+ΔT=80.67°C <100°C.

Where: Rca is the thermal resistance from case to ambient environment. Ta is ambient temperature and Tc is case temperature.

Note: C4 UNITED CHEMI-CON KXJ series or equivalent, CY1, CY2 MURATA Y1 capacitors or equivalent, L1, L2 BULL WILL URT24-05055H or

equivalent.

08 March 18

Airflow Derating Graph

EMC Filter - EN55032 Emissions and Immunity

+Vo

-Vo

-Vin

GND

+Vin

L1

L2

D1

C1

C4

C2

C3

C6

CY1

CY2

RDF50

CASE

+Vin

+S

-S

-Vin

+Vout

-Vout

C5

C1, C3, C3

C4

C5

C6

CY1, CY2

D1

L1, L2

1 µF/250 V 1812

Ceramic Cap.

82 µF/250 V

KXJ Series

Aluminium Cap.

1 µF/100 V 1206

Ceramic Cap.

22 µF/100 V

Solid Aluminium

Cap.

1500 pF

1.5 KE 180 A

URT24-50055H

5.5 mH

Thermal Resistance Information

Power Dissipated vs Ambient Temperature and Air Flow without heatsink

Ambient Temperature ,Ta(Deg. C)

Natural Convection

20 ft./min. (0.1 m/s)

100 ft./min. (0.5 m/s)

200 ft./min. (1.0 m/s)

300 ft./min. (1.5 m/s)

400 ft./min. (2.0 m/s)

Air Flow Rate

Typical Rca

Natural Convection 20 ft/min (0.1 m/s) 10.1 °C/W

100 ft/min (0.5 m/s)

8.0 °C/W

200 ft/min (1.0 m/s)

5.4 °C/W

300 ft/min (1.5 m/s)

4.4 °C/W

400 ft/min (2.0 m/s)

3.4 °C/W