QSB15048W Series

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DC-DC Converter

Output Voltage Adjustment Examples

Thermal Resistance Information

Example (Without Heatsink)

As an example, to trim-down the output voltage of 24 V module

(QS15048WS24) by 5% to 22.8 V, Rd resistor is calculated as follows: Δ%=5%

And, to trim-up the output voltage of 24 V module

(QS15048WS24) by 5% to 25.2 V, Ru resistor is calculated as follows: Δ%=5%

To determine the minimum airflow necessary for a QS15048WS24 operating at an input voltage of 36 V, an output current of 6.25 A, and a maximum

ambient temperature of 30°C:

Determine Power dissipation (Pd):

Pd = Pi-Po = Po(1-

η)/η,

Pd =24 V× 6.25 A×(1-0.895)/0.895=17.6Watts

Where Pi = Input power, Po = Output Power and

η=Efficiency

Determine airflow from airflow derating graph using data points for Pd=19.5 W and Ta = 30 °C

Minimum airflow= 400 ft./min.

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

Maximum temperature rise is

ΔT = Pd × Rca=17.6×3.64=64°C.

Maximum case temperature is

Tc=Ta+ΔT=94°C <100°C.

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

Note: C1, C2 NICHICON PW series aluminum capacitors, CY1, CY2

are ceramic capacitors, L1 Core use SM CM20*12*10 Winding 5 turns

(double wire).

Power Dissipated vs Ambient Temperature and Air Flow

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)

500 ft./min. (2.5 m/s)

600 ft./min. (3.0 m/s)

700 ft./min. (3.5 m/s)

800 ft./min. (4.0 m/s)

Air Flow Rate

Typical Rca

Natural Convection 20 ft/min (0.1 m/s)

7.12 °C/W

100 ft/min (0.5 m/s)

6.21 °C/W

200 ft/min (1.0 m/s)

5.17 °C/W

300 ft/min (1.5 m/s)

4.29 °C/W

400 ft/min (2.0 m/s)

3.64 °C/W

500 ft/min (2.5 m/s)

2.96 °C/W

600 ft/min (2.5 m/s)

2.53 °C/W

700 ft/min (2.5 m/s)

2.37 °C/W

800 ft/min (2.5 m/s)

2.19 °C/W

Model Number

C1

C2

CY1

CY2

L1

L2

QSB15048WS12 220 µF/100 V 220 µF/100 V 1500 pF 1500 pF 0.2 mH Short

QSB15048WS15 220 µF/100 V 220 µF/100 V 1500 pF 1500 pF 0.2 mH Short

QSB15048WS24 220 µF/100 V 220 µF/100 V 1500 pF 1500 pF 0.2 mH Short

QSB15048WS28 220 µF/100 V 220 µF/100 V 1500 pF 1500 pF 0.2 mH Short

QSB15048WS48 220 µF/100 V 220 µF/100 V 1500 pF 1500 pF 0.2 mH Short

10 Oct 17

Airflow Derating Graph

Conducted Emissions

C2

C4

L1

L2

+Vin

QSB

-Vin

+Vout

-Vout

CY2

CY1

C1

+Vin

-Vin

Load

- 100 kΩ

(24 - 5% x 24 - 2.5)

20x

=

5% x 24

= 238.3 kΩ

kΩ

(2.5

0.46 x 100

100 + 5.6

-

-

20x

=

5% x 24

5.6 x 100

100 + 5.6

k