DC-DC Converter
QHL600 Series
Application Notes
Thermal Resistance Information
Airflow Derating Graph - Without Heatsink
Power Dissipated vs Ambient Temperature and Air Flow
90
Natural Convection
80
70
60
50
40
30
20
10
0
20 ft./min. (0.1 m/s)
100 ft./min. (0.5 m/s)
Air Flow Rate
Natural Convection 20 ft/min (0.1 m/s)
100 ft/min (0.5 m/s)
Typical Rca
3.82 °C/W
3.23 °C/W
2.71 °C/W
2.28 °C/W
1.92 °C/W
1.68 °C/W
1.50 °C/W
1.35 °C/W
1.23 °C/W
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)
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 (2.5 m/s)
700 ft/min (2.5 m/s)
800 ft/min (2.5 m/s)
0
10
20
30
40
50
60
70
80
90
100
Ambient Temperature ,Ta(Deg. C)
Example (Without Heatsink)
To determine the minimum airflow necessary for a QHL600300S12 operating at an input voltage of 300 V, an output current of 25 A, and a maximum
ambient temperature of 40°C:
Determine Power dissipation (Pd):
Pd =12 V× 25 A×(1-0.89)/0.89 = 37.1
Pd = Pi-Po = Po(1-η)/η,
Where Pi = Input power, Po = Output Power and η = Efficiency
Determine airflow from airflow derating graph using data points for Pd=33.1 W and Ta = 40 °C
Minimum airflow= 600 ft./min.
To check that the maximum case temp of 100 °C is not exceeded:
Maximum temperature rise is
ΔT = Pd × Rca= 37.1 x 1.5 = 55.65°C.
Maximum case temperature is
Tc=Ta+ΔT=95.65°C <100°C.
Where: Rca is the thermal resistance from case to ambient environment. Ta is ambient temperature and Tc is case temperature.
www.xppower.com
5