QM48T50015 DC-DC Converter Data Sheet
36-75 VDC Input; 1.5 VDC @ 50A Output
worst-case but consistent scenario for thermal derating pur-
poses.
All measurements requiring airflow were made in Power-
One’s vertical and horizontal wind tunnel facilities using In-
frared (IR) thermography and thermocouples for thermome-
try.
Ensuring components on the converter do not exceed their
ratings is important to maintaining high reliability. If one an-
ticipates operating the converter at or close to the maximum
loads specified in the derating curves, it is prudent to check
actual operating temperatures in the application. Thermo-
graphic imaging is preferable; if this capability is not avail-
able, then thermocouples may be used. Power-One recom-
mends the use of AWG #40 gauge thermocouples to ensure
measurement accuracy. Careful routing of the thermocouple
leads will further minimize measurement error. Refer to Fig-
ure H for optimum measuring thermocouple location.
Fig. H: Location of the thermocouple for thermal testing.
Efficiency
Fig. 3 shows the efficiency vs. load current plot for ambient
temperature of 25ºC, airflow rate of 300 LFM (1.5 m/s) with
vertical mounting and input voltages of 36 V, 48 V and 72 V.
Thermal Derating
Power Dissipation
Load current vs. ambient temperature and airflow rates are
given in Fig.1 and Fig. 2 for vertical and horizontal converter
mounting. Ambient temperature was varied between 25°C
and 85°C, with airflow rates from 30 to 500 LFM (0.15 to 2.5
m/s).
Fig. 4 shows the power dissipation vs. load current plot for
Ta = 25ºC, airflow rate of 300 LFM (1.5 m/s) with vertical
mounting and input voltages of 36 V, 48 V and 72 V.
Start-up
For each set of conditions, the maximum load current was
defined as the lowest of:
Output voltage waveforms, during the turn-on transient using
the ON/OFF pin for full rated load currents (resistive load)
are shown without and with external load capacitance in
Fig. 5 and Fig. 6, respectively.
(i) The output current at which any FET junction temperature
does not exceed a maximum specified temperature (120°C)
as indicated by the thermographic image, or
(ii) The nominal rating of the converter (50 A).
Ripple and Noise
During normal operation, derating curves with maximum FET
temperature less or equal to 120°C should not be exceeded.
Temperature on the PCB at the thermocouple location
shown in Fig. H should not exceed 118°C in order to operate
inside the derating curves.
Fig. 8 shows the output voltage ripple waveform, measured
at full rated load current with a 10 µF tantalum and 1 µF ce-
ramic capacitor across the output. Note that all output volt-
age waveforms are measured across a 1 µF ceramic capaci-
tor.
The input reflected ripple current waveforms are obtained
using the test setup shown in Fig 9. The corresponding
waveforms are shown in Fig. 10 and Fig. 11.
MAY 14, 2004 revised to NOV 13, 2006
Page 7 of 13
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