QM48T40033
© 2015 Bel Power Solutions, Inc.
866.513.2839
tech.support@psbel.com
BCD.00632_AA
General Information
The converter has been characterized for many operational aspects, to include thermal derating (maximum load current as
a function of ambient temperature and airflow) for vertical and horizontal mounting, efficiency, start-up and shutdown
parameters, output ripple and noise, transient response to load step-change, overload and short circuit.
The following pages contain specific plots or waveforms associated with the converter. Additional comments for specific
data are provided below.
Test Conditions
All data presented were taken with the converter soldered to a test board, specifically a 0.060” thick printed wiring board
(PWB) with four layers. The top and bottom layers were not metalized. The two inner layers, comprising two-ounce
copper, were used to provide traces for connectivity to the converter.
The lack of metalization on the outer layers as well as the limited thermal connection ensured that heat transfer from the
converter to the PWB was minimized. This provides a worst-case but consistent scenario for thermal derating purposes.
All measurements requiring airflow were made in Bel Power Solutions’s vertical and horizontal wind tunnel facilities using
Infrared (IR) thermography and thermocouples for
thermometry.
Ensuring components on the converter do not exceed their ratings is important to maintaining high reliability. If one
anticipates 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. Thermographic imaging is preferable; if this capability is not available, then
thermocouples may be used. Bel Power Solutions recommends the use of AWG #40 gauge thermocouples to ensure
measurement accuracy. Careful routing of the thermocouple leads will further minimize measurement error. Refer to Figure
H for optimum measuring thermocouple location.
Thermal Derating
Load current vs. ambient temperature and airflow rates are given in Figs. 1 and 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).
For each set of conditions, the maximum load current was defined as the lowest of:
(i) The output current at which either any FET junction temperature did not exceed a maximum specified temperature
(120 °C) as indicated by the thermographic image, or
(ii) The nominal rating of the converter (40 A).
During normal operation, derating curves with maximum FET temperature less than 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.
Efficiency
Fig. 3 shows the efficiency vs. load current plot for ambient temperature of 25 ºC, airflow rate of 300 LFM (1.5 m/s) with
vertical mounting and input voltages of 36 V, 48 V and 72 V. Also, a plot of efficiency vs. load current, as a function of
ambient temperature with Vin = 48 V, airflow rate of 200 LFM (1 m/s) with vertical mounting is shown in Fig. 4.
Power Dissipation
Fig. 5 shows the power dissipation vs. load current plot for Ta = 25 ºC, airflow rate of 300 LFM (1.5 m/s) with vertical
mounting and input voltages of 36 V, 48 V and 72 V. Also, a plot of power dissipation vs. load current, as a function of
ambient temperature with Vin = 48 V, airflow rate of 200 LFM (1 m/s) with vertical mounting is shown in Fig. 6.
Start-up
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. 7 and Fig. 8, respectively.
Ripple and Noise
Fig. 10 shows the output voltage ripple waveform, measured at full rated load current with a 10µF tantalum and 1µF
ceramic capacitor across the output. Note that all output voltage waveforms are measured across a 1F ceramic capacitor.
The input reflected ripple current waveforms are obtained using the test setup shown in Fig. 11. The corresponding
waveforms are shown in Fig. 12 and Fig. 13.