UEI30 Series
30W Isolated Wide-Range DC/DC Converters
the C
BUS
and L
BUS
components simulate a typical DC voltage bus. Your specific
system configuration may require additional considerations. Please note that the
values of C
IN
, L
BUS
and C
BUS
will vary according to the specific converter model.
In critical applications, output ripple and noise (also referred to as periodic
and random deviations or PARD) may be reduced by adding filter elements
such as multiple external capacitors. Be sure to calculate component tem-
perature rise from reflected AC current dissipated inside capacitor ESR. In the
figure, the two copper strips simulate real-world printed circuit impedances
between the power supply and its load. In order to minimize circuit errors and
standardize tests between units, scope measurements should be made using
BNC connectors or the probe ground should not exceed one half inch and
soldered directly to the fixture.
located adjacent to the switching controller, approximately in the center of the
unit. See the Performance and Functional Specifications.
CAUTION: If you operate too close to the thermal limits, the converter may
shut down suddenly without warning. Be sure to thoroughly test your applica-
tion to avoid unplanned thermal shutdown.
Temperature Derating Curves
The graphs in the next section illustrate typical operation under a variety of condi-
tions. The Derating curves show the maximum continuous ambient air temperature
and decreasing maximum output current which is acceptable under increasing
forced airflow measured in Linear Feet per Minute (“LFM”). Note that these are
AVERAGE measurements. The converter will accept brief increases in temperature
and/or current or reduced airflow as long as the average is not exceeded.
Note that the temperatures are of the ambient airflow, not the converter
itself which is obviously running at higher temperature than the outside air.
Also note that very low flow rates (below about 25 LFM) are similar to “natural
convection,” that is, not using fan-forced airflow.
C2
SCOPE
R
LOAD
COPPER STRIP
+OUTPUT
C1
−OUTPUT
COPPER STRIP
C1 = 0.1μF CERAMIC
C2 = 10μF LOW ES
LOAD 2-3 INCHES (51-76mm) FROM MODULE
MPS makes Characterization measurements in a closed cycle wind
tunnel with calibrated airflow. We use both thermocouples and an infrared
camera system to observe thermal performance. As a practical matter, it is
quite difficult to insert an anemometer to precisely measure airflow in most
applications. Sometimes it is possible to estimate the effective airflow if you
thoroughly understand the enclosure geometry, entry/exit orifice areas and the
fan flowrate specifications. If in doubt, contact MPS to discuss placement and
measurement techniques of suggested temperature sensors.
CAUTION: If you routinely or accidentally exceed these Derating guidelines,
the converter may have an unplanned Over Temperature shut down. Also, these
graphs are all collected at slightly above Sea Level altitude. Be sure to reduce
the derating for higher density altitude.
Output Overvoltage Protection
This converter monitors its output voltage for an over-voltage condition using
an on-board electronic comparator. The signal is optically coupled to the pri-
mary side PWM controller. If the output exceeds OVP limits, the sensing circuit
will power down the unit, and the output voltage will decrease. After a time-out
period, the PWM will automatically attempt to restart, causing the output volt-
age to ramp up to its rated value. It is not necessary to power down and reset
the converter for the this automatic OVP-recovery restart.
If the fault condition persists and the output voltage climbs to excessive
levels, the OVP circuitry will initiate another shutdown cycle. This on/off cycling
is referred to as “hiccup” mode. It safely tests full current rated output voltage
without damaging the converter.
Output Fusing
The converter is extensively protected against current, voltage and temperature
extremes. However your output application circuit may need additional protection.
In the extremely unlikely event of output circuit failure, excessive voltage could be
applied to your circuit. Consider using an appropriate fuse in series with the output.
Output Current Limiting
As soon as the output current increases to approximately 125% to 150% of
its maximum rated value, the DC/DC converter will enter a current-limiting
mode. The output voltage will decrease proportionally with increases in output
Figure 3 – Measuring Output Ripple and Noise (PARD)
Floating Outputs
Since these are isolated DC/DC converters, their outputs are “floating” with
respect to their input. The essential feature of such isolation is ideal ZERO
CURRENT FLOW between input and output. Real-world converters however do
exhibit tiny leakage currents between input and output (see Specifications).
These leakages consist of both an AC stray capacitance coupling component
and a DC leakage resistance. When using the isolation feature, do not allow
the isolation voltage to exceed specifications. Otherwise the converter may
be damaged. Designers will normally use the negative output (-Output) as
the ground return of the load circuit. You can however use the positive output
(+Output) as the ground return to effectively reverse the output polarity.
Minimum Output Loading Requirements
These converters employ a synchronous rectifier design topology. All models
regulate within specification and are stable under no load to full load conditions.
Operation under no load might however slightly increase output ripple and noise.
Thermal Shutdown
To prevent many over temperature problems and damage, these converters
include thermal shutdown circuitry. If environmental conditions cause the
temperature of the DC/DC’s to rise above the Operating Temperature Range
up to the shutdown temperature, an on-board electronic temperature sensor
will power down the unit. When the temperature decreases below the turn-on
threshold, the converter will automatically restart. There is a small amount of
hysteresis to prevent rapid on/off cycling. The temperature sensor is typically
www.murata-ps.com
Technical enquiries
email: sales@murata-ps.com, tel:
+1 508 339 3000
MDC_UEI Series 30W.A01
Page 7 of 11
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