QLS25 DC-DC Series Data Sheet
where A and B are constants from the table below,
and ΔV is the absolute value of the desired change
in the output voltage in Volts.
3. The QLS25 Series converters will trim down further than the
10% limit. In general, this is permissible. The user must
confirm that the results are acceptable in the application.
Industry Standard Positive Trim (suffix –T)
The -T option units trim up with a resistor from the
TRIM pin to the +Sense pin and trim down with a
resistor from the TRIM pin to the –Sense pin as
shown in the Figure 9.
The QLS25 Series converters feature 1500 Volt DC
isolation from input to output. The input to output
resistance is greater than 10MOhm. These
converters are provided with Basic insulation
between input and output circuits according to all
IEC60950 based standards. Nevertheless, if the
system using the converter needs to receive safety
agency approval, certain rules must be followed in
the design of the system. In particular, all of the
creepage and clearance requirements of the end-use
safety requirements must be observed. These
documents include UL60950 - CSA60950-00 and
EN60950, although other or additional requirements
may be needed for specific applications.
Figure 9. QLS25 Series Positive Trim Schematic
The equations below determine the trim resistor
value required to achieve a ΔV change in the output
− 2⎟⎞ ,
where ΔV% is the output voltage change expressed
in percents of the nominal output voltage, Vout.
1. When the output voltage is trimmed up, the output power
from the converter must not exceed its maximum rating. The
power is determined by measuring the output voltage on the
output pins, and multiplying it by the output current.
2. In order to avoid creating apparent load regulation
degradation, it is important that the trim resistors are
connected directly to the remote sense pins, and not to the
load or to traces going to the load.
The QLS25 Series converters have no internal fuse.
The external fuse must be provided to protect the
system from catastrophic failure as shown in
Figure 7. The fuse with a rating not greater than 4A
is recommended. The user can select a lower rating
fuse based upon the highest inrush transient at the
maximum input voltage and the maximum input
current of the converter, which occurs at the
minimum input voltage. Both input traces and the
chassis ground trace (if applicable) must be capable
of conducting a current of 1.5 times the value of the
fuse without opening. The fuse must not be placed
in the grounded input line, if any.
In order for the output of the QLS25 Series converter
to be considered as SELV (Safety Extra Low
Voltage) or TNV-1, according to all IEC60950 based
standards, one of the following requirements must be
met in the system design:
• If the voltage source feeding the module is SELV
or TNV-2, the output of the converter may be
grounded or ungrounded.
• If the voltage source feeding the module is ELV,
the output of the converter may be considered
SELV only if the output is grounded per the
requirements of the standard.
• If the voltage source feeding the module is a
Hazardous Voltage Secondary Circuit, the
voltage source feeding the module must be
provided with at least Basic insulation between
the source to the converter and any hazardous
voltages. The entire system, including the
QLS25 converter, must pass a dielectric
withstand test for Reinforced insulation. Design
of this type of systems requires expert
SEP 12, 2003 revised to OCT 26, 2006
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