NXJ1 Series
Isolated 1W Single Output SM DC/DC Converters
TECHNICAL NOTES
ISOLATION VOLTAGE
‘Hi Pot Test’, ‘Flash Tested’, ‘Withstand Voltage’, ‘Proof Voltage’, ‘Dielectric Withstand Voltage’ & ‘Isolation Test Voltage’ are all terms that relate to the same thing, a test voltage,
applied for a specified time, across a component designed to provide electrical isolation, to verify the integrity of that isolation.
Murata Power Solutions NXJ1 series of DC/DC converters are all 100% production tested at their stated isolation voltage. This is 4.2kVDC for 1 minute.
A question commonly asked is, “What is the continuous voltage that can be applied across the part in normal operation?”
For a part holding no specific agency approvals, such as the NXJ1 series, both input and output should normally be maintained within SELV limits i.e. less than 42.4V peak, or
60VDC. The isolation test voltage represents a measure of immunity to transient voltages and the part should never be used as an element of a safety isolation system. The part
could be expected to function correctly with several hundred volts offset applied continuously across the isolation barrier; but then the circuitry on both sides of the barrier must
be regarded as operating at an unsafe voltage and further isolation/insulation systems must form a barrier between these circuits and any user-accessible circuitry according to
safety standard requirements.
REPEATED HIGH-VOLTAGE ISOLATION TESTING
It is well known that repeated high-voltage isolation testing of a barrier component can actually degrade isolation capability, to a lesser or greater degree depending on materials,
construction and environment. The NXJ1 series has a PCB embedded isolated transformer, using FR4 as an insolation barrier between primary and secondary windings. While parts
can be expected to withstand several times the stated test voltage, the isolation capability does depend on the FR4 insulation properties. Any material, including FR4 is susceptible
to eventual chemical degradation when subject to very high applied voltages thus implying that the number of tests should be strictly limited. We therefore strongly advise against
repeated high voltage isolation testing, but if it is absolutely required, that the voltage should be reduced by 20% from specified test voltage.
This consideration equally applies to agency recognized parts rated for better than functional isolation where the insulation is always supplemented by a further insulation system
of physical spacing or barriers.
SAFETY APPROVAL
ANSI/AAMI ES60601-1
The NXJ1 series is pending recognition by Underwriters Laboratory (UL) to meet ANSI/AAMI ES60601-1 medical safety standard providing the following MOOP (Means Of Operator
Protection), and MOPP (Means Of Patient Protection). 2 MOOP and 1 MOPP based upon a working voltage of 200Vrms.
UL 60950
The NXJ1 series is pending recognition by Underwriters Laboratory (UL) to UL 60950 for reinforced insulation to a working voltage of 200Vrms.
FUSING
The NXJ1 Series of converters are not internally fused so to meet the requirements of UL an anti-surge input line fuse should always be used with ratings as defined below.
Input Voltage, 3.3V: 1A
Input Voltage, 5V: 0.5A
Input Voltage, 12V: 0.25A
All fuses should be UL recognized and rated to at least the maximum allowable DC input voltage.
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