3kVDC Isolated 2W Single & Dual Output 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 NMK series of DC-DC converters are all 100% production tested at their stated isolation voltage. This is 3kVDC for 1 minute.
A question commonly asked is, “What is the continuous voltage that can be applied across the part in normal operation?”
The NMK series has been recognized by Underwriters Laboratory for functional insulation. 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 sys-
tem. 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 NMK series has toroidal isolation transformers, with no additional insulation between primary and secondary windings of enamelled wire. While
parts can be expected to withstand several times the stated test voltage, the isolation capability does depend on the wire insulation. Any material, including this enamel (typically
polyurethane) 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 be reduced by 20% from specified test voltage.
This consideration equally applies to agency recognized parts rated for better than functional isolation where the wire enamel insulation is always supplemented by a further
insulation system of physical spacing or barriers.
SAFETY APPROVAL
The NMK series has been recognised by Underwriters Laboratory (UL) to UL 60950 for functional insulation in a maximum ambient temperature of 85ºC and/or case temperature
limit of 130ºC. Case temperature measured on the face opposite the pins. File number E151252 applies.
The NMK Series of converters are not internally fused so to meet the requirements of UL 60950 an anti-surge input line fuse should always be used as below:
NMK05xxSC/SAC: 2A
NMK12xxSC/SAC: 0.75A
NMK15xxSC/SAC: 0.75A
NMK24xxSC/SAC: 0.375A
RoHS COMPLIANT INFORMATION
This series is compatible with RoHS soldering systems with a peak wave solder temperature of 260°C for 10 seconds. The pin
termination finish on the SIP package type is Tin Plate, Hot Dipped over Matte Tin with Nickel Preplate. The DIP types are Matte
Tin over Nickel Preplate. Both types in this series are backward compatible with Sn/Pb soldering systems.
For further information, please visit www.murata-ps.com/rohs
APPLICATION NOTES
Minimum Load
The minimum load to meet datasheet specification is 10% of the full rated load across the specified input voltage range. Lower than 10% minimum loading will result in an
increase in output voltage, which may rise to typically double the specified output voltage if the output load falls to less than 5%.
Unbalanced Load
The NMK series offers unbalanced loading capabilities with up to the full 2W available from a single output. However, when operated in this mode there may be a slight
performance decrease in efficiency and load regulation.
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KDC_NMK.E07
Page 3 of 6
NMK Series
3kVDC Isolated 2W Single & Dual Output DC-DC Converters
APPLICATION NOTES (continued)
Ripple & Noise Characterisation Method
All measurement to be taken with the following components connected to the UUT as detailed below.
50 Ohm coax cable, solder connections one end, BNC plug at the other end.
C1
C2
C3
R1
R2
T1
RLOAD
1μF X7R multilayer ceramic capacitor rated at minimum 3 x the output voltage of the UUT
10μF tantalum capacitor rated at minimum 1.5 x the output voltage of the UUT with ESR of less than 100 milliohms at 100 kHz e.g. AVX TPS
100nF multilayer ceramic capacitor, general purpose
450 Ohm resistor, carbon film, ±1%
50 Ohm BNC termination
3T of the coax cable through a ferrite toroid eg Ferroxcube TN32/19/13-3E25
Resistive load at the UUT maximum rating. Connections via twisted wires.
Differential Mode Noise Test Schematic
DC/DC Converter
OSCILLOSCOPE
C1 C2 C3
+
SUPPLY
Input
R1
T1
R2
Y INPUT
+
Output
-
-
R LOAD
EFFICIENCY VS LOAD
NMK05XXSAC
90
80
NMK12XXSAC
90
80
Efficiency (%)
60
50
40
30
20
10
0
0
10
20
30
40
Efficiency (%)
70
15V
12V
9V
5V
70
60
50
40
30
20
10
0
15V
12V
9V
5V
50
Load (%)
60
70
80
90
100
0
10
20
30
40
50
Load (%)
60
70
80
90
100
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KDC_NMK.E07
Page 4 of 6
NMK Series
3kVDC Isolated 2W Single & Dual Output DC-DC Converters
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