NMH Series

Isolated 2W Dual Output DC/DC Converters

KDC_NMH.E03 Page 3 of 6

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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 NMH series of DC/DC converters are all 100% production tested at their stated isolation voltage. This is 1kVDC for 1 second.

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 NMH 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 NMH series has toroidal isolation transformers, with no additional insulation between primary and secondary windings of enameled 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.

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%.

Capacitive loading and start up

Typical start up times for this series, with a typical input voltage rise time of 2.2μs and output capacitance of 10μF, are shown in the table below. The product

series will start into a capacitance of 47μF with an increased start time, however, the maximum recommended output capacitance is 10μF.

Typical Start-Up Wave Form

Start-up time

Start-up time

μs

μs

NMH0505SC

1072

NMH2405SC

1064

NMH0509SC

2481

NMH2409SC

1544

NMH0512SC

3546

NMH2412SC

4398

NMH0515SC

5380

NMH2415SC

4230

NMH1205SC

672

NMH4805SC

966

NMH1209SC

1152

NMH4809SC

1220

NMH1212SC

1580

NMH4812SC

2822

NMH1215SC

3150

NMH4815SC

4275

RoHS COMPLIANCE INFORMATION

This series is compatible with RoHS soldering systems with a peak wave solder temperature of

300°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