Technical enquiries email: mk@murata-ps.com, tel: +44 (0)1908 615232

MER1 Series

1kVDC Isolated 1W Single Output DC/DC Converters

2009/09/15

KDC_MER1.A01 Page 4 of 6

www.murata-ps.com

APPLICATION NOTES (continued)

Output Ripple Reduction

By using the values of inductance and capacitance stated, the output ripple at the rated load is lowered to 5mV p-p max.

Component selection

Capacitor: It is required that the ESR (Equivalent Series Resistance) should be as low as possible, ceramic types are recommended.

The voltage rating should be at least twice (except for 15V output), the rated output voltage of the DC/DC converter.

Inductor: The rated current of the inductor should not be less than that of the output of the DC/DC converter. At the rated current, the DC resistance of the inductor

should be such that the voltage drop across the inductor is <2% of the rated voltage of the DC/DC converter. The SRF (Self Resonant Frequency) should be

>20MHz.

DC

DC

L

C

Load

Power

Source

Inductor

Capacitor

L, μH

SMD

Through Hole

C, μF

MER1S0505SC

10

82103C

11R103C

4.7

MER1S0509SC

22

82223C

11R223C

2.2

MER1S0512SC

47

82473C

11R473C

1

MER1S0515SC

47

82473C

11R473C

1

MER1S1205SC

10

82103C

11R103C

4.7

MER1S1209SC

22

82223C

11R223C

2.2

MER1S1212SC

47

82473C

11R473C

1

MER1S1215SC

47

82473C

11R473C

1

MER1S1505SC

10

82103C

11R103C

4.7

MER1S1509SC

22

82223C

11R223C

2.2

MER1S1512SC

47

82473C

11R473C

1

MER1S1515SC

47

82473C

11R473C

1

MER1S2405SC

10

82103C

11R103C

4.7

MER1S2409SC

22

82223C

11R223C

2.2

MER1S2412SC

47

82473C

11R473C

1

MER1S2415SC

47

82473C

11R473C

1

MER1S4805SC

10

82103C

11R103C

4.7

MER1S4809SC

22

82223C

11R223C

2.2

MER1S4812SC

47

82473C

11R473C

1

MER1S4815SC

47

82473C

11R473C

1

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 MER1 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 MER1 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 MER1 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.