A

Series

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Technical

notes

ISOLATION VOLTAGE

"Hi Pot Test","Flash Tested","Withstand 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.

Professional Power Module A 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 A 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-acssible 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 greatre degree depending on materials.

Construction and environment. The A 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 for better than functional isolation where the wire enamel insulation is always supplemented by a further

insulation system of physical spacing or barriers.

Technical

notes

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: Ceramic chip capacitors are recommended. It is required that the ESR(Equivalent Series Resistance)should be as low as possible.X7R 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 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.

Ripple & Noise Characterisation Method

Ripple and noise measurements are performed with the following test configuration.

C1

1μF X7R multilayer ceramic capacitor, voltage rating to be a minimum of 3 times the output voltage of the DC/DC converter

C2

10μF tantalum capacitor, voltage rating to be a minimum of 1.5 times the output voltage of the DC/DC converter with an ESR of less than 100mΩ at 100 KHz

C3

100nF multilayer ceramic capacitor, general purpose

R1

450Ω resistor, carbon fi lm, ±1% tolerance

R2

50Ω BNC termination

T1

3T of the coax cable through a ferrite toroid

RLOAD

Resistive load to the maximum power rating of the DC/DC converter. Connections should be made via twisted wires

R3

50Ω resistor, carbon film,±1%

Measured values are multiplied by 10 to obtain the specified values.

Differential Mode Noise Test Schematic