8.3.1.1 Operation or Functional Isolation

Operational or functional isolation is defined by the use of a high-potential (hipot) test only. Typically, this isolation is defined as the use of insulated wire in the construction of the transformer as the primary isolation barrier. The hipot one-second duration test (dielectric voltage, withstand test) is a production test used to verify that the isolation barrier is functioning. Products with operational isolation must never be used as an element in a safety-isolation system.

8.3.1.2 Basic or Enhanced Isolation

Basic or enhanced isolation is defined by specified creepage and clearance limits between the primary and secondary circuits of the power supply. Basic isolation is the use of an isolation barrier in addition to the insulated wire in the construction of the transformer. Input and output circuits must also be physically separated by specified distances.

8.3.1.3 Continuous Voltage

For a device that has no specific safety agency approvals (operational isolation), the continuous voltage that can be applied across the part in normal operation is less than 42.4 V_RMS or 60 V_DC. Ensure that both input and output voltages maintain normal SELV limits. The isolation test voltage represents a measure of immunity to transient voltages.

If the device is expected to function correctly with more than 42.4 V_RMS or 60 V_DC applied continuously across the isolation barrier, then the circuitry on both sides of the barrier must be regarded as operating at an unsafe voltage. Further isolation or insulation systems must form a barrier between these circuits and any user-accessible circuitry according to safety standard requirements.

8.3.1.4 Isolation Voltage

Hipot test, flash-tested, withstand voltage, proof voltage, dielectric withstand voltage, and 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. TI’s DCH01 series of dc-dc converters are all 100% production tested at 3.5 kV_DC for 1 second.

8.3.1.5 Repeated High-Voltage Isolation Testing

Repeated high-voltage isolation testing of a barrier component can degrade the isolation capability, depending on materials, construction, and environment. The DCH01 series of dc-dc converters have toroidal, enameled, wire isolation transformers with no additional insulation between the primary and secondary windings. While a device can be expected to withstand several times the stated test voltage, the isolation capability depends on the wire insulation. Any material, including this enamel (typically polyurethane), is susceptible to eventual chemical degradation when subject to very-high applied voltages. Therefore, strictly limit the number of high-voltage tests and repeated high-voltage isolation testing. However, if it is absolutely required, reduce the voltage by 20% from specified test voltage with a duration limit of 1 second per test.