62368-1 and 60950-1 Limited Power Source (LPS) Rated Power Supplies

A Limited Power Source (LPS) as defined in IEC 62368-1 and IEC 60950, is a secondary circuit with an open circuit output voltage, UOC, not exceeding the SELV circuit limits of 42.4 VPEAK or 60 VDC. The maximum apparent power, S, available on the output under any load condition, and the maximum fault current, ISC, available on the output under any load condition, (including a short-circuit), are limited to magnitudes not likely to cause ignition under fault condition in components mounted on, or circuits constructed from, suitably rated materials.

1. For a power supply rated at 30V or less, the following must be met even with a single fault condition:
   1. The output current must not exceed 8A
   2. The output power must not exceed 100W
2. For a power supply rated above 30V, but not exceeding 60V:
   1. The output current must not exceed 150 ÷ Vout
   2. The output power must not exceed 100W

This graph shows the limits for Limited Power Sources:

Providing LPS limitations to part or all of the circuits in a product design gives the mechanical design more flexibility in polymeric material choices and openings in the enclosure, as a fire enclosure need not be provided for LPS-powered circuits.