Medical Power Solutions – Standards deliver safety
Medical appliances often require various DC voltages driving the AP instrument that are different to the main system DC voltage provided. In order to avoid sourcing a custom AC/DC power supplies, this can be resolved by combining IEC 60601, 2 x MOPP rated DC/DC converters together with, for example, an ITE 60950 rated AC/DC power supply. Other times, engineering confidence is simply raised through the assurance of using 2 x MOPP, medical grade DC/DC converters for the AP instrument, even when the selected AC/DC power supply has IEC 60601 approval.
The primary requirements for 2 x MOPP (Figure 1) are 4000 V AC isolation, 8mm creepage distance and double insulation. Most commonly available DC/DC converters (including those that carry EN60950 approval) offer between 500 V DC to around 1600 V DC of isolation and are, therefore, not suitable for medical applications. However, specialised DC/DC converters are available that will meet the requirements for AP when used in conjunction with such standard off-the-shelf power supplies.
By providing up to 5000 V AC of isolation, double insulation and 8mm of creepage distance through its galvanically-isolating transformer, a DC/DC converter can still protect the patient in the event of a failure of the main AC/DC power supply, thereby avoiding mains voltage levels appearing at any patient AP points.