Compact power supplies can be conduction or convection cooled

TDK Corporation has introduced the 250W rated TDK-Lambda brand 2” x 4” footprint CUS250M series of AC-DC power supplies. The series is certified to both IEC 60601-1 and IEC 62368-1 standards for both Class I and Class II (double insulated) installations.

Target applications include medical, home healthcare, dental, test and measurement, broadcast, professional audio and industrial equipment.

Conduction and convection cooling enables silent operation, and the CUS250M can deliver up to 250W in -20°C to +50°C ambient temperatures. Operation at +80°C is also possible with appropriate derating. With 1m/s forced air cooling utilising system airflow or the optional integral fan, the U channel models can deliver 250W in a +50°C ambient, derating to 125W at +70°C.

Options for the CUS250M include a 5V 0.1A standby voltage, remote on/off, DC OK and AC Fail signals and a choice of U channel, U channel with cover or top mounted fan mechanical construction.

12V and 24V models will be available initially, with 15V, 18V, 28V, 36V and 48V outputs following later. The output voltage can be adjusted by the user. The series accepts an 85 to 264V AC input and earth leakage current is less than 150µA – including all tolerances. Touch current is <10µA (Class I) and <70µA (Class II).

With efficiencies up to 94%, less internal heat is generated allowing reliable operation. Average efficiency, measured at 25, 50, 75 and 100% loads, is greater than 91%. Offload power consumption is less than 0.5W when the output is inhibited.

Design features include the use of polymer output capacitors, providing low ESR and high ripple current tolerance to maximise field life. The high-voltage bulk capacitor, used to store energy during short interruptions in AC power, is situated at the edge of the power supply PCB. This and the component layout, enables more effective cooling for both convection and forced air applications, again enhancing reliability.

Careful component layout on the underside of the PCB distributes heat evenly across the base, improving thermal transmission. An output terminal / choke combination (for which a patent is pending) reduces common mode noise.

The CUS250M has an input to output isolation of 4,000V AC (2 x MoPP), an input to ground isolation of 1,500V AC (1 x MoPP) and an output to ground isolation of 1,500V AC (1 x MoPP) for suitability in B and BF rated medical equipment. Safety certification is to IEC/EN 60601-1, ES 60601-1. IEC/EN/CSA/UL 62368-1 and is CE / UKCA marked to the Low Voltage, EMC and RoHS Directives. The models meet EN 55011-B, EN 55032-B radiated and conducted emissions with significant margins (both Class I and Class II) and comply with the EN 60601-1-2:2015 (Edition 4) and EN 61000-4 immunity standards.