Overview
An industrial control cabinet or a machine needs one or more clean DC rails from the mains, and it must meet the EMC and the safety limits without a long design effort. COSEL provides the whole chain: an AC-DC supply for the mains-to-DC stage, an isolated DC-DC converter for a lower rail and an EMI filter for the input, and BeiLuo supplies them with genuine traceability and FAE support. This page shows how the parts fit together in an industrial automation design.
The Main DC Rail
The first stage is an AC-DC supply that converts the mains into the main DC rail, usually 24 V. A COSEL PBA series enclosed supply gives a universal input of about 85 V to 264 V AC, so one part works across the world's mains, with an adjustable output, an operating LED, protection for over-current and over-voltage and a harmonic attenuator that meets the IEC 61000-3-2 requirement. Choose the power with margin above the load and the cooling for the enclosure: convection for a sealed or a quiet panel and a built-in fan for a higher load.
Choosing the Power and the Cooling
Add the load of every rail on the supply, add margin for the start-up and the lifetime, and choose the next standard wattage. A convection supply suits a sealed or a quiet cabinet, because it has no fan to wear out or to draw dust, and a fan-cooled supply suits a higher load where the airflow can be provided. Confirm the derating at the highest ambient, because a supply in a warm cabinet delivers less than its rating at the nominal temperature.
The Isolated Lower Rail
A control board often needs a lower rail, such as 5 V, that is isolated from the 24 V bus. A COSEL DC-DC converter, such as the CBS1002405 open-frame part or the ZUS32405 board-mount part, converts the 24 V bus into a regulated isolated 5 V rail, so the logic is separated from the bus and a ground loop is broken. The open-frame part spreads its heat into the host board, and the board-mount part keeps the design small, so the choice follows the power and the space.
Layout of a DC-DC Converter
Keep the input capacitor close to the converter, follow the recommended input filter for the conducted emissions and keep the switching loop small, and use a ground plane that respects the isolation between the input and the output. These steps keep the rail clean and the emissions within the limit.
The EMI Filter
The input of the equipment must meet the conducted-emissions limit, so a COSEL EMI filter sits between the mains and the supply. The NAC series is a general-purpose compact filter with an optional DIN-rail mount, and the EAC series has a defined attenuation from about 150 kHz to 1 MHz with a set of safety certifications. Choose the current above the load and the line-to-ground capacitor code for the leakage the application allows, and mount the filter close to the input connector with the case bonded to the chassis.
Installation and Grounding
A filter is only as good as its grounding, so bond the case to the chassis, keep the input and output wiring separated and keep the filter close to the connector. A poor installation leaves the noise to bypass the filter and defeats the design.
Verification
Validate the design on the bench by measuring the efficiency and the derating of the supply at the worst-case load and ambient, by checking the ripple and the transient of each rail and by measuring the conducted emissions with the real load. Our FAE team can review the measurements and the layout, so the power design meets its target in the product as well as on the bench.
Getting Help
Send your rails, the current on each, the input and the environment to our FAE team, and we will propose a supply, a converter and a filter, help size the power and the cooling and review the input filtering and the EMC. BeiLuo holds mainstream COSEL parts in regional stock and ships them with an import declaration, a certificate of origin and a RoHS compliance file, so an industrial power design can move from prototype to production without a supply gap.