Introduction

A Mornsun power module delivers its specified performance only when it is integrated with care. The input filter, the layout and the thermal path decide whether the design meets its EMC and reliability targets. This application note explains the practical rules for integrating a Mornsun DC-DC or AC-DC module, covering the EMC filter, the layout and the thermal design.

EMC Filtering

A switching module draws a pulsed input current, so it produces conducted emissions that must be filtered to meet the limits. Choose a module that meets the standard for your market, then add the recommended input filter, which usually combines a common-mode choke and a set of capacitors. Place the filter close to the module and keep the connections short, so the high-frequency current loops are small. For an AC-DC module, the filter sits on the mains side and must be rated for the mains voltage and the surge; for a DC-DC module, the filter sits on the DC input and must handle the reflected ripple current. Measure the conducted emissions with the real load, because a bench source can hide the filter behavior.

Layout for Noise

Keep the input capacitor close to the pins and the switching loop small. Separate the input and output sections and keep sensitive signals away from the switching nodes. Use a ground plane where possible, and cross any unavoidable noise source at right angles rather than parallel to the signal. These disciplines are what make a small module quiet.

Thermal Design

A power module converts with an efficiency, so a fraction of the power becomes heat that must be removed. For a low-power module the board copper is often enough, but for a high-power module the thermal design is the design. Allow clearance for airflow, provide a good thermal path, and use the datasheet derating curves to confirm the margin at the highest ambient. In a dense design the thermal path, not the module, usually sets the limit, so measure the case or baseplate temperature at worst-case load and compare it with the limit.

High-Power Modules

A high-power module such as the 1/2-brick VRF series needs a deliberate thermal path, whether through a heatsink or through the baseplate into the board and the chassis. Plan the mounting and the interface, and consider forced air where natural convection is not enough.

Interaction of EMC and Thermal

EMC and thermal design interact. A tight layout with short loops reduces both radiated noise and the loop area that carries heat-generating current, and a cooler module is more efficient, which reduces the heat. Designing the two together, rather than separately, produces a denser and more reliable result.

Validation

After integration, validate on the bench. Measure the module temperature at worst-case load and ambient, measure the conducted emissions with the real load, and confirm the output ripple and transient response. Our FAE team can review your layout and your measurements and help you interpret them, so the module performs in the product as it does on the datasheet.