Why Board-Mount AC/DC Modules Exist
A board-mount AC/DC module provides only the conversion and isolation stage — rectification, switching, transformer isolation and regulation — delivered as a PCB-mount assembly. Input filtering, protection and the bulk capacitor stay on the designer’s board. For equipment that already has a custom PCB, its own enclosure and its own EMC requirements, that division buys control: the supply’s outline follows your board rather than a supplier’s tooling.
A smart circuit breaker, a building automation gateway and a portable EV charging box have almost nothing in common electrically. What they share is a design situation. Each one already has a custom PCB, an enclosure chosen for the application, its own protection scheme, and a set of EMC and safety requirements that came from the end product rather than from the power supply.
What does an enclosed supply solve that you have already solved?
For a product like that, an enclosed AC/DC supply solves a problem that has already been solved. It brings its own case, its own filter stage designed for someone else’s emissions target, and a mechanical outline the rest of the design has to work around. What the engineer actually needs is the conversion and isolation stage.
What is a board-mount AC/DC module?
Rectification, switching, transformer isolation and regulation, delivered as a PCB-mount assembly. Together, these stages convert the incoming AC mains into a stable, isolated DC output that can safely power the rest of the system. Filtering and input protection are left to the surrounding circuit, which the designer builds to suit the product.
Is “open frame” the same thing?
A note on terminology, since it causes confusion. Open frame describes construction rather than function. MicroPower Direct also builds open-frame supplies that ship as finished units, with their own filtering, an on-board fuse and a published emissions class. The MPL-SC is a different proposition. It provides the conversion and isolation stage, and leaves the filtering and protection for the designer to specify.
What do you gain, and what do you take on?
The main advantage is control rather than size. You decide how much filtering the design needs and where it sits, so the supply’s outline is set by your board instead of by a supplier’s tooling. Thermal design follows the same logic: the module dissipates into your enclosure, under your airflow conditions, and you can plan for that rather than inherit it.
The corresponding responsibility is easy to underestimate, and the MPL-SC datasheets are direct about it. The input bulk capacitor is connected externally and listed as required, not recommended. So is the fuse. So is the inrush limiting element ahead of it. The component selection tables give a value for each one, model by model.
The same applies to the published EMC performance. Class B under EN 55032 is a result these modules reach, and the application circuits inside the datasheet show which combination of external components gets you there. A different combination gives Class A with better surge immunity. Another gives Class B over a narrower ambient range. Those are choices the designer makes, and they are made on the board rather than at the point of purchase.
What does the MPL-SC family cover?
The MPL-SC Series was developed around this design philosophy. Rather than integrating filtering and protection that not every application needs, the family provides the core conversion stage and documents the surrounding circuitry required for different installation environments.
70–430 VDC
70–430 VDC
100–745 VDC
100–430 VDC
Power figures are family designations. Output power varies by model — in the 15 W family the 3.3 V model is rated 9.9 W and the 5 V model 14 W.
The 10 W family’s 85 to 528 VAC input makes it suitable for higher-line industrial and grid-connected applications. The models are not a common footprint, and they are not meant to be. What carries across the family is the design pattern: a pin arrangement that brings AC line, AC neutral, the external bulk capacitor connection and the output to the board; a published component selection table for every model; and a set of recommended peripheral circuits mapped to real application environments, from basic indoor equipment through to outdoor industrial and lightning-prone installations on the 10 W family.
That last part is worth dwelling on, because it is the practical difference between designing with a module like this and guessing. Each circuit comes with its component values, its resulting emissions class, its immunity level and the ambient range over which it was characterized. The engineering decisions are documented rather than left to trial and error.
Common questions
Is a board-mount module the same as an open-frame supply?
No — the terms answer different questions. Open frame describes construction; this is about who specifies the filter. MicroPower Direct’s own open-frame supplies are open frame and still arrive as finished units, with an on-board fuse and a published emissions class.
When is an enclosed supply the better choice?
When there is no custom board to put the filter on, or no EMC strategy of your own to fit it into. An enclosed unit settles those questions once, for every customer — which is precisely its value if you would rather not answer them.
What input ranges does the MPL-SC family cover?
85–305 VAC on the 3 W, 5 W and 15 W families. The 10 W family reaches 85–528 VAC, which is what makes it usable on higher-line industrial and grid-connected equipment.
Selecting the module is the short part. Integrating it is where the schedule risk lives, and most of it is avoidable if the decisions are made early rather than discovered at the test house. Next: exactly which components stay outside the module, and why the list is longer than most engineers expect.
