Modified Standard, Semi-Custom, and Full-Custom Power Supply Designs – The RECOM Approach

One of the reasons RECOM has the broadest power converter portfolio in the industry is the sheer number of variations available within its standard product range. If we take a classic 5W isolated and regulated DC/DC converter in a DIP24 case, such as the REC5 series, the datasheet shows five input and nine output voltage options, including single and dual outputs.

There are three different isolation voltage ratings from 2kV up to 6kV, and three pinning configurations to make it a pin-compatible alternative to competing products, including a version with a remote on-off pin. Additionally, the board mounting pins can be either through-hole or SMT. The case material is available in plastic or metal. Finally, the series comes in either tube or tape-and-reel packaging. Overall, this one DC/DC converter series supports well over two thousand permutations as standard.

The boundary between a semi-custom and a modified standard power converter is not always obvious, so a useful definition is whether safety re-certification is needed. Modifications that affect safety-critical components or separations – such as the transformer construction, the choice of optocoupler or Y-capacitor, or creepage and clearance distances – will almost certainly require a new certification process. However, the safety test reports typically allow a ±10% variation in the output voltage and current ratings to accommodate production tolerances, leaving some scope for flexibility.

The input voltage rating also has at least a ±20% tolerance, and often more. If the required modification stays within these tolerance bands, then safety re-certification may not be necessary. The same applies if the original safety test report lists ‘alternate construction’ options for certain components or potting materials. We have customer applications where silicone potting material is not acceptable, either due to potential outgassing, which could affect other parts, or because silicone could emit smoke in a fire. So, although silicone is an excellent encapsulation material with high thermal conductivity and good adhesion, we can offer epoxy potting as a modified standard.

It may seem surprising, but the label design and text are considered part of the safety documentation and are strictly controlled by the certifying bodies. We regularly receive requests for custom label designs—for example, showing the customer’s own brand name and part number instead of RECOM’s standard label. Although the physical parts are identical, we must apply for a copy certificate with the new label, part number, and customer logo in order to manufacture the modified part with valid safety certification. Fortunately, we have extensive experience handling such requests and aim to make the process as fast, simple, and unbureaucratic as possible.

Once we enter the realm of semi-custom power converters, we can offer significantly more flexibility than simply tweaking specifications. This may include alternative PCB layouts to change the shape of the converter or matching the pinout to replace a competitor’s part that has become obsolete. These changes don’t have to be physical—we have also built semi-custom converters with higher-rated components to extend the operating temperature range, or harder epoxy to meet specific environmental conditions. All of these modifications are based on proven standard designs, so while the semi-custom product is tailored to meet individual requirements for form, fit, or function, it can still be produced efficiently on our standard manufacturing lines with a short time-to-market.

In 2010, a US competitor abruptly discontinued manufacturing a series of switching regulators, leaving their existing customer base ‘in the lurch.’ One customer approached us to ask whether we could modify our standard R-78 series to be pin- and function-compatible with these end-of-life products, even though the format was completely different from our existing design.


In just 12 weeks, we released the R-78T series with three different open-frame SMD pinning options, specifically designed to be pin-compatible with these now-unavailable parts. Our ability to respond so quickly was due to the fact that we didn’t need to start from scratch—we already had extensive experience in designing and manufacturing switching regulator modules, which we used as the foundation for this semi-custom solution.

A full-custom power converter differs from modified standard or semi-custom variants in that it is not based on an existing product. However, it still draws on proven building blocks and established production infrastructure where appropriate. Typical conditions that justify a full-custom power supply project include: no existing product can meet the technical requirements, the development costs (R&D, testing, and production) are acceptable for both parties, and the expected project volume supports the necessary investment in resources.

The typical full-custom power converter project stages are shown in Figure 5:

As can be seen by this brief introduction, a RECOM power converter can be offered as a modified standard, semi-custom, or full-custom product to the customer in several ways. Each variant has advantages and disadvantages (Table 1), so the simplest way to decide is to establish a dialog with us so we can advise and work together with you to offer the optimum solution. To facilitate this, RECOM has set up four dedicated e-mail addresses for customization requests. Someone from RECOM will then contact you to discuss your requirements in more detail.

Contact RECOM to discuss your project and for advice on how to specify your full-custom, semi-custom, or modified-standard power converter for minimum cost and fastest delivery.