New DC/DC Converters Simplify Custom Projects

There are three levels of customization: a modified standard product, which is the simplest option; a semi-custom design; and a full custom design.

A modified standard product starts with an off-the-shelf part and changes it in some small way by changing it from an almost perfect solution to a perfect solution. Examples of such modifications are:

• A small change to the output voltage — for example, 5.1V instead of 5.0V
• A pinout change — for example, removing a pin so the part fits into an existing board.
• A change of encapsulation material — for example, epoxy instead of silicone.
• A longer or shorter pin length, or pins that bent at 90°.

Such requests are easy to implement, in RECOM’s production lines, and qualify as modified standard products. In many cases, the existing certifications for safety and EMC remain valid and save significant costs and time. Furthermore, RECOM has manufactured many ‘modified standards’ in the past, so a solution might already be available for a particular set of requirements, even if it is not given in the datasheet.

A semi-custom design is the next stage of customization. The boundary between a semi-custom and a modified standard power converter is not always obvious, so a useful definition is whether the change will require a safety re-certification.

Modifications that influence safety-critical components or separations—such as the transformer construction, choice of optocoupler or Y-capacitor, or creepage or clearance distances—will almost certainly require a new certification process.

Often, a customer specification can be met using an existing ‘platform’ design that has the advantage of proven performance and reliability in the field. This is a more economical approach than a full custom approach, and product safety assurance and EMC certification are simplified by reducing the risk and accelerating the time to the market. Existing in-house stock components, tooling, and manufacturing processes may be used to result in a cost-effective product.

A full custom power converter is specifically designed for the required application, which is not based on an existing product. Rather than tweaking a standard product, the design team typically begins with proven and tested building blocks and existing production infrastructure to craft a unique solution.

New standard products lend themselves to customization

The DC/DC converter market is continually changing and evolving, and RECOM is always improving its product line to meet new challenges. RECOM’s DC/DC isolated converter products are in the midst of such an improvement program with the introduction of redesigned versions of some of our most popular isolated and non-isolated DC/DC converters. The performance improvements stem from the implementation of advanced circuits and manufacturing techniques. New planar-style transformers can be automatically placed and flexible automation keeps costs down — even reduced for some new products in volume.

The regulated designs now use 2 integrated circuits (ICs), one each on the primary and secondary side of the transformer. The primary-side IC is a wide-input, push-pull transformer driver. The output side has a secondary synchronous buck stage for tight regulation over the full load range. Synchronous rectification improves efficiency by replacing lossy diodes with FETs that switch on and off under the direction of the controller.

The new models can easily be distinguished by the appearance of a “K” in the part number. For example, the 3W SIP8 RS3K-Z series is an enhancement to the RSE series. The -K version has a 4:1 input range and 3kV agency-rated ‘basic’ isolation compared with 2:1 input and 3kV ‘functional’ isolation for the -E series. The RS3K-Z also features a wider operating temperature range without derating to +80°C, higher efficiency, and lower isolation capacitance.

The RSK-RUW series isolated DC/DC 2W converter features an 8:1 input voltage range of 4.5-36 VDC. The series includes ON/OFF control for added convenience, continuous short circuit protection, and an under-voltage lockout (UVLO) for added safety and security. The RSK-RUW offers basic grade isolation of 3kVDC/1min and an industrial operating temperature range of -40°C to 85°C, without derating, making it ideal for use in demanding industrial environments.

An added benefit of this new architecture is that it simplifies the design of custom DC/DC modifications with shorter design cycles and reduced testing requirements.

In some cases, the new products can make a custom design unnecessary. The improved specifications can allow a standard product to meet the needs of an application that would otherwise require a custom solution. For example, the RSK-RUW’s increased input voltage range of 8:1 broadens the range of applications that can use the standard product.

Even if custom is needed, the new architectures may allow the designer to choose a modified standard product rather than a semi-custom or full-custom solution. Many of the new converters have upgraded isolation from functional grade to basic grade with IEC/EN62368-1 certification. This may shorten the design cycle by avoiding the requirement for a lengthy recertification process that comes with an isolated transformer change.

The new designs can also accommodate output voltage changes without changing the transformer windings; changing the values of two internal resistors is all that is needed.

The new DC/DC converters mentioned are only the first in a series of new designs that you can expect to see in the coming months. For more information, contact RECOM.