Custom Power Supply Solutions: AC/DC and DC/DC Designs

Understanding the design considerations for power supplies is critical when evaluating standard options and determining whether a custom design is necessary. The power supply landscape is both complex and dynamic, requiring diverse approaches to address a wide range of application requirements, meet increasing energy efficiency standards, and comply with evolving regulatory demands. While RECOM offers an extensive selection of standard products, certain applications may demand a tailored solution—a fully customized approach.

Several decades ago, designing a power supply was a relatively straightforward task. The power world was linear, and the front end of a typical power supply consisted of a transformer feeding a full-wave bridge rectifier into a large-value filter capacitor. Such a linear design was simple and reliable, and if an unregulated power supply met your requirements, it was quite efficient, too. However, adding regulation caused efficiency to plummet. Linear regulators control the output voltage by dropping it across the pass element (the power transistor), which dissipates significant amounts of heat and results in efficiencies as low as 60%.

Switching power topologies changed all that. By chopping the incoming DC voltage into a high-frequency switched voltage to produce the desired output voltage and current, power transistors spend most of their time in the efficient “on” or “off” states, minimizing power losses. There are many ways to architect a switching power supply; over time, numerous switching topologies have emerged, each with advantages and drawbacks for specific applications. Available options now include boost, buck, buck-boost, Ćuk, flyback, forward, full-bridge, half-bridge, push-pull, SEPIC, synchronous buck, two-switch forward, Weinberg, and zeta topologies.

Moreover, increasingly stringent regulations mandate the addition of a front-end power factor correction (PFC) stage to most AC/DC designs. The quest for higher efficiency has driven an increase in design complexity, evolving from early passive PFCs to conventional boost converters, and more recently to the totem-pole topology. Additionally, there has been a proliferation of power devices. Bipolar transistors have been largely replaced by various MOSFET technologies, and silicon has been joined by silicon carbide (SiC) and gallium nitride (GaN).

Today, switching power supplies operate at frequencies in the MHz range and can achieve efficiencies well over 90%. However, this increased performance has significantly raised the bar for designers, who must now be familiar with a wide range of techniques: high-frequency magnetics, thermal management, electromagnetic compatibility (EMC), switching transistor technology, printed circuit board layout, digital and analog control theory, and more.

DC/DC converters deliver specific voltage levels while providing isolation between input and output circuits. These versatile components can supply all the required voltages for electronic components on a single board. The isolation provided by DC/DC converters ensures compliance with safety regulations and addresses challenges such as interference and fault protection. Additionally, these converters provide a clean and flexible solution for Distributed Power Architecture systems.

A DC/DC converter module is designed to meet one or more of the following objectives:

• Match the secondary load to the primary power supply
• Provide isolation between primary and secondary circuits
• Protect against faults, short circuits, or overheating
• Simplify compliance with safety, performance, or EMC regulations

RECOM’s unregulated DC/DC converters are designed for general-purpose power isolation and voltage-matching applications. These converters operate across a wide industrial temperature range of -40°C to +85°C without derating.

RECOM’s regulated DC/DC converters are ideal for industrial applications. These converters can handle high capacitive loads and maintain stable output voltages even during sudden input voltage changes. They also operate across a broad temperature range without derating.

Key Specifications for DC/DC Converters	Description
Input voltage range	The range within which the converter maintains full performance across the operating temperature range
Load regulation	The percentage change in output voltage over a specified range of output loads
Line regulation	The percentage change in output voltage for a given change in input voltage
Output voltage accuracy	How closely the output voltage matches its nominal specification
Ripple and noise	Voltage drops and high-frequency noise at the input or output during switching cycles
Input-to-output isolation	The dielectric strength between input and output circuits
Insulation resistance	The resistance between input and output circuits
Efficiency at full load	The ratio of delivered output power to supplied input power at 100% load and 25°C
Temperature drift	Voltage change as a percentage of nominal per degree of ambient temperature change
Switching frequency	The operating frequency of the converter’s switching circuit, with ripple typically twice this frequency
No-load power consumption	The energy consumed by the switching circuit when the output load is zero, limiting overall efficiency
Isolation capacitance	The parasitic capacitance between the transformer’s primary and secondary windings
Mean Time Between Failures (MTBF)	Reliability measure calculated per MIL-HDBK-217F for +25°C and maximum operating conditions

In addition to being safe, cost-effective, energy-efficient, reliable, and compact, AC/DC converters must also meet essential regulatory requirements. RECOM’s latest designs prioritize high efficiency across the full load range, including no-load and light-load conditions, to comply with these regulations. Both AC/DC and DC/DC converters must meet safety, EMC, and energy efficiency standards, ensuring compliance with regional and global mandates. The key regulatory requirements are listed below.

The power supply market continues to evolve, driven by stricter regulatory standards and rising customer expectations. To meet these demands, new technologies are emerging regularly.
Recent trends include:

• Wide bandgap devices: Materials like silicon carbide (SiC) and gallium nitride (GaN) are increasingly replacing silicon MOSFETs and IGBTs in power applications
• Advanced topologies: Designs such as the totem pole PFC, enabled by wide bandgap devices, offer higher efficiency and simplified circuitry.
• Innovative packaging: Three-dimensional packaging technologies integrate internal components for greater power density and improved EMC performance.

While RECOM offers over 30,000 standard DC/DC and AC/DC products, certain applications may require customized design. Customization can range from minor specification adjustments to fully bespoke solutions.

RECOM provides three levels of customization:

• Modified standard product: Minor changes to an existing product, such as output voltage adjustments or pin configuration modifications.
• Semi-custom design: More substantial changes, often requiring re-certification of safety-critical components.
• Full custom design: A completely new product tailored to the specific requirements of the application.

The simplest level of customization involves making changes to an existing standard product. RECOM catalog products are often modified to accommodate straightforward customer requests. Common modifications include:

• Adjusting the output voltage, such as changing from 5V to 5.7V to allow for the addition of an OR-ing diode
• Altering the pinout configuration
• Changing the encapsulation material
• Modifying the pin length, either longer or shorter

These requests are typically easy to implement and qualify as modified standard products. In most cases, existing safety and EMC certifications remain valid, significantly reducing costs and development time. RECOM has a history of delivering modified standards, and a product that meets specific requirements may already be available in the catalog.

RECOM‘s RHV2 and RHV3 DC/DC converter families are designed for high-voltage industrial applications, like hard vacuum systems, electrostatic filters, and x-ray generators. These converters feature reinforced insulation, certified to withstand isolation voltages of 20kVDC or 12kVAC. In one instance, a customer required the RHV2-0505S/R20 for a high-voltage application but needed greater input/output pin separation than the standard 30.5mm. The solution involved:

• Changing the secondary side pinout by eliminating pin 14
• Reassigning pin 15 as –Vout, increasing the creepage and clearance distance by an additional 2.54mm to exceed 33mm

Since pin reassignment was already included in the product’s test report specifications, the customer could retain the existing IEC/EN 61010-1 certification for safety requirements in electrical equipment for measurement, control, and laboratory use.


This modification was straightforward, requiring only adjustments to the internal PCB and Standard Operating Procedures (SOP). As a result, the modified standard part was delivered at the normal cost price, with no additional charges for the customization.

A semi-custom design represents the next level of customization beyond modified standard products. The key distinction between a semi-custom and a modified standard design is whether the changes require safety re-certification. Modifications that affect safety-critical components or design elements—such as transformer construction, optocoupler or Y-capacitor selection, or creepage and clearance distances—almost always necessitate a new certification process.

In many cases, customer specifications can be met using an existing platform design. These designs offer proven performance and reliability, providing a cost-effective and efficient alternative to full custom solutions. By leveraging in-house stock components, tooling, and manufacturing processes, semi-custom designs simplify product safety and EMC certification, reducing risk and accelerating time to market.

A customer required a high-frequency generator for endoscopic and laparoscopic surgery. This system supports all common surgical energy forms—monopolar, bipolar, ultrasonic, and advanced bipolar—making it a unique solution in the medical market.

The design presented several challenges:

• Wide range input
• Limited available space
• Medical approval
• High reliability

The proposed solution was a modified RACM1200-48SAV/ENC, adapted to handle a 2.2kW peak load compared to the standard product’s 1.2kW. Key design modifications included:

• Doubling the bulk capacitance
• Modifying the inrush circuit
• Upgrading switching components
• Redesigning the mechanical layout

This semi-custom approach met the customer’s specifications while maintaining cost efficiency and minimizing development time.

A full custom power converter is created specifically for a customer’s application and is not based on any existing product. However, the design process does not start from scratch. Proven building blocks and existing production infrastructure are leveraged where appropriate to streamline development.

A typical custom design project follows these stages:

Stage	Description
Project proposal	The customer submits an initial request detailing the technical requirements (for example, functional specifications, performance needs, technical standards, physical dimensions) and commercial factors (like budget, expected volume, target costs).
Project evaluation	The technical requirements are analyzed for feasibility, manufacturability, and resource availability. A project is considered viable if no existing product can meet the need, the costs for R&D, testing, and production are acceptable, and the project volume justifies the resource investment.
Project plan	A comprehensive plan is developed outlining the project schedule, resource allocation, and milestones for each phase.
Prototype development	Prototypes are built to verify compliance with functional specifications. Specifications may evolve during this phase. Following initial approvals, pre-production prototypes (at least 50 units) are produced for statistically valid performance and stress testing.
Design verification testing (DVT) and production verification testing (PVT)	These tests are critical to project success. RECOM provides datasheets and test documentation to demonstrate the design’s reliability under all expected operational and fault conditions. Testing includes: Electrical and thermal stress tests Safe operating area tests Long-term soak tests Shock and vibration tests Production tolerance testing RECOM’s automated test lab with networked test stations ensures rapid evaluation across environmental conditions.
Production and certification plan	Once DVT testing is sufficiently advanced to initiate a design freeze, the production plan is implemented. This includes sourcing components, ordering custom housing, printing, and packaging. Production-ready prototypes are sent for agency approval (UL, IEC, EN, CB Reports).
Production	An assembly line is established to manufacture, test, and deliver the final product to the customer.
Change management	Changes are inevitable throughout the product life cycle. Updates to technical standards (typically every three years) or the availability of key components may necessitate design modifications. These changes are managed with Product Change Notices (PCNs). Product Life Cycle (PLC) documentation is maintained until the product’s end-of-life, as determined by the customer.

RECOM’s full custom designs range from sub-1W to several kilowatts, with engineering teams in Austria, Italy, Taiwan, and China supporting a wide range of specifications. RECOM Power Systems (RPS) in Italy specializes in high-power single- and three-phase AC/DC converters, DC/DC converters, battery chargers/conditioners, PFC front ends, and inverters. These solutions are tailored for industrial, medical, energy, aerospace, rail, and military COTS markets.

RPS leverages state-of-the-art design techniques to deliver high power density and efficiency at competitive costs. Comprehensive safety certification and EMC compliance testing (in-house pre-compliance or third-party certification) ensure the final product meets all regulatory and operational standards.

In recent years, global interest in methanol and hydrogen as alternative fuels has surged. A customer specializing in fuel cell solutions for mobile and stationary applications across various industries required a high-efficiency system to charge a battery from a fuel cell. The system needed to deliver approximately 7,000 watts of power while meeting additional requirements such as input current tracking (ICT), liquid cooling, and CAN interface compatibility.

The customer’s initial in-house solution used parallel operation of several PCB modules. While functional, it achieved only 92% efficiency, which was insufficient. Additionally, managing currents up to 220A while maintaining ICT presented significant challenges due to the complex and demanding layout design. To address these issues, the RPS team developed the SD7008, a non-isolating converter based on a parallel cascaded, overlapping buck-boost topology. This design delivers an adjustable output voltage that can be lower, equal to, or higher than the widely varying input voltage. Key features include:

• Efficiency exceeding 97%: Achieved through advanced semiconductor technology.
• Input current tracking (ICT): Fully integrated to meet customer specifications.
• Liquid cooling: Implemented to enhance thermal management.
• CAN interface: Upgraded to the CAN J1939 Standard for compatibility with modern communication protocols.

The design leveraged an existing switching topology concept, enabling rapid development while significantly improving efficiency. The liquid cooling system and updated interface were incorporated efficiently, resulting in a short project timeline of 12–14 weeks, meeting both the customer’s schedule and target price.

When evaluating non-standard design options, it’s important to weigh the advantages and disadvantages of each level of customization. The following table summarizes the key considerations for modified standard, semi-custom, and full custom designs:


Each level of customization offers distinct benefits and trade-offs. Modified standard products are ideal for quick, cost-effective adjustments, while semi-custom designs provide more flexibility for specific needs. Full custom solutions, though more complex, offer the ultimate flexibility for unique applications.

In addition to its extensive range of standard products, RECOM offers comprehensive customization options, including full custom, semi-custom, and modified standard designs. With engineering teams in China, Taiwan, Austria, and Italy, RECOM leverages extensive product development expertise to create new designs tailored to specific requirements, supporting efficient production at scale.

Semi-custom designs and modifications to existing products are offered at highly competitive prices. RECOM keeps modification costs low by utilizing automated production lines that benefit from economies of scale. By reusing existing tooling, production equipment, and extensive on-site component stock, RECOM ensures cost efficiency and quick turnaround times.

RECOM maintains a robust library of platform designs which specializes in fast-turnaround, high-power, and full-custom solutions. These platform designs can be readily adapted for specific applications, often eliminating the need for extensive development or re-certification costs.

RECOM’s customization and modification services span a wide range of products, including:

• Low- to high-power AC/DC and DC/DC converters
• Battery chargers and conditioners
• AC inverters
• PFC front ends

These solutions serve key industries such as industrial, medical, energy, aerospace, mobility, and military COTS. Both fully customized and semi-custom products can be delivered with all required safety and EMC certifications to meet customer specifications.

With so many options available, the simplest way to determine the right solution is to contact the RECOM engineering team. Together, we can collaborate to develop the optimum solution for your unique requirements.