BLOG

Top 10 Considerations When Choosing Between Open-Frame vs. External Adapters

What Should OEMs Consider Before Choosing Between Open-Frame and External Adapters?

When designing a modern medical device, one of the earliest and most important architectural decisions is whether to place the power supply inside the product or rely on an external adapter. At first glance, this may seem like a simple packaging choice, but for OEMs it has much broader implications. The decision affects enclosure design, thermal performance, safety strategy, field replacement, certification complexity, and even the way end users interact with the product in hospitals, clinics, and home care environments.

Open-frame power supplies are often attractive when a manufacturer wants a clean, integrated product with no external brick or trailing cable clutter. This can be especially appealing in larger clinical equipment where the entire system is stationary and where internal space can be designed around airflow and shielding requirements. External adapters, by contrast, move the AC to DC conversion outside the enclosure. This can reduce internal heat, lower voltage exposure inside the chassis, and simplify portions of the compliance process. For compact devices, this separation can make a major difference in both product reliability and user comfort.

The choice also has long-term consequences beyond the initial engineering phase. A product that is easy to certify but difficult to service may create problems after launch. A device that looks sleek and self-contained may still run into internal thermal bottlenecks or EMI conflicts if the power stage was not considered early enough. That is why OEMs need to evaluate not only what works on paper, but what works across the full lifecycle of the product, from development and certification to manufacturing, deployment, and ongoing support.

Useful Links

• Explore Phihong medical power solutions
• Learn more about IEC 60601 medical electrical equipment standards
• Review medical device design and engineering resources

Related Articles

• How to Design Internal Medical Power Systems
• Open-Frame vs. External Medical Power Comparison
• How Thermal Design Affects Medical Power Supply Performance

---

Which Factors Have the Biggest Impact on Open-Frame vs. External Adapter Selection?

Selecting the right power architecture is rarely a one-variable decision. Many teams begin by asking which option is cheaper or more compact, but experienced OEMs know that the better question is which solution creates the best total outcome for the product. Thermal behavior, EMI control, user safety, servicing needs, ingress protection, and supply chain flexibility all influence the final answer. The wrong decision can create avoidable cost later in the program, especially if it forces enclosure changes, retesting, or regulatory delays.

For example, a handheld medical product may benefit enormously from an external adapter because it helps keep the device itself lighter, cooler, and easier to certify. On the other hand, a larger stationary platform such as a cart-based diagnostic unit or imaging console may gain advantages from an internal open-frame design if there is enough space to manage airflow and shielding properly. In those cases, the all-in-one form factor may improve the professional appearance of the system and simplify cable management at the point of care.

Another major consideration is how the product will be used and maintained in the field. A home healthcare device may need quick adapter replacement and broad regional flexibility. A permanently installed unit may prioritize clean integration and internal control. The following ten considerations represent the most common and most important factors that engineers, sourcing teams, and product managers should weigh before locking in a power format.

Useful Links

• Browse Phihong power adapter solutions
• Read more about EMI design fundamentals
• Review FDA medical device guidance

Related Articles

• Understanding Medical Power Certifications
• Designing for EMI in Medical Devices
• How to Evaluate Compliance Requirements for Medical Power Supplies

---

Before diving into the details, here are the ten most important considerations that can shape whether an open-frame power supply or an external adapter is the better fit for your medical device. These points are not isolated technical checkboxes. They often overlap, meaning that thermal strategy can influence compliance, serviceability can influence total ownership cost, and enclosure design can influence both safety and user experience. Looking at these decisions holistically gives OEM teams a much better chance of choosing the right architecture the first time.

---

1. Thermal Management and Airflow

Open-frame power supplies depend heavily on the internal environment of the host device. Because they are mounted directly inside the chassis, they rely on the enclosure design to help remove heat through natural convection, conductive transfer, or forced airflow. If airflow is limited or hot components are packed too tightly around the power stage, operating temperatures can climb quickly. In medical devices, this is especially important because excess heat can affect reliability, shorten component life, and create enclosure temperatures that are undesirable in patient-facing products.

External adapters solve much of this problem by moving the primary heat-generating conversion stage outside the device. This helps the product stay cooler internally and can simplify thermal planning for compact, fanless, or handheld systems. Engineers may gain more flexibility in board layout and industrial design because the heat burden is no longer concentrated inside the housing.

This advantage becomes even more important in products where silent operation is preferred and fans are undesirable. A fanless enclosure with an internal supply may require larger venting areas or more thermal engineering effort to maintain margin under worst-case load conditions. With an external adapter, the device can often achieve a cleaner thermal profile with fewer internal compromises. For OEMs trying to balance reliability, comfort, and enclosure simplicity, thermal strategy is often one of the strongest reasons to consider an external format early in development.

2. Device Footprint and Weight

Power architecture has a direct effect on the physical size and weight of the final product. An internal open-frame design can support a fully self-contained system, which many OEMs find attractive from an aesthetic and usability standpoint. There is no external brick to manage, no additional floor clutter, and no need to explain separate accessory handling to the end user. For larger stationary equipment, this integrated approach often feels more professional and intentional.

At the same time, putting the power supply inside the product increases the internal space that must be reserved for electrical safety clearances, mounting, thermal spacing, and airflow. It can also increase the gross weight of the device, which may be a problem for portable or handheld systems. If the product is meant to be moved regularly between treatment rooms or used directly by patients in home care environments, every ounce and every cubic inch matters.

External adapters help reduce the size and weight of the actual medical device because the AC to DC conversion happens elsewhere. That often leads to slimmer, lighter product designs with better ergonomics. In wearable, tabletop, and portable applications, this can improve both usability and product perception. For OEMs targeting sleek industrial design or highly mobile platforms, external power often creates fewer physical constraints and allows more flexibility in how the product is packaged and positioned.

3. Regulatory and Certification Complexity

Certification strategy is one of the biggest dividing lines between open-frame and external power solutions. When an OEM selects an external medical adapter that already carries relevant medical safety approvals, the power stage is often treated as a separate pre-qualified subsystem. That can reduce the amount of high-voltage scrutiny required within the device itself and may help streamline portions of the IEC 60601 certification path. For teams trying to move quickly toward production, that simplification can be very valuable.

An internal open-frame supply changes the situation. In that case, the power unit becomes part of the device’s own safety file, and the OEM must validate how it is mounted, protected, spaced, and integrated within the enclosure. Creepage, clearance, insulation coordination, leakage current, grounding, and barrier design all need to be addressed carefully in the context of the full system. Even when the PSU itself is based on a compliant platform, the way it is installed still matters.

This can increase the burden on engineering and documentation teams, especially if the device is highly compact or includes unusual mechanical constraints. It may also affect test iterations if something in the enclosure layout needs to be revised during compliance evaluation. For many mid-sized OEMs, an external adapter offers a faster and lower-risk path to market. For others with greater internal regulatory resources, an open-frame design may still be worth the extra effort if system integration benefits justify it.

4. Electromagnetic Interference (EMI)

Medical devices often contain sensitive electronics such as imaging circuitry, communication modules, precision sensors, and analog front ends that can be affected by electrical noise. An open-frame power supply, by its nature, has less inherent shielding than a fully enclosed adapter. When it is integrated inside the device, its emissions can interact with nearby electronics, especially if the layout is dense or the enclosure lacks proper shielding strategy. This can lead to unwanted noise, display artifacts, measurement issues, or greater design effort during EMC testing.

External adapters can reduce this challenge because they place a major noise-generating element outside the main device enclosure. Their finished housings also provide a level of containment that open-frame designs do not offer on their own. That separation can create a cleaner internal electrical environment, which is especially useful in products with low-level analog measurement circuits or wireless communication sensitivity.

Of course, external adapters are not automatically immune to EMI concerns. Cable routing, connector quality, grounding strategy, and filtering still matter. However, the burden of internal noise control is often lower when the conversion stage is physically removed from the product. For OEMs working on devices where electrical quietness is a major design priority, the EMI advantage of an external adapter can be significant. It may reduce the need for custom shielding, simplify debugging, and improve the odds of passing EMC testing without expensive redesign cycles.

FEATURED PRODUCTS

MORE INFO >>>

Adapters

AA03A-075A-R

• Output Power - 2.75W
• Output Volt - 7.5V
• Output Current - 0.366A
• Features - Fixed Blade AC Input, Limited Power Source, Class B EMI, Level VI Efficiency, Standard Barrel Connector

MORE INFO >>>

EV Chargers

AC Series

• Output Current - 16A
• Features - Mode 2-chargers can use a circuit ranging from 8Amp to 16Amp with a local standard AC input plug installed for operation, Provides overcurrent, over voltage and short circuit protection, Protected against strong jets of water from all directions, Continuously monitors/supervises the ground connection between the AC supply and EV to ensure safe and reliable charging

MORE INFO >>>

Open Frame / Internal PSU

BF550-234A-R

• Output Power - 550W
• Output Volt - 12Vdc / 54.5Vdc
• Features - Universal AC Input range, Class I Design , Class B EMI , High Efficiency Performance , OVP, OCP, SCP, OTP Protections , Operating Altitude: 5,000M

MORE INFO >>>

Open Frame / Internal PSU

DA1000Z-240AEV-R

• Output Power - 1000W
• Output Volt - 24V
• Output Current - 1000W
• Features - Extended operating temperature range of -40℃ to 70℃, Fan-less aluminum case filled with heat conductive glue, Able to withstand 10G vibration, Power on LED indicator, Short Circuit, Over Current, Over Voltage, and Over Temperature Protections, & Adjustable output through potentiomete

MORE INFO >>>

Battery Charger Solutions

DA60U-240A-R

• Output Power - 60W
• Output Volt - 24V
• Output Current - 2.5A
• # of ports - 1
• Features - RESNA Compliant, CEC Compliant, LED Indicators Charge State, OVP, OTP, SCP, Charges AGM Batteries, Max 12hrs Charging Time

MORE INFO >>>

Battery Charger Solutions

DA200U-250A-R

• Output Power - 200W
• Output Volt - 24V
• Output Current - 8A
• # of ports - 1
• Features - RESNA Compliant, CEC Compliant, LED Indicators Charge State, OVP, OTP, SCP, Dual-Mode Charger, Charges GEL or AGM batteries, Max 12hrs Charging Time

<

>

5. Ease of Field Replacement and Serviceability

Serviceability matters much more after launch than many teams expect during development. If a power supply fails in the field, the way that failure is handled can affect customer satisfaction, downtime, warranty expense, and overall product reputation. With an internal open-frame power supply, replacement generally requires opening the enclosure, disconnecting internal wiring, and involving trained service personnel. In regulated or clinical environments, that may mean shipping the device back, scheduling a technician visit, or taking the product offline for a longer period.

External adapters are much easier to replace. In many cases, the user or facility staff can simply disconnect the failed adapter and plug in a new one. That convenience is one reason why external formats are so common in home care products, portable systems, and devices used across distributed healthcare settings. Fast replacement reduces disruption and lowers the service burden on both the manufacturer and the customer.

There is also a practical inventory advantage. External adapters are often treated as replaceable accessories, which makes them easier to stock and swap globally. For OEMs managing support across multiple regions, this can simplify service logistics and reduce repair turnaround times. If uptime and easy maintenance are important parts of the product value proposition, external power can provide a clear edge. Internal solutions may still make sense for larger installed systems, but the service tradeoff should be considered carefully before finalizing the design.

6. User Safety and Voltage Exposure

One of the strongest arguments for external adapters is that they keep high-voltage AC power outside the main medical device enclosure. When only low-voltage DC enters the product, the internal safety architecture can often be simpler and easier to manage. This reduces the chance of accidental technician exposure to mains voltage during service and can ease some enclosure material and barrier considerations. For lightweight plastic devices, that separation can be especially helpful.

Open-frame internal supplies bring the mains stage directly into the chassis. That means the OEM must provide proper insulation, protective spacing, secure mounting, shielding where needed, and reliable mechanical design to prevent unsafe access or fault conditions. In medical applications, those requirements are not optional and must be handled with great care. Leakage current and isolation strategy are also central concerns, especially when patient proximity is involved.

This does not mean internal designs are inherently unsafe. Many are used successfully in sophisticated medical systems every day. But it does mean that the engineering team assumes more direct responsibility for how high voltage is contained and controlled within the product. For OEMs that want to minimize that complexity or reduce internal voltage risk, external adapters are often the more straightforward path. In many cases, they provide a cleaner safety story from both a design and service perspective.

7. Moisture and Environmental Protection

Medical environments are not always electrically gentle spaces. Devices may be cleaned frequently, exposed to disinfectants, moved through humid areas, or used near fluids. If the product must meet ingress-related expectations, the power strategy becomes even more important. External adapters are generally easier to protect because they are separate finished units with their own enclosure and sealing design. The main device itself only needs to manage the DC entry point rather than the full mains power conversion stage.

An internal open-frame supply creates additional environmental design challenges. Because the PSU is exposed within the enclosure, the device may require more careful gasket design, isolated airflow strategy, conformal coating, or compartment separation to keep moisture away from critical power components. In products that must tolerate frequent wipe-downs or operate in demanding clinical conditions, this can complicate both mechanical engineering and validation.

External adapters can also be selected or replaced according to region, environment, or use case more easily than an internal mains design can be reworked. That flexibility may matter when the same base device is sold into different care settings with different environmental expectations. For OEMs designing products used in treatment rooms, emergency areas, or home environments where spills and aggressive cleaning are realistic, environmental robustness should be part of the power decision from the beginning, not an afterthought added near production.

8. Manufacturing and Assembly Efficiency

A design that looks elegant in CAD does not always translate to efficiency on the production line. Internal open-frame supplies typically require more assembly steps, including mounting hardware, internal AC wiring, connector management, routing, insulation checks, and more complex test considerations. These steps can add labor time and increase the chance of assembly variation if the process is not tightly controlled. They may also require more detailed work instructions and operator training.

External adapters simplify much of that. Because the power conversion stage is already packaged, tested, and separated from the product, final assembly of the medical device can often follow a more modular, plug-and-play model. The production team has fewer high-voltage handling concerns within the product itself, and the device enclosure may be easier to build consistently. This can improve line speed and reduce assembly risk.

It also affects manufacturing scalability. When demand rises, designs with fewer internal integration complexities may be easier to ramp. If adapter sourcing is stable and the device itself is simpler to assemble, the production organization may achieve better throughput with fewer specialized steps. For OEMs with lean internal manufacturing teams or outsourced production partners, external power can sometimes support a faster and more predictable build process. Internal power is not off the table, but the operational cost of that choice should be weighed alongside the electrical and industrial design benefits.

9. Total Cost of Ownership

It is common for sourcing teams to compare only the unit price of an open-frame supply versus an external adapter, but that narrow comparison can be misleading. An open-frame unit may have a lower component cost on paper, which initially makes it look more economical. However, once the full integration picture is considered, the numbers often become more complicated. Internal mounting, wiring, AC inlets, shielding, airflow provisions, assembly labor, and added compliance effort can all increase the true cost of the solution.

External adapters typically cost more per piece because they include a finished enclosure, cable set, strain relief, and the value of pre-packaged certification work. But those added costs often eliminate secondary expenses elsewhere in the product. Final assembly may be simpler, field replacement may be cheaper, and certification timelines may be more predictable. Over time, that can reduce the total cost of ownership, even if the adapter itself is more expensive at procurement level.

This is especially important for medical OEMs building in moderate volumes where engineering hours, service events, and launch timing have meaningful business impact. A design that is technically cheaper but slower to certify or harder to support can end up costing more overall. The right financial comparison is not just the PSU price. It is the entire system cost across design, production, service, and lifecycle risk.

10. Future-Proofing with USB-C and Standardization

The shift toward more standardized and modern power interfaces is accelerating across many electronic product categories, and medical device developers are paying attention. External adapters are often better positioned to support this trend because they can evolve more easily with interface and charging standards such as USB-C Power Delivery. That means an OEM may be able to modernize the power experience for end users without redesigning the entire internal architecture of the device.

An internal open-frame design is usually more fixed in its voltage structure and mechanical integration. Updating that type of design to support a new standard can require substantial rework at both the electrical and enclosure levels. External power gives teams more flexibility to adapt as market expectations shift toward common charging ecosystems, improved cable availability, and global convenience.

This does not mean every medical product should immediately adopt USB-C or externalized charging models. But for categories where portability, modern user expectations, or accessory compatibility matter, the external path can offer more future flexibility. OEMs that want to reduce redesign risk over the next several product generations should think carefully about how much standardization may matter in their category. In many cases, choosing a flexible external format today can help preserve strategic options tomorrow.

---

Choosing between open-frame and external adapters is not about picking a universally better technology. It is about understanding which architecture best supports the intended product, the development timeline, and the realities of use in the field. Internal power can deliver a polished integrated look and may suit larger stationary platforms well, but it typically asks more from the engineering team in terms of thermal planning, shielding, safety integration, and compliance management.

External adapters often reduce that burden by moving critical complexity outside the device. That can simplify certification, improve serviceability, reduce thermal stress, and support more flexible product packaging. For many OEMs, especially those designing portable or fast-to-market products, that tradeoff is extremely attractive. The strongest results usually come when this decision is made early and with a full view of design, manufacturing, service, and long-term product strategy.

Useful Links

• Explore Phihong’s power product capabilities
• Review medical power safety guidance
• Learn more about FDA medical device requirements

Related Articles

• How to Choose an Open-Frame Medical Power Supply
• How Thermal Design Affects Open-Frame Medical Power Supply Performance
• How to Design Internal Medical Power Systems

---

How Phihong Can Help OEMs Choose the Right Power Supply Approach

Phihong supports OEMs that need to evaluate the real tradeoffs between open-frame and external medical power solutions. That includes helping teams align their choice with product size, thermal constraints, certification goals, service expectations, and long-term manufacturing strategy. Rather than treating power as an afterthought, Phihong helps position it as a core part of successful medical device development.

With experience across medical power categories, Phihong can support projects that require efficient open-frame integration as well as those that benefit from globally deployable external adapters. This gives OEMs more flexibility when comparing compact portable products against larger stationary systems. It also helps teams reduce uncertainty when balancing compliance requirements, reliability goals, and user experience expectations.

For device makers looking to avoid redesign risk and move forward with more confidence, choosing the right power partner can make the evaluation process much smoother.

As medical products continue moving toward smaller form factors, cleaner industrial design, and more demanding compliance expectations, the decision between internal and external power will remain a major engineering checkpoint. Making that decision carefully can improve reliability, simplify development, and support a better experience for both OEM teams and end users.