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Open Frame vs. Enclosed Power Supplies —Which Is Right for You?
The power supply you choose for your application needs to meet your performance requirements and fit in the space allocated for it in your equipment, but when choosing an open frame power supply, it is essential to check voltage and efficiency specifications to ensure compatibility and optimal operation. The answer to whether you need an enclosure, of course, depends upon your application.
Open frame power supplies are available in a range of power ratings from 5 to 800 watts and are designed for applications in communications, computing, and industrial equipment.
For example, the needs for a home-use medical application may differ greatly from those when considering use in a manufacturing plant. These power supplies are renowned for their outstanding performance, reliability, and cost-effectiveness, making them a perfect fit for demanding environments. Some considerations are discussed below.
What Is the Difference Between Open Frame and Enclosed Power Supplies?
An open frame power supply typically is constructed by attaching electronic components to a printed circuit board (PCB), often on both sides. Open-frame power supplies are often component-certified, so the final product must meet full safety and EMI standards. Open holes in the corners of the PCB are provided to mount the power supply in its application, using spacers and screws directly to a chassis. In some cases, these mounts are required to provide a conductive path to earth ground for proper safety and/or EMC compliance and overall operation of the power supply. Open frame power supplies are available in various standard form factors, including 2" x 4" and 3" x 5". They can have universal AC input, making them suitable for global use, and many models provide auxiliary outputs for powering fans and standby circuits. Many open frame power supplies are available with a choice of single output or multiple isolated outputs with different voltage combinations. Open frame power supplies often include safety certifications such as UL 60950 and EN 60950. The exposed components of open-frame power supplies facilitate better heat dissipation.
An enclosed power supply takes the open frame format and encloses it in a frame or box. This enclosure is often metal (but can also be another material, such as plastic), and may be either solid or perforated. Indeed, some power supplies are fully-enclosed, sealed units, while others may use an enclosure similar to a fence or cage. The type of enclosure used depends on the environment and application in which the power supply is intended to be used.
What are Some Enclosed Power Supply Considerations?
Operator safety, electromagnetic compatibility, available space, and thermal management are all potential considerations when selecting a power supply for a particular application. It is important to check technical specifications, including voltage and efficiency, to ensure the open frame power supply meets your application's requirements and environmental suitability. Many open frame power supplies feature high efficiency switch-mode designs, which help optimize energy savings and performance. Additionally, open frame power supplies often include protections such as overload, overvoltage, and short circuit protections to enhance safety and reliability.
Operatory Safety
One of the most prevalent concerns related to power supplies is the safety of operators, repair workers, and service technicians. Because power supplies pose a risk of shock or electrocution if handled improperly or if parts of the body come into contact with certain circuits on the supply, many applications require a physical barrier to prevent such incidents. An open frame power supply will not offer much protection from such occurrences, since all its circuitry is exposed. However, many open frame power supplies are available with medical approvals and must be approved to meet stringent standards for safety, low leakage current, and minimal electromagnetic interference, making them suitable for sensitive medical applications. By adding an enclosure to a power supply, the risk of injury is reduced; in some cases, it can be all but eliminated. The type of enclosure and the size of any openings in it should consider each application and usage scenario.
Electromagnetic Compatibility (EMC)
Electromagnetic compatibility (EMC ) is a system's or equipment's ability to function without disturbing – or being disturbed by – its surrounding electromagnetic environment. An enclosed power supply can provide shielding that both protects it from electromagnetic interference and prevents it from interfering with nearby electronic equipment; however, an enclosure is not always necessary to achieve this. The performance specifications for each power supply will list its EMC ratings; look for Class A (less stringent) or Class B (more stringent) emissions ratings.
One detail to pay attention to regarding EMC performance is a requirement for an Earth Ground connection. While Class I safety designs utilize an Earth Ground, Class II safety designs do not require one for safety reasons; however, some Class II power supplies require an Earth Ground connection to meet prescribed EMC performance levels. In such a scenario, the connection to Earth Ground is called “Function Ground.”
Available Space
In many applications, the size of the power supply is a major consideration. Enclosed power supplies will typically have a bigger footprint and require a larger volume than an open frame design; however, an open frame design is not always an advantage for size-constrained applications. Certain spacing requirements, commonly known as “creepage and clearance”, for safety certifications must be considered when developing the complete product design. An enclosed power supply with a metal frame may already accommodate the safety spacing requirements, leading to a similar or even smaller overall application space requirement, versus an open frame power supply.
Thermal Management
Heat is a primary cause of electronic component failure in power supplies, so thermal performance is a significant consideration. All power supplies are rated for operation at specified power levels over a range of temperatures; at higher temperatures the allowed operating power level is lower. Sometimes an open frame power supply will provide a thermal advantage because its circuits are more open to the air, thus allowing for more cooling via free air convection. Depending on the design of an enclosed power supply, its rated operating power may be lower than that of a similar open-frame model; however, this is not always the case. Some power supplies rely on other methods, such as forced air (fan) or conduction cooling, as the primary way to reduce thermal strain, so it is important to review each power supply's performance specifications thoroughly.
Browse Power Supplies From Astrodyne TDI
Whether you’re looking for medical-grade power solutions or power supplies for industrial or commercial projects, Astrodyne TDI offers a wide range of open frame and enclosed power supply models. We design and manufacture a broad variety of innovative power solutions, with some of our products being used in lifesaving applications worldwide. Open frame power supplies can also be customized to meet specific application needs, and FSP Group offers customized designs and modifications to standard specifications for open frame power supplies.
We want to help you meet your unique job specifications. For support or inquiries, email us—email is a convenient way to reach our team for tailored solutions and customer engagement. Contact us today to learn more about our products and services!