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How Long Can It Go? An Introduction to Power Supply Reliability Information

Engineers looking for a power supply have to sort through countless choices. There are countless available models to evaluate, each with a product description or datasheet that touts important characteristics relating to the supply’s performance and operating features. The description may even include pricing information. But when you take a deeper dive into the product information, you’ll see acronyms like MTBF and MTTF. They may not mean much if they go into machines that will only see sporadic use. But, when your device is expected to run 24/7 or go into, for example, a life-saving medical device, reliability should be very high on a designer’s list of selection criteria. If a power supply fails, it can disable a system and also cause major damage to critical equipment.

This blog series will review basic power supply reliability concepts, including mean time between failure (MTBF) and mean time to failure (MTTF). Both terms are deceptively similar yet very different. Moreover, power supply manufacturers use different standards and methodologies to calculate reliability ratings. We’ll also discuss power supplies with internal electrolytic capacitors and how a cap’s lifetime can be just as important as MTBF and MTTF when predicting system reliability. This series intends to help foster a better understanding of the information available to buyers looking to select a power supply that will meet the reliability requirements that their application demands.

Stay tuned for Part Two of this series, and be sure to sign up for our newsletter to receive updates by email.

 

White Paper Demystifies Today’s Complex Power Supply Data Sheets

The operating and safety specifications for power supplies have become more complex, adding to the length, level of detail and complexity of their data sheets. Our latest white paper, Interpreting Complex Data Sheet Specifications for Power Supplies, provides an overview of the extensive technical information that today’s power supply designers must examine as they review product data sheets.


The white paper covers important concepts such as interchangeability considerations, thermal management, and the mechanical drawings that show the relationships between specifications. It also helps engineers sift through the growing number of mounting and remote placement options so they can make efficient use of space in ever-shrinking end products. And since specific industries like medical and railways have special requirements, readers will find a section explaining safety and certification information. While data sheets are becoming longer, the information they provide is now much richer. This white paper will help customers apply that additional knowledge to make well-informed purchasing decisions.

For more information, download our white paper, Interpreting Complex Data Sheet Specifications for Power Supplies.

 

 

 

One MOPP or Two? Select a Medical Power Supply That Prevents Shock

Medical equipment designers have to not only make sure their device performs as intended but also do so without compromising the safety of the patient or operator. Electrical shock is an important safety hazard in medical equipment, and design requirements that address it are strict by necessity. To mitigate shock and other safety risks, power supplies must comply to International Electrotechnical Commission (IEC) 60601-1 3rd edition medical equipment standards pertaining to isolation voltage, leakage current and creepage/clearance distances. This blog will review two of the many safety categories to remember when selecting a power supply for medical devices.

Isolation and Insulation Requirements

Patients can be potentially vulnerable to electric shock when they come in contact with, or come in close proximity to certain medical devices. IEC 60601-1 3rd edition standards for isolation between circuits within the medical power supplies include AC input, internal high-voltage stages and DC output. Isolation is accomplished using either double insulation or reinforced insulation. (Shock prevention in Class I electrical equipment only calls for basic insulation and uses protective earth grounding methods.)

Within IEC 60601-1 3rd edition, isolation protection can be classified as MOOP (means of operator protection), which means the device doesn't have to come into contact with a patient, or MOPP (means of patient protection) in which contact is required. For medical power supplies, the insulation criteria for MOOP or MOPP protection are: one layer of insulation at 240V AC requires a test voltage of 1500 V ac; MOOP requires 2.5 mm of creepage, and MOPP requires 4 mm of creepage.

However, advances in power supply technology allow for an even higher grade of safety. When choosing a medical power supply, consider manufacturers that offer two means of patient protection for devices requiring MOOP or MOPP safety. 2MOPP classified power sources at 240 V AC require a test voltage 4000 V AC and 8 mm of creepage. Supplies that meet these highly stringent 2MOPP requirements not only offer optimal patient shock protection but also help ease the end product approval process in a broad range of medical products.

Medical device designers should work closely with the power supply manufacturer to determine the shock protection they need while also considering other safety and performance factors. Not all power supplies adhere to the values spelled out in IEC 60601-1 3rd edition. Polytron's medical power supplies meet or exceed IEC 60601-1 requirements and offer 2MOPP protection. When combined with their very low leakage current characteristics, they can be an ideal choice for medical devices that contact operators or patients.

For more information, download our white paper, Selecting Power Supplies for Medical Equipment Designs.

 

 

Interpreting Complex Data Sheet Specifications—Part V

In our fifth blog on interpreting complex data sheets, we turn to safety specifications. Many certifications listed on data sheets require rigorous testing—especially for the medical and railway industries. Data sheets are required to indicate all new certifications, testing procedures, special model numbers and designations, which adds to their length but provides a lot of useful information for end-users.

Let’s take a closer look at this trend through the lens of medical and railway, which are the two industries most heavily impacted by increased safety regulations:

 

 

Avoiding EMI In Medical Equipment. The medical industry has many standards related to leakage current, EMI resistance and voltage isolation—all of which must be avoided in machines and devices that come into direct contact with patients. In addition, the close proximity of equipment in hospitals increases the risk of noise interference, which could cause medical devices to work incorrectly at a critical time. Safety specifications, particularly ones related to EMI, therefore ensure power supplies pose no risk of interference. mount—and more.

Some specific examples include:

  • IEC-60601-1: the technical standards for medical electrical equipment in terms of safety and performance
  • 5000 Vac Isolation: a standard stipulating 1000 V more than the required isolation for IEC 60601-1
  • 2 X MOPP: the isolation, creepage and insulation requirements for medical products coming into contact with patients
  • Standards related to low leakage currents under 75 uA

Protecting Train Passengers. Power supplies used in railway applications also have their fair share of standards. Consider the EN 45545-2, which specifies how materials used on trains must be fire-tested, or the EN 50155, which outlines the specifications of electronic equipment used on railcars. The EN 50155 also requires power supplies to pass various tests related to electrical insulation, power surges, ESD and voltage transients—all of which are intended to protect the passengers onboard.

Additionally, the railway industry requires its own special input voltage range of 43 to 160 V, which doesn’t exist for other applications. To account for this, Polytron and other power supply manufacturers have had to add more models to their product portfolios.

Effect On Data Sheets. Because of the increase in safety specifications and, in many cases, the addition of new products that comply with these standards, data sheets have become longer. While on the one hand, this trend has complicated data sheets, the addition of these details makes data sheets much more useful for customers who require power supplies for medical and railway applications.

Keep an eye out for our new white paper, which breaks down all the specifications you can expect to see on power supply data sheets. In the meantime, sign up for our newsletter (left-hand toolbar) to receive updates by email.

 

 

Interpreting Complex Data Sheet Specifications—Part IV

Next up in our ongoing series on interpreting complex data sheets is packaging. In the past, power supply manufacturers typically offered only two mounting options: PC or chassis. But now, products must be available in a variety of other mounting options—all of which require mechanical drawings that must be included on data sheets.

Let’s take a more detailed look at this trend:

 

 

More Mounting Options Than Ever. Originally, power supplies were mounted one of two ways: PC mount with pins or chassis mount with screw terminal. But now, customers want smaller power supply packages to fit ever-shrinking end products. Manufacturers have responded by providing more mounting and remote placement options, including DIN rail, open-frame and enclosed types, terminal block, surface mount—and more.

Here’s a rundown of some of these options:

  • In a PC mount, the power supply is soldered directly onto the printed circuit board using pins. This was the standard for producing larger circuits contained in even larger multi-board designs.

  • Chassis mounts allow you to remotely mount the power supply in a variety of ways: close to the load, on a frame inside the enclosure or outside the enclosure. What you ultimately choose depends on available real estate, the dimensions of your power supply and the operating environment.

  • DIN rails let you mount power supplies and other industrial control equipment within enclosures or equipment racks. This mounting option utilizes space efficiently, as devices can be mounted next to each other in a variety of ways to meet system requirements.

  • Surface mounts are the future of the PC mount. Nowadays, many products—and power supplies, for that matter—are getting smaller. Surface mount technology favors this trend: it utilizes solder paste rather than larger pins, taking up less space.

More Options Means More Drawings. But your options don’t end there. Depending on the direction of your connection, you may require a right angle, straight on or vertical mount. You may also require mounting types that integrate fans, heat sinks, input and output cables, connectors and safety tabs.

Not only do these various packages have to be listed on data sheets, but they must be accompanied by mechanical drawings that outline their dimensions and in some cases, provide a view from the top, front and bottom. Additional graphs, indicating derating curves versus ambient temperature, for example, are also needed when adding fans and heat sinks.

More on power supply specifications. Stay tuned for more on this series. In next month’s blog post, we’ll delve into our final topic: safety specifications. In the meantime, sign up for our newsletter (left-hand toolbar) to receive updates by email.