Frequency Matched Power Supply Solves Unique Challenge In Ultrasound Equipment
By Marshall Wright (COO),
Art Alva (Application Engineer)
and Ryan Benhard (Product Engineer),
Elpac Power Supplies
Overview
Recently a major medical device company approached Elpac with a technical challenge regarding their development of new ultrasound equipment. This challenge led to Elpac developing a new product – a “synchronized frequency power supply.” This article describes the project, including a discussion of how ultrasound equipment can benefit from the innovative design approach Elpac took to solve the customer’s problem.
Simplified Ultrasound System
Ultrasound – Background
Ultrasound or ultrasonography is widely used as a diagnostic tool in the field of medicine. Ultrasound provides physicians with a noninvasive method to look inside the human body in a way that is much safer than surgical methods. Ultrasound is used in virtually every branch of medicine to help medical personnel observe, study, and treat a large variety of conditions. It is used in the field of obstetrics (sonogram) to study the sex, age, and level of development of the fetus and to determine the presence of birth defects and other potential health problems. Ultrasound is also used in cardiology to study heart problems and has many other important medical applications.
Ultrasound works by scanning the body with a probe that emits highfrequency sound wave pulses. When these sound waves contact the areas of concern in the body they are reflected back to the probe. The probe transmits these reflected sound waves to the central processing unit of the ultrasound machine where an image is generated based on the distance and intensities of the reflected sound waves. A two dimensional image is then displayed on a monitor screen which allows the physician or technician to view an accurate depiction of the area of concern. The condition can then be properly evaluated and diagnosed and the best course of treatment can be determined. Medical professionals expect and rely on the displayed images to be accurate in order to make the correct analysis.
Insight to a Design Issue
However, as one specific manufacturer of this equipment has discovered, ultrasound is particularly sensitive to interference and this interference may cause a degraded, or in extreme cases, false image to be displayed. Inaccurate images may lead to an inappropriate diagnosis or treatment, which would be unacceptable in the medical profession.
Ultrasound equipment is sensitive to interference because it uses analog waveforms (sound waves) to “see” inside of the body. However analog waveforms can be subject to distortion stemming from different types of electrical interference such as EMI and RFI. This interference can cause variations that could be misinterpreted as data by the ultrasound’s central processing unit and cause the degraded or false images to be generated and displayed. The ultrasound manufacturer’s engineering team had designed filters into the system to protect the central processing unit from any internally produced interference that is generated at the operating frequency of the equipment. However, the engineers also realized that the power source, a switching power supply connected to power to their equipment, could also be a major source of interference. Since the power supply and theultrasound system can operate at different frequencies, a complex array of harmonic noise could result. Designing filters in the central processing unit to eliminate the resulting harmonic noise would be very difficult. The selected solution was to develop a power supply that operated at a switching frequency matching the operating frequency of the ultrasound machine.
Power Supply Design Challenge
Designing a power supply with a switching frequency that matches the operating frequency of the ultrasound equipment is straight forward. However, there was another requirement adding to the engineering expertise needed to design this supply. Because the operating frequency of the ultrasound equipment could vary during normal use, the power supply needed the ability to sense the ultrasound’s operating frequency and adjust its own switching frequency to match. Furthermore, this “frequency matching or synchronization” would have to be done dynamically, in a real world environment.
Based on these requirements, the ultrasound manufacturer developed a
specification for the “Synchronized Frequency” power supply that they
envisioned. Among the requirements were the following specs:
• Medical Grade Combination Power Supply and Battery Charger
• Universal input (85-264VAC@47-440Hz or 120-375VDC)
• Output 1: +15VDC, 2.0-3.4A
• Output 2: +12.6VDC, current source for battery charging
• Synchronized Switching frequencies at either 62.5KHz or 83.3KHz
The ultrasound manufacturer invited several major power supply manufacturers to submit a development bid to their specification. Of the seven companies that were invited to submit a bid, six said it could not be done. Elpac, however, was confident they could meet the challenge. The ultrasound manufacturer was pleased with Elpac’s positive reply but, because consensus among the other technical teams was clearly negative, requested a technical explanation from Elpac.
Innovative Design Approach
The Elpac team presented their technical approach. They explained that their design would add a dedicated timing circuit to the switching power supply’s normal circuitry. This timing circuit would receive a signal from the ultrasound system via a RATE/SYNC line that would indicate the operating frequency of the ultrasound in real time. Based on this signal, the timing circuit would set the power supply’s system clock to operate at the matching frequency. When the frequency of the ultrasound system changed, the timing circuit in the power supply would receive a new RATE/SYNC signal and adjust the power supply system clock to change frequency accordingly. By this method the power supply and the ultrasound system’s operating frequencies would always be synchronized and the production of harmonics that could adversely affect the ultrasound image would be eliminated.
The Engineering team also explained that the same advanced design and manufacturing methods that have made Elpac a leader in innovative and very high reliability power supplies would be employed, ensuring that the customer’s requirements would be met at all stages of development and production. Satisfied by this explanation, the customer concluded that Elpac possessed the technical and manufacturing capability needed to meet their expectations and the stringent requirements for a “synchronized frequency power supply.” As a result, Elpac was engaged to design and manufacture it.
Implementation – with an Unexpected Twist
All phases of engineering development proceeded smoothly and on schedule. Prototypes were built and delivered to the customer for approval in less than eight weeks. After customer approval, regulatory agency approval was obtained and volume production was started. The product was delivered in eight weeks as promised to meet the customer’s product launch schedule.
Unfortunately, one week before the product launch was to occur, the customer realized that a design change was needed in their equipment, and that this change would require a change in the Elpac power supply. The product launch included an international sales meeting bringing in people from all over the world. The plan was to have each of them leave with a working piece of the ultrasound equipment to begin selling worldwide. Canceling this meeting was not an option. However, in order to successfully launch the product and provide the sales people with equipment working to the new specification, the customer needed two hundred power supplies modified to their new requirements.
The call went out to Elpac on a Thursday afternoon that the modified power supplies would be needed by the following Monday morning. Elpac brought in the needed Engineering and Production personnel to work throughout the weekend, implement the changes, and perform the re-work necessitated by the customer’s modified specification. Early Monday morning an Elpac employee boarded a plane with the newly revised power supplies, and while the sales people were still having their morning coffee and donuts, hooked up the new power supplies to the customer’s equipment. The sales people at the meeting never knew what these two technical teams had pulled off. Every one of the sales people left that meeting with a working unit to demonstrate to the customers in their local market. The ultrasound company, needless to say, was quite pleased with Elpac’s level of service and summed it up by telling Elpac, “you guys are awesome!”
Elpac is proud that their innovative and advanced design and manufacturing capabilities allowed its employees to participate in this project. The synchronized frequency power supply they developed plays a role in helping medical professionals to better diagnose and treat disease and illness, thereby increasing the overall quality of life for patients worldwide.
About Elpac
Elpac Electronics, Inc. is a leading manufacturer of power supplies, AC/DC adapters, custom docking stations and battery chargers. Based in Irvine, CA with manufacturing at a company-owned and operated facility in Shenzhen, China, Elpac is a privately-held firm that combines innovative U.S. design capabilities with Chinese production efficiency. Elpac customers are major international OEMs, typically leaders in their fields, who utilize the firm’s ability to custom-design products to meet their most challenging requirements.
The company emphasizes design and manufacturing techniques that far surpass industry norms. For example, all products are tested to “demonstrate” MTBF (Mean Time Between Failures) of at least 100,000 hours at 40 degrees Celsius (compared to many manufacturers who merely “calculate” MTBF at a lower temperature).
Elpac is credited with an exceptional customer service record, evidenced by surveys scoring customers’ satisfaction at 92%, far above the national average of 74% (according to the American Customer Satisfaction Index survey conducted by the University of Michigan Business School).
Its most popular products are available in OEM quantities, at OEM pricing, in 3 weeks or less FOB Asia. For more information, visit www.elpac.com.
About the Authors
Marshall Wright is the Chief Operating Officer of Elpac Electronics, Inc. in Irvine, California. He received his BSIE and MSIE from Stanford University.
Ryan Benhard is a Product Engineer at Elpac Electronics, Inc. in Irvine, California. He holds a BSEE/ME from Rose-Hulman Institute of Technology.
Art Alva is an Application Engineer at Elpac Electronics, Inc. in Irvine, California and has been in the electronics industry for over 20 years.
For Additional Information
Elpac Electronics, Inc.
1562 Reynolds Avenue
Irvine, California 92614 USA
TEL +1 949-476-6070
FAX +1 949-476-6085
info@elpac.com
www.elpac.com
Elpac and Elpac Electronics are trademarks of Elpac Electronics, Inc. All other brand or product names are or may be trademarks of, and are used to identify products or services of, their respective owners.