Inverter Effectively Powers Liquid Crystal Display for New Ventilator System
Bringing a new product to market is an arduous task for any company. But when a human life depends on your product's performance, there is an even more heightened awareness that each facet of the manufacturing process carries equal weight and requires precise and diligent monitoring.
This is business as usual at Nellcor Puritan Bennett (NPB; Carlsbad, CA), a supplier of critical-care ventilators and respiratory care products. NPB recently introduced its 840 ventilator system, which provides sensitive, precision breath delivery for critically ill patients. The system introduced several innovative technologies including DualView LCD touch screens, a Sandbox ventilator settings area, and a SmartAlert alarm system.
Design of the LCD Was Critical
"When clinicians handle a ventilator, they need to locate the settings, set the parameters for the patient, and monitor the information, " says Peter Doyle, marketing manager for NPB's new ventilation technologies. "Having all this information on one screen is confusing—touching a button to get to a menu, then another menu, and often getting lost in a computer maze. It's a critical loss of time in an emergency situation."
"So it's not surprising to learn that when there is a problem with a hospital ventilator, most times it's not a problem with the device, but the result of human error," Doyle adds. "As a result, manufacturers like ourselves are taking a greater responsibility to design units that are much more user friendly to reduce these errors."
To keep it simple, the NPB 840 unit was designed with a unique screen layout that separates information into two screens. The DualView touch screens display monitors data separately from ventilator settings, while the Sandbox area on the screen allows the clinician to set up and preview all proposed ventilator alarm limit settings before applying them to a patient. The DualView liquid crystal display is backlit by two cold cathode fluorescent lamps (CCFLs).
Careful consideration had to be given to the dc-ac inverter that would power the DualView LCD. "Because the display is active all the time, it's one of the critical components of the design," says Jack McIntosh, NPB's engineering section manager for electronic development. "If the backlights are out, the display could be operating, but it won't do you much good."
Selecting the Right Inverter
"Because we had a dual display, we needed a dual inverter—an integrated, encapsulated dual-lamp power supply," says McIntosh. Some of the open-frame inverters that NPB considered could only power one CCFL, which would have required a separate PC board for each inverter/lamp.
Ultimately, NPB selected a vacuum-encapsulated dc-ac inverter from Endicott Research Group Inc., (ERG; Endicott, NY), to power the tubes. Measuring 1.26 x 1.56 x 0.60 in., a single ERG 200II inverter can power two CCFL tubes, provide 10 W maximum output, and is available with standard input voltages of 5 and 12 VDC. C and E configurations are available to provide extra pin control, allowing the inverter to be disabled and/or dimmed without adding series input components.
Two custom variations of the ERG E200II series were selected—the E2075 for the 840 units using the monochromatic display, and the E2019 for the 840 units (to be introduced in the fall of 1998) that have a color display.
The E200II series inverters operate at high efficiencies—typically between 80 and 85%—and are designed and tested using the actual LCD assembly. ERG's customized magnetics are self-shielding to effectively minimize EMI/RFI interference.
ERG Inc. manufactures power supplies for the information display market. For more information, contact ERG Inc., 2601 Wayne Street, Endicott, NY 13760; Phone: (800) 215-5866 ext. 3011; Fax: (607) 754-9255.