In the still-custom and basically OEM transformer business, the cost of quickly spinning new platforms using planar, or flat, transformers in embedded designs is still too high for many applications. As a result, the shift from largely embedded solutions to a standalone-components business is accelerating.
Unlike traditional embedded transformers, which use core halves attached to both sides of a system's highly custom multilayer printed-circuit board and access a portion of the board's foil for their windings, standalone planar transformers have small pc boards mounted within their core pieces, in a construction resembling a traditional wirewound component. They take up somewhat more space in the vertical dimension. But the standalone type can be customized apart from the system circuit-board design they snap into, thus making for a more cost-effective system.
It's a simple end goal for most vendors, a curious mix of ferrite-core manufacturers and dc/dc converter suppliers with varied transformer-making capability. For ferrite makers in particular, the quest also means developing standard component lines. Sensing the shift from an embedded to a standalone philosophy, at least one ferrite-core vendor, MMG North America (Patterson, N.J.), can equip designers with new software tools to speed designs to market.
"We're in preproduction with half a dozen standalone designs just in the last several months," said David Smolik, director of new-product development for magnetics at BI Technologies (Fullerton, Calif.), a magnetics/transformer specialist with experience in both component and embedded technologies. "We're pushing for a standard family of [dc/dc planar] products for telecom."
Such a design implies step-down transformers operating at a few hundred kilohertz, with turns ratios of less than 10:1 and a power-handling capability up to about 100 watts. Once among the less aggressive pursuers of the component transformer, BI has witnessed the shift from embedded designs and taken its cues from the market. "We once felt that customers would forever be using circuit-board [embedded] windings," said Donna Schaefer, design applications engineer. "But we saw that discrete transformers could be cost-competitive in certain applications."
More of the established dc/dc converter makers, many of them with some level of planar-transformer program in-house, tend toward that view. Historically, they've largely favored embedded designs, which conserve real estate and maximize power density, but have found that customers are willing to go only so far when it comes to cost. Less known, perhaps, is that many of the major dc/dc vendors have applied the standalone planar transformer in their own designs for several years.
The advantages of component planars lie in their "pure interchangeability," said Rob Hill, vice president sales and global marketing for C&D Technologies' Power Electronics division (Tucson, Ariz.).
C&D's latest planar transformers for in-house use include one (for 20-W converters) in a construction that can be easily tailored to the specific power application by swapping out the printed-circuit board. The company has also developed an architecture to improve efficiency in an embedded-style transformer that uses what C&D terms a "split secondary," in which the secondary windings are sandwiched between the top layer of windings (half the primary) and the traces of the main pc board (the other half of the primary). It's for the soon-to-be-released WPA60 dual-output quarter-brick.
"We haven't used embedded designs since about 1996," said Don Matthieson, product manager at Texas Instruments Inc. in Warrenville, Ill., which uses component-type planar transformers that can deliver up to about 150 W in the company's dc/dc designs. "The pc board [for the embedded design] is expensive, because it really does have to be special."
While component-type planar transformers appear to be picking up, the migration is not a one-way street for dc/dc makers. At the very least, the experiment is tempered by the best engineering practice suited to a given application. Indeed, the use of both embedded and standalone technologies in a particular system design is not unheard of. "There are really no hard-and-fast rules," said Joel Zaens, dc/dc product-marketing manager at Astec Power (Carlsbad, Calif.), which has developed embedded planar designs for telco. "What's the dividing line?" There is none, Zaens concluded, but he noted that embedded designs are particularly used to advantage when thermal considerations are a major factor, and board pitch and airflow considerations prime design parameters.
Ferrite-core makers, meanwhile, see the future veering more in the direction of the discrete planar transformer, citing the practical need-at least in principle-to do away with the custom parent pc board they would otherwise need.
MMG North America's NeoPlanes design kit is one of the few hardware/software tools to help users specify planar-transformer designs and facilitate fabrication. "Designs are changing continuously," said Brian Wiese, director of sales and marketing at MMG. "A good solution is standalone transformers you just insert into the board."
The NeoPlanes products consist of sets of planar winding elements. Each individual element contains a multilayer pc winding, with solder pads for simple interconnection and assembly. The line is supported by the company's NPgo software, which makes it possible to specify selectable turn variants with one, two, four, six, eight, 12 or 16 turns. Up to eight elements can be stacked in a ferrite EE core set.
Using this system yields a large number of practical designs from relatively few NeoPlanes elements, the company said.
MMG's NeoPlanes hardware/software kit facilitates rapid design and delivery of planar transformers.
BI Technologies Corp.
C&D Technologies Inc.
MMG North America
Texas Instruments Inc.