Court: Court of Appeals for the Federal Circuit; May 24, 2004; Federal Appellate Court
VLT, Inc. appeals four final judgments of noninfringement of reissued U.S. Patent 36,098 in favor of Artesyn Technologies, Inc. and others, as well as Lambda Electronics, Inc., Lucent Technologies, Inc., and Power-One, Inc. Artesyn cross-appeals a ruling that claims 1 and 5 of the patent are not invalid. The court affirmed the district court’s decisions on claim construction and validity, finding no errors in the interpretation of key terms or in concluding that claims 1 and 5 are not indefinite.
The ’098 patent, a reissue of U.S. Patent 4,441,146, pertains to a reset mechanism for a transformer’s core in a single ended forward converter. Claim 1 describes a system for recycling magnetizing energy during the OFF period of a primary switch, including a storage capacitor, an auxiliary switch, and a control circuit. Claim 5 specifies that the auxiliary switch must be a MOSFET transistor with an integral reverse diode.
The district court's claim construction defined several terms: "recycling the magnetizing energy" requires the complete return of magnetizing energy; "said auxiliary switch is opened prior to the ON period" necessitates a delay to discharge parasitic capacitances and reduce heat loss; "ON period" is when the primary switch conducts; "single ended forward converter" refers to a converter controlled by a single switch; and "auxiliary switch" defines a switch in series with the storage capacitor that does not manage power flow from source to load.
In the Artesyn case, the district court determined that the term “ON period” is sufficiently definite, thereby affirming the validity of claims 1 and 5. VLT and the four defendants reached stipulations: Artesyn’s E-series converters infringe claims 1 and 5, while its B-series, N-series, and BXE200-300 converters do not infringe based on the court’s interpretations of “recycling” and “prior” limitations. Additionally, in the Lambda and Lucent cases, it was agreed that certain converters from Lambda and Lucent do not infringe due to the court's construction of the “recycling” limitation. In the Power-One case, Power-One’s Q-series converters with an active clamp were also found not to infringe. The court issued final judgments of partial infringement and noninfringement in these matters, with VLT appealing the noninfringement judgments and Artesyn cross-appealing the judgment of no invalidity. The consolidated appeal focuses on claim construction and validity, with the court reviewing these issues de novo. VLT contends that the “recycling” limitation requires that magnetizing energy removed from the transformer be utilized rather than dissipated. However, Artesyn, Lambda, and Lucent argue that the district court correctly interpreted this limitation to mean that all magnetizing energy must be returned to the transformer for it to reset. The claim language and specification support this interpretation, emphasizing that the recycling mechanism resets the transformer’s core by returning all stored magnetizing energy, thereby maximizing the available flux swing.
VLT contends that the specification describes the use of a current mirror and maximization of flux swing solely as objectives within the preferred embodiment. However, it is clarified that all disclosed embodiments incorporate a current mirror, and the patent consistently describes the invention as employing a magnetizing current mirror as the reset mechanism. The specification indicates that returning all magnetizing energy to the transformer is essential, affirming the district court’s interpretation of "recycling the magnetizing energy stored in said transformer to reset it" to mean complete return of energy for reset, excluding any reset mechanisms that transfer energy to the load.
Regarding the "prior" limitation, VLT argues the district court misinterpreted it, asserting it merely requires a delay between the opening of the auxiliary switch and the closing of the primary switch. Artesyn and Lambda disagree with the district court for different reasons, claiming no delay is necessary. In contrast, Power-One supports the district court’s interpretation, stating it necessitates a useful switching delay to manage parasitic capacitances and reduce heat loss. The district court's construction correctly reflects that the auxiliary switch must open before the primary switch closes. Although the specification does not specify a required delay, it suggests minimizing any delay to avoid “dead time,” while noting that a slight delay can be beneficial for managing parasitic capacitances related to the switches and windings.
A small switching delay is deemed desirable within the context of balancing the reduction of "dead time" with the need to charge and discharge parasitic capacitances. The patentee did not explicitly disavow reset mechanisms that do not incorporate this small delay. However, the prosecution history necessitates interpreting the "prior" limitation as requiring a delay that facilitates the charging and discharging of these capacitances. During reissue proceedings, the patentee highlighted that their invention uniquely incorporates a small switching delay for this purpose, asserting that no prior art referenced such a delay in single-ended forward converters with active reset mechanisms. The patentee's statements during these proceedings, including the assertion that the small delay is essential for a skilled artisan to realize the invention's benefits, indicate a clear disavowal of other reset mechanisms. The examiner's allowance of claims, including claim 1, was based on this characterization, noting that prior art did not teach the timing necessary for effective charging and discharging. Consequently, the "prior" limitation in claim 1 is confirmed to necessitate a small switching delay that is effective for this purpose. Furthermore, the delay must also be sufficient to reduce heat loss, as the inventor criticized prior art for switching losses linked to the energy dissipation in parasitic capacitances. Thus, the conclusion is that the required delay serves to minimize switching losses, aligning with the district court's finding that it should significantly reduce heat loss.
The district court's interpretation of the "prior" limitation is upheld, requiring a small delay between the opening of the auxiliary switch and the closing of the primary switch to allow for the charging and discharging of parasitic capacitances, while also aiming to reduce switching losses. Lambda and Lucent contest the definition of "single ended forward converter," asserting it should be limited to energy transfer occurring only during the ON period of the primary switch. However, VLT counters that energy transfer can occur during both ON and OFF periods. The court agrees with VLT, affirming that the term aligns with the patent's specification, which defines it as a converter where a single switch controls power flow from the primary to the secondary winding during the ON period. Lambda and Lucent's argument lacks intrinsic evidence for a narrower interpretation. Lastly, Lucent's claim regarding the term "auxiliary switch" is not addressed, as it only raises factual issues of infringement without challenging the district court's definition that does not involve controlling power flow.
Artesyn's cross-appeal challenges the district court's determination that claims 1 and 5 of the ’098 patent are not invalid under 35 U.S.C. 112, ¶ 2, arguing that the term “ON period” is indefinite. Artesyn asserts that a person skilled in the art would not discern whether this term is defined in current or voltage terms. In response, VLT contends that the term is not indefinite, and the court agrees, noting that while the patent does not explicitly define “ON period” and it lacks a singular meaning in the relevant field, it is amenable to construction. The court referenced expert testimony indicating that those skilled in the art would interpret “ON period” as having a current-based definition. Citing precedent, the court concluded that a claim is not indefinite if its meaning is discernible, even if challenging to ascertain. Artesyn failed to provide a compelling reason for reversal. Therefore, the court affirmed the district court's ruling that claims 1 and 5 are not invalid for indefiniteness. Additionally, the passage discusses the patentee’s remarks during reissue proceedings concerning delay requirements in claim 1 but indicates that judicial estoppel would not be applied, as the district court did not choose to exercise discretion on this matter. The court also intends to review the term "single ended forward converter," as it is critical to pending infringement issues.
