TEXAS INSTRUMENTS INCORPORATEDDownload PDFPatent Trials and Appeals BoardAug 31, 20212020005192 (P.T.A.B. Aug. 31, 2021) Copy Citation UNITED STATES PATENT AND TRADEMARK OFFICE UNITED STATES DEPARTMENT OF COMMERCE United States Patent and Trademark Office Address: COMMISSIONER FOR PATENTS P.O. Box 1450 Alexandria, Virginia 22313-1450 www.uspto.gov APPLICATION NO. FILING DATE FIRST NAMED INVENTOR ATTORNEY DOCKET NO. CONFIRMATION NO. 15/707,257 09/18/2017 PEI-HSIN LIU TI-77217 8068 23494 7590 08/31/2021 TEXAS INSTRUMENTS INCORPORATED P O BOX 655474, MS 3999 DALLAS, TX 75265 EXAMINER AHMAD, SHAHZEB K ART UNIT PAPER NUMBER 2839 NOTIFICATION DATE DELIVERY MODE 08/31/2021 ELECTRONIC Please find below and/or attached an Office communication concerning this application or proceeding. The time period for reply, if any, is set in the attached communication. Notice of the Office communication was sent electronically on above-indicated "Notification Date" to the following e-mail address(es): uspto@ti.com PTOL-90A (Rev. 04/07) UNITED STATES PATENT AND TRADEMARK OFFICE BEFORE THE PATENT TRIAL AND APPEAL BOARD Ex parte PEI-HSIN LIU and JAMES MICHAEL WALDEN Appeal 2020-005192 Application 15/707,257 Technology Center 2800 Before JEFFREY T. SMITH, DEBRA L. DENNETT, and MERRELL C. CASHION, JR., Administrative Patent Judges. SMITH, Administrative Patent Judge. DECISION ON APPEAL STATEMENT OF THE CASE Pursuant to 35 U.S.C. § 134(a), Appellant1 appeals from the Examiner’s decision to reject claims 1–3, 10, 11, and 16. Final Act. 1. We have jurisdiction under 35 U.S.C. § 6(b). We REVERSE. 1 The term “Appellant” to refers to “applicant” as defined in 37 C.F.R. § 1.42. Appellant identifies the real party in interest as Texas Instruments Incorporated. Appeal Br. 2. Appeal 2020-005192 Application 15/707,257 2 CLAIMED SUBJECT MATTER The claims recite a power converter with zero-voltage switching. Claim 1, reproduced below, is illustrative of the claimed subject matter: 1. A power converter circuit comprising: a power stage comprising a transformer and a switch, the switch being controlled in response to a pulse-width modulation (PWM) signal to provide a primary current through a primary winding of the transformer to induce a secondary current in a secondary winding of the transformer to generate an output voltage, the power stage comprising a switching node between the switch and the primary winding having a switching voltage; and a switching controller configured to generate the PWM signal in response to a ramp signal, the ramp signal having a slope that is proportional to a decay rate of a magnetizing current associated with the transformer and generated in response to at least one feedback voltage from the power stage, the switch being activated in response to the switching voltage having an amplitude of approximately zero volts based on the amplitude of the ramp signal. REFERENCES The prior art relied upon by the Examiner is: Name Reference Date Liu US 2015/0256084 A1 Sept. 10, 2015 Zhang US 2016/0329821 A1 Nov. 10, 2016 Fahlenkamp US 2017/0288554 A1 Oct. 5, 2017 Lin US 2018/0301975 A1 Oct. 18, 2018 REJECTIONS I. Claims 1–3 and 11 are rejected under 35 U.S.C. § 103 as unpatentable over Fahlenkamp and Lin. Final Act. 5. Appeal 2020-005192 Application 15/707,257 3 II. Claim 10 is rejected under 35 U.S.C. § 103 as unpatentable over Fahlenkamp, Lin, and Zhang. Final Act. 9. III. Claim 16 is rejected under 35 U.S.C. § 103 as unpatentable over Fahlenkamp, Lin, and Liu. Final Act. 9. OPINION After review of the respective positions Appellant and the Examiner provide, we determine that Appellant has demonstrated reversible error in the Examiner’s rejections under 35 U.S.C. § 103. We limit our discussion to independent claim 1.2 The dispositive issue for this appeal is: Did the Examiner err in determining that it would have been obvious for one skilled in the art to modify the circuit of Fahlenkamp and incorporate the zero voltage switching scheme of Lin to include a clamp circuit? We answer this question in the affirmative. The Examiner finds Fahlenkamp teaches a power converter circuit substantially identical to that recited in claim 1 including a transformer with primary and secondary windings and respective primary and secondary currents, and a switching controller to generate a pulse-width-modulation (PWM) signal in response to a ramp signal having a slope that is proportional to a decay rate of a magnetizing current associated with the transformer. Final Act. 5. The Examiner finds Fahlenkamp does not teach a switching node between the switch and primary winding having a switching voltage, and the switch being activated in response to a switching voltage 2 Our analysis also applies to independent claims 11 and 16. Appeal 2020-005192 Application 15/707,257 4 having an amplitude of approximately zero volts as required by claim 1. Final Act. 5. Addressing this difference, the Examiner finds Lin teaches a power converter circuit similar to Fahlenkamp that further includes a switching node between the switch and the primary winding of the transformer. Final Act. 6. The Examiner finds Lin teaches the switch is activated in response to the switching voltage having an amplitude of approximately zero volts. Final Act. 6. The Examiner determines it would have been obvious to one skilled in the art to modify the circuit of Fahlenkamp and incorporate a clamp circuit to define a switching node and use the zero voltage switching scheme of Lin to reduce switching loss, eliminate overlap between current and voltage, and utilize leakage currents and minimize electromagnetic interference. Final Act. 6. Appellant argues Fahlenkamp and Lin have circuitry that is not properly combinable because there is no motivation to include the features of Lin in Fahlenkamp to diminish the primary side energy because there is no primary side energy in the Fahlenkamp circuit. Appeal Br. 10–12. Appellant argues Fahlenkamp has no current passing through the primary side of the transformer once the electronic switch has been turned off. Appeal Br. 11; Fahlenkamp ¶ 34. Appellant contends the primary side of Fahlenkamp does not have inductors or capacitors for energy storage. Reply Br. 4. Appellant further argues, contrary to Fahlenkamp, Lin teaches that when a first switch is turned off, a second switch is turned on to store energy on the primary side of the transformer to be transferred to an auxiliary capacitor to dissipate energy from the coil/inductor on the primary side and store that energy in primary side capacitor Cr because the stored energy is used to offset energy stored in the parasitic capacitor, Coss, so that primary Appeal 2020-005192 Application 15/707,257 5 side switch S1 is zero voltage switching when turning ON. Appeal Br. 11; Lin ¶ 38. Appellant’s arguments are persuasive of reversible error. Fahlenkamp teaches during the demagnetization period the current switches from the primary side to the secondary side. Fahlenkamp ¶ 34. Contrary to Fahlenkamp, Lin teaches that when a first switch is turned off, a second switch is turned on to store energy on the primary side of the transformer to be transferred to an auxiliary capacitor. Lin ¶ 38. The Examiner has not adequately explained why incorporating the additional components of Lin to the primary side of the Fahlenkamp’s transformer would add to the efficiency of the circuit because any residual energy remaining in Fahlenkamp would have been minimal. Since the primary side current of Fahlenkamp is zero during the demagnetization period, there should not be any switch loss, leakage loss, or EMI during the demagnetization period. Consequently, the Examiner has failed to properly explain how the combination of Fahlenkamp and Lin renders obvious the limitations of independent claims 1, 11, and 16. Accordingly, we do not sustain the Examiner’s 35 U.S.C. § 103 rejections of all the claims on appeal that rely on the combination of Fahlenkamp and Lin together or with additional references. The additional references, Zhang and Liu, fail to cure the deficiency discussed above. Appeal 2020-005192 Application 15/707,257 6 DECISION SUMMARY Claim(s) Rejected 35 U.S.C. § Reference(s)/Basis Affirmed Reversed 1–3, 11 103 Fahlenkamp, Lin 1–3, 11 10 103 Fahlenkamp, Lin, Zhang 10 16 103 Fahlenkamp, Lin, Liu 16 Overall Outcome 1–3, 10, 11, 16 REVERSED Copy with citationCopy as parenthetical citation