TEXAS INSTRUMENTS INCORPORATED

Patent Trials and Appeals Board

Aug 31, 2021

2020005192 (P.T.A.B. Aug. 31, 2021)

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
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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
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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
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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
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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