PTAB

IPR2017-01907

Power Integrations Inc v. Semiconductor Components Industries LLC

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Petition
petition

1. Case Identification

2. Patent Overview

  • Title: Circuit and Method for a Switching Power Supply with Primary Side Transformer Sensing
  • Brief Description: The ’624 patent describes a regulation circuit for a switched-mode power supply. The purported invention uses feedback derived only from the primary side of the power supply’s transformer to regulate the output voltage, which is intended to simplify the design and reduce cost by eliminating the need for secondary-side feedback components like opto-couplers.

3. Grounds for Unpatentability

Ground 1: Claims 6, 15, and 24 are anticipated by Bonte under 35 U.S.C. §102.

  • Prior Art Relied Upon: Bonte (Patent 5,305,192).
  • Core Argument for this Ground:
    • Prior Art Mapping: Petitioner argued that Bonte teaches all elements of the independent claims. Bonte’s “switching regulator control circuit 405” was asserted to be the claimed “regulation circuit.” This circuit includes a “load regulation compensation circuitry” (620) that monitors the primary-side switch current via a peak detector (670) to generate a compensation signal. Petitioner contended this corresponds directly to the ’624 patent’s claimed “compensation circuit” which generates a “variable reference signal” from a “current reference signal representative of the inductor current.” Petitioner argued that Bonte’s circuit uses this primary-side information to adjust the feedback loop and regulate the output voltage, thus anticipating the limitations of claims 6, 15, and 24.

Ground 2: Claim 6 is anticipated by Bindra under 35 U.S.C. §102.

  • Prior Art Relied Upon: Bindra (Ashok Bindra, Ripple Regulator Takes Off On Merced’s Command, 46 ELEC. DESIGN PP. 33-36 (1998)).
  • Core Argument for this Ground:
    • Prior Art Mapping: Petitioner asserted that Bindra, which describes the TPS5210 DC-DC converter, anticipates claim 6. Bindra’s hysteretic controller was mapped to the claimed “switching regulator,” as it receives a feedback signal (VSENSE) and a variable reference signal to provide a drive signal. Bindra’s “user adjustable droop compensation” circuit was mapped to the claimed “compensation circuit.” This droop circuit senses the inductor current (via voltage drop across the switching transistors) and uses this information to create a variable reference signal by summing it with a fixed reference voltage (VREF), thereby meeting the limitations of claim 6.

Ground 3: Claims 15, 24, and 28 are obvious over Bindra in view of Bonte.

  • Prior Art Relied Upon: Bindra and Bonte (Patent 5,305,192).

  • Core Argument for this Ground:

    • Prior Art Mapping: Petitioner argued that Bindra discloses a hysteretic controller that adjusts a reference signal in response to load current, while the ’624 patent claims adjust a feedback signal. Petitioner contended that Bonte explicitly teaches that these two methods—adjusting the reference voltage or attenuating the feedback signal—are functionally equivalent and interchangeable design choices for achieving load regulation.
    • Motivation to Combine: A person of ordinary skill in the art (POSITA), seeking to implement the load regulation described in Bindra, would have been motivated by Bonte’s explicit teaching to use either of the two equivalent methods. Bonte stated that a voltage drop used to attenuate a feedback signal "can be viewed as creating a linear increase in the effective reference voltage." A POSITA would therefore combine Bindra’s primary-side current sensing with Bonte’s teaching on feedback loop adjustment to arrive at the specific method claimed in the ’624 patent.
    • Expectation of Success: As Bonte taught that the two approaches were functionally equivalent ways to achieve the same predictable result (improved load regulation), a POSITA would have had a high expectation of success in applying this alternative but equivalent method to Bindra’s circuit.

  • Additional Grounds: Petitioner asserted an additional obviousness challenge that claims 11 and 12 are obvious over Bonte. This ground argued that specific circuit components recited in the dependent claims, such as the oscillator, amplifier, comparator, and latch/driver circuit, were all disclosed by Bonte or would have been obvious modifications.

4. Key Claim Construction Positions

  • The petition argued for a broad construction of the term "variable reference signal" to mean "a variable signal that modifies the feedback loop to provide voltage regulation compensation."
  • Petitioner contended this construction is supported by the specification and encompasses two distinct but equivalent implementations: (1) using the signal as a separate reference input to an error amplifier, or (2) using the signal to directly adjust the feedback signal itself before it reaches the amplifier.
  • This construction was critical to the anticipation argument over Bonte, as Bonte was argued to disclose the second implementation. Petitioner further argued that even if a narrower construction requiring a separate reference input were adopted, Bonte would still anticipate because it explicitly describes this as an equivalent alternative to adjusting the feedback signal.

5. Key Technical Contentions (Beyond Claim Construction)

  • A central technical argument was the functional equivalence of the two methods of providing load compensation in a feedback loop. Petitioner asserted that adjusting a feedback signal downward (e.g., VFB - VADJ) is mathematically and functionally identical to adjusting a reference signal upward by the same amount (e.g., VREF + VADJ) when these signals are compared in an error amplifier.
  • This equivalence was presented as a simple design choice well known to a POSITA. The argument was foundational to the obviousness grounds, as it framed the claimed invention not as a novel concept but as a selection of one of a finite number of predictable and interchangeable solutions taught by the prior art for improving load regulation.

6. Relief Requested

  • Petitioner requests institution of an inter partes review and cancellation of claims 6, 11-12, 15, 24, and 28 of the ’624 patent as unpatentable.