PTAB

IPR2018-00378

Power Integrations Inc v. Semiconductor Components Industries LLC

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Petition
petition

1. Case Identification

2. Patent Overview

  • Title: SYNCHRONOUS RECTIFICATION CIRCUIT FOR POWER CONVERTERS
  • Brief Description: The ’298 patent discloses a synchronous rectification circuit for switching-mode power converters. The invention describes a switching-control circuit that generates a precisely timed control signal for a secondary-side power switch by emulating the current in the converter’s transformer, based on sensing the transformer's magnetized voltage, demagnetized voltage, and magnetization period.

3. Grounds for Unpatentability

Ground 1: Obviousness over Kyono and Zhou - Claims 1, 2, and 7-11 are obvious over Kyono in view of Zhou.

  • Prior Art Relied Upon: Kyono (Patent 7,120,036) and Zhou (a 2000 IEEE journal article).
  • Core Argument for this Ground:
    • Prior Art Mapping: Petitioner argued that Kyono disclosed the foundational synchronous rectifier circuit for a transformer-based power converter, including a power switch and a control circuit. Kyono’s control circuit timed the rectifier switch using a capacitor charged and discharged according to pre-set time constants to align with the non-conducting periods of the primary switch, thereby approximating the transformer's demagnetization period. However, Petitioner asserted Kyono did not teach making these charge/discharge rates directly responsive to the converter's variable operating voltages. Petitioner contended that Zhou supplied this missing element by teaching a sophisticated current-emulating network. Zhou's circuit explicitly used current sources proportional to the input voltage (related to magnetized voltage) and output voltage (demagnetized voltage) to charge and discharge a capacitor, with the charging period controlled by the primary switch's duty cycle (magnetization period). Combining these teachings allegedly rendered independent claim 1 obvious. Dependent claims 2 and 7-11 were argued to be obvious for similar reasons, as the claimed relationships between voltages, timing periods, and switch control were inherent results of the combined system's operation.
    • Motivation to Combine: A Person of Ordinary Skill in the Art (POSITA) would combine these references because they addressed the same problem—improving synchronous rectifier control—in the same field of switching power supplies. Petitioner contended a POSITA would have been motivated to incorporate Zhou's more precise voltage-proportional current emulation technique into Kyono's transformer-based topology to improve the accuracy of the rectifier's timing, a known design goal that would lead to higher efficiency.
    • Expectation of Success: Petitioner argued that applying Zhou's known technique to modify Kyono's known circuit would be a straightforward implementation. A POSITA would have expected success because the combination involved applying a known improvement to a similar device, which would yield the predictable result of more accurate control.

Ground 2: Anticipation by Zhou - Claims 8-11 are anticipated by Zhou.

  • Prior Art Relied Upon: Zhou (a 2000 IEEE journal article).

  • Core Argument for this Ground:

    • Prior Art Mapping: Petitioner contended that Zhou's detailed disclosure of a synchronous rectifier buck converter anticipated every limitation of claims 8-11. Claim 8, which is broader than claim 1, recites a "magnetic device" instead of a "transformer." Petitioner argued Zhou's inductor (L) met this limitation. Zhou's MOSFET (Q2) was mapped to the "power switch," and its control circuit (shown in Fig. 14) was mapped to the claimed "switching-control circuit." This control circuit generated a signal by charging a capacitor with a current (I1-I2) proportional to the voltage across the inductor when the main switch is on (the magnetized voltage) and for a duration controlled by the main switch's duty cycle (the magnetization period). The enable period of the control signal was shown to be correlated to the demagnetization period, as the signal deactivates the power switch when the capacitor discharges to a threshold, corresponding to the inductor current returning to zero. Petitioner further argued that Zhou expressly taught the limitations of dependent claims 9 (using demagnetized voltage to determine enable period), 10 (functional relationships between the enable period and operating voltages), and 11 (turning the power switch off before magnetization begins).

  • Additional Grounds: Petitioner asserted an additional obviousness challenge (Ground 3) based on the combination of Zhou in view of Kyono, reversing the primary references but relying on similar technical arguments and motivations to combine.

4. Relief Requested

  • Petitioner requests institution of an inter partes review (IPR) and cancellation of claims 1, 2, and 7-11 of the ’298 patent as unpatentable.