PTAB

IPR2020-00836

Satco Products Inc v. Seoul Semiconductor Co Ltd

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1. Case Identification

2. Patent Overview

  • Title: Method and Circuit for Driving LEDs in Multiphase
  • Brief Description: The ’722 patent discloses a method and driver circuit for driving a string of light-emitting diodes (LEDs) in multiphase. The LED string is divided into sequential groups, and as an input voltage increases, the groups are turned on in sequence to illuminate more LEDs.

3. Grounds for Unpatentability

Ground 1: Anticipation/Obviousness over Chiang - Claims 1-3, 10, 15, 19, and 21 are anticipated by or obvious over Chiang.

  • Prior Art Relied Upon: Chiang (Application # 2004/0233145).
  • Core Argument for this Ground:
    • Prior Art Mapping: Petitioner argued that Chiang disclosed every limitation of the challenged claims. Chiang described an LED driving device that uses a voltage detection system to vary the number of LEDs being driven to match a changing input voltage, such as an AC line voltage. This was accomplished by sequentially turning on "current controlling units" to drive an appropriate number of series-connected LED groups as the input voltage rises and turning them off as it falls. Petitioner asserted this directly mapped to the method of independent claim 1 and the circuit of independent claim 15.
    • Key Aspects: Petitioner contended that a figure in Chiang contained an obvious drafting error in its grounding scheme, which a POSITA would have immediately understood and corrected. With this correction, Petitioner argued Chiang fully anticipated the claims. In the alternative, it was argued that making such a correction would have been obvious.

Ground 2: Obviousness over Chiang and Leung - Claims 2-3 are obvious over Chiang in view of Leung.

  • Prior Art Relied Upon: Chiang (Application # 2004/0233145) and Leung (Application # 2003/0164809).
  • Core Argument for this Ground:
    • Prior Art Mapping: This ground focused on dependent claims 2 and 3, which added the limitation of "monitoring a phase voltage of each group." Petitioner argued that Chiang met the base claim limitations and monitored voltage indirectly by measuring the main input voltage. Leung was introduced because it explicitly taught directly "detecting the voltage at the constant current sinks/devices," which were located at the downstream end of each LED group. This constituted a direct measurement of the "phase voltage" as required by the claims.
    • Motivation to Combine: A POSITA would combine Leung's direct phase voltage measurement with Chiang's circuit to improve its design. Chiang's indirect measurement required LEDs with a very narrow range of threshold voltages (Vth), whereas Leung's direct measurement would make the circuit more tolerant of component variations. This would simplify manufacturing and improve reliability.
    • Expectation of Success: Petitioner asserted a POSITA would have a high expectation of success, as it involved applying a known technique (direct voltage measurement from Leung) to a known circuit (Chiang) to achieve a predictable improvement in performance and manufacturability.

Ground 3: Obviousness over Chiang and Hamilton - Claims 11-12, 18, and 21 are obvious over Chiang in view of Hamilton.

  • Prior Art Relied Upon: Chiang (Application # 2004/0233145) and Hamilton (a 1975 electronics textbook titled "Basic Integrated Circuit Engineering").
  • Core Argument for this Ground:
    • Prior Art Mapping: This ground addressed claims related to regulating phase current and dimming. Chiang disclosed that its "current controlling unit" could be "any current controlling circuit" and that its current value could be adjustable, which Petitioner equated to a dimming circuit. Hamilton, a standard electronics textbook, was introduced to provide a specific, well-known implementation for such a circuit. Hamilton taught conventional control and feedback circuits, including using NPN bipolar transistors (claim 18), that translate a reference voltage into a reference current.
    • Motivation to Combine: A POSITA implementing Chiang's generic "current controlling unit" would have been motivated to use a standard, well-known, and reliable circuit design, such as the one taught in Hamilton. The motivation was to implement a disclosed generic function with a conventional and predictable circuit design to achieve stable current regulation and enable dimming.
    • Expectation of Success: Success was expected because it involved implementing a generic circuit block from Chiang with a widely known, time-tested circuit design from a standard textbook like Hamilton, a routine task for a circuit designer.
  • Additional Grounds: Petitioner asserted an additional obviousness challenge (Ground 4) for claims 17-18 over Chiang in view of Hirane (Patent 5,138,310). This ground argued a POSITA would have been motivated to implement Chiang's generic phase switch using the conventional transistor-and-resistor design disclosed by Hirane.

4. Key Claim Construction Positions

  • "phase switch": Petitioner argued this term was explicitly defined in the ’722 patent's specification as a general term for "any device that, when turned on, conducts electrical current." This broad construction was central to arguing that the "current controlling units" in the prior art met the claim limitation.
  • "phase voltage": Based on the specification and figures of the ’722 patent, Petitioner argued a POSITA would understand this term to mean the voltage at the "joint point" at the downstream end of a group of LEDs. This construction was critical to mapping Leung's disclosure of measuring voltage at its current sinks to the limitations of claims 2 and 3.

5. Key Technical Contentions (Beyond Claim Construction)

  • Correction of Obvious Prior Art Errors: A central contention spanning multiple grounds was that a POSITA would immediately recognize and mentally correct obvious drafting errors in the circuit diagrams of the primary prior art references. Petitioner specifically argued that Chiang's FIG. 5A incorrectly showed a ground wire connected back to the input source instead of the rectifier output and that Leung's FIG. 1 was missing a necessary connection. Petitioner asserted that the text of these references made the intended connections clear, rendering the figures obvious to correct.

6. Arguments Regarding Discretionary Denial

  • Petitioner preemptively argued against discretionary denial under Fintiv. The petition identified a co-pending district court case between the parties but stated that the proceeding was in its early stages. It noted that claim construction briefing was not yet complete and no trial date had been set, suggesting that an IPR would be more efficient and would not be a waste of Board resources.

7. Relief Requested

  • Petitioner requested institution of an inter partes review and cancellation of claims 1-3, 10-12, 15, 17-19, and 21 of the ’722 patent as unpatentable.