Obviousness

Obviousness Analysis of US Patent 8,093,830 under 35 U.S.C. § 103

This analysis evaluates whether the independent claims of US Patent 8,093,830 (Claims 1 and 5) would have been obvious to a person having ordinary skill in the art (POSITA) at the time of the invention, based on combinations of the prior art referenced within the patent itself.

Independent Claims Under Consideration:

• Claim 1 (Apparatus): A semiconductor light source driving apparatus comprising a semiconductor light source, a voltage source, an output voltage controlling section, an output current detecting section, a current command section, a current comparing section, and, crucially, an impedance detecting section. The output voltage controlling section controls the output voltage of the voltage source based on both the output of the current comparing section and an output of the impedance detecting section. [cite: The full patent text]
• Claim 5 (Method): A semiconductor light source driving method comprising detecting an output current, comparing the detected current with a reference value, detecting an impedance of the semiconductor light source, and controlling the output voltage of the voltage source based on a result of the comparison and the impedance of the semiconductor light source. [cite: The full patent text]

The core inventive concept of US 8,093,830, as described in the patent, is to achieve stable and constant control performance for a semiconductor light source by compensating for its inherent non-linear electrical characteristics (specifically, the varying gain and impedance) during current control. This compensation is achieved by detecting the semiconductor light source's impedance and using this detected impedance to adjust the gain of the control loop. [cite: The full patent text]

Prior Art References:

The patent itself discusses two main conventional semiconductor light source driving apparatuses:

1. Conventional Semiconductor Light Source Driving Apparatus 10 (FIG. 1): This apparatus performs constant-current control using a single negative feedback closed loop (CL1). It includes a semiconductor light source (12), an output current detecting circuit (14), a current comparing circuit (16), a current command section (18), an output voltage controlling circuit (20) with a proportional gain circuit (22) and compensating circuit (24), and a voltage source (26). [cite: The full patent text]
2. Conventional Semiconductor Light Source Driving Apparatus 40 (FIG. 2) (Patent Literature 1: Japanese Patent Application Laid-Open No. 2007-042758): This apparatus employs a two-fold current control loop (CL1 for supply voltage and CL2 for constant current) to optimize voltage and reduce heat. It also detects voltage across a resistor (48) in series with the semiconductor light source (12) for both control loops. [cite: The full patent text]

Obviousness Analysis:

A strong case for obviousness can be made by combining the teachings of the "conventional semiconductor light source driving apparatus 10" (FIG. 1) with the problem statement explicitly articulated within US 8,093,830, and general knowledge in the field of control systems.

1. Problem Identification in the Prior Art:
The specification of US 8,093,830 clearly identifies a significant problem with conventional constant-current control, exemplified by apparatus 10 (FIG. 1) and apparatus 40 (FIG. 2). It explains that semiconductor light sources exhibit non-linear voltage-current characteristics (FIG. 3A), leading to varying impedance (FIG. 3B) and varying gain (FIG. 3C) depending on the drive voltage/current. [cite: The full patent text]

Crucially, the patent states: "Consequently, the control loop gain becomes proportional to the gain characteristic in FIG. 3C and changes according to the drive current value in semiconductor light source 12." and "the impedance of a semiconductor light source generally changes according to the drive current value." [cite: The full patent text] This variation in control loop gain makes constant-current control unstable, leading to issues like overshoot, ringing, oscillation at high currents, or poor response at low currents, especially when adjusting light brightness. [cite: The full patent text] The stated object of the invention is to provide a driving apparatus that can achieve "constant control performance regardless of whether the drive current value is great or small when a drive current value is increased and decreased while light is adjusted." [cite: The full patent text]

2. Motivation for a Person Having Ordinary Skill in the Art (POSITA):
The patent's explicit identification of the problem—that the conventional control loop's gain varies due to the non-linear electrical characteristics (gain and impedance) of the semiconductor light source—would provide clear motivation for a POSITA to seek a solution. A POSITA in power electronics and control systems, confronted with a feedback loop whose gain varies unpredictably, would be motivated to linearize or compensate for this varying gain to ensure stable and consistent control performance. The patent itself highlights the need for a solution to achieve "constant control performance regardless of whether the drive current value is great or small." [cite: The full patent text]

3. Combination of Prior Art Elements and General Knowledge:

• Conventional Apparatus 10 (FIG. 1) as a starting point: This apparatus already discloses almost all elements of Claim 1, including the semiconductor light source, voltage source, output voltage controlling section, output current detecting section, current command section, and current comparing section, arranged in a feedback loop to control the light source current. [cite: The full patent text]
• Detecting Impedance: Given that the patent explicitly identifies "the impedance of a semiconductor light source generally changes according to the drive current value" as a root cause of the problem, a POSITA would find it obvious to measure this varying impedance. The patent describes the impedance detecting circuit (150) as a divider (152) that determines an "impedance equivalent value" by dividing the output voltage of the voltage source by the output current of the semiconductor light source. [cite: The full patent text] This method (Z=V/I) is a fundamental and well-known principle for calculating impedance in electrical engineering.
• Controlling Output Voltage Based on Impedance: A POSITA familiar with control theory would recognize that if a component in a feedback loop has a varying gain (gm), stability can be improved by introducing an inverse gain or a compensatory factor (Zm = 1/gm) elsewhere in the loop. The patent explicitly states that the gain characteristics of the semiconductor light source (gm) and its impedance characteristics (Zm) "are reciprocals with respect to each other, and, when they are multiplied, the multiplication result becomes a constant value." [cite: The full patent text] This principle provides a clear roadmap.
  • The output voltage controlling circuit (160) in the claimed invention includes a gain circuit (162) with a multiplier (163). This multiplier takes the output of the current comparing circuit (the error signal) and multiplies it by the "impedance equivalent value" detected by the impedance detecting circuit (150). [cite: The full patent text] This precisely implements the known control strategy of compensating a varying forward path gain (gm of the light source) by multiplying the error signal with an inverse gain factor (Zm).

Therefore, a POSITA, motivated by the clearly articulated problem of varying loop gain due to the semiconductor light source's non-linear impedance/gain characteristics in the conventional apparatus (FIG. 1), would find it obvious to:

1. Measure the semiconductor light source's impedance (using a standard V/I divider, as disclosed by the patent's own detailed embodiment of element 152).
2. Incorporate this measured impedance into the existing output voltage controlling section (20 of FIG. 1) to dynamically adjust its gain, thereby compensating for the non-linear gain of the semiconductor light source and stabilizing the overall control loop. The use of a multiplier to achieve this compensation, as described in Claim 4 and element 163, is a direct and logical application of control principles.

This combination of the conventional apparatus with a known method of impedance detection and application of a compensatory factor in a feedback loop to address a clearly identified problem would render the apparatus claims (Claim 1) and method claims (Claim 5) obvious. The same reasoning applies when considering Apparatus 40 (FIG. 2) as the primary prior art, as it suffers from the identical "electrical characteristics of the semiconductor light sources" problem. [cite: The full patent text]