Obviousness

US patent 7960955 focuses on a power supply apparatus designed to generate stable voltage unaffected by noise, particularly in the context of switching power supplies. The patent discloses a system that integrates a switching power supply, a reference voltage source, and a linear regulator. A key feature is that the linear regulator stabilizes the input voltage based on the reference voltage, and its output voltage then powers both the switching controller and the reference voltage source itself. Additionally, the linear regulator can switch between a regulation mode and a bypass mode, operating in bypass during startup until the reference voltage reaches a predetermined value.

Obviousness Analysis under 35 U.S.C. § 103

A patent claim is obvious under 35 U.S.C. § 103 "if the differences between the claimed invention and the prior art are such that the claimed invention as a whole would have been obvious before the effective filing date of the claimed invention to a person having ordinary skill in the art to which the claimed invention pertains." (This is a general statement about obviousness, not directly cited from the provided text).

For a combination of prior art references to render a claim obvious, there must be:

1. A teaching, suggestion, or motivation to combine the references.
2. A reasonable expectation of success in combining the references.

The prior art documents explicitly mentioned in US7960955 are:

• Patent Document 1: JP2004201474A (2004-07-15)
• Patent Document 2: JP2005073483A (2005-03-17)
  These documents disclose an insulating DC/DC converter as a switching power supply, which is relevant to the background of US7960955.

A specific prior art reference, US20090072626A1 (published March 19, 2009), from Rohm Co., Ltd., is also listed in the "Cited By" section, with a priority date of May 26, 2005. This document is titled "Power supply apparatus having switchable switching regulator and linear regulator."

Let's consider combinations of prior art to establish obviousness for some of the claims in US7960955.

Claim 1: "A power supply apparatus for use with an input voltage provided from outside, the power supply apparatus comprising: a switching power supply which stabilizes the input voltage; a reference voltage source which generates a predetermined reference voltage; and a linear regulator which stabilizes the input voltage, based on the reference voltage generated by the reference voltage source; wherein an output voltage of the linear regulator is supplied as a power supply voltage of a controller of the switching power supply and the reference voltage source, and the input voltage is not directly supplied to the controller as a power supply voltage."

Combination 1: JP2004201474A + JP2005073483A + General knowledge in the art (e.g., US20090072626A1 as indicative of the state of the art)

• JP2004201474A and JP2005073483A: These documents disclose insulating DC/DC converters as switching power supplies. The problem addressed by US7960955 is the switching noise generated by such power supplies affecting the reference voltage source, which in turn can hinder the stepping up or down operation.
• Motivation to Combine: A person having ordinary skill in the art (POSITA) would be motivated to combine elements from these switching power supplies with a mechanism to mitigate switching noise impacting sensitive control circuits, particularly the reference voltage source. The patent itself highlights this problem in the "BACKGROUND OF THE INVENTION" section.
• General Knowledge/US20090072626A1: US20090072626A1, titled "Power supply apparatus having switchable switching regulator and linear regulator," explicitly discloses a power supply apparatus with a switchable switching regulator and linear regulator. While its publication date is after the priority date of US7960955, its priority date of May 26, 2005, predates the December 9, 2005 priority date of US7960955, making it prior art. A POSITA would understand the advantages of using a linear regulator to provide a clean power supply to sensitive circuits, such as a reference voltage source and a switching controller, to reduce noise impact from the switching power supply. The concept of regulating a voltage to power a control circuit and a reference voltage source, rather than directly supplying a potentially noisy input voltage, would be a logical step for a POSITA seeking to improve noise immunity.

Therefore, combining a switching power supply (as taught by JP2004201474A and JP2005073483A) with a linear regulator to supply a stabilized voltage to the reference voltage source and the switching controller (a concept implicitly or explicitly known in the art, as exemplified by US20090072626A1), and ensuring the input voltage is not directly supplied to the controller, would be obvious. The motivation stems from the known problem of switching noise affecting reference voltage sources and the general understanding that linear regulators can provide cleaner power.

Claim 2: "A power supply apparatus according to claim 1, wherein the linear regulator is configured to enable switching of a regulation mode in which a voltage is outputted according to the reference voltage, and a bypass mode in which the input voltage is outputted as it is, with no relation to the reference voltage, and when the power supply apparatus is started up, the linear regulator operates in the bypass mode, during a time period until the reference voltage reaches a predetermined voltage value, and when the reference voltage exceeds the predetermined voltage value, operates in the regulation mode."

Combination 2: Combination 1 (JP2004201474A + JP2005073483A + General knowledge) + US20090072626A1

• US20090072626A1: This patent explicitly teaches a "power supply apparatus having switchable switching regulator and linear regulator." The concept of switching between a bypass mode and a regulation mode for a linear regulator during startup is a common technique to ensure stable operation of the reference voltage source before it can reliably generate its intended reference voltage. In the bypass mode, the input voltage is passed directly, allowing the system to power up quickly. Once the reference voltage is stable, the linear regulator switches to regulation mode to provide a more precise and clean supply. This approach is described in US7960955 as ensuring the power supply apparatus "is started up in a preferred manner."
• Motivation to Combine: A POSITA, seeking to implement a robust startup sequence for a power supply incorporating a linear regulator and reference voltage source (as in Claim 1), would be motivated to incorporate a bypass mode during startup. This would address potential instability or insufficient voltage from the reference voltage source during the initial power-up phase, ensuring that critical components receive power quickly before precise regulation is established. This is a known technique for managing startup transients in power supply systems.

Therefore, once the basic architecture of Claim 1 is established, the addition of a switchable regulation/bypass mode for the linear regulator during startup, where the bypass mode operates until the reference voltage stabilizes, would be obvious to a POSITA. US20090072626A1 directly suggests such a switchable operation for power supply apparatuses with linear regulators.

Claim 11: This claim is a semiconductor device claim with similar features to claims 1 and 2, but also includes details about the reference voltage source's mode control signal generation using transistors and a resistor.

Combination 3: Combination 2 + JP2004201474A or JP2005073483A + General knowledge of bandgap reference circuits

• Reference Voltage Source: US7960955 describes its reference voltage source as a "bandgap reference circuit." Bandgap reference circuits are well-known in the art for generating stable reference voltages independent of temperature and supply voltage variations.
• Transistors and Resistors for Mode Control: Claim 11 specifies a first, second, and third transistor forming a current mirror and a resistor to generate the mode control signal when the reference voltage reaches a predetermined value. The internal circuitry for generating a mode control signal based on the stabilization of the reference voltage, using standard transistor configurations like current mirrors, would be within the purview of a POSITA designing such circuits. The patent describes the transistors Q10, Q11, Q12, and resistor R7 as "provided in order to generate the mode control signal MODE" and explains that Q10 turns ON when Vref reaches a predetermined value, causing a current to flow and the MODE signal to go low.
• Motivation to Combine: A POSITA aiming to implement the startup sequence of Claim 2 would need a mechanism to detect when the reference voltage has stabilized to switch from bypass to regulation mode. Using a simple comparator-like circuit within the bandgap reference itself, employing known transistor configurations (like current mirrors for sensing and current generation) and resistors to create a voltage drop to signify stabilization, would be an obvious design choice for a POSITA. The specific implementation using current mirrors (Q11, Q12) and a resistor (R7) to sense the current through a transistor (Q10) that turns on when the reference voltage is stable is a straightforward application of fundamental analog circuit design principles.

Therefore, the specific implementation details of the mode control signal generation within the reference voltage source, using common transistor and resistor configurations to detect when the reference voltage reaches a predetermined level, would be an obvious design choice for a POSITA combining the concepts of Claim 2 with general knowledge of bandgap reference circuits.