USB Host Controller Power Management via Voltage Change Detection
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Solution Overview
Problem
Conventional image forming apparatuses face limitations in saving standby power when in a power save mode due to the inability to effectively sense USB device connections, particularly when operating as a USB host, as wake-up by power sensing is impossible via the voltage bus line.
Innovation Solution
The implementation of a voltage change detector on the VBUS line, which includes a resistor and a comparator to output a wake-up signal to the main controller if a voltage change occurs, allowing the USB host controller to be turned on when a USB device is connected, thereby enabling power save mode management and standby power reduction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If the USB host controller is turned off to save power in power save mode, then standby power is reduced, but the ability to sense USB device connection is lost
Solution Approach 1:
The patent segments the power saving strategy by turning off the USB host controller separately from the voltage change detector. The voltage change detector remains operational to monitor VBUS line voltage changes, while the USB host controller is turned off to save power. This segmentation allows the system to detect USB device connections without maintaining full USB host functionality, thus resolving the contradiction between power saving and connection sensing capability.
2Difficulty of detecting and measuring
If the USB host controller is kept on to maintain connection sensing, then USB device connection can be detected, but standby power cannot be saved
Solution Approach 1:
The voltage change detector acts as an intermediary between the power saving requirement and the connection sensing requirement. It monitors voltage changes on the VBUS line and provides wake-up signals to the main controller when USB devices are connected, enabling the system to wake up the USB host controller only when needed. This intermediary mechanism allows connection sensing without requiring the USB host controller to remain continuously on, thus enabling both power saving and connection detection.
3Difficulty of detecting and measuring
If periodic turning on of USB host controller is used to check for USB device connection, then connection can be detected, but power saving is limited due to frequent wake-ups
Solution Approach 1:
The voltage change detector continuously monitors the VBUS line voltage without requiring periodic wake-ups of the USB host controller. This continuous monitoring ensures that USB device connections are detected immediately when they occur, eliminating the need for periodic checking. The system maintains continuous useful action (voltage monitoring) while keeping the power-intensive USB host controller in a low-power state, thus achieving both continuous connection detection and effective power saving.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This solution allows the image forming apparatus to efficiently sense USB device connections and conserve standby power by turning off unnecessary components during power save mode while ensuring data communication can resume upon device connection, effectively addressing the power save limitations of conventional systems.
Implementation Method 1
a comparator for outputting the wake-up signal if a voltage difference occurs between both ends of the resistor
Implementation Method 2
a resistor on the VBUS line
Data Source
AI summary
An image forming apparatus includes a main controller, a universal serial bus (USB) interface to which an external USB device is connected, a voltage bus (VBUS) power supply to supply power to the USB interface through the VBUS line, a voltage change detector to output a wake-up signal to the main controller if a voltage change occurs on the VBUS line, a USB host controller to perform data communication with the USB device connected through the USB interface, and an image forming job performing unit to perform an image forming job according to control by the main controller.