USB-PD Printer Power Role Switching for Stable External Power Supply
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Solution Overview
Problem
Printers may initiate power supply to external devices in unintended power states, such as when not connected to an external power source, leading to potential instability and inefficiencies.
Innovation Solution
A printer with a USB connector and Power Delivery (PD) circuit that performs a negotiation with external devices based on its power state, switching the power role from sink to source only when connected to an external power source, ensuring stable power supply.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the printer performs power delivery negotiation with external devices, then power supply capability to external devices is improved, but the risk of unintended power supply initiation in inappropriate power states increases
Solution Approach 1:
The printer checks its power state (connected to external power source or not) before initiating power delivery negotiation with external devices. This preliminary check ensures that power supply is only initiated when the printer is in an appropriate power state (connected to external power), preventing unintended power supply initiation and ensuring reliable operation.
2Speed
If the printer initiates power supply without checking power state, then power delivery to external devices is faster, but system stability deteriorates due to unintended power supply in inappropriate states
Solution Approach 1:
The printer performs a preliminary check of its power state (whether it is connected to an external power source) before initiating power delivery. This preliminary action ensures that power supply is only started when appropriate, maintaining system stability while still enabling relatively fast power delivery when conditions are met.
3Measurement precision
If the printer monitors current values to detect power state changes, then power state detection precision is improved, but the complexity of power management increases
Solution Approach 1:
The printer continuously monitors current values from the power supply circuit and uses this feedback to detect changes in power state (connected or disconnected from external power source). This feedback mechanism enables precise power state detection through simple current threshold comparison, avoiding complex multi-parameter monitoring while maintaining accurate detection.
Data Source
AI summary
A printer includes: a Universal Serial Bus (USB) connector to which an external device is connectable; a Power Delivery (PD) circuit; and a processor. The PD circuit is configured to perform a negotiation with the external device according to a Universal Serial Bus Power Delivery (USB-PD) specification in a state where the external device is connected to the USB connector. The processor is configured to perform a power supply initiation process on the basis of a power state of the printer. The power supply initiation process includes outputting a source setting instruction to the PD circuit to cause the PD circuit to initiate supply of power to the external device. The source setting instruction instructs the PD circuit to switch a power role of the printer with respect to the external device from sink to source.