USB Power Path Capacitor Precharge for Inrush Current Protection
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Solution Overview
Problem
The integration of USB-A and USB-C devices often results in initial inrush currents due to voltage potential differences, which can damage devices, and existing solutions like adding transistors or voltage bus capacitors are either ineffective or costly.
Innovation Solution
A controller with a state machine and control signal generator is used to manage the connection by pre-charging a system capacitor to reverse bias the parasitic body diode of a blocking transistor, preventing inrush currents when a USB-A device is connected to a USB-C device.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If USB-A and USB-C devices are integrated without additional components, then device compatibility is improved, but inrush currents occur due to voltage potential differences causing device damage
Solution Approach 1:
The system performs preliminary charging of the capacitor before enabling power transfer between USB-A and USB-C devices. The controller detects connection state and pre-charges the capacitor to the appropriate voltage level before closing the power path, thereby eliminating inrush current while maintaining compatibility across different USB standards
Solution Approach 2:
A capacitor is introduced as an intermediary energy storage element between the USB-A and USB-C power buses. This capacitor acts as a buffer that can be pre-charged to match voltage potentials, mediating the power transfer and preventing direct inrush current flow between devices with different voltage levels
2Object-affected harmful factors
If transistors or voltage bus capacitors are added to prevent inrush currents, then device protection is improved, but system cost and complexity increase
Solution Approach 1:
The controller integrates multiple functions into a single device: it detects connection states, controls capacitor charging, manages power path selection, and prevents inrush currents. This multi-functional approach eliminates the need for separate transistors and voltage bus capacitors, reducing component count while maintaining protection capabilities
Solution Approach 2:
The system dynamically changes the charging state of the capacitor based on detected connection parameters. By monitoring voltage potentials and connection states, the controller adjusts capacitor charge levels in real-time, providing adaptive protection without requiring fixed protective components like transistors
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 effectively reduces the risk of damage from inrush currents by ensuring the parasitic body diode is reverse biased, thereby preventing harmful current flow and enhancing the safety and efficiency of USB connections.
Implementation Method 1
charge a capacitor to a threshold voltage
Implementation Method 2
pre-charging a system capacitor to reverse bias the parasitic body diode of a blocking transistor
Data Source
AI summary
Methods, apparatus, systems and articles of manufacture are disclosed including a capacitor, located in a universal serial bus schematic. The methods, apparatus, systems and articles of manufacture include a controller, include a controller including a state machine and a control signal generator, wherein the controller is configured to be coupled to a connector and to a power supply, the state machine is configured to determine a state of the connector, and the control signal generator is configured to, in response to an indication of a device not connected to the connector, generate a signal to indicate to the power supply to charge a capacitor to a threshold voltage, and wherein the control signal generator is further configured to generate the signal until a second state.