Power Bus Switch Soft-Start Short Circuit Protection
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Solution Overview
Problem
Switching power converters used for charging devices through data interfaces face issues with short circuits, leading to excessive current stress and potential failure of the power bus switch due to 'hard' or 'soft' shorts in the USB interface, which existing technologies fail to adequately protect against.
Innovation Solution
A secondary-side controller in the power converter initiates a soft-start of the power bus switch after detecting a client device connection, making the switch more resistive during the initial period and testing for short circuits by monitoring the power supply voltage; if a short circuit is detected, the switch is opened to prevent excessive current exposure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If the Vbus switch is closed to enable high power delivery over the USB cable, then power delivery capability is improved, but the switch becomes vulnerable to short circuit damage from hard or soft shorts in the cable or interface
Solution Approach 1:
The patent applies preliminary action by implementing a soft-start sequence that gradually activates the Vbus switch after connection detection. The controller waits for a debounce period to confirm stable connection, then enables the Vbus switch in a controlled manner before full power delivery begins, preventing immediate exposure to potential short circuit conditions
Solution Approach 2:
The patent maintains continuous monitoring of the Vbus switch current and operational status throughout the power delivery process. The controller continuously detects connection status and adjusts the Vbus switch operation accordingly, ensuring uninterrupted protection while maintaining power delivery functionality
2Speed
If the Vbus switch is immediately activated upon connection detection, then connection response time is improved, but the switch is exposed to repetitive overcurrent stress that causes irreversible failure
Solution Approach 1:
The patent implements preliminary action by introducing a debounce period after connection detection before activating the Vbus switch. This delay allows the system to confirm stable connection and prevents premature switch activation that would expose it to initial inrush currents and potential short circuit conditions
Solution Approach 2:
The patent applies beforehand cushioning by implementing current limiting and soft-start mechanisms that gradually increase current flow through the Vbus switch. This cushioning effect protects the switch from repetitive overcurrent stress that would otherwise cause irreversible failure, extending its operational lifespan
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 approach effectively protects the power bus switch from overcurrent damage by reducing short circuit current during the soft-start period and preventing repetitive stress that could lead to irreversible states, thereby extending the switch's lifespan.
Implementation Method 1
During the soft-start of the power bus switch, the power bus switch is more resistive than when driven fully on
Implementation Method 2
output capacitor C1 charged to the 5.0 V power supply voltage
Implementation Method 3
a primary winding T1 of a transformer having a secondary winding T2
Data Source
AI summary
A switching power converter is provided with an overvoltage protection circuit that softly switches on a power bus switch during a soft-start period responsive to a device connecting to a data cable for receiving power over a power bus coupled to the power bus switch.