Average Input Current Limiting for USB-Powered Devices
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Solution Overview
Problem
Existing methods for limiting input current in USB-powered devices are inefficient, as they either fail to accurately control the average current supplied by the power source or increase circuit complexity and cost, leading to wasted energy and thermal issues.
Innovation Solution
A method and apparatus that limit the average value of the input current by using a switching circuit, a current average circuit, and a current limit circuit to sense and regulate the input current, ensuring the power source supplies the intended average current through a Buck circuit topology, with a threshold correction circuit to maintain accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If peak current limiting method is used to limit the peak value of input current, then the peak current is controlled, but the average input current is not accurately limited and large current range is wasted
Solution Approach 1:
The patent introduces an intermediate capacitor to convert peak current sensing into average current sensing. The capacitor integrates the peak current pulses over time, transforming the discontinuous peak current signal into a continuous average current signal that accurately represents the actual power source supply, thereby enabling precise average current limiting without energy waste.
Solution Approach 2:
The patent replaces the direct peak current limiting approach with an electrical integration mechanism using a capacitor. Instead of directly controlling peak current through mechanical switching alone, the system uses electrical integration to accumulate and average the current over time, providing more accurate control of the actual power source supply.
2Measurement precision
If resistor is used to sense current supplied by power source, then current sensing is achieved, but circuit complexity and cost increase
Solution Approach 1:
The patent merges the current sensing function with the existing switching circuit by using the switch's own on-resistance for sensing. Instead of adding a separate sensing resistor, the system utilizes the inherent resistance of the switching element, integrating the sensing function into the existing power conversion circuitry, thereby reducing component count and circuit complexity.
Solution Approach 2:
The switching element serves dual purposes: power conversion and current sensing. The on-resistance of the switch automatically provides the sensing function without requiring external sensing components. The circuit uses its own inherent properties (switch on-resistance) to perform measurement, eliminating the need for additional dedicated sensing components.
3Measurement precision
If switch is used to limit current supplied by power source, then current control is achieved, but power loss increases and thermal issues occur
Solution Approach 1:
The patent extracts the current sensing function from the power limiting function. Instead of using a switch to directly limit current (which causes power loss), the system uses the switch only for power conversion while a separate control mechanism based on capacitive integration handles current limiting, separating the functions to minimize power loss.
Solution Approach 2:
The system performs preliminary current measurement and integration during the switching cycle, accumulating current information in the capacitor before making control decisions. This preliminary action allows the system to control average current accurately without requiring the switch to work harder, thereby reducing power loss.
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
Effectively limits the average input current, ensuring proper operation of USB devices by accurately regulating the current supplied by the power source, reducing energy wastage and thermal issues while maintaining circuit simplicity and cost-effectiveness.
Implementation Method 1
a current average circuit (302) coupled to the switching circuit (301) to sense the input current and generate a signal representing an average value of the input current
Data Source
AI summary
The embodiment of invention discloses an average input current limit method and apparatus thereof. The apparatus comprises a switching circuit, a current average circuit and a current limit circuit. The current average circuit samples the input current of the switching circuit and generates a signal representative of the average value of the input current. The current limit circuit limits the signal so as to limit the average value of the input current.