Sensor-less USB Charger Current Limit Control
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Solution Overview
Problem
Existing USB chargers face issues with power loss and increased manufacturing costs due to the use of current sensing resistors, which are necessary to monitor and regulate charging current within the limited USB port current limits, and require additional trim circuitry for accuracy.
Innovation Solution
A sensor-less current limit scheme is implemented, where the input current is directly sensed through switching transistors and inductors, eliminating the need for polysilicon resistors by using power balancing principles to calculate the maximum current limit, allowing the charger to deliver maximum current without exceeding USB port limits.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If current sensing resistors are used to monitor and regulate charging current, then charging current can be regulated within USB port limits, but power loss increases and manufacturing costs increase
Solution Approach 1:
The patent extracts and eliminates the current sensing resistor from the charging circuit by implementing a sensor-less current limit scheme. The controller directly monitors and regulates the charging current through switching transistors and inductors without requiring external sensing resistors, thereby removing the source of power loss while maintaining current regulation capability within USB port limits.
Solution Approach 2:
The patent replaces the passive electrical sensing mechanism (resistors) with an active control mechanism using switching transistors and inductors under controller management. This substitution eliminates the need for power-dissipating sensing resistors while achieving the same current regulation function through dynamic switching control.
2Reliability
If current sensing resistors are used to monitor and regulate charging current, then charging current can be regulated within USB port limits, but manufacturing costs increase
Solution Approach 1:
The patent extracts and eliminates the current sensing resistors and associated trim circuitry from the charging circuit. By implementing sensor-less current limiting, the design removes these additional components, thereby reducing component count, simplifying the bill of materials, and lowering manufacturing costs while maintaining current regulation capability.
Solution Approach 2:
The patent makes the switching transistors and inductors serve dual functions: both as power conversion elements and as current sensing elements. This multi-functionality eliminates the need for separate sensing resistors and trim circuitry, reducing component count and manufacturing complexity.
3Measurement precision
If polysilicon resistors are used for current sensing, then current can be monitored, but additional trim circuitry is required for accuracy
Solution Approach 1:
The patent extracts and removes the polysilicon resistors and trim circuitry entirely from the design by implementing a sensor-less current limit approach. The controller directly controls the switching elements to maintain current within limits without requiring precision sensing resistors or associated trimming components, thereby simplifying the circuit while maintaining accuracy.
Solution Approach 2:
The patent implements self-regulating current control where the controller monitors the charging current and automatically adjusts the switching duty cycle to maintain current within USB port limits. This self-service mechanism eliminates the need for external sensing resistors and trim circuitry, as the system self-corrects without additional components.
Data Source
AI summary
A universal serial bus charger comprises a universal serial bus connector for providing a connection to a voltage source. An output voltage connector provides a charging voltage to a connected battery. A switching voltage regulator generates the charging voltage responsive to the voltage source. Control circuitry monitors an actual charging current applied to the connected battery and provides a programmed current signal enabling the actual charging current to operate at a programmed level if the actual charging current does not exceed a programmed charging current level. The control circuitry provides a charging current limit signal enabling the actual charging current to operate at a predetermined charge current limit if the actual charging current exceeds the programmed charging current level. PWM control circuitry generates switching control signals to control operation of the switching voltage regulator responsive to the control circuitry.