Closed-Loop Gate Drive for AC Load Overcurrent Limiting
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Solution Overview
Problem
Existing load control devices, such as dimmer switches, face challenges in efficiently controlling power delivery to electrical loads while preventing overcurrent conditions, particularly when dealing with inductive and capacitive loads.
Innovation Solution
A load control device with a closed-loop gate drive circuit and control circuit that adjusts the maximum current limit and control time of a semiconductor switch during AC mains line voltage half-cycles, using forward and reverse phase-control techniques to manage power delivery and limit current magnitude, incorporating feedback mechanisms for precise control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If a bidirectional semiconductor switch is used to control power delivery to the load, then power control capability is improved, but overcurrent protection capability deteriorates
Solution Approach 1:
A current sense resistor is introduced as an intermediary element in series with the semiconductor switch to detect load current. This mediator enables the control circuit to monitor current levels and implement overcurrent protection without directly modifying the semiconductor switch itself, thus maintaining power control capability while adding protection functionality.
Solution Approach 2:
The patent implements a feedback mechanism where the control circuit continuously monitors the load current through the current sense resistor and adjusts the semiconductor switch operation accordingly. When overcurrent conditions are detected, the control circuit modifies the gate drive signal to limit current, creating a closed-loop control system that maintains both power control and overcurrent protection.
Data Source
AI summary
A load control device may include a closed-loop gate drive circuit coupled to a semiconductor switch and configured to render the semiconductor switch conductive or non-conductive at a control time during half-cycles of an AC mains line voltage. The gate drive circuit may limit a magnitude of the load current conducted through the semiconductor switch to a maximum current limit. The load control device may include a control circuit that is configured to set the maximum current limit to a second magnitude for a period of time following a control time of the semiconductor switch during a conduction period of a half-cycle of the AC mains line voltage, and set the maximum current limit to a first magnitude after the expiration of the period of time during the conduction period of the half-cycle of the AC mains line voltage.