Trailing Edge Dimmer Circuit Short-Circuit Protection
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Solution Overview
Problem
Existing trailing edge phase control dimmer circuits for AC power face challenges in providing effective short-circuit protection, particularly due to the complexity and cost associated with monitoring MOSFET ON-state voltage drops, which can lead to high current surges damaging the circuit or load.
Innovation Solution
A trailing edge phase control dimmer circuit with a zero-crossing detection circuit that initiates conduction and prematurely terminates it based on threshold values of rectified dimmer voltage, utilizing MOSFETs with gate-driven latches and a fast-OFF circuit to rapidly turn off during short-circuit conditions, leveraging the MOSFET ON-state resistance as a current-sense element for protection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If voltage drop monitoring across MOSFET channel resistance is used for short-circuit protection, then short-circuit detection capability is improved, but device complexity increases due to additional comparator circuit requirements
Solution Approach 1:
The MOSFET's intrinsic diode is utilized to perform the short-circuit detection function without requiring external comparator circuits. The diode's forward voltage drop serves as the detection mechanism, allowing the component to monitor its own state and trigger protection automatically, thereby eliminating additional complexity while maintaining reliability
Solution Approach 2:
The intrinsic diode of the MOSFET acts as an intermediary element that converts the hard-to-measure channel resistance voltage drop into an easily detectable forward voltage signal. This intermediary transformation enables simple voltage threshold detection without complex measurement circuits
2Measurement precision
If MOSFET ON-state resistance is used as current-sense element, then measurement precision is improved, but device complexity is reduced by eliminating additional comparator circuits
Solution Approach 1:
The MOSFET's own ON-state resistance and intrinsic diode are employed as the sensing elements, allowing the device to monitor its conduction state without external sensing components. This self-sensing approach maintains measurement precision while minimizing additional circuitry
Solution Approach 2:
The MOSFET performs multiple functions simultaneously: power switching, current sensing through its ON-state resistance, and short-circuit detection via its intrinsic diode. This multi-functionality eliminates the need for separate comparator and sensing circuits, reducing overall device complexity while maintaining measurement capability
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 provides robust short-circuit protection by quickly identifying and responding to short-circuit conditions, reducing energy dissipation and electromagnetic interference, while maintaining efficiency and minimizing additional complexity and cost.
Implementation Method 1
a rectifier for rectifying the AC power in the non-conduction period to generate rectified dimmer voltage
Implementation Method 2
a zero-crossing detection circuit configured to detect zero crossings of the AC and to detect crossings of a first threshold value and a second threshold value of the rectified dimmer voltage
Implementation Method 3
leveraging the MOSFET ON-state resistance as a current-sense element for protection
Data Source
Figure 1
Figure 2
Figure 3A
AI summary
A trailing edge phase control dimmer circuit for controlling alternating current (AC) power to a load with short-circuit protection, wherein a switching control circuit includes a zero-crossing detection circuit configured to detect zero crossings of the AC and to detect crossings of a first threshold value and a second threshold value of the rectified dimmer voltage, and wherein the zero-crossing detection circuit is further configured to initiate the switching circuit to commence one of the conduction periods when the rectified dimmer voltage crosses below the first threshold value and to initiate the switching circuit to prematurely terminate one of the conduction periods when the rectified dimmer voltage crosses above the second threshold value to provide short-circuit protection for the trailing edge phase control dimmer circuit.