Leakage Protection Circuit with Pull-Down Current Generation
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Solution Overview
Problem
Existing leakage protection circuits in switched-mode power supplies, particularly those driving LED loads, face challenges in accurately detecting electric leakage without causing excessive energy loss or requiring high-energy switch transistors, and fail to function effectively with large inductance at input terminals.
Innovation Solution
A leakage protection circuit that includes a pull-down current generation circuit and a control circuit to generate a pull-down current during a predetermined time interval, determining leakage based on a voltage detection signal representative of the output voltage of a rectifier circuit, allowing energy transfer only when no leakage is detected, thereby reducing the need for high-energy switch transistors and ensuring accurate detection even with large inductance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If existing leakage protection circuits are used to detect electric leakage, then leakage detection function is provided, but excessive energy loss occurs and high-energy switch transistors are required
Solution Approach 1:
The control circuit generates a pull-down current during a predetermined time interval (first time period) after power-on or reset, proactively creating a reference current state before normal operation begins. This preliminary action establishes a baseline for comparison that enables accurate leakage detection without requiring continuous high-energy switching operations
Solution Approach 2:
The circuit dynamically changes the current parameter by generating a time-limited pull-down current only during the predetermined interval, rather than maintaining continuous high-energy switching. The control circuit adjusts current flow based on timing signals, transforming the detection mechanism from continuous high-energy operation to periodic low-energy measurement
2Measurement precision
If existing leakage protection circuits are used, then leakage detection is attempted, but accurate detection fails when large inductance is present at input terminals
Solution Approach 1:
By generating the pull-down current during a predetermined time interval before normal operation, the circuit establishes a reference state that is independent of subsequent inductive effects. This timing-based separation ensures that the reference current is established when inductive interference is minimal, enabling accurate comparison even when large inductance is present during normal operation
Solution Approach 2:
The control circuit anticipates and counteracts the potential interference from large inductance by establishing the reference current state during a controlled time interval when the inductive effects have not yet manifested. This preliminary anti-action prevents inductive interference from corrupting the reference measurement
3Reliability
If high-energy switch transistors are used for leakage detection, then detection capability is maintained, but device complexity and cost increase
Solution Approach 1:
The circuit uses low-cost, standard switch transistors instead of specialized high-energy devices. The control circuit achieves reliable detection through intelligent timing and pull-down current generation rather than relying on the inherent high-energy capabilities of expensive transistors. The switch transistors operate briefly during the predetermined time interval rather than requiring continuous high-power capability
Solution Approach 2:
The invention replaces the mechanical/electrical approach of using high-energy switch transistors with a control-based approach using pull-down current generation and timing. Instead of relying on transistor power handling capability, the system uses intelligent control to generate reference currents and compare states, substituting physical power with control intelligence
Data Source
AI summary
A leakage protection circuit can include: a pull-down current generation circuit coupled between output terminals of a rectifier circuit; and a control circuit configured to control the pull-down current generation circuit to generate a pull-down current during a predetermined time interval, and to determine whether leakage occurs in accordance with a voltage detection signal that is representative of an output voltage of the rectifier circuit.