LED Driver Overcurrent Protection Circuit
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Solution Overview
Problem
DC driver circuits for LED lighting often overshoot or exceed current limitations when an output short circuit occurs, posing a risk and necessitating a reliable method to control output current effectively.
Innovation Solution
An output current limiting circuit that includes a positive input terminal, ground input terminal, positive output terminal, ground output terminal, an output switch, and a control circuit, which senses output voltage and closes or opens the switch to limit current flow when the voltage exceeds or falls below a predetermined limit, preventing damage from short circuits.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If DC driver circuits operate near UL CLASS-2 limits with maximum output current of 8A, then power delivery capability is improved, but output current control reliability deteriorates when output short circuit occurs
Solution Approach 1:
The patent applies preliminary anti-action by implementing an overcurrent protection circuit that proactively limits output current before excessive current can damage the circuit. The circuit includes a sense resistor that continuously monitors output current and triggers a shutdown mechanism when current exceeds the 8A UL CLASS-2 limit, preventing reliability failures during short-circuit conditions while maintaining full power delivery capability during normal operation.
2Power
If output switch provides low resistance current path to enable high current flow, then power delivery is improved, but current limitation capability during short circuit deteriorates
Solution Approach 1:
The patent applies dynamics by making the output switch controllable and dynamic rather than static. The switch can transition between low-resistance closed state during normal operation (enabling high current flow for power delivery) and high-resistance open state during overcurrent conditions (blocking current flow to prevent damage). This dynamic switching capability, controlled by the overcurrent protection circuit monitoring voltage across the sense resistor, resolves the contradiction between needing low resistance for power delivery and high resistance for current limitation during faults.
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
The solution effectively limits and eliminates output current during shorted conditions, ensuring compliance with industry standards and preventing damage to LED driver circuits.
Implementation Method 1
The output switch provides a low resistance current path from the positive input terminal to the positive output terminal when closed and substantially prevents current flow from the positive input terminal to the positive output terminal when open
Implementation Method 2
The control circuit is connected to a control terminal of the output switch and senses an output voltage between the positive output terminal and the ground output terminal
Data Source
AI summary
A light fixture includes a ballast operable to drive a light source of the light fixture. The ballast includes a DC driver circuit and an output current limiting circuit. The output current limiting circuit is operable to minimize current overshoot in the event that an output of the ballast is shorted such as if the light source fails in a short circuit condition. The output current limiting circuit includes an output switch for limiting the current to the load (e.g., light source) and a control circuit. The control circuit senses the short circuit and clearing of the short circuit and controls the output switch accordingly to prevent excess output current to the shorted circuited load.