LED Driver Protection Circuit for Short Cathode Faults

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Solution Overview

Problem

Existing LED driver systems face challenges in detecting inadvertent electrical contacts between LED strings and the metal chassis, leading to potential damage due to increased current, which is difficult to detect and requires expensive high-voltage signal level translators.

Innovation Solution

A fully ground-referenced protection circuit that monitors voltage at the LED string cathode, LED current sense voltage, and dimming switch state to detect fault conditions, allowing integration with the LED driver control IC and reducing component count and cost.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If high-voltage signal level translator circuit is used to detect short circuit condition, then detection capability is improved, but device complexity and cost increase

Engineering Contradiction:

Improvedetection capabilityVSAvoidcircuit complexity

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The patent introduces an intermediary ground-referenced voltage detection circuit that translates high-voltage cathode conditions into ground-referenced signals. This mediator circuit allows the control IC to indirectly detect short circuit conditions without requiring direct high-voltage interfacing, thus improving detection capability while avoiding the complexity of high-voltage signal level translators

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The patent replaces the electrical/mechanical high-voltage signal level translator circuit with a voltage detection method that uses ground-referenced voltage measurements. By substituting the complex electrical translation mechanism with a simpler voltage monitoring approach, the patent achieves the same detection function with reduced circuit complexity

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

2Reliability

If high-voltage signal level translator circuit is used to detect short circuit condition, then detection capability is improved, but manufacturing cost increases

Engineering Contradiction:

Improvedetection capabilityVSAvoidmanufacturing cost

Core Design Contradiction:

ReliabilityVSEase of manufacture

Solution Approach 1:

The patent employs inexpensive ground-referenced voltage detection circuitry instead of costly high-voltage signal level translators. By using readily available, low-cost components that can be easily integrated into the control IC, the patent achieves reliable short circuit detection while significantly reducing manufacturing costs

Inventive Principle:

Principle #27Cheap short-living objects (Disposable)

3Device complexity

If current feedback is derived at cathode terminal referenced to chassis potential, then circuit simplicity is improved, but detection of short circuit condition becomes difficult

Engineering Contradiction:

Improvecircuit simplicityVSAvoidfault detection difficulty

Core Design Contradiction:

Device complexityVSDifficulty of detecting and measuring

Solution Approach 1:

The patent transitions from chassis-potential-referenced voltage measurements to ground-referenced voltage measurements at the cathode. This dimensional change in reference potential allows the same simple cathode-tap circuit to simultaneously provide current feedback and enable easy detection of short circuit conditions, as ground-referenced voltage directly indicates chassis contact faults

Inventive Principle:

Principle #17Another dimension (Dimensionality change)

Data Source

PatentUS8461777B1Protection from short cathode condition in LED driver and method therefor

Publication Date: 2013.06.11 POLARIS POWERLED TECHNOLOGIES LLC

AI summary

A Light Emitting Diode (LED) driver for preventing shorting has an LED driver circuit. A protection circuit is coupled to the LED driver to detect a fault condition by monitoring a cathode of an LED string of the LED driver, an LED current sense voltage of the LED driver, an LED current feedback error voltage of the LED driver circuit, and a state of a dimming switch of the LED driver.