LED Driver Circuit with Open-Circuit Detection and Segmented Current Control
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Solution Overview
Problem
Existing electronic circuits driving series connected LEDs face issues with power dissipation due to variations in forward voltage drops and potential damage from open-circuit conditions, leading to excessive power dissipation and risk of component damage.
Innovation Solution
An electronic circuit with a current regulator and open-circuit detection circuit that senses current thresholds, disconnecting the faulty LED string to prevent excessive power dissipation and allow temporary faults to be reconnected, along with a short circuit protection scheme and pulse width modulation for dimming to reduce noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a common boost switching regulator supplies high voltage to all LED strings to ensure the string with greatest voltage drop operates correctly, then all LED strings can be driven, but power dissipation increases unnecessarily for strings with lower voltage drops
Solution Approach 1:
The patent divides the LED driver system into individual current sink modules, each independently controlling a specific LED string. Each current sink module includes its own control circuit that senses the voltage drop across its LED string and adjusts the current accordingly, rather than using a single common regulator for all strings. This segmentation allows each string to receive precisely the voltage and current it needs, eliminating unnecessary power dissipation in strings with lower voltage requirements.
2Reliability
If the boost switching regulator increases output voltage in response to sensing a high voltage drop from an open-circuit fault, then the faulty condition is detected, but excessive power dissipation occurs and remaining healthy LED strings are damaged
Solution Approach 1:
The patent implements preliminary protective action by monitoring the current through each LED string via sense resistors in each current sink module. When an open-circuit fault is detected in one string, the system immediately responds by reducing or shutting off power to the boost switching regulator before excessive voltage can build up and damage remaining healthy LED strings. This preliminary detection and response prevents the harmful effects of fault conditions.
3Loss of energy
If individual current sinks are used for each LED string to enable independent voltage adjustment, then power dissipation is reduced, but device complexity increases
Solution Approach 1:
The patent merges multiple current sink control functions into a single integrated control circuit that can manage multiple LED strings. The control circuit senses voltage drops across different LED strings and adjusts current distribution accordingly, combining what could be separate complex circuits into one unified control mechanism. This merging approach maintains the power efficiency benefits of individual string control while reducing overall device complexity.
Data Source
AI summary
An electronic circuit includes circuit portions for identifying a largest voltage drop through one of a plurality of series connected diode strings and for controlling a boost switching regulator according to the largest voltage drop. The electronic circuit can sense an open circuit series connected diode string, which would otherwise have the largest voltage drop, and can disconnect that open circuit series connected diode string from control of the boost switching regulator. Another electronic circuit includes a current limiting circuit coupled to or within a boost switching regulator and configured to operate with a diode load. Another electronic circuit includes a pulse width modulation circuit configured to dim a series connected string of light emitting diodes.