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LED Lamp overvoltage protection

IP.com Disclosure Number: IPCOM000218334D
Publication Date: 2012-Jun-04
Document File: 6 page(s) / 67K

Publishing Venue

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Abstract

2011ID08333

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Title of the invention : LED Lamp overvoltage protection

2011ID08333

Abstract of the invention :

detailed description to be provided on next page

A method to protect LEDs in an array used for STOP/TURN and TAIL mode for a motor vehicle lamp assembly is presented. The lamp assembly consists of an array of LEDs arranged in a series parallel configuration and driven passively using a resistor diode circuit topology. A detection circuit is used to monitor the STOP/TURN input voltage to indicate an overvoltage circuit condition. When triggered (in STOP/TURN mode only), a circuit engages the TAIL mode drive resistors to protect the LEDs and STOP/TURN mode resistors for excessive current and power dissipation. The method is also applied to single mode functions to protect from overvoltage conditions.

Detailed description of the invention

Background of the invention

In modern automobiles, light emitting diode (LED) has replaced incandescent bulb as the source of light in exterior lighting applications, such as rear combination lamps (RCLs). In most designs, a cluster of LEDs are arranged in series parallel configuration to achieve the required optical radiation pattern to meet industrial standards and governmental regulations. Electrically, power to the LED array is provided by an electrical circuit designed around passive or active components. Electrical circuit with passive components, such as resistors, is widely used in automotive exterior lighting applications due to its low cost and design simplicity. For lower intensity modes (TAIL) due to the lower drive current, the LED power dissipation in overvoltage conditions (16 < V < 27) is within the LED maximum rated conditions. The drive resistors can also be sized (power) to handle power dissipation at these overvoltage conditions in an economical manner.

However in higher intensity modes (STOP/TURN), the LED power dissipation in overvoltage conditions could cross the absolute maximum LED power dissipation value. Moreover, the drive resistor power dissipation in these overvoltage conditions would require an enormous amount of resistors which would make component layout on the Printed Circuit Board not feasible.

The challenge is to create a low cost driver to drive the LEDs at rated current and protect both the driver and the LED during overvoltage conditions.

Problems or disadvantages overcome by the invention

In order to achieve the minimum lumens from an LED array that have a limited LED count, a regulated linear or switching driver is employed. In this design approach, the LEDs can be driven close to rated maximum current at nominal voltage (12.8V, 13.5V) and since the driver limits the power delivered to the LED array, the LEDs are protected during overvoltage conditions. The limitations in these approaches include, cost, EMC consideration and reliability.

The design presented depicts a novel method to use low cost resistor diode drivers and protect the LED power dissipation in ove...