Intrinsically safe display device with an array of LEDs

摘要

An intrinsically safe LED display device with an array of LED circuit cells is provided. Each cell comprises a LED or a group of LEDs, which are individually made intrinsically safe in a conventional way, by limiting a dissipated power through the LED circuit cell by means of a resistor or group of resistors in series with the LED or group of LEDs. In addition a switching type PTCs with a switching temperature between 80 and 125 degrees centigrade are added in each cell, in series with the resistors or group of resistors of the LED circuit cells respectively, in thermal contact with the resistor or group of resistors of the LED circuit cell. In this way intrinsic safety is provided for mutual heating of adjoining LED circuit cells wherein the LEDs or groups of LEDs are short circuited.

主权项

1. An intrinsically safe LED display device with a two-dimensional array of LEDs, comprising
a mounting board, a spatial array of separate LED circuit cells located on the mounting board, each LED circuit cell comprising an electrical series arrangement of a switching type PTC, a resistor or group of resistors, and a LED or group of LEDs, located in a same relative location in each LED circuit cell, the switching type PTC being in thermal contact with the resistor or group of resistors of the circuit cell, wherein the switching type PTC of each LED circuit cell has a switching temperature between 80 and 125 degrees centigrade, wherein the resistor or group of resistors of each LED circuit cell has a resistance value and a heat contact to the switching type PTC of the LED circuit cell so that heat dissipated in the LED circuit cell per se, due to current through the series arrangement of the LED circuit cell in the case that the LED or group of LEDs of the circuit cell are short circuited, is insufficient to raise the temperature of the switching type PTC of the LED circuit cell above its switching temperature when the LED or group of LEDs of none of the LED circuit cells adjoining the LED circuit cells are short circuited, whereas the resistance value and the heat contact are such that heat generated by a combination of heat generated by the series arrangement the particular one of the LED circuit cells and its adjoining cells, when the LED or group of LEDs of the particular one of the LED circuit cells and its adjoining cells are short-circuited, is sufficient to raise the temperature of the switching type PTC of the particular one of the LED circuit cells above the switching temperature.