US Patent 9226361 Intrinsically safe display device with an array of LEDs

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.