| 摘要 |
PURPOSE:To provide a direct self-control means for the luminiscent output of a device to prevent damage on the device by causing an element having pnpn tetralayer structure to be connected to a luminiscent element of p-n junction. CONSTITUTION:A p layer 31 of pnpn element 35 and a positive electrode of LED41 are joined together on a substrate 42, and n layer 34 of the element 35 and the negative electrode of LED are connected to a conductor 43 which is insulated from the substrate 42. The element 35 is placed at a position which is irradiated by a part of a radiant beam on LED41. Normally the element 35 is located at an action point 55 with less quantity of light, and an electric current almost does not flow. An electric current in the element 35 increases due to an overcurrent, reducing an electric current in LED41 and reducing a luminiscent output. Consequently, LED is protected from the breakdown by an overcurrent and an excess luminiscent output. In addition, once a large volume of electric current flows, the element 35 maintains an action of the large volume of electric current until a power supply is put in OFF position, even if the light is intercepted. The current/voltage characteristics of the element 35 are S shaped as shown by a curve 51 and a switching voltage drops under light irradiation, shifting to a curve 52. |
