The present invention relates to a thyristor, and more particularly, to a mechanism for accurately positioning its light-sensitive area and trigger guide in registry.
This mechanism is hereunder described with particular reference being made to a light pulse triggered thyristor. A typical example of a conventional light pulse triggered thyristor is shown in cross-section in FIG. 1, wherein a thyristor element 1 has a trigger section or light-receiving area 1ain the center of its upper surface. A reinforcing disk 2 made of a metallic material having a coefficient of thermal expansion close to that of the element 1 is secured to the lower surface thereof. A first electrode unit 3 is pressed against an electrode that is formed to surround the light-receiving area 1a on the upper surface of the element 1. A second electrode unit 4 is pressed against the lower surface of the reinforcing disk 2. An insulating tube 5 for positioning and reinforcing the metal disk 2 is made of a material like alumina ceramic and peripherally surrounds the element 1, the disk 2, and the electrode units 3 and 4. The inside diameter of the insulating tube 5 is slightly larger than the outside diameter of the disk 2. Upper and lower annular metal plate flanges 6 and 7, respectively, are hermetically secured to the upper and lower sides of the insulating tube 5. The inner peripheral surfaces of the flanges 6 and 7 are similarly secured to the outer peripheral surfaces of the electrode units 3 and 4, respectively. A transverse groove 8 is provided in the first electrode unit 3 on the side thereof facing the element 1. Said groove 8 extends radially inward from the outer peripheral surface of the first electrode unit 3 to a point beyond the light-receiving area 1a and is wider in a direction perpendicular to the section of FIG. 1 than the diameter of the light-receiving area 1a. A transverse through-hole 9 is made in an area of the insulating tube 5 corresponding to the groove 8. A light guide 10 for directing external trigger light signals to the light-receiving area 1a comprises a glass rod permitting a high degree of light transmission. The outer peripheral surface of the portion of said guide 10 which is closer to its outside end is sealed to the inner wall of the through-hole 9 so that the inside end of said guide is positioned along the central axis of the insulating tube 5 at a point close to the light-receiving area 1a. Said outside end passes through the transverse groove 8 and the through-hole 9 to extend outside of the insulating tube 5.
In the apparatus of FIG. 1, the outer peripheral surface of the portion of the light guide 10 which is closer to its outside end is sealed to the inner wall of the through-hole 9 in the insulating tube 5 so that the inside end of the guide 10 is positioned along the central axis of the insulating tube 5. The reinforcing metal disk 2 is held in position by being pressed into the insulating tube 5. Therefore, in order for both the inside end of the light guide 10 and the light-receiving area 1a of the element 1 that is secured to the upper surface of the metal disk 2 to be positioned along the central axis of the insulating tube 5, the element 1 must be fixed to the upper surface of the metal disk 2 so that the center of the light-receiving area 1a is positioned on the line that is normal to the center of said upper surface of the metal disk 2. But this is very difficult to achieve and it sometimes occurs that the center of the light-receiving area 1a is not in registry with the line that is normal to the center of the upper surface of the metal disk 2. If this misalignment occurs, the inside end of the light guide 10 becomes offset with respect to the center of the light-receiving area 1a and the amount of light being transmitted from the inside end of the light guide 10 toward the light-receiving area 1a is not sufficient to retain the desired high sensitivity of triggering by light pulses.