A Thyristor Controlled by Electromagnetic Field
The constantly sophisticating scientific and technical applications involving the use of power semiconductor electronic systems are setting forth requirements according to which the semiconductor devices should be controlled not only through varying the control current parameters, but also through applying external effects that allow control circuits to be electrically isolated from the power circuits. Light emission techniques, which are widely used for control purposes (photothyristors, phototransistors, etc.) involve the need to set up optical channels (emission source - light guide - photoreceiver) the use of which entails additional expenditures for converting an electric signal into an optical one. The proposed technical solution involving a thyristor controlled by electromagnetic field, by means of which contactless switching can be implemented, can be used in converters for electrical machines and to protect electric circuits from external impacts, like network overvoltages and electromagnetic field impulses. For solving the above-mentioned problem, it is proposed to use a tubular superconducting structure instead of the conventional planar one. With a semiconductor shaped in such manner, it becomes possible to use coaxial coils for organizing electromagnetic coupling, specifically, a screw-shaped control electrode and an inductor coil arranged externally with respect to the tubular semiconducting structure. When a current impulse is applied to the inductor coil, an EMF is induced in the screw-shaped electrode, which is equivalent to applying control current in a usual thyristor. The proposed basic idea of the method for switching a thyristor by means of electromagnetic field is supplemented with a theoretical analysis of interrelation between the inductor magnetic flux characteristics and accumulation of critical charge in the thyristor’s p-base causing the thyristor switching to occur. The article presents mathematical dependences for calculating the magnetic flux variation rate sufficient for accumulation of the critical charge that will cause the thyristor switching to occur within the specified time taking into account the impedance the semiconducting layers offer to the intertum current. It has been demonstrated that the use of a screw-shaped electrode design makes it possible to achieve a shorter thyristor closing time.