CONTROL CIRCUITRY USING A PULL-DOWN TRANSISTOR FOR HIGH VOLTAGE SOLID-STATE SWITCHES

Pour commuter un premier commutateur a diode portillonnee (p.ex. GDS61) sur l'etat "OFF" (coupure) il est necessaire d'appliquer une tension sur la porte qui soit plus positive que celle de l'anode ou de la cathode et la source de courant dans la porte qui est du meme ordre de grandeur que celui qui passe entre l'anode et la cathode. Un circuit de commande, qui utilise un second commutateur de commande (p.ex. GDSC) couple par la cathode a la porte du premier GDS, est utilise pour commander l'etat du premier GDS. L'etat du second GDS est commande par un circuit de derivation (p.ex. 510A) ayant une capacite de courant relativement modeste. Un transistor a jonction n-p-n (p.ex. T1) possede l'emetteur et le collecteur couples a la cathode et a la porte, respectivement du premier GDS, et possede la base couplee par l'intermediaire d'un transistor p-n-p (p.ex. T2) a la borne d'entree du circuit de commande. Le transistor n-p-n facilite une mise sous tension rapide du premier GDS en amenant rapidement les potentiels de la porte et de la cathode du premier GDS a des niveaux proches l'un de l'autre. To switch a first gated diode switch (GDS) to the "OFF" state requires a voltage applied to the gate which is more positive than that of the anode or cathode and the sourcing of current into the gate which is of the same order of magnitude as flows between the anode and cathode. Control circuitry, which uses a second GDS coupled by the cathode to the gate of the first GDS, is used to control the state of the first GDS. The state of the second GDS is controlled by a branch circuit having a relatively modest current handling capability. An n-p-n junction transistor has the emitter and collector coupled to the cathode and gate, respectively, of the first GDS, and has the base coupled through a p-n-p transistor to the input terminal of the control circuitry. The n-p-n transistor facilitates a quick turn-on of the first GDS by rapidly bringing the potentials of the gate and cathode of the first GDS to levels which are close together.