Semiconductor switch with thyristors

Claim 1

In a semiconductor switch comprising a main thyristor having an anode, a cathode and a control electrode and an auxiliary thyristor having an anode, a cathode and a control electrode, with both of said thyristors being of the type which can be switched on and off by a control current fed to the control electrode of same, and with said anode of said main thyristor being connected to said anode of said auxiliary thyristor and to a first load current terminal for said switch, said cathode of said main thyristor being connected to a second load current terminal for said switch, said control electrode of said main thyristor being connected with said cathode of said auxiliary thyristor, and said control electrode of said auxiliary thyristor being connected to an input terminal for a control current for said semiconductor switch to turn same on and off; the improvement wherein said auxiliary thyristor has a turn-off gain and a holding current which are sufficiently less than the turn-off gain and the holding current respectively of said main thyristor so that said auxiliary thyristor will remain conducting during the current conducting switched-on state of said main thyristor and continuously feed a control current to said control electrode of said main thyristor to reduce the forward voltage drop of said main thyristor, whereby the on-state behavior of said semiconductor switch is improved and the holding current of said semiconductor switch is reduced.