PURPOSE: To speed up turn-off by driving a transistor (TR) extracting a base storage electric charge of an output stage TR of a TTL logic circuit via a switching diode turned on when the output stage TR turns off.

CONSTITUTION: When inputs A, B are logical H, a TRQ6 is turned on, TRs Q4, Q3 are turned off, a TRQ1 is turned on and an output Y goes to logical L. Diodes D4∼DN are turned off in this case and the state of the TRQ2 is close to the turn-off state. When either or the inputs A, B or both of them are logical L, the TRQ6 is turned off, the TRs Q3, Q4 are turned on and the TRQ1 is turned off and then the output Y goes to logical H, but a potential at a point (b) is increased more than that at a point (a), a diode D3 is turned off, the diodes D4∼DN are turned on and then a base current is applied to the TRQ2, thus the storage electric charge in the TRQ1 is discharged and the TRQ1 is turned off at high speed.