| 摘要 |
PURPOSE:To prevent the breakdown of the buffer transistor in the TTL gate circuit by providing a protective transistor to cut off the short-circuit current of the buffer transistor. CONSTITUTION:In the TTL gate circuit equipped with the buffer, protective transistor TRT15 is provided with the base voltage set by resistance R14 and R13 so that the emitter voltage may be turned on under the fixed voltage Vx. And the collector of TRT15 is connected to the base of buffer TRT12, and the emitter is connected to the output terminal of output TRT13 each. As a result, if the output of the gate circuit is logic H and the circuit of under Vx is connected to output terminal 13, TRT13 is turned on with TRT12 turned off, thus preventing the breakdown. In this circuit, even if the output terminals are connected directly between the logic ''H'' output and the logic ''L'' output, the amount of the current is very small with no breakdown of TR. Furthermore, the circuit which is capable of the dot CR coupling of the negative logic can be formed with the output terminals themselves. |
