| 摘要 |
PURPOSE:To increase the fan-out number of a TTL circuit and to stabilize the input threshold voltage by providing a PNP transistor (TR) operated when a current flowing from an NPN TR of an input circuit section reaches a prescribed value and absorbing part of the current. CONSTITUTION:When the input IN is at a low level, a base current flows to the NPN TR T1 via the 2nd resistor R1. Thus, the NPN TR T1 is turned on and a collector current flows via the 1st resistor R2 and the 2nd resistor R1. When the collector current of the NPN TR T1 reaches a prescribed value or over, the base potential of a PNP TR T5 is lowered by the voltage drop by the 1st resistor R2, then the PNP TR T5 is turned on and part of the current flowing to the NPN TR T1 is absorbed. Thus, the unreasonable increase in the current flowing to the input via the NPN TR T1 is prevented.
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