| 摘要 |
1,093,408. Transistor logic circuits. THOMSON-AUTOMATISMES. March 18, 1965 [March 18, 1964], No.11549/65. Heading H3T. A fail-safe logic circuit comprises a complementary pair of transistors T1, T2 connected in cascade, the base-emitter path of T1 being connected across a bridge formed of resistors R1 . . . R4 and a diode D1. A regenerative feedback loop may be provided via R7. In the absence of input signals at E, E1, E2 diodes D1, D11, D21 are conductive so that T1, T2 are non-conductive, giving a binary 0 at terminal S. When a binary 1 is applied to all terminals E, E1, E2, the diodes become non- conductive so that both T1 and T2 become saturated giving a binary 1 at S. The output at S remains 0 in the event of failure of either of the supplies P or M. The AND circuit Z may be replaced by a conventional OR circuit as in Figs. 5a, 5b (not shown). In Fig. 9 (not shown) one of the inputs E is provided by a diode OR circuit, one input of which is provided by the output of a two-input AND gate (similar to that shown at Z), the two inputs of which are provided by diode OR circuits. |
