Patent GB-1193155-A (GB)
Title: Improvements in Control Circuits suitable for Controlling Bistable Circuits
Inventor: KARDASH JOHN J
IPC: H03K3/012
Filed: 1967-06-19
Abstract: 1,193,155. Transistor bi-stable circuit. SYLVANIA ELECTRIC PRODUCTS Inc. 19 June, 1967 [17 June, 1966], No. 28231/67. Heading H3T. [Also in Division G4] A control circuit 14, for controlling a flip-flop 11, Fig. 1, over an output line 12 (and 13) includes a control device such as a transistor QG which only in its OFF state allows a semiconductor switching means, such as a transistor Q E , to store charge in response to a trigger signal applied (from 15) to its two inputs, namely base and emitter, one input being through an impedance R C  ; the switching transistor Q E  conducting to discharge the stored charge when the trigger signal is removed. The flip-flop consists of two transistors Q A , Q D  crosscoupled through multiemitters transistors QB, Qc, one emitter of each of which constitutes the input from the control circuit 14, and one emitter of Q c  being a "clear" input. If QA is ON and QD OFF, the emitter of Q B  connected to Q D  collector is effectively connected to a high impedance; and as Q E  and Q F  are normally in a low conduction state the other emitter of QB is also connected to a high impedance, and no current flows through the base resistor RA to the emitter. Consequently the base is at a high potential (due to B +) and the collector junction becomes forward biased, supplying current to QA base to hold the latter ON. Switch over is effected by making Q F  conduct so that an emitter of QB conducts through Q F  to Earth. This lowers QB base potential due to the current in RA, and its collector current is blocked to turn Q A  OFF. Cross-coupling ensures complete switch over. QF is made to conduct to achieve this, by a positive pulse from an appropriate one of the inputs 15, 17 (J, K) or from a single input if a connection 18 is made. Thus a positive pulse at K appears at the base resistor R D  of Q F  and at its emitter, and causes Q F  emitter-base junction to conduct when the pulse voltage reaches a value at which the emitter of QF is clamped by diodes D C , D N . This value is sufficiently high however relative to the collector of QF (i.e. B+ volts, minus the drop across RA) for no collector current to flow, and charge is stored in QF. When the pulse K ends, the base and emitter fall in potential and the stored charge produces a collector current which must flow out of the corresponding emitter of QB ; thus change over of the flip-flop is achieved. Using separate J and K inputs (connection 18 removed), J-K type operation results since whichever of Q A  and QB is ON produces a current in a base resistor R E , RG of the corresponding control transistor Q G , QH to turn it ON; the ON transistor then shorts out any positive trigger pulse through the corresponding resistor RC, R D , and prevents conduction of the associated transistor Q E , Q F . Diodes DA, DB limit the recovery of the stored charge. Four of the Fig. 1 circuits (21, 22, 23, 24, Fig. 2, not shown) are linked by gates (27, 28, 29) and provided with input and output circuits (25, 26) to operate as a divide by 10 counter. Feedback connections in the counter include inhibit lines such as a connection through a diode (D12) to the base of the QQ transistor (Q15) of the first stage. Other inhibit connections in Fig. 1 are a further transistor QI in parallel with Q G  or QF, as used in the modified counter of Fig. 3 (not shown); and a multiemitter transistor D B , one function of which performs the same function as DA, and the others serving as inhibit inputs.