Patent GB-854910-A (GB)
Title: Transistor two-state apparatus
IPC: H03K3/281
Filed: 1957-02-11
Abstract: 854,910. Transistor bistable circuits. MINISTER OF NATIONAL DEFENCE OF H. M. CANADIAN GOVERNMENT. Feb. 11, 1957 [Sept. 14, 1956], No. 4677/57. Class 40 (6). A bistable circuit comprises two complementary transistors having their base and collector electrodes cross coupled, or an equivalent transistor structure, the arrangement having conducting and non- conducting conditions and means which clamp the output electrode potential in each condition and prevents at least one of the transistor elements from bottoming when the circuit is conducting. In Fig. 1, complementary transistors 10 and 11 have their base and collector electrodes cross connected so that both are either conducting or non-conducting In the non-conducting or off condition the emitter output electrode is clamped by a diode 17. The leading edge of a positive triggering pulse applied at terminal 30 will cause a capacitor 31 to charge while the trailing edge will cause it to discharge into transistor 11, so making the transistor conductive. This will render transistor 10 conductive and by regenerative action both transistors quickly become highly conductive, so clamping the output electrode 16 to earth potential through diode 25. Transistor 10 bottoms but transistor 11 is prevented from doing so either by the provision of a resistor 39 or a diode connected at the same points or by choosing the transistors so that transistor 10 bottoms before 11. The circuit is returned to the "off" state by applying positive pulses at terminal 33. The leading edge causes a capacitor 37 to charge while the trailing edge applies a negative potential to the base of a transistor 26 arranged in a blocking oscillator circuit. The transistor 26 accordingly becomes highly conductive, lowering the voltage at the base of transistor 11 and so by regenerative action cutting off both transistors. The blocking oscillator is returned to its non- conducting state when transistor 10 is no longer bottomed and transistor 26 becomes starved of collector current. Fig. 3 shows a similar circuit in which neither transistor bottoms. When the transistors are in the "off" condition the potential of the electrodes are clamped by diodes 17, 40 and 41 while in the "on" condition they are clamped by diodes 25, 42 and 43. This circuit is switched to the non-conducting condition by pulses applied to terminal 33. The leading edges of these pulses charge capacitor 37 while the trailing edges momentarily render a transistor 26 conducting. This causes a rectifier 45 to increase the potential of the base of transistor 10 and thus causes the two transistors to cut-off. When the collector to base capacitance of transistor 26 is sufficiently low a direct connection may be made from the collector 29 to the base of transistor 10 and the components 45, 48 and the 11À25 volt supply omitted. The pairs of diodes 40, 42 and 41, 43 may each be replaced by a single Zener diode with appropriate breakdown voltages (Figs. 4 and 5, not shown). In addition a further diode may be connected to resistor 44 so that the circuit may be arranged to draw a constant current from the source (Fig. 6, not shown). A more rapid discharge of any capacitance connected to output terminal 21 may be affected by connecting an emitter follower before the output terminal with a diode between the emitter and base to supply the A.C. and D.C. current in the conducting condition (Fig. 8, not shown). Fig. 7 shows a circuit similar to Fig. 3 with zener diodes 49, 50 replacing diodes pairs 40, 42 and 41, 43 and with a direct connection between the collector of input transistor 28 and the base of transistor 10. In addition, both "on" and "off" triggering pulses are applied to terminal 30 and a routing circuit is provided to direct the pulses to the appropriate points. The connection to the previous stage normally holds the potential at terminal 30 at -10 volts. An input pulse raises the potential to 0 volts and when the driven circuit is in the "off" condition the leading edges permit a capacitor 31 to charge through resistor 59 the upper end of which is maintained at earth potential by clamping diode 17. The trailing edge of the pulse permits capacitor 31 to discharge into the transistor circuit causing it to be rendered conducting. The next input pulse at terminal 30 will not cause capacitor 31 again to charge because the upper end of resistor 59 is now held at -10 volts, the potential of the output terminal. However, the leading edge will cause a capacitor 37 to charge while the trailing edge will cause the capacitor to render transistor 26 conductive, so to change the circuit back to its non-conductive condition. The next pulse will not cause transistor 26 to conduct again because the rise in potential of the output terminal 21 when the circuit is in the non-conductive condition is applied through a Zener diode 70 to the base of transistor 26 to raise the base potential to some 19 volts so that the 10 volt triggering pulse is insufficient to produce conduction. Two circuits 90, 91 (Fig. 2) such as are shown in Fig. 1 or 3 may be interconnected by a routing circuit 52 directing the output pulses of the driving unit 90 to alternate inputs 30b, 33b of the driven unit 91. When the driven unit is in the non-conducting condition the leading ledge of the output from the driving unit charges capacitor 57 so that the trailing edge will momentarily lower the potential at terminal 33b, causing the driven unit to be changed to the conducting condition. The potential of terminal 21b thereupon rises rendering the circuit through capacitor 57 inoperative and cutting off diode 54 so that the leading edge of the next input pulse will cause capacitor 31b to charge so that the trailing edge changes the driven unit back to its original state. The cross-coupled transitors form an N.P.N.P equivalent structure and this may be replaced by a complementary P.N.P.N. arrangement.