Patent GB-798188-A (GB)
Title: Improvements in or relating to electric trigger circuits, oscillator circuits and the like employing transistors
Inventor: WOLFENDALE ERIC
IPC: H03K3/3565
Filed: 1955-04-04
Abstract: 798,188. Transistor oscillator, one and two stable state circuits. MULLARD RADIO VALVE CO., Ltd. Feb. 17, 1956 [April 4, 1955; Aug. 10, 1955], Nos. 9804/55 and 23113/55. Class 40 (6). In a circuit comprising two transistors of opposite conductivity type, one being a field effect transistor and the other a junction or field transistor, with the main current paths in series, a load impedance is arranged in series with the combination and a feedback loop is provided between the junction of the load and transistor and the control electrode of the other transistor. A field effect transistor F, Fig. 1, is arranged with the source-drain path of n conductivity connected in series with the emittercollector path of a junction transistor T and load resistor Rc with a feedback connection to the gate electrode g. When transistor T is fully conducting, the potential of the collector and thus the gate g is raised sufficiently for the field effect transistor F to be conducting, thus maintaining the transistor T in the conducting condition. When transistor T passes to the cut-off state, the fall in collector potential lowers the gate potential thereby cutting off the current in the field effect transistor F. The resistor Rc may be such that the transistor T is bottomed in the on condition and a resistor may be added in the drain circuit so that the field effect transistor is also bottomed. Catcher diodes may be added, Fig. 2 (not shown), to avoid either transistor operating in the bottomed condition. In order to reverse the state of conduction of the circuit by pulses of one plurality P, Fig. 3, a steering network is provided. Assuming the circuit is in the off state diode D2 is biased off and a positive pulse passes through diode D1 to trigger the circuit into the on state, the resulting flow in current through the collector resistor Rc and the drain resistor reversing the state of bias on the diodes D1, D2. As a result, the next pulse is fed over diode D2 and capacitor C3 to the base of transistor T causing it to pass to the off state together with transistor F. A circuit is also described (Provisional 23113/55) in which two junction transistors T1, T2 are employed with feedback between the collector of transistor T1 and the base of transistor T2 which may include a battery to provide the correct operating potential. Alternatively a potentiometer comprising resistors Rp, Rl and Rc may be provided with the resistor Rf providing the feedback connection, shunted by a capacitor if desired to enhance the speed of operation. A resistor may be provided in the collector circuit of transistor T2 and a catcher diode to prevent the collector circuit from bottoming. A steering network similar to that of Fig. 3 may also be employed. In a modification, two field effect transistors F1, F2 are employed (Complete Specification), feedback being provided over resistors R2, R5, which may be shunted by capacitors. Since the circuit is symmetrical the connection between the two sources should remain constant but it may be preferable to return this connection to a potential intermediate that of the two supply lines. By employing a load impedance comprising an inductor L the circuit may be made astable or monostable, Fig. 4, according to whether the potential - Ec is less than or greater than the cut-off potential of the gate electrode g. Alternatively a capacitor may be arranged between the collector and gate with a resistor returned to a negative potential which if greater than the cutoff potential causes the circuit to be monostable and if less astable. Further if the potential is such as to cause transistor F to pass a current sufficient to bottom transistor T then the circuit is monostable. By the addition of a capacitor C to the astable circuit a sinusoidal oscillator is produced. Output may be taken from the drain load resistor at terminal O which since it is not in the feedback loop has little effect on the operation of the circuit.