GB955153A - Improvements in or relating to voltage generation - Google Patents

Abstract

955,153. Transistor linear sweep generating circuits. FERGUSON RADIO CORPORATION Ltd. Nov. 14, 1961 [Nov. 23, 1960], No. 40310/60. Heading H3T. In a transistor " Miller " circuit for generating a linear sweep the " Miller " condenser is connected to the junction of two similarly poled rectifiers connected between base and emitter and the charging source for the " Miller " capacitor is disconnected from the collector and the capacitor during the generation of the sweep. In Fig. 3 a " Miller " capacitor 15 is maintained normally charged through a circuit comprising a normally conducting transistor 11<SP>1</SP> and diode 14 while terminal 17 is normally maintained at earth potential so that diode 13 prevents the flow of charging current through the base emitter path of transistor 10. On the application of a pulse to terminal 19 a trigger circuit 18 causes a transistor 11<SP>1</SP> to become non-conducting and a negative potential to be applied to terminal 17 whereby the capacitor 15 discharges linearly in "Miller" fashion through diode 13, diode 14 being non-conducting. A linear change of voltage is accordingly produced across a capacitor 24. Transistor 11<SP>1</SP> could be replaced by a diode in which case the trigger circuit would switch the supply to the collector of transistor 10 through the diode (Fig. 1, not shown). Fig. 4 shows a circuit for producing a linear change of voltage at output terminal 73 after a predetermined delay with respect to an input pulse at terminal 19 the final voltage of the rise being maintained for a predetermined time before restoration to the initial voltage. The circuit comprises separate circuits of the type shown in Fig. 3 each comprising a transistor 10, 10<SP>1</SP> or 10<SP>11</SP> corresponding to transistor 10, a common transistor 11<SP>1</SP> corresponding to the similar transistor in Fig. 3 and a further transistor 42 connected in series with resistors 43, 44 and 45 corresponding to resistor 16. The trigger circuit comprises a normally conducting transistor 31 having its collector coupled through a diode 33 to a normally non-conducting transistor 35 the collector outputs from this trigger circuit being connected to the collector and base feed transistors 11<SP>1</SP> and 42. A positive triggering pulse applied at terminal 19 passes through diode 59 and capacitor 60 to the base of transistor 31 to cut this transistor off and accordingly to render transistor 35 conducting. Transistor 11<SP>1</SP> accordingly becomes non- conducting and 42 conducting whereby the " Miller " capacitor 15 of stage 10 commences to linearly discharge and this continues until the collector potential is caught by a transistor 66. During this time the current in a capacitor 48 exceeds that in a resistor 32 and that in capacitor 49 exceeds that in resistor 44 and that in capacitor 50 exceeds that in resistor 45 so that transistors 31, 10<SP>1</SP> and 10<SP>11</SP> remain cut off. However, when the collector of transistor 10 is caught, the current in resistor 44 switches transistor 10 on and " Miller " action starts in transistor 10<SP>1</SP>, continuing until the transistor bottoms. During this period the currents through capacitor 47 exceeds that through resistor 32 and the current through capacitor 51 exceeds that through 45 so that transistors 31 and 1011 remain non-conducting. However, when transistor 10<SP>1</SP> bottoms, transistor 10<SP>11</SP> is switched on and " Miller " action continues in this circuit the time constant of capacitor 46 and resistor 52 being such that transistor 31 remains conducting. When transistor 10<SP>1</SP> bottoms transistor 31 is switched on and the circuit returns to its initial condition. The desired output waveform is derived from the collector or potential of transistor 10<SP>1</SP> through a double emitter follower circuit 71, 72. The transistor 25 stabilizes the potential on line 26, diodes 38, 49 and 40 isolate the " Miller " capacitors from each other and resistor 76 in the output circuit prevents damage to diode 39 and transistors 10<SP>1</SP> and 11<SP>1</SP> should transistors 71 or 72 develop a base to emitter short-circuit.