Patent GB-789412-A (GB)
Title: Improvements in or relating to arrangements for controlling power to be fed to a load by means of semi-conductor resistances more especially transistors
IPC: H02M3/04
Filed: 1955-12-02
Abstract: 789,412. Transistor amplifying and pulse-generating circuits. SIEMENS-SCHUCKERTWERKE AKT.-GES. Dec. 2, 1955 [Dec. 3, 1954; May 31, 1955; Aug. 25, 1955], No. 34649/55. Class 40 (6). In a circuit for controlling the power in loads 3, 4 arranged in circuit with semi-conductor devices 1, 2 the control element of each device 1, 2 is connected over capacitors 8, 9 to the current carrying electrode of the other device and the time during which each device 1, 2 conducts is made variable by altering the discharge time of the capacitors. Control may be effected by applying a signal to transistor 11, Fig. 3, energized over resistors 12, 13 from a supply 14 having twice the potential of and the opposite polarity from supply 5. A battery 18 having the same potential as supply 5 is connected to the emitter of transistor 11. With transistor 11 non-conducting a negligible potential exists across resistor 12 and the transistor 1 remains conducting. As the signal 15 is increased, the collector potential becomes increasingly negative and transistor 1 is cut off for an increasing time. In a similar manner the potential of the emitter of transistor 11 rises and the time during which transistor 2 is cut off is reduced. When transistor 1 conducts, the collector potential falls by nearly the potential supply 5 and drives the base of transistor 2 negative until diode 17 conducts. By varying the bias on the diode 16, 17 the potential to which the respective bases can be driven is limited and hence the time during which the transistor is cut off. By separating the power supply to the transistors 1, 2, a single battery supply may be used, Figs. 3a and 3b (not shown). To obtain a smoother control, transistor 11 may be shunted by two resistors and the control signal applied between their join and the base of the transistors, Fig. 5 (not shown). Alternatively the resistors 12, 13 may be shunted by biased diodes, Fig. 6 (not shown). In a further modification, Fig. 8, the loads 3, 4 are returned to the bases of transistors 21, 22 to control larger output loads 23, 24. The bases of the transistors 21, 22 may be connected over high resistors to a supply positive with respect to the supply 5, Fig. 8a (not shown). In a further modification, Fig. 9, amplifiers 31, 32 are connected in the feedback paths. The resistor 6, 7 may be connected to taps on resistors 3, 4, Fig. 9a (not shown) so that when transistor 2 is fully conducting and transistor 1 is cut off capacitor 8 discharges towards zero with the resistor 6 connected to a lower potential than supply 5 whereas when transistor 2 is cut off resistor 6 is connected to a potential near that of the supply. In a further modification, Fig. 10, the bases of transistors 1, 2 are connected over diodes 76, 77 to capacitors 78, 79 with a variable resistor 75 connected to the supply 5. A steady state is established and this may be varied by adjustment of resistor 75, a control potential applied at terminals 74 varying the potential on the capacitors 78, 79 and hence the ratio of the conducting times of transistors 1, 2. Alternatively two high resistors could be placed across capacitors 78, 79 and varied in opposite senses. In a further modification, Fig. 13, the supply to the two halves of the transistor circuit are varied by applying the control signal 15 to transistor 92 which controls directly the potential supplied to transistor 1 and through transistor 94 the potentials applied to transistor 2. The resistors 6, 7 may be replaced by transistors, Fig. 14, and signals applied to the bases A, B to control the effective resistance. By applying an audio signal 15 to the input of transistor 11, Fig. 15, an amplified audio signal may be obtained and a loud-speaker 20 connected in one of the collector leads. In order to avoid the effects of the D.C. component the loud-speaker 20a may be connected between the collectors. An impulse converter may be arranged in the collector lead which transforms the D.C. pulses to A.C. pulses, whereupon they are amplified and rectified before being applied to the loud-speaker. In a modification, Fig. 16, a transformer 22 is connected in the collector lead with a compensating winding 22c in series with a resistor 24. A supply 21 is arranged to bias the transistor 11 to the centre of the operating characteristic. A push-pull circuit may be employed. Fig. 17 (not shown), comprising two transistor pairs each amplifying during one half-cycle of the input wave. The output transformer has two primary windings one connected to each of the transistor pairs. The recurrence frequency of the transistor pairs is arranged to exceed 25 kc/s. The control windings of a magnetic amplifier may be energized from the collector circuits of a pair of transistors, Fig. 18 (not shown). The semiconductors may be protected from overload by employing an ohmic shunt, to replace the load when it is removed.