Patent GB-1072264-A (GB)
Title: Circuit arrangement for controlling with low losses electric dc consumers
IPC: H02M3/137
Filed: 1964-04-27
Abstract: 1,072,264. Semi-conductor Circuits. FRAKO KONDENSATOREN - UND APPARATEBAU G.m.b.H. April 27, 1964 [April 26, 1963], No. 17439/64. Heading H3T. [Also in Division H2] In a bi-stable switching circuit of the type comprising a main controllable electronic switch GR1 connected to the load R and through a quenching capacitor C1 to the junction point of a quenching electronic switch GR2 and a charging path for the capacitor, the charging path includes a switch GR3 which is rendered conductive when the quenching switch is off. By this means the current drain through the charging path while the quenching switch is on may be avoided. In Fig. 1, the load R is energized when a thyristor GR1 is fired, a reactor DR2 limiting the rise of current until it is saturated. Thyristor GR3 is fired simultaneously with GR1 so that a quenching capacitor C1 is charged resonantly through chokes DR1 and DR2, the completion of the charging causing the charging current to reduce to zero and thus GR3 to be extinguished. GR1 is extinguished by firing GR2 to cause the quenching capacitor resonantly to discharge through DR2 and so reduce the current in GR1 to zero, a rectifier GR4 being provided to minimize the back voltage generated across GR1. The two oscillatory circuits which include the quenching capacitor are preferably tuned to a multiple of the switching frequency of GR1. Resistance-capacitor elements are connected across all the thyristors to protect them. An electromagnetic switch may replace GR3. The mean power in the load may be varied by repeatedly firing GR1 and varying the duration of the conducting period. A suitable circuit for this (Fig. 2, not shown) comprises a free-running multivibrator (10) producing pulses which are integrated at (11) to produce a sloping wave applied to a comparator (VG) so that an output pulse is produced when the sloping wave exceeds the comparison voltage. This pulse feeds a monostable multivibrator, the output of which is differentiated at (14) and provides pulses for the thyristors. The comparison voltage (U 0 ) applied to (12) may be provided by a further free-running multivibrator (7) the output of which is integrated at (18) and applied via a rectifier (19) to the comparator, the level of the voltage applied to the integrator being varied by a capacitive potentiometer (15, 16) by a light-sensitive semi-conductor, a Hall effect device or by a variometer. Overload protection may be provided by a condition sensitive device (20) the output of which is amplified (at 21) and integrated (at 22) to provide through a rectifier (23) a comparison voltage which limits the peak current. A further rectifier and integrator (25) provides (through 26) an additional control voltage which limits the mean current. For vehicle motors it is desirable to limit the rate of increase of the comparison voltage and thus the acceleration and this may be effected by connecting a pulse delaying network to the output of the free-running multivibrator 17. In the pulse delay network (Fig. 3) the input pulses are applied at 30, 31 through a capacitive potential divider 32, 33, 34, 35, including a transistor 36. The leading edge of the pulse causes the large capacitor 40 and the smaller capacitor 39 to charge through 38 to produce a slow rise in voltage whereas at the trailing edge rectifier 41 blocks the discharge of the larger capacitor but allows the smaller capacitor to discharge quickly so that a high braking torque is produced.