GB1527911A - Device for controlling the pulsating operation of electromagnets in knitting machines - Google Patents

Abstract

1527911 Transistor switching circuit ELITEX 29 Sept 1975 [28 Sept 1974] 39725/75 Heading H3T In a circuit to control the energizing of an electromagnet, e.g. in a knitting machine, a capacitor C, the coil M of an electromagnet, and a control element, e.g. transistor T 1 , are connected in series in that order, with a first voltage source U b2 applied across capacitor C via a blocking diode D 2 , and with a switchable stabilized current circuit controlling the current through the control element: a second higher voltage source is led in via a switch element, e.g. thyristor T y to the connection between the control element T 1 and coil M. After initial charging of C via thyristor T y to second source voltage U b1 , input of a control signal at B, amplified at terminal 9 allows integrated amplifier ÁA 723 to be energized, supplying base current to transistor T 1 . C then discharges rapidly via coil M, transistor T 1 and resistor R 1 , the current overshooting to a peak, (Fig. 2, not shown), accelerating closure of the magnet armature. In the stabilizing circuit the voltage across R 1 applied to inverting input 2 of amplifier ÁA 723 is compared with the adjustable fraction, set by R 5 , of a reference voltage supplied by the amplifier at terminal 4 and tapped off to non-inverting input 3; at this stage capacitor C, holds down the voltage across R 1 , allowing the current through C and M to overshoot before falling. After time t 1 (Fig. 2, not shown), C will have discharged sufficiently to allow voltage source U b2 to begin to feed current through diode D 2 , and shortly afterwards at time t 2 when C, has charged to allow the full volt-drop to appear across R 1 , the coil current is stabilized at a constant value determined by R 5 . Finally the signal is removed from B, cutting off the amplifier and transistor T 1 , and at the same time a pulse G to thyristor T y allows source U b1 to supply reverse current through coil M, shunted in part by diode D 1 and resistor R 2 , to charge C, the current continuing in damped oscillation, via circuit C, M, R 3 &c. The current reversal removes remanent magnetism in the electromagnet, ensuring that its armature drops out. The control and switching elements may be other than semi-conductor devices.