Patent GB-740284-A (GB)
Title: Improvements in or relating to trigger circuits
IPC: H03K3/49
Filed: 1953-08-04
Abstract: 740,284. Non-contact-making relays. PHILIPS ELECTRICAL INDUSTRIES, Ltd. Aug. 4, 1953 [Aug. 7, 1952; Nov. 12, 1952], No. 21465/53. Class 40 (4). In a bi-stable trigger arrangement comprising a series or parallel resonant circuit in which either the inductance or the capacitance has a non-linear current/voltage characteristic, a D.C. bias is applied to the non-linear component to an extent such that on application of a signal pulse thereto, the voltage across the component is triggered from a low to a high value or vice versa, according to the polarity of the pulse. Negative or positive feedback may be utilized to influence the operating conditions, and a third stable operating point may be obtained. The basic arrangement is shown in Fig. 1, in which an inductance L having a core of variable permeability is connected in series with a condenser C and a resistor R to a constant A.C. supply G. A biasing direct current I is applied to the inductance over a winding W. By varying this current the inductance will alter in a non-linear manner between the limits L min. and L max. Provided that the value of C is chosen to be such that the condition is met, where f is the supply frequency, the A.C. voltage Veff across L will vary in response to I in the manner shown in Fig. 2. In this Figure the damping effect of increased resistance R is illustrated by curves 1 to 4 respectively. When this resistance is small, the A.C. voltage Veff will trigger between the points A-A<1> and B-B<1> on curve 1 when the bias current is increased from zero, and between the points C-C<1> when this current is subsequently reduced. A disconnection is necessary to restore the arrangement to normal after I is reduced to zero. By establishing the bias at Io, Fig. 3, between the current values corresponding to C-C<1> and B-B<1>, the A.C. voltage Veff may be readily triggered in either direction without disconnection by applying signals to winding W of magnitude not less than #I2 and #I1 for high and low A.C. voltages respectively. Alternatively the signal pulses may modulate the supply voltage. Induced A.C. voltages in the winding W may be eliminated by the provision of opposed half-windings arranged on separate cores or a common three-limbed core, Figs. 4 and 5 (not shown). A parallel resonant circuit may be employed, Fig. 6, in which case an impedance Z may be provided in the external circuit so that the requirement in this case of a high circuit impedance is met. Use may be made of a non-linear barium titanate capacitor C, Fig. 7, which is biased by a D.C. voltage.Vo. This voltage and a series-connected signal source T may be substantially decoupled from the A.C. supply by the use of the push-pull circuit shown in Fig. 8, in which non-linear condensers Cl, C2 have series-connected inductances L1, L2 constituted by the primary windings of an odd-harmonic output transformer. Even harmonic output may be obtained from a transformer S. Successive changes in Veff may be effected by D.C. pulses of one polarity by arranging the signal input circuit as an aperiodically-damped resonant circuit. Each D.C. pulse is then converted into a pair of adjacent pulses 1, 2 of opposite polarities, Fig. 9. Due to the inertia of the trigger arrangement, changes in Veff will be effected by only one pulse in each adjacent pair. The basic arrangement shown in Fig. 1 may be modified by a feed-back circuit, Fig. 10, comprising an additional winding T, a half-wave rectifier RF and a regulating resistor RT, the rectifier direction determining the type of feed-back. If negative feed-back is provided, a higher input pulse is required to trigger the voltage but the response time is lowered. The change in Veff due to triggering is also somewhat increased. The reverse occurs if positive feed-back is used. When negative feedback is used, the level of the signal pulses required for triggering may be reduced if an impedance Z is connected in shunt with L. By providing a high degree of negative feed-back a third and intermediate stable operating condition may be obtained, Fig. 13. In the transition from a low to a high value of Veff in response to a pulse 1, the curve 1 is intersected at B and a stable operating point occurs at C. Asucceed. ing pulse 2 of opposite polarity then triggers Veff from C to F. Pulse 3 of the same polarity as pulse 2 then triggers the circuit through the points G and H to the stable starting point J. Pulse 4 then recommences another operating cycle. The second stable condition at F will only be obtained by a suitable choice of pulse 2; if its amplitude or duration are in excess of a certain value, direct transition through C to point J will occur. Where a three-limbed core is used to avoid induced supply currents in winding W, the feedback winding T is arranged on the centre limb, Fig. 15 (not shown). Feedback in the basic and push-pull circuits using non-linear capacitors may be incorporated as shown in Figs. 14 and 16. Condenser C4 acts as a smoothing condenser and preferably has a large value. In the arrangements in Figs. 15 and 16, the feedback is obtained from the evenharmonic output. According to the Specification the arrangement may be used as an impulse regenerator or as an amplifier for pulsatory signals, and has the inherent property of a pulse-shaping circuit. In all the arrangements described, the supply frequency must be high with respect to the repetitive frequency of the signal pulses. Specification 593,755 is referred to.