GB900228A - Circuit for producing an alternating voltage proportioned to the absolute value of a variable input voltage - Google Patents

Abstract

900,228. Phase-sensitive circuits. ACF. INDUSTRIES Inc. July 28, 1959, No. 25840/59. Class 38 (4). [Also in Group XXXIII] A circuit for converting a variable amplitude A.C. input which may be either in phase or 180 degrees out of phase with a reference into an A.C. output whose amplitude varies with the input amplitude, but is always in phase with the reference consists of a full-wave rectifier bridge gated on alternate half-cycles by the reference voltage. The input signal is applied by a transformer 10 to a full-wave rectifier bridge 13, 14, 15, 16. A pair of equal resistors 25, 26 are connected across the output diagonal AB of the bridge. The output to an amplifier 28 is taken between the centre tap of the transformer 10 and the midpoint 27 of resistors 25, 26. The resistors 25, 26 also form, together with diodes 22, 23 a second bridge having AA as the output diagonal, the input diagonal 24, 27 being connected in series with resistor 29 across a further centre-tapped transformer (unreferenced) connected to the reference voltage source. The centre taps of both transformers are connected to earth. The reference voltage is always greater than the input signal. Thus on alternate half-cycles of the reference voltage, diode 22 passes current through resistors 25 and 29, and diode 23 passes current through resistors 26 and 29. All three resistors being of equal value, there is no resultant output voltage between the point 27 and the transformer centre tap in the absence of an input signal to the first bridge. The conduction of diode 22 blocks diodes 13 and 14 and the conduction of diode 23 blocks diodes 15 and 16. Thus during one half-cycle of the reference voltage, with 13 and 14 blocked, either 15 or 16 conducts to provide a half-wave output pulse of a fixed polarity regardless of the phase of the input signal and conversely on the other half-cycle of the reference. The circuit is stated to simulate rudder drag in an A.C.- operated flight trainer.