Patent GB-962802-A (GB)
Title: Improvements in or relating to magnetic amplifier circuits
Inventor: BLACKABY BENJAMIN EDWARD
IPC: H03F9/04
Filed: 1959-07-17
Abstract: 962,802. Magnetic amplifiers. DE HAVILLAND AIRCRAFT CO. Ltd. July 15, 1960 [July 17, 1959], No. 24720/59. Heading H3B. A magnetic amplifier circuit includes derivative feedback means operative to control the frequency response of the circuit to sinusoidal alternating current input signals and so arranged that the output of the circuit leads the input in phase over at least one range of input frequencies and lags the input of the circuit in phase over at least one other range of input frequencies. The circuit preferably comprises a magnetic amplifier stage having a derivative negative feedback connection between the output of the stage or of a succeeding stage and a control winding of the stage and having a derivative positive feedback connection between the output of the stage or of a succeeding stage and a further control winding of the stage. Over at least one range of input frequencies the derivative positive feedback connection is operative to cause the output of the circuit to lead the input in phase and over at least one other range of input frequencies the derivative negative feedback connection is operative to cause the output of the circuit to lag the input in phase. The magnetic amplifier circuit comprises three series connected stages, the first stage comprising push-pull amplifiers 17, 18, the second comprising push-pull amplifiers 19, 20 and the third comprising output amplifier 21. A.C. power input signals are applied to the first two stages through the secondary windings 29, 42 of two transformers (not shown). The first stage includes control windings 22, 23, 24, 30, 31, 32, bias windings 25, 33 and negative feedback windings 26, 34. The second stage includes bias windings 38, 44 and negative feedback windings 39, 45. Input signals to the first stage are applied across windings 15, 16 and the output of the second stage is derived across resistors 48, 49. Gain limiting negative feedback is provided through resistor 50 from resistors 48, 49 to windings 24, 32 of the first stage, while positive derivative feedback is applied across windings 23, 31 through resistors 51, 52 and capacitor 53. Negative derivative feedback is applied across windings 22, 30 through resistors 54, 55 and capacitors 56, 57, 58. A rectifier 59 cuts out this negative feedback if the magnitude of the change in input signal is greater than a predetermined amount. By appropriate choice of circuit components the frequency response to sinusoidal alternating current input signals is such that the output of the circuit leads the input of the circuit in phase over ranges of input frequency of 0 to 1 c.p.s. and of 1.5 to 1.8 c.p.s. and lags the input of the circuit in phase over ranges of input frequency of 1 to 1.5 c.p.s. and of 1.8 to 4 c.p.s. The input signal to amplifiers 17, 18 is derived as a function of the speed of rotation of the free turbine rotor of a gas turbine engine by means of a tachogenerator and frequency responsive circuits. One application is to aircraft (e.g. helicopters) where the fuel supply is controlled as a function of the rate of change of turbine speed. Specification 962,801 is referred to.