Patent GB-599880-A (GB)
Title: Improvements in or relating to static frequency changers
IPC: H01F38/04
Filed: 1945-09-25
Abstract: 599,880. Frequency changers; transformers. AUTOMATIC TELEPHONE & ELECTRIC CO., Ltd. Sept. 25, 1945, No. 24777. Convention date, Nov. 23, 1944. [Class 38 (ii)] Two coils on a core having a saturable portion common to both coils are arranged so that they have no mutual inductance, but so that if one be supplied with A.C. at one frequency the common portion of the core is periodically saturated and A.C. of a harmonic or subharmonic frequency is obtained from the other coil. The common portion of the core may, for example, include two intersecting flux paths, the primary coil producing flux in both paths while the secondary coil is acted on differentially by the two fluxes. For frequency multiplying, an initial biassing flux is provided in the core by D.C. or rectified current and this may also be used as the means of starting oscillations of sub-harmonic frequency. In Fig. 1, the core has two connected flux paths 10a and 10b, of which the common portion carries coil A across one diagonal and coil B across the other. Coil A when energized produces fluxes in both paths; coil B is linked by the difference between these fluxes. Windings Ca and Cb supplied through a rectifier and smoothing choke from the A.C. source supplying coil A, magnetically bias the core, which may be made up of iron strips spirally coiled and interlaced. Figs. 2 and 3 show another form of core which may be made up by stacking laminations around pre-formed coils, as shown in Fig. 6. In Fig. 2, the biassing coil C is not supplied from an external source, but has its circuit closed through a rectifier 19 and resistance 20. In Fig. 3, a uni-directional component is produced in coil A by connecting across this coil the inductance 21 and rectifier 22, flow of this component through the A.C. source being blocked by condenser 23. Coil B is shunted by a condenser 18. When the A.C. input to one coil tends, on one half wave, to increase the flux in one path already saturated and decreases and possibly reverses the flux in the other path, current at twice the input frequency will be induced in the other coileither in a continuous cycle or, if the flux is reversed and reaches the saturation point in the reverse direction, in a series of peaked impulses. In the latter case, some desired higher even harmonic of the input frequency can be obtained by tuning the output circuit. If the biassing flux in one path be reversed relatively to that in the other-e.g. by reversing coil Ca or Cb-or if the input and output coils be interchanged, so that the connections are as shown in the Figures, the A.C. input to coil A will tend on one half-wave to increase the flux in both paths, already saturated, and will decrease the flux in both paths on the other half-wave. The arrangement then acts as a frequency divider if the condenser 18 across coil B be approximately tuned to the even subharmonic frequency and if the A.C. in coil A can alone magnetize the core beyond the knee of the saturation curve, the action will continue even if the D.C. bias be interrupted. The output voltage remains constant with load increase until a point is reached where, with a large condenser 18, the output pulsates or stops and the device cannot be restarted until the load is removed, or, with a smaller condenser, the output drops rapidly with increased load beyond this point. The intersecting arms of the core may be of reduced cross-section so that they saturate more readily.