| 摘要 |
<p>890,571. Valve oscillating circuits. SOC. DE TRAITEMENTS ELECTROLYTIQUES ET ELECTROTHERMIQUES. Jan. 13, 1959 [Jan. 24, 1958; Sept. 20, 1958], No. 1236/59. Class 40(6). An oscillation for induction heating comprises a high frequency tuned circuit, having an inductor which forms the primary of the output transformer, a low frequency tuned circuit having an induction in series with the high frequency tuned circuit, and means for switching from low frequency to high frequency operation. In one embodiment (Fig. 1), the switching is effected by four ganged twoway switches. When the switches are moved to the left, the high frequency tuned circuit 33, 34 is connected to the valve anode, the feedback coil 33 is connected to the grid, and the inductor 30, capacitor 31 and feedback coil 32 are isolated from the valve. With the switches moved to the right, the inductor 30 is connected in series with the high frequency tuned circuit and forms, with the capacitor 31, the low frequency tuned circuit, and the coil 35 is replaced by the coil 32. A high frequency choke 23 in series with the low frequency choke 22 is also shorted out in the high frequency position. The inductor 33 forms the primary of the output transformer which has a ferrite core to improve the coupling with the output circuit 36. In an alternative embodiment (Fig. 2) the output transformer is aircored and has a series L.C. 39, 40 connected across the primary to increase its inductance at low frequencies. The coil 32 is omitted, and instead the coil 35 has a suitable inductance for low frequency feedback and has a capacitor 41 connected across a portion of it which acts as a short circuit at high frequencies, the portion 43 then providing the required feedback. The inductor 40 is made variable to adjust the high frequency.</p> |
