Patent GB-421546-A (GB)
Title: Improvements in and relating to the supply of electrical energy to varying loads, for example to thermionic valve apparatus
IPC: H02M1/14
Filed: 1933-06-16
Abstract: 421,546. Impedance networks; valve circuits. ELECTRIC & MUSICAL INDUSTRIES, Ltd., Blyth Road, Hayes, Middlesex, and BLUMLEIN, A. D., 32, Woodville Road, Ealing, London. June 16, 1933, Nos. 17259 and 22005. [Classes 40 (iii) and 40 (v)] In television amplifiers and other apparatus in which the load varies over a range of frequencies, variations in the impedance of the source and its associated impedance elements, which would cause variations in the E.M.F. supplied, are prevented, preferably by adding impedance elements to give the source and its associated impedance elements a resultant resistive impedance when viewed from the load. When the source has a small regulation resistance so that it has no appreciable adverse effect upon the constancy of supply at very low frequencies, the added impedance elements are such as to prevent the reactive impedance from rising at any frequency to an unduly high value, i.e. to a value not exceeding three times the regulation resistance. As applied to a normal smoothing circuit L3, C2, C4, Fig. 1, associated with a source 10 and supplying two valves 1, 2 in push-pull modulated by a valve 5, each element of the supply network is supplemented with a mirror image impedance so that the network when viewed from terminals 8, 9 possesses a substantially pure resistive impedance. Thus, the source 10 may have an impedance consisting of a resistance R1, Fig..2, and inductance L1 ; this is associated with a condenser C1 and resistance R2 in known manner to produce an effective impedance which is resistive. Similarly, the reactive impedances of condensers C2, C4 and inductance L3 are neutralized by networks L2, R3 ; L4, R5 ; and C3, R4 respectively in known manner. A condenser 11 or acceptor circuit 12 may be used to byepass the carrier frequency. In an alternative arrangement, the correction is applied to the load circuit, e.g. the modulating valve 5. This method requires that the impedance associated with the source shall have a finite maximum value and this is achieved by providing a resistance 13, Fig. 3, across terminals 8, 9. The valve 5 then has arranged between its anode and resistance 4 a resistance 15 whose value is that of resistance 13 divided by the voltage amplification between the anode of valve 5 and the output of valves 1, 2. The resistance 15 is shunted by an impedance network 16, the mirror-image of the network associated with the source, and whose value is proportioned in the same manner as that of resistance 15. The load impedance thus contains a component varying inversely with the source impedance. A combination of the methods illustrated in Figs. 2, 3 may be used. It may be necessary to take account of stray impedances, e.g. the resistance R6, Fig. 4, of the inductance L3 and source 17. The condenser C4 is then replaced by the condenser C5 and resistance R7, Fig. 5, where R6=R7 and L3 (C5=R6<2>. At frequencies below f1 = 1/2##L3C5, the branch L3R6 will be the dominant impedance of the network and at frequencies above f1, the impedance of the branch L3R6 will be small compared to that of the branch C5R7. If the inductance has a self capacity C6, however, the impedance of the branch L3R6 may become large at a frquency f2 > f1. This may be compensated by connecting an inductance L5, Fig. 6, of low self capacity, a resistance R8 and a condenser C7 as shown in Fig. 6, where L5/C7=R8<2>=R6<2>. The critical frequency f3= 1/2##L5C7 above which the branch C7R8 has the larger impedance is made lower than f2. A capacity C8, e.g. due to wiring, may be neutralized by a resistance R9 and inductance L6, Fig. 6, or a series inductance and parallel condenser and resistance (Fig. 7, not shown). Where the regulation resistance of the source is small, the impedance of the smoothing circuit may rise to high values and make the regulation impedance large at high frequencies. To overcome this, damping resistances may be introduced, e.g. a resistance R11, Fig. 8, shunting the inductance L3, or the resistance R7, Fig. 5, may have a value larger than that given above. In the case of a battery, the impedance may be measured over the range of frequencies at which it is to operate and then be represented by a network which can be neutralized as described above. (Figs. 9, 10, not shown.) When the impedance of the battery is constant up to a frequency f1 an inductance L10, Fig. 11, resistance R16 and condenser C12 is used, where f1=1/2##L10C12 and L10/C12 = R16<2>, R16 being the total resistance of the battery 18 and inductance L10. Or the battery may be shunted by a condenser and built out to a resistance as described in reference to Fig. 1 (Fig. 12, not shown). In these two latter examples the impedance of the battery 18 is masked for frequencies well above f1. In order to stabilize the regulation resistance of the source, so that the impedance, after neutralizing, shall be a constant resistance, a dead load may be bridged across the source. Such a load may be a resistance or a triode arranged to take a certain current at no load. The invention is applicable to de-coupling circuits.