GB664216A - Sawtooth wave generator - Google Patents

Abstract

664,216. Saw-tooth generating circuits. RADIO CORPORATION OF AMERICA. Aug. 24, 1949 [Sept. 21, 1948], No. 22037/49. Class 40 (vi). In a saw-tooth wave generator energy is stored in an inductor during the flyback period. by coupling it through an auto-transformer and a gas discharge tube to a voltage source and allowed to discharge through a biased diode during the whole of the forward stroke. In the circuit shown the diode biasing capacitor 27 is charged to produce a substantially steady positive potential so that when the gas discharge valve 7 becomes conductive (i.e. during the flyback) the capacitor potential acts in series with the H.T. potential to cause a large current to build up in the primary winding 15, 17 of the autotransformer. This produces a large negative voltage at the secondary terminal 19 and thus causes a large current to flow through the deflection coils 5 and the series blocking capacitors 21 and 31. The build up of primary current soon decreases due to the voltage drop in the circuit resistance and the secondary current therefore diminishes producing a back E.M.F. which lowers the anode voltage and extinguishes the valve. The flux in the deflection coils then begins to collapse causing the diode anode to become positive and producing the linear decay of current required for the forward stroke. The D.C. component of the charging current of capacitor 27 is supplied during the forward stroke by the collapse of the flux in a choke 33 and the secondary of the transformer. Extinction of valve 7 may be assisted by increasing the time the anode is negative for example by inserting a small inductance between the anode and terminal 17 or by ensuring that the transformer has appreciable leakage inductance. It is pointed out that the D.C. supply is not boosted by the biasing circuit voltage if the H.T. supply is connected directly to terminal 15 of the transformer.