High-Power Sawtooth Current Synthesis from Square Waves

Steps towards a new and more efficient method of generating scanning sawtooth currents are discussed. A sawtooth wave S, with rounded peaks but with a straight slope extending over nearly 90 per cent of the period, is obtained by the following steps: 1. Synthesis of a step wave from three or four members of a series of square waves Pnwhose amplitudes and periods decrease with 2ⁿ, namely, S = P1+ 0.5P2+ 0.25P4+ 0.125P8+ ··· + 1/2ⁿP2n; and by 2. Smoothing the step wave by attenuating its higher harmonics in a simple low-pass filter network with negligible transmission at, and beyond, the lowest missing harmonic. Networks having good transient response are shown to be most suited. The efficiency of a tube circuit for this sawtooth current synthesis approaches 50 per cent when comparing power output with power supplied to the tube anodes. A modification of this circuit, using gated square waves, has an efficiency approaching 100 per cent.