Minority-carrier storage

Abstract

for such an oscillator and gives formulae for total power consumption, power dissipated in the transistor, and power output.For the purpose of simplified analysis the author assumes sinusoidal operation of the oscillator. In actual fact, deviations from this ideal condition must always occur, and they are usually quite considerable. Operation based solely on the limiting action due to the gradual reduction of the effective amplification factor as the amplitude rises is generally unreliable, and in practice slightly more regeneration is provided than would be 3 Oscillator unit required to satisfy the maintenance equation. In other words, the transistor is driven slightly into saturation for a small fraction of the operating cycle. The loop gain falls as soon as the transistor enters the saturation region, and in this way the amplitude is limited at the desired level 162 with better accuracy and without the risk of collapse of oscillations due to insufficient loop gain. This technique obviously introduces further deviations from sinusoidal operation. A convenient basis for the analysis of these derivations is provided by representation of the oscillator by a parallel RLC circuit driven by a negative-conductance device. A graphical method based on Lienard's construction is used to assess the effects of non-linearities and to predict the deviations from sinusoidal operation that can be expected from a particular design.Based on these considerations, design formulae for a Class B oscillator are derived, and the practical design of an oscillator for the conversion of 10 volts d.c. into 250 volts a.c. at 200 c/s is described. Such an oscillator was constructed as an a.c. supply source for the demonstration of electro-luminescent panels.The unit, which is shown in Fig. 3, is capable of delivering 2 watts at an overall efficiency of 41 -5%. This is by no means an optimum value since the transformer is less than 70 % efficient, and-the transistor used required more driving power than some others of more recent design. The collector efficiency of the oscillator is reasonably close to the theoretical Class B limit of 78 %.