Abstract :
The operation of the silicon-controlled rectifier in the basic form of parallel inverter circuits with resistive loads is investigated, and analysis is carried out to determine the conditions for optimum performance. Two fundamental parameters in terms of time-constants are introduced, one relating to the ballast inductance and the other to the commutating capacitance, as opposed to the method of defining design parameters in terms of a required triggering period hitherto employed in analysing thyratron circuits. The analysis shows that the basic circuit has three main modes of operation, two of which are undesirable. Within the range of the desirable mode square-wave and sine-wave operations are found to be feasible, and a procedure is given for determining the optimum triggering points in terms of time-constants. Expressions are derived for the maximum repetition rates for the generation of both types of waveforms in terms of relevant time-constants and turn-off times of the silicon-controlled rectifiers; with currently available high-current silicon-controlled rectifiers repetition rates of the order 6kc/s for square-wave operation and 12kc/s for sine-wave operation are found to be readily obtainable. With low-current diffused types, the corresponding repetition rates would be of the order of 35 and 70kc/s, respectively. The complete design procedure is illustrated by applying the analytical results to the practical design of a d.c./d.c. convertor, which is essentially an inverter followed by a bridge-rectifier filter unit.
