A pulse generator capable of providing square-wave pulses whose on-time (pulse duration), off-time (pulse interval) and frequency (repetition rate) can be variably set has become increasingly important to the industry. Typical examples are found in the art of electrical machining. Thus, in EDM, high-frequency electroerosive machining pulses of precisely regulated pulse on-time and off-time are required having these pulse parameters desirably varied in a wide range of settings. The need for electrical pulses of adjustable time settings has also been recognized in electrochemical machining (ECM), electrochemical-discharge machining (ECDM), electrical sintering, electroplating, arc welding and so forth.
Pulse generators which have hitherto been utilized and proposed either entail extremely complex circuit configurations or have severe restrictions in the possible width and number of settings. Thus, in conventional circuit arrangements of relatively high grade designed to possess a wider range of settings and a fine intersetting pitch, a high-capacity memory is employed to secure ease of setting. Data for all selectable on-times and off-times are registered in the memory and, among them, a desired on-time and off-time are selectively read out and retrieved through an address selection circuit. Each output pulse is held on or off until clock pulses occurring at a preselected frequency reach a set value corresponding to the on-time of off-time retrieved. Then the address selection circuit is acted upon to control the on-time or off-time duration of output pulses. The device therefore is highly complicated and unavoidably expensive. As the capacity of the memory is increased, the access time cannot be negligible and this imposes a severe limitation on the width of the range of selectable on-time and off-time settings, the number of applicable setting steps and the maximum operable frequency.