1. Field of the invention
Much present-day electronic equipment operates with optimum performance and reliability only when supplied with reasonably accurately sinusoidal alternating voltage. In many applications the available alternating voltage supplies are, or often become, of seriously imperfect waveform. This is particularly so if, as is often the case it is found necessary to employ a constant-voltage transformer in order to ensure that the voltage supplied to an equipment shall remain within close tolerances. 2. Description of the Prior Art
It has been proposed in order to supply a load with an accurately predetermined alternating waveform to employ accurate-waveform generators, which are very expensive to construct and maintain or to employ low-frequency oscillators which seldom have sufficiently accurate waveforms. Elaborate arrangements using photoelectric cells cyclically exposed to light passing a moving mask or appropriate shape have also been used, but such apparatus involving moving elements is insufficiently reliable for many applications.
It is also advantageous in some applications to be able to provide an a.-c. supply of a frequency other than those normally available.