A Royer oscillator is an electronic relaxation oscillator that employs a saturable-core transformer in the main power path. It was invented and patented in April 1954 by Richard L. Bright & George H. Royer, who are listed as co-inventors on the patent.[1] It has the advantages of simplicity, low component count, rectangle waveforms, and transformer isolation. As well as being an inverter, it can be used as a galvanically-isolated DC-DC converter when the transformer output winding is connected to a suitable rectifying stage, in which case the resulting apparatus is usually called a "Royer Converter".
It has some disadvantages, the most notable being that its output voltage (both amplitude and frequency thereof) is strongly dependent on the input voltage, and this cannot be overcome without significant changes to the original design as patented by Royer. The other disadvantage is that the power loss in the transformer can be very significant since it must operate at its maximum (saturating) magnetic flux density at the design frequency. Hence, the transformer is a critical component of the Royer inverter which has an impact on (a) its function (the amplitude & frequency of the output voltage), and (b) how well it performs that function (overall efficiency).