A Royer oscillator is an electronic oscillator which has the advantages of simplicity, low component count, rectangle waveforms and easy transformer isolation. It was first described by George H. Royer in December 1954 in Electrical Manufacturing[1].
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The circuitry consists of a saturable-core transformer with a primary winding, a feedback winding and (optionally) a secondary winding. The primary winding is centre-tapped, with each half driven by a transistor collector. The feedback winding couples a small amount of the transformer flux back in to the transistor bases to generate the oscillations. The oscillation frequency is determined by maximum magnetic flux density power supply voltage and inductance of the primary winding.
The Royer oscillator circuit was an old circuit, and it was being used for past DC-AC inverter. There is collector resonance circuit which often be mistaken be called with the Royer oscillator circuit. The inventor of the collector resonance type oscillator is not George H. Royer but another inventor. As for the oldest invention, it is known as the Bell Telephone Laboratories's invention[2]. These are being used for drive the cold cathode fluorescent lamp (CCFL) backlight of an LCD display. CCFL inverters produce a sinusoidal waveform for good efficiency, which is necessary for good battery life on portable equipment.