Royer oscillator
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.
The oscillation frequency is determined by the maximum magnetic flux density, the power supply voltage, and the inductance of the primary winding.
This drawback is alleviated by inserting an inductor between the input power supply and the transformer center tap.
This step-down converter may be used to regulate the current flowing in the choke, allowing the output voltage to be controlled.
Firstly, a choke (inductor) is connected in series with the supply voltage to the transformer primary tap.
Switching between the two transistors is brought about simply through the natural resonance that occurs between an inductor and a capacitor, and NOT by the saturation of a magnetic component.
In this manner, a sinewave is able to be generated while allowing the transistors to switch alternately fully on and off in push-pull mode.
As the transformer acts like a 2:1 autotransformer on the primary, the "off" transistor collector voltage reaches double, or pi times Vcc.
A circuit employing a similar idea appears in a 1973 patent for a DC-DC converter assigned to Bell Telephone Laboratories[9] which, interestingly, uses both resonance and magnetic saturation.
CCFLs exhibit degradation in their current-to-light output efficiency in the presence of harmonics, so it is better to drive them with a sinewave than a square wave.
[11] In order to provide light intensity adjustment, an integrated circuit typically drives a pulse-width modulated signal in the gate of an additional transistor, forming a step-down ("buck") converter with the feeding choke.
[13] The Baxandall converter has been used recently in driving fluorescent tubes from low-voltage sources, often using rechargeable batteries, for emergency lighting and camping etc.
There are other examples of self-oscillating inverters (and converters) that are sometimes referred to by the same name "Royer" (or variations thereof), despite the fact that they operate by completely different principles.
Magnetic saturation is usually highly undesirable in a Baxandall oscillator, and in fact, is something designers of most power conversion equipment take great care to avoid.
Unfortunately, this naming confusion has become prevalent in the modern literature (for example, in datasheets,[14] and is one of the topics of this exchange between two highly respected practitioners of the art of circuit design.
Furthermore, the word "Royer" or "Royer-class" is more convenient than writing "self-oscillating inverter/converter circuit based on magnetic saturation of the main power transformer".
