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A
royer oscillator is an
electronic oscillatorAn electronic oscillator is an electronic circuit that produces a repetitive electronic signal, often a sine wave or a square wave.A low-frequency oscillator is an electronic oscillator that generates an AC waveform at a frequency below ≈20 Hz...
which has the advantages of simplicity, low component count, sinusoidal waveforms and easy
transformerA transformer is a device that transfers electrical energy from one circuit to another through inductively coupled conductors—the transformer's coils. A varying current in the first or primary winding creates a varying magnetic flux in the transformer's core, and thus a varying magnetic field...
isolationThe term Isolation may refer to:isolation: the act of being alone; separation.* Solitude, a social state* Solitary confinement* Isolation - defence mechanism....
. It was first described by George H. Royer in December 1954 in
Electrical Manufacturing.
Circuit description
The circuitry consists of a 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
transistorA transistor is a semiconductor device commonly used to amplify or switch electronic signals. A transistor is made of a solid piece of a semiconductor material, with at least three terminals for connection to an external circuit. A voltage or current applied to one pair of the transistor's...
collector. The feedback winding couples a small amount of the transformer flux back in to the
transistorA transistor is a semiconductor device commonly used to amplify or switch electronic signals. A transistor is made of a solid piece of a semiconductor material, with at least three terminals for connection to an external circuit. A voltage or current applied to one pair of the transistor's...
bases to generate the oscillations. A
capacitorA capacitor or condenser is a passive electronic component consisting of a pair of conductors separated by a dielectric. When a voltage potential difference exists between the conductors, an electric field is present in the dielectric. This field stores energy and produces a mechanical force...
across the primary winding gives the transformer a
resonanceIn physics, resonance is the tendency of a system to oscillate at larger amplitude at some frequencies than at others. These are known as the system's resonant frequencies . At these frequencies, even small periodic driving forces can produce large amplitude vibrations, because the system...
, which sets the oscillation
frequencyFrequency is the number of occurrences of a repeating event per unit time. It is also referred to as temporal frequency.The period is the duration of one cycle in a repeating event, so the period is the reciprocal of the frequency....
. An
inductorAn inductor or a reactor is a passive electrical component that can store energy in a magnetic field created by the electric current passing through it. An inductor's ability to store magnetic energy is measured by its inductance, in units of henries...
in the centre-tap transformer supply reduces
harmonicIn acoustics and telecommunication, a harmonic of a wave is a component frequency of the signal that is an integer multiple of the fundamental frequency. For example, if the fundamental frequency is...
content and improves efficiency.
Applications
The most common use of the royer oscillator is to drive the cold cathode fluorescent lamp (CCFL)
backlightA backlight is a form of illumination used in liquid crystal displays . Backlights illuminate the LCD from the side or back of the display panel, unlike frontlights, which are placed in front of the LCD...
of an LCD display. CCFL lamps need a sinusoidal waveform for good efficiency, which is necessary for good battery life on portable equipment.
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