Wien bridge oscillator with FET
Wien bridge oscillator is sine wave oscillator. It can generate a big of frequencies. The oscillator has based on a bridge circuit, which compose four resistors and two capacitors.
The oscillator can also be viewed as a positive gain amplifier combined with a band pass filter that provides positive feedback.
The field effect transistor (FET) Q1 works in the linear resistive region to give automatic gain control.
For the reduction of the RC network is one-third at the zero phase-shift tremble frequency,
The amplifier gain determined by resistor R1 and equivalent resistor RT must be just equal to three to make up the unity gain positive feedback requirement needed for stable oscillation.
Resistors R2 and R3 are set to approximately 1000 ohm less than the required R1 resistance.
The FET – 2N5020 dynamically provides the trimming resistance needed to make RT one-half of the resistance of R1.
The circuit composed of R4, D1, and C1 isolates, rectifies, and filters the output sine wave, converting it into a dc potential to control the gate of the FET.
For the low drain-to-source voltage used, the FET provides a symmetrical linear resistance for a given gate to source voltage.
Related Links
Bridge oscillator circuit
Fet oscillator circuit
Wien bridge oscillator circuit
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