COMMON SOURCE JFET AMPLIFIER

JUNCTION FIELD EFFECT TRANSISTOR (JFET) is a unipolar voltage controlled device. Because Drain current is controlled by the voltage applied to gate-source terminal.

Likewise in Transistors, JFET amplifiers can also be setup in the three configurations namely, Common Drain, Common Source and Common Gate.

Transistor Configurations

Common source configuration is almost similar to Common emitter configuration of BJT's (Common Emitter RC Coupled Amplifier). JFET can also be biased as Voltage Divider or Self Bias.

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Digital Fan Regulator Circuit Diagram

This is the project of Digital Fan Regulator Circuit diagram. The circuit presented here can be used to control the speed of fans using induction motor. The speed control is nonlinear, i.e. in steps. The current step number is displayed on a 7-segment display. Speed can be varied over a wide range because the circuit can alter the voltage applied to the fan motor from 130V to 230V RMS in a maximum of seven steps. The triac used in the final stage is fired at different angles to get different voltage outputs by applying short-dura-tion current pulses at its gate. For this pur-pose a UJT relax-ation oscillator is used that outputs sawtooth waveform. This waveform is coupled to the gate of the triac through an optocoupler (MOC3011) that has a triac driver output stage. Pedestal voltage control is used for varying the firing angle of the triac. The power supply for the relaxation oscillator is derived from the rectified mains via 10-kilo-ohm, 10W series dropping/limit-ing...

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FM transmitter using UPC1651

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