Monday, April 25, 2011

Colpitts Oscillator

Colpitts oscillator is very similar to the shunt-fed Hartley oscillator. The principal difference is in the tank circuit. In the Colpitts oscillator, two capacitors are used as replacement coils are divided. Basic oscillator Feedback oscillator colpitts developed using the "electrostatic field" through the capacitor divider network.

Oscillator Colpitts

Colpitts oscillator frequency is determined by two capacitors connected in series and inductors. Voltage to the base provided by R1 and R2 while for emiitor given by R4. Collector voltage given back by connecting to the positive part of the VCC through R3. This resistor (R3) also functions as a collector load. Transistor is connected with the emitter-joint configuration. When the DC power supplied to the circuit, current flows from the negative part of V CC through R4, Q1 and R3. IC currents flowing through R3 causes a decrease in the voltage VC with a positive price. Voltage changes to negative direction are supplied to the top of the C1 through C3. The lower part of C2 positively charged and the voltage flowing to the base voltage so that the IB price rises.

Transistors Q 1 will increasingly berkonduksi until the saturation point. When Q 1 to the saturation point there was no increase in IC and VC changes will also be halted. There is no feedback to the C2. Magnetic fields C1 and C2 will be disarmed through the L1 and the subsequent magnetic field around it will disappear. Emptying flow persists for a moment. C2-chip bottom becomes negatively charged and pieces of the upper positively charged C1. This will reduce the forward voltage of Q 1 and the IC will be decrease. Price V C will begin to rise. This increase will be fed back to the top of the chip C1 through C3. C1 will charge more positive and the bottom of the C2 becomes more negative.

This process continues until Q 1 to the cutoff point. When Q 1 to the cutoff point, no current I C. No feedback voltage to the C1. Combined charge collected on the C1 and C2 stripped through L1. Currents flowing from the bottom of disarmament to the top of C1 C2. C2 negative charge will eventually run out and the magnetic field around L1akan disappeared. Currents that flow continues. C2 puck into the lower positive charge and the chips C1 upper negative charge. Positive voltage on C2 interesting Q 1 of the cutoff region. Furthermore, the IC will begin to flow again and the process starts again from this point.

Feedback energy is added to the tank circuit for a moment on any changes. The amount of feedback on Colpitts oscillator circuit is determined by the "ratio
capacitance "C1 and C2. The price of C1 in this circuit is much smaller than the C2 or C1 X> X C2. The voltage on C1 is greater than C2. By creating a smaller C2 would obtain feedback voltage is greater. But by raising the feedback too high will cause distortion. Usually around 10-50%, the collector voltage is returned to the tank circuit as a feedback.

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