When Q 1 reaches its saturation point, there is no longer a change of current in L 2. Current flows from B– to B+.Įxamine Figure 5. Step 1 in Armstrong oscillator operation. It charges C 2 in the polarity shown.įigure 4. The expanding magnetic field of L 2 makes the base end of L 1 positive. L 2 is sometimes called a tickler coil because it provides feedback to L 1. When the voltage is applied to the circuit, current flows from B–, through the transistor and coil L 2, to B+. Circuit Diagram of an Armstrong oscillator.Įxamine Figure 4. Follow the sequence of events in this circuit.įigure 3. This determines the frequency of the oscillator. From this circuit, the basic theory of oscillators can be explained. The principles of the tank circuit operation are an essential part of the timing and feedback portion of many oscillator circuits.Īn Armstrong oscillator is shown in Figure 3. There must be enough feedback voltage amplitude to replace the energy lost by circuit resistance.The oscillator depends upon this regenerative feedback or positive feedback. The energy fed back to the tuned circuit must be in phase with the first voltage.Two conditions must exist to sustain oscillation in a tuned circuit: The basic block diagram of an oscillator is shown in Figure 2.įigure 2. These valves feed energy to tuned circuits to maintain the oscillation. These devices do not actually oscillate, but they act as valves. These are generated with semiconductor devices used as oscillators. In our studies of electronics, voltages and currents of much higher frequencies are used. The current is generated by dynamos driven by steam, water, or atomic power. it alternates at a frequency of 60 Hertz. We learned earlier that the electricity used in homes and factories is an alternating, or oscillating, current. The number of cycles occurring per second is measured and given as the frequency in Hertz. The time that passes during one cycle is called the period of the cycle.
One cycle, a complete set of events in a repeated series, has been completed.Īs oscillation continues, it repeats this cycle. Then it rises to its peak in the opposite direction and returns to zero. It starts from its reference line and rises to its peak in one direction and then falls to zero. The ac waveform maintains a steady frequency using a feedback circuit.įollow the voltage amplitude in Figure 1. The oscillator circuit changes dc from a power supply input into an ac waveform. You can compare the oscillator circuit output to a typical ac sine wave. It moves first in one direction and then the other. The oscillator is the very heart of radio transmission, microwave communications, radar, and much more.Īn oscillating current is one that flows back and forth. Notice the similarities between the clock pendulum and the oscillating current.
The swinging pendulum can be thought of as an oscillator, Figure 1.įigure 1.
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