6.1 State TWO categories of amplifiers - NSC Electrical Technology Electronics - Question 6 - 2022 - Paper 1

The maximum voltage across the collector terminal is found to be 20 V as shown in the characteristic curve of FIGURE 6.2.

Using the formula: $I_C = \frac{V_{CE}}{R_C}$ Substituting the values from the figure: $I_C = \frac{20}{R_C}$ Assuming R_C = 3.3k\Omega, $I_C \approx 6 mA.$

To draw the load line, plot the maximum collector current (IC) on the Y-axis against the maximum voltage (VCE) on the X-axis. The load line will intersect the characteristic curves of the transistor.

The bias point, also known as the Q-point, can be indicated at the intersection where the load line meets the characteristic curve, usually at a specific IC and VCE.

The value of the collector current at the class A bias point can be found from the load line or characteristic curve. For this transistor, it is approximated to be 3 mA.

R1 and R2 act as voltage dividers that set the base bias voltage (Vbe) necessary for proper transistor operation.

Larger values for coupling capacitors ensure that they can handle a wider range of frequencies, allowing for effective signal transmission without significant attenuation.

Re provides temperature stability and increases the linearity of the transistor's characteristics, improving the overall amplifier performance.

RC coupling allows each stage of an amplifier to maintain its own DC operating point while preventing DC interference between stages, ensuring that the AC signals can be amplified without distortion.

One application is in audio amplifiers where the transformer matches impedance between different stages of amplification.

1. Better impedance matching, which maximizes power transfer.
2. Isolation between stages, reducing unwanted feedback.

1. AC Relay
2. AC Motor

Ce provides an AC path to ground, bypassing the DC component and allowing only AC signals to pass through.

The radio-frequency amplifier selects the required signal frequency and provides a degree of amplification to that frequency, ensuring strong signal transmission.

C1 and C2 allow for tuning of the amplifier circuit to specific frequencies by varying capacitance, while blocking any DC current.

When the switch is moved to position 2, the capacitor will discharge through the inductor, leading to damped oscillations as it releases stored energy.

The waveform will show a damped oscillation pattern, typically starting from a positive peak and gradually decreasing to zero.

The frequency can be increased by decreasing the values of the inductor L or the capacitor C, as frequency is inversely related to these components.

The Hartley oscillator is often used in radio frequency applications to generate sine waves.

C1 and C2 filter the frequencies and maintain the oscillation feedback in the tank circuit while blocking DC.

The state of oscillation is maintained by ensuring positive feedback from the collector back to the tank circuit.

Q1 creates a 180° phase shift essential for ensuring the overall phase shift in the oscillator circuit.

The frequency can be adjusted by changing the values of the capacitors in the feedback loop, allowing for fine-tuning while keeping the resistor values constant.

Transistor amplifiers typically use negative feedback to stabilize gain, while oscillator circuits use positive feedback to sustain oscillations.

LC oscillators generate higher frequency signals compared to RC oscillators, which are limited to lower frequency signals due to their component values.