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

The maximum voltage across the collector terminal of the transistor in FIGURE 6.2 is 20 V, as per the graph provided.

The maximum collector current can be calculated using Ohm's law:

$I_C = \frac{V_{CC}}{R_C}$
Substituting the known values:
$I_C = \frac{20 \, \text{V}}{3.33 \times 10^3 \, \Omega} = 6 \, \text{mA}$

The load line can be drawn on the characteristic curve by plotting the points derived from the maximum voltage and current calculated. Ensure you accurately represent the Q-point on the graph.

The bias point can be indicated on the load line graph at the intersection of the DC load line and the characteristic curve.

The value of the collector current at the class A bias point is found to be 3 mA from the load line intersection.

Resistors R1 and R2 function as voltage dividers, setting the base bias voltage for the transistor.

The coupling capacitors are chosen to be large to ensure they can handle a wide range of frequencies, allowing AC signals to pass while blocking DC.

The purpose of Re (emitter resistor) is to provide stability and improve linearity by reducing the impact of temperature on the transistor's operation.

RC coupling allows each stage of the amplifier to maintain its own DC operating point while facilitating signal coupling between stages without blocking AC signals.

One application of the transformer-coupled amplifier is in applications requiring large current outputs, such as driving loudspeakers.

1. It utilizes transformers to provide impedance matching between stages.
2. It allows for isolation of different circuit sections, minimizing interference.

Two devices that can be connected are:

1. AC motor
2. AC relay.

The purpose of the coupling capacitor Ce is to provide an AC path to ground, thereby preventing signal degradation.

The radio-frequency amplifier selects the required signal frequency and amplifies it, making it suitable for further processing in the circuit.

Variable pre-set capacitors C1 and C2 are used to allow tuning of the amplifier to the desired frequency and to maintain stability while blocking DC.

When switch S is moved to position 2, the capacitor will discharge its stored energy, providing a damped oscillation output.

The voltage waveform across the capacitor will initially rise, reach a peak, and then decay exponentially, illustrating damped oscillations.

The frequency of oscillation can be increased by decreasing the value of the inductor L or the capacitor C in the tank circuit.

One application of the Hartley oscillator is in radio-frequency signal generation.

C1 and C2 are coupling capacitors that allow AC signals to pass while blocking DC, enabling the tank circuit to correctly function.

Oscillation is maintained by applying positive feedback from the output back to the input, ensuring the overall phase shift in the circuit supports continuous oscillation.

Transistor Q1 functions to amplify the oscillating signal, providing necessary gain for sustained oscillation.

The frequency can be adjusted by changing the values of the capacitors in the circuit, as this directly affects the resonant frequency without altering the resistors.

In transistor amplifiers, negative feedback is typically employed to stabilize gain, whereas oscillators utilize positive feedback to sustain oscillation.

LC oscillators generate high-frequency signals due to the resonant properties of inductors and capacitors, while RC oscillators produce lower frequency signals due to their reliance on resistive components.