4.1 Identify the semiconductor device symbols in QUESTIONS 4.1.1 and 4.1.2 below - NSC Electrical Technology Electronics - Question 4 - 2023 - Paper 1

The symbol represents a P-channel depletion MOSFET.

The construction of a MOSFET typically includes a gate, source, and drain. The regions between the source and drain terminals are heavily doped. The gate terminal is insulated from the channel region, usually by a thin layer of dielectric material. This allows for electrical control of the channel conductivity.

R1 and R2 function as potential dividers to bias the MOSFET and set its operating point.

A MOSFET can be operated as a linear amplifier by selecting appropriate biasing resistors to place it in the active region of the transfer characteristic. This allows for proper amplification of the input signal.

During the first 90° of the input signal, the voltage across the gate-source terminal (Vgs) gradually increases, causing the channel conductance and thus the drain-source current (Ids) to increase. This results in an amplified output signal opposite the input.

The transistor used to produce the characteristic curve in FIGURE 4.4 is an enhancement mode MOSFET.

Point A on the characteristic curve represents the quiescent point, where the MOSFET operates in a steady state without input signal fluctuations.

The switching mode of the UJT is multi-shot, meaning it allows for continuous switching operations.

R3 limits the discharge current of the capacitor through the UJT to a safe level, ensuring that the capacitor discharges fully before the next cycle.

The op-amp circuit in FIGURE 4.7 is a non-inverting amplifier.

Infinite bandwidth means that the operational amplifier can operate without a frequency limitation, providing the same amplification across all frequencies.

The voltage gain, A_v, can be calculated using the formula: $A_v = 1 + \frac{R_f}{R_{in}}$ Substituting values gives: $A_v = 1 + \frac{47 \times 10^3}{10 \times 10^3} = 5.7$

If a 100 mV signal is applied to the input, the output voltage can be calculated as: $V_{out} = A_v \times V_{in} = 5.7 \times 100 \times 10^{-3} = 0.57 V = 570 mV$

Pin A is the Control Voltage and Pin B is the Trigger.

The discharge pin (pin 7) provides a discharge path for the timing capacitor during the timing cycle.

Comparator 1 compares the threshold voltage on pin 6 to two-thirds of the capacitor voltage and determines the output state based on this comparison.

Two uses of the 555 IC include: 1) Timer applications for generating delay; 2) Pulse-width modulation for controlling servos or motors.