Assignment - Theoretical Worksheet
Section 3 (Assessment Criteria 3.1)

1. a) Draw the Schematic diagram of a Power Supply with the following specification:
230V Input Voltage
Double Pole On / Off Switch
1A Input Fuse
8A Output Fuse
Transformer
2 x 120V primary windings
2 x 12V secondary windings
Full wave rectification
Capacitor Smoothing
Transistorized Voltage Stabilization
Output = 12V @ 8 Amps
b) Show how an LED with Vf = 1.7V and Vf = 10mA can be connected to indicate the presence of an output voltage .
c) Explain how the above circuit would be built into an enclosure employing Class I protection.

2. a) Obtain and provide a printed table of preferred value resistors for general
purpose design circuits.
b) Using only preferred values of resistors and the Class A Amplifier Circuit defined in Section 2 Q4, complete the design given the following parameters: Load Current = 5mA
Voltage across RE = 2V
Lowest input frequency = 50 Hz
Transistor:
hfe = 50 Vice = 4V Vbe = 0.5V
Find preferred values for R1, R2, RL, RE and CE b) Draw the complete schematic.

3. a) Show how a switch and resistor can be used to create a logic level 1 or 0 for a digital input circuit.
b) Obtain a data sheet for a Passive Infra Red Detector and show how it can be configured to provide a logic level 1 when it detects the presence of a person in a room.
c) Obtain a data sheet for a light sensor module and show how it can be configured to provide a logic level 1 when the outside light level is in darkness.
d) Design a Logic circuit to give a logic level 1 when it's dark outside and a person has just walked into a room.
e) Show how the above circuit could be used to switch the room light on using an isolation relay using a Field Effect Transistor.
f) Explain why the light sensor cannot be placed in the same room as the person.
g) Explain the difference between CMOS and TTL Logic families