1. EXERCISE 1
1. A Silicon-Controlled Rectifier, or SCR, is essentially a Shockley diode with an extra terminal
added. This extra terminal is called the gate, and it is used to trigger the device into conduction
(latch it) by the application of a small voltage.
2. Silicon controlled rectifier (SCR) is a unidirectional devices that acts as close switch when
a positive signal is applied to the gate.
i. State TWO (2) methods of commutating the SCR
ii. Draw and label the symbol of LASCR
iii. State the commutating technique that shown in Figure 1
Q
+-
IF
IR
Figure 1
3. SCRs may be fired by intentional triggering of the gate terminal, excessive voltage (breakdown)
between anode and cathode, or excessive rate of voltage rise between anode and cathode. SCRs
may be turned off by anode current falling below the holding current value (low-current
dropout), or by "reverse-firing" the gate (applying a negative voltage to the gate). Reverse-firing
is only sometimes effective, and always involves high gate current.
4. Data sheets are important as it helps to determine the value of the voltages and
currents required for operation. It also determines the SCR that can be used in design or
maintenance
i. Describe the term of “gate trigger voltage (VGT)” as stated in typical data sheet of
SCR
ii. Calculate the firing angle for the SCR for half wave phase control which delivered
38.7V of average voltage to the load with RL=15Ω and Vp=170V.

2. 5. Typically, the load current through an SCS is carried by the anode gate and cathode terminals,
with the cathode gate and anode terminals sufficing as control leads.
6. Other types of solid state devices that can be used for triggering pulse to the gates of
SCR are Unijunction Transistor (UJT) and Programmable Unijuntion Transistor (PUT).
i. Identify a different of determining peak voltage (Vp) in Unijunction
Transistor(UJT) and Programmable Unijunction Transistor(PUT)
ii. Draw the equivalent circuit for the UJT with bias voltage applied
7. UJT and PUT can be used for providing sharp pulse to TRIAC or SCR gate.
i. Explain the operation of Unijunction Transistor(UJT) as tringgering device.
ii. Determine the intrinsic standoff ratio of UJT if rB1= 75KΩ andrB2= 25KΩ.
8. A photodiode is a type of photo detector capable of converting light into either current
or voltage, depending upon the mode of operation.
i. State TWO (2) mode operations of photodiode.
ii. Draw and label the symbol of optocoupler
9. A TRIAC acts much like two SCRs connected back-to-back for bidirectional (AC) operation.
10. In industrial electronic circuits, output device or actuator is a hardware device that
converts a command signal into a change in various physical parameters.
i. Describe the solenoid principle which used as output device.
ii. Figure 2 show the typical op amp circuit for proportional valve.
Figure 2
11. What is the function of potentiometer and capacitor in this circuit?
12. Three basic types of control valves are available as proportional control valves are called
directional control valve, flow-control valve and pressure-control valve.
i. Explain the operation of directional control valves
ii. Determine TWO (2) effect of using directional control valves for controlling fluid
flow in hydraulic motor system
13. An electrical motor uses electrical energy to produce mechanical energy.
i. State TWO (2) types of AC motor

3. ii. List THREE (3) advantages of induction motor
14. Main terminals 1 and 2 on a TRIAC are not interchangeable.
15. Electric motors are found in applications as blowers and pumps. They may be powered
by direct current or by alternating current.
i.Describe the term of “slip” in the induction motor
ii.What is the disadvantage of induction motor compared with synchronous motor?
16. A stepper motor has a step angle = 7.5 number of step is 48 step angles. Calculate;
i Number of pulses that are required for the motor to rotate through five (5)
complete revolutions
ii. Pulse frequency is required for the motor to rotate at a
speed of 200 rev/min