Semester 4 electronics is an extension of Semester 3 electronics. It is designed to further develop the technicians understanding and confidence in meeting the challenge of modern electronics in the electrical trades. After a review, we begin with calculations on the DC output of controlled rectification circuits and RC networks. We look at the use of a UJT in an oscillator circuit, and for firing as SCR. We compare the use of an RC network, a pulse transformer and a UJT for phase control of an SCR. We then continue with the use of diodes and SCR's for both uncontrolled and controlled rectification of three phase half and full wave systems. We look at the relationship between firing angle, load voltage, and power consumption of these systems. We look at the use of a 555 timer for chopper operation of a DC drive controller with respect to the relationship between duty cycle, on-time, load voltage, and motor speed. Next we will examine and connect DC drive systems examining the major components and operation from an electricians perspective of operation and troubleshooting with respect to the relationship between firing angle, load voltage, CEMF, and motor speed, four quadrant control, open and closed loop speed control, operation and application of encoders, resolvers and tacho-generators as feedback devices. We will proceed to examine an SCR speed control of a DC motor and calibrate the controller for operation, and testing of the SCR for proper operation. On completion of DC control systems we will move into AC variable speed drive systems and examine rectification, power supplies, and inverter components. We review the operation of three phase AC variable speed drive controllers and connect, calibrate and confirm operation of various systems. We will explain the procedure to test, remove and replace if necessary the output transistor in a variable speed AC drive systems. Next we study harmonics and how they are created and the effects on AC systems and how reactors are used to control them. The course will conclude with the operation and principles behind serial communication.